Plant, Soil and Environment - In Press

Effects of foliar application of potassium dihydrogen phosphate on the physiological responses of rice seedlings under high temperature stressOriginal Paper

Hui Xu, Lei Wang, Dongyue Sun, Wei Liu, Shuhua Jiang, Lijun Zhou, Lu Tang, Xin Gu, Muhammad Ahmad Hassan

To explore the alleviating effect and physiological mechanism of foliar spraying potassium dihydrogen phosphate (KDP) on rice seedlings under high temperature (HT) stress, the high temperature-sensitive early indica hybrid rice YLY17 was used as the test material. Four treatments were set up: normal temperature (NT), HT, and foliar spraying with different concentrations of KDP (0.1%, 0.2%, 0.3%, 0.4%) (KDP and KDP+HT). Rice seedlings were subjected to simulated HT stress (32~38℃ during the day and 26~32℃ at night) for 10 days. Growth indicators, photosynthetic parameters, antioxidant characteristics, osmotic adjustment substances and related metabolic enzyme activities of seedlings were determined, and the alleviating effect of KDP was comprehensively evaluated by principal component analysis. The results showed that HT stress significantly inhibited the growth of rice seedlings, reduced plant height, fresh weight and dry weight, decreased chlorophyll content and SPAD value, lowered net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), while increased intercellular carbon dioxide concentration (Ci). At the same time, it led to the accumulation of superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and induced the increase of antioxidant enzymes and osmotic adjustment-related enzyme activities. Foliar spraying of KDP could effectively alleviate the above damage caused by HT stress, among which 0.3% KDP had the best effect. Compared with HT treatment, 0.3% KDP treatment significantly increased plant height, fresh weight and dry weight by 7.6%, 10.6% and 10.2% respectively, improved chlorophyll content and photosynthetic parameters, enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), reduced the accumulation of reactive oxygen species (ROS) and MDA, and promoted the accumulation of osmotic adjustment substances such as soluble protein (SP), proline (Pro), soluble sugar (SS) and sucrose (SUC), as well as increased the activities of nitrate reductase (NR), glutamine synthetase (GS), sucrose synthase (SUS) and sucrose phosphate synthase (SPS). Principal component analysis showed that the order of comprehensive physiological activity index was KDP > NT > KDP+HT > HT, which confirmed that KDP could enhance the heat resistance of rice seedlings by synergistically regulating the three core physiological processes of photosynthetic system, antioxidant defense and osmotic adjustment. This study provides a theoretical basis and technical reference for using KDP to alleviate HT stress in rice seedlings and ensure the safe growth of rice.