Grasslands Roundup: Several new papers confirm CO2’s benefits to savannah regions

Grasslands Roundup: Several new papers confirm CO2’s benefits to savannah regions
January 1, 2001

Most studies of carbon dioxide’s effect on plant life are fairly short in duration—a year or two at most. But one research team stayed with their experiment for six years.

Swiss and Portuguese scientists grew ryegrass near Zurich in open fields with atmospheric carbon dioxide levels maintained at 350 parts per million, or ppm, and 600 ppm.

They found that in the first year of the enrichment, the grass increased its dry weight by 7 percent; but by year six, the increase in dry weight had risen to 25 percent, thanks to higher carbon dioxide (CO2) concentrations. The longer the experiment ran, the better the news about CO2! Furthermore, their results suggest that the many one- and two-year studies may be grossly underestimating the goodness of increased atmospheric CO2 levels.

Another team of scientists from Switzerland, some of whom were involved in the Zurich study, grew various grasses in an open field in 1994 and 1995 with atmospheric CO2 concentrations maintained at normal and doubled levels. Under low levels of nitrogen, the grassland increased overall biomass by 13 percent; under high nitrogen levels, the grasses responded with a 30 percent increase.

Van Ginkel grew that same ryegrass specie for 115 days in growth chambers with atmospheric CO2 concentrations of 350 ppm and 700 ppm, after which some chambers had the temperature increased by 2°C for 230 days.

Van Ginkel and his colleagues observed that elevated CO2 increased root biomass substantially, and the authors wrote “root biomass is the driving parameter for all subsequent below-ground processes in our plant-soil system.” Further, the beneficial microbial biomass increased by 46 percent for the elevated CO2 concentration, and the increased temperatures appeared to have little negative effect on the benefits of higher CO2. Elevated CO2? Great! Higher temperatures? No problem.

With all that grasslands stand to gain as CO2 increases, the pessimists among us might start searching for reasons it’s all just too good to be true. For example, won’t some herbivore come along and ruin the green parade?

That question is so important that a research team headed by scientists from Cambridge and Harvard came together to investigate whether those slimy interlopers we call slugs will gain the upper hand in the pasturelands of generations to come.

Peters and colleagues grew a variety of grassland species at natural (356 ppm) and elevated (600 ppm to 650 ppm) CO2 concentrations and fed the forage to some slugs.

As with hundreds of other studies, they found that elevated CO2 significantly increased biomass of the pasture species. Even more important, they noted, “In terms of the total amount of plant material consumed, there was no evidence that consumption of plants grown at elevated CO2 was any different than consumption on controls grown at ambient CO2.”

In the battle between plants and slugs, elevated CO2 favored the plants.

Again, the message rings loud and clear: If you want a greener planet, increasing (not decreasing) atmospheric CO2 concentrations is just what the biosphere ordered.


Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.


References

Daepp, M., et al., 2000. Yield response of Lolium perenne swards to free air CO2 enrichment increased over six years in a high N input system on fertile soil. Global Change Biology, 6, 805-816.

Lüscher, A., et al., 2000. Direct evidence that symbiotic N2 fixation in fertile grassland is an important trait for a strong response of plants to elevated atmospheric CO2. Global Change Biology, 6, 655-662.

Peters, H.A., et al., 2000. Consumption rates and food preferences of slugs in a calcareous grassland under current and future CO2 conditions. Oecologia, 125, 72-81.

Van Ginkel, J.H., et al., 2000. Elevated atmospheric carbon dioxide concentration: Effects of increased carbon input in a Lolium perenne soil on microorganisms and decomposition. Soil Biology and Biochemistry, 32, 449-456.