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Title: RESPONSES OF SEEDLINGS OF FIVE WOODY SPECIES TO CARBON DIOXIDE ENRICHMENT

Author
item Tischler, Charles
item Derner, Justin
item Polley, Herbert
item Johnson, Hyrum

Submitted to: Seed and Soil Dynamics in Shrubland Ecosystems Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2003
Publication Date: 2/1/2004
Citation: Tischler, C.R., Derner, J.D., Polley, H.W., Johnson, H.B. 2004. Responses of seedlings of five woody species to carbon dioxide enrichment. In: Hild, A.L., Shaw, N.L., Meyer, S.E., Booth, D.T., McArthur, E.D., editors. Proceedings of the Seed and Soil Dynamics in Shrubland Ecosystems, August 12-16, 2002, Laramie, Wyoming. p. 161-163.

Interpretive Summary: Woody shrubs and trees are becoming an increasing problem on grazing lands in the Southwestern United States. These unwanted plants use water that could grow grass, thereby reducing the number of cattle that the area can support. This is an ongoing problem, but recent increases in the amount of carbon dioxide in the air could make this problem worse. Most woody shrubs and trees grow faster when more carbon dioxide is in the air, while most grasses do not. Woody plants are most vulnerable to being killed when they are in the seedling stage, and anything that speeds up their growth in this phase would benefit them. We studied the effects of elevated carbon dioxide on five woody species that commonly invade rangelands in the Southwest. By one week after they germinated, seedlings of all the species were heavier in the higher carbon dioxide atmosphere than they were in a normal atmosphere. The stimulation of growth was greatest for mesquite and huisache, the two species out of the five that are the biggest problem. These same trends continued over the 23 day duration of the experiment. These results indicate that further increases in the amount of carbon dioxide in the atmosphere will greatly increase seedling growth rate in these woody invasive plants. This outcome would result in less and less water and light being available for the grasses, resulting in even lower production of animal protein. Because the amount of carbon dioxide in the air is expected to keep increasing, the problem of woody plant competition with grasses will continue to get worse.

Technical Abstract: Encroachment of woody species into formerly productive rangeland is an immense problem in the Southwest. Effects of predicted global change scenarios on seedlings of such species are largely unstudied. Seedlings of five invasive woody legume species (honey mesquite [Prosopis glandulosa], huisache [Acacia farnesiana], honey locust [Gleditsia triacanthos], Eve's necklace [Sophora affinis], and Paloverde [Parkinsonia aculeate]) were grown for 23 days in glasshouses in Temple, TX, at ambient and twice ambient levels of atmospheric carbon dioxide. Plants were kept well watered and fertilized. Seedlings of all species responded positively in CO2 enrichment, with significant differences in seedling mass observed 1 week after emergence. Mesquite and huisache responded most strongly to elevated CO2. Other work from our laboratory suggests that at least for honey mesquite and huisache, seedling mortality is near zero beyond 3 weeks postemergence, even under water stress conditions. Thus, these invasive species will likely become even more problematic in the future as atmospheric CO2 increases.