Abstract
Future climate scenarios forecast a 10-50% decline in rainfall in Eastern Amazonia. Altered precipitation patterns may change important ecosystem functions like decomposition through either changes in physical and chemical processes or shifts in the activity and/or composition of species. We experimentally manipulated hydroperiods (length of wetdry cycles) in a tank bromeliad ecosystem to examine impacts on leaf litter decomposition. Gross loss of litter mass over 112 days was greatest in continuously submersed litter, lowest in continuously dry litter, and intermediate over a range of hydroperiods ranging from eight cycles of 7 wet7 dry days to one cycle of 56 wet56 dry days. The resilience of litter mass loss to hydroperiod length is due to a shift from biologically assisted decomposition (mostly microbial) at short wetdry hydroperiods to physicochemical release of dissolved organic matter at longer wetdry hydroperiods. Biologically assisted decomposition was maximized at wetdry hydroperiods falling within the range of ambient conditions (12-22 consecutive dry days) but then declined under prolonged wetdry hydroperiods (28 and 56 dry days. Fungalbacterial ratios showed a similar pattern as biologically assisted decomposition to hydroperiod length. Our results suggest that microbial communities confer functional resilience to altered hydroperiod in tank bromeliad ecosystems. We predict a substantial decrease in biological activity relevant to decomposition under climate scenarios that increase consecutive dry days by 1.6- to 3.2-fold in our study area, whereas decreased frequency of dry periods will tend to increase the physicochemical component of decomposition.