Effects of salt stress on photosynthetic characteristics of beach plum and other Prunus species

The photosynthetic and gas exchange characteristics of seven Prunus species, including four genotypes of beach plum (Prunus maritima Marshall, BO from North Carolina, Bl, B5 from Massachusetts, B3 from Michigan), sun plum (P salicina Lindl, SP), wild peach (P persica (L.) Batsch, WP) and purple-leaf plum (P cerasifera Ehrh, PL), were evaluated under salt stress to assess their relative salt-tolerance. The oneyear-old seedlings were treated with 100 mM NaCl solution for 30 d, while various physiological indexes of leaf were evaluated. The results showed that the net photosynthesis rate (PN), stomatal conductance (gs) and transpiration rate (Tr) of seven Prunus plants all decreased under salt stress, but differences existed among these plants regarding the extent by which each were impacted. For example, the rate of PN reduction was ranked as B1 (27.84%)< B5 (40.03%)< WP (52.99%)< B3 (55.81%)< SP (74.76%)< B0 (84.01%)< PL (86.93%). Under salt stress, the intercellular CO2 concentration (Ci of the four beach plum genotypes decreased (B1 < B5 < B3 < B0) while it increased in the others (WP > PL > SP). In addition, the water utilization efficiency (WUE) of four beach plum genotypes increased under salt stress while the others decreased. The increase rate was ordered as B0 > B3 > B5 > B1, and the rate of declination was ordered as PL < SP < WP. It was found that the photosynthetic capacity under salt stress of four Prunus species could be sorted as beach plum > wild peach > sun plum > purple-leaf plum, and the four beach plum genotypes could be sorted as B1 > B5 > B3 > BO.This indicates that beach plum had better salt-tolerance than other 3 Prunus species, and B1 and B5 had better salt-tolerance among 4 beach plum genotypes.