Grasslands occupying the most terrestrial land surface display multiple functions. The long-term overgrazing of livestock often occur, and additional climate changes brings about the negative effects on the ecological stability, and therefore, grassland degradation is worldwide prevailing, which reduce the multiple functions of grasslands, and how to restore those degraded grasslands remains a crucial challenge for the human beings. For the past several decades, most researches on grassland restoration have focused on restoration practice rather than underlying theoretical basis, and the general restoration theory is lacking. Consequently, it is hard to have a practical solution for degraded grasslands due to lack of the available techniques. In this paper, the authors summarize the previous grassland restoration theories or models from restoration succession trajectory to the threshold model, the alternative state model and the filter model. A new concept, named as “systematic restoration for degraded grasslands” is put forward, which emphasizes three dimensions as key structure components (trophic species and dominant species of plant-animal-microbe), self-organized processes (water-nutrient coupling, linkage between aboveground and belowground), and multi-functionality (synergy and stability of grassland multiple functions), and also give the further explanations for contexts and mechanisms of the grassland systematic restoration (GSR): system structure integration, self-organization of ecological processes, and multi-functionality. Generally, the target of grassland restoration is approaching to the climax community or primordial state of ecosystem. The authors here emphasize the restoration of system self-organization, resulting from the interactions among the species like plant-soil feedback, as well as grassland multiple functions (goods and ecological services)characterized by their synergism and coupling. At last, the authors discuss the potential restoration practices like natural restoration by fencing and resting, intervening restoration with artificial inputs, and stimulating restoration with utilizing such as grazing and cutting, and perhaps the latter is the feasible mean for practical grassland restoration. The restoration mechanisms and practices for degraded grasslands are more complicated than thought, and here we attempt to establish a comprehensive conceptual framework to provide a new insight into grassland restoration theory. Certainly, it needs more evidence and experiments to enrich this new concept, GSR.
Leymus chinensis (Trin.) Tzvel. is a Gramineous plant which is widely distributed in Eurasian steppe. It often forms dominant or single dominant species communities in different steppe types in China, such as dominance typical steppe and meadow steppe, or recessive meadow. This paper traces the references on the scientific names of L. chinensis, refers to the research of phylogenetic evolution position of L. chinensis in the genus and the origin and diffusion pathway of Leymus Hochst., and makes a comprehensive analysis and inference according to the systematic literature on the divergence and adaptation of L. chinensis. The type specimens of L. chinensis was collected by Russian botanist A. Bunge in Beijing, China in 1831. After German botanist B. Trinius and A. Bunge named the species to the type specimens in 1833, there were five historical changes of generic names and five species names, and up to 15 plant taxonomists participated successively. In the phylogenetic Sect. Racemosus, Sect. Leymus and Sect. Anisopyrum, L. chinensis was mostly divided into the Sect. Leymus, and its evolutionary level was lower in Sect. Leymus. The leaf color of L. chinensis in different habitats is generally grey-green and yellow-green ecotypes. In the same habitat, the morphological, physiological and molecular genetic characteristics of the two ecotypes are all obviously differentiated. The genetic diversity was higher in gray-green ecotype than in the yellow-green ecotype. The genetic diversity of two ecotypes decreased gradually from east to west in the 900 km longitude transect of northeast grassland. Through comprehensive analysis, it is inferred that between the two ecotypes, the yellow-green ecotype is primitive and the grey-green ecotype is evolutionary. In the grassland of northeast China, L. chinensis is the most primitive in the westernmost in Inner Mongolia plateau, while it is more evolutionary in the eastern Songnen plain. The two ecotypes both extend from west to east in the grassland of northeast China. This paper can provide important reference for further research on the origin and evolution of L. chinensis, the formation process of different types of L. chinensis grassland and their community assembly.
【Objective】 Plant community characteristics are sensitive indicators to changes in ecosystem function of grasslands. In order to understand the processes and mechanisms characterizing grassland degradation with grazing, the characteristics and quality changes of grassland plants under different grazing intensities were examined to provide theoretical grounds for ecological restoration of degraded grasslands. 【Method】 Based on a grazing experiment with six different grazing intensities that targeted at the Hulunber meadow steppe, changes in community characteristics, community diversity, and community functional groups were measured by the standard rangeland ecological methodology, whilst the nutritional quality of herbage plants was determined by the national procedure for chemically analyzing crude cellulose, crude protein and raw fat components of vegetal feed. The six grazing intensities are control area G0.00: 0, light grazing G0.23: 0.23 cow.AU/hm2, lighter grazing G0.34: 0.34 cow.AU/hm2, moderate grazing G0.46: 0.46 cow.AU/hm2, heavier grazing G0.69: 0.69 cow.AU/hm2, and heavy grazing G0.92: 0.92 cow.AU/hm2. 【Result】 The canopy height, coverage, total biomass, biomass of the dominant species, root biomass, and litter biomass had decreased significantly at the grazing intensities greater than 0.34 cow.AU/hm2 (P<0.05), whereas the phytomass of increasers (Artemisia frigida, Potentilla bifurca, Potentilla acaulis, and Carex duriuscula) increased significantly (P<0.05). With the increase in grazing intensity, the community diversity index showed a trend of first increasing and then decreasing, with the maximum community diversity index occurred at the grazing intensities of 0.34-0.46 cow.AU/hm2. The dominance value of grasses decreased significantly with increases in grazing intensity. In stark contrast, those for forbs and annuals increased apparently with increasing grazing intensity. The important values of functional groups of grasses and their dominant plants gradually decreased with the increase of grazing intensity. When the grazing intensity was greater than 0.23 cow.AU/hm2, the important values of dominant plants significantly decreased (P<0.05), and the important values of sedges and degenera significantly increased (P<0.05). Of special note, the various grazing intensities all enhanced the contents of crude protein, crude ash, total phosphorus, calcium, and nitrogen-free exudates to varying degrees of all plant species as a whole, but significantly reduced the contents of crude fat, neutral detergent fiber, and crude fiber (P<0.05). The four indexes of α diversity were positively correlated with one another (P<0.01), positively correlated with the important values of legumes and heterophytes, and negatively correlated with the important values of gramineae. The important values of gramineae and ranunculaceae were significantly negatively related to the contents of acid washing fiber and calcium of the plants, whilst they were significantly positively related to the neutral washing fiber. 【Conclusion】 Different grazing intensities differed substantially in their effects on the community traits, diversity characters and nutritional quality of this meadow steppe. The appropriate grazing intensity was between 0.23-0.34 cow.AU/hm2. Moderate grazing was conducive to improving the species diversity of the community, maintaining the stability of the grassland plant community, and promoting the sustainable development of the grassland ecosystem.
