Mechanisms Of Microbes And Soil Respiration And Q₁₀ Under Vegetation Restoration On The Chinese Loess Plateau

The survival and development of human beings have been threatened by global warming.In order to alleviate climate warming and seek a sustainable and green-friendly way,China has set a goal of reaching a peak in carbon dioxide emissions and achieve carbon neutrality.Soil respiration is the second largest carbon flux in terrestrial ecosystems,the annual CO₂ flux of which is about ten times higher than that of the annual emissions from fossil fuel.The feedback between soil respiration and global warming has always been a hotspot.For accurately assessing the global carbon cycle,predicting climate change and achieving the goal of carbon peak and carbon-neutral as scheduled,it is important to clarify the changes of soil respiration and its influencing factors.Since 1999,China has implemented large-scale vegetation restoration projects,which greatly affected the soil physicochemical properties,such as vegetation coverage,soil carbon and nitrogen storage,as well as microbial properties.These factors are also important factors affecting soil respiration and its temperature sensitivity(Q₁₀).At present,a series of studies have been conducted on soil carbon dynamics in vegetation restoration zones,whereas,the response of soil respiration and its temperature sensitivity to microorganisms remains unclear.To systematically reveal the response of soil respiration and temperature sensitivity to microbes after revegetation,the typical revegetation types（including Robinia pseudoacacia forest,abandoned cropland,apple orchard,Coronilla varia grassland and cropland）have been selected to do researches.Coupling high throughput sequencing,quantitative microbial element cycling functional genes（QMEC）and microbial co-occurrence network analysis,this study has revealed the effect of soil microbes on soil respiration and its temperature sensitivity,with the aspects of microbial diversity and community composition,co-occurrence network,key species and functional genes.The main conclusions are as follows:（1）Revealing the mainly influential factors of soil respiration and its temperature sensitivity.The soil respiration was decreased by 19.2%-52.9%and Q₁₀value was decreased by 39.1%-66.3%（P<0.05）after revegetation.The changes of soil respiration showed a fluctuating pattern with the stand ages going on,which is initially decreased,then increased and decreased again.However,the Q₁₀ values are decreased all the time.The active components of soil organic carbon and the abundance of fungi had great effects on soil respiration（R²=44.5%,P<0.05）,and Q₁₀ values were significantly associated with the bacterial community composition.（2）The study has pointed out that soil microbial properties are the key factors affecting soil respiration and its temperature sensitivity.Coupling the results of VPA and correlation analyses illustrated that it is the joint effect of soil physicochemical properties and bacterial properties on soil respiration,instead of the single one,and both Rs and Q₁₀was influenced by the community composition of the bacteria,which were shifted by SWC and AN（R²=45.7%,P<0.05）.Thus,it was concluded that SWC and AN affected soil respiration and its temperature sensitivity via changing the composition of the microbial community.The results showed that the effects of microorganisms on soil respiration were confused by the environmental factors,and the most direct cause of soil respiration was soil microorganisms.The co-occurrence network revealed that the Mod 0 ecological clusters mainly composed of copiotrophs groups（such as Actinobacteria,Chloroflexi,Proteobacteria,and Bacteroidetes）were significantly associated with soil respiration.（3）The important effects of functional genes related to carbon degradation on soil respiration and its temperature sensitivity were clarified.The results of least-squares regression fitting and correlation analysis showed that it is the carbon-degradation function genes affected soil respiration and its temperature sensitivity（R²=35.5%,P<0.05）,instead of microbial diversity.Soil respiration and it’s temperature sensitivity are largely driven by the carbon-degradation functional genes related to relatively easily decomposed organic carbon（such as the of carbohydrates-degradation related genes R²=0.355,P<0.05,starch-degradation related genes R²=0.273,P<0.05,hemicellulose-degradation related genes R²=0.316,P<0.05 and cellulose-degradation related genes R²=0.330,P<0.05）,rather than the carbon-degradation functional genes related to relatively difficultly decomposed organic carbon（e.g.,chitin,pectin and lignin）.In conclusion,this study revealed that soil physicochemical factors indirectly affect soil respiration and its temperature sensitivity via influencing microbial community structure,and the soil microorganisms were the main factors directly affecting soil respiration and its temperature sensitivity.The Mod 0 ecological clusters mainly composed of copiotrophs groups were significantly associated with soil respiration.It is the carbon-degradation functional genes related to soil respiration,instead of the microbial diversity.The carbon-degradation functional genes related to relatively easily decomposed organic matter are the main reasons for the differences in soil respiration and temperature sensitivity in vegetation restoration areas.This study provided a theoretical basis for the accurate assessment of the terrestrial ecosystem carbon cycle and the goal of achieving carbon peak and carbon neutral.