The mechanisms that control adaptation and acclimation of plants to high temperature soils are essential to our understanding of natural, agricultural and leisure environments. Respiration is a major avenue of carbohydrates loss. Shortage of assimilates due to high respiratory losses has long been proposed to be a primary factor responsible for root growth inhibition. In the current study, responses of root membrane permeability, RGR, root maximal length, total respiration rates and its components (maintenance, growth and ion uptake), RQ and net NO3– uptake rates (NNUR) to high soil temperature were evaluated in two Agrostis species: Agrostis scabra, a heat tolerant grass collected from the Yellowstone National Park is adapted to high-temperature soils, and two creeping bentgrasses (A. palustris) cultivars, ‘L-93' and ‘Penncross' that differ in their heat sensitivity. The plants were studied following subjection of roots either to high temperature (37oC) or to the optimum temperature (20oC). Total root respiration and the specific respiratory costs for maintenance and ion uptake increased under high temperatures in all species. Agrostis scabra exhibited higher heat tolerance in all parameters including moderate decreases under 37oC in RGR, root maximal length and NNUR. In addition it had the smallest increases for root respiration and for the specific respiratory costs of maintenance and ion uptake. Our results indicate that carbon utilization may play an important role under high soil temperatures. Heat tolerance of roots was related to the ability to control respiratory costs and increase their respiratory efficiency by lowering their maintenance and ion uptake costs.