Effects of Elevated Carbon Dioxide On Rooting Characteristics and Consequential Impact On Drought Tolerance in Creeping Bentgrass (Agrostis stolonifera).

Atmospheric carbon dioxide (CO₂) levels continue to rise and are predicted to double over the next century.  Previous studies on grass and agronomic species reported increased root biomass when plants were grown under elevated CO₂.  However, the specific rooting characteristics or traits that may account for the improved root growth as well as metabolic factors controlling CO₂-enhanced root growth are not well documented.  The goals of this study were to 1) describe the specific changes in root morphology for creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) plants grown from tillers in elevated (800±10 ppm) CO₂ as compared to plants in ambient (400±10 ppm) CO₂ and 2) evaluate whether the increased root growth would lead to improved drought tolerance and higher turf quality during soil water deficit.  Tillers were transplanted into pots containing fritted-clay medium and allowed to establish under elevated or ambient CO₂ levels.  Plants were harvested after 34 days for evaluation of root morphological characteristics in the 0-10, 10-20, 20-30, and 30-40 cm root zones.  Additional plants were exposed to drought stress by withholding irrigation for 18 days with soil water content dropping below 7%.  Bentgrass grown under elevated CO₂ showed a 30% increase in root length, surface area, and total volume in the 0-10 cm zone compared to plants under ambient CO₂ levels.  When irrigation was withheld and drought stress imposed, leaves of creeping bentgrass under elevated CO₂ maintained higher water content and membrane stability indicating better drought performance.  However, under elevated CO₂ conditions, plants showed a decrease in leaf chlorophyll content which may indicate rapid nutrient (nitrogen) depletion from the root zone.  Future work may investigate biochemical aspects associated with enhanced drought tolerance of creeping bentgrass under elevated CO₂.