[Protective effects of La (NO3)3 on ryegrass seedlings photosynthetic apparatus under NaHCO3 stress].

This paper studied the effects of foliar spraying different concentration La(NO3)3 on the photosynthesis, chlorophyll fluorescence parameters, Mehler reaction, and xanthophyll cycle of ryegrass seedlings under the stress of 150 mmol NaHCO3 x L(-1). Foliar spraying low concentration (0.05 mmol x L(-1)) La (NO3)3 could significantly decrease the decrement of net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and stomatal limited value (Ls) and the increment of intercellular CO2 concentration (Ci) under NaHCO3 stress, efficiently alleviate the inhibitory effects of NaHCO3 stress on PS II photochemical quenching (q(p)), actual photochemical efficiency (phi(PS II)), photosynthetic carbon assimilation- dependent electron transport rate (ETRp), and Mehler reaction- dependent electron transport rate (ETRm), enhance the activities of superoxide dismutase, peroxidase, and ascorbate peroxidase, the non-photochemical energy dissipation (NPQ), the xanthophyll cycle pool (V+A+Z), and the de-epoxidation extent of xanthophyll cycle (A+Z)/(V+A+Z), and thereby, alleviate the damage of photosynthetic apparatus caused by NaHCO3 stress. However, treating with high concentration (0.5 mmol x L(-1)) La(NO3)3 had no obvious alleviation effects. It was suggested that foliar spraying an appropriate concentration La (NO3)3 could not only alleviate the decrease of ryegrass seedling' s photosynthetic rate induced by nonstomata factors and the inhibition of photochemical efficiency, but also accelerate the Mehler reaction under NaHCO3 stress. With the accelerated Mehler reaction, excessive excitation energy could directly be consumed, and the xanthophyll cycle-dependent thermal dissipation could be promoted to efficiently protect the photosynthetic apparatus against photo-damage under NaHCO3 stress. Also, the active oxygen produced by the accelerated Mehler reaction could be scavenged by the enhanced anti-oxidative enzyme activities.