Maize is among the most significant crops in the world regarding production and yield, but it is highly sensitive to drought, which reduces the growth, photosynthetic efficiency, grain quality, and yield production of a plant. Quantum yield efficiency of photosystem II is a critical photosynthetic component that is susceptible to drought stress. This study intended to investigate the effects of drought stress on growth and morpho-physiological parameters using three maize hybrids ('P-3011w', 'P-3092' and 'iku20') with contrasting soil moisture contents (100%, 40%) at the pre-flowering stage. The stress treatment (40%) was initiated at stage V7, for a period of 15 days; the experimental units were established in a completely randomized design with split-plot arrangement along with three repetitions in 42 L pots using a substrate of peat moss, black soil and poultry manure (1:2:1). The morphological, growth-related and physiological parameters were assessed, including chlorophyll fluorescence (Fv/Fm), which was measured using a LiCor-6400-40 fluorometer. The results showed that all morphological, growth-related and physiological variables decreased under drought stress during the reproductive stage, with the exception of leaf temperature and intercellular CO2 concentration, which increased by 12% and 54%, respectively. Drought stress significantly reduced the photosynthetic chlorophyll fluorescence (43%), due to damage to photosystem II. The lowest percentage of damage to photosystem II (34%) was observed in the iku20 genotype. In contrast, P-3011w and P-3092 had the highest levels of significantly similar damage (49% and 46%, respectively). The correlation analysis showed a highly positive interaction of chlorophyll fluorescence (Fv/Fm) with net photosynthetic rate and stomatal conductance under drought conditions, and multiple regression analysis revealed that the maximum effect on net photosynthetic rate under drought was due to the damage it caused to photosystem II. Thus, iku20 might have a tendency to be able to withstand drought stress in the dry northeast region of Mexico. Overall, we concluded that the photosystem II was negatively impacted by drought stress thus causing a reduction in all physiological, morphological and growth-related variables.

The warming of the planet in recent decades has caused rapid, widespread permafrost degradation on the Qinghai-Tibet Plateau. These changes may significantly affect soil moisture content and nutrient supply, thereby affecting ecosystem structure and function. This study aimed to describe the dynamic changes in thaw depth, assess the relationship between thaw depth and soil moisture content, and analyze the changes in species composition and water-use efficiency in response to permafrost degradation. We surveyed species composition, thaw depth, ground temperature, soil moisture, nutrient content, and foliar stable carbon isotope compositions to gain insights into the response of alpine grassland ecosystems to permafrost degradation on the Qinghai-Tibet Plateau. Moisture content of the surface layer decreased with increasing thaw depth. The correlation between thaw depth and surface soil moisture content was strongest in June and decreased in July and August. The strongest correlation occurred at a depth of 20 cm to 30 cm. The dominant species shifted from Cyperaceae in alpine meadow to mesoxerophytes in alpine steppe before finally shifting to xerophytes in alpine desert steppe. Thaw depth correlation was significantly negative with organic C content (r = -0.49, P < 0.05) and with total N content (r = -0.62, P < 0.01). The leaf delta C-13 of Carex moorcroftii increased with increasing thaw depth and followed a linear relationship (R (2) = 0.85, P = 0.008). Permafrost degradation decreases surface soil moisture and soil nutrient supply capacity. Increasing permafrost degradation decreases the number of plant families and species, with hygrophytes and mesophytes gradually replaced by mesoxerophytes and xerophytes. The water-use efficiency of plants improved in response to increasing water stress as surface layers dried during permafrost degradation. Permafrost on the Qinghai-Tibetan Plateau is expected to further degrade as global warming worsens. Therefore, more attention should be dedicated to the response of alpine ecosystems during permafrost degradation.