Limited acclimation in leaf anatomy to experimental drought in tropical rainforest trees.
Dry periods are predicted to become more frequent and severe in the future in some parts of the tropics, including Amazonia, potentially causing reduced productivity, higher tree mortality and increased emissions of stored carbon. Using a long-term (12 year) through-fall exclusion (TFE) experiment in the tropics, we test the hypothesis that trees produce leaves adapted to cope with higher levels of water stress, by examining the following leaf characteristics: area, thickness, leaf mass per area, vein density, stomatal density, the thickness of palisade mesophyll, spongy mesophyll and both of the epidermal layers, internal cavity volume and the average cell sizes of the palisade and spongy mesophyll. We also test whether differences in leaf anatomy are consistent with observed differential drought-induced mortality responses among taxa, and look for relationships between leaf anatomy, and leaf water relations and gas exchange parameters. Our data show that trees do not produce leaves that are more xeromorphic in response to 12 years of soil moisture deficit. However, the drought treatment did result in increases in the thickness of the adaxial epidermis (TFE: 20.5 ± 1.5 µm, control: 16.7 ± 1.0 µm) and the internal cavity volume (TFE: 2.43 ± 0.50 mm3cm-2, control: 1.77 ± 0.30 mm3cm-2). No consistent differences were detected between drought-resistant and drought-sensitive taxa, although interactions occurred between drought-sensitivity status and drought treatment for the palisade mesophyll thickness (P = 0.034) and the cavity volume of the leaves (P = 0.025). The limited response to water deficit probably reflects a tight co-ordination between leaf morphology, water relations and photosynthetic properties. This suggests that there is little plasticity in these aspects of plant anatomy in these taxa, and that phenotypic plasticity in leaf traits may not facilitate the acclimation of Amazonian trees to the predicted future reductions in dry season water availability.
School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK O.Binks@ed.ac.uk.
Oliver
O
Binks
School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK.|Research School of Biology, Australian National University, Canberra, ACT 2601, Australia.
Patrick
P
Meir
College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4QD, UK.
Lucy
L
Rowland
Centro de Geosciências, Universidade Federal do Pará, Belém 66075-110, Brasil.
Antonio Carlos Lola
AC
da Costa
EMBRAPA Amazônia Oriental, Belém 66095-903, Brasil.
Steel Silva
SS
Vasconcelos
Centro de Geosciências, Universidade Federal do Pará, Belém 66075-110, Brasil.
Alex Antonio Ribeiro
AA
de Oliveira
Museu Paraense Emílio Goeldi, Belém 66077-830, Brasil.
Leandro
L
Ferreira
School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK.|ICREA at CREAF , 08193 Cerdanyola del Vallés, Spain.
Maurizio
M
Mencuccini
D000064:Acclimatization; D055864:Droughts; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000502:physiology; D065947:Rainforest; D014197:Trees / Q000033:anatomy & histology / Q000502:physiology*
Amazon; anatomical plasticity; gas exchange; leaf physiology; through-fall exclusion; water relations; water stress