Nutrient acquisition in plants can be represented by a suite of intercorrelated root traits such as root diameter, nitrogen content, root tissue density, and specific root length. However, it is unclear how a plant's ability to precisely forage for nutrients in a heterogeneous soil environment (i.e., the precision of placing roots into nutrient-rich areas) relates to these traits. Mycorrhizal symbiosis also affects the relationship between the fine root traits and root foraging precision because fungal hyphae may be used for foraging instead of roots. Hypotheses matching high root foraging precision with low mycorrhizal colonization or "fast" acquisitive strategies of plants have been raised based either on data from tree species or a limited number of herbaceous species.

To test these hypotheses, we compiled data quantifying the experimentally measured degree to which root biomass responded to patchy substrate nutrient concentrations (i.e., root foraging precision) for 123 herbaceous grassland species using a partial meta-analysis. We tested root foraging precision relationship with root traits involved in nutrient acquisition and mycorrhizal symbiosis (root diameter, specific root length, root tissue density, root tissue nitrogen content, and mycorrhizal colonization). The root foraging precision data came from four different pot experiments, and the trait data were extracted from publicly available trait databases. We used a phylogenetically informed approach in order to detect the degree of conservation of the relationships. 

We found that root foraging precision was not significantly correlated with other fine root traits and mycorrhizal colonization. Thus, it appears unrelated to the main dimensions of the nutrient acquisition space of herbaceous species, namely acquisitive-conservative strategy and outsourcing of acquisition to the fungi. Also, we found only a very weak phylogenetic signal in root foraging precision of 123 species. Our results suggest that root foraging precision constitutes another distinct, evolutionarily independent dimension in herbaceous species' trait space.

We collected data about the root foraging potential of 123 herbaceous species from four different studies conducted between 2010 and 2017 (Belter 2014, Keser et al. 2014, 2015, Weiser et al. (2016 + unpublished data)). Root foraging precision was calculated for each plant separately as log (root biomass in rich patch/root biomass in poor patch).

Plant root traits were extracted from the "Global root traits (GRooT) database" (Guerrero-Ramirez et al. 2021) and from the Alberta grassland plant trait database (Cahill 2020). The traits used here were: root diameter (62 species, [cm]), nitrogen (N) content in roots (60 species, [mg/g]), root tissue density (RTD; 66 species, [g/cm³]), and specific root length (SRL; 74 species, [m/g]).

Specific leaf area (SLA, [mm²/mg]) was collected from the LEDA Traitbase (Kleyer et al. 2008) for 91 species. 

We collected mycorrhizal data from the "FungalRoot: Global online database of plant mycorrhizal associations" (Soudzilovskaia et al. 2020). We classified species solely noted as having arbuscular mycorrhiza (AM) associations as "obligatorily mycorrhizal" (55 species), species with both AM and non-mycorrhizal (NM) records as "facultatively mycorrhizal" (44 species), and species with only NM records as "non-mycorrhizal" (7 species). We also extracted data about the intensity of mycorrhizal colonization from the same database (60 species). 

Belter, P. R. 2014. Relationships among diverse root foraging behaviours: understanding plant behavioural types - supporting data. - ERA

Cahill, J. F. 2020. Alberta grassland plant trait data. - ERA

Guerrero-Ramirez, N. R. et al. 2021. Global root traits (GRooT) database. - Glob. Ecol. Biogeogr. 30: 25–37.

Keser, L. H. et al. 2014. Invasive clonal plant species have a greater root-foraging plasticity than non-invasive ones. - Oecologia 174: 1055–1064.

Keser, L. H. et al. 2015. Herbaceous plant species invading natural areas tend to have stronger adaptive root foraging than other naturalized species. - Frontiers in Plant Science 6: 273.

Kleyer, M. et al. 2008. The LEDA Traitbase: a database of life-history traits of the Northwest European flora. - Journal of Ecology 96: 1266–1274.

Soudzilovskaia, N. A. et al. 2020. FungalRoot: global online database of plant mycorrhizal associations. - New Phytol. 227: 955–966.

Weiser, M. et al. 2016. Root Foraging Performance and Life-History Traits. - Frontiers in Plant Science 7: 779.

Missing values are marked as "NA".

The variable names used in the dataset are described at ReadMe file.

For more details about data processing see Materials and Methods section of the paper.