Temporal shifts in iso/anisohydry revealed from daily observations of plant water potential in a dominant desert shrub

Abstract

Plant species are characterized along a spectrum of isohydry to anisohydry depending on their regulation of water potential (Ψ), but the plasticity of hydraulic strategies is largely unknown. The role of environmental drivers was evaluated in the hydraulic behavior of Larrea tridentata, a drought-tolerant desert shrub that withstands a wide range of environmental conditions.With a 1.5 yr time-series of 2324 in situ measurements of daily predawn and midday Ψ, the temporal variability of hydraulic behavior was explored in relation to soil water supply, atmospheric demand and temperature.Hydraulic behavior in Larrea was highly dynamic, ranging from partial isohydry to extreme anisohydry. Larrea exhibited extreme anisohydry under wet soil conditions corresponding to periods of high productivity, whereas partial isohydry was exhibited after prolonged dry or cold conditions, when productivity was low.Environmental conditions can strongly influence plant hydraulic behavior at relatively fast timescales, which enhances our understanding of plant drought responses. Although species may exhibit a dominant hydraulic behavior, variable environmental conditions can prompt plasticity in Ψ regulation, particularly for species in seasonally dry climates.

Interannual variability of ecosystem iso/anisohydry is regulated by environmental dryness

“…In our collected species field measurement dataset, most of the species only have 2‐yr records of Ψ MD and Ψ PD data due to challenges of in situ Ψ L measurements. This limitation in data temporal coverage can possibly be alleviated in the future by the use of automated and continuous leaf psychrometers (Brodribb et al ., 2016; Reddy et al ., 2017; Guo et al ., 2020). We also acknowledge that we used a different dryness proxy at the ecosystem level (aridity index) and at the species level (annual Ψ PD ), with the consideration that ecosystem‐level aridity index would lead to different root‐zone water potentials for different species in a pixel because of different rooting depths, etc.…”

“…both soil water supply and atmosphere demand) and plant properties (e.g. hydraulic architecture and root depth) (Hochberg et al ., 2018; Feng et al ., 2019; Novick et al ., 2019; Guo et al ., 2020). This may confound the conventional interpretation of iso/anisohydry as an intrinsic hydraulic trait reflecting phenotypic variation in plant physiology (e.g.…”

Non‐structural carbohydrate dynamics associated with antecedent stem water potential and air temperature in a dominant desert shrub

“…Xylem water potential was measured half‐hourly using automated stem psychrometers (PSY1, ICT International, Armidale, Australia) on the same shrubs that were sampled for NSC (see Guo, Hultine, Koch, Kropp, & Ogle, ). Stem psychrometers utilize a pair of thermocouples to generate the wet bulb depression and correct for temperature gradients within the chamber (Dixon & Tyree, ), such that Ψ can be measured non‐destructively.…”

Squandering water in drylands: the water‐use strategy of the phreatophyte Ziziphus lotus in a groundwater‐dependent ecosystem

“…Sarg. and the shallow‐rooted Larrea tridentata DC., which also shows plasticity in its hydraulic behavior related to environmental conditions (Guo et al, 2020).…”

“…Thus, anisohydric species generally show higher water usage and primary productivity in drylands than isohydric species, which reduce their stomatal conductance ( g s ) under drought stress imposed by conditions such as high atmospheric demand and low soil water availability (McDowell et al, 2008). However, several studies have challenged the concept of fixed hydraulic behavior by showing that individual plants can vary along the isohydry–anisohydry continuum, according to differences in spatiotemporal environmental conditions (Feng et al, 2019; Guo et al, 2020). Whether phreatophytes are more or less iso‐ or anisohydric has important implications for the productivity of arid regions (Nolan et al, 2017) and for the ecohydrology of the GDEs (van der Molen et al, 2011; Roman et al, 2015).…”