Biostimulant-Induced Modulation of Photosynthetic Efficiency in Alfalfa (Medicago sativa L.)

Enhancing photosynthetic efficiency via biostimulant application could offer a sustainable pathway to improve alfalfa forage yield, quality traits and resilience against unfavourable environmental conditions. This current study was conducted at the University of Debrecen to evaluate the impact of two biostimulants on gas exchange parameters and chlorophyll fluorescence in alfalfa under field conditions. The experiment was arranged in a randomized complete block design with three treatment levels, namely, Tricho Immun (T1) (21.6 g/3 L), a biostimulant containing Si, MTU^®, and pidolic acid (T2) (2 ml/3 L) and a control (T3) (no biostimulant). Parameters measured include net photosynthetic rate (A), transpiration rate (E), intercellular CO₂ concentration (Ci), ambient CO₂ concentration (Ca), water use efficiency (WUE) and quantum yield of PSII (ΦPSII). Data gathered were subjected to analysis of variance using Genstat statistical software edition 18, where significant means were separated at a 5% probability level using the least significant difference, and DMRT was used to rank the performance of the individual treatment on measured traits. The results show that biostimulant application significantly improved net photosynthetic rate, transpiration rate, intercellular CO₂ concentration, water use efficiency, and quantum yield of PSII, indicating improved photochemical efficiency. However, no significant changes were observed in ambient CO₂ concentration. Our findings indicated that T2 significantly increased ΦPSII by 43.9%, net photosynthetic rate by 37.8%, and transpiration rate by 97.6%, while T1 also increased ΦPSII, net photosynthetic rate, and transpiration rate by 11.7%, 9.8%, and 39.5%, respectively, compared to the control (T3). These results suggest that biostimulants can enhance photosynthetic performance and resource-use efficiency in alfalfa under field conditions, offering a promising approach for sustainable forage production.