Relax and refill: xylem rehydration prior to hydraulic measurements favours embolism repair in stems and generates artificially low PLC values |
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Authors: | PATRIZIA TRIFILÒ FABIO RAIMONDO MARIA A LO GULLO PIERA M BARBERA SEBASTIANO SALLEO ANDREA NARDINI |
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Institution: | 1. Dipartimento di Scienze Biologiche e Ambientali, Università di Messina, , 98166 Messina, Italy;2. Dipartimento di Agraria, Università Mediterranea di Reggio Calabria, , 89122 Reggio Calabria, Italy;3. Dipartimento di Scienze della Vita, Università di Trieste, , 34127 Trieste, Italy |
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Abstract: | Diurnal changes in percentage loss of hydraulic conductivity (PLC), with recorded values being higher at midday than on the following morning, have been interpreted as evidence for the occurrence of cycles of xylem conduits' embolism and repair. Recent reports have suggested that diurnal PLC changes might arise as a consequence of an experimental artefact, that is, air entry into xylem conduits upon cutting stems, even if under water, while under substantial tension generated by transpiration. Rehydration procedures prior to hydraulic measurements have been recommended to avoid this artefact. In the present study, we show that xylem rehydration prior to hydraulic measurements might favour xylem refilling and embolism repair, thus leading to PLC values erroneously lower than those actually experienced by transpiring plants. When xylem tension relaxation procedures were performed on stems where refilling mechanisms had been previously inhibited by mechanical (girdling) or chemical (orthovanadate) treatment, PLC values measured in stems cut under native tension were the same as those measured after sample rehydration/relaxation. Our data call for renewed attention to the procedures of sample collection in the field and transport to the laboratory, and suggest that girdling might be a recommendable treatment prior to sample collection for PLC measurements. |
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Keywords: | cavitation pressure collar refilling |
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