Abstract
Increasing temperature poses a serious threat to rice productivity. This study investigated the impact of various biochar treatments and phosphorous (P) fertilization on osmolyte accumulation, ROS development, and antioxidant activity in two rice cultivars (IR-64 and Huanghuazhan) under high-temperature stress. All plants of both cultivars were grown in a controlled environment under ambient temperatures (AT), high day temperatures (HDT) or high night temperatures (HNT). The different fertilization treatments were biochar alone, P alone and biochar + P with control. In the leaves and xylem sap of both rice cultivars, particularly in the susceptible cv. IR-64, high-temperature stress increased the production of MDA and H
2
O
2
. HDT and HNT decreased total soluble sugars, protein, and proline levels in both rice cultivars. HNT was observed as more harmful compared to HDT during most of the studied characteristics. The response of antioxidant enzyme activities, viz, SOD, POD, CAT, APX, ASC, GSH, GR, and GSSC activities, to the temperature treatments varied between the two cultivars. Antioxidant activities decreased in the leaves and xylem sap of IR-64 but increased in those of Huanghuazhan upon exposure to high-temperature stress. Huanghuazhan exhibited better heat tolerance compared to IR-64, which was linked to its increased antioxidant enzyme activation and metabolite synthesis. As compared to the control, all soil fertilization treatments considerably reduced the adverse impacts of high temperature on the rice cultivars. The combination of biochar and P resulted in better performance compared to the other treatments in terms of all studied attributes.