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ARS Home » Research » Publications at this Location » Publication #72965


item Tischler, Charles
item Polley, Wayne
item Johnson, Hyrum
item Mayeux Jr, Herman

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mesquite is a woody plant which invades rangeland in the southwestern United States. Although large mesquite plants normally live for decades, during the first year of growth a mesquite plant may be killed by drought, gnawing rodents, or competition from neighboring plants. Increasing atmospheric carbon dioxide is known to increase the growth rate of large mesquite plants, but the effects on seedlings have not been studied. We tested the effect of elevated carbon dioxide on growth of mesquite seedlings grown both with and without fertilizer and on survival of mesquite seedlings after the shoot was clipped. We found that elevated concentrations of carbon dioxide made the mesquite seedlings grow faster, especially if they were fertilized. The plants grown at elevated carbon dioxide were not only bigger, but were further developed, as they lost their first leaves faster than plants grown at the present carbon dioxide concentration. Also, we found that even at the present carbon dioxide concentration, two-day-old mesquite seedlings could survive if the developing shoot was cut off above the cotyledons. These results indicate that increasing atmospheric carbon dioxide will make mesquite seedlings better able to survive their first year, and thus develop into a large plant which will persist for decades. Because of this, mesquite will very likely become even a greater problem on rangelands in the Southwest in the future.

Technical Abstract: Herbivory by small mammals is a major factor controlling survival and growth of honey mesquite (Prosopis glandulosa Torr. var. glandulosa) seedlings. Young mesquite seedlings are killed when the shoot is cut below the cotyledons. Removal of the epicotyl may not be lethal but can severely limit seedling growth. Though not reported for mesquite, seedlings of other woody species sometimes compensate for epicotyl removal by prolongin the life of cotyledons. Objectives of this study were to determine effects of atmospheric CO2 concentration, soil fertility, and seedling age at epicotyl removal; factors potentially influencing seedling growth and recovery from defoliation; on (1) shoot and root growth of young honey mesquite seedlings, (2) cotyledonary leaf longevity, and (3) seedling survival. Mesquite seedlings were grown at 350, 700, and 1,000 ppm CO2 both with and without fertilizer addition to a nutrient-poor silty clay loam soil. Clipping treatments (epicotyl removal, unclipped controls) wer imposed at dates ranging from 2 to 12 days post-emergence. Root and shoot characteristics of plants were measured 14 days after clipping. Cotyledonary leaf fresh mass and chlorophyll content were strikingly higher in clipped than control plants in all cases. Root and shoot mass of both clipped and unclipped plants generally increased at higher CO2 concentrations when mineral nutrition was adequate, but responded little to CO2 when grown in nutrient-poor soil. All seedlings survived epicotyl removal. The responses of mesquite seedlings to epicotyl removal appear to be influenced by many factors.