Carbon, Nitrogen, and Sulfur Pools in Particle‐Size Fractions as Influenced by Climate

Abstract

Abstract The response of soil organic matter (SOM) dynamics to climate change may be deduced from changes in the distribution of SOM among different C pools. The distribution of soil organic carbon (SOC), total N, and total S in particle‐size fractions were measured to assess the influences of climate. Clay (<2 µm), silt (2–20 µm), fine sand (20–250 µm), and coarse sand (250–2000 µm) fractions were obtained from composite soil samples from the top 10 cm of 21 native grassland sites along temperature and precipitation transects from Saskatoon, Canada, to southern Texas, USA. The clay fraction contained about 43% of the total SOC, 56% of the total N, and 62% of the total S. The SOC and total‐N concentrations in the clay fraction, relative to those in the bulk soil, increased significantly across sites with increasing annual temperature, decreasing annual precipitation, and decreasing clay content (multiple R 2 = 0.80*** [significant at P = 0.001] for SOC and 0.83*** for N); the concentration of SOM in the fine sand fraction showed the opposite trends. Principal axis component analyses confirmed that both clay and fine sand fractions comprised sensitive SOC and N pools related to climate, whereas S seemed to be controlled by factors other than those regulating the dynamics of SOC and N. These results suggest that SOM is preferably decayed from pools of the fine sand fractions with increasing temperature, resulting in a relative enrichment of SOM stabilized on clay.