The global-scale temperature and moisture dependencies of soil organic carbon decomposition: an analysis using a mechanistic decomposition model

Abstract

Since the decomposition rate of soil organic carbon (SOC) varies as a function of environmental conditions, global climate change is expected to alter SOC decomposition dynamics, and the resulting changes in the amount of CO 2 emitted from soils will feedback onto the rate at which climate change occurs. While this soil feedback is expected to be significant because the amount of SOC is substantially more than the amount of carbon in the atmosphere, the environmental dependencies of decomposition at global scales that determine the magnitude of the soil feedback have remained poorly characterized. In this study, we address this issue by fitting a mechanistic decomposition model to a global dataset of SOC, optimizing the model's temperature and moisture dependencies to best match the observed global distribution of SOC. The results of the analysis indicate that the temperature sensitivity of decomposition at global scales (Q 10 =1.37) is significantly less than is assumed by many terrestrial ecosystem models that directly apply temperature sensitivity from small-scale studies, and that the maximal rate of decomposition occurs at higher moisture values than is assumed by many models.These findings imply that the magnitude of the soil decomposition feedback onto rate of global climate change will be less sensitive to increases in temperature, and modeling of temperature and moisture dependencies of SOC decomposition in global-scale models should consider effects of scale.

Substrate quality and the temperature sensitivity of soil organic matter decomposition

“…In contrast to our findings, a recent modelling study, based on current litter 470 input rates and soil-C stocks, estimated that the global temperature sensitivity of SOM 471 decomposition equated to a Q 10 value of just 1.37 (Ise and Moorcroft, 2006). SOM 472 accumulation is the result of small differences between inputs and outputs, and links 473 between plant productivity and soil respiration, which probably cannot be represented 474 simply by differences in current litter input rates (Ise and Moorcroft, 2006), may 475 affect the relationship between temperature and SOM accumulation.…”

“…SOM 472 accumulation is the result of small differences between inputs and outputs, and links 473 between plant productivity and soil respiration, which probably cannot be represented 474 simply by differences in current litter input rates (Ise and Moorcroft, 2006), may 475 affect the relationship between temperature and SOM accumulation. In our model, the 476 input rate remained constant throughout but one consequence of higher decomposition 477 rates could be increased nutrient availability, which could feedback on plant 478 productivity and therefore the rate of C input to the soil.…”

Sensitivity of soil respiration to moisture and temperature

“…The former value is very close to the overall mean values of 2.3 reported by Lenton and Huntingford (2003), whereas the latter value is closer to the overall mean value of 1.3 reported by Ise and Moorcroft (2006).…”

Latitude-dependent underestimation of microbial extracellular enzyme activity in soils

“…1 Glucosidase (a, b, g) and protease (c-f, h) (Craine et al 2010;Fierer et al 2006;Ise and Moorcroft 2006;Townsend et al 1992). Enzymatic activities in soil and sediment samples measured during the present study showed maximum rates at temperatures above 50°C.…”

“…Generally, enzymatic activity shows maxima at a temperature slightly higher than the optimum for growth of a microorganism (Burton et al 2002;Kube et al 2013;Madigan et al 2003;Tang et al 2010). However, enzymatic activity sharply decreases at increasing temperatures beyond its optimum (Ise and Moorcroft 2006;Madigan et al 2003). As a consequence, increasing temperatures above the experimental threshold for mesophiles (i.e., temperatures for optimum microbial activity and growth) should reflect highly diminished microbial enzymatic activities and consequently a decrease of the estimates for the expected decomposition of organic matter in soils (Conant et al 2011;Davidson and Janssens 2006).…”