Testing four methods to assess leaf area in young olive trees

Assessment of leaf area is of fundamental importance to calculate diverse physiological parameters such as the total rate of transpiration or photosynthesis of a plant or its leaf area index (LAI). This paper reports the determination of total leaf area in 3 year-old olive trees of two varieties using four different methods and leaf counting as the control method. Leaf area was determined on 7 plants of each variety, Arbequina and Cobrançosa, by thoroughly counting the total number of leaves on each plant and then multiplying by the average leaf area for each variety Leaf area of the same plants was then estimated by (1) the analysis, with software ImageJ, of a photo of each plant from a side or from the top, (2) the crown light scattering measured with a ceptometer (AccuPAR Model LP-80) in the ground at 10 and 20 cm from the trunk, (3) the analysis with software Hemisfer of a photo of the plant from the top, and finally (4) by the determination of the transpiration (mmol s-1) of each plant over a 2 hour period by a weighing method and dividing this value by the mean transpiration rate (E) of each plant, calculated from the measurement of stomatal conductance (gs) on 10 leaves with a porometer and mean air RH and leaf and air temperature over the same period. Both the ceptometer and the Hemisfer software give a value of leaf area index (LAI). In order to obtain the leaf area, LAI was divided by the projected area of the crown obtained on photos from the top. Average leaf area (n = 7 × 30) was 0,238 × 10-3 m2 and 0,264 × 10-3 m2 for Arbequina and Cobrançosa, respectively. Total leaf area of each plant varied from 3,38 m2 and 4,85 m2 for Arbequina and 0,86 m2 and 3,99 m2 for Cobrançosa. Ceptometer and analysis of photos from a side gave estimates of leaf area under 50% of the actual leaf area. Analysis of photos from the top gave on average 70% the actual values. The most accurate methods were analysis with software Hemisfer and by the ratio of transpiration by E which gave values 5% bellow or 20% above actual values, respectively.