Typhoon enhancement of N and P release from litter and changes in the litter N:P ratio in a subtropical tidal wetland

Abstract

Litter production and decomposition are key processes controlling the capacity of wetland to store and cycle carbon (C) and nutrients. Typhoons deposit large amounts of green and semi-green (between green and withered) plant tissues and withered litter (normal litter) on wetland soils, generating a pulse of litter production. Climatic models project an increase in typhoon intensity and frequency. Elucidating the impacts of typhoons on C, N and P cycles and storage capacities in subtropical and tropical wetland areas is thus important. We analyzed the patterns and changes of litter decomposition after a typhoon in the Minjiang River estuary in southeastern China. Green litter decomposed the fastest, and the loss of mass did not differ significantly between semi-green litter, withered litter and mixed litter (all soil litter after a typhoon). During the decomposition process the remaining green litter had the highest, and withered litter the lowest N and P concentrations. The biomass loss rate of litter during the studied period was related to the initial litter N and P concentrations. Remaining litter generally increased its N:P ratio during decomposition. The ratio of the released N and P was consequently lower than the initial N:P ratio in all litter types. The typhoon enhanced the release of C, N and P from the litter (884, 12.3 and 6 kg ha−1, respectively) by 264 days after the typhoon. The soil was accordingly enriched with organic matter and nutrients for several months, which should favor microbial growth rates (higher C, N and P availability and lower C:nutrient and N:P ratios) and increase the rates of C and nutrient cycling. If the frequency and/or intensity of typhoons increase, a constant increase in the release of N and P to the soil with lower N:P ratios could change the N and P cycles in wetlands and provide better conditions for the spread of fast-growing species.