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Small understorey trees have greater capacity than canopy trees to adjust hydraulic traits following prolonged drought in a tropical forest
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  • André Giles,
  • Lucy Rowland,
  • Paulo Bittencourt,
  • David Bartholomew,
  • Sarah Coughlin,
  • Patrícia de Britto Costa,
  • Tomas Domingues,
  • Raquel Miatto,
  • Fernanda Barros,
  • Leandro Ferreira,
  • Peter Groenendijk,
  • Alex Oliveira,
  • Antonio da Costa,
  • Patrick Meir,
  • Maurizio Mencuccini,
  • Rafael Oliveira
André Giles
University of Campinas Institute of Biology
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Lucy Rowland
University of Exeter
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Paulo Bittencourt
University of Campinas
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David Bartholomew
University of Exeter College of Life and Environmental Studies
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Sarah Coughlin
University of Sao Paulo
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Patrícia de Britto Costa
University of Campinas
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Tomas Domingues
University of São Paulo
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Raquel Miatto
Universidade de São Paulo
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Fernanda Barros
University of Campinas
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Leandro Ferreira
Museu Paraense Emílio Goeldi
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Peter Groenendijk
University of Campinas
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Alex Oliveira
Museu Paraense Emílio Goeldi
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Antonio da Costa
Universidade Federal do Pará
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Patrick Meir
The Australian National University
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Maurizio Mencuccini
University of Edinburgh
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Rafael Oliveira
University of Campinas
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Abstract

The future of tropical forests is dependent on the capacity of young trees to adjust to drought. We evaluated multiple hydraulic traits indicative of the drought tolerance of small trees across nine common genera at the world’s longest-running tropical throughfall exclusion experiment and compared their responses with surviving large canopy trees. Small understorey trees increased specific hydraulic conductivity by 56.3% and leaf:sapwood area ratio by 45.6% in response to the drought treatment. However, understorey trees in both a control and the throughfall exclusion treatment had significantly lower minimum stomatal conductance and maximum hydraulic leaf-specific conductivity relative to the large trees, as well as significantly greater hydraulic safety margin (HSM) and PLC and embolism resitance, occupying a distinctly different hydrualic niche. The greater HSM of small understorey trees relative to large canopy trees likely enables them to adjust other aspects of their hydraulic systems to take advantage of increases in light availability in the understorey, driven by drought-induced mortality of canopy trees. Our results suggest that small understorey trees can adjust their hydraulic systems in response to changes in water and light availability and this has major implications for the regeneration potential of tropical forests following droughts.