Effects Of Snow Reduction On The Microbial Community And Extracellular Enzyme Activity During Litter Decomposition In A Subalpine Forest

Forest litter is an important link between the biogeochemical cycles of above-ground and below-ground ecosystems,and its decomposition is regulated by the structure and function of microbial communities.As a key ecological factor in alpine regions,changes in seasonal snow cover may affect the decomposition of litter in subalpine forests,but the microbial mechanisms are still unclear and need to be studied.Therefore,in this study,two common deciduous tree species,Betula albosinensis)and Larix mastersiana,were subjected to snow control and litter decomposition in the subalpine coniferous forests of western Sichuan through a field experiment.The effects of snow reduction on leaf decomposition in subalpine forests and its microbial mechanisms were investigated by artificially simulating 100% snow reduction(100% SR),50% snow reduction(50% SR)and natural snow cover(control),and monitoring the remaining mass,fungal/bacterial phospholipid fatty acid biomass,microbial community structure and extracellular enzyme activity of foliar litter at different decomposition periods for 2 consecutive years,combined with environmental factors and initial chemical of litter,to reveal the effect of snow reduction on leaf litter decomposition in subalpine forest and its microbial mechanism.The main findings are as follows:1.Snow reduction significantly reduced the water content of leaf litter and daily mean temperature in winter,and increased the frequency of freeze-thaw cycles.After two years of decomposition,the remaining mass of Betula albosinensis and Larix mastersiana litter were 62.82-77.17% and 68.8-85.58%,respectively,and the decomposition rates k were 0.11-0.20 and 0.07-0.16,respectively.Both species had high remaining mass at 100% SR throughout the decomposition process,indicating that snow reduction significantly inhibited the decomposition of Betula albosinensis and Larix mastersiana litter.2.During the two years of decomposition,microbial biomass carbon,total phospholipid fatty acid and bacterial biomass of Betula albosinensis litter was generally higher than that of Larix mastersiana litter,while microbial biomass nitrogen of both species peaked after one-year decomposition.At the same time,snow reduction significantly reduced microbial biomass carbon,nitrogen,total phospholipid fatty acid biomass,bacterial and Gramnegative bacterial biomass,and was influenced by significant differences in species and decomposition period.3.Proteobacteria,Actinobacteriota and Bacteroidota were the dominant groups at the phylum level in the two litter bacterial communities.Snow reduction significantly reduced the diversity of litter bacterial community,as evidenced by a relatively low bacterial Alpha diversity in both 50% SR and 100% sSR in the second year of decomposition.Ascomycota and Basidiomycota were the two dominant litter fungal communities,with their cumulative relative abundance ranging from 87.89 to 99.42% of the total fungal community,but did not differ significantly between snow treatments.This suggests that the bacterial community diversity and structure were more sensitive to snow reduction than the fungi.4.In the winter of the first year of decomposition,snow reduction significantly inhibited Betula albosinensis litter hydrolase activities(β-glucosidase,cellobiose hydrolase,β-Nacetylglucosaminidase,leucine aminopeptidase and acid phosphatase),but this inhibition diminished as decomposition progressed.However,the hydrolase and oxidase(peroxidase and polyphenol oxidase)activities of Larix mastersiana litter were relatively low under the snow reduction treatment in both years of decomposition,suggesting that the inhibitory effect of snow reduction on the enzymatic activities of leaf litter with low initial litter chemical and slow decomposition was more persistent.5.Daily mean temperature and initial phosphorus content of leaf litter were key factors influencing microbial biomass variation,while initial nitrogen content and Gram-negative bacterial biomass were key factors influencing extracellular enzyme activity.Microbial Alpha diversity was significantly influenced by daily mean temperature,while freeze-thaw cycles,initial structural carbon fraction(cellulose,lignin)and daily mean temperature,and initial nutrient content(nitrogen,phosphorus)were key influences on the abundance of the dominant bacterial communities,Proteobacteria and Actinobacteriota,respectively,during the decomposition.From two years of decomposition,the effect of snow reduction on both the remaining mass and decomposition rate k was regulated by a combination of environmental factors(daily mean temperature and litter moisture)and microbial community structure and function(microbial biomass,bacterial diversity,enzyme activity).In summary,snow reduction decreased microbial biomass,bacterial diversity and extracellular enzyme activity through changes in ambient temperature and moisture,thereby inhibiting the decomposition of apoplastic leaves in subalpine forests.Bacterial community biomass and structure and their regulation of extracellular enzyme activity were more sensitive to changes in snow than fungi,while snow reduction had a more sustained inhibitory effect on enzymatic activity of leaf litter,which have a low initial quanlity and decompose more slowly.The results of this study shed light on the effects of snow reduction on the decomposition of leaf litter in subalpine forests and its microbial mechanisms,which will help to understand the material cycling processes in forest ecosystems and provide a scientific basis for the management of subalpine forests under climate change scenarios.