【Objective】 The objective of this study was to study the response of important value (IV) and functional traits of dominant species of Leymus chinensis to grazing intensity in meadow steppe and to observe whether Leymus chinensis adapts to changes in the external environment by adjusting its various functional traits (such as plants, stems, leaves and so on) , so as to provide reference for rational grazing utilization of grassland. 【Method】 Six grazing intensities were set by control experiments, including control (G0: 0), mild (G0.23: 0.23 cow.AU/hm 2), light to moderate (G0.34: 0.34 cow.AU/hm2), moderate (G0.46: 0.46 cow.AU/hm2), heavy(G0.69: 0.69 cow.AU/hm2), and extremely very heavy (G0.92: 0.92 cow.AU/hm2), with three replicates. The IV of the dominant species of Leymus chinensis and its plant traits (plant height, stem weight, leaf weight, stem﹕leaf, and plant weight) and leaf traits (morphological traits:leaf area, single leaf weight, specific leaf area (SLA), leaf length, and leaf width; physiological traits: leaf carbon(C) and nitrogen (N) content, and C/N) were determined in each treatment. Among them, IV of Leymus chinensis was obtained by randomly selecting five 1 m×1 m plant community plots in the experiment plots. The functional characteristics of Leymus chinensis were determined by randomly selecting individual Leymus chinensis plants in each experiment plot. 【Result】 (1) Compared with G0, the decrease of Leymus chinensis IV was 42.9%, 66.0%, 82.7%, 91.8%, and 91.2% with the increase of grazing intensity. (2) Leymus chinensis plant traits (plant height, stem weight, leaf weight, and stem﹕leaf) decreased gradually with the increase of grazing intensity. The stem﹕leaf of Leymus chinensis plants was less than 1 in different grazing intensities, and G0.92 was significantly reduced by 39.22% compared with G0. The leaf area, leaf weight, leaf length and leaf width of leaf traits gradually decreased with the increase of grazing intensity. However, the SLA increased with the increase of grazing intensity, and it was the largest at G0.92, with a value of 136.61 cm 2·g-1, which increased 23.7%, 19.0%, 17.8%, 20.2%, and 13.2%, respectively, compared to G0, G0.23, G0.34, G0.46, and G0.69. (3) Leymus chinensis leaves C and N content was 44.2% and 2.8% under extremely heavy grazing (G0.92), respectively. With the increase of grazing intensity, the overall change of Leymus chinensis leaves C content was relatively stable, but leaves N content increased continuously. Compared with G0, the Leymus chinensis leaves N content in G0.69 and G0.92 increased by 21.8% and 43.2%, respectively. (4) Correlation analysis showed that Leymus chinensis leaves SLA was a significant positive correlation with N content and a significant negative correlation with C content. The leaf morphological traits were significantly correlated with physiological traits, the morphological traits were mainly with single leaf weight, and the physiological traits were mainly with C/N. 【Conclusion】 The grazing intensity changed the dominance of Leymus chinensis and made the individual Leymus chinensis plants smaller, reduced stem: leaf, but Leymus chinensis changed the leaves SLA and N content in response to changes in the external environment. Especially under extremely heavy grazing conditions, the SLA and N content increased synergistically.
【Objective】 Mowing is one of the main utilization methods of grassland, and plant functional groups and community species diversity are important ecological indicators for evaluating the degradation of grassland ecosystem under interference conditions. The plant functional groups and diversity in Leymus chinensis meadow grassland under different mowing were studied to understand the change process and mechanism of grassland functional groups and diversity, so as to provide a theoretical basis for ecological restoration of degraded mowing grassland. 【Method】 Taking the Hulunber Leymus chinensis meadow steppe as the experimental platform, the community vegetation was investigated by the sample method in the season with the most vigorous plant growth from 2014 to 2018 (early August of every year). The changes of community function groups and species diversity, as well as the interaction between different cutting time and cutting treatments, were analyzed under the conditions of annual cutting (G1), biennial cutting (G2), missed cutting 10 m (G3), missed cutting 10 m (G4) and control (CK), and the correlation between plant function groups and community species diversity was discussed. 【Result】 It was found that Leymus chinensis was the dominant species under different cutting systems, but with the increase of cutting frequency, the important value of Leymus chinensis decreased gradually, and the important value of the degraded indicator species such as Potentilla acaulis and Thermopsis lanceolate increased. The important values of leymus chinensis, Cleistogenes squarrosa, Adenophora stenanthina, Bupleurum scorzonerifolium and Poa ratensis were higher than those of other treatments. The proportion of important values of gramineae and leguminous plants decreased under annual and perennial mowing treatment, and the proportion of compositae and sedge plants increased, which were mostly degraded plants. After mowing treatment for 5 years, the species diversity index of plant communities under different mowing systems increased, among which shannon-wiener diversity index and Simpson dominance index increased significantly under the treatment of 10 m of mowed zone. The change trend of evenness index of 5 mowed treatments was different, among which, the evenness of community of G3 and G4 treated grassland showed an increasing trend, increasing by 16% and 5.8%, respectively. The evenness index under G1, G2 and CK grassland decreased, among which G1 decreased the most (by 1.8%), followed by CK (by 1.6%), and G2 grassland decreased the least. According to the change analysis of plant community species diversity index, it was found that the plant community species diversity was improved after 5 years of different mowing treatments and 10 m of missed mowing treatments. There was a significant negative correlation between community species diversity index and important values of plant functional group of Gramineae, and a significant positive correlation between community species diversity index and important values of Ranunculaceae and Compositae. 【Conclusion】 Long-term and high-frequency mowing would lead to grassland degradation, and long-term non-utilization of grassland would also lead to retrograde succession of grassland. Mowing every two years and a missed cut zone of 10 m could alleviate the decrease of the proportion of dominant plants such as Gramineae in the community and promote the increase of the proportion of Ranunculaceae. After five years of different mowing treatment, the community diversity of mowing treatment with 10 m mowing zone was improved, that is, moderate mowing disturbance to the grassland (two-year mowing and missed cut 10m) was conducive to the sustainable development of the grassland.
