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Description
Cadmium (Cd) is one of the most toxic elements in soil, affecting plant morphological, physiological, and biochemical processes. Many strategies have been developed to improve plant resilience against heavy metal stresses. Mineral plant nutrition was tested as an effective approach to mitigate Cd stress in several crop species. In this regard, the present study aims to elucidate how different phosphorus (P) fertilization regimes can improve some biophysiological processes in tomato plants exposed to Cd stress. In a hydroponic experiment, the impact of two P fertilizer forms (orthophosphate and polyphosphate) on the photosynthetic activity, plant growth, and nutrient uptake and acquisition was assessed under three levels of Cd stress (0, 12, and 25 µM of CdCl2). The results confirmed the negative effects of Cd stress on the chlorophyll content index and the efficiency and performance of the photosynthesis machinery, as assessed by the chlorophyll fluorescence technique. The application of highly polymerized polyphosphate fertilizer significantly improved the chlorophyll stability index under Cd stress, as compared to the ortho-P form. The analysis of the OJIP transient curve revealed that the amplitude of the Cd effect on the different steps of electron transfer between PSII and PSI was significantly reduced under the poly-P fertilization regime compared to ortho-P, especially under medium Cd stress (Cd12). The evaluation of the RE0/RC parameter showed that the electron flux reducing end electron acceptors at the PSI acceptor side per reaction center was significantly improved in the poly-P treatment. Similarly, the performance index for energy conservation from photons absorbed by PSII until the reduction of intersystem electron acceptors (PIAbs) was significantly ameliorated under the poly-P regime. This enhancement of photosynthesis activity under poly-P treatment resulted in higher biomass accumulation and nutrient uptake and reduced Cd accumulation.
