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• Salinity reduces carbon uptake in avocado contributing with mortality and yield losses. • Salinity change the isotopic composition in avocado leaves. • The performance of the avocado rootstocks was similar under salinity conditions. With increasing demands on both potable and agricultural water supplies, drought, and extreme temperatures worldwide, agricultural production is challenged with reduced water availability and lower water quality. Salinity, which is associated with low water quality is a critical issue for California avocado growers and, coupled with avocado root rot, threatens the long-term sustainability of the industry since avocados (Persea americana Mill.) are known to be extremely salt sensitive. Salt tolerance of the 'Hass' variety, the most commonly grown scion in California, is influenced by rootstock. We investigated 'Hass' scions grafted onto three different avocado rootstocks under control (irrigation using water with EC = 0.65 dS/m) and salinity (irrigation using water with EC = 1.5 dS/m) conditions. Results indicated that, compared to control conditions, the irrigation of avocado trees using water with EC = 1.5 dS/m increased canopy damage by 44%, reduced survival by half of the trees tested, and caused yield losses of more than 63%. Avocado leaves visibly damaged by the salinity treatment (named as partially burned or PB leaves) experienced photoinhibition, and reduction of photosynthetic rate and water-use efficiency, suggesting that the poor performance in carbon assimilation contributed to reductions in yield and increases in mortality. The salinity treatment did not cause water stress and the poor performance of treated trees was attributable to chloride accumulation previously reported. Leaf carbon isotopic composition was affected in trees under salinity treatment by increasing the values of δ13C however, this affect was nor correlated with water-use efficiency. Overall, 'R0.05', 'PP40' and 'Dusa' performed similarly and, considering the conditions of the experiment and the intrinsic susceptibility of avocado trees to salinity, were superior to all other rootstocks tested. Future screenings for salinity tolerant rootstocks are required to improve yield when poor quality soil or water is used. Overall, our results showed a coordination between the physiological performance, health and productivity of the 'Hass' scion and how these parameters were negatively affected by salinity. [ABSTRACT FROM AUTHOR]