【Objective】 This study was designed to explore differences in rhizosphere effects and photosynthetic physiological activities between the grey green (GG) and yellow green (YG) ecotypes of Leymus chinensis (L. chinensis) in Songnen plains in response to saline-alkali stress, and to provide a theoretical basis for selecting the ecotype of L. chinensis suitable for the restoration of degraded saline-alkali grasslands. 【Method】 Using a pot experiment, the changes of soil and plant under the control, moderate salt-alkaline stress and severe salt-alkaline stress treatments for 30 days were studied, including pH, electrical conductivity, total organic carbon content, total nitrogen content, NH4 +-N content, NO3--N content, microbial biomass carbon content and microbial biomass nitrogen content of rhizosphere soil and bulk soil, as well as leaf net photosynthetic rate, leaf proline content, leaf soluble sugar content and plant height, aboveground biomass and belowground biomass of the two ecotypes of L. chinensis. The moderate saline-alkali stress was achieved by mixing 40 mmol·L -1 NaCl solution, 40 mmol·L-1 Na2CO3 solution, 360 mmol·L-1 Na2SO4 solution and 360 mmol·L-1 NaHCO3 solution at 1﹕1﹕1﹕1. The severe saline-alkali stress treatment was reached by mixing 200 mmol·L-1 NaCl solution, Na2SO4 solution, NaHCO3 solution and Na2CO3 solution at 1﹕1﹕1﹕1. 【Result】 The NH4+-N content, NO3--N content, available nitrogen content, microbial biomass carbon content and microbial biomass nitrogen content of rhizosphere and bulk soil under the moderate salt-alkaline stress treatment were significantly higher than those under the severe salt-alkaline stress treatment. For both ecotypes, the rhizosphere soil had a significantly lower pH value than that of the bulk soil. Moreover, the rhizosphere soil had greater available nitrogen content, microbial biomass carbon content and microbial biomass nitrogen content relative to the bulk soil. The rhizosphere effects of pH in the GG ecotype of L. chinensis were significantly higher than that of the YG ecotype under the control and moderate salt-alkaline stress treatment. The rhizosphere effects of available nitrogen content and microbial biomass carbon content in the GG ecotype of L. chinensis were significantly higher than those of the YG ecotype. For both ecotypes, the net photosynthetic rate, leaf soluble sugar content and leaf proline content under the moderate salt-alkaline stress treatment were significantly higher than those under the severe salt-alkaline stress treatment. The aboveground biomass, belowground biomass and total biomass under the salt-alkaline stress treatments were significantly lower than those under the control treatment. The loss rate of plant height and belowground biomass, and harm percentage of net photosynthetic rate in the YG ecotype of L. chinensis were significantly higher than them in the GG ecotype. Compared to the YG ecotype, the GG ecotype had significantly higher sensitive indexes of leaf proline content, leaf soluble sugar content and osmotic pressure. 【Conclusion】 The GG ecotype of L. chinensis could more effectively alleviate the adverse effects of saline-alkali stress on soil physical and chemical properties and showed stronger saline-alkali resistance than the YG ecotype.
【Objective】 Circles of mushrooms coupled with regular rings or arcs of greener plants are commonly observed in grassland. This pattern is often referred to as ‘fairy rings’. Indeed, fairy ring funguses not only affect plant growth but also greatly modify the soil quality and microbial populations, thus indirectly have impact on soil respiration. The aim of this study was to observe soil respiration of the fairy rings to accurately estimate greenhouse gas emissions from grassland soil. 【Method】 Measurement of soil respiration of the outside (OUT), on (ON) and inside (IN) the rings was conducted by Li-8100 automatic instrument. Meanwhile, soil temperature and soil water content were measured by the monitoring instrument CJTP-101 and TDR 300. The biomass and soil nutrients through field investigation on fairy rings were also measured. 【Result】 The average aboveground biomass of ON zone was 246.2 g·m -2, significantly higher than that of IN (153.1 g·m-2) and OUT (132.6 g·m-2) zones, which was 1.62 times of IN zone and 1.86 times of OUT zone. The average belowground biomass of ON zone was 763.9 g·m-2, less than that of IN (927.4 g·m-2) and OUT (824.8 g·m-2) zones, and there was no significant difference (P>0.05) of the belowground biomass among them. The litter of ON zone was 17.9 g·m-2, higher than that of IN (13.1 g·m-2) and OUT (9.6 g·m-2) zones, and there was no significant difference in different zones (P>0.05). The available nitrogen and phosphorus of ON zone were 52.2 and 7.8 mg?kg-1, significantly higher than that in IN and OUT zones (P>0.05), respectively. The available nitrogen was 42% and 40% higher than the IN and OUT zones, and the available phosphorus was 53% and 59% higher than the IN and OUT zones, respectively. The organic matter and total nitrogen of ON zone were 3 560.1 and 319.8 mg?kg-1, respectively, less than that in IN and OUT zones. The total phosphorus of ON zone was 502.2 mg?kg-1, higher than the IN and OUT zones, but the difference was not significant (P>0.05). The average soil respiration rate (SRR) of ON zone was 5.26 μmol·m-2·s-1, significantly higher than IN and OUT zones which were 4.07 and 4.17 μmol·m -2·s-1, respectively. The significantly relationship were found between the SRR and soil temperature and soil water content (P<0.01). 【Conclusion】 It was suggested that the soil temperature and soil water content were not the dominant factors. And the enhancement of soil respiration in the ON zone was related to the higher available nutrients and stronger microbial and enzyme activities.
【Objective】 Overgrazing and mowing of grassland in north China caused serious vegetation degradation and soil nutrient deficiency. The purpose of this study was to investigate the effects of nitrogen and phosphorus fertilizers on plant community diversity and productivity in the degraded grassland. 【Method】 A four-year nitrogen and phosphorus addition experiment was conducted with two kinds of fertilizers, including calcium superphosphate and ammonium nitrate, scheduled 2 nitrogen rates (0, and 10 g N·m-2·a-1) and 6 phosphorus rates (0, 2, 4, 6, 8 and 10 g P·m-2·a-1) with interaction between the both, a total of 12 treatments, and each treatment repeated 5 times. Fertilizers were applied when grassland was turning green in late May, and the community was investigated in the period of maximum biomass in the middle of August every year. In the process of research, the community productivity, species diversity and relative biomass of four functional groups were analyzed. 【Result】 From 2014 to 2017, it was found that the species richness decreased by year, and the average species of the control treatment (neither nitrogen nor phosphorus) was 20.2, 17.1, 14.7 and 15.2, respectively. Based on plant community α diversity index (richness and Simpson dominance index) , the study showed that nitrogen addition significantly decreased the species diversity of the community, but phosphorus addition and cumulative effects of phosphorus did not affect the species diversity of the community. There was a significant difference in diversity index among years, and the interaction between nitrogen and year had a significant effect on it. The aboveground net primary productivity (ANPP) of grassland community varied significantly among years, with the highest in 2014 and the lowest in 2015, the range was from 400 g·m -2 to 100 g·m-2, and which in dry years was significantly lower than that in normal precipitation years. Phosphorus addition had little effect on ANPP, while nitrogen addition significantly increased ANPP, and the effect of nitrogen and phosphorus addition together was greater than that of phosphorus alone. In the normal precipitation growing season, nitrogen was the main limiting factor of Hulunber meadow steppe. Nitrogen addition significantly affected the relative biomass of functional groups, while phosphorus addition had little effect on it, and there was a significant difference in the relative biomass of each functional group between years. Nitrogen addition alone significantly increased the relative biomass of the perennial rhizomatous grass (PR), but reduced the relative biomass of the perennial fobs (PF) and perennial bunch grass (PB). Phosphorus addition alone increased relative biomass of PB and perennial leguminous (LE), while had no effect on relative biomass of PR and PB. Combined addition of nitrogen and phosphorus significantly increased the relative biomass of PR, but significantly decreased the relative biomass of the other functional groups. In addition, the nitrogen and phosphorus combined addition partly reduced the plant community stability. 【Conclusion】 The differentiation of different functional types’ responses caused by nitrogen and phosphorus addition led to the changes of the original hierarchical level between different functional groups, especially nitrogen addition could cause a rapid increase in PR relative biomass, and thus led to the plant community structure developing towards the direction of increasing dominance of PR, and decreasing species diversity and community stability.
