Photosynthetic Behavior of Wheat in Reclaimed Fly Ash Amended Soil-Probed by MINI-PAM (Photosynthetic Yield Analyzer)

Fly ash (FA) management is a global environmental concern. Although FA has been widely studied as a soil amendment to improve crop growth and productivity, its utilization remains limited due to the presence of toxic heavy metals (HMs). Reclamation of FA using tolerant plant species is a sustainable strategy to mitigate adverse environmental effects and improve its suitability as a soil mulcher. However, studies evaluating the use of reclaimed fly ash (RFA) as a soil amendment remain limited. In the present study, wheat was cultivated under six conditions: T1 (normal soil, NS; control), T2 (fresh fly ash, FFA), T3 (RFA), and mixtures of RFA and NS at ratios of 1:1 (T4), 1:2 (T5), and 1:3 (T6). Prior to sowing, 12 targeted HMs were quantified using inductively coupled plasma-mass spectrometry (ICP-MS). To assess the photosynthetic behavior of wheat, chlorophyll fluorescence parameters, including Fv/fm (variable to maximum chlorophyll fluorescence), Y(II) (effective quantum yield of photosystem II), Y(NPQ) (quantum yield of regulated non-photochemical energy dissipation), and Y(NO) (quantum yield of non-regulated energy dissipation), were measured with a pulse-amplitude-modulated chlorophyll fluorometer (MINI-PAM). Results showed that Fv/fm and Y(II) were highest in T1, followed by T6, whereas Y(NPQ) and Y(NO) were lowest in T6, followed by T1. Spearman's correlation analysis revealed that Cr (chromium), Mn (manganese), Ni (nickel), Cu (copper), and Zn (zinc) were positively correlated with Fv/fm and Y(II) (p < 0.01), while As (arsenic), Se (selenium), and Mo (molybdenum) showed significant negative correlations (p < 0.001); opposite trends were observed for Y(NPQ) and Y(NO). Although heavy metal concentrations remained below established critical thresholds, even sub-threshold variations influenced physiological performance. Overall, these findings highlight the potential of reclaimed fly ash as a soil amendment for sustainable wheat cultivation.