科研之友
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摘要
A recent study found that cutting shoots under water while xylem was under tension (which has been the standard protocol for the past few decades) could produce artefactual embolisms inside the xylem, overestimating hydraulic vulnerability relative to shoots cut under water after relaxing xylem tension (Wheeler etal. 2013). That study also raised the possibility that such a Wheeler effect' might occur in studies of leaf hydraulic vulnerability. We tested for such an effect for four species by applying a modified vacuum pump method to leaves with minor veins severed, to construct leaf xylem hydraulic vulnerability curves. We tested for an impact on leaf xylem hydraulic conductance (K-x) of cutting the petiole and minor veins under water for dehydrated leaves with xylem under tension compared with dehydrated leaves after previously relaxing xylem tension. Our results showed no significant cutting artefact' for leaf xylem. The lack of an effect for leaves could not be explained by narrower or shorter xylem conduits, and may be due to lesser mechanical stress imposed when cutting leaf petioles, and/or to rapid refilling of emboli in petioles. These findings provide the first validation of previous measurements of leaf hydraulic vulnerability against this potential artefact. Recently, an artifact has been demonstrated that called into question all previous measurements of stem hydraulic decline - and possibly also of leaf hydraulic decline, because cutting stems under water while under tension (which has been the standard protocol for the past several decades) was found to lead to low hydraulic conductivity (Wheeler etal. 2013). To test for this artifact in leaves, we developed a new method using the vacuum chamber to construct leaf xylem hydraulic vulnerability curves, and determined the differences in leaf xylem hydraulic conductance of petioles cut under while under tension vs. while the xylem tension was relaxed in four diverse species. Using this detailed approach, we found no significant differences among the cutting treatments, and that the lack of an effect for leaves could not be explained by xylem conduit dimensions, and may be due to lesser mechanical stress imposed when cutting leaf petioles, and/or to rapid refilling of emboli in petioles.
- 出版日期2015-3
