Resistance to cavitation is a major determinant of plant survival under severe drought and can be used to quantify species adaptive potential. Interspecific variation in this key trait is well ...defined in woody species, but intraspecific variation (level and structure) resulting from standing genetic variation and phenotypic plasticity has never been determined.
Combining for the first time in situ characterization of natural populations and two reciprocal common gardens in dry and wet sites, we estimated variance components (phenotypic, genetic, environmental, and genetic 9 environmental) of cavitation resistance based on 513 genotypes of a Mediterranean pine, Pinus pinaster.
Despite the selected populations being climatically contrasted, phenotypic plasticity in resistance to cavitation remained low and was essentially attributed to family level. Between-population variation in cavitation resistance for both phenotypic and genetic variation was limited.
These results strongly suggest that cavitation resistance is buffered against genetic and to a lesser extent environmental variation (canalization) in maritime pine. Consequently, in a drier world, the increasing drought tolerance of Pinus species might be severely constrained by the low level of cavitation resistance variation, resulting in a large-scale loss of productivity.
Drought-induced forest dieback has been widely reported over the last decades, and the evidence for a direct causal link between survival and hydraulic failure (xylem cavitation) is now well known. ...Because vulnerability to cavitation is intimately linked to the anatomy of the xylem, the main objective of this study was to better understand the xylem anatomical properties associated with cavitation resistance. An extensive data set of cavitation resistance traits and xylem anatomical properties was developed for 115 conifer species, with special attention given to the micro-morphology of bordered pits. The ratio of torus to pit aperture diameter, so-called torus overlap, increased with increasing cavitation resistance, while the flexibility of the margo does not seem to play a role, suggesting that air-seeding is located at the seal between the aspirated torus and pit aperture. Moreover, punctured tori were reported in various Pinaceae species. Species resistant to cavitation had thicker tracheid walls, while their lumen diameter (conduit size) was only slightly reduced, minimizing the impact on hydraulic conductance. The results also demonstrated (i) the existence of an indirect trade-off between hydraulic safety and mechanical strength; and (ii) a consistency between species distribution and xylem anatomy: species with a wide torus overlap and high valve effects are found in arid environments such as the Mediterranean region.
Plants can be highly segmented organisms with an independently redundant design of organs. In the context of plant hydraulics, leaves may be less embolism resistant than stems, allowing hydraulic ...failure to be restricted to distal organs that can be readily replaced.
We quantified drought‐induced embolism in needles and stems of Pinus pinaster using high‐resolution computed tomography (HRCT). HRCT observations of needles were compared with the rehydration kinetics method to estimate the contribution of extra‐xylary pathways to declining hydraulic conductance.
High‐resolution computed tomography images indicated that the pressure inducing 50% of embolized tracheids was similar between needle and stem xylem (P50 needle xylem = −3.62 MPa, P50 stem xylem = −3.88 MPa). Tracheids in both organs showed no difference in torus overlap of bordered pits. However, estimations of the pressure inducing 50% loss of hydraulic conductance at the whole needle level by the rehydration kinetics method were significantly higher (P50 needle = −1.71 MPa) than P50 needle xylem derived from HRCT.
The vulnerability segmentation hypothesis appears to be valid only when considering hydraulic failure at the entire needle level, including extra‐xylary pathways. Our findings suggest that native embolism in needles is limited and highlight the importance of imaging techniques for vulnerability curves.
The main goal of this paper is to test the vulnerability segmentation hypothesis in Pinus pinaster, which suggests that needles are more vulnerable to drought‐induced cavitation than stems. Results based on high resolution X‐ray computed tomography (HRCT) provide unambiguous evidence that xylem tracheids in needles of P. pinaster are not more vulnerable to cavitation than stem xylem. However, comparison of vulnerability curves based on HRCT with the rehydration kinetics method show that the vulnerability segmentation hypothesis is valid when hydraulic conductance is considered at the whole needle level. This paper illustrates the importance of visualizing embolism at the tissue level to interpret vulnerability curves of stems and leaves, and raises questions about earlier reports of daily embolism formation and refilling in gymnosperm xylem.
Key message
Variability of embolism resistance within individual trees was assessed in four Pinaceae species by using a single method of measurement
:
the Cavitron. Contrary to what has been ...previously observed
,
our findings show a small variability in embolism resistance within and between organs. Indeed
,
we found (i) a lack of variability between branches within the crown
,
and (ii) that roots and trunks are either equally resistant or slightly more vulnerable to embolism than branches. This contradicts the vulnerability segmentation hypothesis proposed in the early 1990s. This paper also demonstrates that only few branches are necessary to determine the embolism resistance of a given tree
.
Context
Embolism formation in xylem has an important impact on plant growth and survival. Since most studies on xylem embolism resistance focus on branches, it remains questionable how the entire plant deals with embolism across organs.
Aims
In this study, we aimed to evaluate the variability of embolism resistance within a given organ and between different organs within a single tree.
Methods
Based on the Cavitron method, we estimated the intra-organ and the intra-plant variability of embolism resistance for four Pinaceae species. In addition, we compared pit anatomical characters for wood of all organs and species.
