Does repeated wetting and drying accelerate decay of leaf litter?

Abstract

Needle litter of lodgepole-jack pine ( Pinus contorta Loud. × P. banksiana Lamb.) previously wetted and dried 14 times absorbed water faster than needles wetted only once for the same total duration (controls); trembling aspen ( Populus tremuloides Michx.) leaf litter showed the reverse response. Wetting-drying did not enhance leaching in either species. Aspen litter decaying in laboratory microcosms at 26°C decomposed faster than controls for 1 month if wetted and dried either previously (14 times) or while decomposition proceeded. However the difference was not maintained past 2 or 3 months decay. Accelerated water absorption by treatment leaves accounted for some, but not all, of the difference in decay rates. Similarly treated pine needles showed a slightly greater mass loss after 1 month, but no consistent difference after 2 or 3 months. Litter layers on the forest floor exhibited persistent trends of increasing (occasionally decreasing) moisture content with depth; only the top centimetre experienced wetting-drying cycles, and no more than 10–15 cycles yr − are likely. In these ecosystems, repeated wetting-drying is probably not a significant influence on litter decomposition rates.