Interactive Effects of Elevated Carbon Dioxide and Drought Stress on Hormone Profiles and Associated Changes in Tiller/Stolon Formation and Rooting Characteristics in Creeping Bentgrass.

Atmospheric carbon dioxide (CO₂) concentration has been increasing and is predicted to further increase in the future along with climate changes, such as decline in water availability. Previous studies suggest that elevated CO₂ increases rates of lateral spread for creeping bentgrass plants under well-watered conditions.  Furthermore, the total root length and surface area are increased in the upper 0-10 and 10-20 cm root zones due to elevated CO₂ treatment.  Changes to metabolic pathways and molecular factors, namely hormones, in different plant parts may be responsible for the observed changes in growth and may have great effects on subsequent stress response.  Specifically, the antagonistic or synergistic effects of auxins and cytokinins in a commonly-used perennial turfgrass grown under elevated CO₂ demand further investigation. This study aimed to determine if elevated CO₂ causes changes to hormone profiles in roots versus shoots of creeping bentgrass (Agrostis stolonifera) under well-watered or drought stress conditions and if hormonal changes are associated with changes in tiller formation, stolon elongation and root development and subsequent effects on drought stress mitigation. Tillers from vegetatively-propagated clonal plants were grown in fritted clay medium and exposed to either elevated CO₂ concentration (800 µl L^-1) or ambient CO₂ concentration (400 µl L^-1) for 28 d in growth chambers under well-watered conditions and subsequently subjected to drought stress by withholding irrigation.  Plants were destructively harvested at 20 d drought stress to determine number of tillers per plant, root length, and number of roots per individual tiller as well as IAA, IAA-Asp, cis-Zeatin, trans-Zeatin and trans-Zeatin Riboside (ZR) amounts in shoots and roots via LC/MS-MS method. The elevated CO₂ concentration and drought stress interaction resulted in significant changes to tiller formation and rooting characteristics.  Significant changes to hormone profiles in shoots and roots were also observed and will be discussed.