Results
We found no variability of embolism resistance for a given organ within a tree. At the tree level, trunks and roots were either equally or more vulnerable to embolism than branches. For all species, organs that showed a similar range of embolism resistance presented similar torus-aperture overlap values. However, the least negative
P
50
value for roots of
Pinus pinaster
was associated with the lowest torus-aperture overlap value.
Conclusion
Our findings suggest that
P
50
values are constrained within a particular organ and that intra-tree variation in embolism resistance is less substantial than previously reported. Moreover, our data do not support the vulnerability segmentation hypothesis which suggests that distal organs are more vulnerable to xylem embolism.
Summary
Resistance to cavitation is a major determinant of plant survival under severe drought and can be used to quantify species adaptive potential. Interspecific variation in this key trait is ...well defined in woody species, but intraspecific variation (level and structure) resulting from standing genetic variation and phenotypic plasticity has never been determined.
Combining for the first time
in situ
characterization of natural populations and two reciprocal common gardens in dry and wet sites, we estimated variance components (phenotypic, genetic, environmental, and genetic × environmental) of cavitation resistance based on 513 genotypes of a Mediterranean pine,
Pinus pinaster
.
Despite the selected populations being climatically contrasted, phenotypic plasticity in resistance to cavitation remained low and was essentially attributed to family level. Between‐population variation in cavitation resistance for both phenotypic and genetic variation was limited.
These results strongly suggest that cavitation resistance is buffered against genetic and to a lesser extent environmental variation (canalization) in maritime pine. Consequently, in a drier world, the increasing drought tolerance of
Pinus
species might be severely constrained by the low level of cavitation resistance variation, resulting in a large‐scale loss of productivity.
Resistance to embolism of conifer branches has commonly been studied with the flow-centrifuge technique (Cavitron) to carry out routine measurements. The aim of this study was to test the accuracy of ...the Cavitron for measurements on conifer roots. Based on earlier findings, it was suggested that the application of the flow-centrifuge technique to roots may not be free from artefacts due to potential torus aspiration when the pressure gradient between the sample ends is high. Here, three different protocols were used to obtain vulnerability curves in Pinus pinaster and Pseudotsuga menziesii roots: no water pressure gradient, and low and high water pressure gradient. In addition water extraction curves were obtained to only estimate the water released from conduits by embolism. Water extraction curves showed no water release caused by embolism before -1.3 and -2.5 MPa for P. pinaster and P. menziesii, respectively. The results illustrated discrepancies between these protocols: roots measured with the high and low pressure gradient protocols appeared erroneously more vulnerable to embolism than roots measured with no pressure gradient. In addition, pit anatomical observations of roots showed non-punctured tori and a high flexibility of the margo, which may increase the risk of torus aspiration. All together these results suggest that the early loss of hydraulic conductivity observed for the low and high pressure gradient protocols was not due to embolism but rather to a torus aspiration artefact when the pressure gradient is too high. We conclude that the no pressure gradient protocol provides a suitable method and that high vulnerability to embolism reported in previous studies for conifer roots should be interpreted with caution in the light of our findings.
Resistance to embolism of conifer branches has commonly been studied with the flow-centrifuge technique (Cavitron) to carry out routine measurements. The aim of this study was to test the accuracy of ...the Cavitron for measurements on conifer roots. Based on earlier findings, it was suggested that the application of the flow-centrifuge technique to roots may not be free from artefacts due to potential torus aspiration when the pressure gradient between the sample ends is high. Here, three different protocols were used to obtain vulnerability curves in Pinus pinaster and Pseudotsuga menziesii roots: no water pressure gradient, and low and high water pressure gradient. In addition water extraction curves were obtained to only estimate the water released from conduits by embolism. Water extraction curves showed no water release caused by embolism before -1.3 and -2.5 MPa for P. pinaster and P. menziesii, respectively. The results illustrated discrepancies between these protocols: roots measured with the high and low pressure gradient protocols appeared erroneously more vulnerable to embolism than roots measured with no pressure gradient. In addition, pit anatomical observations of roots showed non-punctured tori and a high flexibility of the margo, which may increase the risk of torus aspiration. All together these results suggest that the early loss of hydraulic conductivity observed for the low and high pressure gradient protocols was not due to embolism but rather to a torus aspiration artefact when the pressure gradient is too high. We conclude that the no pressure gradient protocol provides a suitable method and that high vulnerability to embolism reported in previous studies for conifer roots should be interpreted with caution in the light of our findings.
Polypharmacy of elderly oncology patients and fragmented medication management are well‐known risk factors for drug–drug interactions (DDIs). These interactions can occur among antineoplastic, ...ongoing chronic treatment(s) and chemotherapy‐associated treatments, like antiemetics. Clinically relevant interactions based on enzyme‐ or transporter‐inhibition phenomena of active drugs can increase the frequency of their DDIs. We describe a strongly suspected elderly cancer patient's DDI between aprepitant and opium powder in the context of an irinotecan‐based regimen manifested by nightmares and visual hallucinations. We discuss this DDI's hypothetical pharmacological mechanisms and management.
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