贡嘎山树线过渡带土壤胞外酶活性及其化学计量比特征

Soil extracellular enzyme activities and their stoichiometric ratio in the alpine treeline ecotones in Gongga Mountain, China

土壤胞外酶及其化学计量比是反映土壤养分可用性和微生物底物限制的敏感指标。然而,对全球变化敏感的高山树线过渡带土壤酶活性和化学计量比的变化特征及其关键驱动因素仍不清楚。该研究在青藏高原东南部的川西贡嘎山高山树线过渡带(森林、树线、灌丛)进行土壤采样,测定了树线过渡带土壤中5种水解酶(β-葡萄糖苷酶(BG)、纤维素二糖水解酶(CBH)、木聚糖水解酶(XYL)、N-乙酰氨基葡萄糖苷酶(NAG)、亮氨酸氨基肽酶(LAP))和2种氧化酶(多酚氧化酶(POX)、过氧化氢酶(CAT))的活性,并计算土壤胞外酶活性化学计量比(碳、氮(N)酶活性比和碳质量指数)。结果表明:灌丛土壤LAP、POX、CAT活性显著低于树线和森林土壤,XYL活性在树线最低,其他胞外酶活性在树线过渡带不同位置差异不显著。灌丛土壤lnBG/lnLAP显著高于森林和树线处土壤,lnBG/ln(NAG+LAP)在树线过渡带没有显著变化,碳质量指数在树线处最高。非度量多维尺度分析表明,土壤有机碳、全氮、硝态氮含量和植物叶片木质素:N是影响树线过渡带土壤酶活性差异的主要因素,植物叶片碳氮比、木质素:N和土壤可溶性氮含量是影响树线过渡带土壤胞外酶活性化学计量比差异的主要因素。综上所述,贡嘎山地区的部分土壤酶活性及其化学计量比沿树线过渡带会发生明显的变化,这种变化可能是由不同植物类型下微生物群落差异导致。这表明,未来气候变化引起的树线迁移可能会改变胞外酶活性进而影响土壤养分循环。

Aims Soil extracellular enzymes and enzyme stoichiometry are indicators of soil nutrient availability and microbial substrate limitation.Subalpine treeline ecotones are special areas which are sensitive to global change.However,the patterns in soil enzyme activities and stoichiometry,and their key drivers remain unclear in the subalpine treeline ecotones.Methods In this study,soils from a subalpine treeline ecotone in Gongga Mountain in Southeast of Qingzang Plateau were collected.The activities of five hydrolases(β-1,4-glucosidase(BG),cellobiohydrolase(CBH),xylosidase(XYL),β-N-acetyl glucosaminidase(NAG),leucine aminopeptidase(LAP))and two oxidases(polyphenol oxidase(POX),catalase(CAT))were detected.The stoichiometric ratios of soil extracellular enzyme activities(carbon and nitrogen enzyme activity ratio and carbon quality index)were calculated.Important findings Our results showed that LAP,POX and CAT activities of the shrub soils were significantly lower than those of the treeline and forest soils,XYL activity was the lowest at the treeline,and the activities of other extracellular enzymes did not differ significantly among locations in the treeline ecotone.The lnBG/lnLAP of the shrub soil was significantly higher than those of the forest and treeline soils,lnBG/ln(NAG+LAP)did not vary significantly at the treeline ecotone,and the carbon quality index was highest at the treeline.Soil extracellular enzyme activity stoichiometric ratios were not significantly related to microbial nutrient status.Non-metric multidimensional scaling analysis showed that total carbon,total nitrogen,nitrate nitrogen content and lignin to nitrogen ratio of plant leaves were the main factors influencing soil extracellular enzyme activities in the treeline ecotone.The main drivers of the stoichiometric ratios of extracellular enzyme activities were soil dissolved nitrogen,carbon to nitrogen ratio,and lignin to nitrogen ratio of plant leaves.In summary,some soil enzyme activities and their stoichiometric ratios varied significantly along the treeline ecotone,which was mainly influenced by the changes in vegetation type,possibly via its influences on plant-associated microbial communities.Treeline migration induced by future climate change may change extracellular enzyme activities and thus affect soil nutrient cycling.