Scientia Agricultura Sinica

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Effects of Grazing Intensity on Plant Community Characteristics and Nutrient Quality of Herbage in a Meadow Steppe

ZHANG Yu, HOU LuLu, YAN RuiRui, XIN XiaoPing

Scientia Agricultura Sinica 2020, 53 (13): 2550-2561. DOI: 10.3864/j.issn.0578-1752.2020.13.004

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【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.

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Effects of Grazing Intensity on Functional Traits of Leymus chinensis in Meadow Steppe

HOU LuLu,YAN RuiRui,ZHANG Yu,XIN XiaoPing

Scientia Agricultura Sinica 2020, 53 (13): 2562-2572. DOI: 10.3864/j.issn.0578-1752.2020.13.005

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【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.

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Effects of Mowing Disturbance on Grassland Plant Functional Groups and Diversity in Leymus chinensis Meadow Steppe

YAN RuiRui,ZHANG Yu,XIN XiaoPing,WEI ZhiJun,Wuren qiqige,GUO MeiLan

Scientia Agricultura Sinica 2020, 53 (13): 2573-2583. DOI: 10.3864/j.issn.0578-1752.2020.13.006

Abstract （291）

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【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.

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Salt-Alkalinze Stress Induced Rhizosphere Effects and Photosynthetic Physiological Response of Two Ecotypes of Leymus chinensis in Songnen Meadow Steppe

YAO Yuan,XU YueQiao,WANG Gui,SUN Wei

Scientia Agricultura Sinica 2020, 53 (13): 2584-2594. DOI: 10.3864/j.issn.0578-1752.2020.13.007

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【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, Na₂SO₄solution, 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.

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Effect of Fairy Rings on Soil Respiration in Hulunber Meadow Steppe

FAN KaiKai,TONG XuZe,YAN YuChun,XIN XiaoPing,WANG Xu

Scientia Agricultura Sinica 2020, 53 (13): 2595-2603. DOI: 10.3864/j.issn.0578-1752.2020.13.008

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【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.

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