Soil Carbon Sequestration Mediated By Soil Microorganisms Under Warming Conditions In An Alpine Meadow Ecosystem

Soil organic carbon（SOC）reflects the core of soil function and plays an important role in maintaining soil nutrition and biodiversity.The alpine meadow ecosystem of the Qinghai-Tibet Plateau stores a large amount of SOC,and the SOC in high-altitude and alpine system is more susceptible to climate warming.Therefore,the SOC dynamics of alpine meadows on the Qinghai-Tibet Plateau have gradually attracted attention under the climate warming.However,under the current climate warming situation,the research on the impact of SOC dynamics in the alpine meadow ecosystem on the Qinghai-Tibet Plateau is still not in-depth,especially the following problems are still unresolved:how does climate warming affect plants,soil physicochemical properties,microorganisms on the dynamics of SOC during the growing season?What are the effects of climate warming on plant-derived soil carbon inputs（including roots and symbiotic AMF）?What is the further effect of warming on SOC due to the priming effect of plant-derived carbon input（including roots and symbiotic AMF）?And what role did soil physicochemical properties and microbial properties play in this process?Based on these problems,this study designed and implemented a gradient warming experiment in the alpine meadow ecosystem of the Qinghai-Tibet Plateau,investigated plant properties,soil physicochemical properties,microbial properties and enzymatic activities,and explored the effect of experimental warming on SOC dynamics in a growing season.After two growing seasons,the effect of experimental warming on the new derived organic carbon from roots and AMF mycelia were investigated,and the effect of warming on the priming effects induced by new derived organic carbon of roots and AMF mycelia and their effects on SOC were investigated,and roles of soil physicochemical properties,microbial properties,and enzymatic activities during these processes were also investigated.The main findings are as follows:（1）In order to investigate the effect of experimental warming on the dynamics of SOC during the growing season,we established a gradient warming experiment consisting of five warming treatments.Then investigated potentially associated variables with changes in SOC during a growing season,such as plant attributes,soil physicochemical properties,microbial properties and enzymatic activities at the beginning（May）and end（August）of the growing season.The results showed that the SOC in August was lower than that in May,and the SOC storage decreased by an average of 18.53 Mg C per hectare in August.Regardless of growing season,warming not only had not changed SOC,but also had not affected changes in SOC during the growing season.Among all measured variables,microbial biomass carbon was highly coupled to changes in SOC.However,plant attributes,soil physicochemical properties（except dissolved organic carbon）,other microbial properties,and enzymatic activities did not affect SOC.These findings suggest that alpine meadow soil is a carbon source during the growing season,but climate warming has no significant effect on it.There is a strong link between microbial biomass carbon and SOC.（2）In order to elucidate the effect of climate warming on plant underground carbon input（including plant roots and mycelia of AMF）,and its effects on it induced priming,and effects on SOC.In the above-mentioned gradient warming experimental site,we adopted the method of embedding two different size of ingrowth cores（50μm and 0.45μm）which filled with the in situ soil and collecting the in situ soil before and after the embedding,and combined withδ¹³C stable isotope labeling.In order to distinguish the response of new derived organic carbon from roots and mycelia to warming after the two years embedding,and the effects of new derived organic carbon on the native SOC and the induced priming effects,respectively.The production of new carbon,the changes of native organic carbon,and priming effects induced by plant roots and mycelia separately,and the associated changes in soil physicochemical and microbial properties during this process were also investigated.The results shown that:1)Warming had no effect on the input of new derived organic carbon from roots and mycelia.Regardless of warming,new derived carbon from both roots and mycelia were negative inputs（-2.40 g/kg,averaged-4.02 Mg C per hectare）.Overall,the contribution induced by roots（-15%）was smaller than that the contribution induced by mycelia（-63%）for new carbon inputs.2)The together of roots and mycelia caused a negative priming effect,which increased the SOC.Among them,the roots induced a negative priming effect（-68%）,which resulted in a gain of SOC;the mycelia induced a positive priming effect（32%）,which resulted in a loss of SOC.3)Warming weakened the positive priming effect which induced by mycelia through changing soil dissolved organic carbon and soil dissolved organic nitrogen,microbial biomass carbon and peroxidase activity,but it did not affect the priming effect induced by roots.However,if the coexistence of roots and mycelia was considered,the input of new derived organic carbon from both roots and mycelia had no significant effect on the priming effect caused by both roots and mycelia under the warming condition.Microbial biomass carbon was the variable most significantly correlated with changes in the priming effect induced by roots and mycelia,and both the correlations were negative.The above research results show that in the regulation of carbon"sources"or carbon"sinks"in alpine meadow ecosystems,more attention should be paid to the dynamic changes of SOC by changing growing seasons,and the effects of climate warming on the SOC should be weakened.Warming did not affect SOC through the changes of aboveground parts of plants,and priming effects induced by the new derived organic carbon from both plant roots and AMF mycelia,and soil microorganisms were not affected by warming.The study emphasizes that the sequestration of SOC had not affected by changes in plant attributes,soil physicochemical properties,soil microorganism（AMF）and enzymatic activities under experimental warming conditions.In this study,from the perspective of intra-season variation and the priming effects induced by roots and mycelia,it was expounded that the SOC dynamics of alpine meadows on the Qinghai-Tibet Plateau had not changed significantly under experimental warming.This study provides a basis for understanding SOC dynamics under global warming scenarios.