Competition between isoetids and invading elodeids at different concentrations of aquatic carbon dioxide

Abstract

1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large-scale invasions of fast-growing elodeid species, replacing the isoetid vegetation, have been observed. 2. In a laboratory experiment, we tested how rising aquatic carbon availability, in interaction with different densities of the isoetid Littorella uniflora, affected the growth (and thereby the potential invasion success) of the elodeid Myriophyllum alterniflorum. For this purpose, the growth of M. alterniflorum was determined at a combination of three concentrations of dissolved CO 2 (15, 90, 200 lmol L )1 ) and three densities of L. uniflora (0, 553, 1775 plants m )2 ). 3. At an ambient CO 2 of 15 lmol L )1 , M. alterniflorum could not sustain itself, whereas at raised CO 2 concentrations, growth became positive and increased with higher CO 2 availability. 4. The presence of L. uniflora, independent of its density, reduced the growth of M. alterniflorum by 50%. Whether this is related to nutrient availability or other factors is not clear. 5. Despite the growth reduction of M. alterniflorum by L. uniflora, at CO 2 ‡90 lmol L )1 , L. uniflora was still overgrown by M. alterniflorum. This may imply that, in field situations, M. alterniflorum can invade softwater systems with relatively high CO 2 availability, even in the presence of dense stands of L. uniflora.

Carbon dioxide and submersed macrophytes in lakes: linking functional ecology to community composition

“…This correlation is consistent with our central hypothesis that high [CO 2 ] favors species with higher SCRI values, and with the idea that isoetids (and probably other sediment CO 2 users) tend to dominate in low CO 2 systems (Spierenburg et al. ).…”

Long‐term effects of liming in Norwegian softwater lakes: the rise and fall of bulbous rush (Juncus bulbosus) and decline of isoetid vegetation

“…Based on the number of macrophyte species in the limed lakes in 2010, one could argue that liming has increased the diversity of macrophytes as well. The possibility of elodeid plant species to colonise isoetid-dominated softwater lakes by these factors was also shown in competition experiments (Spierenburg et al, , 2010. The slow colonisation and expansion of other non-isoetid submerged macrophytes also occurred on experimental plots that were limed four times in lake Dybingsvatn (Lucassen et al, 2012).…”

Historical changes in the macrophyte community of a Norwegian softwater lake

“…During periods of high photosynthetic activity, the uptake of CO 2 might result in very low CO 2 levels in the water, B440 lg l -1 (100 lg CO 2 = 2.27 lmol) (Robe and Griffiths 1992). Such low CO 2 concentrations are insufficient to sustain the growth of C. hamulata, as has been shown experimentally (Spierenburg et al , 2010. Callitriche hamulata needed CO 2 concentrations of 2,200 lg l -1 to show positive growth and [4,400 lg CO 2 l -1 to approach maximal growth rates.…”

“…8) are likely to have increased terrestrial-derived DOC input. According to laboratory experiments, a small increase in CO 2 levels is sufficient to sustain abundant elodeid growth in softwater lakes like Steigatjørna (Spierenburg et al , 2010 and trigger the invasion and expansion of C. hamulata at the expense of isoetid macrophytes.…”