Sheep Story

Higher atmospheric concentrations of carbon dioxide hardly are baaaaad news for sheep.

Lupin (a legume) is increasingly popular as a feed for sheep. Lupin contains higher protein than does oats or wheat. They provide higher digestibility. They experience increased resistance to weevil attack.

In Perth, Australia, Palta and Ludwig grew narrow-leafed lupin in chambers within an evaporatively-cooled glasshouse. The atmospheric CO2 concentration was maintained at 355 ppm (ambient) and 700 ppm. The elevated CO2 increased the final number of pods, the number of pods with large seeds, and dry matter of the branches. Total dry matter per plant increased from 47 percent to 56 percent, while the seed yield per plant increased from 44 percent to 66 percent.

Meanwhile, a team of plant biologists in South Africa grew a local grass species for 178 days inside open-top chambers at both ambient and elevated atmospheric CO2 concentrations (360 and 660 ppm). Wand et al. found that "stomatal conductances decreased (in six out of eight species, by a mean of 46%) and instantaneous leaf water-use efficiency increased (in all species, by a mean of 89%) in elevated CO2." In other words, this favorite forage became much more water-use efficient and drought resistant thanks to the elevated CO2.

Hu et al. in central California grew a grassland ecosystem in open-top chambers where the atmospheric CO2 concentration was maintained at 360 ppm (ambient) and 720 ppm over the course of five-years. The researchers found that the elevated CO2 substantially increased the soil’s microbial biomass, which in turn increased the amount of carbon that was stored in the ecosystem.

Poring over their results, they concluded, "Carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO2" confirming anew a central premise in efforts by the U.S. to seek credit for CO2 sinks (carbon sequestration programs) in negotiation of provisions of the Kyoto Protocol in the Hague, Netherlands, in late 2000.

Campbell et al. reviewed 165 peer-reviewed scientific journal articles that were published between 1994 and 1999 and dealt with elevated CO2 and its impact on pastures and rangelands. They concluded, "The stimulatory effect of double ambient CO2 on grassland production averages about +17% in ecosystem-based experiments."

USDA researcher Lewis Ziska grew velveltleaf at 370 ppm and 740 ppm atmospheric CO2 and found a photosynthetic enhancement ranging from 13 percent to 60 percent, depending on the mean temperature in the controlled environment chambers.

References

Campbell, B.D., Stafford Smith, D.M., Ash, A.J., Fuhrer, J., Gifford, R.M., Hiernaux, P., Howden, S.M., Jones, M.B., Ludwig, J.A., Manderscheid, R., Morgan, J.A., Newton, P.C.D., Nosberger, J., Owensby, C.E., Soussana, J.F., Tuba, Z., and ZuoZhong, C. 2000. A synthesis of recent global change research on pasture and rangeland production: reduced uncertainties and their management implications. Agriculture, Ecosystems and Environment, 82:39-55.

Hu, S., Chapin III, F.S., Firestone, M.K., Field, C.,B. and Chiariello, N.R. 2001. Nitrogen limitation of microbial decomposition in a grassland under elevated CO2. Nature, 409:188-191.

Palta, J.A., and Ludwig, C. 2000. Elevated CO2 during pod filling increased seed yield but not harvest index in indeterminate narrow-leafed lupin. Australian Journal of Agricultural Research, 51:279-286.

Wand, S.J.E., Midgley, G.F., and Stock, W.D. 2001. Growth responses to elevated CO2 in NADP-ME, NAD-ME and PCK C4 grasses and a C3 grass from South Africa. Australian Journal of Plant Physiology, 28:13-25.

Ziska, L.H. 2001. Growth temperature can alter the temperature dependent stimulation of photosynthesis by elevated carbon dioxide in Albutilon theophrasti. Physiologia Plantarum, 111:322-328.