Iso/Anisohydry: A Plant–Environment Interaction Rather Than a Simple Hydraulic Trait

Plants are frequently classified as isohydric or anisohydric in an attempt to portray their water relations strategy or ecological niche. However, despite the popularity of the iso/anisohydric classification, the underlying biology remains unclear. We use here a simple hydraulic model and the extensive literature on grapevine hydraulics to illustrate that the iso/anisohydric classification of a plant depends on the definition used and the environment in which it is grown, rather than describing an intrinsic property of the plant itself. We argue that abandoning the iso/anisohydric terminology and returning to a more fundamental hydraulic framework would provide a stronger foundation for species comparisons and ecological predictions. In recent years there have been a growing number of studies that use the terminology isohydric or anisohydric to portray plant hydraulic strategies. These classifications are considered to derive from genetic differences and are thus used for species comparison and modeling. There is more than one definition of isohydrocity, and the different definitions are not always in agreement.