Humic acids affect photosynthetic quantum efficiency in rice under water deficit

Agriculture is responsible for consuming the largest amount of water in the world. Water availability is the environmental factor that most limits the sustainability of agricultural systems. The adoption of sustainable technologies that improve plant water use efficiency has become increasingly important in modern agriculture. Humic acids (HA) acts as a rhizospheric bioeffector, stimulating the biochemical and physiological activities of plants. The objective of this study was to evaluate the potential of humic acids from vermicompost (HAVC), previously characterized by ATR-FTIR and 1 H-NMR, in stimulating the emission kinetics of the transient fluorescence of chlorophyll a, the concentrations of photosynthetic pigments and soluble metabolites, development of the root system and accumulation of fresh and dry biomass in rice (Oryza sativa L.) under normal growth conditions and water deficit. The experimental design was completely randomized, with four treatments (Control; HAVC; PEG-6000; HAVC + PEG-6000). The application of HAVC in plants under water deficit was efficient in maintaining photosynthesis, with an effect as an eustressor. HAVC triggered the increase of plant biomass and root development of plants under water deficit. HAVC acted on osmotic regulation and the influx and remobilization of different forms of nitrogen, enhancing protection against stress. HAVC in the rhizosphere induced plants with higher root biomass, partially due to better photosynthetic performance.