Observational insights on the effects of land use and precipitation seasonality on water-driven circulation of phosphorus in the tropical Andes.
In tropical montane ecosystems, forest conversion into agricultural uses, combined with changes in climate can alter ecosystem hydrological and biogeochemical processes in multiple ways. A deeper understating of the interactions and couplings between land use/land cover, ecohydrological, and biogeochemical processes is needed to identify and evaluate the potential impacts of a changing environment. In this study, we compare the combined effects of forest conversion into agricultural uses and rainfall seasonality, in the dynamics of water-driven phosphorus circulation in a tropical montane area in Colombia. More specifically, we analyze water-driven phosphorus circulation from rainfall to infiltration as it moves through different hydrological compartments, in a case study that includes four types of land use, including two stages of intervention in native oak-dominated forests, transitory crops (vegetative periods of less than 1 year) and non-native pastures. Our results show that mean phosphate (PO4-P) fluxes in infiltration and surface runoff were higher in agroecosystems than in natural forests, while both types of forests exhibited canopy absorption of PO4-P from rainfall, typical of P-limited ecosystems. These differences were exacerbated by rainfall seasonality (P < 0.05). Our results indicate that a large portion of nutrient extra-inputs in agroecosystems from fertilization may be lost to surface runoff or infiltration and may not be available for plant nutrition and potentially causing other impacts downstream. Overall, our results highlight how, from growing on relatively phosphorus-poor soils, natural ecosystems are more effective in controlling phosphorus losses, both in the canopy as well as in the soil.