Will elevated atmospheric CO2 boost the growth of an invasive submerged macrophyte Cabomba caroliniana under the interference of phytoplankton?

The growth of most submerged macrophytes is likely to be limited by the availability of carbon resource, and this is especially true for the obligatory carbon dioxide (CO2) users. A mesocosm experiment was performed to investigate the physiological, photophysiological, and biochemical responses of Cabomba caroliniana, an invasive macrophyte specie in the Lake Taihu Basin, to elevated atmospheric CO2 (1000 μmol mol-1); we also examined the possible impacts of interferences derived from the phytoplankton proliferation and its concomitant disturbances on the growth of C. caroliniana. The results demonstrated that elevated atmospheric CO2 significantly enhanced the biomass, relative growth rate, and photosynthate accumulation of C. caroliniana. C. caroliniana exposed to elevated atmospheric CO2 exhibited a higher relative maximum electron transport rate and photosynthetic efficiency, compared to those exposed to ambient atmospheric CO2. However, the positive effects of elevated atmospheric CO2 on C. caroliniana were gradually compromised as time went by, and the down-regulations of the relative growth rate (RGR) and photosynthetic activity were coupled with phytoplankton proliferation under elevated atmospheric CO2. This study demonstrated that the growth of C. caroliniana under the phytoplankton interference can be greatly affected, directly and indirectly, by the increasing atmospheric CO2.