Temperature sensitivity of biomass‐specific microbial exo‐enzyme activities and CO₂ efflux is resistant to change across short‐ and long‐term timescales

Abstract

Accurate representation of temperature sensitivity (Q10) of soil microbial activity across time is critical for projecting soil CO2 efflux. As microorganisms mediate soil carbon (C) loss via exo‐enzyme activity and respiration, we explore temperature sensitivities of microbial exo‐enzyme activity and respiratory CO2 loss across time and assess mechanisms associated with these potential changes in microbial temperature responses. We collected soils along a latitudinal boreal forest transect with different temperature regimes (long‐term timescale) and exposed these soils to laboratory temperature manipulations at 5, 15, and 25°C for 84 days (short‐term timescale). We quantified temperature sensitivity of microbial activity per g soil and per g microbial biomass at days 9, 34, 55, and 84, and determined bacterial and fungal community structure before the incubation and at days 9 and 84. All biomass‐specific rates exhibited temperature sensitivities resistant to change across short‐ and long‐term timescales (mean Q10 = 2.77 ± 0.25, 2.63 ± 0.26, 1.78 ± 0.26, 2.27 ± 0.25, 3.28 ± 0.44, 2.89 ± 0.55 for β‐glucosidase, N‐acetyl‐β‐d‐glucosaminidase, leucine amino peptidase, acid phosphatase, cellobiohydrolase, and CO2 efflux, respectively). In contrast, temperature sensitivity of soil mass‐specific rates exhibited either resilience (the Q10 value changed and returned to the original value over time) or resistance to change. Regardless of the microbial flux responses, bacterial and fungal community structure was susceptible to change with temperature, significantly differing with short‐ and long‐term exposure to different temperature regimes. Our results highlight that temperature responses of microbial resource allocation to exo‐enzyme production and associated respiratory CO2 loss per unit biomass can remain invariant across time, and thus, that vulnerability of soil organic C stocks to rising temperatures may persist in the long term. Furthermore, resistant temperature sensitivities of biomass‐specific rates in spite of different community structures imply decoupling of community constituents and the temperature responses of soil microbial activities.

Central metabolic responses of microorganisms to years and decades of soil warming

“…This functional response was similar in medium-term and long-term warmed soils. Thus, our study provides evidence for a decoupling of microbial community structure and functions, as recently suggested from several ecosystems including soil [41][42][43][44] .…”

Short-and long-term temperature responses of soil denitrifier net N<sub>2</sub>O efflux rates, inter-profile N<sub>2</sub>O dynamics, and microbial genetic potentials

“…The apparent lack of long-term, denitrifier adaptation to rising temperatures (i.e. continued enhancement of N2O production with long-term exposure to warmer temperatures that outstrips enhancement of N2O reduction) is consistent with recent work in soils from these same sites demonstrating no change in the responses of microbial biomass-specific decay or CO2 efflux rates to warmer temperatures over decadal timescales (Min et al, 2019). However, results from the current study contrast with our predictions of microbial adaptations to a warmer climate over the long term, which assume that a soil denitrifying community well-adapted to its temperature regime is adept at complete denitrification with relatively little N2O byproduct.…”

Temperature sensitivity of SOM decomposition is linked with a K‐selected microbial community

“…The soil samples collected from the elevational gradient of the Tibetan grassland, from a naturally degrading permafrost region in Central Alaska, and from a latitudinal gradient of temperate mixed forests in this study (Figure 1) were all undisturbed for centuries. However, the short‐term soil warming and transplantation experiments are strongly disturbed ecosystems, representing the effects only over short periods (Min et al, 2019). Thus, we must be cautious in drawing conclusions from disturbed experiments.…”