Seasonal Dynamics Study On Photosynthetic Physiological Characteristics Of Japanese Yew(Taxus Cuspidata)Seedlings

Four years Japanes yew seedlings were chosen as experimental materials. Photosynthetic and fluorescence characteristics as well as several physiological and biochemical indexes of two groups of Japanes yew seedlings which are under the condition of annual seasonal variation were studied respectively. One group was growing in nature, the other group was growing indoor before the experiment. The results are as follows:The annual variation trends of net photosynthetic rate, transpiration rate, intercellular CO2concentration, stomatal conductance, water use efficiency, apparent quantum efficiency and dark respiration rate in these two groups of seedlings were similar, with a maximum value in summer and a slowly decline in autumn, then they began to decrease rapidly, reaching at the lowest point in winter, afterwards gradually rose again in spring. Both of the compensation point and the light saturation point in the two groups of seedlings were low. According to the photosynthesis response curves of the two groups of Japanes yew seedlings, the sequence of photosynthetic capacity was:summer> autumn> spring> winter.The variation trends of Fm, Fv/Fo, Fv/Fm, qP and ETR were consistent, with a maximum value in summer and a minimum value in winter. In contrast, the annual variation trends of F and qN were opposite to former five indicators, with a minimum value in summer and a maximum value in winter.The chlorophyll content of two groups of seedlings was highest in summer, lowest in winter for the perspective of change of seasons throughout the year. The chlorophyll content of the growing in nature seedlings were higher than that of the other group. It existed extremely significant difference between two groups. The peak values of the cell membrane permeability occured in summer and winter, respectively. Nevertheless, the peak value in summer was lower than in winter. The change range of the cell membrane permeability of and the semilethal temperature of the growing in nature seedlings were lower than the other group. It also existed significant difference between two groups. The change tendency of the content of soluble sugar, soluble protein and free proline kept consistent. The peak values occurred in summer and winter, respectively. Furthermore, the peak value of winter was higher than in summer. Moreover, The content of osmotic adjustment substances of the growing in nature seedlings was higher than the other group. From summer to winter, POD and SOD enzyme activity of two groups increased gradually. The damage degree of cell membrane was slight. In addition, the accumulation of MDA content was more slowly. The two kinds of protective enzyme activity decreased obviously when it entered into the coldest month. Meanwhile, the damage degree of cell membrane was the most serious and the accumulation of MDA content was up to the maximum. The SOD and POD activity of the growing in nature seedlings were higher than the other group. However, the MDA content of the other group was higher than the growing in nature seedlings.According to the results of principal component analysis, the contribution rates of the median lethal temperature, relative electrical conductivity and soluble sugar were high, which illustrated that these three principal component factors played a key role. Furthermore, Multitude indexes demonstrated that the seedling group in nature had stronger tolerance to low temperature than the other group. Therefore, in the artificial cultivation of Japanes yew seedlings, the indoor seedings should not be moved outside to overwinter for the first time until cold-proof measures were taken.