Drought stress and tree size determine stem CO2 efflux in a tropical forest

• DOI: 10.1111/nph.15024
• Publication Date: 2018-02-03T18:16:46Z
• Authors: Lucy Rowland; Antonio C. L. da ...; Alex A. R. Oliveira; Rafael S. Oliveira; Paulo L. Bittencourt; Patricia B. Costa; Andre L. Giles; Azul I. Sosa; Ingrid Coughlin; John L. Godlee; Steel S. Vasconcelos; João A. S. Junior; Leandro V. Ferreira; Maurizio Mencuccini; Patrick Meir
• Keywords: tropical rainforests; 0301 basic medicine; 550; Cell Respiration; drought; Forests; 551; Trees; 03 medical and health sciences; Stress, Physiological; Maintenance respiration; growth respiration; stem CO2 efflux; Tropical Climate; maintenance respiration; woody tissue respiration; Drought; Plant Stems; Research; Carbon Dioxide; 15. Life on land; Stem CO2 efflux; 6. Clean water; Droughts; Tropical Rainforests; Growth respiration; Woody tissue respiration; Seasons; Tropical rainforests

Summary

CO2 efflux from stems (CO2_stem) accounts for a substantial fraction of tropical forest gross primary productivity, but the climate sensitivity of this flux remains poorly understood. We present a study of tropical forest CO2_stem from 215 trees across wet and dry seasons, at the world's longest running tropical forest drought experiment site. We show a 27% increase in wet season CO2_stem in the droughted forest relative to a control forest. This was driven by increasing CO2_stem in trees 10–40 cm diameter. Furthermore, we show that drought increases the proportion of maintenance to growth respiration in trees > 20 cm diameter, including large increases in maintenance respiration in the largest droughted trees, > 40 cm diameter. However, we found no clear taxonomic influence on CO2_stem and were unable to accurately predict how drought sensitivity altered ecosystem scale CO2_stem, due to substantial uncertainty introduced by contrasting methods previously employed to scale CO2_stem fluxes. Our findings indicate that under future scenarios of elevated drought, increases in CO2_stem may augment carbon losses, weakening or potentially reversing the tropical forest carbon sink. However, due to substantial uncertainties in scaling CO2_stem fluxes, stand‐scale future estimates of changes in stem CO2 emissions remain highly uncertain.