Kimberly O’Keefe & Jesse B. Nippert
Plants lose water from their leaves through the process of transpiration. While transpiration primarily occurs during the day, recent research has discovered that many plant species also lose water at night. This “nocturnal transpiration” can have substantial consequences on plant functioning and on ecosystem water budgets. However, what causes nocturnal transpiration is still unknown. Understanding the drivers of nocturnal transpiration among coexisting species of varying plant types will be particularly important for predicting how ecosystem water budgets may change during future climate changes.
In this study we assessed how nocturnal transpiration varies across different plant groups (grasses, shrubs, and broad-leaved plants), what factors impact nocturnal transpiration for these different groups, and whether these factors differ from those impacting daytime transpiration. We measured daytime and nocturnal transpiration in eight plant species located in a North American tallgrass prairie. We also measured a variety of environmental factors that might influence how much water is lost by these plants at night.
We found that nocturnal transpiration varied across different plant groups, with grasses having the highest rates of nocturnal water loss. In grasses and shrubs, nocturnal transpiration was greater when water was more available to plants and decreased when the soil became dry. Nocturnal transpiration also decreased when the atmosphere became drier. Daytime transpiration responded differently to these same environmental factors.
The high rates of nocturnal water loss observed in grasses, as well as the widespread global occurrence of grasses, suggests that nocturnal transpiration may contribute more to water cycling in ecosystems than previously estimated. These results also suggest that nocturnal transpiration may act as a competitive strategy within a plant community. We propose that tallgrass prairie grasses transpire at night during periods of greater water availability to maximize resource consumption, which in turn reduces the amount of water available in the soil to other plant species.