Adaptability of leaves of Cistus ladanifer to widely varying environmental conditions

Resumen

1. Photosynthetic pigment composition, leaf area and leaf mass per area (leaf sclerophylly index, LSI) were analysed seasonally on young and mature leaves of three height levels of Cistus ladanifer, a drought semi-deciduous Mediterranean shrub, along a latitudinal transect within the Iberian Peninsula. 2. Climate and soil conditions varied widely along the transect. Annual rainfall ranged from 471 to 792 mm, mean annual temperature from 10.2 to 18.1°C, winter type from warm to cold, soil pH from 3.6 to 6.2 and organic matter from 0.46% to 6.96%. 3. Leaf characteristics showed very wide ranges: 0.38-4.42 mg g-1 DW and 103-901 mg cm-2 for total chlorophyll, 1.72-4.91 for chlorophyll a/b ratio, 1.77-6.80 for the ratio of optical densities OD430/OD665,0.9-11 cm2 for leaf area and 9.6-34.6 mg cm-2 for LSI. 4. The localities of the transect were ordinated by Principal Component Analysis (PCA) on the basis of climate and soil conditions. A third PCA, based on leaf characteristics, was more related to the climatic PCA than to the edaphic one, differentiating two groups of sites with extreme latitude values and a third group with intermediate latitudes. 5. Leaf characteristics of Cistus ladanifer were especially influenced by seasonal changes. A reduction in chlorophyll content and leaf area, and concomitant increases in OD430/OD665 and LSI, were detected in summer. The highest chlorophyll contents and the lowest OD430/OD665 ratios were found in autumn or winter, whereas the largest leaves were found in spring and the less sclerophyllous ones in winter. These findings are discussed in relation to the seasonal cycle of growth of Mediterranean semideciduous shrubs. 6. Plants from the localities of both latitudinal extremes of the transect showed suboptimum leaf characteristics as compared with plants from intermediate localities. Leaf differences caused by soil, leaf age and leaf location within the canopy were generally of little significance. The importance of leaf plasticity in the ability of Cistus ladanifer to grow in a range of harmful environments is emphasized.