Effects Of Changes In Plant Resource Inputs On Soil Nematodes Energy Fluxe And Microbial Community Across Forest Ecosystems

Forests generally display greater biological and structural complexity and they cover approximately 30%of the earth’s land surface,but harbor 80% of terrestrial plants and animals.Plants play an important role in nutrient cycling and energy transfer in terrestrial ecosystems.Meanwhile,they also exert a profound influence on the soil organisms and their ecological functions.Plant-derived litter,dead roots,root and root exudates are main resources for the soil food webs and the changes of their quantity and quality have the potential to influence the soil organisms in the soil food webs.Thus,plant-derived litter,dead roots,and root exudates are closely related to food acquisition and resource utilization of soil organisms.Such changes in soil community composition and biodiversity may alter predator-prey interactions and correspondingly energy fluxes in soil food webs.Thus,exploring the effects of plant-derived carbon input on the energy fluxes through soil food webs can help generate a better mechanistic understanding of the regulating forces of soil biodiversity,especially at different latitudes.Here,we explored the effects of variations in plant-derived resource inputs on the energy flux of soil nematodes and soil microbial community characterized by phospholipid fatty acids(PLFAs)and neutral fatty acids(NLFAs)in soil food webs based on the manipulative field experiments,including litter reduction,tree root removal and understory removal treatments in three typical forest ecosystems at different latitudes.The main findings are as follows:(1)After one year of treatment,litter reduction and understory removal did not alter nematode energy fluxes in low-latitude forests,but litter reduction reduced the energy fluxes of fungal-feeding nematodes in high-latitude forests.And we found a significant interaction between litter reduction and understory removal,compared with the control,the litter reduction alone increases or tends to increase the energy flux of plant-feeding nematodes,fungal-feeding nematodes,omnivorous-predatory nematodes,and total nematodes,but the litter reduction after understory removal tends to reduce the energy flux of these groups.Similarly,litter reduction and understory removal did not alter the relative energy fluxes of nematodes in low-latitude forests.However,litter reduction reduced the relative energy fluxes of fungal-feeding nematodes in mid-latitude forests,and understory removal reduced the relative energy fluxes of omnivorous-predatory nematodes in high-latitude forests.In most cases,nematode energy fluxes in different trophic groups increased or tend to increase with the increasing nematode diversity,except for plant-feeding nematodes in high-and mid-latitude forests and fungal-feeding nematodes in low-latitude forests.After two years of treatment,litter reduction and/or root removal did not alter nematode energy fluxes in high-and mid-latitude forests.However,litter reduction and root removal reduced the nematode energy fluxes of plant-feeding or bacterial-feeding nematodes in low-latitude forests,thus reducing the energy fluxes of total nematodes in low-latitude forests.In addition,root removal reduced the relative energy fluxes of plant-feeding nematodes in all forests at different latitudes,but increased the relative energy fluxes of bacterial-feeding nematodes in high-latitude forests and the relative energy fluxes of bacterial-feeding nematodes and omnivorous-predatory nematodes in mid-latitude forests.In most cases,nematode energy fluxes in different trophic groups increased with increasing in nematodes diversity with the exception of fungal-feeding nematodes in all forests.(2)After two and a half years of treatment,litter reduction and understory removal did not alter soil microbial PLFAs in low-latitude forests,but we found a significant interactive effect between litter reduction and understory removal on soil microbial NLFAs in low-latitude forests,the main performance is shrubs removal alone had no effect on the NLFAs of arbuscular mycorrhizal(AM)fungi and gram-positive bacteria,but their neutral fatty acids increased in the understory removal after litter reduction.Root removal reduced the biomass of actinomycetes,AM fungi,fungi,gram-positive bacteria,protozoa,total microbial PLFAs and the bacterial stress index,F:B ratios,gram-positive: gram-negative in high-latitude forests and reduced the biomass of actinomycetes and fungi in mid-latitude forests.In addition,root removal increased the soil fungal NLFAs: bacterial NLFAs ratios in mid-latitude forests and NLFAs/PLFAs of AM fungi in high-latitude forests,promoting the accumulation of fungal NLFAs in mid-latitude forests and AM fungi in high-latitude forests.Collectively,litter reduction,understory removal and root removal reduced the input of plant-derived resources into the soil,which further reduced the food and energy resources of soil microbes and nematodes and altered their habitats,thus influencing nematode energy fluxes as well as soil microbial community characterized by PLFAs and NLFAs.However,all the effects of changes in plant resource inputs on energy fluxes of soil nematodes and microbial community composition are affected by climate and plant resource type.For instance,although root removal had different influences on the energy fluxes of plant-feeding nematodes,it reduced the relative energy flux of plant-feeding nematodes in all forests at different latitudes,suggesting a closer relationship between plant root inputs and plant-feeding nematode energy fluxes.Furthermore,in most cases,nematode energy fluxes in different trophic increased with increasing diversity to nematodes,suggesting that nematode communities can maintain greater activity at higher levels of diversity and thus causing more resources entering the nematode communities in the same amount of time.However,we only selected a single population in the soil food webs,and this could not fully reflect the relationship between real diversity and energy flow dynamics at the food web level and the relationship between diversity and energy flux may not be a simple linear relationship,which is worthy of further study.