Analysis of hydraulic conductance components in field grown, mature sweet cherry trees

As a necessary step towards understanding soil water extraction and plant water relationships, the components of hydraulic conductance (K) of mature sweet cherry (Prunus avium L.) trees were evaluated in situ based on a Ohm's law analog method. In June 2004, K was determined for 10-yr-old 'Bing'/'Gisela (R) 5' trees, from simultaneous measurements of whole canopy gas exchange and leaf (sunlit and shaded) and stem water potentials (Psi). Leaf water potential of sunlit leaves was lower than shaded leaves, reaching minimum values of ca. -2.3 MPa around 14:00 h (solar time). Average total hydraulic conductance was 60 +/- 6 mmol s(-1) MPa(-1), presenting a slight decreasing trend as the season progressed. The analysis of tree K components showed that it was higher on the stem-leaf pathway (150 +/- 50 mmol s(-1) MPa(-1)), compared to the root-stem component (100 +/- 20 mmol s(-1) MPa(-1)), which is in agreement with literature reports for other fruit trees. A weak hysteresis pattern in the daily relationship between whole-canopy transpiration (weighted sunlit and shaded leaves) vs. Psi was observed, suggesting that water storage within the tree is not a significant component of sweet cherry water balance.