Optimisation of photosynthetic carbon gain and within-canopy gradients of associated foliar traits for Amazon forest trees J. Lloyd1, S. Patiño2, R. Q. Paiva3,*, G. B. Nardoto4, C. A. Quesada1,3,5, A. J. B. Santos3,5,†, T. R. Baker1, W. A. Brand6, I. Hilke6, H. Gielmann6, M. Raessler6, F. J. Luizão3, L. A. Martinelli4, and L. M. Mercado7 1Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, UK 2Grupo de Ecología de Ecosistemas Terrestres Tropicales, Universidad Nacional de Colombia, Sede Amazonia, Instituto Amazónico de Investigaciones-Imani, km. 2, vía Tarapacá, Leticia, Amazonas, Colombia 3Institito National de Pesquisas Amazônicas, Manaus, Brazil 4Centro de Energia Nuclear na Agricultura, Av. Centenário 303, 13416-000, Piracicaba-SP, Brazil 5Departamento de Ecologia, Universidade de Brasília, DF, Brazil 6Max-Planck-Institut für Biogeochemie, Postfach 100164, 07701, Jena, Germany 7Centre for Ecology and Hydrology, Wallingford, UK *now at: Secretária Municipal de Desenvolvimento e Meio Ammbiente ma Prefeturia Municipal de Maués, Maués, Brazil †Alexandre Santos died in the Amazon plane crash of 29 September 2006
Abstract. Vertical profiles in leaf mass per unit leaf area (MA), foliar 13C
composition (δ13C), nitrogen (N), phosphorus (P),
carbon (C) and major cation concentrations
were estimated for 204 rain forest trees growing in 57 sites across the
Amazon Basin. Data was analysed using a multilevel modelling approach,
allowing a separation of gradients within individual tree canopies
(within-tree gradients) as opposed to stand level gradients occurring because
of systematic differences occurring between different trees of different
heights (between-tree gradients). Significant positive within-tree gradients
(i.e. increasing values with increasing sampling height) were observed for
MA and [C]DW (the subscript denoting on a dry weight basis) with
negative within-tree gradients observed for δ13C, [Mg]DW
and [K]DW. No significant within-tree gradients were observed for
[N]DW, [P]DW or [Ca]DW. The magnitudes of between-tree
gradients were not significantly different to the within-tree gradients for MA,
[C]DW, [K]DW, [N]DW, [P]DW and [Ca]DW. But for
[Mg]DW, although there was no systematic difference observed between trees of
different heights, strongly negative within-tree gradients were found to occur.
When expressed on a leaf area basis (denoted by the subscript "A"),
significant positive gradients were
observed for [N]A, [P]A and [K]A both within and between trees, these being
attributable to the positive intra- and between-tree gradients in MA
mentioned above. No systematic within-tree gradient was observed for either
[Ca]A or [Mg]A, but with a significant
positive gradient observed for [Mg]A between trees (i.e. with taller trees
tending to have a higher Mg per unit leaf area).
Significant differences in
within-tree gradients between individuals were observed only for
MA, δ13C and [P] A. This was best associated
with the overall average [P]A for each tree,
this also being considered to be a surrogate for a tree's average leaf area based photosynthetic capacity, Amax. A new model is
presented which is in agreement with the above observations. The model
predicts that trees characterised by a low upper canopy Amax should have
shallow, or even non-existent, within-canopy gradients in Amax, with optimal intra-canopy
gradients becoming sharper as a tree's upper canopy Amax increases.
Nevertheless, in all cases it is predicted that the optimal within-canopy
gradient in Amax should be substantially less than for photon
irradiance. Although this is also shown to be consistent with numerous observations as
illustrated by a literature survey of gradients in photosynthetic capacity for broadleaf trees,
it is also in contrast to previously held notions of optimality.
A new equation relating gradients in photosynthetic capacity within
broadleaf tree canopies to the photosynthetic capacity of their upper canopy leaves is presented.
Citation: Lloyd, J., Patiño, S., Paiva, R. Q., Nardoto, G. B., Quesada, C. A., Santos, A. J. B., Baker, T. R., Brand, W. A., Hilke, I., Gielmann, H., Raessler, M., Luizão, F. J., Martinelli, L. A., and Mercado, L. M.: Optimisation of photosynthetic carbon gain and within-canopy gradients of associated foliar traits for Amazon forest trees, Biogeosciences, 7, 1833-1859, doi:10.5194/bg-7-1833-2010, 2010.