Carbon isotope discrimination and photosynthetic gas exchange in coffee hedgerows during canopy development
1994
Gutierrez, M.V. (Hawaii Univ., Honolulu (USA). Dept. of Horticulture) | Meinzer, F.C. (Hawaiian Sugar Planters' Assoc., Aiea (USA). Crop Science Dept.)
For measurements encompassing a range of leaf area index (LAI) from 0.7 to 7.5, assimilation was highest in sun leaves, but stomatal conductance was highest in shaded leaves. There was a high correlation between assimilation and stomatal conductance in sun, but not in shaded leaves. Carbon isotope discrimination (delta) was about 0.2 percent lower in sun than in shaded leaves, and varied by 0.23 percent among leaves at different positions along two-year-old branches. These differences in delta were the result of changes in carbon isotope composition that occurred in mature, fully expanded leaves as they became shaded during subsequent canopy growth. Results from a mass balance model suggested that about 50 percent of the C originally fixed during leaf development in the sun may have subsequently been turned over in the shade. Delta of sun leaves from the upper canopy decreased by about 2 percent with increasing LAI, indicating that intrinsic water-use efficiency (WUE) of this canopy layer increased during canopy development. Instantaneous WUE seemed to decrease with increasing LAI. PNUE of upper canopy sun leaves decreased with increasing LAI, suggesting a physiological compromise between WUE and PNUE mediated by stomatal conductance, which also decreased with increasing LAI. A strong negative correlation between leaf delta and N content was consistent with a trade-off between intrinsic water- and N-use efficiency.
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