Detrimental effects of Cd and temperature on rice and functions of microbial community in paddy soils

Heavy metal (HM) contamination and high environmental temperature (HT) are caused by anthropogenic activities that negatively impact soil microbial communities and agricultural productivity. Although HM contaminations have deleterious effects on microbes and plants; there are hardly any reports on the combined effects of HM and HT. Here, we reported that HT coupled with cadmium (Cd) accumulation in soil and irrigated water could seriously affect crop growth and productivity, alternatively influencing the microbial community and nutrient cycles of paddy soils in rice fields. We analyzed different mechanisms of plants and microflora in the rhizospheric region, such as plant rhizospheric nitrification, endophytes colonization, nutrient uptake, and physiology of temperature-sensitive (IR64) and temperature-resistant Huanghuazhan (HZ) rice cultivars against different Cd levels (2, 5 and 10 mg kg-1) with rice plants grown under 25 °C and 40 °C temperatures. Consequently, an increment in Cd accumulation was observed with rising temperature leading to enhanced expression of OsNTRs. In contrast, a greater decline in the microbial community was detected in IR64 cultivar than HZ. Similarly, ammonium oxidation, root-IAA, shoot-ABA production, and 16S rRNA gene abundance in the rhizosphere and endosphere were significantly influenced by HT and Cd levels, resulting in a significant decrease in the colonization of endophytes and the surface area of roots, leading to a decreased N uptake from the soil. Overall, the outcomes of this study unveiled the novel effects of Cd, temperature, and their combined effect on rice growth and functions of the microbial community. These results provide effective strategies to overcome Cd-phytotoxicity on the health of endophytes and rhizospheric bacteria in Cd-contaminated soil by using temperature-tolerant rice cultivars.