Microbial Community Dynamic Mediates The Priming Effects Caused By In Situ Decomposition Of Abnormal Litterfall

Extreme climate events like freezing damage will destroy the structure and function of forests,and the formation of a large number of abnormal litter(AL)is one of its characteristics.The input of exogenous carbon(C)could accelerate or inhibit the decomposition of soil organic carbon(SOC),which is defined as priming effect(PE).Soil C pool is the largest C pool in terrestrial ecosystem,and a slight change in its decomposition rate will have a great impact on C budget.Therefore,it is important to understand the effect of AL decomposition on PE and the microbial mechanism behind the phenomenon for understanding forest C cycle and SOC accumulation.In this paper,we chose ¹³C labelled AL of four species(Castanopsis fissa,CF;Pinus massoniana,PM;Machilus chekiangensis,MC;and Castanopsis chinensis,CC)as experiment objects,carrying out a 110 day decomposition experiment in a subtropical coniferous and broad-leaved mixed forest.Combining with the static box method and high-throughput sequencing technology,we measured the CO₂ emissions of AL and soil,as well as the species composition and diversity of soil bacterial and fungal communities during the incubation,to explore the decomposition dynamics of AL,changes in PE and their relationship with microbial composition and diversity.The main conclusions are as follows:1.The CK group and the PM group had similar C flux dynamic,that is,the C emission rate decreased first and then rised and then decreased with time;while the CF,MC,and CC groups have similar C flux dynamic,that is,the C emission rate increased first and then decreased and then increased and then decreased.The maximum C emission in the CK group appeared at 34d,which was 1153.32±72.50mg m^-2 h^-1;the maximum C emission in the AL-added treatments all appeared at 45d.During the 110d incubation,more than 77%C lost of AL was discharged into the atmosphere in the form of CO₂,indicating that AL is the main energy source for microbial metabolism.2.Different species of AL could cause similar PE pattern during 0-110d:negative PE was triggered at 0-60d,and it converted to positive PE at 61-110d.In the early stage of decomposition(0-5d),the PE intensity of the MC group was significantly lower than that of the other three treatments;while in the middle stage of decomposition(6-60d),the PE intensity of the PM group was significantly lower than that of the other three treatments;in the late stage of decomposition(61-110d),there was no significant difference in PE intensity among treatments(P>0.05).The decomposition rate of AL in each treatment had a very significant correlationship with PE intensity(P<0.01).3.At the genus level,the species diversity indexes of bacteria and fungi had a better correlationship with C emissions.At 7d,the fungal alpha diversity index was significantly negatively correlated with PE and SR(P<0.05);at 24d,the bacterial alpha diversity index was significantly correlated with PE,soil respiration(SR),and abnormal litter decomposition(RR).At the OTU level,the species composition of microorganisms had a better correlation with C emissions.The bacterial species composition was significantly correlated with PE and RR at 24,45,and 110d;the fungal species composition was significantly correlated with SR at 45,110d,and also significantly correlated with PE at 110d(P<0.05).This experiment firstly discovered the three-stage PE pattern caused by the decomposition of abnormal litter:strong negative PE(0-5d)to moderate PE(6-60d)to positive PE(61-110d).Each stage was dominated by different microbial mechanisms.Bacteria,especially Actinobacteria phyla,played an important role in triggering and maintaining PE.This study provides a scientific reference for quantifying the impact of extreme climate on the forest carbon cycle and exploring the role of microorganisms in the triggering and maintenance of PE.