【Objective】 In order to provide a practical and scientific basis for improvement, restoration and reasonable use of degraded grassland, the effects of different organic fertilizers on soil nutrient status and soil bacterial diversity were revealed in the natural Leymus chinensis steppe degraded grassland in Hulunbeier. 【Method】 The field experiments were designed by single factor randomized block design, and the seven treatments were as follows: the control (ck), vermicompost 15 t·hm-2(a1), 30 t·hm-2(a2), 45 t·hm-2(a3), mushroom residues 15 t·hm-2(b1), 30 t·hm-2(b2), 45 t·hm-2(b3). Combined with the physical and chemical properties of soil, this study used the high-throughput sequencing technology of Miseq to analyze the effects of different organic fertilizer treatments on the diversity of soil bacterial communities, and to explore the environmental drivers of bacterial community changes under different organic fertilizer treatments. 【Result】 The results showed that organic fertilization improved the soil nutrient status and shaped the distinct bacterial communities. Compared with ck, the AP content increased significantly by 37.27% under a3 treatment. AK content under b3 and a3 treatments increased significantly by 62.99% and 40.53% compared with the control, respectively. And aboveground biomass was significantly higher than other treatments under b3 treatment (244.11 g·m-2). Moreover, vermincompost and mushroom residues fertilizers significantly increased the richness of the bacterial community. Compared with ck, the richness index increased significantly under a1 and b2 treatments. At the phylum level, a total of 31 taxa were obtained from 21 samples. Actinobacteria, Proteobacteria, Acidobacteria, Verrucomicrobia and Chloroflexi were the dominant groups, and relative abundances account for the bacterial community 85% or more. Actinomycetes were the most abundant under a2 treatment (36.79%). Proteobacteria was higher under b1 and b3 treatments (23.29% and 22.32%, resptectively). Acidobacteria was the highest under a1 treatment (20.69%). And LEfSe showed that more bacterial taxonomic groups were detected under b3 treatment (17 clades, 1 class, 1 order, 4 families and 11 genera). In addition, AN (P=0.001), AK (P=0.005), and SOM (P=0.006) had extremely significant effects on the composition of bacterial communities in the soil (P<0.01), while TK (P=0.014) had not. The composition of soil bacterial community had a significant effect (P<0.05). It showed that AN, AK, SOM and TK were the main driving factors of bacterial community. 【Conclusion】 Organic fertilizer changed the soil bacterial community structure in Leymus chinensis steppe. Our results indicated vermicompost and mushroom residues at 45 t·hm-2 increased available nutrient content, but also enhanced the biodiversity of soil bacterial communities in the grasslands of Leymus chinensis, which contributed to the sustainable development of grassland agro-ecosystems.
【Objective】 The aim of this study was to improve soil nutrients in haying steppe, to increase grassland productivity, and to maintain sustainable utilize of grassland. 【Method】 Five nitrogen application levels (0, 10, 20, 30, and 40 g N·m-2·a-1) and two mowing heights (4 and 8 cm) were set in the haying field of Hulunbuir Grassland Agro-ecosystem Experiment Station with spit-plot design, which was carried out in mid-June and mid-August from 2016 to 2019, respectively, and the responses of nitrogen application and clipping height to community and plant functional group’s species richness and aboveground biomass, crucial species’ important value, dominant species’ functional traits, and soil properties were investigated. 【Result】 The results showed that nitrogen application and mowing height had no significant effect on community and plant functional group’s species richness (P<0.05). Nitrogen application significantly increased the aboveground biomass of grasses and community by 69.2%-115.3% and 36.5%-84.8%, respectively (P<0.05), but there was no significant difference within 10-40 g·m-2·a-1. Lower cutting height significantly reduced the aboveground biomass of grasses by 18.3% (P<0.05). Nitrogen application significantly increased and reduced the important value of Leymus chinensis and Bromus inermis, respectively (P<0.05). Lower mowing height significantly reduced the important value of Leymus chinensis, which increased the value of Bromus inermis; nitrogen application increased the important value of Leymus chinensis, which reduced the important value of Bromus inermis(P<0.05). Lower cutting height significantly increased the important value of Potentilla bifurca and Potentilla acaulis and reduced the important value of Cleistogenes squarrosa (P<0.05). Nitrogen addition significantly increased the plant height, leaf area and shoot nitrogen content of Bromus inermis and Leymus chinensis (P<0.05), but there was no significant difference within 20-40 g·m-2·a-1. The soil pH and soil water content decreased significantly along with the increase of nitrogen application rate, while NH4+-N, NO3--N and inorganic nitrogen (ION) in soil increased (P<0.05). The species richness of community, grasses and nongraminous forbs was positively correlated with soil water content, while the aboveground biomass of community and grasses was negatively correlated with soil water content (P<0.05). 【Conclusion】 Short-term nitrogen application and suitable clipping height were beneficial to improve vegetation productivity and maintain community composition, and the effects of nitrogen addition were strongly dependent on water availability. It was suggested that the suitable mowing height of grassland in Hulunber haying meadow steppe was 8 cm, and the comfortable nitrogen application rate was 10-20 g·m-2·a-1.
【Objective】 Nitrogen input affects the sustainability of the global grassland ecosystem. Paying attention to the soil microbial community and its molecular ecological network can provide a theoretical basis for grassland degradation restoration. 【Method】 Taking Songnen degraded Leymus chinensis grassland as the research object, the molecular ecological network of soil microbial community was constructed by applying high-throughput sequencing and random matrix network construction with and without nitrogen treatment. To explore the effects of nitrogen management on the soil microbial community structure and network in degraded Leymus chinensis grassland, the key microbial changes in the microbial network structure under the condition of nitrogen addition was studied, and the interaction between microorganisms during the process were investigated, and the conditions for external nitrogen addition key points and regularity of soil bacterial dynamic change were analyzed. 【Result】 At the level of phylum classification, there were 22 bacterial phylum in nitrogen-applied grassland and 23 without nitrogen. The 7 phylum were the dominant phylum of the nitrogen-applied and non-nitrogen-applied grasslands. Among them, Proteobacteria was the phyla containing the largest number of OTUs, accounting for about 30.46% of the total sequence. The next largest genus was about 30.15% of the total sequence. The genus Gemmatimonadetes was the third genus containing OTUs, accounting for 8.14% of the total sequence. Actinomycete accounted for about the total 6.15% of the sequence, while Chloroflexi, Bacteroidetes and Nitrospirae accounted for 17.16% of the total sequence. The relative abundances of Proteobacteria, Actinomycota and Bacteroides in soil microorganisms in nitrogen-applied grassland were significantly higher than those in non-nitrogen applied grassland soil; The relative abundances of Proteobacteria, Actinomycete and Bacteroidetes were significantly higher than the soils of nitrogen-applied grassland (P<0.01), and no significant difference was found between the nitrogen application and non-nitrogen treatment of other bacteria. The forward connection ratio, the average path length, the average clustering coefficient, and the modularity of the characterizing network were all significantly lower than the nitrogen-free treatment (P<0.001). In the molecular ecological network of soil, there were 16 modular hubs without nitrogen treatment (Zi>2.5, Pi≤0.62), and there were 6 modular hubs under nitrogen treatment, all of which belong to Acidobacteria, Gemmatimonadetes and Actinomycete. Nitrogen application led to changes in soil microbial species relationships, which in turn changed the overall soil ecological network. 【Conclusion】 Nitrogen application reduced the complexity and tightness of soil network structure of degraded grassland, and reduced the relative abundance of Acidobacteria and Chloroflexi in degraded grassland, while which improved the relative abundance of Proteobacteria, Actinomycete and Gemmatimonadetes. The number of microbial key species (OTU) in soil decreased from 16 (no nitrogen application) to 6 and there was no overlapping OTU in both soils, indicating that nitrogen application regulated key species of its community network and thus changes its molecular ecological network.
