Leaf water status of field-grown olive trees (Olea europaea L., cv Kalamata) under water regimes

Olive trees (Cv. Kalamata, 4-year old in 1995) in an orchard at the C.N.R.-ISPAIM experimental farm in southern Italy (41° 06' North, 250 m above sea level) were subjected to different water regimes, 0%, 33% and 66% of ETc. The paper reports the preliminary results of water regime effects on leaf midday water potential (LWP) and stomatal resistance (rs) during the irrigation seasons of 1995 and 1996. In the rainy year of 1995, LWP remained high in all treatments, with a value of -2.0 MPa observed in the rainfed control (T0) at the end of August. Stomatal resistance showed a similar pattern with values ranging from 3.2 to 5.6 s cm-1 in T0. The latter value was observed at DOY 186 when, during the daytime trend, recovery of LWP in the afternoon was not accompanied by a reduction in rs. In the dry year of 1996, water stress was more pronounced than the previous year. LWP decreased during the season, reaching the lowest value in mid-August in TO (-3.4 MPa) which was double the corresponding value of the previous year, and 0.8 MPa lower than T66. Water stress markedly affected rs, with highest values for T0 which increased from 4.0 to 7.8 s cm-1 during the season. The relationship between LWP and rs was not found in 1995 but was evident in 1996 (R2=0.65).