Leaf CO2 exchange of Erythrina poeppigiana (Leguminosae: Phaseolae) in humid tropical field conditions
An idealized model was developed to describe leaf CO2 exchange in the leguminous tree Erythrina poeppigiana (Walpers) O.F. Cook under well-watered field conditions. Photosynthetic rate in mature leaves (p) was modeled as a rectangular hyperbolic function of photon flux density (q) and ambient CO2 concentration (ca), relative photosynthetic capacity (pi) was modeled as a logistic s-function of leaf age (la), metabolic dark respiration rate (rm) was modeled as an exponential function of leaf temperature (Tl), and photorespiration rate (rp) was modeled as a hyperbolic function of ca. Assimilation rate (ac) was modeled as the difference between the product of p and pi and the sum of rm and rp: ac = p(q,ca)pi(la) - [rm(tl) = rp(ca)]. The model parameters were estimated separately for five sources of E. poeppigiana (Clones 2660, 2662, 2687 and 2693 and half-sib Family 2431) from field data measured with a portable closed-loop gas exchange system at a humid tropical site in Costa Rica. The between-source differences in leaf CO2 exchange characteristics were small, but statisticaly significant. Aboveground biomass production was highest in sources that maintained high relative photosynthetic capacity throughout the leaf life span. Quantum yield varied between 0.046 and 0.067, and light-saturated assimulation rate (q = 2000 micromol m-2 s-1 and tl = 28 degrees C at natural atmospheric ca (350 micromol mol-1) was 16.8-19.9 micromol m-2 s-1. Increasing ca to 1000 micromol mol-1 resulted in an approximate doubling of the light-saturated assimilation rate. Foliole nitrogen concentration, which was 45.3-51.2 mg g-1 in mature leaves, was positively correlated with relative photosynthetic capacity. Foliole nitrogen concentration, quantum yield and maximum assimilation rate of E. poeppigiana are among the highest values observed in tropical woody legumes.
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