Ecosystem respiration and net primary productivity after 8–10 years of experimental through-fall reduction in an eastern Amazon forest.

Background:There is much interest in how the Amazon rainforest may respond to future rainfall reduction. However, there are relatively few ecosystem-scale studies to inform this debate. Aims:We described the carbon cycle in a 1 ha rainforest plot subjected to 8–10 consecutive years of ca. 50% through-fall reduction (TFR) and compare these results with those from a nearby, unmodified control plot in eastern Amazonia. Methods:We quantified the components of net primary productivity (NPP), autotrophic (Ra) and heterotrophic respiration, and estimate gross primary productivity (GPP, the sum ofNPPandRa) and carbon-use efficiency (CUE, the ratio ofNPP/GPP). Results:The TFR forest exhibited slightly lowerNPPbut slightly higherRa, such that forestCUEwas 0.29 ± 0.04 on the control plot but 0.25 ± 0.03 on the TFR plot. Compared with four years earlier, TFR plot leaf area index and small tree growth recovered and soil heterotrophic respiration had risen. Conclusions:This analysis tested and extended the key findings of a similar analysis 4 years earlier in the TFR treatment. The results indicated that, while the forest recovered from extended drought in some respects, it maintained higher overallRarelative to the undroughted control, potentially causing the droughted forest to act as a net source of CO2. [ABSTRACT FROM PUBLISHER]