What was done
The authors, in their words, "present data on 18 years of measurement of above and belowground biomass, tissue N concentration and total standing crop of N for a Scirpus olneyi-dominated (C3 sedge) community, a Spartina patens-dominated (C4 grass) community and a C3-C4-mixed species community exposed to ambient and elevated (ambient + 340 ppm) atmospheric CO2 concentration [via open-top chamber technology] in natural salinity and sea level conditions of a Chesapeake Bay wetland."

What was learned
Erickson et al. report that "elevated atmospheric CO2 enhancement of C3 biomass was sustained through time in the S. olneyi-dominated community, averaging about 40% for shoots and 26% for roots, whereas elevated CO2 had no significant overall effect on biomass production in the C4 grass community." In addition, they determined that "the greatest amount of carbon was added to the S. olneyi-dominated community during years when shoot N concentration was reduced the most, suggesting that the availability of N was not the most or even the main limitation to elevated CO2 stimulation of carbon accumulation in this ecosystem."

What it means
The four researchers say the results of their record-setting 18-year study "demonstrate that elevated CO2 effects on biomass production can be sustained through time," even when N availability is at the lowest of levels typically encountered in the Chesapeake Bay environment, noting further that CO2-induced "sustained enhancement of growth has [also] been found in a scrub oak ecosystem (Dijkstra et al., 2002; Hymus et al., 2002), a tallgrass prairie (Owensby et al., 1999) and several forested ecosystems (Norby et al., 2005), indicating that increased productivity of many ecosystems will follow global increases in atmospheric CO2 concentration."

References
Dijkstra, P., Hymus, G.J., Colavito, D. et al. 2002. Elevated atmospheric CO2 stimulates shoot growth in a Florida scrub oak ecosystem. Global Change Biology 8: 90-103.

Hymus, G.J., Pontailler, J.Y., Li, J. et al. 2002. Seasonal variability in the effect of elevated CO2 on ecosystem leaf area index in a scrub-oak ecosystem. Global Change Biology 8: 931-940.

Norby, R.J., DeLucia, E.H., Gielen, B. et al. 2005. Forest response to elevated CO2 is conserved across a broad range of productivity. Proceedings of the National Academy of Science 102: 18,052-18,056.

Owensby, C.E., Ham, J.M., Knapp, A.K. et al. 1999. Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2. Global Change Biology 5: 497-506.