Tomato root and shoot responses to salt stress under different levels of phosphorus nutrition

Crops differ in their ability to grow under saline conditions and their responses are quite variable and not fully understood. This study was conducted to evaluate the root and shoot responses of tomato to salt stress conditions under different levels of phosphorus (P) nutrition. Tomato seedlings (cv Riogrande) were grown in 500 mt glass jars containing Hoagland's solutions which were salinized by four levels of NaCl salt (0, 50, 100, and 150 mM NaCl) and/or enriched with three P levels (0.5, 1, and 2 mM P) making nine combination treatments. Plants were harvested at the vegetative growth stage and data were collected for root and shoot characteristics. The results indicate that increasing salinity stress was accompanied by significant reductions in shoot weight, plant height, number of leaves per plant, and a significant increase in leaf osmotic potential and peroxidase activity regardless of the level of P supplied. Both root length and root surface area per plant were decreased significantly under higher salinity conditions at all levels of phosphorus. On the other hand, increasing the phosphorus levels enhanced root growth through increasing both root length and root surface area. This phenomenon was observed at all levels of salinity. It can be concluded that root morphology parameters and peroxidase activity are additional sensitive parameters which are affected by salt stress and, therefore, can be employed as a criteria for monitoring plant response mechanisms to salt stress conditions.