Calcium amendment improved the performance of fragrant rice and reduced metal uptake under cadmium toxicity

Cadmium (Cd) toxicity has detrimental effects on plant metabolism and yield formation. This study examined the effects of Cd stress in rice and the possible role of calcium (Ca) in mitigating oxidative damage caused by Cd in two fragrant rice cultivars, i.e., Guixiangzhan and Meixiangzhan 2. The experimental treatments were composed of various Ca and Cd levels as individual, i.e., Ca at 2.5 and 5.0 mg/kg soil (Ca1 and Ca2, respectively), Cd at 50 and 100 mg/kg soil (Cd50 and Cd100, respectively), and combined, i.e., Ca1+Cd50, Ca1+Cd100, Ca2+Cd50, and Ca2+Cd100. Plants without Ca and Cd application were taken as control (CK). Results showed that Cd stress led to a substantial decline in the photosynthetic pigments, i.e., Chl a, Chl b, and carotenoids, while enhanced oxidative damage in terms of increased levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) and electrolyte leakage (EL) in both rice cultivars. Moreover, Cd stress hampered the activities of enzymatic antioxidants, i.e., superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), with lowest antioxidant activities were recorded at Cd100. The overall trend (lowest to highest) for antioxidant activities across treatments was recorded as Cd100 < Ca2+Cd100 < Cd50 < Ca1+Cd100 < CK < Ca1 < Ca1+Cd50 < Ca2+Cd50 < Ca2. Similarly, Ca amendment improved the proline, soluble protein, and soluble sugar contents in both rice cultivars under Cd stress condition. Comparing Ca2 with CK, the yield and related components, i.e., number of panicles, spikelets per panicle, seed setting rate, 1000 grain weight, and grain yield, were found to increase by 13.08, 2.39, 4.03, 5.86, and 27.53% for Guixiangzhan and 16.48, 5.19, 6.87, 15.44, and 51.16% for Meixiangzhan, respectively. Furthermore, Cd contents in roots, stems, leaves, and grains increased with increased Cd concentration applied and reduced with Ca amendment. The Cd contents in grains for all Ca+Cd levels are statistically at par with each other and significantly lower (P < 0.05) than those for individual Cd application. Hence, Ca amendment can be an appropriate approach to ameliorate the toxic effects of Cd in crops grown under Cd-contaminated soils.