TCS Daily

Aerial Fertilizer

By Robert C. Balling - July 21, 2003 12:00 AM

One of the global problems formally addressed by the United Nations for more than a decade is desertification, particularly in Africa. In many of the world's dryland areas, poverty, political instability, deforestation, overgrazing, bad irrigation practices, and naturally-occurring periodic droughts have degraded the landscape and created economic hardship for local residents. Developing countries with agricultural economies closely tied to the state of the land have been hit hardest with at least 200,000 human deaths and millions of animal deaths linked directly to desertification.

The United Nations hosted a major conference on desertification in 1977 in Kenya, and in 1992, desertification was a prominent theme at the famed Conference on Environment and Development held in Rio de Janeiro. In 1994, the United Nations adopted the Convention to Combat Desertification in Paris (I served on the scientific advisory panel to the secretariat and wrote a book for the United Nations on desertification and climate). The Russian Federation recently became the 187th country to ratify the Convention; the United States ratified the Convention in November of 2000.

Whether you are aware of it or not, you are doing something every day to alleviate desertification problems in Africa and elsewhere (other than pouring money into the United Nations). If you are using any electricity, chances are that the energy is coming from a power plant burning coal, oil, or natural gas. If you drive a car, ride a bus, or fly in a plane, some kind of fossil fuel is being burned to get you from place to place. The result of all of these activities is a release of carbon dioxide (CO2) into the global atmosphere, and while CO2 is often linked to potential global warming, the scientific literature is full of articles showing that elevated CO2 is wonderful for plants. In virtually every case, higher levels of CO2 increase plant photosynthesis, growth rate, water-use efficiency, and tolerance to disease and a wide range of stresses. Plants evolved when CO2 concentrations were much higher than today, and as we continue to drive atmospheric CO2 levels upward, the plants relax as they feel much more at home.

Hardly a week goes by without an article appearing in the professional scientific literature about how well grasses respond to elevated CO2 concentrations. For example, a team of scientists from the United States and Europe grew ryegrass outdoors with ambient (365 ppm) and elevated (600 ppm) CO2 concentrations. The Ainsworth et al. team took over 3,000 measurements each year, and they found that over the 10 years as a whole, the elevated CO2 caused a 43 percent increase in the rate of photosynthesis and a 30 percent decrease in stomatal conductance. The decrease in stomatal conductance means that less water transpired from the leaves -- once again, grasses grew faster and used less water! They concluded, "In contrast with theoretical expectations and the results of shorter duration experiments, the present results provide no significant change in photosynthetic stimulation across a 10-year period." The grasses loved the extra CO2 and never got tired of the extra treat.

Another recent example comes from a team of rangeland scientists from Fort Collins, Colorado. LeCain et al. grew pasture grasses in open-top chambers for four years with ambient and twice ambient atmospheric CO2. They found that during a wet year, the elevated CO2 resulted in a 17 percent increase in biomass, but "during the drought year of 2000, biomass was increased by 95% in elevated CO2 plots." The combination of higher rates of photosynthesis with greater water use efficiency really shows off when times are tough!

These two studies, along with literally thousands of others, reinforce the view that elevated atmospheric CO2 will produce biological miracles all over the world. Dryland areas are full of struggling countries, people, and domesticated animals. With higher levels of CO2, the grasslands will grow better in their present habitats, and they will expand into areas that are unable to support growth today given limiting levels of CO2. The evidence is overwhelming that the Earth is becoming more green, despite all the publicity about our negative impact on the environment. And before anyone plays the "but what about the effect of global warming" card, most of these grasses have an optimum growth temperature several degrees above modern levels.

The dryland grasses are praying for higher levels of CO2, and while we hope United Nations can really combat desertification, we should take comfort knowing that anything we do to elevate global atmospheric CO2 will have enormous benefits for the countries of Africa and elsewhere who feel the brunt of the desertification problem.

We have been programmed to think of CO2 as a pollutant capable of generating apocalyptic global warming and untold environmental calamities. Based on the biological literature, we can easily counter that CO2 is an aerial fertilizer benefiting the biosphere, particularly in areas of limited rainfall.

The United Nations Convention to Combat Desertification is ambitious and supported by 187 countries at present. But surprisingly, our continued burning of fossil fuels may do more to combat desertification than a thousand conventions adopted by the United Nations.

Ainsworth, E.A., Davey, P.A., Hymus, G.J., Osborne, C.P., Rogers, A., Blum, H., Nösberger, J., and Long, S.P. 2003. Is stimulation of leaf photosynthesis by elevated carbon dioxide concentration maintained in the long term? A test with Lolium perenne grown for 10 years at two nitrogen fertilization levels under Free Air CO2 Enrichment (FACE). Plant, Cell & Environment, 26, 705-714.

LeCain, D.R., Morgan, J.A., Mosier, A.R., and Nelson, J.A. 2002. Soil and plant water relations determine photosynthetic responses of C3 and C4 grasses in a semi-arid ecosystem under elevated CO2. Annals of Botany, 92, 41-52.

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