What was done
Specimens of submerged Littorella uniflora (L.) were collected along the shores of Lake Hampen in Denmark and propagated under sterile conditions in the absence of symbiotic arbuscular mycorrhizal fungi (AMF), after which half of the plants were re-infected with AMF and both groups were allowed to grow for 60 days in water of either high (150 µM) or low (ambient, about 15 µM) CO2 concentration in conditions where concentrations of NO3- and PO³4- were low enough to be limiting to plant growth.

What was learned
In the words of the authors, "both in treatments with and without AMF, high CO2 concentration resulted in a significantly higher total biomass of L. uniflora, and the same was observed for both shoots and roots," although "the biomass of roots increased more than the biomass of shoots." More specifically, they report that "in treatments without AMF, increasing the CO2 concentration 10 times resulted in a change from a slightly negative growth to a twofold increase in biomass over the 60-day period," while "in treatments with AMF, the increase in CO2 concentration resulted in a fourfold increase in biomass."

As an added bonus, the researchers' work demonstrated that "L. uniflora's symbiosis with mycorrhiza improved the retention of N and P in the plants at very low nutrient concentrations in the water." Consequently, since they additionally observed that "hyphal infection increased fivefold under the raised CO2 concentration," it is evident that elevated aquatic CO2 concentrations may also help isoetids by enhancing the magnitude and stability of their AMF symbiosis, which helps them retain vital nutrients.

What it means
The ongoing rise in the air's CO2 content would appear to portend nothing but good for the isoetids of the world, just as it does for most of the rest of the biosphere, even at concentrations far beyond anything ever imagined to be reached by the world's most pessimistic climate alarmists.