Abstract: Soil enzymes and stoichiometry are key indicators for soil nutrient availability and microbial nutrient limitation. However, the variations and key driving factors of soil enzyme activities and stoichiometric ratios after the conversion of subalpine natural forests to plantations in western Sichuan remain unclear. In this study, we measured soil physicochemical properties and enzyme activities in a natural secondary forest and a plantation of subalpine spruce in western Sichuan. The results showed that: (1) Soil C∶N ratio of natural forest was significantly lower than that of plantation (P<0.05), while soil C∶P and N∶P ratios were significantly higher than that of plantation (P<0.05). (2) The C∶N_EEA and C∶P_EEA of natural forest were significantly higher than that of plantation, while N∶P_EEA was significantly lower than that of plantation (P<0.01). The carbon quality indices (CQI1 and CQI2) of plantation were significantly higher than natural forest (P<0.05), while vector length and vector angle were significantly lower than natural forest (P<0.01). (3) Soil microorganisms were limited by C and P in the natural forest, but by N in the plantation. (4) The results of redundancy analysis showed that soil total N was the main factor affecting the enzyme stoichiometric ratio. Our results suggest that the N requirements of microorganisms should be fully considered in soil nutrient management of plantations in this region.

Key words: western Sichuan subalpine, natural forest, plantation, enzyme stoichiometric ratio, Picea asperata