Canopy position affects the relationships between leaf respiration and associated traits in a tropical rainforest in Far North Queensland.
We explored the impact of canopy position on leaf respiration (R) and associated traits in tree and shrub species growing in a lowland tropical rainforest in Far North Queensland, Australia. The range of traits quantified included: leaf R in darkness (RD) and in the light (RL; estimated using the Kok method); the temperature (T)-sensitivity of RD; light-saturated photosynthesis (Asat); leaf dry mass per unit area (LMA); and concentrations of leaf nitrogen (N), phosphorus (P), soluble sugars and starch. We found that LMA, and area-based N, P, sugars and starch concentrations were all higher in sun-exposed/upper canopy leaves, compared with their shaded/lower canopy and deep-shade/understory counterparts; similarly, area-based rates of RD, RL and Asat (at 28 °C) were all higher in the upper canopy leaves, indicating higher metabolic capacity in the upper canopy. The extent to which light inhibited R did not differ significantly between upper and lower canopy leaves, with the overall average inhibition being 32% across both canopy levels. Log-log RD-Asat relationships differed between upper and lower canopy leaves, with upper canopy leaves exhibiting higher rates of RD for a given Asat (both on an area and mass basis), as well as higher mass-based rates of RD for a given [N] and [P]. Over the 25-45 °C range, the T-sensitivity of RD was similar in upper and lower canopy leaves, with both canopy positions exhibiting Q10 values near 2.0 (i.e., doubling for every 10 °C rise in T) and Tmax values near 60 °C (i.e., T where RD reached maximal values). Thus, while rates of RD at 28 °C decreased with increasing depth in the canopy, the T-dependence of RD remained constant; these findings have important implications for vegetation-climate models that seek to predict carbon fluxes between tropical lowland rainforests and the atmosphere.
Division of Plant Sciences, Research School of Biology, Building 46, The Australian National University, Canberra, ACT 0200, Australia Faculty of Agriculture, University of Peradeniya, Peradeniya 20400, Sri Lanka.
Lasantha K
LK
Weerasinghe
Hawkesbury Institute for the Environment, University of Western Sydney, Locked bag 1797, Penrith, NSW 2751, Australia.
Danielle
D
Creek
Hawkesbury Institute for the Environment, University of Western Sydney, Locked bag 1797, Penrith, NSW 2751, Australia.
Kristine Y
KY
Crous
Division of Plant Sciences, Research School of Biology, Building 46, The Australian National University, Canberra, ACT 0200, Australia Chengdu Institute of Biology, Chinese Academy of Sciences, No. 9, Section 4, Renmin South Road, Chengdu, Sichuan 610041, China.
Shuang
S
Xiang
Department of Chemistry & Centre for Tropical Environmental and Sustainable Sciences, James Cook University, Cairns 4870, Australia.
Michael J
MJ
Liddell
School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealand.
Matthew H
MH
Turnbull
Division of Plant Sciences, Research School of Biology, Building 46, The Australian National University, Canberra, ACT 0200, Australia owen.atkin@anu.edu.au.
Owen K
OK
Atkin
D019069:Cell Respiration; D008027:Light; D010641:Phenotype; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D011793:Queensland; D065947:Rainforest; D013696:Temperature; D014197:Trees / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects
Q10; functional traits; light; photosynthesis; temperature