Department of Biology, California State University, San Bernardino, California 92407 USA;
Am J Bot. 2005 Nov;92(11):1811-9. doi: 10.3732/ajb.92.11.1811.
Dieffenbachia longispatha (C3) and Aechmea magdalenae (Crassulacean acid metabolism, CAM) are syntopic, neotropical forest perennials in central Panama that are restricted to shaded habitats. This is of particular interest for A. magdalenae because, like other understory CAM bromeliad species, it appears functionally and structurally to be better suited to life in full sun. Growth irradiance (GI) effects on photosynthesis and growth in both species were explored in the context of sun/shade trade-off concepts largely derived from studies of C3 plants. Potted plants were grown outdoors in 1, 55, and 100% full sun for 5 mo under well-watered conditions. While both species grew faster in high compared to low light, maximum relative growth rates (RGR) in full sun were still extremely slow with A. magdalenae showing a RGR approximately half that of D. longispatha. Photosynthetic capacity increased with GI in D. longispatha but not in A. magdalenae. Aechmea magdalenae responded to GI with shifts in the activity of the different CAM phases. Both species were photoinhibited in full sun, but more so in A. magdalenae. Despite possessing many traits considered adaptive in high light, these results suggest that A. magdalenae is unlikely to attain sufficient growth rates to thrive in productive, high-light habitats.
巴拿马中部同域生长的多年生植物长叶大丝兰（C3 植物）和紫凤梨（景天酸代谢，CAM），局限于遮荫生境。这对于紫凤梨尤其有趣，因为与其他林下 CAM 凤梨物种一样，它在功能和结构上似乎更适合生活在阳光充足的地方。在很大程度上源自 C3 植物研究的日-荫权衡概念的背景下，研究了光照强度（GI）对这两个物种光合作用和生长的影响。盆栽植物在充分浇水的条件下，在户外 1%、55%和 100%的全光照下生长了 5 个月。尽管与低光照相比，两种植物在高光下生长更快，但在全日照下的最大相对生长率（RGR）仍然非常缓慢，紫凤梨的 RGR 约为长叶大丝兰的一半。长叶大丝兰的光合能力随 GI 增加而增加，但紫凤梨则不然。紫凤梨根据 GI 变化调整不同 CAM 阶段的活性。两种植物在全日照下都发生光抑制，但紫凤梨更严重。尽管具有许多被认为在高光下适应性的特征，但这些结果表明，紫凤梨不太可能达到足够的生长速度在高生产力、高光环境中茁壮成长。
