Life span and dynamics of leaves of herbaceous perennials in high‐elevation environments: ‘news from the elephant’s leg’

Abstract

1. Leaf life spans, determined as half‐lives, of 16 herbaceous perennial plant species from the aseasonal, tropical Andes at altitudes between 4000 and 4600 m were on average 193±19 days and thus two to three times greater than those of herbaceous perennials from the seasonal northern hemisphere. The duration of lamina expansion was positively correlated with life span. Growth was continuous all year round, but rates of leaf initiation in the high‐elevation tropics were lower than in the temperate zone. 2. Significant positive inter‐relationships were found between leaf life span and mass‐based foliar nitrogen concentration of Andean taxa. The correlation between life span and leaf mass per area (LMA) was marginally significant, while life span and area‐based foliar N content were unrelated. 3. Leaf traits of 46 Andean herbaceous perennials (forbs and graminoids), spanning an altitudinal range of 1500 m, indicated that the 16 taxa utilized for growth and leaf life span determinations were representative. For graminoids no altitudinal changes in LMA or foliar N were observed across species. However, in forbs LMA and area‐based foliar N increased significantly with altitude. No differences in leaf traits were observed between herbaceous rosette and cushion growth forms. 4. The Andean data set was used in conjunction with data from the temperate, subarctic and arctic zones to evaluate the significance of leaf life spans in herbaceous plants from a biogeographical perspective. Leaf life span declined significantly with increasing seasonality, expressed as latitude and duration of the annual growth period. Because temperature regimes are similar along this gradient during the respective growth periods (Diemer 1996), observed differences should be the result of variation in the day length and/or duration of the growing season. 5. Data on leaf life spans and leaf traits of herbaceous plants from contrasting latitudes were used to evaluate the validity of general inter‐relationships proposed by Reich (1993). The high correlation between LMA and life span observed in both data sets indicates that this relationship holds for various growth forms. On the other hand, the apportionment of mass‐based foliar N concentration in relation to life span appears to differ between herbaceous and woody growth forms.