Plant-soil interactions and acclimation to temperature of microbial-mediated soil respiration may affect predictions of soil CO2 efflux

Abstract

It is well known that microbial-mediated soil respiration, the major source of CO 2 from terrestrial ecosystems, is sensitive to temperature. Here, we hypothesize that some mechanisms, such as acclimation of microbial respiration to temperature and/or regulation by plant fresh C inputs of the temperature sensitivity of decomposition of soil organic matter (SOM), should be taken into account to predict soil respiration correctly. Specifically, two hypotheses were tested: (1) under warm conditions, temperature sensitivity (Q 10 ) and basal rates of microbial-mediated soil respiration (Bs 20, respiration at a given temperature) would be primarily subjected to presence/absence of plant fresh C inputs; and (2) under cold conditions, where labile C depletion occurred more slowly, microbial-mediated soil respiration could adjust its optimal temperatures to colder temperatures (acclimation), resulting in a net increase of respiration rates for a given temperature (Bs 20 ). For this purpose, intact soil cores from an oak savanna ecosystem were incubated with sufficient water supply at two contrasting temperatures (10 and 30°C) during 140 days. To study temperature sensitivity of soil respiration, short-term temperature cycles (from 5 to 40°C at 8 h steps) were applied periodically to the soils. Our results confirmed both hypotheses. Under warm conditions ANCOVA and likelihood ratio tests confirmed that both Q 10 and Bs 20 decreased significantly during the incubation. Further addition of glucose at the end of the incubation period increased Bs 20 and Q 10 to initial values. The observed decrease in temperature sensitivity (Q 10 ) in absence of labile C disagrees with the broadly accepted fact that temperature sensitivity of the process increases as quality of the substrate decreases. Our experiment also shows that after 2 months of incubation cold-incubated soils doubled the rates of respiration at cold temperatures causing a strong increase in basal respiration rates (Bs 20 ). This suggest that microbial community may have up-regulated their metabolism at cold conditions (cold-acclimation), which also disagrees with most observations to date. The manuscript discusses those two apparent contradictions: the decrease in temperature sensitivity in absence of labile C and the increase in microbial-mediated soil respiration rates at cold temperatures. While this is only a case study, the trends observed could open the controversy over the validity of current soil respiration models.

Soil microbes and their response to experimental warming over time: A meta-analysis of field studies

“…Researchers have previously suggested that acclimation of soil microbes (Bradford et al, 2010;Crowther and Bradford, 2013;Malcolm et al, 2008;Tucker et al, 2013;Yuste et al, 2010), shifts in microbial community composition (Luo et al, 2014;Treseder et al, 2016;Wei et al, 2014) Any combination of these mechanisms could have influenced the temporal trends in soil respiration.…”

“…Several mechanisms could drive this pattern by altering microbial C use as warming proceeds (Allison et al, 2010b;Bradford et al, 2008;Frey et al, 2013;Pritchard, 2011 al., 2012; Sierra et al, 2010). These include acclimation of individual microbes (Allison et al, 2010b;Crowther and Bradford, 2013;Malcolm et al, 2008;Tucker et al, 2013;Yuste et al, 2010), shifts in microbial communities (Bárcenas-Moreno et al, 2009;Luo et al, 2014;Rousk et al, 2012;Treseder et al, 2016;Wei et al, 2014), and evolutionary adaptation of microbial populations to higher temperatures (Romero-Olivares et al, 2015). In addition, labile C pools in the soils could become depleted owing to higher microbial activity (Bradford et al, 2008;Eliasson et al, 2005;Kirschbaum, 2004;McHale et al, 1998).…”

Warming effects on root morphological and physiological traits: The potential consequences on soil C dynamics as altered root exudation

“…The results observed in our study may be primarily attributed to C substrate availability limitation. Previous studies have clearly demonstrated the critical role of C substrate inputs in regulating soil respiration and its temperature sensitivity of SOM decomposition (Gershenson et al, 2009;Curiel Yuste et al, 2010). The organic matter inputs into the soils come primarily from plants through two sources, including rhizosphere labile C supplies (e.g., root exudation) and litter inputs (Wan and Luo, 2003;Högberg and Read, 2006).…”

“…More importantly, the contribution of root exudates to substrate availability was relatively limited because all of the experimental small plants were seedlings younger than 9 years old in 2011. As a result, continuous soil warming tends to deplete the pool of labile SOC over the short-term period and may create a negative feedback that reduces subsequent soil CO 2 efflux over time in the two species plots (Hartley et al, 2007;Curiel Yuste et al, 2010). However, it should be stressed here that the variations in soil CO 2 efflux may be also affected by photosynthesis and above-ground plant growth (Pumpanen et al, 2012), because a substantial proportion of soil CO 2 efflux originates directly from root and rhizosphere respiration using recent photosynthate (Kuzyakov and Gavrichkova, 2010).…”

Modelling temperature acclimation effects on the carbon dynamics of forest ecosystems in the conterminous United States

“…Acclimation of soil respirations has also been found (Oechel et al, 2000;Luo et al, 2001;Melillo et al, 2002;Curiel Yuste et al, 2010). Luo et al (2001) indicated the temperature sensitivity of soil respiration (Q10) decreases under warming, and increases at low temperatures through acclimation.…”