Xylem vessels are responsible for conducting water, in a metastable state, to the transpiring leaves. As tension increases,
hydraulic failure may occur. At any given tension, the resistance of the xylem vessels to cavitation depends on their
morphology, of which vessels diameter has been pointed out as relevant. Grapevines (
Vitis vinifera
L.) are often
cultivated in Mediterranean climates and mostly under controlled water deficit conditions. Besides, a high variability in
the stomatal sensitivity exists in different varieties. ‘Cabernet Sauvignon’ (CS) is recognized as isohydric, ‘Syrah’ (S)
as anisohydric, and no clear information exist for ‘Carménère’ (C), an important grapevine variety for the Chilean wine
industry. In the present study, xylem morpho-anatomical traits from stems in CS, S, and C, growing in a single vineyard,
were analyzed, inferring their specific theoretical hydraulic conductivity. Also, the maximal hydraulic conductivity
and vulnerability to cavitation, the latter expressed as the xylem water potential reducing a 50% loss in hydraulic
conductivity (PLC
50) were assessed in stems collected from the field. Higher vessels diameter was found in S and C,
followed by CS, in general ranging from 21 to 120 μm, resulting in an expected proportional theoretical hydraulic
conductivity of nearly 40 to 43 kg s
-1 m
-1 MPa
-1 in C and S, and merely 23 kg s
-1 m
-1 MPa
-1 in C. This values were similar
-but not proportionally- to maximal actual hydraulic conductivity measured in stems with median values, in average, of
28, 17, and 13 kg s
-1 m
-1 MPa
-1 in S, C, and CS, respectively. Even though wider xylem vessels have been correlated with
higher xylem vulnerability to cavitation, PLC
50 was significantly higher in S (-2.3 MPa) compared to C (-1.1 MPa), and
even though xylem vessels diameter were similar between S and C, C was as vulnerable as CS. We found no such tradeoff
between hydraulic efficiency and vulnerability.
