Zinc fertilization and water stress affects plant water relations, stomatal conductance and osmotic adjustment in chickpea (Cicer arientinum L.)

Chickpea (Cicer arietinum) is an important dryland pulse crop in many parts of the world. Productivity is often limited by periods of water deficit and in a number of regions zinc deficiency occurs, but the interaction between zinc nutrition and water stress has not been studied extensively. This interaction was examined in two glasshouse experiments. Chickpea was grown under deficient (no applied Zn) or adequate (2.5 mug Zn/g soil) levels of zinc in pots for either 53 days (Experiment 1) or 40 days (Experiment 2) before being exposed to a single period of water stress that lasted for 12 days (Experiment 1) or 23 days (Experiment 2). In one experiment four genotypes (Tyson, ICC-4958, T-1587 and NIFA-88) differing in their sensitivity to zinc deficiency were compared during a single drying cycle, and in the second experiment a single cultivar (Tyson) was compared under well-watered and water stress conditions. Water stress was induced by allowing the soil to dry gradually and the responses in shoot biomass, water use, plant water relations and carbon isotope discrimination (Delta, parts per thousand) were measured. Shoot biomass, water use and water use efficiency were reduced by zinc deficiency. Stomatal conductance was lower in zinc-deficient plants as well. Zinc deficiency reduced Delta by about 1parts per thousand and there were significant differences in Delta between genotypes which were independent of the level of zinc nutrition. At an adequate level of zinc there was a significant negative correlation between Delta and shoot biomass and between Delta and water use efficiency among the four chickpea genotypes. but these correlations were not significant under zinc deficiency. Osmotic potential was lower and turgor higher in the leaves of zinc-deficient plants. but the ability to adjust osmotically was reduced by zinc deficiency as stress developed. In conclusion, zinc-deficiency reduced the efficiency with which the water was used for biomass production and compromised the plant's capacity to respond to water stress by osmotic adjustment.