Microbial biomass in forest soils under altered moisture conditions: A review

Microbial biomass is known to decrease with soil drying and to increase after rewetting due to physiological assimilation and substrate limitation under fluctuating moisture conditions, but how the effects of changing moisture conditions vary between dry and wet environments is unclear. Here, we conducted a meta-analysis to assess the effects of elevated and reduced soil moisture on microbial biomass C (MBC) and microbial biomass N (MBN) across a broad range of forest sites between dry and wet regions. We found that the influence of both elevated and reduced soil moisture on MBC and MBN concentrations in forest soils was greater in dry than in wet regions. The influence of altered soil moisture on MBC and MBN concentrations increased significantly with the manipulation intensity but decreased with the length of experimental period, with a dramatic increase observed under a very short-term precipitation pulse. Moisture effect did not differ between coarse-textured and fine-textured soils. Precipitation intensity, experimental duration, and site standardized precipitation index (dry or wet climate) were more important than edaphic factors (i.e., initial water content, bulk density, and clay content) in determining microbial biomass in response to altered moisture in forest soils. Different responses of microbial biomass in forest soils between dry and wet regions should be incorporated into models to evaluate how changes in the amount, timing, and intensity of precipitation affect soil biogeochemical processes.

Automated summary

A meta-analysis was conducted to evaluate the effects of elevated and reduced soil moisture on microbial biomass C (MBC) and microbial biomass N (MBN) in forest soils across dry and wet regions. It was found that the influence of altered soil moisture on MBC and MBN concentrations was greater in dry regions. The intensity of manipulation and length of experimental period were significant factors affecting the response of microbial biomass to altered moisture.