Foliar nutrient resorption differs between arbuscular mycorrhizal and ectomycorrhizal trees at local and global scales

Aim: Trees associating with ectomycorrhizal (ECM) fungi typically occur in infertile soils and use nutrients more conservatively than arbuscular mycorrhizal (AM) trees. We hypothesized that ECM trees would have greater nutrient resorption (i.e., proportion of nutrients resorbed during leaf senescence) than AM trees. Location: Global. Methods: We synthesized nitrogen (N) and phosphorus (P) resorption data from 378 species from sub/tropical, temperate and boreal forests, including 43 studies where ECM and AM trees co-occurred, and conducted a meta-analysis. Additionally, we quantified N resorption in 45 plots varying in ECM-AM tree abundances in the temperate deciduous forests of southern Indiana, USA. Results: Overall, resorption patterns were driven primarily by mycorrhizal type, climate zone, and to a lesser degree, leaf habit. In the boreal forest, P resorption was 76% greater for ECM than AM trees (p <.05). In the sub/tropics, AM trees resorbed 30% more N than ECM trees. At the sites where AM and ECM trees co-occurred, ECM trees resorbed more N in temperate forests (15% greater; p <.001) whereas AM trees tended to resorb more N in sub/tropical forests (by 29%; p =.08). Besides, deciduous ECM trees resorbed more N (10%) and P (15%) than deciduous AM trees, while evergreen ECM and AM trees did not differ. In the deciduous forests of Indiana, where ECM and AM trees co-occurred, the relative abundance of ECM trees in a plot was positively correlated to plot-scale N resorption (R2 =.25, p =.001), indicating greater nutrient conservatism with increasing ECM-dominance. Main conclusions: Our results indicate that mycorrhizal association – in addition to other factors – is correlated with the degree to which trees recycle nutrients, with the strongest effects occurring for N resorption by temperate deciduous trees.