What was done
In a study designed to explore the initial phases of CO2-induced stimulation of nitrogen fixation in the common garden bean (Phaseolus vulgaris L.), the authors soaked sterilized seeds for five hours in 10 mM CaSO4, after which they were placed in rolls of moist filter paper soaked with 2.5 mM CaSO4 and maintained in darkness for four days (with daily moistening with the same medium) under both ambient (400 ppm) and elevated (800 ppm) atmospheric CO2 concentrations. At this point in time, a 16-hour light period was initiated, and plants were harvested at 6, 8, 10 and 12 days after seeding (DAS), while other seedlings were transferred to soil culture in rhizoboxes at 7 DAS, where they were grown in well N-supplied and low N-supplied treatments until 18 DAS, throughout which entire period various types of measurements were made on periodically-harvested plants.

What was learned
Haase et al. report that, "surprisingly, the CO2 effect was already detectable during germination of very young seedlings (6 DAS)," when they observed "CO2-stimulated root exudation of total phenolics and of nod-gene-inducing flavonoids (genistein, daidzein and coumestrol)," the latter of which compounds they say "was released over the whole root system" with "potential stimulatory effects on N2 fixation." Thereafter, they report that "elevated CO2 increased the accumulation of malate as a major carbon source for the microsymbiont and of malonate with essential functions for nodule development," after which they observed "a significantly higher number, biomass and an elevated fraction of leghaemoglobin-producing nodules," reflecting "promoted Rhizobium-plant interactions, particularly in the N-deficient bean plants."

What it means
Germinating bean sprouts are quick to sense the presence of high-CO2 air, responding almost from the time of germination with chemical reactions that prepare them to take full advantage of elevated levels of this basic resource, which increases their growth and enhances their abilities to fix nitrogen from the atmosphere and make it available to themselves and, ultimately, other plants as well. Surely, there can be no question about it: earth's plants are genetically programmed to function at a superior level of activity in CO2-enriched air.