农业生态环境-土壤微生物Agro-ecosystem & Environment—Soil microbe
The species richness and propagule number of arbuscular mycorrhizal fungi (AMF) are high in intensively-managed agricultural soils. Past research has shown that AMF improve crop phosphorus (P) uptake under low soil P conditions, however it is unclear if AMF play a role in high Olsen-P soils. In this study, we investigated whether native fungal benefits exist under high P input field conditions in-situ and contribute to P utilization. We installed in-grow tubes which were sealed with different membrane pore sizes (30 or 0.45 µm) to allow or prevent AMF hyphae access to the hyphal compartment and prevent cotton roots from penetrating the chamber. We used the depletion of soil available P (Olsen-P) in the hyphae accessed compartment to indicate P uptake by the native AMF community. Our results showed that the native AMF mediated P depletion and microbial biomass P (MBP) turnover and caused the largest Olsen-P depletion ratio and MBP turnover ratio in the high P treatments (Olsen-P: 78.29 mg kg–1). The cotton roots in each fertilization regime were colonized by a unique AMF community and Glomus and Paraglomus were the dominant genera, implying the long-term fertilization regimes domesticated the AMF community. We conclude that native AMF caused the P depletion and P turnover even under high soil Olsen-P conditions.
The soybean rhizosphere has a specific microbial community, but the differences in microbial community structure between different soybean genotypes have not been explained. The present study analyzed the structure of the rhizosphere microbial community in three soybean genotypes. Differences in rhizosphere microbial communities between different soybean genotypes were verified using diversity testing and community composition, and each genotype had a specific rhizosphere microbial community composition. Co-occurrence network analysis found that different genotype plant hosts had different rhizosphere microbial networks. The relationship between rhizobia and rhizosphere microorganisms in the network also exhibited significant differences between different genotype plant hosts. The ecological function prediction found that different genotypes of soybean recruited the specific rhizosphere microbial community. These results demonstrated that soybean genotype regulated rhizosphere microbial community structure differences. The study provides a reference and theoretical support for developing soybean microbial inoculum in the future.
The yield of winter wheat is hindered by drought and low temperature in the Loess Plateau of China. Two common mulching methods to conserve soil moisture, ridge furrows with plastic film mulching (RP) and flat soil surfaces with plastic film mulching (FP) are helpful for wheat production. Our previous study indicated that FP could improve wheat yield more effectively than RP, but the reason remains unclear. The effect of mulching method on functional bacteria also needs to be further studied. In this study, winter wheat was employed to evaluate the impacts of mulching method on soil temperature, moisture content, microorganisms and grain yield. The results showed that FP had a warming effect when the soil temperature was low and a cooling effect when the temperature was too high. However, the ability to regulate soil temperature in the RP method was unstable and varied with year. The lowest negative accumulated soil temperature was found in the FP treatment, which was 20–89 and 43–99% lower than that of the RP and flat sowing with non-film mulching control (NP) treatments, respectively. Deep soil moisture was better transferred to topsoil for wheat growth in the FP and RP treatments than the NP treatment, which made the topsoil moisture in the two treatments (especially FP) more sufficient than that in the NP treatment during the early growing stage of wheat. However, due to the limited water resources in the study area, there was almost no difference between treatments in topsoil water storage during the later stage. The wheat yield in the FP treatment was significantly higher, by 12–16 and 23–56%, respectively, than in the RP and NP treatments. Significant positive correlations were observed among the negative accumulated soil temperature, spike number and wheat yield. The Chao1 and Shannon indices in the RP treatment were 17 and 3.9% higher than those in the NP treatment, respectively. However, according to network relationship analysis, the interspecific relationships of bacteria were weakened in the RP treatment. Phosphorus solubilizing, ammonification and nitrification bacteria were more active in the RP than in the FP treatment, and microbes with nitrate reduction ability and plant pathogens were inhibited in the RP treatment, which improved nutrient availability and habitat for wheat.
A chorismate mutase from Radopholus similis plays an essential role in pathogenicity
In the process of infecting plants, plant parasitic nematodes release a series of proteins that play an essential role in the successful infection and pathogenesis of plant cells and tissues through stylets or body walls. In this study, based on transcriptome data, a chorismate mutase gene of Radopholus similis (RsCM) was identified and cloned, which is a single copy gene specifically expressed in the oesophageal gland and highly expressed in juveniles and females. Transient expression of RsCM in tobacco leaves showed that it was localised in the cytoplasm and nucleus of tobacco leaf cells, which inhibited the pattern-triggered immunity (PTI) induced by flg22, including callose deposition and defence gene expression, and cell death induced by immune elicitors BAX, but could not inhibit cell death induced by immune elicitors Gpa2/RBP-1. The RNA interference (RNAi) transgenic tomato of RsCM obviously inhibited the infection, pathogenicity, and reproduction of R. similis. However, the resistance of the overexpression transgenic tomato of RsCM to R. similis infection was significantly reduced, and the expression levels of two salicylic acid (SA) pathway genes (PR1 and PR5) in roots infected by the nematode were significantly down-regulated, which indicated that RsCM might be involved in the inhibition of SA pathway. The results of this study demonstrate that RsCM suppresses the host immune system and might be a new target for the control of R. similis, which also provides new data for the function and mechanism of CM genes of migratory parasitic plant nematodes.
