Plasticity of Root Traits under Competition for a Nutrient-Rich Patch Depends on Tree Species and Possesses a Large Congruency between Intra- and Interspecific Situations

Abstract

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.

Plasticity in response to plant–plant interactions and water availability

“…Trait plasticity may “enhance species’ ability to coexist” (Pfennig et al 2006), but this depends on other factors (see review by Turcotte and Levine 2016). Because plasticity has the potential to reduce niche overlap, we might expect competitors to exhibit plasticity in response to severe conditions, such as drought (Lak et al 2020, Lorts and Lasky 2020). We found plasticity in all traits for Potentilla in intraspecific or interspecific competition, and for root mass and root : shoot ratios for Leucanthemum in intraspecific competition.…”

Root System Traits Contribute to Variability and Plasticity in Response to Phosphorus Fertilization in 2 Field-Grown Sorghum [ Sorghum bicolor (L.) Moench] Cultivars

“…We assessed root phenotypic plasticity for all features having CoV values ≥ 30% and for which there was a significant difference between genotypes. We adapted the procedure of Lak et al [ 42 ] to calculate RDPI. The RDPI ranges from 0 (no plasticity) to 1 (maximum plasticity) [ 20 , 43 , 44 ].…”

Root litter decomposition is suppressed in species mixtures and in the presence of living roots

“…This finding suggests that interactions between roots of different species growing together did not affect root litter quality. This is in contrast with the limited evidence showing that intraspecific and interspecific interactions can induce changes in plant litter quality (Genung et al, 2013;Lak et al, 2020;Semchenko et al, 2017). For instance, it has been shown that root N concentrations under interspecific competition were lower than under intraspecific competition and single plants (Lak et al, 2020).…”

“…This is in contrast with the limited evidence showing that intraspecific and interspecific interactions can induce changes in plant litter quality (Genung et al, 2013;Lak et al, 2020;Semchenko et al, 2017). For instance, it has been shown that root N concentrations under interspecific competition were lower than under intraspecific competition and single plants (Lak et al, 2020). Also, more genetically diverse mixtures of the same species produced root litter with higher N content (Semchenko et al, 2017).…”