Soil Protists Assemblage Across Precipitation Gradient And Its Response To Simulated Warming

Changes in regional precipitation patterns caused by climate warming are projected to profoundly affect terrestrial ecosystems functions.At present,relevant studies mainly focus on the response of macro-organisms,especially aboveground plants and animals,while little attention was paid to soil communities.Given the important role of soil communities in the biogeochemical cycle,their response to changes in precipitation patterns and climate warming is of great significance for understanding changes in ecosystem structure,especially its feedback on climate change.Soils in most regions of the world are expected to experience drought in the face of climate warming.Soil organisms,especially soil protists within soil micro-food webs,are very sensitive to drought,which can sensitively respond to drought caused by changes in precipitation patterns.However,we know little about the response of soil protists to climate change.On the one hand,drought will directly cause stress to the soil organisms and affect their survival and reproduction;on the other hand,drought will also affect soil biotas through the physical processes of dissolution,diffusion and transportation in the soil,which determines the supply of microbial substrates.In the meanwhile,drought may interact with other climate change factors such as warming and nitrogen deposition.Understanding the interaction of multiple climate change factors is of great significance for projecting the response of ecosystems to future complex climate change scenarios.In this study a large-scale investigation was firstly conducted to explore the diversity and community structure of soil protists to understand the key factors affecting their communities.Then,an incubation experiment was conducted to further explore whether the drought legacy effect would further affect the response of soil micro-food web to warming.The following results were the investigation of soil protists communities under different precipitation gradient: 1)The species abundance and diversity of soil protists were sensitive to the decrease of water content.When the soil moisture conditions were reduced to a certain threshold,the species diversity of soil protists began to decline sharply;2)SAR(Stramenopiles,Alveolata,Rhizaria)and Amoebozoa supergroup in soil protists were relatively dominant taxa groups.Among the functional groups,the consumer groups consist bacterivores and omnivores dominated(the relative abundance was 50%–80%).Annual precipitation and electrical conductivity are the dominant predictors of relative abundance of different soil protist functional groups;3)Climate factors ware the best predictor soil protists diversity.The quantity of substrate(including soil total carbon,total nitrogen and total phosphorus)better explain the species diversity of native organisms than the quality(including soil C: N,C: P and N: P).The community structure of soil protists(represented by Bray-Curtis dissimilarity)was significantly correlated with both climate(R = 0.287,P <0.001)and soil(R = 0.221,P < 0.001)factors.The laboratory incubation experiment further revealed that: 1)Annual precipitation shaped soil micro-food webs with different complexity,and generally the complexity of soil micro-food webs decreased with the decrease of precipitation.2)The effects of simulated warming on the complexity of soil micro-food web depends on historical precipitation.Simulated warming reduces the complexity of soil micro-food web of soil with more abundant historical precipitation,and increases the complexity of soil micro-food web with less historical precipitation,which might be attributed to the alteration of soil fungi/ bacteria ratio under simulated warming.3)In order to explore the effect of warming on soil ecosystem function across different precipitation gradient,soil multifunctionality was calculated based on soil enzyme activity and soil available nutrient content.The results showed that simulated warming had no significant effect on the soil multifunctionality of soils with most abundant precipitations,increased the soil multifunctionality of soils from drier sites,and reduced the soil multifunctionality of soils from remaining intermediate precipitation gradient sites.The interaction of precipitation and warming had significant effects on soil multifunctionality(P< 0.001).Structural equation model showed that soil multifunctionality was driven both by species diversity and structure of soil micro-food web.In summary,changes in precipitation patterns will affect soil protist community,thereby affecting the structural response and functional feedback of the entire soil micro-food web.This result indicates that the drought effects caused by the change of precipitation pattern will profoundly impact ecosystem structure and function through influencing soil communities belowground.