Winter Klaus, Garcia Milton, Holtum Joseph A M
Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancon, Republic of Panama.
J Exp Bot. 2009;60(11):3167-77. doi: 10.1093/jxb/erp149. Epub 2009 Jun 1.
Photon flux density (PFD) and water availability, the daily and seasonal factors that vary most in tropical environments, were examined to see how they influenced expression of crassulacean acid metabolism (CAM) in 3-year-old Clusia shrubs native to Panama. Instead of the commonly used single-leaf approach, diel CO(2) exchange was measured for whole individual canopies of plants in large soil containers inside a naturally illuminated 8.8 m(3) chamber. In well-watered C. rosea, a mainly constitutive CAM species, nocturnally fixed CO(2) contributed about 50% to 24 h carbon gain on sunny days but the contribution decreased to zero following overcast days. Nonetheless, CO(2) fixation in the light responded in such a way that 24 h carbon gain was largely conserved across the range of daily PFDs. The response of C. rosea to drought was similarly buffered. A facultative component of CAM expression led to reversible increases in nocturnal carbon gain that offset drought-induced reductions of CO(2) fixation in the light. Clusia cylindrica was a C(3) plant when well-watered but exhibited CAM when subjected to water stress. The induction of CAM was fully reversible upon rewatering. C. cylindrica joins C. pratensis as the most unambiguous facultative CAM species reported in the genus Clusia.
研究了热带环境中变化最大的日变化和季节变化因素——光子通量密度（PFD）和水分可利用性，以了解它们如何影响原产于巴拿马的3年生克鲁西亚属灌木中景天酸代谢（CAM）的表达。与常用的单叶方法不同，在一个自然光照的8.8立方米的室内，对大土壤容器中植物的整个个体冠层进行了昼夜CO₂交换测量。在水分充足的玫瑰克鲁西亚（一种主要为组成型CAM的物种）中，夜间固定的CO₂在晴天对24小时碳积累的贡献约为50%，但在阴天之后，这一贡献降至零。尽管如此，光照下的CO₂固定以这样一种方式做出反应，即24小时碳积累在每日PFD的范围内基本保持不变。玫瑰克鲁西亚对干旱的反应也同样得到了缓冲。CAM表达的兼性成分导致夜间碳积累可逆增加，抵消了干旱引起的光照下CO₂固定的减少。圆柱克鲁西亚在水分充足时是C₃植物，但在水分胁迫下表现出CAM。重新浇水后，CAM的诱导是完全可逆的。圆柱克鲁西亚与草原克鲁西亚一样，是克鲁西亚属中报道的最明确的兼性CAM物种。
