The Research On Photosynthetic Characteristics Of Four Rhododendron Species In Hunan

Rhododendron L. is the largest genus of the Ericaceae plants. Hunan has rich resources about it. Based on reading relevant specimens and documents, it also systematically studied the species of Rhododendron L. and recorded the wild ornamental characteristics and distributions of 38 species of Rhododendron L. in Hunan. At last, it researched the soil properties and photosynthetic characteristics of the Rhododendron moulmainense, Rhododendron rivulare, Rhododendron latoucheae and Rhododendron fortunei. The results showed that:(1)58 species (including 1 variety) Rhododendron species is distributed in Hunan, and two species were new distribution. The distribution center of Rhododendron L. in the west and south of Hunan. The plant diversity is gradually increased with the increase of the elevation in this altitudinal gradients and the Tsutsusi subgenus altitudinal gradients span is biggest. The vertical distribution center in elevation 800-1500 m and the horizontal distribution center in northern latitude 27°-25°and longitude 108°-114°.(2) The results showed that 4 kinds of the Rhododendron' soil moisture content at different levels (0-15,15-30,30-45 cm) is between 21.02-21.95%, and R.latoucheae'is highest. The soil bulk densities showed a trend from low to high, were 1.335,1.3425,1.42 g/cm3. R.rivulare'soil organic matter content at 0-15 cm is highest(85.25 g/kg), which of R.latoucheae at 15-30 cm is lowest(19.17 g/kg). The average of total N is 0.52 g/kg, which of R.moulmainense at 0-15 cm is highest(1.07 g/kg) and R.moulmainense and R.rivulare was significantly higher than R.latoucheae and R.fortunei. The average contents of P, K and Mg were 0.17,3.58 and 1.95 g/kg. The sequence of microelement concentrations in the soil was Fe> Mn> Zn> Ni> Cu> Pb> Co> Cr.(3) The different species of Rhododendron have big difference on net photosynthetic rate. The highest net photosynthetic rate is R.latoucheae and the lowest is R.moulmainense with a difference of 2.214μmol·m-2·s-1. The descending sequence of net photosynthetic rate is R.latoucheae, R.rivulare, R.fortunei and R.moulmainense. In the four Rhododendron species, the biggest transpiration rate are R.latoucheae and R.rivulare and the lowest is R.moulmainense with a difference of 0.802 mmol·m-2·s-1. The descending sequence of transpiration rate is R.latoucheae, R.rivulare, R.fortunei and R.moulmainense which is the same of the net photosynthetic rate.The biggest intercellular CO2 concentration is R.latoucheae and the smallest is R.moulmainense with a difference of 115.07μmol·m-2·s-1. The diurnal variation curve of net photosynthetic rate of four Rhododendron species showing two peaks which showed high photosynthetic capacity and production potential. It is showed that the 4 speicies of Rhododendron are adapting to application and promotion in the subtropical regions such as Hunan..