Soil detrital inputs increase stimulate bacterial saprotrophs with different timing and intensity compared to fungal saprotrophs

Abstract

Soils contain microbial inhabitants that differ in sensitivity to anthropogenic modification. Soil reclamation relies on monitoring these communities to evaluate ecosystem functions recovery post-disturbance. DNA metabarcoding and soil enzyme assays provide information about microbial functional guilds and organic matter decomposition activities respectively. However bacterial communities, fungal communities, and enzyme activities may not be equally informative for monitoring reclaimed soils. We compared effects of disturbance regimes applied to forest soils on fungal community composition, bacterial community composition, and potential hydrolase activities (N-acetyl-β-D-glucosaminidase, acid phosphatase, and cellobiohydrolase) at two times (14 days and 5 months post-disturbance) and depths (LFH versus mineral soil). Using disturbance versus control comparisons allowed us to identify genus-level disturbance-indicators and shifts in hydrolase activity levels. We observed declines in disturbed LFH fungal biomass (ergosterol) and declines in ectomycorrhizal fungi abundance across all disturbed samples, which prompted us to consider necromass-induced (fungal, root) saprotroph increases as disturbance indicators. Fungal community composition strongly shifted away from ecotmycorrhizal dominance to saprotroph dominance (i.e. increased Mortierella, and Umbelopsis) in disturbed plots at 5 months, while bacterial community composition did not shift to distinguish control plots from disturbed ones at either sampling time. Soil potential hydrolase data mainly indicated that mixing LFH material into mineral soil increases the measured activity levels compared to control and replaced mineral soil. Bacterial saprotrophs previously associated with mycelial necromass were detected across multiple regimes as disturbance indicators at 14 days post-disturbance. Our results confirm that ectomycorrhizal fungal genera are sensitive and persistently impacted by soil physical disturbances. Increases in saprotrophic bacterial genera are detectable 14 days pot-disturbance but only a few persist as disturbance indicators after several months. Potential hydrolase activities appear to be most useful for detecting the transfer of decomposition hotspots into mineral soils.