The competition between Bidens pilosa and Setaria viridis alters soil microbial composition and soil ecological function
Soybean (Glycine max) rhizosphere organic phosphorus recycling relies on acid phosphatase activity and specific phosphorus-mineralizing-related bacteria in phosphate deficient acidic soils
Bacteria play critical roles in regulating soil phosphorus (P) cycling. The effects of interactions between crops and soil P-availability on bacterial communities and the feedback regulation of soil P cycling by the bacterial community modifications are poorly understood. Here, six soybean (Glycine max) genotypes with differences in P efficiency were cultivated in acidic soils with long-term sufficient or deficient P-fertilizer treatments. The acid phosphatase (AcP) activities, organic-P concentrations and associated bacterial community compositions were determined in bulk and rhizosphere soils. The results showed that both soybean plant P content and the soil AcP activity were negatively correlated with soil organic-P concentration in P-deficient acidic soils. Soil P-availability affected the ɑ-diversity of bacteria in both bulk and rhizosphere soils. However, soybean had a stronger effect on the bacterial community composition, as reflected by the similar biomarker bacteria in the rhizosphere soils in both P-treatments. The relative abundance of biomarker bacteria Proteobacteria was strongly correlated with soil organic-P concentration and AcP activity in low-P treatments. Further high-throughput sequencing of the phoC gene revealed an obvious shift in Proteobacteria groups between bulk soils and rhizosphere soils, which was emphasized by the higher relative abundances of Cupriavidus and Klebsiella, and lower relative abundance of Xanthomonas in rhizosphere soils. Among them, Cupriavidus was the dominant phoC bacterial genus, and it was negatively correlated with the soil organic-P concentration. These findings suggest that soybean growth relies on organic-P mineralization in P-deficient acidic soils, which might be partially achieved by recruiting specific phoC-harboring bacteria, such as Cupriavidus.
Land use influences soil biota community composition and diversity, and then belowground ecosystem processes and functions. To characterize the effect of land use on soil biota, soil nematode communities in crop land, forest land and fallow land were investigated in six regions of northern China. Generic richness, diversity, abundance and biomass of soil nematodes was the lowest in crop land. The richness and diversity of soil nematodes were 28.8 and 15.1% higher in fallow land than in crop land, respectively. No significant differences in soil nematode indices were found between forest land and fallow land, but their network keystone genera composition was different. Among the keystone genera, 50% of forest land genera were omnivores-predators and 36% of fallow land genera were bacterivores. The proportion of fungivores in forest land was 20.8% lower than in fallow land. The network complexity and the stability were lower in crop land than forest land and fallow land. Soil pH, NH4+-N and NO3–-N were the major factors influencing the soil nematode community in crop land while soil organic carbon and moisture were the major factors in forest land. Soil nematode communities in crop land influenced by artificial management practices were more dependent on the soil environment than communities in forest land and fallow land. Land use induced soil environment variation and altered network relationships by influencing trophic group proportions among keystone nematode genera.
Characteristics of the microbial communities regulate soil multi-functionality under different cover crop amendments in Ultisol
The use of cover crops is a promising strategy for influencing the soil microbial consortium, which is essential for the delivery of multiple soil functions (i.e., soil multifunctionality). Nonetheless, relatively little is known about the role of the soil microbial consortium in mediating soil multifunctionality under different cover crop amendments in dryland Ultisols. Here, we assessed the multifunctionality of soils subjected to four cover crop amendments (control, non-amended treatment; RD, radish monoculture; HV, hairy vetch monoculture; and RDHV, radish–hairy vetch mixture), and we investigated the contributions of soil microbial richness, network complexity, and ecological clusters to soil multifunctionality. Our results demonstrated that cover crops whose chemical composition differed from that of the main plant crop promoted higher multifunctionality, and the radish–hairy vetch mixture rendered the highest enhancement. We obtained evidence that changes in soil microbial richness and network complexity triggered by the cover crops were associated with higher soil multifunctionality. Specifically, specialized microbes in a key ecological cluster (ecological cluster 2) of the soil microbial network were particularly important for maintaining soil multifunctionality. Our results highlight the importance of cover crop-induced variations in functionally important taxa for promoting the soil multifunctionality of dryland Ultisols.
Phthalate esters (PAEs) are an emerging pollutant due to widespread distribution in environmental mediums that have attracted widespread attention over recent years. However, there is little information about tea plantation soil PAEs. A total of 270 soil samples collected from 45 tea plantations in the major high-quality tea-producing regions of Jiangsu, Zhejiang, and Anhui provinces in China were analyzed for seven PAEs. The detection frequency of PAEs in tea plantation soil was 100%. DBP, DEHP, and DiBP were the main congeners in tea plantation soil. The PAEs concentrations in the upper soil were significantly higher than those in the lower soil. The concentration of tea plantation soil PAEs in Jiangsu Province was significantly lower than those in Zhejiang and Anhui provinces. Intercropping with chestnuts can effectively reduce the contamination level of PAEs in tea plantation soil. Correlation analysis, redundancy analysis, partial correlation analysis, and structural equation modeling methods further confirmed the strong direct influence of factors such as chestnut–tea intercropping, temperature, and agricultural chemicals on the variation of PAEs in tea plantation soil. The health and ecological risk assessments indicated that non-carcinogenic risk was within a safe range and that there was a high carcinogenic risk via the dietary pathway, with DBP posing the highest ecological risk.