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Title: EFFECTS OF ELEVATED CO2 ON GROWTH RESPONSES OF HONEY MESQUITE SEEDLINGS FROM SITES ALONG A PRECIPITATION GRADIENT.

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

Submitted to: Wildland Shrub Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/20/2003
Publication Date: 2/1/2004
Citation: Derner, J.D., Tischler, C.R., Polley, H.W., Johnson, H.B. 2004. Effects of elevated co2 on growth responses of honey mesquite seedlings from sites along a precipitation gradient. pp. 156-160. Wildland Shrub Symposium Proceedings. Laramie, WY.

Interpretive Summary: Plants that grow along wide environmental gradients may display different responses to increased concentrations of atmospheric carbon dioxide (CO2). Honey mesquite is a woody plant that has invaded grasslands in dry areas of western Texas as well as wet areas of central Texas. Our findings indicate that seedlings of plants from along this environmental gradient displayed similar above- and belowground growth enhancement with increases in CO2, suggesting that plants in both dry and wet areas equally respond to elevated CO2. Therefore, this invasive species will likely continue to be a problem species in the future on rangelands of the southern Great Plains. This species may even increase competitiveness at the expense of grasses which grow during the warm portion of the season, and currently dominate these rangelands, as these grasses are generally not as responsive to elevated CO2 as is honey mesquite.

Technical Abstract: We collected seeds from two honey mesquite (Prosopis glandulosa var. glandulosa) trees at each of three sites along an east-west precipitation gradient in Texas: Marlin (93.2 cm mean annual precipitation, MAP), Menard (62.0 cm MAP) and Bakersfield (36.6 cm MAP) to test the hypothesis that CO2 enrichment would differentially affect plant responses along this gradient. However, significant interactions between CO2 and the site of origin were not observed at either harvest (8- or 16-days post-emergence). Growth responses of genotypes of honey mesquite collected from the east-west precipitation gradient were inconsistent with respect to the gradient. Significant growth responses to elevated CO2 often were of small absolute and relative magnitude, especially at the 16-day harvest. If genetic differences exist among the genotypes used in this investigation, they do not affect growth responses to elevated CO2 under well-watered conditions. Similar enhancement of seedling plant growth to elevated CO2 in genotypes of honey mesquite from a wide precipitation gradient suggests that this invasive, woody plant will respond comparably to CO2 enrichment regardless of precipitation at the site of origin. Whether this genetic potential is displayed in the field, however, is uncertain as existing environmental conditions may constrain responses to CO2 enrichment. This invasive species likely will continue to be a problem species on rangelands in the future.