Effects Of Litter Addition And Removal On Soil Organic Carbon Fractions And Microbial Characteristics Vary With Soil Depth In Chinese Fir Plantation

Cunninghamia lanceolata is the most important fast-growing timber species in southern China.Litter is the main source of forest soil organic carbon input and nutrient return.The role of litter input in forest ecosystem carbon(C)cycle and nutrient cycling such as nitrogen(N)and phosphorus(P)has been a research hotspot in forestry and other related disciplines.In order to explore the effects of increased or decreased litterfall on organic carbon components and microbial characteristics of soil profile in subtropical forest under the background of global climate change and human activities,this study took Chinese fir plantation as the research object,and set up a complete randomized block experiment with four replicates in three treatments of litter removal(LR),litter addition(LA)and control(CK)in 2013.After six consecutive years of treatment,a total of four layers of soil(0-10 cm,10-20 cm,20-40 cm and 40-60 cm)were collected along the soil profile in 2019.The physical and chemical properties,organic carbon components,hydrolase activity and microbial community structure were determined,and the effects of litter addition and removal on carbon storage and key ecological processes of soil profile in Chinese fir plantation and their microbiological mechanisms were clarified,providing scientific and technological support for litter management and sustainable management of Chinese fir plantation.The main results are as follows:(1)LA significantly increased soil nutrient content,organic carbon components,hydrolase activity,microbial diversity and abundance of major groups in 0-10 cm layer.LR significantly increased soil p H and available P(Olsen-P)in 0-20 cm layer,but significantly decreased available nitrogen.LA significantly increased the activities of total nitrogen,total phosphorus,ammonium nitrogen(NH₄⁺-N),microbial biomass carbon(MBC),?-1,4-glucosidase(BG),cellobiase(CB),leucine aminopeptidase(LAP),acid phosphatase(AP)(except?-1,4-N-acetylglucosaminidase(NAG)),protozoa and gram-negative bacteria(G-)in the 10-20 cm layer.LR significantly reduced the activity of organic carbon labile carbon components,CB,NAG and AP.LA significantly increased the available nitrogen nutrients,soluble carbon(DOC),CB activity and microbial community structure in the 20-40 cm soil layer.LR also significantly increased the total microbial biomass,fungi,bacteria and Gram-positive bacteria(G+)biomass,and reduced AP activity.In the 40-60 cm soil layer,LA significantly increased NH₄⁺-N,DOC and CB activities;LR only decreased the activities of CB and NAG,and neither LA nor LR affected the microbial community structure.(2)The soil nutrient content,organic carbon components,five enzyme activities,biomass of microbial community structure and its diversity under different litter treatments decreased with the increase of soil layer,and the biomass of surface layer was significantly higher than that of deep layer(20-60 cm).AP activity was significantly higher than C,N hydrolase activity in each soil layer.The ratio of ln(BG+CB):ln(NAG+LAP):ln(AP)in the whole soil layer was 1:0.40-0.90:1.82-2.54.Carboxylic acids and amino acids are the main carbon sources for soil microorganisms,and amines and phenolic acids are the least used.In addition,fungi/bacteria,G+/G-and environmental pressure(cy17:0/16:1?7)increased with soil profile depth.(3)With the deepening of soil layer,the correlation between enzyme activity,microbial community structure composition and diversity and soil physical and chemical properties and organic carbon components also weakened.In the surface layer,TP,NH₄⁺-N and acid hydrolysis organic carbon components are the key factors affecting the activity of hydrolytic enzymes,microbial community structure and diversity.Total nutrients at 20-40 cm and p H,labile carbon and recalcitrant carbon(RP-C)at 40-60 cm soil layer were the main factors affecting enzyme activity and stoichiometric ratio.N/P and SWC were the key factors affecting soil microbial community structure and diversity in 20-40 cm and 40-60cm soil layers,respectively.In summary,litter removal had neutral,negative and positive effects on soil physical and chemical properties,organic carbon components,enzyme activities and microbial communities,respectively.Litter addition often had positive effects on these characteristics,and these characteristics were more sensitive to litter addition than litter removal.Almost all nutrients,organic carbon fractions,enzyme activities and microbial biomass decreased with the increase of soil depth,but the differences among different soil layers under litter treatment were inconsistent.It can be seen that litter plays a key role in maintaining long-term soil fertility of Chinese fir plantation by affecting soil profile abiotic characteristics,hydrolytic enzyme activity and microbial community characteristics.