Trend of a) net photosynthetic rate ( P
), b) stomatal conductance ( g
), c) intrinsic water use efficiency (IWUE) of P. lentiscus ( close squares ), P. latifolia ( open circles ), M. communis ( close triangles ), and Q. ilex ( open squares ) during the study period. The mean values for each month (±SE) are shown (n = 40 leaves). Mean values with the same letters are not significantly different (p ≥ 0.05). Lowercase letters indicate the differences among the species for each month, capital letters indicate the intra-specific differences during the study period.