Seasonal changes in CO 2 assimilation in leaves of five major Greek olive cultivars

Abstract

Leaf CO 2 assimilation rate, stomatal conductance ( g s), internal CO 2 concentration ( C i), chlorophyll ( a + b) content, specific leaf weight (SLW) and stomatal density were measured during the season, under field conditions, for five major Greek olive cultivars, ‘Koroneiki’, ‘Megaritiki’, ‘Konservolia’, ‘Lianolia Kerkiras’, and ‘Kalamon’, with different morphological and agronomic characteristics and diverse genetic background. Measurements were taken from current-season and 1-year-old leaves, and from fruiting and vegetative shoots, throughout the season, from March to November in years 2001 and 2002. CO 2 assimilation rates showed a substantial seasonal variation, similar in all cultivars, with higher values during spring and autumn and lower values during summer and late autumn. Stomatal conductance ( g s) followed similar trends to leaf CO 2 assimilation rates, increasing from March to July, following by a decrease during August and increasing again in autumn. ‘Koroneiki’ had the highest leaf CO 2 assimilation rate and g s values (21 μmol m −2 s −1 and 0.45 mol m −2 s −1, respectively) while ‘Lianolia Kerkiras’ and ‘Kalamon’ showed the lowest leaf CO 2 assimilation rate and g s values (13–14 μmol m −2 s −1 and 0.22 mol m −2 s −1, respectively). One-year-old leaves had significantly higher leaf CO 2 assimilation rate than current-season leaves from April to June, for all cultivars. From August and then, leaf CO 2 assimilation rate in current-season leaves was higher than in 1-year-old leaves. There were no significant differences in leaf CO 2 assimilation rate between fruiting and vegetative shoots. Total chlorophyll ( a + b) content increased with leaf age in current-season leaves. In 1-year-old leaves chlorophyll content increased in spring, then started to decrease and increased slightly again late in the season. Chlorophyll content was higher in 1-year-old leaves than in current-season leaves throughout the season. Total specific leaf weight (SLW) increased throughout the season for all cultivars. Stomatal density in lower leaf surface was lowest for ‘Koroneiki’ (399 mm −2) and highest for ‘Megaritiki’ (550 mm −2). Our results showed differences in leaf CO 2 assimilation rate among the five different olive cultivars, with a diverse genetic background, ranging from 12 to 21 μmol m −2 s −1. From the five cultivars examined, ‘Koroneiki’, a drought resistant cultivar, performed better and was able to maintain higher leaf CO 2 assimilation rate, even under high air vapor pressure deficit. All cultivars had a pronounced seasonal variation in leaf CO 2 assimilation rate, affected by date of the year, depending on ambient conditions. The high temperatures and high air vapor pressure deficit occurring during summer caused a reduction in leaf CO 2 assimilation rate in all cultivars. Leaf CO 2 assimilation rate was also affected by leaf age for all cultivars, with old leaves having significantly higher leaf CO 2 assimilation rate than young leaves early in the season.