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黑云杉(Piceamariana[Mill.]B.S.P.)和白云杉(Piceaglauca[Moench]Voss.)是同属物种,两者都是适度耐阴,并且在北美北方针叶林中广泛分布.为了了解光照对CO2浓度升高的生理生态反应的影响,在三种光照条件下(温室中光照设置为100％、50％和30％)将一年生的两种幼苗暴露在360和720μmolmol-1浓度的CO2环境中,测定了其中后期叶面气体交换量.研究结果表明,CO2的浓度升高提高了净光合速率(Pn)和光合水分利用效率,但降低了气孔导度和蒸腾作用.CO2对光合作用的刺激在50％光照下最大,在100％光照下最小.光合作用、最大羧化速率(Vcmax)和光饱和电子传递速率(Jmax)均随光照强度的降低而降低.升高的CO2在所有光照处理中显著降低了Vemax,在生长季节中期,两种云杉的Vcmax均显著降低,但在生长季节后期,当光照达到30％时,这一影响变得不明显,而且黑云杉的响应大于白云杉.CO2浓度升高也降低了白云杉的Jmax,但在生长季后期30％光照时,这种影响变得不显著.但CO2浓度升高对黑云杉的影响随时间而变化.在所有光照处理中,CO2浓度升高降低了黑云杉生长中期的Jmax,且在生长后期30％光照时影响不显著,但在100％和50％光照时,Jmax升高.这些研究结果表明,两个树种植物都受益于CO2浓度的升高,但它们的响应机制随着光照的增加而变化:即在100％和50％光照下,它们的响应主要是生理上的,而在30％光照下,它们的响应主要是形态上的.“,”Aims Black spruce(Picea mariana[Mill.]B.S.P.)and white spruce(Picea glauca[Moench]Voss.)are congeneric species.Both are moderately shade tolerant and widely distributed across North American boreal forests.Methods To understand light effects on their ecophysiological responses to elevated CO2,1-year-old seedlings were exposed to 360 μmol mol-1 and 720 μmol mol-1 CO2 at three light conditions(100％,50％and 30％of full light in the greenhouse).Foliar gas exchanges were measured in the mid-and late-growing season.Important Findings Elevated CO2 increased net photosynthesis(Pn)and photosynthetic water use efficiency,but it reduced stomatal conductance and transpiration.The stimulation of photosynthesis by elevated CO2 was greatest at 50％light and smallest at 100％.Photosynthesis,maximum carboxylation rate(Vcmax)and light-saturated rate of electron transport(Jmax)all decreased with decreasing light.Elevated CO2 significantly reduced Vcmax across all light treatments and both species in mid-growing season.However,the effect of elevated CO2 became insignificant at 30％light later in the growing season,with the response being greater in black spruce than in white spruce.Elevated CO2 also reduced Jmax in white spruce in both measurements while the effect became insignificant at 30％light later in the growing season.However,the effect on black spruce varied with time.Elevated CO2 reduced Jmax in black spruce in mid-growing season in all light treatments and the effect became insignificant at 30％light later in the growing season,while it increased Jmax later in the season at 100％and 50％light.These results suggest that both species benefited from elevated CO2,and that the responses varied with light supply,such that the response was primarily physiological at 100％and 50％light,while it was primarily morphological at 30％light.