Increased cuticular carbon sequestration and lignin oxidation in response to soil warming

Rising temperatures are predicted to accelerate the decomposition of labile soil organic compounds such as proteins and carbohydrates, whereas biochemically resistant compounds, such as lipids from leaf cuticles and roots and lignin from woody tissues, are expected to remain stable on decadal to centennial timescales(1,2). However, the extent to which soil warming changes the molecular composition of soil organic matter is poorly understood(3,4). Here we examine the impact of soil warming in a mixed temperate forest on the molecular make-up of soil organic matter. We show that the abundance of leaf-cuticle-derived compounds is increased following 14 months of soil warming; we confirm this with nuclear magnetic resonance spectra of soil organic matter extracts. In contrast, we find that the abundance of lignin-derived compounds is decreased after the same treatment, while soil fungi, the primary decomposers of lignin in soil(5), increase in abundance. We conclude that future warming could alter the composition of soil organic matter at the molecular level, accelerating lignin degradation and increasing leaf-cuticle-derived carbon sequestration. With annual litterfall predicted to increase in the world's major forests with a 3 degrees C warming(6), we suggest that future warming may enhance the sequestration of cuticular carbon in soil.