Growth and Photosynthetic Responses of Muskmelon (Cucumis melo L.) Seedlings to Phosphorus Availability under Hydroponic Conditions

Abstract Phosphorus (P) is an essential macronutrient involved in energy metabolism, regulation of physiological processes, and biomass production in plants. P deficiency is a major constraint to plant growth, and its direct effects are often obscured in soil-based studies due to phosphorus fixation and microbial interactions. The Present study evaluated the varying inorganic phosphate (Pi) concentrations (0.001, 0.025, and 0.25 mM Pi) on morphology, dry matter allocation, gas exchange, PS II efficiency, and photosynthetic pigment composition on 21-day-old muskmelon (Cucumis melo L.) seedlings grown under hydroponic conditions. Adequate Pi (0.25 mM Pi) supply significantly enhanced the shoot growth, total dry weight, photosynthetic rate, stomatal conductance, and transpiration. These responses were closely associated with higher PS II efficiency, indicated by increased Fv/Fm and Fv/Fo ratios and photosynthetic pigments chlorophyll a, chlorophyll b, and carotenoid. Reduced Pi (0.001 mM Pi) limited the growth, gas exchange, PS II efficiency, and photosynthetic pigments, and while promoting root growth and increasing root-to-shoot ratio. The coordinated modulation of growth, physiological, and photochemical responses of muskmelon seedlings under controlled Pi supply demonstrates that phosphorus availability directly regulates photosynthetic functionality and biomass allocation.