Photosynthetic traits of canopy leaves of dinizia excelsa (Fabaceae)

Abstract

The response of leaf traits to irradiance and [CO2] in canopy leaves of several tall trees remains to be determined under natural conditions. Thus, the objective of this work was to determine gas-exchange parameters in sun and shade leaves of Dinizia excelsa Ducke in 35–45 m tall trees of Central Amazonia. We assessed light saturated photosynthesis (Amax), stomatal conductance (gs), mesophyll conductance (gm), transpiration rates (E), water use efficiency (WUE), intrinsic water use efficiency (WUEi), maximum electron transport rate (Jmax), the maximum carboxylation rate of Rubisco (Vcmax), intercellular CO2 concentration (Ci) specific leaf area (SLA) and fresh leaf thickness. We also estimated the CO2 concentration at the chloroplast level (Cc) and determined the light and CO2 saturated photosynthesis (Apot). Amax was obtained at light saturation (1200 μmol m–2 s–1), whereas Apot, Vcmax, Jmax and gm were obtained after constructing A/Ci response curves. There was a significant difference between sun and shade leaves in Ci and Cc, but for other parameters no differences were observed. Amax was positively correlated with gs, gm and E, and there was also a significant correlation between gs and gm (p ≤ 0.05), as well as between Jmax and Vcmax. Thicker leaves had higher values of Amax, gs, Ci, Cc and E. Apot was limited by the electron transport rate and by low gm. The canopy of the tree caused a decrease in irradiance (30-40%), but this reduction was not enough to reduce important photosynthetic parameters. Thus, all resources allocated to leaf production led to maximum use of the solar energy received by the leaves, which allowed this species to grow at fairly rapid rates.