Variations Of Soil Extracellular Enzymes Activity Along An Elevation Gradient In Wuyishan National Park

Alpine ecosystems have attracted much attention because of their abundant species diversity and sensitivity to climate change.Soil enzymes are primarily produced by microorganisms and are important in the process of obtaining nutrients to meet their microbial growth and metabolic needs.Therefore,their stoichiometric characteristics can determine the relationship between soil microbial nutrient demand and soil nutrient supply and can be used as an index of soil microbial nutrient acquisition ability.In mountain ecosystems,with a large vertical gradient over a short horizontal distance,it is important to understand the changes of soil enzymes activity and enzyme stoichiometry to evaluate soil nutrient availability and soil microbial nutrients limitation.However,our understanding of the response of and factors driving changes in soil enzymes activity and soil microbial metabolism limitation with elevation gradient is unclear.To further understand soil enzymes activity and its stoichiometry characteristics,we selected the northern area of Wuyi Mountains in northwest Fujian with a1500 m elevation difference(650m-2150m).Vegetation types were evergreen broad-leaf forest,coniferous and broad-leaf forest,coniferous forest,subalpine dwarf forest and subalpine meadow.Soil samples at different elevations and soil depths(0-40cm)were collected,and soil properties and soil enzymes activity related to carbon(C),nitrogen(N)and phosphorus(P)metabolism were measured.The spatial distribution characteristics of soil microbial nutrients limitation were determined by using a vector analysis,and the key factors affecting soil enzymes activity and soil microbial nutrients limitation were explored.The main results are:(1)Changes of soil enzymes along elevation gradientElevation and soil depth have significant effects on the activities of C-,N-and P-acquiring enzymes.The activities of C-,N-,P-acquiring enzymes increased with increasing elevation and decreased with increasing soil depth.Decreases in C-and P-acquiring enzymes were much more substantial with increasing soil depth at higher elevations.Interactions of elevation and soil depth largely affected C-acquiring enzymes,but did not significantly affect N-and Pacquiring enzymes.(2)Changes of soil microbial nutrients limitation along elevation gradientThe vector analysis showed that microorganisms were primarily limited by C and P.Soil microbial C limitation increased with increasing elevation,the soil microbial P limitation decreased with increasing elevation.Soil microbial C and P limitation both increased with increasing soil depth.Interactions of elevation and soil depth did not significantly affect soil microbial C and P limitation.(3)Regulations on soil enzymes activity and microbial nutrients limitationSoil chemical properties greatly regulated variation in soil enzymes activity.Random forest analysis demonstrated that total nutrients,including SOC and TN,were the most influential on soil enzymes activity.Our SEM results further showed that total soil nutrients were dominant in positively affecting the activity of C-,N-and P-acquiring enzymes.In addition,soil chemical properties also greatly regulated variation in soil microbial C and P limitation.Random forest analysis showed that C:N was the most influential variables on soil microbial C and TN was the most influential for P limitation.Our SEM provided further statistical evidence that total nutrient ratios and total nutrients negatively regulated soil microbial C and P limitation,respectively.In summary,our results showed that C-,N-and P-acquiring enzymes activity consistently increased and decreased with the elevation gradient and soil depth,respectively.We also found that the limitation of soil microbial C intensified but P alleviated along the elevation gradient.In addition,soil total nutrients and their ratios dominantly regulated soil enzymes activity and stoichiometry.Our results provide useful insights linking soil microbial metabolic characteristics to the environmental gradients.On the other hand,our study provides a basis for understanding the dynamics of C,N,P and nutrient cycling process in mountain ecosystems under climate change,and could help to better predict impacts of climate change on soil biogeochemical process.