Interactive effects of silicon and potassium on photosynthesis and physio-biochemical traits of rice (Oryza sativa L.) leaf mesophyll under ferrous iron toxicity

Abstract

Iron toxicity originated from excess ferrous ion (Fe2+) availability within plant growth medium remains a potent stress severely limiting rice productivity via alteration of photosynthetic and metabolic processes. Silicon (Si) or potassium (K) individually can enhance plant tolerance to abiotic stresses, including metal toxicity. However, their combined mitigation effects lack proper exploration even though greater alleviation potential could possibly be achieved. The objective of the present study was to evaluate the potential of combined application of Si and K in mitigating Fe2+ toxicity impairments to rice leaf mesophyll tissue. The experiment was laid out in a factorial combination of two Fe2+ levels (0 and 300 mg L−1), two Si levels (0 and 56 mg L−1), and two K levels (0 and 200 mg L−1) following a completely randomized design. Excess Fe2+ impaired leaf mesophyll performance by negatively affecting all tested parameters; however, Si and K significantly reduced those impairments. The integrated application of Si and K resulted in the maximum mitigation effects as high as 23%, 27%, 14%, 40%, 25%, 37%, 24%, 48%, 34%, 28%, 41%, and 15% for total chlorophyll content, maximum quantum yield of photosystem II, membrane stability index, relative cell death, lipid peroxidation, total protein content, free proline content, total polyphenol content, hydrogen peroxide content, total antioxidant activity, net photosynthetic rate, and plant biomass, respectively, compared with the control, with 29% decrease in Fe content and 4.2-fold and 1.7-fold respective increase in Si and K content of rice leaf mesophyll. Silicon or K enhanced photosynthetic performance by boosting antioxidant activity, proline content, and polyphenol content, thereby reducing oxidative damages from Fe2+-generated free radicals like hydrogen peroxide; however, K was comparatively more effective than Si. The combined application of Si and K resulted in significantly better Fe2+ toxicity alleviation response over their sole application for the maximum studied traits. The findings would contribute to the present understanding of Fe2+ toxicity alleviation and help in strategizing crop management practices for sustainable rice production in Fe2+-toxic lowlands.