Effects Of Light Intensity, Nitrogen Level And Storage Temperature On Quality And Physiological Metabolism Of Taraxacum Mongolicum Hand.-Mazz.

In order to provide theoretical basis for building high quality cultivation system and storage technical system of Taraxacum mongolicum Hand.-Mazz., photosynthetic characteristics, quality, yield physiological and biochemical index were studied, under different light intensity, nitrogen level and storage temperature. The results showed that:1. The diurnal change of net photosynthetic rate and photosynthetic response to light and CO₂ of Taraxacum mongolicum Hand.-Mazz. were studied, which were used CIRAS-2 portable photosynthesis system. The diurnal change of net photosynthetic rate was two-peak curve, and maximum net photosynthetic rate appeared at 11 o'clock; Gs and Ci were the most important factors of the net photosynthetic rate diurnal change. The apparent quantum yield of photosynthesis was 0.0267, light compensation points (LCP) and saturation light (SL) were 91.78μmol·m^-2·s^-1 and 1438μmol·m^-2·s^-1. Carboxylation efficiency of was 0.0626, the CO₂ compensation points (CCP) and saturation CO₂ (SC) were 38.23μmol·mol^-1 and 1190μmol·mol^-1.2. With the decrease of light intensity, photosynthetic midday-depress was weakened, contents of crude-fibre and chlorogenic acid were reduced, while contents of chlorophyll and nitrate were increased. Under the 75% natural light intensity (910μmol·m^-2·s^-1), the Pn, contents of soluble protein, soluble sugar and vitamin C were the highest among the four treatments; the chlorogenic acid content was higher, contents of nitrate and crude-fibre were lower than the others. When the light intensity for cultivating Taraxacum mongolicum Hand.-Mazz. was 910μmol·m^-2·s^-1, its photosynthetic efficiency and quality could be improved.3. There were significant differences in net photosynthetic rate, contents of chlorophyll, nitrate, chlorogenic acid, soluble protein and yield among different nitrogen level treatments. With the increase of nitrogen levels, net photosynthetic rate, contents of chlorophyll, nitrate, chlorogenic acid and soluble protein increased, leaf area and yield per plant increased until nitrogen level reached 0.250 g·kg^-1 medium and then decreased, but contents of crude-fibre had contrary trend. Under nitrogen level 0.250g·kg^-1 medium, as well as produced 1kg edibility fresh weight needed 4.4g nitrogen, leaf area(506.010cm2), yield per plant(17.000g)and activity of NR (10.100U·g^-1FW) were the highest among the four treatments, contents crude-fibre (15.36%g·g^-1DW) were lowest, nitrate contents(0.310 mg·g^-1FW)were lower, while the contents of chlorogenic acid (2.300 mg·g^-1DW), vitamin C (315.96mg·kg^-1FW) and soluble protein (61.285mg·g^-1FW)were higher.4. Under different storage temperatures (25℃, 10℃, 2℃and -18℃), the postharvest physiology and quality of Taraxacum mongolicum Hand.-Mazz. were studied. The results indicated that with the increasing of storage days, leaves of Taraxacum mongolicum Hand.-Mazz. etiolated, contents of crude-fiber increased, while vitamin C, chlorogenic acid and nitrate contents decreased. Stored under 2℃, the contents of chlorophyll, vitamin C, chlorogenic acid were higher, nitrate and crude-fiber contents were lower. The lower of membrane permeability and MDA contents, the higher activity of SOD significantly delayed senescence process and prolonged storage life of Taraxacum mongolicum Hand.-Mazz. .