Plants use a variety of physiological, biochemical, and molecular mechanisms to mitigate salt stress impacts. Many techniques, including the application of nanoparticles (NPs), are being used to increase plant stress tolerance. To assess the growth and productivity of Vigna unguiculata L. (cowpea) plants exposed to salt stress, cowpea has been cultivated using different saline water levels and subjected to green synthesized zinc NPs (ZnNPs) and iron NPs (FeNPs) applied via foliar spraying. The cowpea plants that grew under the lowest saline water level showed the best leaf traits, leaf water content per area (LWCA), pods, and seed yields, but when salinity levels increased, the plants’ growth and productivity slightly declined. ZnNP and FeNP treatments slow down the degradation of photosynthetic pigments and greatly mitigate the negative effects of salt stress. In both stressed and unstressed plants, ZnNP treatments produced the highest osmoprotectant concentrations (proline, protein, and total carbohydrates). As a result of salt stress, cowpea seeds showed a marked decrease in dry matter and protein content, but ZnNP and FeNP treatments increased it. Conclusively, the results obtained indicated that ZnNPs and FeNPs foliar application to cowpea plants stimulated leaf pigment and polyphenol production, which in turn increased seed dry matter, seed yield, protein content, and the plants’ ability to withstand saline stress.

Several bioactive compounds, including phenolic and flavonoid substances, have been identified in the aqueous leaf extract of Schinus terebinthifolius (ALE). These compounds are active ingredients in green nanoparticle biosynthesis. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), zeta potential analysis, and FTIR spectral analysis were used to characterize copper oxide nanoparticles (CuNPs) and silver nanoparticles (AgNPs). According to TEM results, AgNPs exhibited somewhat larger diameters (12 ± 4 nm), were spherical with significant aggregation, and displayed a fairly uniform distribution, while CuNPs were primarily quasi-spherical with a narrow size range of about 4–5 nm. CuNPs showed a much more negative zeta potential value of −25.8 mV, indicating good to high colloidal stability, whereas AgNPs had a zeta potential of −15.5 mV, suggesting moderate stability. The main compounds included chlorogenic acid (10,375.28 µg/g), gallic acid (7015.59 µg/g extract), ellagic acid (1571.29 µg/g extract), and rutin (1485 µg/g extract). The antifungal activity of CuNPs and AgNPs was tested at concentrations of 6, 12, 25, 50, and 75 μg/mL on Quercus rubra wood against Fusarium circinatum and Pythium tardicrescens. The greatest inhibition of F. circinatum growth was observed with CuNPs and AgNPs at 75 µg/mL, showing fungal inhibition percentages (FIPs) of 61.48 and 60.74%, respectively. CuNPs and AgNPs at 75 µg/mL exhibited moderate activity against P. tardicrescens, with FIPs of 21.48% and 15.92%, respectively. The MICs for AgNPs and CuNPs were 1.5 and 85 µg/mL with F. circinatum and P. tardicrescens, respectively. Overall, CuNPs and AgNPs demonstrated potential antifungal activity against F. circinatum but moderate activity against P. tardicrescens compared to the control. This ALE from S. terebinthifolius is rich in flavonoids and phenolic compounds, including gallic acid, chlorogenic acid, rutin, ellagic acid, and p-coumaric acid, as identified by HPLC analysis. These biomolecules act as both capping agents, which stabilize the nanoparticles, and reducing agents. Using S. terebinthifolius ALE’s rich phytochemical profile as a reducing and stabilizing agent provides an environmentally friendly method for the green synthesis of CuNPs and AgNPs.