Warming and the dependence of limber pine (Pinus flexilis) establishment on summer soil moisture within and above its current elevation range.

摘要: Continued changes in climate are projected to alter the geographic distributions of plant species, part by affecting where individuals can establish from seed. We tested hypothesis that warming promotes uphill redistribution subalpine tree populations reducing cold limitation at high elevation and enhancing drought stress low elevation. seeded limber pine (Pinus flexilis) into plots with combinations infrared heating water addition treatments, sites positioned lower forest, treeline ecotone, alpine tundra. In 2010, first-year seedlings were assessed for physiological performance survival over snow-free growing season. Seedlings emerged midsummer, about 5–8 weeks after snowmelt. Low temperature was not observed limit seedling photosynthesis or respiration between emergence October, thus experimental did appear reduce Instead, gas exchange potential all indicated a prevailing effect summer moisture on carbon balance. Infrared heaters raised soil degree days (base 5 °C, p < 0.001) August–September mean (p < 0.001). Despite marked differences vegetation cover meteorological conditions across sites, volumetric content (θ) 5–10 cm below 0.16 0.08 m3 m−3 consistently corresponded moderate severe indications midday stem potential, stomatal conductance, photosynthesis, respiration. Seedling greater watered than heated (p = 0.01), negatively related duration exposure θ < 0.08 m3 m−3 stepwise linear regression model (p < 0.0001). concluded seasonal surface imposed strong establishment broad gradient, including treeline, these limitations likely be enhanced further warming.