The relation among soil microorganism, enzyme activity and soil nutrients under subalpine coniferous forest in Western Sichuan

Soil microorganism and enzymes are important parts of forest ecosystem and sensitive to environmental changes. They have many critical functions in energy conversion and material cycle of forest soil. However, there are few studies about soil biological properties under subalpine coniferous forest, in particular, a serial of spruce plantation chronosequences following clear-cutting of natural coniferous forest in western Sichuan. We measured the quantity of soil microorganism (including bacteria, fungi and actinomyces), enzyme activity and soil nutrients under spruce plantation chronosequences in western Sichuan to investigate soil biological properties and their relationship with soil nutrients. The results showed that soil microorganism, enzyme activity and soil nutrients of the mature spruce plantation were significantly lower than those of the young spruce plantation and secondary broad-leaved forest. Soil fertility degraded greatly with the increasing of spruce plantation age and was mainly affected by forest micro-environment. There were significant correlation between the amounts of soil microorganisms, soil enzyme activities and nutrients (e.g. soil organic matter, total N, total P, alkali-hydrolyzable N and available K). Therefore soil biological indices can be used to evaluate soil fertility. In order to accelerate the course of restoration and rehabilitation of degraded pure plantation, the strategy and measures were put forward, including application of thinning rationally for existing dense plantations and establishment of mixture forest of coniferous and broad-leaved trees for new afforestations, which would create good forest micro-environment for plant growth.