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

Abstract

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 (R _a) and heterotrophic respiration, and estimate gross primary productivity (GPP, the sum of NPP and R _a) and carbon-use efficiency (CUE, the ratio of NPP/GPP).

Results: The TFR forest exhibited slightly lower NPP but slightly higher R _a, such that forest CUE was 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 overall R _a relative to the undroughted control, potentially causing the droughted forest to act as a net source of CO₂.

Keywords:

• drought
• carbon cycling
• Caxiuanã National Forest Reserve
• climate change
• tropical rainforest
• biomass allocation
• CUE
• GPP
• NPP
• PCE

Acknowledgements

This paper is dedicated to the late Samuel Almeida, valued collaborator and friend. This research contributes to the Brazil-led Large-Scale Biosphere – Atmosphere (LBA) Experiment in Amazonia of the Brazilian Ministry of Science, Technology and Innovation. The experimental infrastructure and measurements were supported by the LBA, UK Natural Environmental Research Council grants (GR3/11706, NER/A/S/2002/00487, NE/J011002/1, NE/B503384/1, and NE/F002149/1), the EU Fifth Framework CARBONSINK-LBA project and Sixth Framework PAN-AMAZONIA project and, most recently, a major grant from the Gordon and Betty Moore Foundation to the Amazon Forest Inventory Network (RAINFOR). PM is supported by the Australian Research Council (FT110100457) and The Royal Society of Edinburgh. YM is supported by the Jackson Foundation. Annual meteorology data were provided by the Tropical Ecology Assessment and Monitoring (TEAM) Network, a collaboration between Conservation International, the Missouri Botanical Garden, the Smithsonian Institution, and the Wildlife Conservation Society, and partially funded by these institutions, the Gordon and Betty Moore Foundation, and other donors. We are deeply indebted to the Museu Paraense Emilio Goeldi, the Ferreira Penna Scientific Field Station at Caxiuanã and numerous field assistants for invaluable field support.

Notes

†Deceased