Abstract: Changes in the input of leaf litter can affect soil enzyme activity and stoichiometric ratios by changing soil biochemical properties. However, it is not yet clear whether the magnitude of the effects of changes in leaf litter input on soil enzyme activity and stoichiometric ratios differed across stands with different densities. With an indoor simulated experiment with four treatments (leaf litter removal, 50% leaf litter reduction, control, and double leaf litter addition), we examined the effects of leaf litter quantity on soil biochemical properties, extracellular enzyme activity, and stoichiometry ratio of high-density and low-density spruce plantations in the subalpine of western Sichuan. The results showed that leaf litter double addition significantly decreased soil organic carbon content of the high-density stand, as well as the total dissolved nitrogen and nitrate nitrogen contents of the two stands, but signi-ficantly increased soil microbial biomass carbon and nitrogen of the two stands. Compared with litter removal and reduction treatments, leaf litter double addition significantly reduced β-glucuronidase activity and acid phosphatase activity in both stands. However, soil β-glucosidase was more sensitive to leaf litter double addition treatment in the low-density stand, showing that the soil β-glucosidase activity under leaf litter double addition treatment decreased by 28.6%. With increasing leaf litter input, the ratio of enzyme nitrogen to phosphorus (0.69-0.65), the ratio of enzyme carbon to nitrogen (0.50-0.44), and the ratio of enzyme carbon to phosphorus (0.34-0.28) showed a decreasing trend. The soil nitrogen, phosphorus, and enzyme carbon-nitrogen ratios in the high-density stand were significantly lower than those in the low-density stand. The results of RDA analysis showed that soil total nitrogen, ammonium nitrogen, total phosphorus, and dissolved organic carbon were the main factors affecting soil enzyme activity and stoichiometric ratios. In summary, soil nitrogen limitation of the high-density stand is more evident than that of the lower-density stand, and both stands gradually changed from nitrogen limitation to phosphorus limitation with the increases of leaf litter input.

Key words: western Sichuan subalpine, soil enzyme, stoichiometric ratio, leaf litter input, stand density