Studies On Carbon Dioxide Assimilation Characteristics Of Phyllostachys Edulis In Tianmu Mountain

In this paper, Phyllostachys edulis in Tianmu Mountain Natural Reserves was selected as test material. The experiments were carried out during 2007.1-2007.10 by using the portable photosynthetic measurement LI-6400. We first established a three-crown tower to measure these photosynthetic parameters. The diurnal changes and seasonal changes of physio-ecological factors were researched. The responses of photosynthesis to some factors such as relative chlorophyll content, PAR and so on were researched. This paper also analyzed the correlation between photosynthetic parameters and physio-ecological factors and then compared the photosynthetic characters between different crowns. We last estimated the net photosynthesis at the level of unit leaf area (m2) in a day and at the level of every hectare in the whole year. The results are as follows:1. Diurnal changes in Pn of Phyllostachys edulis have different tendencies in different months, but the whole trend presents single-peak curve and double-peak curve. Diurnal changes of Pn on 29th Jan. and 19th Jul. present the trend of single-peak curve, and double-peak curve on 5th Mar., 6th Apr., 13th May and 11th Oct. When it presents double-peak curve, there will be the phenomenon of photosynthesis midday depression. The seasonal change of Pn presents a non-obvious double-peak curve. The day average Pn was highest on 19th July while lowest on 6th April. The relationship between Pn and physio-ecological factors has great differences in different months. As a whole, the PAR, T, Ci and Gs has a big relation coefficient with various kinds of physiological parameters. The diurnal changes in different months and the seasonal changes of WUE and LUE have complicated trends.2. The relative chlorophyll content has a great relationship with the seasonal change of Pn, and the relative chlorophyll contents in different crowns have many differences. The Pn in different crowns were gradually increasing with the PAR increasing when the PAR was lower than LSP. The Pn in the upper crown is higher than that in lower crown when both at the same PAR. The light compensation point of Phyllostachys edulis is 6.3-27.1μmolm-2s-1and the light saturation point is 98.3-304μmolm-2s-1. The CO2 compensation point of Phyllostachys edulis is 28.8-32.1μmol·mol-1, the CO2 saturation point is 389.7-462.1μmol·mol-1, and the carboxylation efficiency is 0.039-0.049.3. Compared to others months, the CO2-absorbing and O2-releasing of Phyllostachys edulis at July are best of all months and that at April are the lowest. The net photosynthesis at the whole year was about 2238008mol·hm-2·a-1. The net photosynthesis at the summer is the highest, and that at the autumn is lower than that at the summer. The net photosynthesis at the spring and at the winter is much lower.