Osmotic and elastic adjustments in cold desert shrubs differing in rooting depth: coping with drought and subzero temperatures

Abstract

Physiological adjustments to enhance tolerance or avoidance of summer drought and winter freezing were studied in shallow- to deep-rooted Patagonian cold desert shrubs. We measured leaf water potential (Ψ(L)), osmotic potential, tissue elasticity, stem hydraulic characteristics, and stomatal conductance (g (S)) across species throughout the year, and assessed tissue damage by subzero temperatures during winter. Species behavior was highly dependent on rooting depth. Substantial osmotic adjustment (up to 1.2 MPa) was observed in deep-rooted species exhibiting relatively small seasonal variations in Ψ(L) and with access to a more stable water source, but having a large difference between predawn and midday Ψ(L). On the other hand, shallow-rooted species exposed to large seasonal changes in Ψ(L) showed limited osmotic adjustment and incomplete stomatal closure, resulting in turgor loss during periods of drought. The bulk leaf tissue elastic modulus (ε) was lower in species with relatively shallow roots. Daily variation in g (S) was larger in shallow-rooted species (more than 50 % of its maximum) and was negatively associated with the difference between Ψ(L) at the turgor loss point and minimum Ψ(L) (safety margin for turgor maintenance). All species increased ε by about 10 MPa during winter. Species with rigid tissue walls exhibited low leaf tissue damage at -20 °C. Our results suggest that osmotic adjustment was the main water relationship adaptation to cope with drought during summer and spring, particularly in deep-rooted plants, and that adjustments in cell wall rigidity during the winter helped to enhance freezing tolerance.

Freezing avoidance by supercooling inOlea europaeacultivars: the role of apoplastic water, solute content and cell wall rigidity

“…Scholz et al . () found a negative correlation between the observed percentage of leaf damage at −20 °C and ε in shrub species of cold deserts that are tolerant to extracellular freezing, indicating that the elastic adjustment from summer to winter plays a key role in the ability to resist low temperatures. Olive cultivars do not tolerant extracellular freezing, as Patagonian shrubs do, but instead avoid ice formation by supercooling.…”

“…; Scholz et al . ). Plants can avoid extracellular ice formation by thermal insulation of freezing‐sensitive organs (Rada et al .…”

“…), whereas tissue elastic adjustments (more rigid cell wall) was one of the responses found in shrubs from cold deserts to cope with sub‐zero temperatures during winter (Scholz et al . ). Deposition of lipids and others structural changes in the cell wall during cold acclimation may increase cell wall rigidity preventing cell contraction and collapse when ice nucleation occurs in intercellular spaces and thus enhancing tolerance to extracellular ice formation.…”

Shrub persistence and increased grass mortality in response to drought in dryland systems

“…C. ramosissima also has the ability to split into clonal fragments as a potential mechanism to avoid whole-plant mortality (Schenk, 1999) and this may further explain results from our experiment. Shrubs themselves have differing rooting profiles that can confer an advantage or disadvantage during periods of drought; including the ability to osmotically adjust tissues to prevent desiccation or cavitation (Hacke, Sperry, & Pittermann, 2000;Scholz, Bucci, Arias, Meinzer, & Goldstein, 2012). Shrubs themselves have differing rooting profiles that can confer an advantage or disadvantage during periods of drought; including the ability to osmotically adjust tissues to prevent desiccation or cavitation (Hacke, Sperry, & Pittermann, 2000;Scholz, Bucci, Arias, Meinzer, & Goldstein, 2012).…”

Grazing increases evapotranspiration without the cost of lowering soil water storages in arid ecosystems

“…Indeed, this is a little‐known ecosystem with respect to plant–atmosphere interactions (Cristiano et al, ; Paruelo & Sala, ; Verón, Paruelo, & Oesterheld, ), and there is no empirical information relying on field measurements of ET and its components. In this ecosystem, the precipitation is scarce and occurs mainly in winter when air temperature falls below 0 °C, and thus, available water as well as soil and air temperature play a key role in ecosystem functioning (Bucci, Scholz, Goldstein, & Meinzer, ; Bucci, Scholz, Iogna, & Goldstein, ; Scholz, Bucci, Arias, Meinzer, & Goldstein, ). Long‐term heavy grazing along with climate change had led to changes in species composition of Patagonian steppes (Golluscio, Bottaro, & Oesterheld, ) and possibly, to changes in the soil–water balance and plant sensibility to water availability.…”