Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland

Abstract

• Open-Top Chambers were used to raise air temperature by up to 1°C in a peatland.• Interaction between peat temperature and moisture content was investigated.• Impact on peat decomposition was assessed by combining various microbial proxies.• The effect of air warming occurred when comparing distinct moisture sites.• We describe a change in microbial structure and enzymatic activities. a b s t r a c t a r t i c l e i n f o Several studies on the impact of climate warming have indicated that peat decomposition/mineralization will be enhanced. Most of these studies deal with the impact of experimental warming during summer when prevalent abiotic conditions are favorable to decomposition. Here, we investigated the effect of experimental air warming by open-top chambers (OTCs) on water-extractable organic matter (WEOM), microbial biomasses and enzymatic activities in two contrasted moisture sites named Bog and Fen sites, the latter considered as the wetter ones. While no or few changes in peat temperature and water content appeared under the overall effect of OTCs, we observed that air warming smoothed water content differences and led to a decrease in mean peat temperature at the warmed Bog sites. This thermal discrepancy between the two sites led to contrasting changes in microbial structure and activities: a rise in hydrolytic activity at the warmed Bog sites and a relative enhancement of bacterial biomass at the warmed Fen sites. These features were not associated with any change in WEOM properties namely carbon and sugar contents and aromaticity, suggesting that air warming did not trigger any shift in OM decomposition. Using various tools, we show that the use of single indicators of OM decomposition can lead to fallacious conclusions. Lastly, these patterns may change seasonally as a consequence of complex interactions between groundwater level and air warming, suggesting the need to improve our knowledge using a high time-resolution approach.

Differential responses of carbon‐degrading enzyme activities to warming: Implications for soil respiration

“…Indeed, several studies suggest that warming‐induced changes in soil microbial community composition cause differential responses of cellulase and ligninase activities (Deangelis et al., ; Pold, Grandy, Melillo, & Deangelis, ). This explanation is also consistent with studies showing that fungi are main contributors to ligninase production (De Gonzalo et al., ; Kinnunen, Maijala, Jarvinen, & Hatakka, ) and that experimental warming increases fungal abundance (A'bear, Jones, Kandeler, & Boddy, ; Delarue et al., ). However, warming may also directly or indirectly cause physiological adaptation of soil microorganisms to increase enzyme production (Manzoni, Taylor, Richter, Porporato, & Gren, ; Nie et al., ; Schindlbacher et al., ), even when warming decreases total microbial biomass (Pold et al., ; Sistla & Schimel, ; Sorensen et al., ).…”

Managing peatland vegetation for drinking water treatment

“…This could be significant as, for example, Molinia produces ten-times the annual root biomass of Calluna 39 and root exudation can destabilise peat organic matter by adding labile carbon which ‘primes’ the decomposition of peat1540. Vegetation type also affects the microbial community diversity in peatlands41 which may have implications for carbon sequestration and DOC flux.…”

Predator–prey mass ratio drives microbial activity under dry conditions in Sphagnum peatlands

“…A. polifolia, V. oxycoccos , Calluna vulgaris, and E. vaginatum were the dominant vascular plant species in hummocks (Buttler et al., ). As a result of these micro‐topographical patterns, the water level was on average three centimeters lower in hummocks than in lawns (Buttler et al., ; Delarue et al., ); equivalent to a 9% reduction in Sphagnum moisture (see below for details) content in the top three centimeters (Table ). In total, 12 plots (1 m 2 each) were randomly assigned to these two microhabitats, six in hummocks (hereafter named “moderately dry, MD”) and six in lawns (hereafter named “moderately wet, MW”).…”