Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests
Authors: Tavares Julia Valentim , Oliveira Rafael S. , Mencuccini Maurizio , Signori-Müller Caroline , Pereira Luciano , Diniz Francisco Carvalho , Gilpin Martin , Marca Zevallos Manuel J. , Salas Yupayccana Carlos A. , Acosta Martin , Pérez Mullisaca Flor M. , Barros Fernanda de V. , Bittencourt Paulo , Jancoski Halina , Scalon Marina Corrêa , Marimon Beatriz S. , Oliveras Menor Imma , Marimon Ben Hur , Fancourt Max , Chambers-Ostler Alexander , Esquivel-Muelbert Adriane , Rowland Lucy , Meir Patrick , Lola da Costa Antonio Carlos , Nina Alex , Sanchez Jesus M. B. , Tintaya Jose S. , Chino Rudi S. C. , Baca Jean , Fernandes Leticia , Cumapa Edwin R. M. , Santos João Antônio R. , Teixeira Renata , Tello Ligia , Ugarteche Maira T. M. , Cuellar Gina A. , Martinez Franklin , Araujo-Murakami Alejandro , Almeida Everton , da Cruz Wesley Jonatar Alves , del Aguila Pasquel Jhon , Aragāo Luís , Baker Timothy R. , de Camargo Plinio Barbosa , Brienen Roel , Castro Wendeson , Ribeiro Sabina Cerruto , Coelho de Souza Fernanda , Cosio Eric G. , Davila Cardozo Nallaret , da Costa Silva Richarlly , Disney Mathias , Espejo Javier Silva , Feldpausch Ted R. , Ferreira Leandro , Giacomin Leandro , Higuchi Niro , Hirota Marina , Honorio Euridice , Huaraca Huasco Walter , Lewis Simon , Flores Llampazo Gerardo , Malhi Yadvinder , Monteagudo Mendoza Abel , Morandi Paulo , Chama Moscoso Victor , Muscarella Robert , Penha Deliane , Rocha Mayda Cecília , Rodrigues Gleicy , Ruschel Ademir R. , Salinas Norma , Schlickmann Monique , Silveira Marcos , Talbot Joey , Vásquez Rodolfo , Vedovato Laura , Vieira Simone Aparecida , Phillips Oliver L. , Gloor Emanuel , Galbraith David R. 
Published: April 2023

Tropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, $$\varPsi $$
Ψ
50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters $$\varPsi $$
Ψ
50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both $$\varPsi $$
Ψ
50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.