No evidence for increased loss of old carbon in a temperate organic soil after 13 years of simulated climatic warming despite increased CO₂ emissions

Abstract

Determining the temperature sensitivity of terrestrial carbon (C) stores is an urgent priority for predicting future climate feedbacks. A key aspect to solve this long‐standing research gap is to determine whether warmer temperatures will increase autotrophic activities leading to greater C storage or promote heterotrophic activities that will drive these systems to become C sources. We experimentally addressed this critical question by subjecting intact plant‐soil systems in a UK upland ecosystem to simulated climate warming under natural field conditions. We report the results of a 13‐year field‐based climate manipulation experiment combining in situ respiration measurements with radiocarbon (14C) analyses of respired CO2, dissolved organic carbon (DOC), soil and the tissue contents of the dominant soil fauna (enchytraeids). We found that warming during the growing season produced the largely expected increases in ecosystem respiration (63%) and leaching of DOC (19%) with no evidence for thermal acclimation or substrate exhaustion over the whole 13‐year experimental period. Contrary to expectations, we found no evidence to support an increased release of old soil C after more than a decade of simulated climatic change, and indeed, 14C analyses indicated that warming caused a significant shift towards mineralisation of more recent plant‐derived C inputs. Further support came from the radiocarbon analyses of the enchytraeid tissues, which showed a greater assimilation of the more recent (plant‐derived) C sources following warming. Therefore, in contrast to subarctic ecosystems, our results suggest that changes in C storage in this UK upland soil are strongly coupled to plant activities and that increasing temperatures will drive the turnover of organic material fixed only within recent years, without resulting in the loss of existing old carbon stores.

Low carbon availability in paleosols nonlinearly attenuates temperature sensitivity of soil organic matter decomposition

“…In contrast to real Q 10 described by Arrhenius law, the apparent Q 10 , which reflects substrate availability and is described by Michaelis–Menten equation, decreased linearly with declining C availability (Gershenson et al, 2009; Li et al, 2020). Other studies demonstrated that Q 10 is independent on soil depth (Briones et al, 2021; Fang et al, 2005; Hicks Pries et al, 2017). These findings, however, could result from the narrow range of [ S ] in the soils they tested.…”

Preferential substrate use decreases priming effects in contrasting treeline soils

“…Preferential substrate use could therefore also shape C cycling at the ecosystem scale. For example, in a large-scale warming experiment in the UK, Briones et al (2021) found no evidence for positive priming, while enhanced turnover of recently fixed C suggests that preferential substrate use can take place at the landscape scale. While substrate use was mostly independent from substrate C:N, it was idiosyncratic of land cover type and soil horizon (Fig.…”

Moisture and temperature effects on the radiocarbon signature of respired carbon dioxide to assess stability of soil carbon in the Tibetan Plateau

“…In recent decades, it has been widely observed that temperature plays a major role on the dynamics of SOM (Knorr et al, 2005;Davidson and Janssens, 2006;Feng and Simpson, 2008) and the mean age of respired CO 2 (Hopkins et al, 2012;Chen et al, 2021) by increasing the decomposition rates from fast-cycling pools (Trumbore et al, 1996) and mobilizing old C in warming conditions (Dutta et al, 2006;Briones et al, 2010). In contrast, other studies have suggested that warming does not lead to release of old C (Briones et al, 2021;Dioumaeva et al, 2002) and that non-labile C decomposition is insensitive to temperature increase (Liski et al, 1999). By comparison, drying phenomena increased the release of modern 14 CO 2 from shallow soil layers but preserved the old soil carbon pools in deeper layers (Kwon et al, 2019).…”