Herman S. Mayeux

Viewpoint: atmospheric CO2, soil water, and shrub/grass ratios on rangelands.

The abundance of woody plants on grasslands and savannas often is controlled by the availability of water and its location in soil. Water availability to plants is limited by precipitation, but the distribution of soil water and period over which it is available in these ecosystems are influenced by the transpiration rates of grasses. We discuss implications of recent and projected increases in atmospheric CO2 concentration for transpiration, soil water availability, and the balance of grasses and shrubs. An increase in CO2 concentration often reduces potential transpiration/leaf area by reducing stomatal conductance. On grasslands where effects of stomatal closure on transpiration are not negated by an increase in leaf temperature and leaf area, rising CO2 concentration should slow the depletion of soil water by grasses and potentially favor shrubs and other species that might otherwise succumb to water stress. Predicted effects of CO2 are supported by results from CO2-enrichment studies in the field and are compatible with recent models of interactions between resource levels and vegetation pattern and structure.

Growth and Gas Exchange of Oats (Avena sativa) and Wild Mustard (Brassica kaber) at Subambient CO 2 Concentrations

A repeated sequence of monocultures and mixtures of oats (Avena sativa L.) and wild mustard (Brassica kaber (DC.) Wheeler) was grown along a daytime gradient of CO₂ concentrations ([ CO₂]) from near 330 to a minimum of <tex-math>

Leaf and Plant Water use Efficiency of C4 Species Grown at Glacial to Elevated CO2 Concentrations

150\ \mu {\rm mol}\ {\rm mol}^{-1}

Diurnal measurements of honey mesquite transpiration using stem flow gauges.

</tex-math>. The objectives were to determine effects of subambient [ CO₂] on leaf gas exchange, biomass production, and competitive interactions of these C₃ species. A decrease in stomatal conductance did not prevent a nearly linear increase in leaf internal [ CO₂] and net assimilation of oat leaves as [ CO₂] increased. Net assimilation of oats and wild mustard increased from 5.0 and <tex-math>

Environment and seedling age influence mesquite response to epicotyl removal.

2.5\ \mu {\rm mol}\ {\rm m}^{-2}\ {\rm s}^{-1}

Increase in C3 plant water-use efficiency and biomass over Glacial to present CO2 concentrations

</tex-math> at <tex-math>

Stomatal Density and Aperture Length in Four Plant Species Grown Across a Subambient CO 2 Gradient

150\ \mu {\rm mol}\ {\rm mol}^{-1}

12 – Are Some of the Recent Changes in Grassland Communities a Response to Rising CO2 Concentrations?

</tex-math>, respectively, to 16.1 and <tex-math>

Acclimation of whole-plant Acacia farnesiana transpiration to carbon dioxide concentration.

15.9\ \mu {\rm mol}\ {\rm m}^{-2}\ {\rm s}^{-1}

CRP increases soil organic carbon

</tex-math> at <tex-math>