Water stress and phosphorus nutrition effects on growth, phosphorus uptake, and some physiological traits in sorghum and beans

Water stress and sub-optimal phosphorus levels are reported to induce modifications in plant metabolism and limit plant growth. Growth, P uptake, and some physiological responses associated with water stress and P fertilization in sorghum (Sorghum bicolor (L.) Moench. cv. NB9040, SA7078, and Redlan), common (Phaseolus vulgaris L. cv. Emerson), and tepary bean (P. acutifolius A. Gray. cv. Tepary #21 or Nebr. #1) were studied under greenhouse and growth chamber conditions in soil and nutrient solution with different levels of P and water stress. Dry matter yields and leaf areas decreased in response to water stress, but increased with increasing P supply in all experiments for sorghum and beans. Phosphorus contents, but not necessarily concentrations, in plant tissues of both sorghum and beans increased with increasing P level whether plants were water-stressed or nonstressed. Total root length and root volume were decreased significantly by PEG-induced water stress and low P, and increased with increasing P supply in both sorghum and bean plants. SA7078 had greater total root length and root volume, and lower shoot/root dry matter ratio than Redlan when these genotypes were grown under different P levels and water stress. Tepary #21 had greater total root length, but not root volume or root dry matter yield than Emerson when these beans were grown under PEG-induced water stress and different P levels. Reduced transpiration rates per unit leaf area and leaf water potentials and increased leaf diffusive resistances were observed in both sorghum and bean plants with increased severity of water stress over time regardless of P level. Low P generally increased sensitivity of plants to water stress in both sorghum and beans. Genotypic variability for leaf water potential, transpiration rate per unit leaf area, and leaf diffusive resistance were noted in sorghum and beans in response to different P levels and water stress. High proline concentrations in water-stressed plants were observed for NB9040 and Redlan sorghums, and increased with increasing P supply, and remained high five days after water stress was relieved. On the other hand, high proline concentrations were detected when bean plants were water-stressed and grown at the lowest P level. Proline concentrations in water-stressed bean plants almost returned to nonstressed plants levels five days after water stress was alleviated.