土壤微生物生物量碳的表观周转时间测定方法

土壤微生物生物量碳周转对土壤有机质和养分循环起着决定作用。本研究建立了土壤微生物生物量碳周转时间的测定方法。培养条件下 (2 5℃、10 0 %湿度 ) ,加入14 C标记葡萄糖标记土壤微生物生物量碳 ,在 10 0d培养期内 ,每隔 2 0d测定一次14 C标记微生物生物量碳 (14 C BC) ,采用一级热力学方程拟合测定期内 (2 0～ 10 0d) 14 C BC 的周转速率常数 (k) ,由此计算土壤微生物生物量碳的表观周转时间。测定的 5个土壤在培养条件下微生物生物量碳的周转时间为 93～ 4 0 0d ,根据培养温度和实际田间年平均温度推算得到田间条件下土壤微生物生物量碳的周转时间为 1 0～ 4 1a。其主要影响因子为土壤质地 ,土壤利用方式的影响较小。土壤微生物生物量碳的周转时间能较好地反映土壤微生物生物量的周转状况及其与土壤有机质的周转和积累的关系。

MEASURING THE GROSS TURNOVER TIME OF SOIL MICROBIAL BIOMASS C UNDER INCUBATION

The turnover of the microbial biomass plays key roles in the cycling of organic matter and nutrients in soil.Although the microbial biomass-C is generally accounted for only 1%~4% of total soil organic, the balance between the rate of microbial processes determines the turnover and consequently the accumulation of soil organic matter and nutrients (e g.N, P and S).In this study, the procedure for measuring the turnover time of soil microbial biomass-C has been developed.¹⁴C-labelled glucose was used to label the biomass-C by incubating soils at 25 and 100% humidity.The labelled biomass-C, total biomass-C, and extractable-C were measured by every 20 days during a 100-day incubation period, using the fumigation-extraction method.Data obtained were then used to calculate the turnover rate constant of biomass-C, and hence its turnover time Under the incubation condit ions, the turnover t ime of biomass-C, calculated from the gross turnover rate constant of labelled biomass-C, varied between 93 and 400 days.This is equivalent, by extrapolation, to 1.0~4.1 years under the field conditions where soils were from.It was demonstrated that the turnover time of soil biomass- C was largely affected by soil texture but little by management.Measuring the turnover times of soil biomass-C provides a good indication of microbial activities in relating to the turnover and accumulation of soil organic matter.