【Objective】 The introduction of Nitrogen-fixing legumes into grasslands is the economical and ecological measurement to improve soil fertility and to increase forage yield and quality in grasslands. In legume-grass mixture grasslands, the proportion of legume plants is the key factor to determine their N fixation function. This research studied the influence of legume proportion on nitrogen fixation efficiency of Medicago sativa-Leymus chinensis mixture grassland and underlying physiological and ecological mechanism, aiming to improve our understanding to the relationship between community structure and biological N fixation in mixed grassland, and to assist the establishment and management of legume-grass mixture grassland for increasing the biological nitrogen fixation and soil fertility, and thus to improve the resources production and ecological stability of mixed grassland. 【Method】 In May 2017, using M. sativa and L. chinensis as experimental materials, a completely randomized block design with four repeats was applied to establish Medicago sativa-leymus chinensis mixture grassland with different legume proportion (25%, 50%, 75%, and 100%) in the field in Changling grassland farming research station. One year after establishment, based on the quadrat survey procedure, the changes in community structure, and growth status of leaf, shoot and root, physiological and metabolic characteristics were measured. After measuring nodulation of root, nitrogen fixation efficiency of M. sativa was measured using 15N natural isotope abundance method in mixed grasslands. Finally, the effect of legume proportion on biological nitrogen fixation of M. sativa and its mechanism were analyzed in combination with monitoring soil moisture. 【Result】 (1) One year after sowing, the observed proportions of legume plants were 11%, 27%, 53% and 100%, corresponding to initially sowed legume proportion of 25%, 50%, 75% and 100% in mixed grasslands, respectively. (2) Compared with the initial legume sowing proportions of 25%, 75% and 100%, the initial legume sowing proportion of 50% increased the mean soil moisture content within growing season by 21.4%, 36.4% and 51.7%, respectively. (3) M. sativa had greater shoot and root biomass, leaf number, leaf area, leaf thickness and leaf biomass under the legume sowing proportion of 50%. The minimum value of the above variables was found in the legume sowing proportion of 100%. (4) M. sativa had the greatest photosynthetic rate and the greatest starch concentrations in shoot and root, but the lowest soluble sugar concentration in shoot and root when legume sowing proportion was 50%. (5) Under initial legume sowing proportion of 50%, root nodule development of M. sativa was better and its biological nitrogen fixation capacity was increased by 13.5%, 44.6% and 79.2%, respectively, compared with initial legume sowing proportions of 25%, 75% and 100%. Regression analysis showed that the biological nitrogen fixation of M. sativa was positively correlated with soil water content following change in legume proportion. 【Conclusion】 In Medicago sativa-leymus chinensis mixture grassland, the relationship between biological nitrogen fixation and legume proportion was non-linear. M. sativa had the highest nitrogen fixation efficiency when the initial legume sowing proportion was 50% in mixed grassland. Legume proportion drived change in soil water availability, thus to regulate the growth and development of M. sativa and its root nodules via modification in leaf development and photosynthesis, which was the underlying mechanism for legume proportion to influence the biological nitrogen fixation. This study could help in determining the legume-grass ratio during establishment of mixed grasslands, and guiding the water management in mixed grasslands.
【Background】 The climate in the Mollisol area of Northeast China is cold and the growth period is short in the past, alfalfa was planted in degraded grassland or low-yield fields. In order to ensure safe wintering, it is generally only castrated three times a year. Under the background of “grain to feed”, the soil quality of the cultivated land in the Mollisol agricultural area in cold region is relatively fertile, and the field management is relatively standardized. 【Objective】 The purpose of this experiment is to explore the feasibility of alfalfa cutting four times a year under the condition of reasonable fertilization in the Mollisol agricultural area in cold region of northeast cold region. 【Method】 The second year of planting (Medicago sativa L. “Dongnong No.1”) was used as experimental material to study the one-time fertilization of soil 525 kg·hm -2 in the alfalfa spring before returning to green. The 525 kg·hm-2 disposable soil fertilization (the self-developed Mollisol agricultural area in cold region special compound fertilizer, patent application number: 201101193040.0) was studied before the spring return to green, and then sprayed 15 days before each castration. Self-developed alfalfa special foliar fertilizer for Mollisol agricultural area in cold region (patent application number: 201010124670.2), nutrient quality and overwintering rate, and the economic benefit was analyzed. 【Result】 Fertilization can effectively improve the yield and quality of alfalfa. Under the condition of fertilization (soil fertilizer + foliar fertilizer), the annual total hay yield of four and three stubbles of alfalfa was 13 544.44 kg·hm-2and 11 935.26 kg·hm-2, which were 11.45% and 10.77% higher than that of the control, and the average crude protein content was 22.11%, 21.68%, 8.17% and 7.59% higher than that of the control. Increasing the number of cutting times under fertilization (soil fertilizer + foliar fertilizer) can effectively improve the yield and quality of grass, and has little effect on the overwintering rate. Compared with the three cropping, the annual hay yield and the average crude protein content of alfalfa were increased by 13.48% and 2%.And it had little effect on the overwintering rate, only reduced by 2 percentage points, from 96.70% to 94.84%. The output value and input-output ratio of four stubbles of alfalfa with fertilization and annual mowing were 24 380.01 yuan/hm2 and 2.05, which increased the net income of three stubbles by 4 851.68 yuan/hm2 compared with the three stubbles of alfalfa without fertilization. 【Conclusion】 It is feasible to cut four stubbles of alfalfa under reasonable fertilization conditions in Mollisol agricultural area in cold region by comprehensive comparative analysis.
