Marcescence in temperate regions mediates tree litter decomposition through abiotic factors

Most temperate trees shed their senescent leaves in autumn. However, some genera, typically beech and oak, retain a large portion of their dead leaves until the start of the subsequent growing season, a phenomenon termed marcescence. The fundamentally different conditions marcescent and shed senescent leaves are exposed to have the potential to substantially alter litter decomposition. The extent to which marcescence affects decomposition in temperate ecosystems, however, remains unknown, which hampers our understanding of carbon and nutrient cycles. Here, we aimed to resolve this dilemma in a manipulative field experiment by quantifying the effect of solar radiation and precipitation, the major factors marcescent leaves are exposed to in temperate ecosystems, on the decomposition of marcescent leaves relative to that of leaves directly decomposing in the organic layer after their senescence.

Exposure of leaves from the genera Quercus and Fagus to solar radiation before decomposition in the organic layer resulted in a considerably higher mass loss for those leaves than for leaves decomposing directly in the organic layer (37 vs. 23 %). This effect was further amplified upon exposure of leaves to both solar radiation and precipitation (cumulative mass loss of ∼50 % or more). Leaf chemistry analyses via Fourier-transform infrared spectroscopy suggested that disruption of ligno-cellulose complexes and leaching of the released compounds in the solar radiation only and solar radiation and precipitation treatments, respectively, accelerated leaf decomposition. We identify marcescence as an integral driver of litter decomposition and highlight the need to consider marcescence in carbon and nutrient cycling in temperate ecosystems.