The Effects of Enriched CO2 and K Level on Cucumber Photosynthesis

The study in open top chamber was conducted to explore the changes of cucumber leaf net photosythetic rate,stomatal conductance, transpiration rate and its relationship to each other under different CO2 concentrations (1 000 and 380 mol/mol) and K levels (150,300,600 mg/kg). Results showed that:(1) Early CO2 enrichment(1 to 24 days) significantly increased the cucumber photosynthesis, later (27 days) a down-regulation occurred on all K levels, of which 150 mg/kg and 300 mg/kg K levels showed a slightly larger photosynthetic rate. (2) High K levels (600 mg/kg) could suppress photosynthesis in the seedling stage(2 days)of cucumber plants, this inhibitory effect was eliminated after 27 days treatment of enriched CO2,increasing K fertilizer found no signs that can alleviate photosynthetic adaptation on this study. (3) Early CO2 enrichment significantly reduced stomatal conductance, transpiration rate and promote water use efficiency, the late the two photosynthetic parametres of cucumber under general K level (150 mg/kg) increased. In early CO2 enrichment, photosynthetic rate was significantly positively related to stomatal conductance, whereas there was no significant correlation the late. (4) Enriched CO2 concentration increased the dry weight of cucumber plant, and its biomass increase with higher K levels, while cucumber biomass between different K levels grown under ambient CO2 concentration showed no significant difference.