Effects Of Bamboo Litter Input On Soil Enzyme Activity,Microbial Community And Soil Organic Carbon Mineralization In A Broad-leaved Forest

Forest litter is the link connecting the exchange of matter and energy between the aboveground and underground of terrestrial ecosystem,and nutrient return caused by its decomposition is an important process of material cycle and energy flow in forest ecosystem.The expansion of bamboo into the adjacent broadleaved forest has been a common phenomenon in East Asia in recent decades.One of the significant changes during the expansion is that the composition of the litter of dominant tree species is gradually replaced by that of bamboo,which improves the quality of the mixed litter.Changes in the quality of input litters will strongly affect microbial metabolism and soil nutrient cycling.At present,researches on litter mainly focus on the decomposition of litter and microbial communities.But it is rarely explores its effect on soil nutrient cycling,microbial metabolic function and other ecological from an ecological perspective,which are related to the sustainability of soil ecosystem.In view of this,this study performed an incubation experiment in laboratory,using soil with broad-leaved forest located at the Lingfeng Mountain Reserve(30°60?N,119°63?E),An'ji County,Zhejiang Province,China.On the one hand,incubation treatments were as follows:CK(control);0%PP,33%PP,50%PP,67%PP,100%PP(the addition ratio of broad-leaved leaf litter to bamboo leaf litter was 1:0,2:1,1:1,1:2,0:1,respectively).Changes in soil physical and chemical properties,microbial biomass,soil enzyme activity,basal respiration and soil microbial community were determined after 5,15,30,90,and 180 days to investigate the effects of time and litter on microbial metabolism of broadleaved forest soil by using enzyme stoichiometry.On the other hand,by using ¹³C stable isotope tracer technique,three treatments were as follows:CK(control);Phoebe sheareri(Hemsl.)Gamble and Phyllostachys edulis.Changes in soil enzyme activity,basal respiration and soil readily oxidizable carbon were determined after 10,30,and 60 days to investigate the direction and intensity of the priming effect of bamboo litter on soil organic carbon(SOC)mineralization in broadleaved forest soil.This study aims to reveal that the gradual replacement of broad-leaved litter by bamboo litter caused by the expansion of bamboo forest.The effects of litter type and quality on soil nutrients and microbiological characteristics and its mechanism provide a scientific basis for further understanding the synergy of litter-soil-microorganisms in the process of bamboo forest expansion,and provide a basis for assessing the ecological risk of bamboo forest expansion,sustainable management and improving the carbon pool of forest ecosystem.Our main results are as follows:(1)Litter addition changed soil nutrient,soil microbial biomass,enzyme activity and their stoichiometric ratioThe addition of litter decreased the content of soil organic carbon(SOC),but increased soil p H(P<0.05)and the content of total nitrogen(TN)(P>0.05).With the increase of bamboo litter(0%PP?100%PP)significantly decreased the soil p H,TN and dissolved organic carbon(DOC),while increased nitrate nitrogen(NO₃^--N),ammonium nitrogen(NH₄⁺-N)and dissolved nitrogen(DN),which resulted in a significant decrease in DOC:DN(R_DOC:DN)(P<0.05).Litter addition stimulated the increase of soil microbial biomass carbon(MBC),C-and N-acquiring enzyme activities.Compared with 0%PP,100%PP increased the soil MBC(12.68%-35.44%),the activities of?-Glucosidase(by 1.86%-13.93%),?-Cellobiosidase(by 32.02%-48.92%)and?-N-Acetylglucosamidase(by 16.44%-53.57%).During the incubation,soil p H,SOC,TN,R_C:N,DOC/DN,R_DOC:DN,C/N imbalance between resources and microbial biomass(R_C:N/B_C:Nand R_DOC:DN/B_C:N),and the bacterial and fungal gene copy numbers are the key parameters affecting enzyme activity.(2)Litter addition changed the direction and intensity of priming effect during SOC mineralizationCompared with CK,litter addition significantly increased the soil respiration rate(10.67%-235.62%)(P<0.05).While the soil respiration rate decreased and the microbial carbon use efficiency(CUE)increased with the increase of bamboo litter(0%PP?100%PP).Threshold element ratio(TER)and net nitrogen mineralization further showed that the nutrient metabolism of microorganisms was restricted by energy(C)after bamboo litter addition.Correlation analysis showed that soil p H,R_DOC:DN,R_DOC:DN/B_C:Nand C-to N-acquiring enzyme activity ratio were significantly negatively correlated with microbial CUE.In addition,through ¹³C stable isotope tracer technique showed that the addition of bamboo litter decreased the soil respiration rate(P<0.05)compared with P.sheareri.After 21 days of incubation,the positive priming effect of P.sheareri was significantly higher than that of bamboo litter,while the negative priming effect of P.sheareri was significantly lower than that of bamboo litter after 30 days of incubation.(3)Litter addition changed the diversity of soil microbial community and the diversity of microbial community was affected by many soil factorsCompared with CK,litter addition increased the?-diversity of bacteria and fungi communities.In particular,the?-diversity of bacterial community was decreased with the increased of bamboo litter(0%PP?100%PP),while the?-diversity of fungal community was the highest in the mixed litter(33%PP?67%PP).There were differences in the?-diversity of soil bacteria community at different incubation stages and were greatly affected by the physical and chemical properties of the soil(P<0.05),while the?-diversity of soil fungi has no significant change(P>0.05).Redundancy analysis showed that soil p H,NO₃^--N,NH₄⁺-N,DN,C-and N-acquiring enzyme activities were the main factors affecting the community structure of bacteria and fungi(P<0.001).(4)The addition of litters changed the composition and function prediction of soil microbial community,and its composition was affected by a variety of soil factorsThe changes of microbial composition were mainly caused by soil p H,NO₃^--N,NH₄⁺-N,DN and C-acquiring enzyme activities.Compared with 0%PP,the addition of bamboo litter(33%PP?100%PP)increased the relative abundance of Actinobacteria,Proteobacteria and Ascomycota,but decreased the relative abundance of Acidobacteria and Basidiomycota.Soil bacteria have an active metabolism function.The functional genes related to carbohydrate,amino acid metabolism and membrane transport were increased with the increase of bamboo litter(0%PP?100%PP).According to FUNGuild prediction,the saprophytic trophic type was the most important trophic type.