Exploring potentials of the physical and biochemical characteristics of Gracilaria gracilis and Gracilaria edulis for enhancing plant growth under abiotic stress

Seaweed may assist agricultural crops to adapt with abiotic stress and are widely used in agriculture, especially as biostimulants that improve plant growth and resistance to abiotic stressors. The study focuses on the biochemical characteristics of these seaweeds and their effect as plant biostimulant to improve germination and crop growth. Seaweeds were collected from Mandapam area of Ramanathapuram district and identified as Gracilaria gracilis and Gracilaria edulis from AJC Bose Indian Botanic Garden, West Bengal and their physico-chemical properties were evaluated. Higher protein levels were obtained in G. edulis (16.72 %), swelling capacity (SWC) in G. gracilis (23.25 mL g-1) is more compared to G. edulis, however, water holding capacity (WHC) of G. edulis (11.31 g g-1) was higher. The findings demonstrate that G. edulis has superior WHC, whereas G. gracilis has higher SWC, which improves soil moisture retention and nutrient availability. Further study shows that the two species' mineral compositions differ significantly, with G. gracilis being higher in potassium (6413.5 ppm) and sodium (1051.5 ppm), which may help with osmotic management in plants. Growth parameters were significantly improved by the treatment (T2–T5). In comparison to control T1, treatment T5 (10 % papermill effluent + G2 sps @ 7.5 %) exhibited the longest roots (51 ± 0.37 cm) and shoots (34 ± 0.35 cm), remarkable seed vigor index (26.88 ± 0.30) and a high germination percentage (96 ± 0.06 %). Overall, the results provide support to the usage of these seaweeds as organic fertilizers in difficult environmental situations to enhance crop growth.