Death from drought in tropical forests is triggered by hydraulics not carbon starvation

• Published in: Nature (London) Vol. 528; no. 7580; pp. 119 - 122
• Main Authors: Rowland, L., da Costa, A. C. L., Galbraith, D. R., Oliveira, R. S., Binks, O. J., Oliveira, A. A. R., Pullen, A. M., Doughty, C. E., Metcalfe, D. B., Vasconcelos, S. S., Ferreira, L. V., Malhi, Y., Grace, J., Mencuccini, M., Meir, P.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03.12.2015; Nature Publishing Group
• Subjects: 704/158/2165; 704/158/2445; Agricultural Science, Forestry and Fisheries; Agricultural Sciences; Analysis; Biomass; Body Size; Brazil; Carbohydrate Metabolism; Carbohydrates; Carbon; Carbon - metabolism; Drought; Droughts; Environmental aspects; Forest Science; Forests; Forests and forestry; Health aspects; Health risks; Humanities and Social Sciences; Hydraulics; Lantbruksvetenskap och veterinärmedicin; Lantbruksvetenskap, skogsbruk och fiske; letter; Moisture availability; Mortality risk; multidisciplinary; Photosynthesis; Physiological aspects; Plant Leaves - metabolism; Plant Stems - metabolism; Rain; Rainforest; Rainforests; Science; Seasons; Skogsvetenskap; Soil - chemistry; Soil moisture; Starvation; Trees; Trees - growth & development; Trees - metabolism; Tropical Climate; Tropical forests; Water - metabolism; Xylem - metabolism; Brazil
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature15539

It has been suggested that carbon starvation, owing to reduced availability of non-structural carbohydrates (NSCs), is an important contributor to tree mortality during drought in tropical rainforests; however, data from the world’s longest-running experimental drought study presented here show no evidence of carbon starvation, and instead the researchers conclude that impaired water hydraulic processes (involving the transport of water from soil to leaf) have a more important role in triggering tree death from long-term drought. Hydraulic failure kills drought-hit trees It has been suggested that carbon starvation, caused by reduced availability of non-structural carbohydrates, is an important contributor to tree mortality during drought in tropical rainforests. Using data from the world's longest-running experimental drought study in tropical rainforest, these authors assess the importance of non-structural carbohydrates stores and how they are affected by drought in the long term. They find no evidence of carbon starvation, but instead conclude that impaired water hydraulic processes (involving the transport of water from soil to leaf) has a more important role in triggering tree death from drought. Drought threatens tropical rainforests over seasonal to decadal timescales 1 , 2 , 3 , 4 , but the drivers of tree mortality following drought remain poorly understood 5 , 6 . It has been suggested that reduced availability of non-structural carbohydrates (NSC) critically increases mortality risk through insufficient carbon supply to metabolism (‘carbon starvation’) 7 , 8 . However, little is known about how NSC stores are affected by drought, especially over the long term, and whether they are more important than hydraulic processes in determining drought-induced mortality. Using data from the world’s longest-running experimental drought study in tropical rainforest (in the Brazilian Amazon), we test whether carbon starvation or deterioration of the water-conducting pathways from soil to leaf trigger tree mortality. Biomass loss from mortality in the experimentally droughted forest increased substantially after >10 years of reduced soil moisture availability. The mortality signal was dominated by the death of large trees, which were at a much greater risk of hydraulic deterioration than smaller trees. However, we find no evidence that the droughted trees suffered carbon starvation, as their NSC concentrations were similar to those of non-droughted trees, and growth rates did not decline in either living or dying trees. Our results indicate that hydraulics, rather than carbon starvation, triggers tree death from drought in tropical rainforest.