Leaf water potential

We routinely measure leaf water potential during the growing season. Since 2004, we’ve measured the predawn leaf water potential of six species at weekly to biweekly intervals. In recent years, we’ve also made periodic measurements of midday leaf water potentials.

Trees in the MOFLUX forest experience a broad range of water deficit stress. In some years there is very limited stress (e.g., 2009) and in others, intense stress (e.g., 2012). We quantify tree water status by measuring the predawn leaf water potentials (Ψ_leaf,pd) of different species. As trees dehydrate, the Ψ_leaf,pd falls from 0 MPa to more negative values. When values fall below −1.5 MPa, the trees are experiencing severe water deficit stress. In years that trees experienced mild to severe water stress, variations of Ψ_leaf,pd through time often closely track rainfall events, which provide partial rehydration (e.g., 2006, 2011, 2012).