Abstract:

Aims Soil enzymes often play an important role in maintaining soil fertility and the biogeochemical cycle in soil ecosystems. Many soil enzyme studies have examined decomposition of leaf litter, but few have addressed decomposition of fine roots. Our objectives were to determine soil enzyme dynamics during fine root (including grass root) decomposition and whether variation of soil enzymes is linked to chemical composition of fine roots.

Methods We placed 560 intact soil cores in nylon bags with 0.25 mm mesh in Betula luminifera-Hemarthria compressa (HN), Betula luminifera plantation (H), Hemarthria compressa grassland (NC) and Cryptomeria fortunei plantation (LS) for 1 year. Intact soil cores were sampled at 30, 90, 180, 270 and 365 d from the starting date. On each sampling date, we collected fine root (including grass root) and soils from each soil core and measured decomposition rates, chemical composition of fine root (including grass root), soil enzymes and soil microbes.

Important findings Soil urease, sucrase and acid phosphatase activities were highest in HN. Soil urease and acid phosphatase activities were lowest in LS (p < 0.05). Soil urease activity in HN, NC and LS was positively correlated to root decomposition rates. Sucrase activity in HN, soil acid phosphatase activity in NC and soil polyphenoloxidase in LS were positively correlated to root decomposition rates (p < 0.05). Soil urease activity was negatively correlated to C/N and absolute content of cellulose in decomposing roots, except for H (p < 0.05). Soil polyphenoloxidase activities in HN, H and LS were negatively correlated with absolute content of cellulose in decomposing roots. The correlation between soil urease activity and the number of aerobic azotobacter and soil fungi was significant. Moreover, soil surcease activity was significant positively correlated with cellulolytic bacteria numbers in HN. Soil acid phosphatase activity in H and NC was significant positively correlated with bacteria and cellulolytic bacteria numbers (p < 0.05). We concluded that it is beneficial to improve soil enzymes activities in HN, which is formed by two different plant life forms, soil urease activity provided information on the fine root (including grass root) decomposition rate, C/N in fine root (including grass root) was one of the important factors influencing soil urease activity in these plantations, and soil enzyme activity was associated with the number of soil fungi, soil aerobic azotobacter, soil cellulolytic bacteria and soil bacteria.

Key words: conversion of farmland to forest (grass), decomposition, fine root (including grass root), soil enzyme