Soil microbial respiration adapts to ambient temperature in global drylands

Abstract

Heterotrophic soil microbial respiration – one of the main processes of carbon loss from soils to the atmosphere – is sensitive to temperature in the short-term. However, how this sensitivity is affected by long-term thermal regimes is uncertain. There is an expectation that soil microbial respiration rates adapt to the ambient thermal regime, but whether this adaptation magnifies or reduces respiration sensitivities to temperature fluctuations remains unresolved. This gap in our understanding is particularly pronounced for drylands as most studies conducted so far have focused on mesic systems. Here, we conducted an incubation study using soils from 110 global drylands encompassing a wide gradient in mean annual temperature. We tested how mean annual temperature affects soil respiration rates at three assay temperatures while controlling for substrate depletion and microbial biomass. Estimated soil respiration rates at the mean microbial biomass were lower in sites with higher mean annual temperatures across the three assayed temperatures. The patterns observed are consistent with expected evolutionary trade-offs in the structure and function of enzymes under different thermal regimes. Our results therefore suggest that soil microbial respiration adapts to the ambient thermal regime in global drylands.

Scientists’ warning to humanity: microorganisms and climate change

“…Two studies assessed the effects of elevated temperatures on microbial respiration rates and mechanisms and outcomes of adaptation 179,180 . The studies examined a wide range of environmental temperatures (−2 to 28 °C), dryland soils (110 samples) and boreal, temperate and tropical soils (22 samples), and evaluated how communities respond to three different temperatures (~10-30 °C).…”

“…The studies examined a wide range of environmental temperatures (−2 to 28 °C), dryland soils (110 samples) and boreal, temperate and tropical soils (22 samples), and evaluated how communities respond to three different temperatures (~10-30 °C). Thermal adaptation was linked to biophysical characteristics of cell membranes and enzymes (reflecting activity-stability trade-offs 180 ) and the genomic potential of microorganisms (with warmer environments having microbial communities with more diverse lifestyles 179 ). Respiration rates per unit biomass were lower in soils from higher-temperature environments, indicating that thermal adaptation of microbial communities may lessen positive climate feedbacks.…”

Vegetation and Microbes Interact to Preserve Organic Matter in Wooded Peatlands

“…As microbial biomass itself is a factor regulating soil respiration rates, standardized CO2 emissions at the microbial biomass were calculated based on the elevated CO2 concentration, time and air volume in the jar and the amount of added microbial biomass carbon from the inoculum. To prevent microbial acclimation to the assay chemistry (13,24), we only incubated the soils shortly. A chloroform fumigation-extraction method (0.5 M K2SO4 to extract biomass C) (44) was used to determine soil microbial biomass carbon by the difference in measured carbon contents between fumigated and control replicates of each sample.…”

“…Such cascading events could invoke a catastrophic positive feedback to global warming (7)(8)(9). However, long-term warming experiments in grasslands (10,11) and studies spanning a wide range of mean annual temperature (MAP) globally (12,13) show declining microbial metabolism over time under experimental warming or in warmer regions. By now most experimental studies in peatlands have lasted only for months to decades, and such time scales are deemed too short to detect long-term (>100 years) effects of climate change on millennial peatlands that may have complex evolutions/successions during past climatic fluctuations (14).…”

Abiotic and biotic drivers underly short- and long-term soil respiration responses to experimental warming in a dryland ecosystem

“…Multiple mechanisms have been hypothesized to explain such transient effects of warming on soil respiration. For instance, the thermal acclimation of soil microorganisms to the ambient temperature regime (Bradford et al, 2019; Dacal, Bradford, Plaza, Maestre, & García-Palacios, 2019) and the depletion of labile soil C sources (Hartley, Hopkins, Garnett, Sommerkorn, & Wookey, 2008; Schindlbacher, Schnecker, Takriti, Borken, & Wanek, 2015) may drive soil respiration responses to warming over time. Additionally, and given that soil temperature and moisture are the most important controls on soil respiration (Conant, Dalla-Betta, Klopatek, & Klopatek, 2004), warming-induced changes in microclimatic variables may alter soil microbial activity, leading to shifts in soil respiration rates (Luo et al, 2001).…”