Roots affect the response of heterotrophic soil respiration to temperature in tussock grass microcosms.

While the temperature response of soil respiration (R-S) has been well studied, the partitioning of heterotrophic respiration (R-H) by soil microbes from autotrophic respiration (R-A) by roots, known to have distinct temperature sensitivities, has been problematic. Further complexity stems from the presence of roots affecting R-H, the rhizosphere priming effect. In this study the short-term temperature responses of R-A and R-H in relation to rhizosphere priming are investigated. Temperature responses of R-A, R-H and rhizosphere priming were assessed in microcosms of Poa cita using a natural abundance C-13 discrimination approach. The temperature response of R-S was found to be regulated primarily by R-A, which accounted for 70 of total soil respiration. Heterotrophic respiration was less sensitive to temperature in the presence of plant roots, resulting in negative priming effects with increasing temperature. The results emphasize the importance of roots in regulating the temperature response of R-S, and a framework is presented for further investigation into temperature effects on heterotrophic respiration and rhizosphere priming, which could be applied to other soil and vegetation types to improve models of soil carbon turnover.