Response Mechanism Of Soil Micro-food Webs To Exogenous Stover Carbon Input Under No-tillage System

In soil micro-food webs,resource transfer between microorganisms(bacteria,fungi)and microbivorous nematodes govern the transformation and cycling of soil organic carbon,productivity and sustainability of soil ecosystems.However,changing the amount and frequency of stover mulching affects the resources available in the bacterial versus fungal decomposition pathways of soil micro-food webs.Therefore,we investigated the response mechanism of the soil micro-food webs to maize stover mulching amounts(33% and 67% of the stover remaining at harvest)and frequencies(high frequency with continuous mulching every year,low frequency with mulch application once every three years)during a 10-year mulching experiment in a no-tillage system.Soil microorganisms and nematode communities were significantly affected by the frequency,but not the amount of stover mulching.Higher abundance of bacterial PLFAs correlated with bacterivores occurred in the high frequency mulching treatments.In the low frequency mulching treatments,higher abundance of fungal PLFAs correlated with fungivores was observed.Greater nematode enrichment in the high frequency mulching indicated more carbon flow from mulch into the soil micro-food web,whereas low frequency mulching tended to develop a relatively stable soil micro-food web.Stover as exogenous organic carbon,changes the composition of soil carbon.In this study,no significant differences were found among the microbial PLFAs and nematode biomass carbon with different stover mulching amount.However,a certain "trade-in" effect was definitely existed.In other words,part of the stover carbon will replace the soil original organic carbon,and this fixed "new carbon" is exactly related to the amount of stover input.Thus,the more stover mulching,the more exogenous carbon flow through the soil micro-food web,and then greater contribution to "trade-in" effect of soil carbon was attained.It is concluded that trophic interactions regulate the bidirectional coupling between bacteria and bacterivores with high frequency mulching and between fungi and fungivores with low frequency mulching.Consequently,the structure and activity of decomposition pathways in soil micro-food webs are determined by the bottom-up effect of stover mulching.