Abstract: In order to elucidate the regulation functions of salicylic acid (SA) o n the photosynthesis of cucumber under low temperature and light intensity, the seedlings of cucumber ‘Jinyou 3’ under low temperature and light intensity wer e foliar-sprayed with different concentration SA, and the leaf gas exchange par ameters, photochemical efficiency, MDA content, and antioxidant enzyme activitie s were measured. The results showed that under low temperature and light intensi ty, the leaf photosynthetic rate (Pn), stomatal conductance (Gs), tr anspiration rate (Tr), actual photochemical efficiency of PSⅡ(ΦP SⅡ), and maximal photochemical efficiency of PSⅡ (Fv/Fm) of the seedlings all decreased but the intercellular CO2 concentration (Ci) inc re ased, suggesting that non-stomatal limitation was the main cause of the decreas e of Pn under low temperature and light intensity stress. Low temperature and light intensity also led to the increase of leaf malondialdehyde (MDA) conte nt and superoxide dismutase (SOD) activity, the decrease of catalase (CAT) activ ity, and the decrease after an initial increase of peroxidase (POD) activity. Ho wever, foliar-spraying 05〖KG-*2〗-〖KG-*7〗25 mmol ·L-1 of SA before the stress increased the leaf Pn, Gs, T r, ΦPSⅡ, Fv/Fm, and activities of SOD, POD and CAT whi le decreased the Ci and MDA content, suggesting that SA could regulate the leaf photosynthetic functions of cucumber seedlings, and enhance the see dlings resistance against low temperature and light intensity. The optimum conce ntration of SA for the foliar-spraying was 1 mmol·L-1.

Key words: ammonia-oxidizing archaea, long-term fertilization, ammonia-oxidizing bacteria, diversity