PS 32-129 - Root trait trade-offs within and across phylogenetic clades of tallgrass prairie plants

Background/Question/Methods

Identifying the plant functional traits that best predict community assembly and ecosystem functioning may enhance restoration success. As tallgrass prairies have largely been eradicated from North America, they have been a large focus of restoration efforts. Given their proximity to soil microbes, root traits likely play a larger role in shaping soil ecosystem functioning than aboveground traits. When a phylogenetically diverse range of taxa are examined, root traits appear to be multidimensional and best explained by phylogenetic history. However, when studies are taxonomically narrow, there do appear to be consistent, one-dimensional root trait trade-offs. In this study, we characterized the functional and whole-system root traits of 106 greenhouse-grown tallgrass prairie species to assess trait trade-offs across an evolutionarily broad set of species and within phylogenetic functional groups. We harvested two individuals of each species and measured morphological, chemical, architectural, and symbiotic traits. Across all species, we expected to find trade-offs between specific root length (SRL) and average diameter, with forbs and nitrogen-fixers having greater root diameters and lower specific root lengths than graminoids. However, we hypothesized that the strength of the relationship between SRL and average diameter would vary across functional groups.

Results/Conclusions

We found that eudicots had greater root diameters and lower SRLs than monocots (P < 0.001). Similarly, forbs and nitrogen-fixers had greater root diameters than graminoids (P < 0.001) and nitrogen-fixers had lower SRL than graminoids and forbs (P ≤ 0.01). In general, we observed a tradeoff between SRL and root diameter, with SRL increasing as diameter decreases (P < 0.001, R2 = 0.57). The model fit was better for non nitrogen-fixing forbs and graminoids (R2 ≥ 0.61) than for nitrogen-fixers (R2 = 0.40). Our findings are consistent with the newly-proposed gradient of fungal collaboration, which predicts that plants at one end of the root trait spectrum have a “do-it-yourself” approach to resource acquisition and produce cheap roots with higher SRL for efficient soil exploration while plants at the other end of the spectrum “outsource” resource acquisition through investment in higher diameter roots that facilitate mycorrhizal colonization. Our results suggest that considering resource acquisition strategies across phylogenetic clades when establishing a restoration may help increase its success by filling more available niches.