Emergent Climatic Controls on Soil Carbon Turnover and Its Variability in Warm Climates

Climate plays a critical role in altering soil carbon (C) turnover and long-term soil C storage by regulating water availability and temperature, and in turn biological activity. However, a systematic analysis of how key climatic factors shape the global patterns of soil C turnover is still lacking. Using global observation-based data sets and a transit time theory, here we show that-excluding croplands and cold regions-soil C turnover time (tau TO) and its variability are strongly related to ecosystem aridity through a power law scaling. According to such a relation, soil C turnover is faster but also more variable in wetter regions, suggesting more complex C cycling processes. The observed scaling of tau TO and its coefficient of variation with aridity underlines the fundamental controls of climate on soil C turnover and may help reconcile soil C models with empirical observations for improved projection of soil C dynamics under climate change. Climate regulates the metabolic activity of both plants and soil microorganisms by regulating temperature and water availability of ecosystems and, in turn, influences how fast C cycles through soils. Recent observation-based data sets provide global estimates of both soil C age and turnover time, paving the way for novel analyses exploring how they simultaneously change across climates. Here, by analyzing these data we show that, excluding croplands and cold regions, soil C turnover time and its variability are related to ecosystem aridity through simple power laws across a broad range of aridity. Such relations reveal that, especially in wet regions, C cycling through soils is mostly young C and can consist of C with a broad range of turnover times. Our findings may help us improve the structure of soil C models and hence projections of soil C cycling under climate change. The ratio of soil C turnover time to age shows a strong sensitivity to aridity in warm regionsSoil C turnover in warm regions is more variable under wetter conditionsThe scaling of soil C turnover time and its variability with aridity follows a self-similar power law

Automated summary

Climate has a critical role in influencing soil carbon turnover and storage by regulating water availability and temperature. This study shows that soil carbon turnover time and its variability are strongly related to ecosystem aridity. Wetter regions have faster but more variable soil carbon turnover, indicating complex carbon cycling processes. These findings are important for improving soil carbon models and predicting soil carbon dynamics under climate change.