Detritus diversity increases decomposition rates under several precipitation scenarios

Background/Question/Methods

Changes on the rainfall distribution and temperature have been largely projected based on different climate scenarios, but these changes do not include the effects on biological communities and/or ecological processes. Species-rich environments are expected to be more stable to ecosystem disturbances than species-poor environments, but studies that aim to verify how changes on biodiversity interact with climate alterations have rarely been able to also consider potential moderation by community-level processes. Natural microcosms (i.e. tank-bromeliads) have been successfully used to experimentally test some ecological theories since they are complete ecosystems with high complexity, yet still easy to manipulate. Here, we performed a field experiment to test how detritus diversity and precipitation changes interact to determine the magnitude of decomposition. We used a full-factorial design composed of five rain scenarios and all detritus combinations of three plant species, for a total of 180 experimental microcosms (5 rain scenarios x 7 detritus combinations x 5 replicates + 5 control microcosms). The rain scenarios were established based on the projections for Southeastern Brazil, which mainly involves an increase of extreme rainfall events. The detritus species were determined based on different metabolic groups (C3, C4 and CAM). Rain events were fully manipulated by adding water in the bromeliads, according to specific precipitation scenarios, while the natural precipitation was prevented with plastic tents over each experimental microcosm. Decomposition was measured as loss of detrital dry mass.  

Results/Conclusions

We found significative positive effects of detritus diversity (GLM, p <0.05; F_detritus=4.5451) on decomposition, but no effects of precipitation scenario nor the interaction factor between diversity and precipitation. Decomposition rate was about 20% higher in the mixtures than observed in the monocultures, but such effects were not non-additive (Dt values, T-test, p>0.05). We suggest that organic matter identity is the most important factor determining the magnitude of decomposition rates even under extremely irregular rain scenarios. Decomposing organisms may modify their behavior to accommodate fluctuations in water level in naturally temporary environments, like tank bromeliads. Many studies have demonstrated the importance of organic matters quality to decomposition; nevertheless this is the first one to emphasize the consistence of its effects over large changes in climate that result in the conversion of wet to dry environments.