ARS | Publication request: SEEDLING GROWTH OF TWO HONEY MESQUITE VARIETIES UNDER CO2 ENRICHMENT

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2004
Publication Date: May 15, 2005
Citation: Derner, J.D., Tischler, C.R., Polley, H.W., Johnson, H.B. 2005. Seedling growth of two honey mesquite varieties under CO2 enrichment. Rangeland Ecology and Management. 58:292-298.

Interpretive Summary: Land managers need to understand whether plant species vary in their responses to rising atmospheric carbon dioxide (CO2) concentrations, and how those responses vary in different environments. Honey mesquite (Prosopis glandulosa) is a noxious shrub that has invaded many former grasslands in the southwestern US, with one ecotype that grows in wet environments and another in dry environments. An experiment was conducted to determine how these two shrub ecotypes respond to increased levels of CO2. Carbon investment was initially allocated aboveground to develop photosynthetic area (leaves) for honey mesquite seedlings, and then allocated later to root systems. Both ecotypes responded similarly to elevated CO2 with ample soil water, suggesting that this species will continue to be problematic for land managers across many environments.

Technical Abstract: Seedlings of two varieties of honey mesquite (Prosopis glandulosa) were exposed to two concentrations of atmospheric CO2 (368 and 704 µmol mol-1) in environmentally-controlled glasshouses under near-optimal temperature and soil water conditions to determine if CO2 enrichment alters above- and belowground growth responses. CO2 enrichment substantially enhanced both above- and belowground growth variables of honey mesquite seedlings for all harvest dates (8-, 16- and 24-days post emergence). This growth enhancement was greater for aboveground variables (21-35%) at the first harvest, greater for belowground variables (36-40%) at the second harvest, and similar for both above- (13-68%) and belowground (10-40%) variables at the last harvest. Differences in temporal growth enhancement associated with CO2 enrichment suggest changing carbon allocation priorities with initial carbon investment allocated primarily aboveground to develop photosynthetic machinery, and carbon predominately allocated later to increased investment in roots. The absence of significant CO2 X variety interactions at any harvest date provides evidence that CO2 enrichment did not exaggerate intraspecific variation in above- and belowground responses between the two honey mesquite varieties. Although CO2 enrichment did not exaggerate intraspecific variation in this species, it is evident that honey mesquite seedlings possess the capacity to markedly respond to CO2 enrichment; as such, this species should continue to be a problematic species for rangeland managers.