Temporal variations in microbial biomass C and cellulolytic enzyme activity in arable soils: effects of organic matter input

Abstract

Temporal variations in soil microbial biomass C concentration and in activity of extracellular enzymes of the cellulolytic complex were investigated in a field experiment after eight years of cultivation with either low organic matter input (low-OM) or high organic matter input (high-OM). The cultivation systems differed in whether their source of fertiliser was mainly mineral or organic, in whether a winter cover crop was grown, and whether straw was mulched or removed. Sampling occurred at approximately monthly intervals, over a period of two years. Distinct temporal variations in microbial biomass C concentration and activity of extracellular enzymes of the cellulolytic complex were observed. The temporal pattern was generally similar in the low-OM and high-OM cultivation systems. Temporal variations may have been driven by environmental factors (e.g., temperature and moisture) and crop growth, i.e. by factors common to both systems but not differences in organic matter input. Pronounced and constant increases in β-glucosidase activity (40%) and endocellulase activity (30%) in high-OM were detected across all sampling periods. The increases in microbial biomass C concentration and cellobiohydrolase activity varied over the sampling periods (0–60% and 24–92%, respectively). Over the experimental period a mean of 148 ± 6.0 μg biomass C g −1, a β-glucosidase activity of 123 ± 3.3 nmol g −1 h −1, a cellobiohydrolase activity of 122 ± 2.4 nmol g −1 h −1 and an endocellulase activity of 33.8 ± 0.9 nmol g −1 h −1 were recorded in the low-OM soil (0–20 cm). The corresponding means in the high-OM treatment were 189 ± 6.6 μg biomass C g −1, a β-glucosidase activity of 174 ± 4.1 nmol g −1 h −1, a cellobiohydrolase activity of 173 ± 3.4 nmol g −1 h −1 and an endocellulase activity of 44.2 ± 1.1 nmol g −1 h −1.