Gas exchange and hydraulics during drought in crops: Who drives whom?

The correlation between stomatal, mesophyll and leaf hydraulic conductance (K_leaf), and the timing of each during regulation under drought, are not fully understood. Studies which make precise, parallel measurement of these variables during progressive imposition of drought are needed. Wang et al. (2018) provide novel insights, showing that, in rice, a decline of K_leaf is the earliest response to decreasing water availability, and they propose that it triggers the later decline of stomatal and mesophyll conductance. Comparison with results from other species intensifies the debate about the relationships between these variables, as well as between photosynthesis (i.e. productivity) and hydraulic failure (death).