Published for the Annals of Botany Co. by Academic Press
Annals of Botany vol:105 issue:2 pages:301-309
• Background and aims: Photosynthetic plasticity in response to a range of environmental factors that include [CO2], 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.
• Methods: 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 4 times a year, i.e. in winter, spring, summer and autumn.
• Key results: During the brighter seasons (spring and summer) day-time Phases II and IV were dominated by C4 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 CO2 uptake showed a significant depression at the end of the day in the darker months when supplementary illumination went off. Remarkable seasonal consistency was found in the amount of storage reserves available for nocturnal carboxylation, a consequence of predominantly day-time export of carbohydrate in spring and summer whilst nocturnal export was the major sink for carbohydrate in autumn and winter.
• Conclusions: Throughout the different seasons Aechmea ‘Maya’ showed considerable plasticity in the timing and magnitude of C3 and C4 carboxylation processes over the diel cycle. Under low PPF (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 optimising 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 .