Functional Morphology of Mountain Plants )

Abstract

Summary A quantitative survey of the differences in morphology and anatomy in shoots and leaves from contrasting altitudes in different mountain areas, including the tropics, is provided. The majority of data was obtained for herbaceous perennial plants in the Central Alps, where traits of 20 to 30 species from low (600m) and high (3,000m) altitude have been analysed. These results are representative of trends observed in other mountain areas and can be summarized as follows: 1. Individual plants at high altitude occupy 1/5 of the ground area, attain 1/7 of the height, and 1/9 of total shoot leaf area of low elevation taxa, although the mean number of leaves per individual (21) remains similar. Leaf inclination tends to be steeper, and self-shading by leaves and flowers is greater at high altitude. 2. Leaves from high altitude taxa attain 1/11 of the area of leaves of low altitude species. Turgid water content and degree of succulence are not different. At high altitude specific leaf area (SLA) is reduced and leaf thickness is increased. Length and dry matter fraction of petioles are drastically reduced at high altitude. 3. Leaf tissue: in alpine species air space volume in the mesophyll and mesophyll surface/leaf area ratio are one third larger, and the palisade tissue, on an average, consists of 2.7 instead of the 1.7 cell layers found in low altitude forbs. 4. Cell size in leaves and fine roots shows no statistically significant difference between elevations. Some of the highest ranging alpine species exhibit particularly large cells. 5. The thickness of cell walls, particularly in the epidermis, is greater at high altitude. 6. Stomata: Plants from high altitude show a greater fraction of adaxial stomata. In a global comparison stomatal density correlates with the radiation regime and thus shows no uniform altitudinal trend. In most areas investigated, however, density rises with elevation and then declines near the upper elevational limit of a species. A large portion of the leaf characteristics observed at high altitude is lost when plants are transplanted to low elevations. It is suggested that low temperature at high elevation is responsible for small plant and organ size, increased cell wall thickness, and in part, also greater leaf thickness. High light intensities exert additional increases of mesophyll thickness and affect distribution and density of stomata. Nutrient supply and partial pressure of CO 2 appear to be uneffective in this respect. Thus, low temperature and strong light co-determine leaf structures at high altitude in the Alps, leading to highly efficient leaves with respect to photosynthesis (Korner & Diemer 1987). The fact that cell size is not reduced at high altitudes, indicates that mountain plants and their respective organs are small because they produce fewer cells.