Metabolic Characteristics Of Soil Microorganisms Along An Elevation Gradient In The Eastern Slope Of Gongga Mountain

Alpine ecosystems are gaining increasing attention due to their biodiversity and sensitivity to climate change.Recently,more and more attention has been paid to the roles of microbial communities in regulating the biochemical processes in terrestrial ecosystems.Soil extracellular enzymes are products secreted by microorganisms to meet their nutrient demands.The activities of extracellular enzymes can reflect the relationships between the metabolic requirements of microbial communities and the availability of nutrients in the environment.However,there is still a lack of understanding of the characteristics and driving mechanisms of microbial metabolic limitation in alpine ecosystems along a large altitudinal gradient.This study investigated the variation of soil nutrient and extracellular enzyme activities involved in carbon?C?,nitrogen?N?and phosphorus?P?acquisition with altitude gradient?2300-4000 m?and soil depth?O,A,B,C?on Gongga Mountain,eastern Tibetan Plateau.The spatial distribution of microbial metabolic limitation through the models of soil extracellular enzymatic stoichiometry was quantified and compared,and then the key drivers of the limitation were evaluated.The main results are as follows:?1?Changes in altitude and soil depth in this alpine ecosystem significantly affected soil properties.Further,except for microbial biomass carbon:microbial biomass nitrogen?MBC:MBN?that was greatly affected by elevation gradient,the soil properties were affected by soil depth than by elevation and the interaction between them to a greater extent.In the O layer,soil organic carbon?SOC?,total nitrogen?TN?,total phosphorus?TP?,nitrate and ammonium nitrogen,biomass microbial carbon?MBC?,microbial biomass phosphorus?MBP?and MBC:MBN,MBN,MBC:MBP and MBN:MBP showed obvious change trend with the elevation,while in other soil layers,there was no obvious change trend with the elevation.The differences in soil properties between different elevation gradients decreased with the increase of soil depth.The factors affecting nutrient distribution were different among soil layers.?2?Both of the elevation gradient and soil depth significantly affected the C,N and P acquiring enzyme activities,and except for N acquiring enzyme activities and the ratio of C acquiring enzyme activities and N acquiring enzyme activities(E_C:N)which were mainly affected by the elevation gradient,the effects of soil depth on other enzyme activities and the enzyme stoichiometry were greater than the influence of altitude and the interaction between them.However,the enzyme activities and E_C:N had no significant change trend,and except that the E_C:P and E_N:P decreased with the increase of soil depth from O to B layers.The microbial biomass in the O layer had little influence on enzyme activities and enzyme stoichiometry,and the nutrient factors that affected enzyme activities and enzyme stoichiometry increased with the increase of soil depth.?3?The vector model analysis showed that the microbial metabolisms in this ecosystem were mainly limited by soil C and P.In O and A layers,the microbial C limitation increased with the elevation,the microbial P limitation showed a unimodal pattern with the increase of altitude,and the maximum value occurred in 2800 m.Microbial C and P limitations in B layer increased with elevation.In C layer,the microbial C limitation at the high-altitude sites was smaller than at the low-altitude sites,and the microbial P limitation was larger at high-altitude sites than at the low-altitude site.?4?C and P limitation in different soil layers was regulated by different factors with the change of altitude gradient.The results from partial least squares path model showed that the microbial metabolic limitation in O layer was affected by nutrient and environmental factors.The microbial C limitation in A layer and B layer was positively affected by the microbial biomass and soil nutrient content,respectively.Whereas the microbial C limitation on C layer was negatively affected by the microbial biomass.Microbial P limitation in A and C layers was positively affected by soil total nutrients and available nutrients respectively,while the microbial P limitation in B layer was negatively affected by the ratio of soil nutrient.