Carbon economy in plants is closely linked with nitrogen economy and both processes play a major role in plant adaptation to environmental stresses. We studied changes in the acquisition and partitioning of carbon and nitrogen associated with root tolerance to high soil temperature for two Agrostis species: thermal Agrostis scabra, a species adapted to high-temperature soils in geothermal areas in Yellowstone National Park, and two cultivars of a cool-season turfgrass species, A. stolonifera (creeping bentgrass), ‘L-93' and ‘Penncross', that differ in their heat sensitivity. Roots of thermal A. scabra and both creeping bentgrass cultivars were exposed to high soil temperature (37oC) or optimum soil temperature (20oC). Net Photosynthesis rate (Pn), photochemical efficiency (Fv/Fm), NO3- assimilation and root viability decreased with increasing soil temperatures in both species. However the decreases were less pronounced for A. scabra than for both creeping bentgrass cultivars (e.g., Fv/Fm decreased by 25% for A. scabra upon exposure to high temperature for 28 days, as compared with 57and 73% in ‘L-93' and ‘Penncross', respectively). Carbon expenditure in growth of plants exposed to 37oC decreased significantly in both creeping bentgrass cultivars as compared to A. scabra. Exposure to 37oC for 28 days resulted in total carbon allocation only to respiration in both creeping bentgrass cultivars, whereas in A. scabra, carbon was allocated to both respiration and growth. Exposure to 37oC resulted in an increased nitrogen allocation to roots correlated with a decreased allocation to the shoots. However, at 37oC nitrogen allocation to the shoots, in A. scabra was higher than the shoot nitrogen allocation in both creeping bentgrass cultivars throughout the whole experiment. The ability of roots to tolerate high soil temperatures could be related to the capacity to control carbon and nitrogen budgets by increasing the efficiency of carbon and nitrogen metabolism.