Mitigative Effects of Superabsorbent Polymers on the Growth of Pakchoi (Brassica rapa subsp. Chinensis) Under Drought Stress

This study systematically investigated the regulatory effects of different types of superabsorbent polymers (SAPs) on the growth and physiological characteristics of pakchoi (Brassica rapa subsp. chinensis) under drought stress. A pot-controlled experiment was conducted with two stress levels (severe drought and mild drought) and four SAP application ratios (0%, 0.25%, 0.5%, 0.75%). The acrylamide-based SAPs included a self-developed attapulgite clay hydrogel (ACH) and two commercially available mainstream SAPs. The results indicated that: (1) All SAP treatments mitigated the inhibitory effects of drought stress on pakchoi growth to varying degrees, with the 0.5% ACH application showing the most significant effect. Under severe drought, this treatment significantly increased leaf area, shoot fresh weight, and root fresh weight by 184.6%, 127.8%, and 24.6%, respectively, compared to the drought-stressed control without SAP. (2) At the physiological response level, ACH significantly optimized the osmotic adjustment system of pakchoi, manifesting as a significant 53.2% decrease in proline content and a significant 60.1% increase in soluble sugar content. Concurrently, it effectively maintained cell membrane stability, reducing malondialdehyde (MDA) content by a significant 51.6%, and effectively regulated the antioxidant defense system, modulating the activities of key antioxidant enzymes (SOD, CAT, and POD) to prevent oxidative damage. This study reveals that SAPs can effectively alleviate drought stress in pakchoi. Even under severe drought stress, leaf fresh weight reached approximately 67.99% of the normal level. An application rate of 0.5% ACH is identified as an efficient and recommended dose, offering a promising technological option for water-saving and sustainable vegetable production in arid and semi-arid regions.