Controls of hydrochemical fluxes via stemflow in tropical lowland rainforests: Effects of meteorology and vegetation characteristics

Abstract

summary So far stemflow has been underrepresented in studies of ecosystem ecology as it usually contributes less than 10% to hydrological input to the forest floor. However, in terms of nutrient cycling, stemflow may constitute an important pathway for the localized input of highly enriched solutes to the forest floor. We measured stemflow hydrology and biogeochemistry in three different ecosystem types (primary forests on ridge and ravine, as well as secondary forest) in South-West Costa Rica. Stemflow hydrochemistry was mainly controlled by meteorology (precipitation magnitude and duration), ecosystem characteristics (topography and plant area index) and species-specific traits (stem diameter and tree height). Stemflow was enriched 7.5-fold in nutrients compared to bulk precipitation and 2.9-fold compared to throughfall. In net stemflow most solutes (especially DOC and K) were leached, while inorganic nitrogen and phosphorus (i.e. NO3 and PO4) were retained along the stemflow pathway. Computation of multiple regression models allowed dissecting the contributions of canopy exchange and dry deposition processes to net stemflow fluxes. Net stemflow was dominated by canopy exchange processes and to a lesser extent by dry deposition fluxes. Including throughfall and litterfall nutrient flux data we calculated that stemflow comprised 1–10% of dissolved internal recycling of nutrients and up to 1.5% of total aboveground nutrient returns. However, dissolved returns by canopy exchange via throughfall plus stemflow contributed up to 50% of total aboveground nutrient return. This demonstrates that stemflow per se represents a small but localized proportion of total above nutrient recycling but that total dissolved returns of (highly available) nutrients and DOC can be important as a part of the internal nutrient cycle of tropical rainforests.