Nutrient Allocation and Responses to Defoliation in Tundra Plants

Abstract

The deciduous shrubs Salix pulchra and Betula nana and the deciduous graminoids Eriophorum vaginatum and Carex aquatilis have high rates of nutrient absorption and growth and large belowground storage reserves relative to the evergreen shrub Ledum palustre. Because of these characteristics, deciduous species can rapidly translocate nutrients into new growth early in the season and are most vulnerable to herbivores at this time. In contrast, the evergreen Ledum has a constant large allocation of nutrients to leaves throughout the year; these nutrient reserves are always accessible to herbivores and are chemically protected to a corresponding degree. Removal of leaf nutrients by defoliation causes greater mortality and reduction in productivity in Ledum than in deciduous species. Defoliation of the graminoids Eriophorum and Carex results in a large nutrient investment in leaf regrowth. Under such circumstances roots increase phosphate absorption and respiration rates, which helps to maintain plant nutrient reserves. Root growth rate decreases following defoliation, but root mortality increases only after severe, chronic defoliation.