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Abstract Although rarely assessed, small‐scale heterogeneity in soil nutrient availability is suggested to be an important factor determining intraspecific variation in below‐ground plant resource acquisition strategies. We tested how increased resource availability and its small‐scale (0.25 m 2 ) spatial heterogeneity affect the nutrient acquisition strategy of Vaccinium myrtillus , a dominant ericoid shrub species in the forest understorey, by quantifying intraspecific root trait variation in an extensive set of root traits associated with nutrient acquisition. We hypothesized that increased nutrient availability would constrain the expression of traits that enhance nutrient acquisition, whereas spatial nutrient heterogeneity would promote a diversity of root trait values. Over 3 years, we applied spatially homogeneous and heterogeneous fertilization treatments (subplots of 6.25 m 2 in 10 sites of 1 ha) in a temperate forest in the Southern Black Forest (Germany). After 3 years, rooting units of Vaccinium myrtillus were sampled, and nine traits representing complementary aspects of nutrient uptake strategies were quantified, including aspects of root morphology, architecture and mycorrhizal association. Increased nutrient availability induced intraspecific trait adjustments: specific root length and mycorrhizal colonization were reduced, whereas root diameter, tissue density and branching intensity increased, suggesting a shift in plant investment strategies for nutrient acquisition. Heterogeneous nutrient availability did not increase trait variability, except for root phosphatase activity, indicating a more variable investment in phosphate extraction from organic matter. Overall, intraspecific trait variation was structured along the two main axes proposed by the interspecific root economics space. However, when additional traits tightly linked to nutrient acquisition were included, these formed independent axes of variation, suggesting that the root economics space only partially represents intraspecific adjustments relevant to soil resource acquisition. Synthesis . This study shows that intraspecific root traits respond to small‐scale changes in nutrient availability and are constrained along similar axes as global interspecific variation, extending the validity of the root economics space to the intraspecific level. However, in support to recent claims at the interspecific level, traits strongly conceptually tied to resource acquisition deviate from the root economics space, emphasizing the need to further explore the multiple ecological dimensions of plant nutrient acquisition.
Meyers et al. (Mon,) studied this question.