鄱阳湖苔草洲滩湿地土壤胞外酶活性和化学计量比的高程变化特征

Variations in the activities and stoichiometry of soil extracellular enzyme along the elevation gradient at the Carex lakeshore of Lake Poyang wetland

土壤胞外酶参与土壤的生物化学过程,其活性和化学计量比能够反映土壤微生物的功能动态.然而,目前湿地生态系统中催化不同生物地球化学关键过程的土壤胞外酶的活性和化学计量比随高程的变化特征还不清楚.以鄱阳湖苔草洲滩湿地6个不同高程样带的表层土壤(0~10 cm)为研究对象,通过测定与土壤碳、氮、磷循环相关的7种水解酶的活性,分析了洪泛平原洲滩湿地土壤碳、氮、磷循环相关酶活性和化学计量比随高程的变化特征和调控机制.结果表明:随着高程增加,鄱阳湖苔草洲滩湿地土壤与碳循环相关的α-葡萄糖苷酶(AG)活性逐渐减小,β-葡萄糖苷酶(BG)活性没有显著变化,纤维二糖水解酶(CBH)活性先减小后增加,木聚糖酶(XYL)活性逐渐增加;与氮循环相关的N-乙酰氨基葡萄糖苷酶(NAG)和亮氨酸氨基肽酶(LAP)活性逐渐减小;与磷循环相关的磷酸酶(PHOS)活性没有显著变化.高程增加后,土壤中BG:NAG逐渐增加,BG:PHOS逐渐减小,NAG:PHOS没有显著变化.结构方程模型表明,鄱阳湖洲滩湿地土壤碳、氮、磷循环相关酶活性最大的影响因素分别为高程、植物物种丰富度和土壤总磷.土壤碳氮酶化学计量比主要是受高程的综合影响,而土壤碳磷和氮磷酶化学计量比主要受土壤pH的直接作用.

Soil extracellular enzymes participate in soil biochemical processes.Their activities and stoichiometry can reflect the functional dynamics of soil microorganisms.However,the variations and the deternining factors of the activities and stoichiometry of soil extracellular enzymes that catalyze different hiogeochemical processes in wetland ecosystems along the elevation gradient are still unclear.Therefore,in the current study,we measured the activities of seven soil hydrolytic enzymes which related to carbon,nitrogen,and phosphorus cycling using the surface soil samples(0-10 cm) of a typical Carex lakeshore at Lake Poyang wetland,China.The results showed that the a-glucosidase(AG) activity gradually decreased with the increase of elevation,but the β-xylosidase(XYL) activity showed the opposite trends.Along the elevation gradient,β-glucosidase(BG) activity did not significantly change;while the cellobiohydrolase(CBH) activity first decreased and then increased.With the increase in elevation,the activities of β-N-acetylglucosaminidase(NAG) and leucine aminopeptidase(LAP) gradually decreased;whereas the phosphatase(PHOS) activity had no significant variation.Along the elevation gradient,BG:NAG ratio gradually increased,AG:PHOS ratio gradually decreased,while NAG:PHOS ratio had no significant change.The structural equation model(SEM) analyses showed that the most important determining factors of soil extracellular enzyme activities were elevation,plant species richness and soil total P.BG:NAG ratio was mainly affected by elevation,and AG:PHOS ratio and NAG:PHOS ratio were mainly impacted by soil pHs.