Soil Temperature Effects on Root Respiration and the Ecology of Alpine and Subalpine Plants

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Abstract
Root respiration rates of Geum rossii (R. Br.) Ser. G. triflorum Pursh and populations of Achillea millefolium L. from elevations of 2400-3220 m were compared at 4, 10, 18 and 25.degree. C to determine whether soil temperature is important in controlling distribution of plants relative to alpine timberlines. Respiration was measured as a function of O2 uptake by detached roots and was determined with an O2 electrode. Comparisons of rates of roots and caudex tissue from mature plants collected in the field before and after 3 wk of growth in cold (4-10 C) or warm (15-25 C) soils and again following reversal of conditions showed that the alpine endemic G. rossii maintained higher rates than the subalpine G. triflorum; alpine populations of Achillea likewise had higher rates than populations from more subalpine habitats. Aerial conditions for all plants were about the same. Similar results were obtained in comparing respiration rates of 14 day old Achillea seedlings germinated and grown at 26.degree. C for 20 h and 10.degree. C for 4 h, with a 16 h photoperiod daily. No differences were observed between seedlings of the 2 Geum spp., apparently due to a strong selection for heat-resistant individuals as indicated by the differences in seedling mortality. There are apparently inherent tendencies for alpine plants to have higher root respiration rates than subalpine plants, which could make them more competitive under alpine conditions, but could produce a wasteful metabolic rate in the warmer conditions of the subalpine. Estimations of root and shoot growth support the conclusion that soil temperatures could be an important factor in determining plant distribution patterns about alpine timberlines.