Impact of zinc and molybdenum, in bulk and nano forms, on red bean: photosynthesis, root traits, nitrate reduction, antioxidant enzymes, and yield under drought stress

Abstract

The limitation of water and unfavorable soil conditions for plant’s nutrient absorption present a hurdle to the growth and yield of red beans under drought stress conditions. Micronutrients, particularly zinc and molybdenum, show promise in mitigating drought effects. Various irrigation levels (100% and 70% of field capacity) and nutrient application methods were tested in the field (two locations) and the greenhouse in 2022. Parameters such as photosynthesis, gas exchange, root characteristics, nitrate reductase, antioxidant enzymes, and yield were evaluated. The combination of nano zinc priming (NZnP 150 mg L−1) and foliar spraying of nano zinc (FSNZn 0.04 mg L−1) at 100% field capacity resulted in the highest photosynthesis, gas exchange, and yield. Water stress increased the activity of antioxidant enzymes. In greenhouse test, NZnP (150 mg L−1) + FSNZn (0.04 mg L−1) at 100% field capacity promoted maximum root length and nitrate reductase activity. Overall, NZnP + FSNZn at 100% field capacity proved most effective for morphological and biochemical root characteristics and yield. Drought stress reduced red bean yield, but NZnP + FSNZn mitigated some adverse effects. Nano forms of zinc and molybdenum were more effective in mitigating drought stress. Location significantly influenced plant development, with lower temperatures delaying reproductive phase transition, leading to better vegetative and reproductive traits compared to the location with higher temperature.