Abstract:
Quantifying the relative contributions of plant physicochemical traits and environmental con-ditions to leaf decomposition is essential to increase our understanding of ecosystem processes in forestedterrestrial and aquatic habitats. This is particularly crucial in tropical rainforests that display high levels oftree diversity and environmental heterogeneity over relatively small spatial scales. For example, in Amazo-nia, detritus from hundreds of tree species fuels carbon cycling in watersheds, but much remains to belearned about how species traits interact with environmental conditions to mediate decomposition. Weinvestigated the leaf-litter decomposition of 17 tree species with contrasting traits in soil and stream habi-tats in Yasun ıNational Park, Ecuador. We hypothesized that (1) habitat type would be the major determi-nant of leaf decomposition (faster in stream than soil systems), (2) species would be ranked similarly interms of leaf decomposition rates, according to decomposability traits (i.e., litter quality), within each habi-tat, and (3) the variability of leaf decomposition within habitats would be greater for soil than for streamsystems. Contrary to ourfirst hypothesis, we found that leaf-litter decomposition rates for any given treespecies were similar in stream and soil systems. However, we found that the relative importance of littertraits for decomposition such as concentrations of micronutrients (Mn and Cu, in particular) was consistentacross habitats. Finally, we found that decomposition was equally highly variable in both terrestrial andaquatic systems. This variability was explained by differences in microhabitat within soils, but appeared tobe more stochastic in streams. Overall, we found that plant traits had an overwhelming effect on thedecomposition process in the intertwined aquatic and terrestrial matrices of the Yasun ırainforest, withsignificant effects of microhabitat features. This study sheds light on the fate of the pool of dead organicmatter in tropical rainforests and highlights the need for further studies of the mechanisms underlyingmicrohabitat variability.