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

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(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.