The excess of phosphorus in soil reduces physiological performances over time but enhances prompt recovery of salt-stressed Arundo donax plants

Arundo donax L. is an invasive grass species with high tolerance to a wide range of environmental stresses. Theresponse of potted A. donax plants to soil stress characterized by prolonged exposure (43 days) to salinity (+Na),to high concentration of phosphorus (+P), and to the combination of high Na and P (+NaP) followed by 14 daysof recovery under optimal nutrient solution, was investigated along the entire time-course of the experiment.After an exposure of 43 days, salinity induced a progressive decline in stomatal conductance that hampered A.donax growth through diffusional limitations to photosynthesis and, when combined with high P, reduced theelectron transport rate. Isoprene emission from A. donax leaves was stimulated as Naconcentration raised inleaves. Prolonged growth in P-enriched substrate did not significantly affect A. donax performance, but decreasedisoprene emission from leaves. Prolonged exposure of A. donax to + NaP increased the leaf level ofH2O2, stimulated the production of carbohydrates, phenylpropanoids, zeaxanthin and increased the de-epoxidationstate of the xanthophylls. This might have resulted in a higher stress tolerance that allowed a fast and fullrecovery following stress relief. Moreover, the high amount of ABA-glucose ester accumulated in leaves of A.donax exposed to + NaP might have favored stomata re-opening further sustaining the observed prompt recoveryof photosynthesis. Therefore, prolonged exposure to high P exacerbated the negative effects of salt stressin A. donax plants photosynthetic performances, but enhanced activation of physiological mechanisms that alloweda prompt and full recovery after stress.+