Drying intensity and acidity slow down microbial growth recovery after rewetting dry soils

Soil microbes perceive drying and rewetting (DRW) events as more or less harsh depending on the previous soil moisture history. If a DRW event is not perceived as harsh, microbial growth recovers rapidly after rewetting (referred to as 'type 1' response), while a harsh DRW will be followed by a delayed growth recovery ('type 2' response). Predicting these responses based on pedoclimatic factors is important because they can determine how carbon is partitioned between growth (soil C stabilization) and respiration (C loss to the atmosphere). To characterize the microbially perceived harshness between the two extreme types 1 and 2, and its pedoclimatic drivers, we described microbial growth with a single logistic function and respiration with a rescaled gamma distribution using similar to 100 growth and respiration datasets. These functions captured microbial growth and respiration rates well during the recovery phase after rewetting. Therefore, the fitted parameters from these functions could help us to capture the continuum of microbial recovery between type 1 and 2 and characterize harshness levels. The product of growth parameters tau (delay time) and b (the slope of the growth curve at time tau) was an effective index that could capture and quantify perceived harshness because it allowed separating type 1 and 2 responses better than tau or b alone or than any other parameter describing the growth or respiration response. The drier the soil before rewetting and the lower the pH, the higher was the perceived harshness (tau x b), the longer the delay of growth recovery, and the larger the CO2 loss at rewetting. Overall, this study places soil microbial responses to DRW along a continuous gradient from fast to slow recovery, where the faster the recovery, the better adapted the microbial community is to the DRW event.

Automated summary

Soil microbes perceive drying and rewetting events differently based on previous soil moisture history. The severity of the event determines the microbial growth response, with 'type 1' response being rapid and 'type 2' response being delayed. This study characterizes the perceived harshness between these two responses and identifies the pedoclimatic drivers that contribute to it, such as soil moisture and pH levels. The findings highlight the impact of these factors on carbon partitioning and microbial community adaptation to drying and rewetting events.