Belowground competition is an important structuring force in terrestrial plant communities. Uncertainties remain about the plasticity of functional root traits under competition, especially comparing interspecific vs. intraspecific situations. This study addresses the plasticity of fine root traits of competing Acer pseudoplatanus L. and Fagus sylvatica L. seedlings in nutrient-rich soil patches. Seedlings’ roots were grown in a competition chamber experiment in which root growth (biomass), morphological and architectural fine roots traits, and potential activities of four extracellular enzymes were analyzed. Competition chambers with one, two conspecific, or two allospecific roots were established, and fertilized to create a nutrient ‘hotspot’. Interspecific competition significantly reduced fine root growth in Fagus only, while intraspecific competition had no significant effect on the fine root biomass of either species. Competition reduced root nitrogen concentration and specific root respiration of both species. Potential extracellular enzymatic activities of β-glucosidase (BG) and N-acetyl-glucosaminidase (NAG) were lower in ectomycorrhizal Fagus roots competing with Acer. Acer fine roots had greater diameter and tip densities under intraspecific competition. Fagus root traits were generally more plastic than those of Acer, but no differences in trait plasticity were found between competitive situations. Compared to Acer, Fagus roots possessed a greater plasticity of all studied traits but coarse root biomass. However, this high plasticity did not result in directed trait value changes under interspecific competition, but Fagus roots grew less and realized lower N concentrations in comparison to competing Acer roots. The plasticity of root traits of both species was thus found to be highly species- but not competitor-specific. By showing that both con- and allospecific roots had similar effects on target root growth and most trait values, our data sheds light on the paradigm that the intensity of intraspecific competition is greater than those of interspecific competition belowground.

Aims Specific root respiration (RRS) is a key root trait, determining i.e. nutrient foraging and uptake efficiencies. However, a considerable uncertainty exists regarding the effects of storage time and conditions on RRS measurements. Methods Fine root CO2 efflux rates of three plant types (tree seedling Carpinus betulus, legume Pisum sativum, grass Lolium perenne) were measured as depending on storage time (30–1440 min post-rinsing) and conditions (i.e. attached to plant, warm and cold water storage, and storage under dry conditions). Results Short-term storage conditions (30 min) had a significant effect on measured RRS rates, in specific, RRS rates of all three species were significantly lower under dry storage. Irrespective of plant species or temperature, storage of excised roots in water did not affect RRS for 300 min,. RRS measurements remained stable for 1 day if roots were stored cold. Conclusions Our results have important implications on measurement routines of RRS—a generally understudied root trait. Henceforth it seems reasonable to collect roots in the field and transport them, hydrated but even uncooled, to the laboratory for subsequent measurements for at least 300 min post-rinsing.