Physiological and Biochemical Responses of Plantain Trees (Platanus orientalis L.) Derived from Different Ages to Drought Stress and Ascophyllum nodosum L. Extract

Young plane trees (Platanus orientalis L.) in urban settings contrary to the old plane trees suffer from leaf chlorosis and early leaf loss in the summer due to drought stress and heat waves as the consequences of climate change. The present study investigated the effects of Ascophyllum nodosum extract (ANE) and tree age class on mitigating drought stress in plane trees. Experimental variables included an irrigation regime with 100% field capacity (FC) (D100), 75% FC (D75); and 50% FC (D50), ANE application with 0% (control or A0), 1.5% (A1), and 3.0% (A2) (v/v); and tree age class i.e cuttings propagated from two types of trees: An old tree (OT) or a young tree (YT). This experiment was carried out using a factorial design with three replications. Results demonstrated that chlorophyll content (Chl), net assimilation rate (Pn), relative water content (RWC), leaf Fe, and Fv/Fm index declined significantly as drought stress severity rose, whereas the ANE treatment, specifically A2, increased Chl content, Pn, RWC, and leaf Fe. In addition, OT age class trees had higher photosynthetic pigments, Pn, Fe content, root volume, APX, and CAT activity than the YT age class. ANE application especially at 3% concentration with increasing antioxidant enzymes activity decreased the negative effect of stress and had a positive influence on Chl and Pn. Our findings indicate that the OT class of propagation source and ANE application was useful for inducing stress tolerance in the plane tree.