Effects Of Glucose Input On The Degradation Of Soil Microbial Necromass

The accumulation and decomposition dynamics of soil organic carbon（SOC）significantly affect the balance of the global carbon cycle.As an important source of soil organic carbon,the accumulation and degradation of microbial necromass are crucial for the long-term stability and accumulation of soil organic carbon.In farmland ecosystems,microbial necromass may be affected by crop root exudates,thereby affecting their long-term stability and accumulation in soil.However,how soil microbial necromass responds to exogenous carbon input patterns and microecological processes remains unclear.In this study,glucose was used to simulate root exudate.The effects of exogenous carbon input frequency on the stability and accumulation of soil microbial necromass and related microecological processes in two typical farmland soils in China were studied by ¹³C isotope labelling technology and high-throughput sequencing technology.The main findings are as follows:（1）Glucose input caused the degradation of soil microbial necromass.The content of microbial necromass in repeated addition treatment decreased faster than that in a single addition.The microbial necromass in black and red soil decreased by 75%and 41%,respectively,compared with 0 days.The content of soil microbial necromass under single addition decreased gradually within 28 days.The priming effect of single addition treatment was 2-3 times that of repeated addition treatment during the whole culture period.（2）Both addition methods significantly reduced theαdiversity of microorganisms.Theαdiversity of bacteria on the 7th day of single addition was 1.7-2.3 times lower than that on the 0th day and higher than that of repeated addition.The fitting analysis showed that there was a significant negative correlation between soil microbial necromass and bacterial community Shannon index and microbial community structure,and the slope of the fitting curve in repeated addition was greater than that in single addition,indicating that the changes of bacterialαdiversity and microbial community structure in repeated addition may lead to the strong degradation of soil microbial necromass.The results of the Micro Resp experiment further showed that the bacterial community of repeated addition treatment had a stronger ability to consume or utilize microbial necromass than that of single addition treatment.（3）Random forest analysis showed that bacteria（53%）,fungi（16%）and protozoa（24%,Conosa）jointly affected the degradation of microbial necromass in repeated addition treatments.Co-occurrence network analysis showed that the number of nodes in repeated addition was higher than that in single addition,and the number of protozoa-bacteria/fungi/protozoa edges increased by 1.84,2.79 and 4.88 times,respectively.At the same time,the sub-network parameters such as nodes,edges,protozoan nodes and cross-trophic edges in the network were significantly negatively correlated with soil microbial necromass,indicating that the enhancement of network complexity and nutrient interaction may accelerate the degradation of soil microbial necromass.In summary,exogenous carbon input methods affect the intensity of soil microbial residue decomposition and priming effects.Repeated input had higher microbial diversity than a single input,and microbial multi-nutrient interaction was stronger,which was the main reason for the rapid decrease in soil microbial residue content.The results provide theoretical support for further understanding the microecological process of soil microbial residue turnover and promote the understanding of the essence of the soil organic matter cycle.