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Research on Models of Light Environment of Planting Ginseng under Forest

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Tutor: YuHaiYe
School: Jilin University
Course: Agricultural Mechanization Engineering
Keywords: ginseng under forest,light encironment,model,prediction and evaluation
CLC: S567.51
Type: PhD thesis
Year:  2007
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Panax ginseng C.A. Mey. is a perennial herbaceous medicinal plant in ginseng family. It survives as a rare plant living fossil of tertiary period, and is distributed in North America, Central Asia and East Asia. Wild ginseng is ranked Plant Resources of National Protection Grade¢ñand Rare and Endangered Plants in China, ginseng under forest is embodied in Chinese Pharmcopoeia (2005) and wild ginseng is deleted, because of forest resource decreasing rapidly and excessive digging. Recently research on planting ginseng under forest has been given more and more attention in all over the world especially in China. Howerer, actual planting depends on experience and reports about studies on ginseng under forest were scarce. The research works are supported by the Emphases projects of Department of Science & Technology of Jilin Province¡°Exploitation and utilization of characterized resource¡ªresearch on digital technique of planting Panax ginseng C. A. Mey. and P. quinquefoliumL¡±(20040207-1). The contents of this research are that models of shadow boundary of an individual conical crown on the slope and distribution of solar radiation understorey, relationships between form and photosynthesis of ginseng and eco-physiological factors and basal frame of prediction and evaluation system of light environment of planting ginseng under forest as follows:1) In the rectangular plane coordinate system,a theoretical model was developed, which took tree height (H), height below branch (h), crown radius( r), longitude (¦Ë), latitude (?), height (ht), slope(¦Á), aspect (¦Â), date (d) and time (t) into account to describe the shadow boundary of an individual conical crown on the slope. The model was based on the apparent motion rules of the sun, geometrical optics theory and the corresponding and imitating principle between shadows on a flat plane and a slope. The precision and error sources of model was analyzed, practical value was intruduced, and advantages and limitations which define how to use this model well with interrelated research were listed. In the simulation tests, the all correlations between measured and calculated values of boundaries were not less than 0.928 and were significant at the 0.01 level (2-tailed), the regression equation between measured and calculated values of area was Y=0.997X+1.262(R2=0.980**), and the result was in accordance with the apparent motion rules of the sun and the correlation was 0.983** between observations and calculations of variable scale of tree-shading of an individual crown.2) The expressions of intantaneous transmissivity of direct and diffuse solar radiation for a random fixed point R (xR, yR, zR) under Larix gmelini forest on the slope were established. The results of simulation test showed that the forest gaps, bigger canopy gaps, irregular limbs and trunk-shading strongly influenced distribution of direct radiation under forest. Without wrong ponits, sunflecks with diameter more than12cm and influence points caused by trunk-shading, there was highly significant correlationship between measured and calculated values of most of measurement points. The best simulated precision (R2=0.746**, MAE%=27.5%, RMSE=3.68) of direct radiation appeared in May. The simulated precision in Suptember was worse than spring and summer. The MAE% and R2 values between measured and calculated diffuse radiation were both close during May to Suptember, and the minimum R2=0.667**, which were better than precision of direct radiation of all fixed points (R2=0.032). Furthermore, the precisions between the accumulative total of measured values and calculated of direct and diffuse radiation at different time for every point were better than intantaneous simulations, that R2 were 0.670** and 0.817**, and MAE% were 15.5% and 3.08% respectively.3) The correlation between form of ginseng and solar radiation under forest was researched, because light hererogeneity was the highest as environmental factors impacted on growth and development of plants. Taking 8 year-old ginseng in JiLe forest farms as an example, the experiment showed when daily accumulative diffuse radiation was 109.45W/m2~202.27 W/m2, the growth of ginseng aerial parts showed negative correlation with it. The plant height depended on PAR. The stem height, leaf width and leaf area showed significant negative correlation with diffuse radiation and no significant negative correlation with PAR, stem height showed significant negative correlation with total radiation and stem diameter showed significant correlation with diffuse radiation and PAR. Several deductions from character of consist of light quality under forest that growth of plant height depended on blue light, infrared impacted on form of ginseng hardly, far-red light had complicated effect on stem height and leaf width and stem diameter was significantly impacted by high content of PAR in diffuse radiation or far-red light or visible blue light.4) Environmental hererogeneity under forests was more complicated than shade. Hererogeneity as basic character of natural ecosystems varied with time and space scale. In this research, the main facors impacted on photosynthesis of ginseng under forest were discussed and several models were established by qualitative and quantitative analysis of photosynthesis character of ginseng and relationship between it and eco-physiological factors. This research showed that there were a wider range of direct radiation than diffuse radiation in different units under forest, and photosynthetically available radiation (PAR) had significant hererogeneity depended on difference of canopy structure and its PAR absorptivity. The maximum of net photosynthesis rate (Pn) was 1.6¦Ìmolm-2s-1, and most of Pn was less than 1¦Ìmolm-2s-1. When PAR values of different units were close, Pn was bigger in the unit whose content of red-orange and green light were both higher, and when PAR values were different, maximal Pn appeared in the unit whose content of blue-violet light was the lowest, content of red-orange was middle and content of green light was the highest. The linearity regression equations of the main factors and Pn and transpiration rate (Tr) respectively was Pn=0.022PAR+0.232Ta+0.012PFDdif-0.317Tl+0.006Gs+1.203Tr+1.494 (R2=0.761 ,F=21.733**), Tr=0.004PAR-0.004RH-0.002Ca+0.002Gs+0.609(R2=0.823,F=68.711**), and Tr=0.004PAR+0.019Ta-0.001Ca+0.002Gs+0.050 (R2=0.832,F=73.077**). The most important factor was PAR for Pn and Tr, and two models were established by curve-fitting.5) The basal frame of prediction and evaluation system of light environment of planting ginseng under forest was designed based on the model of boundary of an individual conical crown on the slope and the models of intantaneous transmissivity of solar radiation for a random fixed point. The initial conditions of this system were degree of closeness, forest and type of soil. Light edge of the forest and range of neighborhood interference were both confirmed by the model of boundary of conical crown. Daily and yearly accumulative radiation, and yearly average radiation were calculated by integration and else methods for the models of intantaneous transmissivity of solar radiation. Based on these results, the system included contours of diffuse radiation and PAR and a set of grade standard which was made according to light adaptability of ginseng under forest.Here establishing spectral characteristics of solar radiation models depended on predecessor¡¯s research mainly, extinction coefficient and accumulative path length were calculated by methods in this research. Deep research was needed to do by a great deal of experiments to find the absorptivity of individual leaves for the specific wave band of interest in the models. Time and conditions of the experiment in this studies limited research on light adaptability of ginseng under forest,and 8-year-old ginseng was only taken as an example in JiLe forest farm, so the results and conclusions had some speciality. To provide all-around grade standard for prediction and evaluation system of light environment of planting ginseng under forest, qualitative and quantitative studies on relationship between environment of understorey and ginsenosides contents in different places for different age ginseng should be developed in the future.
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