Temperature dependence of respiration in roots colonized by arbuscular mycorrhizal fungi

• The arbuscular mycorrhizal (AM) symbiosis is ubiquitous, and the fungus represents a major pathway for carbon movement in the soil-plant system. Here, we investigated the impacts of AM colonization of Plantago lanceolata and temperature on the regulation of root respiration (R). • Warm-grown AM plants exhibited higher rates of R than did nonAM plants, irrespective of root mass. AM plants exhibited higher maximal rates of R (R_max - R measured in the presence of an uncoupler and exogenous substrate) and greater proportional use of R_max as a result of increased energy demand and/or substrate supply. The higher R values exhibited by AM plants were not associated with higher maximal rates of cytochrome c oxidase (COX) or protein abundance of either the COX or the alternative oxidase. • Arbuscular mycorrhizal colonization had no effect on the short-term temperature dependence (Q₁₀) of R. Cold-acclimated nonAM plants exhibited higher rates of R than their warm-grown nonAM counterparts. By contrast, chilling had a negligible effect on R of AM-plants. Thus, AM plants exhibited less cold acclimation than their nonAM counterparts. • Overall, these results highlight the way in which AM colonization alters the underlying components of respiratory metabolism and the response of root R to sustained changes in growth temperature.