No signs of thermal acclimation of heterotrophic respiration from peat soils exposed to different water levels

Partitioning of the net CO2 exchange using an automated chamber system reveals plant phenology as key control of production and respiration fluxes in a boreal peatland

“…The GLM analysis also identified a significant negative WTL‐Ts interaction indicating that the Rh temperature sensitivity was enhanced under drier conditions. This outcome is in contrast with a mesocosm study in which no such interaction effect was noted (Vicca et al., ) and opposite to findings suggesting an increased temperature sensitivity of Rh at higher WTL's in drained peatland forests (Mäkiranta et al., ). These inconsistencies may be explained by differences in the mean WTL's in the various studies and their positioning along the optimum moisture curve that regulates microbial activity (Howard & Howard, ; Ilstedt, Nordgren, & Malmer, ).…”

“…A similar though weaker seasonal pattern was also observed in the plant CUE estimates. It is interesting to note that the 2 year mean growing season NPP/GPP ratio of 0.74 appears initially rather high when compared to forest and grassland ecosystems where the reported values commonly range between approximately 0.30 and 0.70 (DeLucia, Drake, Thomas, & Gonzalez‐Meler, ; Vicca et al., ; Waring et al., ; Zhang, Xu, Chen, & Adams, ). However, the estimate from our Sphagnum dominated fen agrees well with existing studies reporting NPP/GPP ratios of 0.68–0.71 for various Sphagnum species (Street et al., ) and 0.62 for another Sphagnum dominated boreal peatland (Riutta, Laine, & Tuittila, ).…”

Temperature response of soil respiration largely unaltered with experimental warming

“…Although warming has been shown to stimulate soil respiration within many sites, several studies show neutral or even negative responses to warming, often attributed to moisture limitation (9,10), shifts in microbial physiological response or composition (11)(12)(13), or depletion of labile C pools (14)(15)(16)(17). As such, multiple single-site analyses find evidence of acclimation (sometimes termed thermal adaptation) of soil respiration to experimental warming (10-14, 16, 17), although others report no evidence for such shifts in respiration response over time (18)(19)(20). Moreover, the response of soil respiration to temperature is not consistent across all temperature ranges, because the temperature sensitivity of respiration typically decreases under warmer conditions (21,22).…”

Shifts in the microbial community structure explain the response of soil respiration to land-use change but not to climate warming

“…For example, Bradford et al (2008Bradford et al ( , 2010 reported acclimation of soil respiration even in the presence of sufficient substrate availability, suggesting that the microbial community was able to adjust its metabolic activities to increasing temperature. However, other studies reported no acclimation of Rs (Hartley et al, 2007(Hartley et al, , 2008Vicca et al, 2009) and argued that the increasing Rs response to temperature was linked to substrate depletion. Recent studies also described a potential role of shifts in the soil microbial biomass or community structure in Rs thermal response (Thiessen et al, 2013;Wei et al, 2014).…”