Effects Of Snow Cover On Soil Respiration And Microbial Community In Non-growing Season Of Typical Temperate Grassland

The typical temperate grassland located in the Xilin River Basin in the eastern Inner Mongolia Plateau is one of the international biosphere reserves recognized by UNESCO.Studying the key processes of soil carbon dynamics under different snow cover will help to better understand the mechanism of soil carbon decomposition under global climate change and provide a theoretical basis for further clarification of grassland carbon dynamics.In this paper,the grassland near the Xilin River Basin in Inner Mongolia was selected as the research area and the samples were collected in differnent periods of the whole non-growing season.The Rs in different periods was measured by static dark box method.The influence of different snow cover on Rs in different periods of the non-growing season were analyzed,and the main driving factors were discussed by correlation analysis and regression analysis.The physicochemical properties of soil and the vertical differentiation of microbial community composition,which are closely related to soil carbon emissions,were investigated at different soil depths during the spring and thaw stages,and the characteristics of soil microbial communities were determined by 16Sr RNA sequencing technology,laying a foundation for further discussion of carbon emission mechanisms in the future.The main research conclusions of this paper include the following parts:(1)Rs flux under three snow treatments(IS,DS,CK)in different sampling periods(IFP,DFP,SMP)in the non-growing season were 5.87±0.28?55.11±0.71 mg·m^-2·h^-1.Although there was no negative flux of soil respiration under different snow treatments in the whole non-growing season,different snow treatments did not significantly increase or reduce soil CO₂ emissions to the atmosphere(p>0.05).Rs flux were lower under different treatments during IFP and DFP periods,and the emission ranges were5.87±0.28?21.67±7.65 mg·m^-2·h^-1and 6.19±0.67?27.19±1.20 mg·m^-2·h^-1,respectively.By the SMP period,Rs flux increased,and the emission range was10.41±2.23?55.11±0.71 mg·m^-2·h^-1.The peak value of Rs flux under IS and DS treatment was about twice that of CK.(2)The cumulative flux of Rs in different sampling periods(IFP,DFP,SMP)under three snow treatments(IS,DS,CK)in the non-growing season ranged from 22.81±0.68to 26.36±0.41 g C m^-2.In SMP period,Rs cumulative flux under IS and DS treatments were significantly higher than CK(p<0.01),but there was no significant difference in Rs flux under different snow treatments in IFP and DFP periods.The daily average flux of Rs in different sampling periods was SMP>DFP>IFP.(3)Correlation analysis found that there was no significant correlation between environmental factors and Rs flux under different snow treatments in the non-growing season during IFP and DFP periods.However,Rs flux under IS and DS treatments in the SMP period were mainly positively correlated with T0(Soil temperature at 0cm)and T5(Soil temperature at 5cm)and negatively correlated with NH₄⁺-N.CK treatment was positively correlated with T5.Regression analysis found that the main controlling factor affecting Rs was T0 under IS and DS treantments and T5 under CK treatment,which could explain the variation of Rs flux under different snow cover by 90.3%(IS),62.7%(DS),and 44.8%(CK),respectively.(4)There was no significant difference in soil p H under different snow cover(p<0.01).After LSD multiple comparison,it was found that the p H value after IS and DS treatments were significantly higher than CK.But at the depth of other soil layers,there was little change in soil p H under different snow cover.There were significant differences in SWC,T_soil,p H,MBC,NH₄⁺-N,NO₃^--N in different soil depths(p<0.01).There was no significant difference in soil physical and chemical properties under the interaction of different soil depths and snow cover(p>0.05).With the increase of soil depth,SWC and T_soil decreased gradually;soil p H value fluctuated within a small range in different soil layers under different snow cover,with an average value of 8.17±0.03;soil EC value ranged from 89.92 to 127.52 s·m^-1;DOC content varies from 16.28 to49.76 mg·kg^-1,with no obvious variation;The contents of MBC,NH₄⁺-N and NO₃^--N decreased with the increase of soil depth,and the variation ranges were 12.41?39.53mg·kg^-1(MBC),0.13?5.04 mg·kg^-1(NH₄⁺-N)and 0.12?2.41 mg·kg^-1(NO₃^--N),respectively.(5)During the spring thaw period in the non-growing season,through the classification and statistics of OTU species,it was found and identified that there were39 phylum,109 classes,138 orders,177 families,226 genera and 90 species of soil bacteria,with a total of 8519 OTUs.The specific OTUs were not significantly changed under different snow treatments.The dominant species of soil microbial species composition at the phylum level were Actinobacteria,Proteobacteria and Acidobacteria.The dominant species of soil microorganisms did not change significantly among the treatments.The genus-level species composition of soil microorganisms during the spring thaw period was similar to the dominant bacterial community composition of the main bacteria under different snow treatments in different soil layers,but their relative abundances were quite different.In addition,a large number of species with low relative abundance in each group were classified as Other,and their relative abundance ranged from 28.8%to 51.1%,indicating that there were a large number of species with low relative abundance in the soil of each group at the genus level.Bacterial distribution.However,there were significant differences in soil microbial diversity under different snow cover.The analysis of Alpha diversity found that at 0-10 cm,the Shannon index and Chao1 index in CK were higher than those in IS and DS treatments,but in deep soil 40-50 cm layer,the values of IS and DS treatments exceeded CK,and snow treatments altered soil microbial abundance.The PCo A map of Beta diversity analysis showed that the composition of soil microbial community under different snow cover in 20-30 cm layer and 40-50 cm layer was similar,while the composition of soil microbial community under different snow cover in 0-10 cm layer was quite different.The composition of soil microbial communities in different soil layers under the same snow cover was also quite different,but the difference was not significant(p>0.05).Heatmaps analysis found that the dominant soil microbial species Actinobacteria was closely related to T(p<0.01),MBC(p<0.01),NH₄⁺-N(p<0.01),NO₃^--N(p<0.01),SWC(p<0.05)was negatively correlated;Proteobacteria was significantly negatively correlated with p H(p<0.01),and with T(p<0.001),MBC(p<0.001),NH₄⁺-N(p<0.01),NO₃^--N(p<0.001),SWC(p<0.001)were significantly or extremely significantly positively correlated;while Acidobacteria had no correlation with environmental factors.