Effects Of Grazing Intensity On Soil Micro-food Webs In Typical Temperate Steppe

The typical temperate steppe in Inner Mongolia is the main component of the grassland in north China,which is widely distributed and highly representative.It is important for ecological balance and regional economic.Soil microbe and nematodes are important participants in soil material cycling and conservation,and the soil micro-food web formed by them plays a key role in maintaining ecosystem functions.In this study,the soil biological community was analyzed by phospholipid fatty acid method and high-throughput sequencing method,to explore the interaction between soil microbe and nematodes under grazing.The main driving factors of soil quality and ecosystem health were discussed by calculating various ecological indexes and constructing micro-food web structure,so as to provide theoretical basis for realizing reasonable grassland grazing management and sustainable development of grassland ecosystem.The main results are as follows:(1)Grazing significantly changed the contents of soil moisture,ammonium nitrogen and nitrate nitrogen.The results of comprehensive assessment by factor analysis showed that soil quality under enclosure treatment was higher than that of grazing plots.Under different treatments,soil microbial biomass carbon varied from1105.04 mg/kg to 1209.85 mg/kg,which was significantly positively correlated with soil organic carbon content.Microbial biomass nitrogen varied from 62.99 mg/kg to87.63 mg/kg,which was significantly correlated with soil total nitrogen content.The change of grazing intensity did not significantly change soil microbial biomass carbon and microbial biomass nitrogen,while soil microbial biomass phosphorus under light grazing was significantly lower than that under enclosure and heavy grazing.(2)There was no significant difference in microbial community structure under different grazing intensities,but grazing had a significant effect on microbial quantity and diversity index.The total amount of microbial phospholipid fatty acids in the heavy grazing plot(13.29 nmol/g)was significantly lower than that in other plots.It was the highest under light grazing(31.29nmol/g),but there was no significant difference between enclosure and light grazing treatments.Under heavy grazing,the ratio of gram-positive bacteria to gram-negative bacteria was significantly higher than that of other plots,and the ratio of saturated fatty acids to monounsaturated fatty acids was significantly lower,indicating that soil microbial community was subjected to greater environmental stress under this environment.The ratios of fungi and bacteria under different grazing treatments varied from 0.09 to0.10 with no significant changes.Grazing intensity had no significant effect on the anti-interference ability of the ecosystem.(3)Grazing changed the number,composition and ecological index of soil nematode community.Total carbon content was the more important environmental factor affecting the nematode community.Plant parasitic nematodes have always been dominant in nematode communities.The relative abundance of bacterivores was the highest under heavy grazing,while fungivores and omnivores/predators decreased under grazing.The maturity index of free-living nematodes decreased with the increase of grazing intensity.The structure index of soil nematodes under light grazing was significantly lower than that of other plots,and soil nematodes had stronger anti-interference ability and complete soil food web function.The metabolic footprint and functional footprint of soil nematodes were the smallest under heavy grazing,indicating that the life activities of soil nematodes were reduced to some extent under this treatment.(4)The decomposition pathway of soil micro-food web was always dominated by bacteria.Grazing disturbance had a certain negative impact on the connectivity of soil micro-food web,but also reduced the feeding rate of fungal channels,and the soil ecosystem became more dependent on bacterial decomposition pathways.Under different grazing intensities,the feeding intensity of plant parasitic nematodes reached the highest in medium grazing plots,while soil microbe had a higher utilization rate of plant roots under enclosure treatment.The soil carbon and nitrogen mineralization rate was quantified based on the results of soil biological basic physiological parameters and feeding rate.Compared with other treatments,light grazing was more beneficial to soil carbon and nitrogen mineralization.Bacteria and nematodes were the main contributors to carbon and nitrogen mineralization respectively under different plots.They were the key components of soil micro-food web.In typical temperate steppe,grazing affected energy flow and interaction among functional groups in soil micro-food web through the changes of soil microbial and nematode communities.The higher the grazing intensity,the higher the disturbance degree of grazing activity to the typical grassland in temperate zone.Heavy grazing had a significant negative effect on the connectivity and function of soil micro-food web,while grazing management at light level was more conducive to the sustainable development of soil ecosystem.