Stomatal behaviour and photosynthetic rate of unstressed grapevines in semi-arid conditions

This paper explores the possibility to use a model for assimilation rate, A(n), to calculate stomatal conductance, g(s). The relation between stomatal conductance, g(s), and net photosynthetic rate, A(n), is studied for grapevine (Vitis Vinifera L. cv Airen). Data were collected in a dry Mediterranean vineyard in Central Spain, under a wide range of temperature and humidity conditions, but with sufficient water supply. The data confirm the existence of a strong correlation between A(n) and g(s). However, the relation is strongly influenced by leaf-to-air specific humidity deficit, D-s. This influence can be expressed by means of a linear relation between D-s and the ratio f, which is the ratio of internal to external CO2 concentration, C-i/C-s, corrected for CO2 concentration. The data were used to tune a coupled A(n)-g(s) model using as much standard coefficients as possible. Using the linear relation between D-s and f, the model also takes stomatal humidity responses into account. A model test reveals that the current approach is able to simulate the photosynthetic rate and stomatal conductance of grapevines reasonably well.