Rising water-use efficiency in European grasslands is driven by increased primary production

This work is part of eLTER PLUS T9.3 and uses multiple eLTER sites to evaluate already available data from remote sensing and re-analyses. Specifically, eddy covariance data on evapotranspiration and gross primary production is used to validate the spatial data products. Relating the gross primary production to the evapotranspiration, the water-use efficiency of an ecosystem then indicates the water-use strategy of the vegetation and the variability of its functionality. 

We calculated three different indices of water-use efficiency using the spatial data across the pan-European domain and found that Central and Eastern Europe experienced decreasing water-use efficiency within the last two decades and are therefore threatened in their performance. On the other hand, European grasslands drastically increased their water-use efficiency during that time. During droughts, arid and semiarid ecosystems were able to increase their water-use efficiency through adaptation of stomatal conductance. 

These results indicate that Central and Eastern European ecosystems could be threatened by an increasingly dry environment in future, and that an adaptive water-use strategy, as seen in arid ecosystems, is key to maintain functionality with those changes.