ISHS Acta Horticulturae 416: IV International Symposium on Computer Modelling in Fruit Research and Orchard Management
CO2 ASSIMILATION OF CITRUS LEAVES: FROM MESOPHYLL CONDUCTANCE TO GROSS PRIMARY PRODUCTIVITY OF TREES IN DIFFERENT CLIMATES |
| Authors: | J.P. Syvertsen, J. Lloyd |
| Keywords: | stomatal conductance, intercellular air space conductance, mesophyll cell wall conductance, environmental responses |
| Abstract:
Citrus trees have thick hypostomatous leaves that have a waxy cuticle, relatively low rates of net CO2 assimilation (A), and low internal mesophyll conductances (gi) for CO2 transfer from stomata to chloroplasts. Using "on line" 13C isotope discrimination and anatomical measurements of the mesophyll, we modelled gi with regression analyses and determined that component cell wall conductances were more limiting than intercellular air space conductances. Using net gas exchange data from leaves on well fertilized and irrigated grapefruit trees in Florida, we modelled leaf temperature, stomatal conductance (gs), and A responses to photosynthetically active radiation, vapor pressure deficit (D), and CO2 concentration with mathematical equations describing physiological processes. Hourly air temperatures and humidities were simulated from monthly max/min temperatures from selected citrus growing regions, and along with PAR from latitude and day of the year, these variables were used to drive the model. Daily simulations revealed regional affects of D on gs and A. Simulations of A for clear and cloudy days in each region were used to sum monthly and annual gross primary productivity (GPP) per tree canopy surface area. Warmer climatic conditions were reflected in the higher GPP of tropical than of temperate citrus growing regions but higher GPP usually does not translate into greater net productivity or fruit yield in the tropics. | |
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