Single vessel air injection estimates of xylem resistance to cavitation are affected by vessel network characteristics and sample length

Abstract

Xylem resistance to cavitation is an important trait that is related to the ecology and survival of plant species. Vessel network characteristics, such as vessel length and connectivity, could affect the spread of emboli from gas-filled vessels to functional ones, triggering their cavitation. We hypothesized that the cavitation resistance of xylem vessels is randomly distributed throughout the vessel network. We predicted that single vessel air injection (SVAI) vulnerability curves (VCs) would thus be affected by sample length. Longer stem samples were predicted to appear more resistant than shorter samples due to the sampled path including greater numbers of vessels. We evaluated the vessel network characteristics of grapevine (Vitis vinifera L.), English oak (Quercus robur L.) and black cottonwood (Populus trichocarpa Torr. & A. Gray), and constructed SVAI VCs for 5- and 20-cm-long segments. We also constructed VCs with a standard centrifuge method and used computer modelling to estimate the curve shift expected for pathways composed of different numbers of vessels. For all three species, the SVAI VCs for 5 cm segments rose exponentially and were more vulnerable than the 20 cm segments. The 5 cm curve shapes were exponential and were consistent with centrifuge VCs. Modelling data supported the observed SVAI VC shifts, which were related to path length and vessel network characteristics. These results suggest that exponential VCs represent the most realistic curve shape for individual vessel resistance distributions for these species. At the network level, the presence of some vessels with a higher resistance to cavitation may help avoid emboli spread during tissue dehydration.

Stomatal Closure, Basal Leaf Embolism, and Shedding Protect the Hydraulic Integrity of Grape Stems

“…This finding could imply that vessels in the same area of the leaf have similar vulnerability to cavitation or, more probably, that most vessels are not tested before gas is present in a neighbor with which they share pit connections. Combining the wide range of xylem vulnerability shown by single vessel air injection (Christman et al, 2012;Venturas et al, 2016) and our observation that vessels tend to cavitate mostly after their neighboring vessels are embolized suggests that the patchiness phenomenon is caused by highly resistant vessels that, once embolized, expose a whole region of less resistant conduits to gas. In accordance with the aforementioned vulnerability segmentation, it would make sense that these highly resistant vessels are located in hydraulically critical positions.…”

X‐ray microtomography observations of xylem embolism in stems of Laurus nobilis are consistent with hydraulic measurements of percentage loss of conductance

“…Stem segments are cut from larger branches under water and connected to a hydraulic apparatus to measure their hydraulic conductance under low water pressure, before displacing embolism by a high‐pressure ‘flush’ and repeating measurements under low pressure to quantify maximum hydraulic conductance, and finally calculating PLC. Several alternative methods to generate VCs have been proposed and tested, including monitoring of acoustic emissions rate by dehydrating stems (Milburn, ; Tyree & Dixon, ; Jackson & Grace, ; Nolf et al ., ), real‐time measurements of hydraulic conductance of stems spinning in a centrifuge (Cochard, ; Li et al ., ), induction of embolism by positive air pressures applied to stems (Cochard et al ., ; Salleo et al ., ), single‐vessel air injection (Venturas et al ., ) and quantification of the air volume extracted from progressively dehydrated branches (Pereira et al ., ). All these methods can be potentially affected by pitfalls and artefacts (Cochard et al ., ), and the recent literature is rich in controversies regarding their validity (Jansen et al ., ).…”

Wood structure and function change with maturity: Age of the vascular cambium is associated with xylem changes in current‐year growth

“…Different methods used to generate vulnerability to cavitation curves may produce different results. The standard centrifuge technique as used in the present study, when compared with other techniques, has generally been found to produce reliable results (e.g., Sperry, Christman, Torres‐Ruiz, Taneda, & Smith, ; Jacobsen & Pratt, : Hacke et al, : Venturas et al, ); however, some have reported potential measurement errors with similar static rotor designs (Choat et al, ; Torres‐Ruiz et al, ). This has led to the recommendation that more than one method be used in order to evaluate methods within studies (Hacke et al, ; Sperry et al, ).…”

“…We selected a subset of species of special interest to examine using single‐vessel air injection (SVAI) as described in Venturas et al (). The first species that we selected was Laurus nobilis , which is a basal angiosperm that contains very short vessels (Jacobsen et al, ).…”

“…An additional species from the present study, Quercus robur , has also been of recent interest (Cochard et al, ; Tobin et al, ). We examined young samples from this species; and the results of this comparison, which was conducted concurrently to the comparisons mentioned above and on the same individuals included in the present study, have already been published (Venturas et al, ).…”