The Physioecological Characteristics Of The Endangered Species Sinocalycanthus Chinensis

Sinocalycanthus chinensis,the only representative in the Sinocalycanthus in the family Calycanthaceae,was a perennial deciduous shrubs primarily distributed in the narrow range of Linan City and Tiantai County in Zhejiang Province.The resources is rare nowand was listed as the Classâ…¡protected plant in China.In order to explore the endangered mechanisms of this species,the photosynthetic characteristics and the dynamics of calory value of S.chinensis in natural conditions and the flavonoids in different populations of S.chinensis were analyzed.The effects of different light intensity on the morphological and physiological characteristics of the seedlings of S.chinensis were also analyzed in greenhouse conditions.The results were showed as the followings.1.The photosynthetic parameters of S.chinensis in both overstory and understory,including the diurnal change of net photosynthetic rate(P_n),intercellular CO₂ concentration(C_i),dark respiration rate(R_d)and stomatal resistance(r_s),were measured by using a LCA4 Portable Photosynthesis System in July 2006,October 2006 and Apirl 2007,respectively.The photosynthetic parameters of the accompanying plants,such as Boehmeria platanifolia,Rhus chinensis and Weigela japonica var. sinica,were also measured for comparison.The results showed that the diurnal change of photosynthesis of S.chinensis in the overstory took on "double-peak" curve with remarkable midday depression.The midday depression was mainly due to non-stomatal limitations.On the contrary,the diurnal change of photosynthesis of S.chinensis in the understory took on "one-peak" curve with low P_n.The maximai P_n was only half of that of S.chinensis in the overstory.The correlation analysis showed that the limiting factor for this low P_n might be light intensity(p=0.001).Compared with its accompanying plants,S.chinensis was in a disadvantaged status in the community with low photosynthetic capacity,water use efficiency,and the ratio of photosynthetic rate to respiration rate. However,differently With July,In Apirl and October,the diurnal change of P_n of Sinocalycanthus chinensis and its companions took on "one-peak".The average P_n of S.chinensis in three month was lower than its accompanions.2.The ash contents and the free ash caloric values in the leaves of S.chinensis in overstory, forest edge and understory were measured in July 2006,October 2006 and April 2007,respectively. In addition,35 other species in this community were also be analyzed.The ability of fixation and accumulation to the solar in the photosynthesis was analyzed and the the status of the free ash caloric values in this community were discussed.The rank order of ash contents under different light conditions in these three months were consistent,all of them took on:overstory＞edge＞understory. The content in July were higher than those in April without no significant difference,while the content in October were very significant difference that those in April and July(p≤0.001).The change of the free ash caloric values in the leaves of S.chinensis in understory and overstory took on "V" in April,July and October,while the change trend in the leaves of forest edge decreased gradually.The average ash-free caloric values in the leaves decreased in the rank order:Tree layer＞shrub layer＞herb layer＞liana layer.The averaged value of S.chinensis in these three month was lower than those of liana layer.3.The flavonoids in the leaves of S.chinensis from different populations and those in the different organs from the same population were extracted and separated by the means of polyamide TLC-chromatography.Every component was quantitatively analyzed by dual wavelength flying scanning using rutin as the standard sample.The content of flavonoids in Jiwoping population was the highest,while that in Zhongping population took the second place and that in Longtangshang population was the lowest.There was significant difference among pair-wise populations,except for that between Shuangshibian population and Baishuiwu population.In the same population,the content of flavonoids in different organs was different.The content of flavonoids in the leaves was significantly higher than those in other organs.There was no significant difference among stems,one year twigs and two years twigs.Based on the analysis of TLC chromatography,there were senven components found in the flavonoids extracted from the leaves except that there were only 5 components found in the flavonoids extracted from the leaves in Damingshan population.There were 6 components found in the flavonoids extracted from the roots,stems,one year twigs and two years twigs.The component with R_fequal to 0.66 was absent in leaves.4.The greenhouse experiment was developed using two years old seedlings of S.chinensis. Three light treatments were set up using shading method:CK was not shaded,37%RI was shaded with one layer and 10%RI was shaded with three layers.The gas exchange parameters,chlorophyll fluorescence parameters,the pegiment content,morphological characteristics,the membrane permeability,the content of malondialdehyde(MDA),the activities of protective enzymes,the flavonoids content in the leaves of S.chinensis seedlings.In July,the diurnal change of photosynthesis of S.chinensis in three treatment all took on "double-peak" curve with remarkable midday depression.The rank order of P_maxwas 37%RI＞CK＞10%RI.In different light conditons,the light saturation point(LSP)and light compensation point (LCP)were increase with the light intensity,indicating well plastic to the light intensity.The diurnal change of chlorophyll fluorescence parameters indicated that S.chinensis seedlings in three treatments suffered photo-inhibition.The value of F_v/F_m in the morning at CK treatment was lower significantly than the other two treatments(about 0.8),suggesting that the seedlings of this treatment sufferred a long-term photo-inhibition.As the light intensity increases,the chlorophyll content of the seedlings decreased and Chla/b,Car,Car/Chl increased.The decrease of the chlorophyll content and the increase of Chla/b caused by the high light could reduce the light energy capture and reduce photosynthetic apparatus from the risk of oxidation damage.It might be a light-protection mechanism in the adaptation of plants to high light stress.The height,biomass,leaf average area,root length,root surface area,root volume and root average diameter of S.chinensis seedlings in 37%RI treatment had the best advantage.More biomass was allocated to roots for reserves with high root/shoot ratio.The membrane permeability and the content of malondialdehyde(MDA)in leaves were increased with the light intensity.Along the whole experiment time,SOD activity in the leaves showed high-low-high with the increase of light intensity.It suggested that the seedlings in 10%RI and CK were in stress.POD activity in the leaves of S.chinensis seedlings at 37%RI treatment were at the lowest except for those in July.