漓江流域海拔、土壤及植被对土壤养分和酶化学计量比的影响

漓江流域海拔、土壤类型和植被类型多样。为研究其土壤养分和土壤酶活性特征,该研究以漓江流域石灰性土壤及酸性土壤的典型植被类型(自然林、毛竹林、马尾松林、果园、水稻田)的表层土壤(0～20 cm)为研究对象,测定土壤养分含量及碳氮转化相关胞外酶(淀粉酶、蔗糖酶、脲酶、蛋白酶、过氧化氢酶)活性及化学计量比特征。结果表明:(1)高海拔土壤的全氮(TN)、全磷(TP)、有效磷(AP)含量和淀粉酶、蔗糖酶、脲酶、蛋白酶活性相对较高,而过氧化氢酶活性则正好呈现相反的趋势。(2)相对于酸性土壤,石灰性土壤有较高的TP和AP含量。在酸性土壤中,植被类型对氮磷养分影响较大,总体上人工植被使得土壤氮素降低而使磷素增加; 而石灰性土壤养分在不同植被类型间差异相对较小。(3)相比自然林,人工植被的土壤氮转化酶活性极大降低,而土壤碳转化酶活性受人为影响程度相对较小,土壤氮磷酶活性化学计量比显示自然林呈现氮限制而人工林呈现碳限制。(4)典范对应分析(CCA)显示土壤理化性质在第Ⅰ轴和第Ⅱ轴解释了86.56%的土壤酶活性变异,土壤理化性质解释贡献率排序为TN>pH>铵态氮(NH₄⁺)>AP>TP>硝态氮(NO₃^-),其中前3个因子是造成土壤酶活性差异的主要因子。综上结果表明,漓江流域的酸性土壤对人为干扰的生态敏感性较高,植被变化易导致养分失衡,应注重土壤养分管理,防止土壤有机质的损失,提高漓江流域景观资源可持续利用的价值。该研究为当地生态系统的科学保育和开发提供了理论依据。

Effects of altitude, soil and vegetation of the Lijiang River Basin on soil nutrient contents and enzyme stoichiometric ratios

The Lijiang River Basin covers great variation in altitude, soil and vegetation types. In order to study the characteristics of its soil nutrients and enzymes activities, we determined soil nutrient contents and activities of several extracellular enzymes(amylase, sucrose, urease, protease and catalase)of the surface soils(0-20 cm)of typical vegetation types [natural forest, bamboo(Phyllostachys edulis)forest, Pinus massoniana forest, orchard and rice paddy field] with calcareous soils and acid soils in the Lijiang River Basin. The results were as follows:(1)The soils at high altitude had greater total nitrogen(TN), total phosphorus(TP), available phosphorus(AP)contents as well as amylase, sucrose, urease and protease activities, whereas the catalase activity was to the contrary.(2)Compared with the acid soils, the calcareous soils had higher contents of total phosphorus(TP)and available phosphorus(AP). Among the acid soils, vegetation types had greater impact on soil nitrogen and phosphorus contents. In general, anthropogenic vegetation resulted in decrease of nitrogen content and increases of phosphorus content; while the nutrients in the calcareous soils had relatively little variation among different vegetation types.(3)Compared with the natural forest soils, soils from the anthropogenic vegetation had lower nitrogen related enzyme activities; whereas the carbon related enzyme activities was less impacted. The enzymatic stoichiometry revealed that soils of natural forests were nitrogen limited whereas those of anthropogenic vegetation was carbon limited.(4)The results of canonical correspondence analysis(CCA)showed that soil physiochemical properties in the first and second axes explained 86.56% of the variation of soil enzyme activities with the contribution order of TN>pH>NH₄⁺>AP>TP>NO₃^-, with the first three as the main impacts. All the above results indicate that acid soils in the Lijiang River Basin have great ecological sensitivities; vegetation changes easily result in nutrient imbalance, therefore, in order to improve the sustainable utility of landscape resources of the Lijiang River Basin, special attention should be paid to the conservation of soil nutrients and prevention of the loss of soil organic matter. This study provides theoretical base for the scientific conservation and development of local ecosystem.