Two subspecies and a hybrid of big sagebrush: Comparison of respiration and growth characteristics

Environmental temperatures and growth and respiratory characteristics of natural populations of two subspecies and a hybrid of sagebrush ( Artemisia tridentata) that grow on a single hillside were measured to test a hypothesis that adaptation to microclimate temperature patterns restricts these taxa to their native locations and that plant–endophyte associations are important to temperature adaptation. Reciprocal transplants of plants and soil translocation have previously shown that plants grown outside of their native sites or in non-indigenous soil have different respiratory properties and are less vegetatively and reproductively productive than natural populations. A recent study shows that taxa specific endophytes may be responsible for the differences in respiration characteristics and productivity of transplants growing in non-indigenous soils. In this study, hourly temperatures were measured at the upper and lower sites and the newest leaves from natural populations of each subspecies and hybrid were sampled monthly from mid-February to mid-July 2005. Respiratory heat and CO 2 production rates of the leaves were measured at 5 °C intervals from 10 to 35 °C, as well as heats of combustion and carbon and nitrogen contents. Growth rates and substrate carbon conversion efficiencies were calculated from the respiration data. Monthly mean temperature differences of up to 1 °C were measured at the native sites. Differences between the respiratory and growth characteristics of the three populations may explain the hybrid zone architecture of indigenous populations, but are not large enough to explain the different respiratory characteristics and poor survival and productivity of transplants.