Crassulacean acid metabolism contributes significantly to the in situ carbon budget in a population of the invasive aquatic macrophyte Crassula helmsii

Klavsen, Signe Koch; Maberly, Stephen C.. 2009 Crassulacean acid metabolism contributes significantly to the in situ carbon budget in a population of the invasive aquatic macrophyte Crassula helmsii. Freshwater Biology, 54 (1). 105-118.

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1. The ecophysiological significance of Crassulacean Acid Metabolism (CAM) in the invasive aquatic macrophyte Crassula helmsii (T. Kirk) Cockayne was studied in an English soft-water lake. The extent and the contribution of CAM to the carbon budget was examined in spring (April) and summer (July) along a depth gradient (0.5-2.2 m), covering the growth range of C. helmsii in the lake. 2. Significant in situ CAM activity (30-80 meq kg-1 FW) was present in all specimens, although it decreased with depth and hence correlated with the decline in photon irradiance. Potential CAM activity (60-161 meq kg-1 FW), measured after exposure to low concentrations of CO2 in the day and high concentrations at night, were on average 2.7-times greater than in situ CAM activity. Overall CAM activity increased from April to July, which is consistent with higher potential carbon limitation caused by increased temperature and light availability. 3. CAM activity in C. helmsii appeared to be carbon-limited at night because night-time carbon-fixation increased at elevated, compared to ambient, concentrations of CO2. 4. The high in situ CAM activity in C. helmsii was reflected in the contribution of CAM to the total carbon budget which, independent of depth and season, ranged from 18 to 42 %. The amount of CO2 taken up in the night via CAM was 0.74- to 2.94-times the amount of CO2 lost in respiration, thus emphasizing the importance of CAM in refixation of potentially lost respiratory CO2. 5. The onset of decarboxylation in the morning appeared to be under circadian control as there was a delay of up to 5.5 hours between the start of the light period and a decline in cell acidity level. 6. There was little variation in δ13C content (-21.69-23.49 ‰) with season or depth suggesting, along with the estimated contribution to the carbon-budget, that CAM is highly important for the whole population of C. helmsii. CAM may confer a competitive advantage in relation to growth, which may be one of the reasons for the invasiveness of this species.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Programmes pre-2009 publications > Water > WA02 Quantifying processes that link water quality and quantity, biota and physical environment > WA02.3 Physico-chemical processes and effects on freshwater biot
UKCEH and CEH Sections/Science Areas: Parr
ISSN: 0046-5070
Additional Keywords: carbon concentrating mechanism (CCM), depth gradient, inorganic carbon, light, photosynthesis
NORA Subject Terms: Botany
Ecology and Environment
Date made live: 14 Apr 2009 13:34 +0 (UTC)

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