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Crassulacean acid metabolism contributes significantly to the in situ carbon budget in a population of the invasive aquatic macrophyte Crassula helmsii
Author(s) -
KLAVSEN SIGNE KOCH,
MABERLY STEPHEN C.
Publication year - 2009
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.2008.02095.x
Subject(s) - crassulacean acid metabolism , macrophyte , carbon fixation , respiration , biology , potamogetonaceae , rhizome , population , carbon dioxide , carbon fibers , aquatic plant , botany , ecology , horticulture , zoology , photosynthesis , chemistry , materials science , composite number , composite material , demography , sociology
Summary 1. The ecophysiological significance of Crassulacean acid metabolism (CAM) in the invasive aquatic macrophyte Crassula helmsii 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 CO 2 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 raised, compared to ambient, concentrations of CO 2 . 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 CO 2 taken up in the night via CAM was 0.74 to 2.94 times the amount of CO 2 lost in respiration, thus emphasizing the importance of CAM in refixation of potentially lost respiratory CO 2 . 5. The onset of decarboxylation in the morning appeared to be under circadian control as there was a delay of up to 5.5 h between the start of the light period and a decline in cell acidity level. 6. There was little variation in δ 13 C content (−21.69 to 23.49‰) with season or depth suggesting, along with the estimated contribution to the carbon‐budget, that CAM is 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.