Despite the appeal of the iso/anisohydric framework for classifying plant drought responses, recent studies have shown that such classifications can be strongly affected by a plant's environment. Here, we present measured in situ drought responses to demonstrate that apparent isohydricity can be conflated with environmental conditions that vary over space and time. In particular, we (a) use data from an oak species (Quercus douglasii) during the 2012–2015 extreme drought in California to demonstrate how temporal and spatial variability in the environment can influence plant water potential dynamics, masking the role of traits; (b) explain how these environmental variations might arise from climatic, topographic, and edaphic variability; (c) illustrate, through a “common garden” thought experiment, how existing trait-based or response-based isohydricity metrics can be confounded by these environmental variations, leading to Type-1 (false positive) and Type-2 (false negative) errors; and (d) advocate for the use of model-based approaches for formulating alternate classification schemes. Building on recent insights from greenhouse and vineyard studies, we offer additional evidence across multiple field sites to demonstrate the importance of spatial and temporal drivers of plants' apparent isohydricity. This evidence challenges the use of isohydricity indices, per se, to characterize plant water relations at the global scale.
Bibliographical noteFunding Information:
Climate Program Office, Grant/Award Num ber: Climate and Global Change Postdoctoral Fellowship; Division of Integrative Organismal Systems, Grant/Award Numbers: 1441396 and 1457400; Svenska Forskningsrådet Formas, Grant/Award Numbers: 2016‐00998 and 942‐2016‐1; National Science Foundation, Grant/Award Numbers: IOS‐1457400 and IOS‐1441396; Swedish government's Strategic Research Environment “Sustainable use of Natural Resources.”; Swedish Research Council Formas, Grant/Award Numbers: 942‐ 2016‐20001 and 2016–00998; NOAA Climate and Global Change Postdoctoral Fellowship
X.F. was partially supported by NOAA Climate and Global Change Postdoctoral Fellowship. S.M. was partly supported by the Swedish Research Council Formas (2016–00998). G.V. acknowledges the support by Swedish Research Council Formas (942‐2016‐20001) and the project “TC4F—Trees and Crops for the Future” funded through the Swedish government's Strategic Research Environment “Sustainable use of Natural Resources.” The authors also acknowledge support from National Science Foundation IOS‐1441396 and IOS‐1457400.
- intrinsic traits
- plant water potentials