【Background】 Planting of alfalfa in degraded meadow in cold mollisol area of Northeast China is an effective method for rapid vegetation restoration.Reasonable fertilization is an effective measure to improve the yield and quality of alfalfa. In order to reduce the rolling damage of soil and alfalfa plants by machinery in the process of fertilizing. It is generally advisable to fertilize the soil at one time before and after alfalfa plants have returned to green in spring. The turning green period of alfalfa in the mollisol area of Northeast China is from late April to early May, and in this time, fertilizer is often applied. However, there has been few studies on the effect of fertilizer on alfalfa at different time of early spring. 【Objective】 The purpose of this experiment was to study the effects of fertilizer application in different periods of early spring on the performance and nutritional quality of alfalfa, and to determine the best fertilizing period for alfalfa in early spring. In order to provide technical guidance for the restoration of degraded meadow by planting alfalfa in the mollisol area of cold region. 【Method】 Alfalfa in its second years after was used as the experimental material, and the type of fertilizer was self-developed special fertilizer for alfalfa (patent number: 201810193040.0). And the contents of N, P, K is 14.20%, 10.86%, 10.47%. A period of fertilizer was set up every 5 days from April 20 to May 15, and the amount of fertilizer was fixed at 525 mm. The alfalfa was mowed three times every year. The effects of fertilizer on the production performance and nutritional quality of alfalfa in different periods of early spring were investigated. 【Result】 Fertilizer as all time could significantly promote the growth at all cuts, among which earlier fertilizer trend to increase the plant height of the first cut and the average plant height over the whole year, and the late fertilizer trended to increase the plant height of the second and third cut, but the difference was not significant. Early fertilizer could significantly increase the hay yield of each cut, and the early application trend of increase the hay yield of the first cut while decrease the hay yield of the second and third cuts. The effect of different fertilizing time on the average hay yield in the whole year was not significant. The average crude protein content of each harvest and that of the whole year was significantly increased by fertilizer. But the effect of different fertilizing time periods on the annual average crude protein content was not significant. Compared with no fertilizer, the contents of NDF and ADF in all treatments were significantly decreased. Fertilizing early could reduce the contents of NDF and ADF significantly, in the first crop of alfalfa , and the decrease of the contents of NDF and ADF in the second crop was more obvious in the early spring than in the early spring. The difference between the contents of NDF and ADF in the third harvest was not significant. In the whole year, the contents of fiber in April 20 treatment was the lowest. The treatment of April 25 had little difference with the treatment of April 20. And difference between two treatments of April 20 and April 25 and treatments of others is significant. 【Conclusion】 Through the comprehensive analysis, in the mollisol area, the alfalfa which has been planted 2 years fertilizer near April 25 has great nutrition quality and annual output, when fertilizer was carried out once a year.
【Objective】 Establishment of artificial grassland provides one solution for releasing some of the grazing pressure on natural grassland, and thus is conducive to the restoration of degraded grassland. The present study aimed to investigate the effects of nitrogen (N) addition and water supplement on soil organic carbon (SOC) fractionation, composition and activity of soil microbial community on artificial grassland established in Hulunber region, so as to provide insight into the effect of management practices on SOC sequestration and stability of artificial grassland. 【Method Experimental plots were designed with two factors of N addition (0, and 150 kg N·hm-2·a-1) and water addition (0, and 60 mm), and were constructed under three types of artificial grasslands, i.e., alfalfa monoculture, smooth bromegrass monoculture, and the mixed cultivation of alfalfa and smooth bromegrass. Soil samples were collected from experimental plots and SOC of bulk soil was fractionated into different particulate-size fractions by wet-sieving method. The abundance, composition and activity of soil microbial community were measured by phospholipid fatty acids (PLFA) and extracellular enzyme activity. Then, the effects of N addition and watering treatments on SOC fractions and soil microbial community, and investigated the relationship between these two components were analyzed. 【Result】 Three years of N fertilization and water addition exerted significant impact on SOC fractionation. Addition of N generally increased the content of particulate organic carbon (POC) in soils of alfalfa monoculture and the mixed cultivation but decreased the content of mineral associated organic carbon (MAOC), while water addition significantly increased the content of coarse POC in soils of smooth bromegrass monoculture. The activities of four soil extracellular enzymes but not the abundance or composition of soil microbial community were significantly affected by N and water addition. Nitrogen application without water addition significantly inhibited the activity of β-N-acetylglucosidase (NAG) in soils of alfalfa monoculture, but promoted that in soils of smooth bromegrass monoculture. The activities of cellobiohydorlase (CB) and NAG were significantly decreased by water addition in soils of two monoculture grasslands. Nitrogen application with water addition significantly inhibited the activities of β-glucosidase (βG), CB and NAG in soils of alfalfa monoculture, but significantly promoted CB activity in soils of the mixed cultivation. The changes in PLFA concentration of total community and specific microbial groups were positively correlated with changes in content of POC, but negatively correlated with MAOC. There were negative correlations between the activities of βG and CB, as well as the ratio of enzyme C/N and C/P with changes in POC content, and these correlations were stronger under treatments with water addition. 【Conclusion】 Results of the present study showed that in artificial grassland established in semi-arid Hulunbeier region, the addition of N fertilization significantly promoted the accumulation of labile SOC fraction, but decreased the proportion of recalcitrant fraction, which reduced the stability of soil carbon sequestration. Nitrogen fertilization and water supplement induced significant changes in activity of soil microbial communities, and these changes in enzyme stoichiometric ratios were closely related to changes in SOC fractions. These results implied that the differential demands for C, N and P by microbial communities were crucial in regulating the turnover of labile SOC fraction in artificial grassland.
