Growth and carbohydrate metabolism of creeping bentgrass cultivars in response to increasing temperatures

High temperature is a major factor limiting growth of creeping bentgrass (Agrostis palustris Huds.). Physiological causes of turf growth and quality decline with increasing temperature is not well understood. The objective of the study was to examine responses of growth and carbohydrate metabolisms to increasing temperatures in three creeping bentgrass cultivars. Sods of 'Penncross', 'ISI-AP-89150', and 'SR 1020' were grown in growth chambers and exposed sequentially for 20 d to each of the following temperatures: 20, 24, 30, 33, and 38 degrees C. Evaluation and measurements were made at 10 and 20 d after each sequential temperature increase. Decreased root viability and root dry matter production of all cultivars was observed after a 10-d exposure at 30 degrees C and continued to decline with increasing temperatures. A decline in turf quality and leaf chlorophyll content (Chl) was observed at a 20-d exposure to 30 degrees C. Turf quality, Chl content, and root viability of SR 1020 were higher than those of Penncross after a 10-d exposure at 30 degrees C and 20 d at 34 degrees C, and 10 d at 38 degrees C, respectively. Canopy net photosynthetic rate (P-n) decreased with temperature in all cultivars. Dark respiration rates of whole plants (R-plant) increased with temperature up to 34 degrees C, and then declined at 38 degrees C. Daily carbon consumption to production ratio increased dramatically with temperature after 30 degrees C, and R-plant exceeded P-n when temperature increased to 34 or 38 degrees C in all cultivars. Plants grown at 30, 34 and 38 degrees C had lower total nonstructural carbohydrate than those grown at 20 or 24 degrees C. Results suggest that a decline in root activity of creeping bentgrass occurred before a decline in turf quality at temperatures above 30 degrees C, and could be related to the imbalance between photosynthesis and respiration, and limited carbohydrate availability.