Nitrogen and phosphorus resorption efficiency and proficiency in six sub‐arctic bog species after 4 years of nitrogen fertilization

Abstract

Nitrogen and phosphorus resorption efficiency and proficiency in six sub‐arctic bog species after 4 years of nitrogen fertilization

1 Plant growth at high‐latitude sites is usually strongly nutrient‐limited. The increased nutrient availability predicted in response to global warming may affect internal plant nutrient cycling, including nutrient resorption from senescing leaves.

2 The effect of increased N supply (10 g N m−2 year−1) on nitrogen and phosphorus resorption efficiency and proficiency in six sub‐arctic bog species, belonging to four different growth‐forms, was studied in northern Sweden.

3 We hypothesized that while increased N supply would not affect N or P resorption efficiency, it would lead to lower N resorption proficiency (higher N concentrations in leaf litter) and higher P resorption proficiency (lower P concentrations in leaf litter). We also investigated whether the basis on which resorption was expressed (leaf mass, leaf area or unit leaf) influenced the patterns observed.

4 Contrasting with our hypothesis, a general trend of decreased N resorption efficiency occurred in response to increased N supply, but the expected decrease in N resorption proficiency was seen in all species except Betula nana.

5 P resorption efficiency did not change in four species (B. nana, Empetrum hermaphroditum, Eriophorum vaginatum and Rubus chamaemorus) but it decreased in Andromeda polifolia, and increased in Vaccinium uliginosum. P resorption proficiency showed the expected increase in only two species (B. nana and V. uliginosum).

6 Apart from P resorption efficiency, the different calculation methods generally produced similar responses of resorption efficiency and proficiency to N supply.

7 Increased N supply at high‐latitude sites clearly leads to more N being returned to the soil through leaf litter production. However, decomposition of such litter will probably become P‐limited.

8 Considerable interspecific differences in nutrient resorption proficiency were found, indicating that long‐term changes in vegetation composition need to be considered when evaluating plant‐mediated effects on ecosystem nutrient cycling in response to increased nutrient supply.