【Objective】 The study was to investigate the effects of three factors, including water replenishment, nitrogen application, and pasture type, on the biomass, plant nutrient composition and soil quality of artificial grassland communities by planting artificial grassland with different planting patterns of Hulunber, and to reveal the retreat of Hulunbuir area and the water-fertilizer coupling mechanisms of cultivated land artificial grassland, so as to optimize the mode of planting management. 【Method】 The experiment was carried out at the Hulunber Grassland Ecosystem Observation and Research Station. On June 6, 2016, the experiment began with four blocks, each of which included three test factors pasture types (P) and nitrogen application level (N) and Irrigation (I); forage types included three treatments: alfalfa (P1), awnless brome (P2), and alfalfa and awnless brome 1:1 mixed sowing (P3); nitrogen application levels included no nitrogen (N0), low nitrogen (N1: 75 kgN·hm-2·a-1) and high nitrogen (N2: 150 kgN·hm-2·a-1). The hydration included two levels (I0: no water, I1: hydration). There were 72 test plots, each of which was 7 m×10 m, and the row spacing was 1 m; it replenished the water 3 times every year in June, July and August, and the water per unit area was 20 mm. The nitrogen application (chemical pure urea) was twice in the seedling (returning) and tillering stages, respectively. Grassland biomass, nutrients (plant crude protein, neutral detergent fiber and acid detergent fiber) and soil nutrients (soil total nitrogen, soil organic carbon and soil pH) were measured in 2016 and 2017. 【Result】 (1) The response of (N), (I), (P) and (P×I) to yield in the year of planting (2016) reached a significant level (P<0.05), and two measurements in 2017. The total yield of the production reached a significant level (P<0.05) in response to test factors such as (N), (P), (P×I), (P×N), (N×I×P), and mixed (P3). Under low water (I0) conditions, the yield of low nitrogen (N1) was significantly higher than that of the other treatment groups (P<0.05), with an average of 17 801.19 kg·hm-2. (2) The crude protein content in 2016 and 2017 were P1 treatment>P3 treatment>P2 treatment, in 2016. P1, P2 and P3 treatment showed that the CP content increased with the increase of nitrogen level when the hydration (I) conditions were the same, and P1 was not replenished under water (I0) conditions. The crude protein content under P1N2I0 was significantly higher than that under P1N0I0, P1N1I0, and P1N1I1 (P<0.05), reaching a maximum value of 19.08%; in 2017, under P3 at I0 conditions, the CP content of the lower N1 level (15.12%) was significantly higher than that of N0 (P<0.05). (3) Both nitrogen application and water addition promoted the negative growth of soil SOC content, positive TN content, and negative pH growth. The SOC growth of the topsoil and the bromegrass were significantly higher than that of the mixed seeding (P<0.05), and the TN growth of the topsoil was significantly higher than that of the bromegrass and mixed seeding (P<0.05); under the surface and subsurface of 2016, the ratio of soil carbon to nitrogen (C/N) was higher than that of 2017, the average surface layer was 17.39% higher, and the subsurface layer was 15.18% higher. The carbon and nitrogen ratio of surface soil was more obvious. The surface soil carbon and nitrogen ratio was P1N0I1 in 2016, with the highest value of 8.15; in 2017, the highest value under P1N2I0 was 5.67. The carbon and nitrogen in the subsurface soil was 6.36 higher than that under P1N2I1 in 2016, and the highest under P3N2I1 in 2017 was 5.67. 【Conclusion】 In the second year of planting in Hulunber, the coupling effect of herbage, water and nitrogen fertilizer had a significant effect on the biomass of the grass. The coupling effect of water and nitrogen fertilizer had a synergistic effect on the nutrient accumulation of the grass. The construction of artificial grassland plant could reduce a C/N and soil quality to drop, and adding in different kinds of grass, and water and nitrogen levels all showed the 0-20 cm soil SOC content and pH value were lower and soil TN content increased, indicating that soil acidification occurs, bean-grain mixed soil pH lower amplitude was less than unicast, and high nitrogen and filling water could be reduced to a significantly increased the soil pH value.
【Objective】 This study evaluated the comprehensive environmental effect of the process of intensive cow breeding-livestock manure utilization-natural grassland improvement. 【Method】 At first, the life cycle inventory of the milk produced under different dairy cattle cultivation modes was established. Then the comprehensive environment effects (greenhouse gas emissions, land occupation, water consumption and non-renewable energy consumption) and overall economic benefits in the whole life cycle of milk production were quantitatively analyzed by combining the experimental data of intensive cow breeding, manure utilization (including microbial fermentation organic fertilizer, earthworm breeding organic fertilizer, and mushroom breeding) and natural grassland improvement with the input data of local animal production and management. The function unit was 1 ton of standard milk (FPCM) in this analysis. 【Result】 The results showed that the mean gross income of local herdsmen’s grazing farms and intensive dairy farms was 8 900 yuan and 211 yuan per adult cow, respectively. If the operating cost was deducted, the net income of each adult cow in the two modes was 4 200 yuan (herdsmen’s grazing farm) and 4 100 yuan (intensive farm), respectively. The environmental impact caused by the production of 1 ton FPCM in intensive farm was 1.19 hm2 of grassland, 0.15 hm2 of arable land, 216.47 t of water, 1 944.19 MJ of fossil fuel and 0.73 t of CO2eq of greenhouse gas. In addition to the grassland area (3.25 hm2), the environmental impact of milk production by herdsmen’s grazing farms were less than that of intensive dairy farms (0.04 hm2 of cultivated land, 70.70 t of water, 892.80 MJ of fossil fuel and 0.55 t of CO2eq greenhouse gas). Natural clipped grassland improvement could significantly increase the hay yield per hectare grassland (increased for 68.57%) and income (increased for 10.71%), it could reduce the grassland area occupied by 40.50%, but the increase of fertilization and fuel consumption in the improvement would cause environmental problems (such as more greenhouse gas emissions 17.70 times) and more fuel consumption (2.10 times). In terms of the application of livestock manure treatment and utilization technology, the cattle manure produced by intensive farms was treated and utilized through microbial fermentation, earthworm treatment and mushroom cultivation, the net income generated was equivalent to about 5%-12% of the net income generated by milk production, and the overall environmental impact was relatively small. 【Conclusion】 Intensive farms had obvious advantages in improving grassland utilization efficiency, and had great potential in improving feed energy conversion efficiency, as well as milk yield and quality. However, intensive dairy farming would increase the planting area of alfalfa, oats and other high protein forages, and cause adverse environmental effects such as more greenhouse gas emissions, more water and energy consumption. In addition, the technology of natural grassland improvement and livestock manure treatment and utilization had great application potential in Hulunber animal husbandry.
【Background】 Hulunber grassland, as the main part of temperate steppe in China, possesses its important position in grassland animal husbandry production and plays the ecological buffer function with its unique geographical location, typical ecological climate and representative production mode. 【Objective】 Grassland, as one of the most important terrestrial ecosystems, has great significance in agricultural and animal husbandry production, ecological and environmental protection, climate change and other aspects. The spatial distribution and change of different grassland types are the basis of grassland research and management. 【Method】 In this paper, different land cover and grassland types in Hulunber grassland were taken as research objects, remote sensing images in 1992 and 2015 were treated as data sources, support vector machine and object-based image analysis classification were used to obtain the spatial distribution in the study area. The temporal and spatial change characteristics were studied by geostatistics, and the effects of climate change and human activities were analyzed by the potential distribution of zonal grassland types classified by plant-habitat classification, social statistical data and the transformation process. 【Result】 The area of cropland, forestland, sandy and alkaline land, building land increased, while the area of grassland and water decreased. Grassland is the largest coverage type in the study area, the areas were 7 601 258 hm2 and 7 148 085 hm2 in 1992 and 2015 respectively, with a 5.96% reduction. Steppe, meadow steppe and lowland meadow had large distribution areas, accounting for more than 70% of the study area, while mountain meadow and swamp had relatively small distribution area, accounting for about 2%. Except the increase of steppe area, the area of other grassland types decreased. The area of steppe increased by 283 790 hm2, with an increase rate of 7.12%. The area of meadow steppe showed the largest decrease, with a decrease of 563 439 hm2 and a decrease of 28.72%. In the study area, the grassland types with relatively humid water status were mainly converted to relatively arid ones, with the transfered area of 466 687 hm2 from 1992 to 2015, and grassland types with relatively dry water status converted to relatively humid ones with a total area of 212 330 hm2. 【Conclusion】 The spatial distribution of different grassland and land cover types in Hulunber grassland changed dramatically. The impacts of climate change are trend, long-term and hard to recover, and the impacts of human activities are fragmentary, reversible and easy to recover.
