COS 243-3 - Fine-root functional traits across the gymnosperm phylogeny

Background/Question/Methods

Terrestrial plants must acquire multiple limiting resources from highly heterogeneous soil environments, for which they have evolved diverse root traits driving specific resource acquisition strategies. Yet, little is known about the scope and organization of fine-root trait diversity outside of angiosperm groups, which have dominated global syntheses. In this study, we quantified gymnosperm fine-root functional trait variation and determined whether trait relationships observed among gymnosperms are consistent with emerging global trait frameworks. A dataset comprised of 55 gymnosperm species representing seven of the 12 extant gymnosperm families was assembled using new observations made for 27 species growing at The Morton Arboretum in Illinois, USA and The Kórnik Arboretum in western Poland together with existing data from the Fine-Root Ecology Database (FRED). We focused our analyses on five morphological traits (root diameter, length, tissue density, specific root length, and specific root area) as well as branching ratio, root nitrogen concentration, and mycorrhizal colonization. We used summary statistics and Pearson’s correlation coefficient, respectively, to assess root trait variation and trait-trait relationships within the gymnosperm phylogeny. Principal components analysis (PCA) was utilized to determine the multi-dimensional correlation structure among traits across all species.

Results/Conclusions

The ranges of mean trait values were comparable to those observed for the much larger angiosperm group. Some morphological traits were correlated, but the architectural trait branching ratio was largely independent. Our principal component analyses showed root traits organized into a multidimensional space, which contained a collaboration axis defined by root diameter, specific root length, and mycorrhizal colonization, similar to that reported in global trait studies. Further reflecting global root-trait patterns, root tissue density and root nitrogen concentration opposed each other, forming a conservation axis orthogonal to the collaboration axis. Despite the distinct evolutionary history and historical biogeography of gymnosperms, our results indicate substantial functional trait diversity among gymnosperms that often reflects the diversity observed in angiosperms and show that gymnosperm trait relationships support patterns that have been observed in global studies. This consistency in trait variation and organization suggests that, globally, root traits are under similar physical constraints and selective pressures for functioning, resulting in consistent spectrums for belowground resource acquisition strategies. As our research continues, additional species representing four of the five currently unrepresented gymnosperm families will be added to the dataset.