The Comparative Study On The Growth Of Dendrobium Candidum On Rocks And Trees Under Karst Eco-environment Conditions

With closing hillsides for afforestation and returning the grain plots to forestry, the eco-environment in the karst areas has improved. However, karst rocky desertification in Southwest China is still very serious. For further improvement of the environment in the karst areas, planting some economic vegetations is a must, which can also increase the income of farmers living in the karst areas. By investigating the economic species growing in the karst areas, we found that the Dendrobium candidum growing in karst areas is one of the rare Chinese herbal medicines. Dendrobium candidum grows on rocks or tree barks, where soils are in deficit. Therefore, Dendrobium candidum suits to grow in karst areas. However, because of excessive collection, wild Dendrobium candidum is near to extinction. So, the study on Dendrobium candidum growing in shed is necessary. Based on the comparative study on Dendrobium candidum growth on rocks and trees under karst eco-environment conditions, the paper aimed at providing the basis for protecting the limited wild Dendrobium candidum resources and for the Dendrobium candidum planting in shed.Dendrobium candidum could be used as medicine mainly because it contains polysaccharide.This study took Jilong, Yaolan, Yaoqing, located in Libo county, Guizhou province as the sampling places. We examined the main environmental factors for Dendrobium candidum growing on rocks and tree barks. After this, we regulated the habitat factors for Dendrobium candidum growing in shed and made a comparison between the Dendrobium candidum growing in shed and those wild species.The following findings and conclusions were obtained by this study:1. Humidity: the humidity 60-80% for Dendrobium candidum growing was highest at Jilong. The humidity can provide sufficient water. However, the light was in deficit here, so the photosynthetic rate was low. Therefore, the Dendrobium candidum had low production and low polysaccharide content.2. The light intensity:Dendrobium candidum growing on rocks at Yaoqing had sufficient light 300-400μmol/m2s, and the water use efficiency was also higher here. Therefore more organic compounds through photosynthesis were produced. The values measured by Li-6400 photosynthesis measuring instrument showed that the photosynthetic rate at Yaoqing was higher than at Jilong. This was also confirmed by the higher dry weight and higher polysaccharide content of the samples at Yaoqing.3. The water use efficiency of the samples revealed by theδ13C of Dendrobium candidum leaves is consistent with that measured by Li-6400 photosynthesis measuring instrument. The water use efficiency 0.608μmol/mol at Yaoqing was higher, which showed it was poor in water supply. The leaf microstructure of Dendrobium candidum also showed similar results. Determination of polysaccharide with the corresponding results.The resistance of Dendrobium candidum reflects with habita through peroxidase test.4. The contents of different elements in different parts of Dendrobium candidum showed some regularity, that is root>leaf>stem or leaf>root>stem. Although the elements contents in stem were lower than those in leaf and leaf, the element content in stem was enough as a kind of Chinese herbal medicine. The migration regularity of different elements between environment and Dendrobium candidum was also different. The content of elements, such as copper, iron, lead, zinc and calcium in Dendrobium candidum are less affected by matrix, while cadmium and manganese showed stronger influence by matrix. So, we should control the content of those elements affected easily by matrix which made up of the substrate used when growing Dendrobium candidum in shed.5. Based on the findings above, we regulated the Dendrobium candidum habitat factors in the shed experiment. The results showed that the photosynthetic rate and the water use efficiency of Dendrobium candidum growing in shed were the highest. With the higher yield, higher dry weight, higher polysaccharide content 27.02%and abundance in trace elements, the Dendrobium candidum can be used as the raw material of Dendrobium, a kind of Chinese herbal medicine with good quality.6. The suited pH and substrate with induction mechanism were selected out by Dendrobium candidum tissues cultivation in laboratory. This will provide basis for growing Dendrobium candidum in shed.In summary, the relationship between physiological factors and the habitation of Dendrobium candidum have been examined, which provided a basis for establishing the system of Dendrobium candidum growing assessment, and for cultivating Dendrobium candidum in the field.