Preliminary study on the effects of environmental conditions and salinity on tomato plants (Lycopersicon esculentum L.) growth status in semi-arid regions

Balancing plant growth between vegetative and reproductive status is crucial for producing high quality greenhouse tomatoes while maintaining high productivity. The ability to change plant growth characteristics often associated with vegetative or reproductive growth status was demonstrated. Two greenhouse canopy environments were selected for inducing reproductive growth [high vapor pressure deficit (VPD) (2 kPa) and 27°C / 18°C day-night air temperature], and vegetative growth [low VPD (0.8 kPa) and 24°C / 22°C day-night air temperature]. Plant responses from the treatment environments were contrasted with those from a standard commercial greenhouse environment (24°C / 19°C). All environmental treatments were associated with two electrical conductivities (EC) of the nutrient solution: 2.5 dS m-1 (EC 2.5) and 8 dS m-1 (EC 8). Plants were grown under one of two treatment environmental conditions, until significant differences in plant growth characteristics were observed. Out of the five plant growth characteristics monitored, stem diameters were the most responsive to canopy environment and EC treatments. The major factor in changing plant growth responses was EC, for the range of VPD and day-night air temperature differences achieved in the present study, while canopy environment affected the magnitude of the change. Mean stem diameters (SD) were significantly higher under EC 2.5, than for plants growing under EC 8. IN₅ cm and SD 15 cm are the plant growth responses most affected by EC treatments and canopy environment. Single leaf gas exchange measurements had significantly reduced transpiration rate at EC 8 under all canopy environments, while net photosynthetic rate was not affected. This suggests that decreased plant growth responses observed under high salinity treatments resulted from reduced water and nutrient uptake due to suppressed transpiration rate.