Prof. Elise Pendall1, Mr Jinquan Li1,2, Dr Ming Nie2, Dr Jeff Powell1, Dr Andrew Bissett3
1Western Sydney University, Penrith, Australia, 2Fudan University, Shanghai, China, 3CSIRO, Hobart, Australia
Physico-chemical protection has been identified as an important mechanism for predicting soil organic carbon (SOC) and nutrients, but its relative contribution is uncertain when considering concurrent regulatory effects of climate, plant productivity, and soil biodiversity. We used topsoil (0–10 cm) and subsoil (20–30 cm) from 628 sites across the Australian continent, spanning a broad range of climatic conditions and parent materials, and found that physico-chemical protection plays the most important role in determining SOC and nutrients, challenging current models in which these soil resources are controlled by climatic or biotic factors. The importance of protection factors is evident across soil depths and ecosystem types (i.e., tropical, temperate, arid, and cropland ecosystems). We acknowledge that distinguishing between physical and chemical processes can be arbitrary. However, our statistical approach provides insight into the relative importance of chemical protection mediated via redox mineral reactive sites compared to physical protection mediated by surface area. At the continental scale, SOC had the highest correlation with extractable iron (Fe), compared to all the other factors (including climate and biota) (r = 0.59 and 0.52 in topsoil and subsoil, respectively). Moreover, chemical protection had the highest predictive power for SOC in arid and cropland ecosystems while having the second most important predictive power in tropical and temperate ecosystems. Although physico-chemical protection played the most important role in predicting SOC and nutrient availability at continental and ecosystem scales, other drivers should also be considered. Climate, generally regarded as one of the primary controls, had both direct and indirect effects, but played a less significant role in predicting SOC or nutrients. Our results show that the soil matrix ultimately controls the fate of SOC and nutrients, and highlights that maintaining soil physico-chemical protection will help secure ecosystem sustainability.