Rapid plant community responses during the summer monsoon to nighttime warming in a northern Chihuahuan Desert grassland

Global environmental change is altering temperature, precipitation patterns, and resource availability in aridland ecosystems. In 2006, we established a multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric N deposition, and more frequent occurrence of El Niño years on plant community dynamics in a northern Chihuahuan Desert grassland. Here we only report the results of warming and N addition from the first monsoon growing season prior to the imposition of the precipitation treatments. Our passive nighttime warming treatment increased daily minimum temperatures by 1.4–3.0 °C. Fertilization increased NO3N supply, as measured with Root Simulator Probes, by 28% and NO3N supply in warmed plots was 12% higher than in control plots. After one monsoon season we found that warming significantly increased total plant cover. Responses among dominant species varied, however. Warming significantly increased cover of Bouteloua eriopoda (P < 0.05) and tended to increase cover of the shrub Gutierrezia sarothrae (P = 0.064), whereas N addition significantly increased the cover of Bouteloua gracilis (P < 0.05). Our results demonstrate that rapid soil and plant community responses can occur in response to nighttime warming and N fertilization during one monsoon season in this semi-arid desert grassland. The sensitivity of this desert system to key drivers of global environmental change suggests that further increases in temperature and atmospheric deposition will likely alter community structure and ecosystem functioning in this and other aridland ecosystems.