Effect of Elevated CO2 Combined with Two Nitrogen Levels on Photosynthesis, Growth and Leaf Structure in CAM Orchid Phalaenopsis sp.

In C-3 plants, elevated CO2 will increase plant growth and physiological performance through its effect on photosynthesis, but nitrogen (N) usability is a key factor to limit the growth of plants and augment the response to the long-term elevated CO2. To detect whether higher N availability holds back the photosynthetic down-regulation in CAM plant, the effects of photosynthetic physiology, leaf structure and growth of Phalaenopsis sp. in the greenhouses under the combined conditions of two CO2 concentrations (400 and 800 mu mol.mol(-1)) and two N levels (6 and 12 mmol.L-1) was studied. The results showed that elevated CO2 increased net CO2 uptake rate of facilitated the accumulation of starch and soluble sugar in Phalaenopsis leaves, but no marked differences were discovered between two N levels. Meanwhile, long-term elevated CO(2 )reduced the contents of N and soluble proteins, but N application had beneficial effect on the contents of soluble proteins and N in Phalaenopsis leaves under high CO2 concentration conditions. The elevated CO2 combined with N levels markedly increased the activities of photosynthetic enzyme. And elevated CO2 significantly improved the thickness of Phalaenopsis leaves, LE (low N level and elevated CO2 concentration) and HE (high N level and elevated CO2 concentration) increased by 6 and 8% compared with LA (low N level and atmospheric CO2 concentration) and HA (high N level and atmospheric CO2 concentration), respectively; the number of starch grains each chloroplast profile was augmented similar to 60% by elevated CO2, so the chloroplast profile area was added by 19% in LE and 11% in HE, compared with LA and HA. The elevated CO2 significantly accelerated the biomass accumulation in Phalaenopsis, and the high N level further promoted this increase. Thus, increasing supply of N and CO2 simultaneously was not very important in commercial production of CAM orchid Phalaenopsis during short-term elevated CO2 exposure, but it is still necessary to properly increase the supply of N during short-term elevated CO2 exposure. (C) 2019 Friends Science Publishers