Growth, photosynthesis and chlorophyll fluorescence of chinese cabbage in response to high temperature

Abstract

In order to gain insight into the physiological responses of plants to high temperature stress, the effects of temperature on Chinese cabbage (Brassica campestris subsp. napus var. pekinensis cv. Detong) were investigated through analyses of photosynthesis and chlorophyll fluorescence under 3 different temperatures in the temperature gradient tunnel. Growth (leaf length and number of leaves) during the rosette stage was greater at ambient + 4°C and ambient + 7°C temperatures than at ambient temperature. Photosynthetic CO 2 fixation rates of Chinese cabbage grown under the different temperatures did not differ significantly. However, dark respiration rate was significantly higher in the cabbage that developed under ambient temperature relative to elevated temperature. Furthermore, elevated growth temperature increased transpiration rate and stomatal conductance resulting in an overall decrease of water use efficiency. The chlorophyll a fluorescence transient was also considerably affected by high temperature stress; the fluorescence yield F J, F I, and F P decreased considerably at ambient + 4°C and ambient + 7°C temperatures, with induction of F K and decrease of F V /F O. The values of RC/CS, ABS/CS, TRo/CS, and ETo/CS decreased considerably, while DIo/CS increased with increased growth temperature. The symptoms of soft-rot disease were observed in the inner part of the cabbage heads after 7, 9, and/or 10 weeks of cultivation at ambient + 4°C and ambient + 7°C temperatures, but not in the cabbage heads growing at ambient temperature. These results show that Chinese cabbage could be negatively affected by high temperature under a future climate change scenario. Therefore, to maintain the high productivity and quality of Chinese cabbage, it may be necessary to develop new high temperature tolerant cultivars or to markedly improve cropping systems. In addition, it would be possible to use the non-invasive fluorescence parameters F O, F V /F M, and F V /F O, as well as F K, M O, S M, RC/CS, ETo/CS, PI abs, and SFI abs (which were selected in this study), to quantitatively determine the physiological status of plants in response to high temperature stresses.