Plant phenotypic plasticity belowground: A phylogenetic perspective on root foraging trade-offs

Many plants proliferate roots in nutrient patches, presumably increasing nutrient uptake and plant fitness. Nutrient heterogeneity has been hypothesized to maintain community diversity because of a trade-off between the spatial extent over which plants forage (foraging scale) and their ability to proliferate roots precisely in nutrient patches (foraging precision). Empirical support for this hypothesis has been mixed, and some authors have suggested that interspecific differences in relative growth rate may be confounded with measurements of foraging precision. We collected previously published data from numerous studies of root foraging ability (foraging precision, scale, response to heterogeneity, and relative growth rate) and phylogenetic relationships for 1100 plant species to test these hypotheses using comparative methods. Root foraging precision was phylogenetically and taxonomically conserved. Using ahistorical and phylogenetically independent contrast correlations, we found no evidence of a root foraging scale-precision trade-off, mixed support for a relative growth rate-precision relationship, and no support for the widespread assumption that foraging precision increases the benefit gained from growth in heterogeneous soil. Our understanding of the impacts of plant foraging precision and soil heterogeneity on plants and communities is less advanced than commonly believed, and we suggest several areas in which further research is needed.