## 4 Conclusions  
SPs extracted from mangrove leaves showed an inhibitory effect on the seed germination of wheat seedlings, as well as the total chlorophyll and carotenoids contents in each of the foliar or soil applications. This effect may be owed to the autotoxicity of SPs in mangrove plants which was previously reported [58]. The inhibitory effect of SPs on the total chlorophyll and carotenoids contents observed in the soil application was slightly more pronounced than that obtained in the foliar application. The percent reduction in respective total chlorophyll and carotenoids contents amounted to 43.06% and 43.33%, respectively, in the soil application, as well as 49.76% and 70.00% in the foliar application. Previous work reported the impact of allelopathic interactions on plant growth and showed that it affected the growth of the root more than other vegetation parts of the plant since it influenced the absorption of phenolic compounds [59; 60]. On the other hand, Cu NPs showed inhibitory effects that are slightly less pronounced, or rather comparable, to those of the free SPs extract in both seed germination and foliar applications. Therefore, the nanoformulation of Cu NPs can be as effective as the free SPs in its herbicidal effect. In addition to this, the nanoformulation could offer more advantages than that of free SPs. The nanosized metal holds the capping layer of SPs tightly due to the high surface tension which helps in the controlled release of SPs [61]. Consequently, the nutrients in SPs would potentially be delivered to its specific target sites in the plant [62]. Furthermore, the nanoformulation could increase the bioavailability of soil nutrients to be absorbed by the plant root. The photosynthesis of _Spinacia olercea_ plants was enhanced when the soil was treated with CuO NPs at 200 mg/kg concentration after 60 days of application [63]. Along with the benefits offered by the nanoformulation as an herbicide in seed germination and foliar application, it significantly promoted the total chlorophyll and carotenoids in the soil application. This implies that it can be also utilized as a stimulant in soil applications. The difference in the behavior of Cu NPs in seed, foliar and soil applications might be attributed to several reasons. Copper nanoparticles were probably more absorbed by leaves than roots since they got adsorbed by soil particles, yet they were not readily transported by the root system [64]. On the contrary, and in seed germination, it was reported that copper nanoparticles can cross the cell membrane and accumulate in the cell until they reach their toxic level [65]. Figure 6: Dry weight and total phenolic content of wheat seedlings treated by 0.06 mg/L of SPs and Cu NPs after 28 days from foliar and soil applications. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/10/18/6302/s1](http://www.mdpi.com/2076-3417/10/18/6302/s1)]([http://www.mdpi.com/2076-3417/10/18/6302/s1](http://www.mdpi.com/2076-3417/10/18/6302/s1)), Table S1 Constituents of sugars calculated as area percentage from the total chromatogram of HPLC. Figure S1 HPLC chromatogram of SPs. **Author Contributions:** Conceptualization, M.M.H.E.-S.; M.S.A. ; A.S.M. and H.L.E. ; methodology, M.M.H.E.-S.; M.S.A. and A.S.M. ; software, A.S.M. ; validation, H.L.E., and H.A.G. ; formal analysis, M.M.H.E.-S.; investigation, H.L.E. and H.A.G. ; data curation, H.A.G. ; writing--original draft preparation, H.L.E. ; H.A.G. ; writing--review and editing, M.M.H.E.-S.; A.S.M. ; and M.S.A. ; supervision, M.S.A. ; M.M.H.E.-S. and A.S.M. All authors read and approved the final manuscript. **Funding:** This study was supported by the American University in Cairo (proposal UGH 1709695).