Foliar Nutrient Dynamics and Resorption in Naturalized Lonicera maackii (Caprifoliaceae) Populations in Ohio, USA

Abstract

Foliar phosphorus (P) and nitrogen (N) concentrations and nutrient resorption in the forest understory shrub Lonicera maackii (Rupr.) Maxim (Caprifoliaceae) were measured along contiguous topographic gradients in two southwestern Ohio forests during 1992-1994. Mean summer foliar P varied significantly among topographic positions (but not sites or years), with uplands having greatest P concentrations and bottomlands exhibiting the lowest. Unlike for P, the mean summer foliar N concentrations varied little among sites, topographic positions, and years. Mean absolute and proportional P resorption ranged from 0.48 mg/dM2 (33.7%) in slope positions to 0.80 mg/dM2 (53.1%) in bottomland positions. Repeated-measures analysis of variance (RMANOVA) for P resorption indicated significant topographic and year effects, a site X year and a site X year X topographic interaction. Mean absolute and proportional foliar N resorption ranged from 6.82 mg/dM2 (30.7%) in bottomlands to 8.41 mg/dM2 (37.3%) in slope positions. RMANOVA indicated a significant topographic effect for both absolute and proportional N resorption and a significant year effect for absolute N resorption. These significant year effects for P and N stemmed from lowest resorption of nutrients in 1993. The results for P resorption support the hypothesis that foliar resorption is greater in forested sites with lower P fertility. However, resorption rates for N did not support the hypothesis clearly, as slopes with intermediate N availability had greater N resorption rates than did N-rich bottomlands.