Climate change regulates trophic effects on carbon dioxide and methane emission

Background/Question/Methods

Biosphere is experiencing significant changes in its physical, chemical and biological aspects. Climate change has been documented as the most important disturbance and it has been attributed mainly to the anthropic activity. The reasons of these changes are related to the increasing concentration of greenhouse gases in the Earth, mainly CO₂ and CH₄, those are resulted from industrial and biological activities. It is expected that altered climates will affect how organisms determine ecosystem functioning. Organisms play a major role in the nutrient loading in aquatic ecosystems, mainly in the carbon cycle, through their activity and trophic behaviour. Here, we test how predicted rainfall changes and litter diversity interact to influence the CO₂ and CH₄ concentration in aquatic ecosystems. For that, we used tank-bromeliad ecosystems because their great potential for experimentation in Ecology. Litter fuels a complex and diverse community in tank-bromeliad ecosystems. We used a full-factorial design, composed by five rainfall scenarios crossed with all combinations of three litter species with five replicates. Our experimental rainfall manipulation was based on two of the main general predictions for Southeastern Brazil: i) increase in the temporal clustering of rainfall and ii) increase in the occurrence of extreme rainfall events.

Results/Conclusions

We demonstrated that both CO₂ and CH₄ concentrations in aquatic ecosystems were influenced by rainfall changes and trophic interactions played a crucial role in explaining these effects. Rainfall changes disrupted the link between top-predators and filter-feeders, the main responsible for algae removal in the water column (GLM, F_1,155=8.43, P=0.004) which promotes an increase in CO₂ concentration in altered rainfall scenarios (GLMM; F_4,162=2.78, P=0.028). On the other hand, CH₄ was strongly determined by litter diversity and its combined effect with rainfall changes (GLMM; F_4,162=2.83, P=0.024). Litter diversity positively affected decomposition F_1,169=5.17, P=0.024) that are significantly correlated to CH₄ concentration in the water (GLM; F_1,172=6.872, P=0.001), but only in control rainfall conditions. This effect is correlated to the role of the most abundant but less preferred prey by top-predators on decomposition. Freshwater worms are not regulated by top-predators but they need microbial conditioning to decompose organic matter in aquatic ecosystems, negatively affected by rainfall changes (GLM; F_4,165= 4.46, P=0.002). Here, we demonstrated that predicted rainfall changes will affect the trophic effects on the CO₂ and CH₄ dynamics in freshwater ecosystems. We argued that the negative effects on CH₄ production can trigger negative feedbacks of climatic disturbances over greenhouse emissions in aquatic environments.