Drought stress is becoming a structural phenomenon in cropping systems challenged by climate change and soil fertility degradation. A balanced fertilization strategy based on nitrogen, phosphorus, and potassium as well as on silicon supplementation was tested as an efficient practice to improve maize tolerance to short-term drought stress. Three fertilization strategies (control: treatment with zero NPK fertilizer application; NPK: granular NPK fertilizer, and NPK + Si: granular NPK fertilizer enriched with 5% silicon) were evaluated under three irrigation regimes simulating three probable water deficit levels in the Mediterranean climate (I1, well-watered conditions: 80% of soil field capacity; I2, medium drought stress: 60% of soil field capacity; and I3, severe drought stress: 30% of soil field capacity). Drought stress was applied at V10 growth stage of maize and maintained for 15 days, then plants were rewatered according to the optimal irrigation regime. Results showed that medium and severe drought stress down-regulated maize plant growth and yield, especially under nutrient deficient conditions (control). Plants amended with NPK and NPK + Si recorded higher chlorophyll a pigment content (+ 22 to + 64%), stomatal conductance (+ 6 to 24%), and leaf relative water content (+ 7 to 23%) than those of the control, depending on the drought stress level. Silicon supplementation attenuated the down-regulation effects of drought stress on maize photosynthesis and biomass accumulation by improving stomatal conductance and electron transfer efficiency between PSII and PSI. Silicon supply improved the performance index for energy conservation from photons absorbed by PSII to the reduction of intersystem electron acceptors (PIabs) and reduced the dissipation energy flux (DIo/RC), responsible for the protection of PSII from photo-damage under drought stress, which resulted in significant enhancement of maize photosynthesis recovery and grain yield (+ 59 to 69%). Findings from the present study demonstrate that granular NPK-fertilizer fortified with silicon could be an efficient strategy to increase maize photosynthesis performance, plant growth, and productivity under short-term drought stress conditions.

Toxicity due to excess iron can result in oxidative stress, impacting photosynthetic processes, particularly those related to the electron transport chain and CO2 assimilation. The present study investigated how oxidative damage caused by excess iron affects the hydraulic and diffusive traits and the photobiochemistry of two contrasting rice cultivars regarding their iron sensitivity. Two rice cultivars, IRGA 424 (tolerant to excess iron) and IRGA 417 (sensitive to excess iron), in V6 growth stage were submitted to four concentrations of Fe2+ (0.019 control, 2, 4, and 7 mM) in nutrient solution for 8 days. Excess Fe associated with oxidative damage in the roots decreased the leaf water potential and the root xylem sap flow in both cultivars. The tolerant cultivar IRGA 424 exhibited increased photosynthetic efficiency with a longer exposure but did not change carboxylation efficiency and stomatal conductance up to 2 mM of Fe. The sensitive cultivar experienced greater oxidative damage, which may have contributed to decreased quantum yields, specific efficiencies, and energy fluxes of PSII, thereby increasing photoinhibitory processes. Photoprotective mechanisms and antioxidant enzymes were more efficient in the tolerant cultivar IRGA 424 than in the sensitive cultivar with increased Fe concentrations. The sensitivity of rice to excess iron was associated with the inability to prevent oxidative damage in the roots, with constraints in root xylem sap flow, and with limitations in stomatal function and photobiochemical processes. This knowledge could support the development of iron-tolerant rice cultivars, contributing to increased productivity in soils with excess Fe.

Significant efforts have been made to develop environmentally friendly remediation methods to restore petroleum-damaged ecosystems. One such approach is cultivating plant species that exhibit high resistance to contamination. This study aimed to assess the impact of petroleum-derived soil pollutants on the photosynthetic performance of selected plant species used in green infrastructure development. A pot experiment was conducted using both contaminated and uncontaminated soils to grow six plant species under controlled conditions. Biometric parameters and chlorophyll a fluorescence measurements were taken, followed by statistical analyses to compare plant responses under stress and control conditions. This study is the first to simultaneously analyze PF, DF, and MR820 signals in plant species exposed to petroleum contamination stress. The results demonstrated that petroleum exposure reduced the activity of both PSII and PSI, likely due to increased nonradiative energy dissipation in PSII antenna chlorophylls, decreased antenna size, and/or damage to the photosynthetic apparatus. Additionally, petroleum contamination affected the electron transport chain efficiency, limiting electron flow between PSII and PSI. The most resistant species to petroleum-induced stress were Lolium perenne, Poa pratensis, and Trifolium repens.

In China, high copper (Cu) and low organic matter often occur in some citrus orchard soils. However, the underlying mechanisms by which humic acid (HA) stimulates growth and mitigates Cu toxicity of citrus seedlings are unclear. After being treated with 0, 0.1, or 0.5 mM sodium humate and 0.5 or 400 mu M CuCl2 (Cu excess) for 24 weeks, sweet orange [Citrus sinensis (L.) Osbeck cv. Xuegan] seedlings were used to examine the impacts of HA-Cu interactions on seedling growth, nutrient uptake, leaf pigments, and photosynthetic performance that was revealed by chlorophyll a fluorescence transient. Copper excess reduced root, stem, and leaf dry weight (DW) by 42.4%, 65.4%, and 61.6%, respectively at 0 mM HA, and by 17.3%, 25.4%, and 31.4%, respectively at 0.5 mM HA; and that the levels of Cu in leaves, stems, and roots declined with elevating HA supply. Copper excess caused some rotten and dead fibrous roots at 0 mM HA, but not at 0.5 mM HA. Adding HA lowered Cu uptake per root DW (UPR), the levels of Cu in leaves, stems, and roots, and the competition of Cu2+ with Mg2+ and Fe2+, and therefore mitigated root impairment caused by Cu excess. The HA-mediated alleviation of root damage caused by Cu excess increased the uptake per plant and UPR of nitrogen, potassium, magnesium, phosphorus, calcium, sulfur, boron, and manganese, and therefore alleviated Cu excess-induced decline in seedling growth, impairment to leaf photosynthetic electron transport chains, and decrease in leaf pigments. For 0.5 mu M Cu-treated seedlings, adding HA promoted seedling growth by improving root nutrient uptake and leaf photosynthetic performance. Cu excess aggravated the impacts of HA supplementation on seedling growth, leaf photosynthetic performance, and root nutrient uptake.

While morphological and functional traits enable hydrophytes to survive under waterlogging and partial or complete submergence, the data on responses of psammophytes-sand plants-to flooding are very limited. We analyzed the effect of 5- and 10-day soil flooding on the photosynthetic apparatus and the synthesis of alcohol dehydrogenase (ADH), heat shock proteins 70 (HSP70), and ethylene in seedlings of psammophytes Alyssum desertorum and Secale sylvestre using electron microscopy, chlorophyll a fluorescence induction, and biochemical methods. It was found that seedlings growing under soil flooding differed from those growing in stationary conditions with such traits as chloroplast ultrastructure, pigment content, chlorophyll fluorescence induction, and the dynamics of ADH, HSP, and ethylene synthesis. Although flooding caused no apparent damage to the photosynthetic apparatus in all the variants, a significant decrease in total photosynthesis efficiency was observed in both studied plants, as indicated by decreased values of phi R0 and PIABS,total. More noticeable upregulation of ADH in S. sylvestre, as well as increasing HSP70 level and more intensive ethylene emission in A. desertorum, indicate species-specific differences in these traits in response to short-term soil flooding. Meanwhile, the absence of systemic anaerobic metabolic adaptation to prolonged hypoxia causes plant death.