Pfitsch William A, Pearcy Robert W
Department of Botany, University of California, 95616, Davis, CA, USA.
Oecologia. 1989 Sep;80(4):471-476. doi: 10.1007/BF00380068.
The gas exchange characteristics under steadystate and transient light conditions were determined for a redwood forest understory herb Adenocaulon bicolor, that depends on use of sunflecks for a large fraction of its daily carbon gain. Measurements under steady-state conditions indicated that this species has photosynthetic characteristics that are typical for understory plants. The mean light-saturated assimilation rate was 5.26 μmol CO m s; the light saturation and compensation occurred at 243 and 2 μmol photons m s, respectively. This light compensation point was much less than the photon flux density under diffuse light in the understory so that positive assimilation could be maintained throughout the day. When leaves that had been in diffuse light for at least 2 h were exposed to a sudden increase in PFD to saturating levels, 10-30 min were required for both assimilation and stomatal conductance to reach maximum values. Calculation of intercellular CO pressures, however, suggest that for the first 10 min after the light increase, biochemical factors were responsible for most of the increase in assimilation. Thereafter stomatal opening caused a further increase in assimilation that was no more than 25% of the total. When fully induced leaves were returned to low light, induction was rapidly lost even though stomatal conductance decreased only slowly. This rapid loss of induction limited the capacity of A. bicolor to use sunflecks after low light periods that lasted longer than 1-2 min. However, during periods when sunflecks are more frequent there is probably little loss of induction. Under these conditions, sunflecks are used with high efficiency for assimilation.
对一种红木林林下草本植物双色腺茎草（Adenocaulon bicolor）在稳态和瞬时光照条件下的气体交换特性进行了测定，该植物每日碳获取的很大一部分依赖于对光斑的利用。稳态条件下的测量表明，该物种具有林下植物典型的光合特性。光饱和同化率的平均值为5.26 μmol CO₂ m⁻² s⁻¹；光饱和点和补偿点分别出现在243和2 μmol光子 m⁻² s⁻¹ 处。这个光补偿点远低于林下漫射光下的光子通量密度，因此全天都能维持正同化作用。当在漫射光下至少照射2小时的叶片突然暴露于光合有效辐射（PFD）增加至饱和水平时，同化作用和气孔导度达到最大值都需要10 - 30分钟。然而，细胞间CO₂ 压力的计算表明，在光照增加后的前10分钟，生化因素是同化作用增加的主要原因。此后气孔开放导致同化作用进一步增加，但增加量不超过总量的25%。当完全诱导的叶片回到低光照条件下时，诱导作用迅速丧失，即使气孔导度只是缓慢下降。这种诱导作用的迅速丧失限制了双色腺茎草在持续时间超过1 - 2分钟的低光照期后利用光斑的能力。然而，在光斑更频繁出现的时期，诱导作用可能几乎没有损失。在这些条件下，光斑被高效用于同化作用。
