Hydraulic traits of co-existing conifers do not correlate with local hydroclimate condition: a case study in the norther
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PHYSIOLOGICAL ECOLOGY – ORIGINAL RESEARCH
Hydraulic traits of co‑existing conifers do not correlate with local hydroclimate condition: a case study in the northern Rocky Mountains, U.S.A Tim Clute1 · Justin Martin1 · Nate Looker2 · Jia Hu3 Received: 8 November 2019 / Accepted: 29 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, we examined the inter- and intra-specific variation of hydraulic traits of three conifers of the Northern Rockies: Pinus ponderosa, Picea engelmannii, and Pseudotsuga menziesii to understand the mechanisms that allow different plant species to co-exist across a watershed. We quantified differences in plant xylem water potential (ψx), xylem tissue vulnerability to cavitation (P50, or ψ causing 50% loss of hydraulic conductivity), and safety margins for co-occurring trees from low and high elevations. We then investigated xylem vulnerability to cavitation with rooting depth. We found that xylem vulnerability to cavitation did not correspond to where tree species were found in the landscape. For example, P. ponderosa grew in more xeric locations, while P. engelmannii were largely confined to more mesic locations, yet P. engelmannii had more negative P50 values. P. menziesii had the lowest P50 value, but displayed little variation in vulnerability to cavitation across the hydroclimatic gradient. These patterns were also reflected in the safety margins; P. menziesii had the widest safety margin, P. engelmannii was intermediate, and P. ponderosa displayed the narrowest safety margin. All three species were also using water sources deeper than 30 cm in depth, allowing them to persist throughout the mid-summer drought. Overall, species-specific hydraulic traits did not necessarily follow a predictable response to the environment; instead, a combination of physiological and morphological traits likely allow trees to persist across a broader hydroclimatic gradient than would be otherwise expected from hydraulic trait measurements alone. Keywords Conifers · Water potential · Hydraulic vulnerability · Safety margin · Source water
Introduction
Communicated by Christiane Roscher. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00442-020-04772-z) contains supplementary material, which is available to authorized users. * Tim Clute [email protected] 1
Department of Ecology, Montana State University, Bozeman, MT 59715, USA
2
Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA
3
University of Arizona, School of Natural Resources and the Environment, Tucson, AZ 85721, USA
Water transport in plants is driven by large differences in water potential (ψ) between the atmosphere and soil, where transpiration creates tension between the leaves and roots. This can cause the water potential in the roots to become increasingly negative as soil water is depleted (Tyree and Sperry 1988). Additionally, high transpiration demand, caused by hot and dry conditions, can
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