Combined effects of water stress and salinity on growth, physiological, and biochemical traits in two walnut genotypes.

Due to its great economic value, walnut (Juglans regia L.) has received increasing attention during recent years. However, water stress and salinity limit walnut growth, production, and quality. We employed two walnut genotypes, precocious walnut, and late-bearing walnut, to investigate their growth, photosynthetic capacity, non-structural carbohydrate contents, Cl- allocation, reactive oxygen species (ROS) accumulation, and osmotic regulation under water stress, salinity, and their combination. We found that late-bearing walnut showed higher total biomass and net photosynthetic rate, higher activities of antioxidant enzymes, higher osmoregulation, and lower ROS accumulation than precocious walnut under stressful conditions. In addition, late-bearing walnut restricted salt transport and allocated more Cl- into roots, whereas precocious walnut allocated more Cl- into leaves when exposed to salinity stress. These data collectively demonstrated that late-bearing walnut possesses better stress tolerance under water stress, salinity, and especially under their combination. Such knowledge of genotype-specific responses and tolerances to water stress and salinity is important for walnut plantation management under increasing drought and aggravated soil salinization occurring with climate change.