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Title: RESPONSE OF SEEDLINGS OF TWO HYPOGEAL BRUSH SPECIES TO CO2 ENRICHMENT

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

Submitted to: Wildland Shrub Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/28/2006
Publication Date: 7/25/2007
Citation: Tischler, C.R., Derner, J.D., Polley, H.W., Johnson, H.B. 2007. Response of seedlings of two hypogeal brush species to co2 enrichment. Proceedings: Shrubland dynamics - fire and water. p. 104-106.

Interpretive Summary: Research has demonstrated that elevated levels of atmospheric carbon dioxide make young plants grow and develop more rapidly. Most of this research has been done with plants with small seed and leaves that are already formed in the seed, and just expand when the plant emerges from the soil. We studied the effects of elevated atmospheric carbon dioxide on seedlings of two woody shrub plants, Guajillo and Cat Claw Acacia. Each of these species has relatively large seed, and does not have pre-formed leaves in the seed. We found that these two species responded to elevated carbon dioxide much slower than small-seeded species with pre-formed leaves. These results indicate that the growth form of a seedling has a direct influence on how it responds to elevated carbon dioxide. Therefore, seedling growth form must be considered when predicting effects of increasing atmospheric carbon dioxide on competitiveness of woody brush species.

Technical Abstract: Previous work demonstrated that epigeal woody invasive plants (with expanding, photosynthetic cotyledons) such as honey mesquite (Prosopis glandulosa L.) respond positively to elevated atmospheric CO2 concentrations within three days after emergence. The behavior of larger seeded, hypogeal invasive plants (common in South Texas) exposed to elevated CO2 has not been addressed. We studied two such species, Guajillo (Acacia berlandieri Benth.) and Cat Claw Acacia (Acacia greggii var. wrightii), to quantify growth stimulation at a doubled concentration of CO2. Seedlings were grown in glasshouses in 1.5 m tubes at Temple, TX in the late summer of 2000. Only seeds within a narrow range of masses were selected for each species, to limit effects of seed mass on seedling size. Plants were harvested 15 days after emergence. Leaf area, shoot weight, leaf weight, root weight, and depth of root penetration were determined for each plant. Both species exhibited appreciable root length at sampling, with mean values of about 75 and 90 cm for A. berlanderi and greggii var. wrightii, respectively. For both species, all parameters demonstrated a positive numerical response to elevated CO2, although no differences were statistically significant. The lack of statistical verification was likely caused by the variability observed within each species. For example, values for specific parameters varied by as much as a factor of six within a species and CO2 treatment. These results suggest that seedling growth responses to elevated CO2 may be smaller in hypogeal than in co-occurring epigeal species.