Interactions of local climatic, biotic and hydrogeochemical processes facilitate phosphorus dynamics along an Everglades forest-marsh gradient

[摘要] Ecosystem nutrient cycling is often complex becausenutrient dynamics within and between systems aremediated by the interaction of biological and geochemicalconditions operating at different temporal and spatial scales.Vegetated patches in semiarid and wetland landscapes havebeen shown to exemplify some of these patterns and processes.We investigated biological and geochemical factorssuggested to contribute to phosphorus (P) movement andavailability along a forest-marsh gradient in an Evergladestree island. Our study illustrated processes that are consistentwith the chemohydrodynamic nutrient (CHNT) hypothesisand the trigger-transfer, pulse-reserve (TTPR) model developedfor semiarid systems. Comparison with the TTPRmodel was constructive as it elaborated several significantpatterns and processes of the tree island ecosystem including:(1) concentration of the limiting resource (P) in thesource patch (High Head which constitutes the reserve) comparedwith the resource-poor landscape, (2) soil zone calciteprecipitation requiring strong seasonality for evapotranspirationto promote conditions for secondary soil developmentand calcium phosphate reprecipitation, (3) rewetting of previouslydry soils by early wet season precipitation events,and (4) antecedent conditions of the source patch, includinglandscape position that modulated the effect of the precipitationtrigger. Thus, our study showed how water availabilitydrives soil water P dynamics and, potentially, stability ofmineral soil P in this tree island ecosystem. In landscapes with extensive water management, these processes can beasynchronous with the seasonality of hydrologic dynamics,tipping the balance between a sink and source of a limitingnutrient.

[学科分类] 地球化学与岩石