Influence of Microclimate and Growth Form on Plant Temperatures of Early Spring Species in a High-elevation Prairie

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Abstract
The influence of microhabitat, growth form and leaf morphology on plant temperatures was investigated for 9 spp. (5 families [Agropyron spicatum (Pursh) Scribn. et Smith, Artemisia frigida Willd., Cirsium centaureae (Rydb.) K. Schum, Gutierrezia sarothrae (Pursh), Britt. et Rusby, Haplopappus acaulis (Nutt.) Gray, Hymenoxis acaulis (Pursh) Paker, Lesquerella ludoviciana (Nutt.) Wats., Penstemon eriantherus (Pursh) and Zigadenus venenosus Wats.]) that were first to appear in early spring at a high-elevation, shortgrass prairie site in southeastern Wyoming [USA]. Aboveground plant growth prior to the measurement period was restricted to south-facing slopes, and all species, except one, had leaf temperatures that were substantially higher than air temperature during the daytime. Maximum increases (> 15.degree. C) above ambient air temperature occurred in a cushion plant (Haplopappus acaulis) and a broadleaf species (Penstemon eriantherus) that had relatively large leaves in close contact with the soil surface. Leaf temperatures > 10.degree. C above air temperature also occurred for 2 spp. (Hymenoxys acaulis and G. sarothrae) whose current-year growth was sheltered by old vegetative growth. Artificially disturbing microsite and growth characteristics resulted in major reductions in plant temperatures to within about .+-. 2.degree. C of ambient air temperature. Only 1 (Z. venenosus) of the 9 spp. that first appeared in early spring did not have elevated leaf temperatures or any apparent growth characteristics that would contribute to such elevations. Thus, variation in microsite, growth form and leaf morphology in these early spring species appears to contribute substantially to the avoidance of low temperatures during a portion of the season when growth may be limited by temperature.