Chlorophyll fluorescence performance of sweet almond [Prunus dulcis (Miller) D. Webb] in response to salinity stress induced by NaCl

One-year old sweet almond (Prunus dulcis) seedlings were submitted to four levels of salt stress induced by NaCl, namely 0.3, 0.5, 0.7, and 1.0 S m(-1). Effects of salt stress on a range of chlorophyll (Ch1) fluorescence parameters (Ch1 FPs) and Ch1 contents were investigated in order to establish an eco-physiological characterization of P. dulcis to salinity. Salt stress promoted an increase in F-0, F-s, and F-0/F-m and a decrease in F-m, F'(m), F-v/F-m, q(p), Delta F/F'(m), F-v/F-0, and UQF((rel)), in almost all Ch1 fluorescence yields (FY) and FPs due to its adverse effect on activity of photosystem 2. No significant changes were observed for quenchings q(N), NPQ, and q(N(rel)). The contents of Ch1 a and b and their ratio were also significantly reduced at increased salt stress. In general, adverse salinity effects became significant when the electric conductivity of the nutrient solution (ECn) exceeded 0.3 S m(-1). The most sensitive salt stress indicators were F-v/F-0 and Ch1 a content, and they are thus best used for early salt detection in P. dulcis. Monitoring of a simple Ch1 FY, such as F-0, also gave a good indication of induced salt stress due to the significant correlations observed between the different Ch1 FYs and FPs. Even essential Ch1 FYs, like F-0, F-m, F'(m), and F-s, and mutually independent Ch1 FPs, like F-v/F-0 and q(P), were strongly correlated with each other.