Responses Of Photosynthetic Characteristics Of Davidia Involucrata Baill Seedlings To Drought Stress, Shading And Carbon Dioxide Elevation

Dovetree(Davidia involucrata Baill) is a protected plant of China, resrearches on the responses of photosynthetic character to drought, shading and carbon dioxide elevation has an important value on reveal the endergened meachanism and forecast the adaptability to environment change of dovetree.Two years old dovetree seedlings were used during experiment. Three treatments including drought, shading and high concentration carbon dioxide were applied to involucrata seedlings.Using CIRAS-2 photosynthesis analyzer, Chlorophyll fluorometer (PAM-2100) and paraffin sections, biomass, chlorophyll content, diurnal variation of photosynthesis and fluorescene parameters, light response curve and carbon dioxide response curve had been examined. The effects of soil water content descrise, light intensity change and carbon dioxide elevate to photosynthesis character were investrated. Based on the experiment, The conclusion were as followings:1. Under conditions of soil water deficit, the seedlings'biomass reduced and leaf area decreased, resulting in reduced photosynthesis area, the net assamition rate and light saturation point were lower than contral, meaning a weaked assamilation capacity. The fluorescene parameters showed that drought destroyed the lighe response system, reduced the light use efficiency, and increased the non-photochemical dissipation. In the same time, drought reduced the seedlings'respiration rate ans water use efficency, but havo no signigicant impact on chlorophyll content per unit area.2. Dovetree seedlings had a strict requirement on light intensity. When the seedlings grown in high light intensity, the total chlorophyll content, chlorophyll a content and chlorophyll b content all descreased, but chlorophyll a/chlorophyll b rised. The seedlings grown in high light intensity environment had higher light compensation point and a lower light saturation point, and the resparition also higher than contral, then resulting a low assimilation capacity. The high light intensity also raise the non-photochemical dissipation and transpiration rate, inhibited the accumulation of photosynthetic organisms. When grown in low light intensity, the seedlings had a lower light saturation point and light use efficiency, and a higher total chlorophyll content, chlorophyll a content and chlorophyll b content, but in the same time, it have a lower chlorophyll a/chlorophyll b, root shoot ratio and leaf mass per area, and also a less photosynthesis organisms accumulation.3. High concentration CO2 had no significant effect on leaf thickness, but it made spongy tissue closed, the gap in spongy tissue smaller and the palisade tissue take a bigger proportion in leaf. Seedlings grow in High concentration CO2 had a low chlorophyll content and a high chlorophyll a/chlorophyll b ratio. High concentration CO2 made light compensation point, light satuation point, CO2 compensation point and CO2 satuation point rised, carboxylation efficiency and maximal light yield descreased.We investigated the ability of adaption to environment change of the endangered and treasured plant dovvetree through study the photosynthesis response to environment. It is the first time of systemic study the effect of CO2 concentation to dovetree photosynthetic. The study has an important meaning on interprate the dovetree endangered mechanism and predicts the future adaptability to changing environmental conditions.