Xylem density, biomechanics and anatomical traits correlate with water stress in 17 evergreen shrub species of the Mediterranean‐type climate region of South Africa

Jacobsen, Anna L.; Agenbag, L.; Esler, Karen J.; Pratt, R. Brandon; Ewers, Frank W.; Davis, Stephen D.

doi:10.1111/j.1365-2745.2006.01186.x

Cited by 193 publications

(238 citation statements)

References 57 publications

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“…Specific sites were located at Jonaskop in the Riviersonderend mountain range (lat 33°15′ 48.34′′ S, long 19°31′ 33.97′′ E, elevation of 981 m), the Kogelberg Biosphere (lat 34°19′ 02.57′′ S, long 18°57′ 39.74′′ E, elevation of 61 m), and the Silvermine section of the Table Mountain National Park (lat 34°06′ 26.45′′ S, long 18°26′ 31.37′′ E, elevation of 375 m). These study sites were chosen because they contain particularly diverse floral communities that have been the focus of previous ecophysiological studies, including assessments of the variation in vulnerability of stem xylem to cavitation and long-term drought response investigations (14,(56)(57)(58).…”

Section: Methodsmentioning

confidence: 99%

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Predicting plant vulnerability to drought in biodiverse regions using functional traits

Skelton

West

Dawson

2015

Proc. Natl. Acad. Sci. U.S.A.

280

305

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Attempts to understand mechanisms underlying plant mortality during drought have led to the emergence of a hydraulic framework describing distinct hydraulic strategies among coexisting species. This framework distinguishes species that rapidly decrease stomatal conductance (g s ), thereby maintaining high water potential (P x ; isohydric), from those species that maintain relatively high g s at low P x , thereby maintaining carbon assimilation, albeit at the cost of loss of hydraulic conductivity (anisohydric). This framework is yet to be tested in biodiverse communities, potentially due to a lack of standardized reference values upon which hydraulic strategies can be defined. We developed a system of quantifying hydraulic strategy using indices from vulnerability curves and stomatal dehydration response curves and tested it in a speciose community from South Africa's Cape Floristic Region. Degree of stomatal regulation over cavitation was defined as the margin between P x at stomatal closure (P g12 ) and P x at 50% loss of conductivity. To assess relationships between hydraulic strategy and mortality mechanisms, we developed proxies for carbon limitation and hydraulic failure using time since P g12 and loss of conductivity at minimum seasonal P x , respectively. Our approach captured continuous variation along an isohydry/anisohydry axis and showed that this variation was linearly related to xylem safety margin. Degree of isohydry/anisohydry was associated with contrasting predictions for mortality during drought. Merging stomatal regulation strategies that represent an index of water use behavior with xylem vulnerability facilitates a more comprehensive framework with which to characterize plant response to drought, thus opening up an avenue for predicting the response of diverse communities to future droughts. drought | functional traits | plant hydraulics | xylem vulnerability | stomatal response

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Section: Methodsmentioning

confidence: 99%

“…For the remaining species, we extracted P min values from published sources (17,19,56,58). A potential limitation of using midday P shoot values to estimate PLC is that midday P shoot will be more negative than stem P x , resulting in an overestimation of the amount of cavitation in stems (64).…”

Section: Methodsmentioning

confidence: 99%

Predicting plant vulnerability to drought in biodiverse regions using functional traits

Skelton

West

Dawson

2015

Proc. Natl. Acad. Sci. U.S.A.

280

305

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“…Previous significant correlations between root morphology parameters as SRL and hydraulic conductivity in herbaceous and woody species have also been reported (Rieger and Litvin 1999;Pemán et al 2006), highlighting the role of root architecture in plant water status. Indeed, root structure has been related to the variability in physiological traits, including the vulnerability to cavitation in Mediterranean shrubs of California (Jacobsen et al 2005(Jacobsen et al , 2007a. M. communis was the species that displayed the lowest SRL, K As , and stomatal conductance (g s ) values but the highest K RRL .…”

