Relationships of photosynthetic photon flux density, air temperature and humidity with tomato leaf diffusive conductance and temperature

the objective was to study the leaf temperature (lt) and leaf diffusive vapor conductance (gs) responses to temperature, humidity and incident flux density of photosynthetically active photons (ppfd) of tomato plants grown without water restriction in a plastic greenhouse in santa maria, rs, brazil. the plants were grown in substrate and irrigated daily. the gs was measured using a steady-state null-balance porometer on the abaxial face of the leaves during the daytime. both leaf surfaces were measured in one day. the ppfd and lt were measured using the porometer. leaf temperature was determined using an infrared thermometer, and air temperature and humidity were measured using a thermohygrograph. the leaves on the upper layer of the plants had higher gs than the lower layer. the relationship between the gs and ppfd was different for the two layers in the plants. a consistent relationship between the gs and atmospheric water demand was observed only in the lower layer. the lt tended to be lower than the air temperature. the mean value for the gs was 2.88 times higher on the abaxial than adaxial leaf surface.