The coordination between root and leaf functional traits across 33 woody plant species shifts between mycorrhizal types

Root and leaf traits are expected to converge on the plant economics spectrum (PES). Some studies have focused on correlation between specific root length (SRL) and specific leaf area (SLA), which reflect resource acquisition per invested mass in root and leaf, respectively. However, the results have been inconsistent amongst previous studies. We hypothesized that this discrepancy was due to overlooked variations in root traits depending on mycorrhizal types because SRL can be influenced by not only PES but also mycorrhizal types. To assess how mycorrhizal type inherently mediates the coordination of root and leaf traits, we determined the leaf and root traits of current-year seedlings of 33 species encompassing different leaf habits and mycorrhizal types, AM (arbuscular mycorrhizal) and ECM (ectomycorrhizal) species, grown under a common condition. Root and leaf traits correlated with the first axis of the principal component analysis, and this axis represented PES. Root diameter (RD) also correlated with the second axis, which differed between mycorrhizal types. Specific root length (SRL) and SLA were correlated positively to each other, but ECM species had higher SRL than AM species when compared at the same SLA. This was because (i) SRL is negatively related to root tissue density (RTD) and RD, (ii) RTD was negatively correlated with SLA and (iii) RD was smaller in ECM. Leaf and root traits are tightly coordinated with each other across species, but the relationship shifts between the mycorrhizal types.