Faculty of Bioscience Engineering, Department of Biosystems, Division of Crop Biotechnics, Katholieke Universiteit Leuven, Willem De Croylaan 42, B-3001 Heverlee, Belgium.
Ann Bot. 2010 Feb;105(2):301-9. doi: 10.1093/aob/mcp275. Epub 2009 Nov 12.
Photosynthetic plasticity in response to a range of environmental factors that include [CO(2)], water availability, light intensity and temperature, is ubiquitous among plants with crassulacean acid metabolism (CAM). The present study examined how seasonal changes in light availability, as experienced by greenhouse CAM crops in northern latitude regions, influence diel carboxylation patterns and impact on carbon gain and seasonal accumulation of biomass.
In the CAM bromeliad Aechmea 'Maya' integrated measurements of leaf gas exchange, diel metabolite dynamics (e.g. malate, soluble sugars and starch) and biomass accumulation were made four times a year, i.e. in winter, spring, summer and autumn.
During the brighter seasons (spring and summer) daytime Phases II and IV were dominated by C(4) carboxylation, whilst the higher diurnal uptake in the autumn and winter was characterized by equal contributions of both Rubisco and PEPC. As a consequence, net CO(2) uptake showed a significant depression at the end of the day in the darker months when supplementary illumination was turned off. Remarkable seasonal consistency was found in the amount of storage reserves available for nocturnal carboxylation, a consequence of predominantly daytime export of carbohydrate in spring and summer whilst nocturnal export was the major sink for carbohydrate in autumn and winter.
Throughout the different seasons Aechmea 'Maya' showed considerable plasticity in the timing and magnitude of C(3) and C(4) carboxylation processes over the diel cycle. Under low PPFD (i.e. winter and autumn) it appears that there was a constraint on the amount of carbohydrate exported during the day in order to maintain a consistent pool of transient carbohydrate reserves. This gave remarkable seasonal consistency in the amount of storage reserves available at night, thereby optimizing biomass gain throughout the year. The data have important practical consequences for horticultural productivity of CAM plants and suggest a scenario for reconciling carbohydrate partitioning between competing sinks of nocturnal acidification and export for growth.
具有景天酸代谢（CAM）的植物普遍具有对包括[CO2]、水分可用性、光强和温度在内的一系列环境因素的光合作用适应性。本研究探讨了北方地区温室 CAM 作物经历的光可用性季节性变化如何影响昼夜羧化模式，并影响碳增益和季节性生物量积累。
在 CAM 凤梨 Aechmea 'Maya'中，每年四次（冬季、春季、夏季和秋季）综合测量叶片气体交换、昼夜代谢物动态（例如苹果酸、可溶性糖和淀粉）和生物量积累。
在较亮的季节（春季和夏季），白天的相位 II 和 IV 主要由 C4 羧化作用主导，而在秋季和冬季更高的日吸收则由 Rubisco 和 PEPC 共同贡献。因此，当关闭补充照明时，在较暗的月份，在一天结束时净 CO2 吸收会出现显著下降。在春季和夏季，碳水化合物主要白天输出，而在秋季和冬季，夜间输出是碳水化合物的主要汇，因此可用于夜间羧化的储存储备量具有显著的季节性一致性。
在不同季节，Aechmea 'Maya'在昼夜周期中 C3 和 C4 羧化过程的时间和幅度上表现出相当大的适应性。在低 PPFD 下（即冬季和秋季），为了维持瞬态碳水化合物储备的稳定池，似乎存在白天输出的碳水化合物量的限制。这使得夜间可用储存储备量具有显著的季节性一致性，从而优化了全年的生物量增长。这些数据对 CAM 植物的园艺生产力具有重要的实际意义，并提出了一种方案，以协调夜间酸化和用于生长的出口的竞争汇之间的碳水化合物分配。
