Terrestrial plants must acquire multiple limiting resources from highly heterogeneous soil environments, for which they have evolved diverse root traits and resource acquisition strategies. Fine-root functions affect plant health, species’ population distributions, and ecosystem nutrient cycles, but little is understood about the scope and organization of fine-root trait diversity outside of angiosperm groups. This study sought to characterize functional trait variation in fine roots of gymnosperms. First-order to third-order roots were sampled from 14 phylogenetically-diverse gymnosperm species representing 6 of the 12 extant gymnosperm families. Samples were collected from trees growing at The Morton Arboretum in Lisle, Illinois, USA. For each species, one architectural trait (branching ratio) and five morphological traits (root diameter, length, tissue density, specific root length, and specific root area) were measured. Trait-trait relationships were inspected using standard linear regression.
Results/Conclusions
Mean trait values expressed wide variation across species. For example, first-order root diameter ranged from 0.21 to 0.77 mm and first-order root length ranged from 1.47 to 10.44 mm. When compared to similar studies focused on angiosperm species, these results suggest that gymnosperm functional diversity may be comparable to that of the much larger angiosperm group. Some morphological traits were correlated with each other. For example, first-order root diameter was negatively correlated with first-order specific root length (r = -0.66, P = 0.01). However, morphological traits were not correlated with branching ratio. From a qualitative assessment of trait shifts along the gymnosperm phylogeny, no clear, directional shifts in fine-root trait values from ancestral species to relatively derived species were observed, though increased species coverage would enable more formal phylogenetic analysis. These results indicate substantial functional trait diversity among gymnosperms and emphasize the need for comprehensive fine-root trait studies that widely represent gymnosperm evolutionary history and adaptations to different environments.