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 daysafter 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.