| This experiment used annual apple rootstock M9T337 seedlings as the test material and five treatments including normal water supply (CK), moderate drought (MD), moderate drought + seaweed extract (MD+SE), severe drought (SD), and severe drought + seaweed extract (SD+SE) to study the changes in biomass, photosynthetic characteristics, antioxidant enzyme activity, osmotic adjustment substance content, and plant nutrient contents of the seedlings impacted by seaweed extracts. The results showed that, under moderate drought stress,the total plant biomass increased by 15.4% and the net photosynthetic rate increased by 12.1% compared with that of MD treatment. The activities of SOD, POD, CAT, and APX increased by 4.5%, 8.4%, 30.6%, and 9.8%,respectively. Osmotic regulation substances such as soluble protein and proline increased by 19.1% and 13.1% compared to that of MD treatment. The nitrogen, phosphorus, and potassium contents of plants increased by 19.2%, 22.7%, and 40.5%, respectively, compared to that of MD treatment. Under severe drought stress, the total biomass after foliar spraying seaweed extracts increased by 13.7% compared to that of SD treatment, the net photosynthetic rate increased by 10.2% compared to that of SD treatment, and the activities of SOD, POD, CAT, and APX compared to SD increased by 16.6%, 18.1%, 30.2%, and 8.9%, respectively. Soluble protein and proline and other osmotic regulation substances increased by 14.1% and 13.1% compared to that of SD treatment, respectively.Plant nitrogen, phosphorus, and potassium contents increased by 12.4%, 21.7%, and 38.4%, respectively, compared to that of SD treatment. Under different degrees of drought conditions, seaweed extracts spray had good relief effect, and the relief effect on moderate drought stress was more significant. |