There is a general consensus that there has been an anthropogenic warming signal over the past half century and that the warmer temperatures are due to a twofold greater increase in minimum than maximum temperatures.  Increased tree growth, crop yield and NDVI indices have been related to the warmer night temperatures, presumably due to longer growing seasons.  However, chamber and modeling results have been unable to reproduce these observed growth increases, but instead show reduced growth due to higher respiratory costs.  Here, I present the results of whole ecosystem gas exchange measurements of twelve reconstructed prairie ecosystems exposed to ambient, symmetric, asymmetric and night-warming-only treatments.  Results from first season measurements show that increased carbon gain with concomitantly warmer mornings helped to offset the increased respiratory costs.  Future comparisons after several years of treatment exposures will show whether these offsetting C fluxes lead to alterations in system C storage, or whether changes in species composition or altered water or N availability interact with expectations based on first season measurements.