Foliar-nitrogen and phosphorus resorption patterns differ among nitrogen-fixing and nonfixing temperate-deciduous trees and shrubs

Nutrient resorption from senescing leaves enables plants to conserve nutrients. Low foliar-nitrogen (N) resorption levels have been estimated in past studies for some N-fixing woody plant taxa. To determine whether this trait is characteristic of N-fixing temperate species, N-resorption proficiency estimates were derived for several species during two seasons in central Illinois, United States. Nutrient-resorption proficiencies were measured for 24 species of temperate-deciduous woody plants. Thirteen actinorhizal species and three non-N-fixing species in families with actinothizal species were sampled. One N-fixing woody legume, four non-N-fixing legumes, and two species lacking N-fixing capabilities and unrelated to these groups were also sampled. Nitrogen resorption, based on resorption proficiency values, was less in N-fixing species (1.78% N retained in abscised leaves) than in non-N-fixing species (1.01% N). Phosphorus (P) resorption, however, was greater in N-fixing species (0.06% P retained in abscised leaves) than in non-N-fixing species (0.26% P). Resorption of P may have been low in a group supporting ectomycorrhizal symbionts. Results indicate a consistent pattern in which N-fixing species are less proficient at N resorption than other temperate-deciduous woody species.