土壤呼吸和胞外酶在高山林线上下的差异及其影响因子

Differences in soil respiration and extracellular enzymes between upper and lower limits of the treeline and their influencing factors

土壤呼吸和土壤胞外酶是陆地生态系统生物地球化学循环中的重要组成部分,对维持生态系统稳定性起到关键作用.高山林线作为林木与灌丛(或草地)生态系统的过渡带,对全球气候变化极为敏感.为揭示高山林线上下限之间土壤呼吸和胞外酶活性的差异及其调控因素,以白马雪山和色季拉山的林线过渡带作为研究对象,测定其林线上限和下限的土壤理化、呼吸和胞外酶活性,并进行对比分析.结果表明白马雪山林线下限的土壤温度(ST)、含水率(SM)、全氮(TN)和全碳(TC)均高于林线上限(P<0.001),土壤呼吸与大多数土壤胞外酶均表现为林线下限高于林线上限,并与ST、SM、TN和TC呈正相关;色季拉山林线下限的ST低于林线上限(P<0.001),土壤蔗糖酶(SSC)和β-木糖苷酶(XYL)表现为林线下限低于林线上限(P<0.001)并与ST呈正相关,β-1,4-N-乙酰氨基葡萄糖苷酶(NAG)表现为林线下限高于林线上限(P=0.02)且与ST呈负相关.冗余分析(RDA)发现受ST、SM、TN和TC的影响,白马雪山土壤呼吸和胞外酶活性在林线上下限之间差异显著,色季拉山则较为相似.本研究表明,林线上下限之间ST、SM和由地上植被类型差异(由灌木变为乔木)造成的土壤养分变化是导致其土壤呼吸和胞外酶活性差异的重要原因,结果对预测高山土壤生态功能对未来气候变化的响应具有重要意义.(图4表2参47)

Soil respiration and extracellular enzymes are key components of the biogeochemical cycles in terrestrial ecosystems and are critical for maintaining ecosystem stability.The alpine treeline,a transitional zone between forest and shrub(or grass)ecosystems,is extremely sensitive to global climate change.The primary factors determining soil respiration and extracellular enzyme activities of the uppermost and lowermost alpine treelines were investigated by determining the soil physicochemical properties,respiration,and extracellular enzyme activities on the Baima Snow and Sejila Mountains.On Baima Snow Mountain,the soil temperature(ST),soil water content(SM),soil total nitrogen(TN),and soil total carbon(TC)of the lowermost treeline were significantly higher than those of the uppermost treeline(P<0.001).Soil respiration and most of the extracellular enzyme activities exhibited the same trend and were significantly and positively correlated with ST,SM,TN,and TC.On Sejila Mountain,the ST of the uppermost treeline was significantly higher than that of the lowermost treeline(P<0.001).Soil sucrase(SSC)and β-xylosidase(XYL)of the uppermost treeline were significantly higher than those of the lowermost treeline(P<0.001)and positively associated with soil temperature.However,N-acety1-β-D-glucosaminidase(NAG)activity was lower in the uppermost treeline than in the lowermost treeline(P=0.02)and negatively correlated with ST.The results of redundancy analysis showed that soil respiration and enzyme activities differed significantly between the uppermost and lowermost treelines of Baima Snow Mountain due to the influence of ST,SM,TN,and TC but varied little on Sejila Mountain.Our findings indicate that variations in soil nutrients,likely caused by ST,SM,and aboveground vegetation shifts(shrubs to trees),between the uppermost and lowermost treelines can strongly influence soil respiration and extracellular enzyme activities,thereby providing new insights into how alpine soil functions may respond to future climate change.