Wetland plant water-use strategies: species composition drives trends in wetland evapotranspiration

Background/Question/Methods

In Colorado, wetlands comprise only 2% of total land mass, but provide outsized benefits in terms of wildlife habitat and flood mitigation. However, much of the wetland area have been impacted by human development, and so many wetlands are restored or created to mitigate development. Therefore, whether these created and/or restored wetlands function the same as native wetlands is unknown. Understanding plant water use patterns in restored wetlands is critical in water-scarce Colorado, because if a restoration project increases water demand on a riparian system, it must obtain water rights. Little research has explored differences in daily transpiration across wetland plant species. To investigate the water-use patterns of different species growing across a range of wetland types, we collected water-use data from five restored wetlands on the Front Range. We measured the turgor loss point for each species, and then measured diurnal patterns of stomatal conductance, leaf water potential, and micrometeorological variables to identify when plants reduced water loss. We correlated the stomatal to leaf water potential and VPD to evaluate how these variables impacted the water-use of species at different temporal scales (daily and seasonal).

Results/Conclusions

Our preliminary data demonstrate different wetland plant species exhibit unique patterns and amounts of water use throughout the day. Given these disparate patterns, we asked how much water are wetlands using in the front range, and does species composition drive differences between wetland water use? Second, what are the physiological mechanisms that vary in wetland plants, and what triggers stomatal closure? To address these questions, we quantified the daily transpiration per species with a porometer and scaling up this data to the wetland canopy to model diurnal water use of wetlands with different species composition. We also investigated the diurnal plant-water relations of five dominant species in detail, to understand the drivers of stomatal conductance. Some species, including Salix exigua and Populus deltoides, display conservative water-use strategies and limit stomatal conductance when approaching turgor loss point. Other species, including Carex emoryi, display less conservative water-use strategies and do not regulate stomatal conductance until leaf water potential reaches turgor loss point. The results of this project will assist water rights holders along Colorado rivers make data-informed restoration decisions about water rights and wetland water use.