Effect of CO_2 concentration on photosynthesis in deciduous broad-leaved tree species

(1)CO_2水平对几种落叶阔叶树种单叶净光合作用的影响：大多数树种的P_n和饱和PAR随CO_2水平的增加而增加。从光-光合作用曲线来看，金合欢(Fagus crenate，FC)为低CO_2-弱光利用型，锯缘金合欢(Zelkova serrata，Zs)为高CO_2-弱光利用型，赤杨(Alnus Firma，Af)为高CO_2-强光利用型，银杏(Ginkgo biloba，GB)为高CO_2-中间型。(2)短期CO_2水平和温度对部分落叶阔叶树种幼苗光合作用和呼吸作用的影响：强光下温度-光合作用曲线表现出明显的优化曲线。最适温度为15-35ﾟC，随CO_2浓度的升高，温度由低向高转变。在5种植物中，灌木Af&W.hortensis(WH)具有较高的Pn和较宽的适宜范围。树种FC、QC和GB表现出不同的格局。(3)CO_2水平对QC、Qd和WH幼苗叶片光合作用的影响：在2种栎属植物中，有2种植物的CO_2浓度达到饱和P_n的900ppm以上，在WH幼苗中达到600ppm以上。不同树种的水分利用效率均随CO_2浓度的升高而提高。(4)高CO_2浓度和水分胁迫对赤杨气体交换的影响：Pn、Tr和g_S速率随水分胁迫程度的增加而降低。临界水势分别为-12、-10、-8巴。在-8bar水势以上的良好水分条件下，Pn和g_S观察到了CoN_2效应。

(1) Effects of CO_2 levels on net photosynthesis of single leaf in several deciduous broad-leaved tree species : P_n and the saturated PAR were generally increased with inceasing CO_2 levels in most species tested. From the light-photosynthesis curves, we classified fagus crenate(Fc) as low CO_2-weak light use type, Zelkova serrata(Zs) as high CO_2-weak light use type, Alnus firma(Af) as high CO_2-strong light use type, and Ginkgo biloba(Gb) as high CO_2-intermediate type.(2) Effects of short-term CO_2 levels and temperatures on the photosynthesis and respiration of some deciduous broad-leaved tree species seedlings : Temperature-photosynthesis curves in strong light showed a distinct optimum curves. The optimum temperatures were found at 15-35ﾟC, the values shifted from low to high temperatures with increasing CO_2 levels. Among five species, Af & W.hortensis(Wh), shrub species, had a higher P_n and the broad optimum ranges. Fc, Qc & Gb, tree species, exhibited a contrasting pattern. (3) Effects of CO_2 levels on a leaf photosynthesis in Qc, Q.dentata(Qd) and Wh seedlings : CO_2 levels that saturated P_n were found above 900ppm in 2Quercus species, and 600ppm in Wh. The water use efficiency enhanced with higher CO_2 levels irrespective of species.(4) Effects of high CO_2 levels and water stress on gas exchange in Alnus firma : The rates of Pn, Tr and g_s decreased with increasing water stress. The critical water potentials were found at -12, -10, -8 bars, respectively. COn_2 effects were observed in Pn and g_s under well-watered conditions above -8 bar water potentials.