Iron homeostasis is critical for plant growth; however, the mechanisms underlying responses to iron deficiency and toxicity remain poorly understood. We investigated the adaptive strategies of Ulmus pumila, focusing on leaf physiological, transcriptomic, and metabolomic responses to iron stresses. Both iron deficiency and toxicity impaired chlorophyll biosynthesis, PS II efficiency, and chloroplast ultrastructure, resulting in reduced photosynthetic capacity and etiolation/wilting phenotypes. Iron deficiency reduced antioxidant enzyme activity and ROS levels, while iron toxicity activated the antioxidant enzyme system in response to the ROS burst. Integrated transcriptomic and metabolomic analyses provided insights into the underlying mechanism of these divergent responses: iron deficiency promoted primary metabolic adjustments, particularly the upregulation of genes (e.g., MDH, ACO, and IDH) and metabolites (e.g., malic acid, citric acid, and fumaric acid) associated with the TCA cycle to meet energy demands. Conversely, iron toxicity triggered a metabolic shift from primary to secondary metabolism, upregulating the genes (e.g., CHS, CHI, and F3H) and metabolites (e.g., laricitrin, trifolin, and rutin) involved in flavonoids biosynthesis to mitigate oxidative stress. Overall, U. pumila employs distinct adaptive mechanisms to balance survival and growth under iron stress: prioritizing energy metabolism and iron uptake to meet energy demands and improve iron uptake efficiency under deficiency, and enhancing the secondary metabolism to mitigate oxidative damage under toxicity. These findings enhance understanding of plant nutrient homeostasis and stress adaptation, providing insights into mitigating the impacts of soil degradation on agriculture and forestry.

Nanotechnology is a vital domain for improving growth, productivity, and abiotic stress resistance of horticultural crops. In this study, semi-spherical shaped biogenic AgNPs with size ranging between 21 nm and 48 nm were synthesized using rambutan fruit extract and characterized using SEM and TEM, and beneficial effects of AgNPs on salt-treated marigold (Calendula officinalis L. cv. Orange King) plants were evaluated. Plants were grown in pots filled with sandy loam soil until reaching up to six leaves and then irrigated with water containing 100 mM NaCl. After a week of salt stress, foliar spray treatments with AgNPs were performed three times every 20 days. Results showed that shoot and root dry weights and total chlorophyll content of salt-stressed plants decreased more than 35 % compared to non-stressed plants, but oxidative biomarkers including electrolyte leakage (EL) and concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) substantially increased. Foliar spraying of AgNPs decreased EL and proline contents, increased leaf chlorophyll and protein contents, and alleviated the growth inhibition of salt-stressed plants. The amelioration of salt stress was accompanied by changes in the activities of antioxidant enzymes (SOD, APX, CAT, POD, PPO, and PAL) and reduction of MDA and H2O2 concentrations. Floral secondary metabolites including carotenoids, total flavonoids, total phenols, as well DPPH improved in response to application of AgNPs. Our data suggest that AgNPs were able to alleviate negative effects of salt stress on marigold plants through its ability to produce enzymatic and nonenzymatic antioxidants. Thus, foliar application of AgNPs could be a viable solution to improve its growth and edible flowers production when grown in salt affected soils.