Mean global surface temperatures have risen by 0.74 °C in the past century, partially due to daily minimum temperatures increasing proportionately greater than daily maximum temperatures. Alterations in daily temperature dynamics have been attributed to greater water vapor in the atmosphere, which dampens temperature extremes by reducing daytime solar radiation at the soil surface and increasing downward longwave radiation at night. Subsequently, we have established soil temperature manipulation experiments to study the importance of dampening soil temperature fluctuations, predicted to occur with climate change, on carbon and nitrogen dynamics in a creosotebush bajada in the Chihuahuan Desert (Big Bend NP, Texas). We dampened soil temperature extremes by suspending 50% white polyethylene shade cloth onto a raised PVC frame over ten 4x3 m quadrats, leaving shrubs uncovered. This design minimized alterations to the soil surface boundary layer and allowed precipitation to reach the soil. Generally, soil temperatures in shaded plots were higher at night and reduced or similar during the day compared to unshaded plots depending on time of year. Shading dampened temperature fluctuations more at the soil surface (fluctuations of 33.4 and 26.8 ºC for unshaded and shaded plots, respectively) than at 15 cm depth (10.3 and 7.4 ºC, respectively).

Results/Conclusions

In 2008 and 2009 the resulting decrease in daily soil temperature fluctuations increased soil moisture by 15% and increased microbial biomass C and N (by 78% and 39%, respectively) and reduced soil available N (26.8% and 13.4% for NH₄⁺-N and NO₃^--N, respectively). The dominant plant species Larrea tridentata (creosotebush) has not shown a physiological response to changes in available soil N levels. Larrea exhibits strong stomatal control of photosynthesis and is more greatly affected by plant water status than by soil nutrient levels. Alterations in soil temperature regimes in arid systems may have greater implications for the C and N balance (either directly, or, indirectly via changes in hydrological balance) than an overall change in mean daily temperature.