Effects of differential air and soil temperature on carbohydrate metabolism in creeping bentgrass

Bentgrass quality often declines under high temperature conditions, The physiological mechanisms of heat stress injury in creeping bentgrass are not well understood. The objective of this study was to determine the relative importance of air vs, soil temperature in the regulation of carbohydrate metabolism in two cultivars of creeping bentgrass (Agrostis palustris Huds,), 'L-93' and 'Penncross', Shoots and roots of both cultivars were exposed to four differential air/soil temperatures: 20/20 (control), 20/35, 35/20, and 35/35 degrees C in growth chambers and water baths, Under high soil (20/35) and high air/soil (35/35 degrees C) temperature conditions, canopy net photosynthetic rate (P-n) of L-93 and Penncross decreased dramatically; however, respiration rates of whole plants (R-plant) and roofs (R-root) increased to levels above those at 20/20 and 35/20 degrees C within 8 d of treatment and then decreased to lower levels by 21 d after treatment. At 35/35 degrees C, daily carbon consumption was 2 to 5 times carbon production for L-93 and 3.5 to 12 times for Penncross, At 20/35 degrees C, carbon consumption exceeded production within 10 d of treatment for both cultivars, Total nonstructural carbohydrate (TNC) contents in shoots and roots were reduced at 20/35, 35/20, and 35/35 degrees C, compared to that at 20/20 degrees C. Reducing soil temperature while exposing shoots to high temperature (35/20 degrees C) increased P-n and carbohydrate content and reduced the carbon consumption to production ratio. The results suggested that roots play more important role than shoots in the mediation of carbohydrate responses to high air temperatures or high soil temperatures, High soil temperature alone or combined with high air temperature caused imbalance between photosynthesis and respiration and decreases in carbohydrate availability, which could contribute to the decline in shoot and root growth under high temperature conditions.