Retention of dead standing plant biomass (marcescence) increases subsequent litter decomposition in the soil organic layer

We evaluated the impact of retaining dead standing biomass (marcescence) on subsequent litter decomposition in the soil organic layer. Litter of plants that naturally keep dead standing biomass in various extents, Calamagrostis epigeios (keeps most of its dead biomass standing), Quercus robur (keeps some dead leaves on the tree), and Alnus glutinosa (all litter falls to the ground after senescence), were either exposed to environmental climate (ambient) conditions for one year or kept in a dry dark place. After a year, both litter treatments were placed in the soil organic layer for another year. We monitored the mass loss and chemical changes during decomposition. Changes in the chemical composition of aromatic components in C. epigeios litter and decreasing amounts of aromatic compounds in Q. robur and C. epigeios litter during exposure to ambient conditions indicate an effect of photodegradation on these compounds. The litter of Q. robur also exhibited accelerated subsequent litter decomposition in the soil organic layer. In contrast, an increase of aliphatic and aromatic compounds and a decrease of carbohydrates in A. glutinosa litter during exposure to ambient conditions rather points to leaching or microbial decay of labile compounds than an effect of photodegradation. Moreover, the subsequent decomposition of A. glutinosa litter in the soil organic layer was decelerated as compared to the unexposed litter. Our results suggest that litter with comparably low quality (Q. robur and C. epigeios), as compared to litter with a high quality (A. glutinosa), is prone to photodegradation. This process facilitates subsequent decomposition in soil.