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.