Abstract
Storing large amounts of organic carbon, soils are a key but uncertain component of the global carbon cycle, and accordingly, of Earth System Models (ESMs). Soil organic carbon (SOC) dynamics are regulated by a complex interplay of drivers. Climate, generally represented by temperature and moisture, is regarded as one of the fundamental controls. Here, we use 54 forest sites in Switzerland, systematically selected to span near-independent gradients in temperature and moisture, to disentangle the effects of climate, soil properties, and landform on SOC dynamics. We estimated two SOC turnover times, based on bulk soil 14C measurements (τ14C) and on a 6-month laboratory soil incubation (τi). In addition, upon incubation, we measured the 14C signature of the CO2 evolved and quantified the cumulated production of dissolved organic carbon (DOC). Our results demonstrate that τi and τ14C capture the dynamics of contrasting fractions of the SOC continuum. The 14C-based τ14C primarily reflects the dynamics of an older, stabilised pool, whereas the incubation-based τi mainly captures fresh readily available SOC. Mean site temperature did not raise as a critical driver of SOC dynamics, and site moisture was only significant for τi. However, soil pH emerged as a key control of both turnover times. The production of DOC was independent of τi and not driven by climate, but primarily by the content of clay and, secondarily by the slope of the site. At the regional scale, soil physicochemical properties and landform appear to override the effect of climate on SOC dynamics.
Highlights
Earth System Models (ESMs) have become a primary tool to project future climate[1]
To unravel the regional-scale effect of temperature and moisture on Soil organic carbon (SOC) dynamics, we developed a statistics-based strategy to select 54 study sites spread over Switzerland with maximized orthogonality of temperature and moisture (Fig. 1)
Τ14C reflects SOC cycling on time scales ranging from years to millennia, which in mineral soils typically constitutes most of the stock[30] and where SOC stabilisation processes prevail
Summary
Earth System Models (ESMs) have become a primary tool to project future climate[1]. Given that soil organic carbon (SOC) is one of the largest terrestrial C pool (~3000 Pg C)[2]; and relevant to terrestrial carbon-climate feedbacks, the adequate representation of soils is critical for these models. To unravel the regional-scale effect of temperature and moisture on SOC dynamics, we developed a statistics-based strategy to select 54 study sites spread over Switzerland with maximized orthogonality of temperature and moisture (Fig. 1). Ran a laboratory soil incubation and measured 14C contents to test concurrently various putative drivers of SOC dynamics. We www.nature.com/scientificreports included site temperature (1981–2010 average air mean monthly temperature) and moisture (1981–2010 dryness index, details in Methods). The 54 study sites were selected so that the effects of biogeographic region, temperature, moisture, and the aggregated soil properties and landform-related variables (PCo1, PCo2) were near-orthogonal, i.e. their effects were independent in the multiple linear regression models summarized by analysis of variance[17,18] (details in Methods). We ran the incubation in the dark at constant temperature and moisture (25 °C and water potential of −20 kPa)
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