Drought is one of the most devastating climate factors in terms of its spatial extent and intensity. Therefore, a study was conducted to evaluate the water stress tolerance in young saplings of Syzygium cumini (L.) Skeels and Populus deltoides Marchall that are cultivated in the rain fed areas of Pakistan. Plants were subjected to three levels of moisture regimes: well-watered (WW, 90% of field capacity), mild stress (MS, 60% field capacity), and severe stress (SS, 30% of field capacity). Results showed that dry biomass production (leaf, stem, and root), chlorophyll a, b and carotenoid contents decreased significantly while osmolyte accumulation increased in both species, with the highest increase was evidenced in Populus deltoides saplings. A significant decrease was evidenced in CO₂ assimilation rate and stomatal conductance that resulted in a significant increase in intrinsic water use efficiency in both species under MS and SS. In both the species, along with a significant increase in the production of hydrogen peroxide and superoxide radical, the antioxidants enzyme activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase also increased significantly in both species under MS and SS with highest activity evidenced in Syzygium cumini. The results suggest that Syzygium cumini saplings showed better a tolerance mechanism to water stress.

中文翻译：

---

小茴香和三角杨的形态生理和生化变化：水分胁迫下幼树的案例研究

就空间范围和强度而言，干旱是最具破坏性的气候因素之一。因此，进行了一项研究，以评估在巴基斯坦雨养地区种植的Syzygium cumini (L.) Skeels 和Populus deltoides Marchall幼树的水分胁迫耐受性。植物经受三个水平的水分状况：充分浇水（WW，田间持水量的 90%）、轻度胁迫（MS，田间持水量的 60%）和严重胁迫（SS，田间持水量的 30%）。结果表明，两个物种的干生物量产量（叶、茎和根）、叶绿素a、b和类胡萝卜素含量显着下降，而渗透物积累增加，其中增量最大的是杨树树苗。CO ₂同化率和气孔导度显着降低，导致 MS 和 SS 下两个物种的固有水分利用效率显着增加。在这两个物种中，随着过氧化氢和超氧自由基产生的显着增加，超氧化物歧化酶、过氧化物酶、过氧化氢酶和抗坏血酸过氧化物酶的抗氧化酶活性也在 MS 和 SS 下在两个物种中显着增加，最高活性证明在孜然。结果表明，丁香树苗对水分胁迫表现出较好的耐受机制。