The Growth And Physiology Characteristics Of Bhesa Sinica Under The Different Natural Light Conditions

The Bhesa sinica is the northernmost distributed genus of the Bhesa which is also the only endemic species of the genus distributed in our country. Due to the disturbance of human activities, the habitats destruction, and the difficulties in regeneration etc,the Bhesa sinica is now considered critically endangered. Therefore, it is necessary to carry out relevant research study of the Bhesa sinica, in order to provide much more reliable scientific data to its effective protection and recovery.With the purpose of studying the growth and physiological characteristics of the Bhesa sinica under the natural conditions, in this paper, the Bhesa sinica saplings and the naturally grown Bhesa sinica mature trees were selected as experimental objects, and they were cultured in three different habitats under natural conditions, namely, the forest edge, forest gap, forest understory. The practical observation for a 1-year period showed that:(1) The plant height of the Bhesa sinica saplings grown fastest in April to June, and in August to October its root collar diameter increase fastest. The growth index differed significantly, under the different lighting conditions. The plant height and the leaf area annual growth of the forest edge Bhesa sinica saplings were significantly greater than those of the forest gap and the forest understory. The root collar diameter increment of the forest edge Bhesa sinica saplings was basically identical with the forest gap but greatly higher than that of the forest understory. Apart from the plant height growth, the root collar diameter increment and the gowth in leaf area of the forest understory Bhesa sinica saplings were extremely small which were far below than those of the edge and the gap.(2) From the perspective of change in a full year (February to December), the curve of the relative conductivity and the MDA content of Bhesa sinica saplings showed a trend that increased firstly, reached the climax, then decreased. In June to October, the MDA content of the forest edge was markedly greater than those of the forest gap and the forest understory. The soluble sugar content and the soluble protein content increased firstly then decreased, while the free proline content increased after decreased. Besides, the soluble sugar content of the forest edges and the forest gaps were significantly higher than those of the forest understory, but the free proline content was observably lower than that of the forest understory throughout the year. Apart from the activity change of POD and CAT of the forest understory Bhesa sinica saplings showed a trend of "W" type, the activity of POD, CAT, SOD of the rest increased at first and then decreased, and the activity of POD, CAT, SOD of the forest edges and forest gaps in general were higher than those of the forest understory.The chlorophyll a, chlorophyll b and carotenoid content increased firstly then decreased and then increased again, and their lowest level throughout the year hit in October. Moreover, the chlorophyll a, chlorophyll b and carotenoid content of the forest understory were dramatically higher than those of the forest edge and the forest gap.The annual changing rule of all the physiological indicators of the Bhesa sinica mature trees were basically the same as the saplings, but their value were slightly different:the relative conductivity, the soluble sugar content, the free proline content, the soluble protein content, the activiy of CAT and SOD indicators etc were almost the same compared to the forest edge. The activity of POD is similar to forests, while the photosynthetic pigment content value was in between the forest edge, the forest gap and the forest understory.(3) The net photosynthetic rate of the forest gap as well as the net photosynthetic rate and the transpiration rate of the forest understory showed a trend of "Unimodal " type, while the net photosynthesis, the stomatal conductance and the transpiration rate of the rest showed a trend of "bimodal" type. In addition, the net photosynthetic rate, the stomatal conductance and the transpiration rate of the forest edge and the forest gap were significantly greater than those of the forest understory in April to October. The annual trend of intercellular CO2 concentration showed a "V" shape which reached its minimum value in August. The annual trend of water use efficiency of Bhesa sinica saplings was "U" type, while the water use efficiency of the forest gap and the forest understory showed a relatively higher amount in December, the data showed its variation was not obvious. The annual changes of the Bhesa sinica mature trees’net photosynthetic rate, the stomatal conductance and the transpiration rate all showed a "single peak" type, while the annual change of the intercellular CO2 concentration, water use efficiency were consistent with saplings, and these five indicators value were similar to the forest edge.From the conclusion above it can be seen that the Bhesa sinica mature trees were largely driven by high light stress, but the impact was weak. As to the Bhesa sinica saplings not only the high-light stress exerts an impact on the growth, but also the low-light stress, especially the low light stress. Therefore, an environment which is full of natural lighting is much more conducive to the growth of Bhesa sinica saplings.