【Objective】 To study the spatio-temporal characteristics of temperature vegetation drought index (TVDI) in the grassland area of Inner Mongolia in the past 18 years and to explore the relationship between TVDI and meteorological factors, so as to provide theoretical reference for ecological warning and ecological restoration of the study area. 【Method】 Based on MODIS enhanced vegetation index (EVI) and land surface temperature (LST) products to build Ts-EVI characteristic space, according to the characteristic space to calculate TVDI, for normal value of accumulated year of TVDI using unary the Theil-Sen Median trend analysis and Mann-Kendall examination to study the spatial distribution, time-varying characteristics and spatiotemporal evolution trend of drought in the study area during 18 years. 【Result】 On the whole, the average drought degree of grassland in Inner Mongolia is high in southwest and low in northeast, and the average annual TVDI of all grassland types is in order of temperate desert type>temperate steppe-desert type>temperate desert-steppe type>marsh type>temperate steppe type>temperate meadow-steppe type>lowland meadow type>montane meadow type. Among them, the desert grasslands (temperate desert type, temperate steppe-desert type and temperate desert-steppe type) are mainly in the state of severe and mild drought, while non-desert grasslands (temperate steppe type, temperate meadow steppe type, lowland meadow type, mountain meadow type and marsh type) are mainly in the state of mild drought, normal state and mild wetness. Over the past 18 years, the desert grassland has been gradually drying out. In contrast, the non-desert grassland is basically getting wet slowly except for temperate steppe type. In terms of spatial distribution, the total area ratios of the three types of desert grasslands with stable drought degree and drying tendency (slight drying, drying and significant drying) are respectively 44.93% and 55.01%. The total area ratios of the five types of non-desert grassland with stable drought degree and wetting trend (slightly wetting, wetting and significantly wetting) were 72.19% and 24.27%, respectively. 【Conclusion】 Therefore, in the past 18 years, the drought situation of desert grassland is mainly stable and continuous drying, and there are more areas that keep drying, so the ecological environment of grassland continues to deteriorate. The drought situation of non-desert grassland is mainly stable, a small part of the area has a tendency of becoming wet, so the ecological environment of grassland is improving steadily. In addition, the lack of precipitation has a significant effect on the drought degree of non-desert grassland, but not on the desert grassland. The increase of temperature only has a significant effect on the drought degree of the temperate steppe type and the temperate steppe-desert type.
【Objective】 This study aimed to simulate the productivity of hay-land in the semi-arid pastoral region, to evaluate the grassland degradation and to explore the impact of climate on grassland production. 【Method】 The potential productivity of hay-land from 2000 to 2017 was calculated by using Miami and Thornthwaite model, and compared with the MODIS NPP products (MOD17A2H), which represented the actual productivity. 【Result】 From 2000 to 2017, both actual productivity and potential productivity of hay-land in semi-arid pastoral region increased with rising precipitation, with mean value of 295.24 and 557.79 g C?m-2?a-1, respectively. Both the potential and actual productivity were the highest in meadow steppe, which were 589.68 and 349.78 g C?m-2?a-1, respectively, and with the lowest coefficient of variation. The potential productivity was the lowest in mountainous meadow with an average value of 518.72 g C?m-2?a-1, while the actual productivity was the lowest in the typical steppe with 269.52 g C?m-2?a-1. The inter-annual change rate of potential productivity was the highest in the meadow steppe, which was 6.30 g C?m-2?a-1, and the actual productivity was the highest in mountainous meadow with 4.44 g C?m-2?a-1. The actual productivity showed significant positive relationship with precipitation in 95.88% of the hay-land steppe, however, showed negative correlation with temperature in 5.70% of the area. 【Conclusion】 The climatic production potential of forage harvesting area increased from west to east. Under the influence of hydrothermal conditions, the actual productivity gradually decreased in the east and west foothills of the Daxing’an Mountain range, and its response to precipitation was higher than that of temperature. The average annual utilization rate of climate resources was the same as the actual productivity, and the average utilization rate of climate resources was 55.09%. The grassland of meadow grassland had the highest utilization rate of climate resources, which was as high as 60.34%.
【Objective】 The grassland ecosystem plays an important role in the global carbon balance. The study of grassland carbon pool and its driving force is a hot point of vegetation ecology. This study investigated the vegetation carbon density and its spatial pattern in the steppe and agro-pastoral ecotones of northern China. The major factors driving the spatial variation of grassland vegetation carbon density were identified, as well as the relative contribution of climate, soil texture, grazing intensity and other factors to the grassland vegetation carbon pool. 【Method】 Using the survey data of the grassland vegetation in northern grassland during 2002 and 2009, combined with the MODIS/NDVI remote sensing data and 1:1 million grassland type map, the estimation model of above- and below-ground biomass in the main grassland types of northern China was established. Based on 255 county-level administrative units in the study area, the relationship between grassland vegetation carbon density and climate factors, soil texture and livestock carrying capacity were explored, and derived the relative contribution of different driving factors to grassland carbon density using the general linear model (GLM). 【Result】 (1) The average above-ground biomass (AGB) of the steppe and agro-pastoral ecotones of northern China was 36.9 g C·m-2, and the below-ground biomass (BGB) was 362.9 g C·m-2, nearly 10 times the AGB. Both the above- and below-ground biomass decreased from east to west, and followed logarithmic normal distribution. The biomass carbon density of grassland types was significantly different. (2) In the whole study region and steppe sub-region, desert sub-region, agro-pastoral sub-region, the AGB showed a significantly positive correlation with mean annual precipitation (MAP) and soil clay content (Clay%), a significantly negative relationship with the mean annual temperature (MAT) and soil sand content (Sand%). The AGB increased with livestock carrying capacity except in the steppe sub-region where were very heavily grazed. (3) General Linear Model (GLM) analysis indicated that the MAP, MAT, Clay% and grazing intensity explained 29.6% (P<0.001), 5.8% (P<0.001), 0.8% (P<0.05) and 1.3% (P<0.001) of AGB variation, respectively, and the MAP, MAT and Sand% contributed to 12.1% (P<0.001), 6.8% (P<0.001) and 1.9% (P<0.005) to BGB variation, respectively, and the grazing intensity had minor contribution to BGB. 【Conclusion】 Climate factors especially MAP was the dominate driving factor of grassland vegetation carbon density, and its impact on AGB was more obvious than on BGB. Soil texture also had a significant contribution to the grassland vegetation carbon density, especially on the BGB. Grazing intensity explained only 1.3% of the AGB and had no impact on BGB. This finding indicated that the climate factors were major contributor grassland vegetation carbon density comparing with grazing intensity.
