Contributions of climate and soil properties to geographic variations of soil organic matter across the East Asian monsoon region

摘要

Soil organic matter (SOM) plays a crucial role in soil functions and the global carbon cycle. Considering the disconnection of research emphasis between soil and ecology, little is known about the large-scale edaphic controls and their interaction with climate in SOM dynamics. This study aimed to explore the geographic evo-lution mechanisms of SOM from the perspective of soil intrinsic properties. A wide range of soil types from quaternary sediments were sampled from three ecosystems (forest, grass, and arable lands) and at different pedogenic horizons along the mid-temperate to tropical climate gradient in the East Asian monsoon region. SOM was measured in terms of organic carbon (SOC, 0.06-4.81 %), total nitrogen (TN, 0.04-0.41 %), and their ratio (C/N ratio, 1.17-12.26), as well as a series of soil properties: porosity, soil texture, clay mineralogy, exchangeable cations and soil aggregation. The indicators of SOM were most influenced by soil horizon (F=233.2-2375.2), followed by soil type (F=84.0-924.1, p < 0.001) and land use (F=4.7-92.2, p < 0.05); SOC, TN and C/N ratio overall decreased with increasing soil depth, and exhibited decrease first and then increase from north to south. Traditional predictors of soil texture and climate variables independently contributed little to SOM (p > 0.05). In contrast, bulk density had the greatest explanatory power (R2 = 0.379, p < 0.01), followed by soil aggregation (p < 0.05), while phyllosilicate minerals and iron oxides explained significant but small variances, all of which were climate-dependent. SOM could be jointly explained by soil properties (0.665) and climate (0.220) with an interaction effect of 0.152, among which bulk density, percentage of aggregate disruption, and mean annual temperature (MAT) were the most powerful predictors with negative effects. Structural equation modeling results indicated that MAT could influence SOM through soil aggregation and exchangeable cations. This study unravels the direct and indirect effects of climate on SOM and highlights the predominant roles of soil structural properties rather than abiotic primary agents at the regional scale, which merits consideration in improving SOM modeling and land management.

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