Physiological Response of Rough Bluegrass (Poa trivialis L.) and Creeping Bentgrass (Agrostis stolonifera L.) to High Temperature Stress.

Roughstalk bluegrass (Poa trivialis L.) exists as both a difficult-to-control weed in cool-season turf and as a valuable overseeding species for bermudagrass (Cynodon dactylon L.) golf greens.  Despite its widespread distribution, little is known of its physiology.  The objective of this study was to evaluate the physiological impact of high temperature on ‘Laser’ and ‘Pulsar’ roughstalk bluegrass and ‘L93’ creeping bentgrass (Agrostis stolonifera L.) to identify mechanisms associated with summer dormancy of roughstalk bluegrass.  The two roughstalk bluegrass cultivars were selected because they exhibited differences in tolerance of summer stress for species in previous field studies.  Plots were established in August 2007 or 2008 from which 10 cm diameter samples were harvested nine times throughout the growing season of the following year.  Turf quality, percent cover, shoot fresh weight, stolon fresh weight, chlorophyll content, electrolyte leakage and root viability data were collected.  Additionally, stolons were individually harvested to collect morphological data.  All collected tissue was later analyzed for total nonstructural carbohydrates, fructans, glucose, total protein and amino-nitrogen.  There was little separation in any measurements between the two rough bluegrass cultivars, however multiple differences were observed between species.  Reductions in shoot dry weight and chlorophyll as well as increased electrolyte leakage indicated elevated stress of both species in response to high temperature stress.  Creeping bentgrass responded to high temperature stress by producing and maintaining more protein in leaves than roughstalk bluegrass.  Alternately, roughstalk bluegrass increased stolon dry weight and protein content in response to high temperature stress.  The differing physiological responses of creeping bentgrass and roughstalk bluegrass to high temperature stress suggests different mechanisms of stress tolerance and helps explain commonly observed decline in quality of roughstalk bluegrass in summer.