Section: Morphological Traits Among Speciesmentioning

confidence: 99%

“…In this context, droughtresistant plant traits have been synthesized in several functional classifications, on the basis of leaf habit (Clemente et al 2005;Jacobsen et al 2007a), rooting structure (Kummerow 1981;Canadell and Zedler 1995;Jacobsen et al 2007a), regeneration strategy (Paula and Pausas 2006) or hydraulic architecture and drought resistance strategy (Levitt 1980;Tyree et al 1994;Valladares et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

et al. 2009

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The distribution of plants is associated with their different patterns of response to their environment. Mediterranean plants have evolved a number of morphological and physiological adaptations that determine their ability to survive and grow, being an effective water uptake and use important factors for drought resistance. In this article, we evaluated interspecific differences in morphology, biomass allocation, and architectural traits and their relationship with water use strategies in seedlings of seven co-occurring Mediterranean species (Anthyllis cytisoides L., Genista scorpius L. DC., Myrtus communis L., Pistacia lentiscus L., Rosmarinus officinalis L., Spartium junceum L. and Ulex parviflorus Pourr.). The results showed that morphological root features vary among species and they are significantly correlated with root hydraulic conductance and leaf gas exchange variables. Species with high specific root length (SRL) showed a low hydraulic conductance per root length (K RRL ) but high specific hydraulic conductance (K As ). M. communis and P. lentiscus showed the most contrasting water use patterns with respect to the other species studied. The results are not affected when considering phylogenetic relatedness. Thus, the variability observed in root hydraulic properties and leaf gas exchange suggests important mechanisms for understanding species coexistence in water-limited ecosystems.

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“…For instance, mechanical strengthening due to hydraulic adaptations could reduce hydraulic effects of mechanical stresses; trees growing in climates with winter frost may be stronger due to larger amounts of sap-or heart wood and drought adaptation may result in a stiffer and stronger plant. 21,24,27 This could explain why the relatively clear trade-off All tissue sections are imaged at the same magnification; the width of each image is 4, 6 mm. In O. asbeckii, where the main rigid element resisting overturning is provided by the taproot and the lower bole, the trunk has smaller and fewer vessels than either of the root sections, as often described in litterature.…”

mentioning

confidence: 99%

Interrelations between hydraulic and mechanical stress adaptations in woody plants

Christensen-Dalsgaard

Ennos

Fournier

2008

Plant Signaling & Behavior

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in the form of positive interactions and trade-offs. In the former case, adaptations with respect to one of the two stresses positively affect the plants ability to withstand the other. Drought adaptation, for instance, is associated with an increase in the density of the tissue, which may result in stiffer and stronger wood. 5,6 Further, increasing the transectional area of the sapwood increases the conductivity as well as the rigidity of the plant and may occur as an adaptation to either drought-or mechanical stress. 7,8 In such cases, because of the importance of hydraulic sufficiency as well as adequate mechanical support, biomass must be partitioned to allow for both functions simultaneously even if this results in a surplus allocation with respect to one. In the case of trade-offs, the hydraulic or mechanical adaptations are detrimental to the plants' capabilities with respect to the other. Within the woody tissue, for instance, larger and more numerous vessels increase the conductivity but may weaken the wood. 1-3,9-11 Analogously, hydraulic optimisation dictates an increase in the transectional sapwood area up though the plant, so that the summed area of all branches at a given height would be greater than that of the trunk 12 but mechanical optimisation a decrease. 13 In the case of physiological parameters within which there are trade-offs, achieving adequate design whilst minimising biomass allocation becomes complex, 4 and a number of possible but less optimal solutions exist.In our study, 14 we looked at how mechanical as well as hydraulic parameters changed along the lateral roots of two tropical tree species, Tachigali melinonii and Xylopia nitida, both of which produce buttress roots. Along the roots of these species there is a strong distal decrease in the magnitude of the locally supported mechanical loads, 15 making them ideal model organisms for investigating mechanical adaptation of the tissue and the impact this has on hydraulic parameters. We measured the density, conductivity, strength, stiffness, sapwood area and second moment of area at various points distally along the roots as well as in the lower trunk, and compared the values to those for strain. In both species, the strength and stiffness of the tissue decreased distally along the roots as the strain dropped, and the conductivity concurrently increased exponentially (Fig. 1). This appeared related to changes in the density of the wood; in both species, the density increased towards the bole and was positively correlated with mechanical properties but negatively with conductivity. As in previous studies, the distal most The fields of plant water relations and plant biomechanics have traditionally been studied separately even though often the same tissues are responsible for water transport and mechanical support. There is now increasing evidence that hydraulic and mechanical adaptations may influence one another. We studied the changes in the hydraulic and mechanical properties of the wood along lateral roots of two species of buttr...

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Xylem density, biomechanics and anatomical traits correlate with water stress in 17 evergreen shrub species of the Mediterranean‐type climate region of South Africa

Cited by 193 publications

References 57 publications

Predicting plant vulnerability to drought in biodiverse regions using functional traits

Predicting plant vulnerability to drought in biodiverse regions using functional traits

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

Interrelations between hydraulic and mechanical stress adaptations in woody plants

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