Warming promotes loss of subsoil carbon through accelerated degradation of plant-derived organic matter

Abstract:

Increasing global temperatures have the potential to stimulate decomposition and alter the composition of soil organic matter (SOM). However, many questions remain about the extent to which differences in the composition of SOM along the soil profile may control its decomposability under future warming. In this study we assessed how +4˚C whole-soil warming affected the quantity and quality of SOM down to 90 cm depth in a mixed-coniferous temperate forest using a combination of biomarker analyses. Our findings indicate that 4.5 years of soil warming led to divergent responses in subsoils (>20 cm) as compared to surface soils. Warming enhanced the accumulation of plant-derived n-alkanes over the whole soil profile at the expense of plant- and microorganism-derived fatty acids in the subsoils. The relative abundance of SOM molecular components shifted from less microbially transformed to more transformed organic matter in the subsoil. Fine root mass declined by 24.0 ± 7.5% with warming over the whole soil profile, accompanied by reduced plant-derived inputs and accelerated decomposition of aromatic compounds and plant-derived fatty acids in the subsoils. Our study suggests that warming accelerated microbial decomposition of plant-derived inputs, leaving behind more degraded organic matter. The non-uniform, and depth dependent SOM composition and warming response implies that subsoil respond as sensitive and complex as surface soils.