Abstract: To clarify the mechanisms of photosynthetic recovery in mangrove from low temperature stress, we examined the changes of chilling injury index (CII), leaf photosynthetic and chlorophyll fluorescence parameters, chlorophyll content, antioxidant enzyme activity, and sucrose metabolis in Kandelia obovata seedlings with three levels of lowtemperature injury. The results showed that leaf net photosynthetic rate (P_n), stomatal conductance (G_s), chlorophyll content (CHL), chlorophyll a/chlorophyll b (Chla/Chlb) ratio, photochemical efficiency of photosystem II (F_v/F_m), actual photochemical efficiency (Φ_PSII), photochemical quenching coefficient (q_P) and APX activity of seedlings gradually decreased with the increasing degree of injury, whereas CII, leaf non-photochemical quenching (NPQ), relative electrical conductivity (REC), and malondialdehyde (MDA) content gradually increased. The activities of sucrose synthase (SS) and sucrose phosphate synthase, and TSS and sucrose contents increased initially and then decreased with the increasing degree of injury. Seedlings under both light low-temperature stress (LLS) and moderate low-temperature stress (MLS) treatments showed no obvious injury symptoms in 15 days after low temperature stress, while seedlings of severe low-temperature stress (SLS) showed leaf scorch and bud withering.  LLS and MLS treatments may alleviate the decline of photosynthetic capacity in leaves by effectively improving defensive system of antioxidants and sucrose metabolism and reducing the damage of photoinhibition of PSII for three days recovery after low temperature stress, while the photosynthetic function of seedlings of SLS could not be recovered from severe damage of low temperature stress in short term. The following indices could be used to evaluate the recovery ability of mangrove plant after low temperature stress, including P_n, G_s, F_v/F_m,Ф_PSII, q_P,NPQ, Chla/Chlb, MDA, APX, POD and REC.

Key words: low temperature stress Kandelia obovata, photosynthesis, chlorophyll fluorescence, sucrose synthesis.