Anisohydric water use behavior links growing season evaporative demand to ring-width increment in conifers from summer-dry environments
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Compared to isohydric Pinaceae, anisohydric Cupressaceae exhibited: (1) a threefold larger hydroscape area; (2) growth at lower pre-dawn water potentials that extended longer into the growing season; and (3) stronger coupling of growth to growing season atmospheric moisture demand in summer-dry environments.
Conifers in the Pinaceae and Cupressaceae from dry environments have been shown to broadly differ in their stomatal sensitivity to soil drying that result in isohydric versus anisohydric water use behavior, respectively. Here, we first employ a series of drought experiments and field observations to confirm the degree of isohydric versus anisohydric water use behavior in species of these two families that are representative of the Interior West of the United States. We then use experimental soil drying to demonstrate how growth of anisohydric Juniperus osteosperma was more closely tied to pre-dawn water potentials than isohydric Pinus monophylla. Finally, we confirm that measured leaf gas-exchange and growth responses to drying hold real-world consequences for conifers from the Interior West. More specifically, across the past ~ 100 years of climate variation, pairwise comparisons of annual ring-width increment responses indicate that growth of Cupressaceae species (J. osteosperma and J. scopulorum) was more strongly coupled to growing season evaporative demand than co-occurring Pinaceae species (Pinus monophylla, P. edulis, P. flexilis, P. longaeva, P. ponderosa, and Pseudotsuga menziesii). Overall, these experimental and observational results suggest that an a priori distinction based on family and associated hydric water use behavior should lead to more accurate and mechanistically correct dendrochronological reconstructions of growing season evaporative demand (i.e., Cupressaceae) versus antecedent precipitation (i.e., Pinaceae) in summer-dry environments. Moreover, these differences in growth sensitivity to evaporative demand among these groups suggest that incorporating hydric water use behavior into models of forest responses to global warming can provide more accurate projections of future forest composition and functioning.
KeywordsDendrochronology Drought tolerance Stomatal conductance Tree growth Water potential Water use behavior
The Wasatch Dendroclimatology Research Group (WADR) was responsible for this project. This paper was greatly improved by the helpful comments of Joshua Leffler. We would like to thank Le Canh Nam, Slaton Wheeler, Eric Allen, Shawn Wortham, Roxy Hedges, Shauna Mecham, and Jackson Deere, Hannah Gray and Jessika Pettit for their contributions to field and laboratory data collection. For access to sampling sites we also would like to thank: Jennefer Parker, Logan Ranger District, Uinta-Wasatch-Cache National Forest; Karl Fuelling, Minidoka Ranger District, Sawtooth National Forest; and Del Barnhurst, Fillmore Ranger District, Fishlake National Forest. We acknowledge Marlee Beers and BYU Think Spatial for cartographic work. This paper was prepared in part by an employee of the US Forest Service as part of official duties and is, therefore, in the public domain.
This research was funded by a Bureau of Reclamation WaterSmart Grant, No. R13AC80039, the Utah State University Center for Water Efficient Landscaping (CWEL), and Utah Agricultural Experiment Station Project 1304.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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