title: Death from drought in tropical forests is triggered by hydraulics not carbon starvation.
abstract: Drought threatens tropical rainforests over seasonal to decadal timescales, but the drivers of tree mortality following drought remain poorly understood. It has been suggested that reduced availability of non-structural carbohydrates (NSC) critically increases mortality risk through insufficient carbon supply to metabolism ('carbon starvation'). 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.
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FF, UK.
authors.forename: L
authors.initials: L
authors.lastname: Rowland
authors.affiliation: Centro de Geosciências, Universidade Federal do Pará, Belém 66075-110, Brazil.
authors.forename: A C L
authors.initials: AC
authors.lastname: da Costa
authors.affiliation: School of Geography, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: D R
authors.initials: DR
authors.lastname: Galbraith
authors.affiliation: Instituto de Biologia, UNICAMP, Campinas 13.083-970, Brazil.
authors.forename: R S
authors.initials: RS
authors.lastname: Oliveira
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FF, UK.
authors.forename: O J
authors.initials: OJ
authors.lastname: Binks
authors.affiliation: Centro de Geosciências, Universidade Federal do Pará, Belém 66075-110, Brazil.
authors.forename: A A R
authors.initials: AA
authors.lastname: Oliveira
authors.affiliation: The University of Cambridge, Cambridge CB2 1TN, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Pullen
authors.affiliation: Environmental Change Institute, The University of Oxford, Oxford OX1 3QY, UK.
authors.forename: C E
authors.initials: CE
authors.lastname: Doughty
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund S-223 62, Sweden.
authors.forename: D B
authors.initials: DB
authors.lastname: Metcalfe
authors.affiliation: EMBRAPA Amazônia Oriental, Belém 66095-903, Brazil.
authors.forename: S S
authors.initials: SS
authors.lastname: Vasconcelos
authors.affiliation: Museu Paraense Emílio Goeldi, Belém 66077-830, Brazil.
authors.forename: L V
authors.initials: LV
authors.lastname: Ferreira
authors.affiliation: Environmental Change Institute, The University of Oxford, Oxford OX1 3QY, UK.
authors.forename: Y
authors.initials: Y
authors.lastname: Malhi
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FF, UK.
authors.forename: J
authors.initials: J
authors.lastname: Grace
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FF, UK.|ICREA at CREAF, 08193 Cerdanyola del Vallés, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Mencuccini
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FF, UK.|Research School of Biology, Australian National University, Canberra, Australian Capital Territory 2601, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Meir
mesh_terms: D018533:Biomass; D049628:Body Size; D001938:Brazil; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D055864:Droughts; D018515:Plant Leaves / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism; D065947:Rainforest; D012621:Seasons; D012987:Soil / Q000737:chemistry; D014197:Trees / Q000254:growth & development / Q000378:metabolism*; D014329:Tropical Climate; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
chemical_list: D012987:Soil; D014867:Water; D002244:Carbon