| Abstract: | Interspecific variation in leaf life span reflects the variation in nutrient conservation ability among different plant species and is considered to be associated with nutrient availability in the characteristic habitat. As defoliation interferes with nutrient conservation by the long-lived leaves, we hypothesized that disturbance rate is another important environmental factor working as a selective force on interspecific variation in leaf life span. In order to investigate this, we measured leaf life span of 32 grass species in mature garden-grown individuals. Variation in leaf life span was compared to measured leaf traits, to available data on species occurrence along gradients of nutrient availability and disturbance, and to published relative growth rates of the species. Leaf life span was associated positively with leaf tissue mass density and negatively with specific leaf area. Leaf life span correlated negatively with the disturbance rate in the characteristic habitat of a species, but not with nutrient availability. The latter relationship did not come about due to the long leaf life spans of species from nutrient-rich habitats with a relatively low disturbance rate, and to some extent also due to the short leaf life spans of annual species from relatively nutrient-poor sites. We conclude that although leaf longevity is an important means of reducing nutrient losses, this is a selective advantage only if the plant is not subjected to frequent defoliation. The frequently postulated association between leaf life span of a species and nutrient availability in its characteristic habitat may occur among species of habitats with positively correlated nutrient availability and disturbance rate. Leaf life span is negatively associated with seedling RGR, but there may be deviations in this relationship due to species with contrasting characteristics at seedling stage and at maturity. |
