Climate change alters global mean surface temperatures and precipitation regimes. This changes the composition and diversity of grasslands worldwide. To date, there are no assessments of plant functional trait responses to experimentally controlled atmospheric drought (separate from soil drought). We examined whether soil and atmospheric drought result in changes to Poa secunda functional traits in monoculture and 8-species grass communities. We focused on SLA, leaf area, stomatal density, root:shoot ratio, and fine root:coarse root ratios. Leaf area and overall growth were higher with increased watering and higher atmospheric moisture in most cases. However, root:shoot ratio significantly increased in atmospheric drought combined with drought watering. Plant energy allocation strategy (measured using PCA) differed when P. secunda was grown in combination soil and atmospheric drought conditions. Our results indicate that methods focused purely on soil water inputs, such as rainout shelters, may be imprecisely predicting drought effects.