Plant growth response to direct and indirect temperature effects varies by vegetation type and elevation in a subarctic tundra

There has been growing recent use of elevational gradients as tools for assessing e? ects of temperature changes on vegeta- tion properties, because these gradients enable temperature e? ects to be considered over larger spatial and temporal scales than is possible through conventional experiments. While many studies have explored the direct e? ects of temperature, the indirect e? ects of temperature through its long-term in? uence on soil abiotic or biotic properties remain essentially unexplored. We performed two climate chamber experiments using soils from a subarctic elevational gradient in Abisko, Sweden to investigate the direct e? ects of temperature, and indirect e? ects of temperature via soil legacies, on growth of two grass species. ? e soils were collected from each of two vegetation types (heath, dominated by dwarf shrubs, and meadow, dominated by graminoids and herbs) at each of three elevations. We found that plants responded to both the direct e? ect of temperature and its indirect e? ect via soil legacies, and that direct and indirect e? ects were largely decoupled. Vegetation type was a major determinant of plant responses to both the direct and indirect e? ects of temperature; responses to soils from increasing elevation were stronger and showed a more linear decline for meadow than for heath soils. ? e in? uence of soil biota on plant growth was independent of elevation, with a positive in? uence across all elevations regardless of soil origin for meadow soils but not for heath soils. Taken together, this means that responses of plant growth to soil legacy e? ects of temperature across the elevational gradient were driven primarily by soil abiotic, and not biotic, factors. ? ese ? ndings emphasize that vegetation type is a strong determinant of how temperature variation across elevational gradients impacts on plant growth, and highlight the need for considering both direct and indirect e? ects of temperature on plant responses to future climate change.