Leaf:wood allometry and functional traits together explain substantial growth rate variation in rainforest trees

Gray, E.F., Wright, I.J., Falster, D.S., Eller, A.S.D., Lehmann, C.E.R., Bradford, M.G., and Cernusak, L.A. (2019) Leaf:wood allometry and functional traits together explain substantial growth rate variation in rainforest trees. AoB Plants, 11 (3). plz024.

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Plant growth rates drive ecosystem productivity and are a central element of plant ecological strategies. For seedlings grown under controlled conditions, a large literature has firmly identified the functional traits that drive interspecific variation in growth rate. For adult plants, the corresponding knowledge is surprisingly poorly understood. Until recently it was widely assumed that the key trait drivers would be the same (e.g. specific leaf area, or SLA), but an increasing number of papers has demonstrated this not to be the case, or not generally so. New theory has provided a prospective basis for understanding these discrepancies. Here we quantified relationships between stem diameter growth rates and functional traits of adult woody plants for 41 species in an Australian tropical rainforest. From various cost-benefit considerations, core predictions included that: (i) photosynthetic rate would be positively related to growth rate; (ii) SLA would be unrelated to growth rate (unlike in seedlings where it is positively related to growth); (iii) wood density would be negatively related to growth rate; and (iv) leaf mass:sapwood mass ratio (LM:SM) in branches (analogous to a benefit:cost ratio) would be positively related to growth rate. All our predictions found support, particularly those for LM:SM and wood density; photosynthetic rate was more weakly related to stem diameter growth rates. Specific leaf area was convincingly correlated to growth rate, in fact negatively. Together, SLA, wood density and LM:SM accounted for 52 % of variation in growth rate among these 41 species, with each trait contributing roughly similar explanatory power. That low SLA species can achieve faster growth rates than high SLA species was an unexpected result but, as it turns out, not without precedent, and easily understood via cost-benefit theory that considers whole-plant allocation to different tissue types. Branch-scale leaf:sapwood ratio holds promise as an easily measurable variable that may help to understand growth rate variation. Using cost-benefit approaches teamed with combinations of leaf, wood and allometric variables may provide a path towards a more complete understanding of growth rates under field conditions.

Item ID: 61841
Item Type: Article (Research - C1)
ISSN: 2041-2851
Keywords: Forest ecology, Functional traits, Growth rate, Leaf:wood allocation, Plant ecological strategies, Specific leaf area
Copyright Information: © The Author(s) 2019. Published by Oxford University Press on behalf of the Annals of Botany Company. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Funders: Macquarie University (MQ), L’Oreal-Unesco (United Nations Educational, Scientific and Cultural Organization), Australian Research Council (ARC)
Projects and Grants: MQ Research Scholarship, L’Oreal-UNESCO For Women in Science Fellowship, ARC DP120103284
Date Deposited: 19 Feb 2020 02:16
FoR Codes: 31 BIOLOGICAL SCIENCES > 3108 Plant biology > 310806 Plant physiology @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 100%
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