Effects of Elevated Atmospheric Carbon Dioxide on Drought Tolerance and Post-Drought Recovery of Kentucky Bluegrass.

Drought stress due to lack of rainfall or irrigation is detrimental to plant growth, including to the critically important meristematic tissues, such as rhizomes, which produce daughter plants or shoots and roots in turfgrass. However, drought stress can induce dormancy of these growing points and in prolonged periods of drought can even cause mortality that can result in permanent loss of turf stands. Thus, the ability to maintain active growth during prolonged stress periods or to quickly recover once the stress has subsided is highly dependent upon the viability or level of damage to the meristematic tissues in these growing organs. Elevated atmospheric CO₂ concentration has been found to enhance drought tolerance, but CO₂ effects on the growth and survival of rhizomes in Kentucky bluegrass are unknown. The study was designed to determine whether elevated CO₂ concentration would alleviate drought damages in rhizomes and enhance drought tolerance and post-drought recovery through regrowth of meristematic and leaf tissues. Plants of rhizomatous Kentucky bluegrass (Poa pratensis cv. Baron) that were grown at elevated CO₂ concentration (800 µL L-1) under drought stress maintained higher membrane stability, leaf water content, and visual turf quality (TQ), and Kentucky bluegrass rhizome nodes exhibited lesser damages, as manifested by higher tissue viability and increased levels of auxin (IAA) and cytokinin (ZR) and decreased levels of abscisic acid (ABA) compared with plants at ambient CO₂ (400 µL L-1). Upon re-watering, plants that were exposed to drought stress under elevated CO₂ exhibited increased growth of total shoot and daughter plant biomasses and an increased number of rhizomes, as well as higher % coverage and greenness compared to plants at ambient CO₂ levels. The results suggest that the enhanced drought tolerance and subsequent regrowth at elevated CO₂ could have protective effects on growing points, facilitating drought survival of Kentucky bluegrass.