Seasonal variability of microbial biomass associated with aggregates in a rice-based ecosystem

Abstract

Temporal variability of soil microbial biomass shows contradictory trends for different ecosystems. Since soils are comprised of many sizes of aggregates and soil particles, we hypothesized that the microbial biomass response to seasonal variation is more sensitive at the aggregate scale than for whole soil. Tillage impacts on seasonal variation of microbial biomass were determined for a hydargric Anthrosol in China from 2008 to 2009. No significant seasonal changes occurred for soil total organic C (TOC), but microbial biomass C (MBC) exhibited distinct seasonal variation. However, seasonal variation patterns of MBC associated with aggregates coincided with patterns for whole soil, regardless of tillage regimes.The MBC in whole soil was significantly higher in spring (272 mg kg−1) than autumn (186 mg kg−1) and winter (165 mg kg−1) under CT (conventional tillage), while MBC was higher in spring and autumn than winter and summer for RNT (ridge with no-till). Microorganisms associated with different sizes of aggregates responded similarly to environmental changes, but the degree of response for different sizes of aggregates varied. The CV (coefficient of variation) for seasonal change was lowest for macroaggregates, while the highest CVs occurred for the silt + clay fraction. The results indicated that soil microorganisms associated with macroaggregates were more stable than with silt + clay fractions to resist seasonal changes in climate and soil properties, and therefore more likely to play a role in enhancing nutrient conservation in the soil. Seasonal variation patterns of microbial biomass associated with aggregates coincided with patterns for whole soil, suggesting that microorganisms associated with different size fractions of aggregates respond to macro- and micro-environmental changes in a similar way.