Rapid plant community responses to nighttime warming in a desert grassland

We report the results of a multifactor global change experiment in a desert grassland, located at the Sevilleta LTER in central New Mexico. Starting the summer of 2006, we imposed nighttime warming and N addition treatments. In 2007 we will add an El Niño treatment of winter water addition. Here we report the results of the first growing season with warming and N addition. We used a novel technique to impose nighttime warming, in which aluminum fabric is unrolled over the vegetation each night and rolled up each morning. This fabric reflects the longwave radiation emitted from the ground, which would otherwise be lost to space, back onto the vegetation and increases daily minimum temperatures by 1.5 – 2 °C. We applied N at a rate of 1 g/m² in July and measured plant species cover in September. Warming and N addition both increased total cover. Control plots had 32% cover, N addition plots had 39% cover, warmed plots had 40% cover, and plots with both warming and N addition had 41% cover. Subshrubs increased from 9 to 20% cover comparing control and warmed plots. NO₃ supply, as measured with Plant Root Simulator probes, increased by 28% in the N addition plots. NO₃ supply in warmed plots was 12% higher than in control plots, but this difference was not statistically significant. Our results demonstrate rapid plant community responses to nighttime warming in a desert grassland.