Physiological Response of Rough Bluegrass and Creeping Bentgrass to High Temperature Stress.

Rough bluegrass (Poa trivialis L.) exists as both a difficult-to-control weed in cool-season turf and as a valuable overseeding species on bermudagrass (Cynodon sp.) 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 temperatures on ‘Laser’ and ‘Pulsar’ rough bluegrass and ‘L93’ creeping bentgrass (Agrostis palustris L.).  The two rough bluegrass cultivars were selected because they exhibited a wide range of tolerance to summer stress in previous field studies.  The study was a split-plot with three temperatures as main plots, and three cultivars and six harvest dates as subplots.  Plants were established in a greenhouse for 60 days and then moved into one of three growth chambers at 23 (control), 28, or 33^oC until destructively harvested 0, 10, 14, 21, 28, or 35 days after temperature treatments were induced.  Shoot dry weight, relative water content in shoot tissue, chlorophyll content, growth rate and root viability all decreased for both rough bluegrass cultivars at 33^oC compared to 23^oC treatments.  Membrane stability measured as electrolyte leakage rapidly increased in both rough bluegrass cultivars at 33^oC after 21 days of exposure and reflected the rupturing of cells at high temperature.  Total carotenoid content of rough bluegrass cultivars differed at 33^oC, warranting further investigation.  However, there was little separation in physiological measurements among the two rough bluegrass cultivars with the exception of carotenoid content.  Rough bluegrass cultivars consistently exhibited poorer heat tolerance than creeping bentgrass for traits tested.