The ecology of a species depends on the traits of that species, but which traits are of greatest ecological and phylogenetic importance? Traits that are easy to measure may not reflect the underlying tradeoffs that underpin species coexistence and their evolutionary history. A growing body of literature is suggesting that data on plant tissue levels of N, P, K, Ca and other elements might offer insight into the functional and phylogenetic differences among species. By using results of a long-term biodiversity experiment, we determined how plant tissue chemistry traits compared in their predictive power to traits related to leaf physiology and morphology.
The experiment was conducted in a prairie-grassland ecosystem with perennial plant species at the Cedar Creek Ecosystem Science Reserve. The experiment, Biodiversity II, manipulates biodiversity with levels of 1, 2, 4, 8, and 16 plant species. A variety of plant traits were collected on-site and others queried from existing plant databases for the fifteen plant species that persisted in monocultures. These 36 plant traits, of which 13 were chemical traits, were used to test for a phylogenetic signal using various statistics with Blomberg’s K reported herein. Additionally, these same traits were run through an agglomerative clustering algorithm.
Results/Conclusions
The plant species within this experiment clustered, based on tissue Ca, K, B and N levels, into functional groups that matched their phylogeny: grasses (Poaceae), legumes (Fabaceae) and forbs (Asteraceae; Lamiaceae; Apocynaceae). Aboveground tissue % calcium and % boron led to the phylogenetic (K >1, P< 0.05) separation of grasses from forbs and legumes, as did leaf width (K >1, P< 0.05). Within the grasses, delta 13 carbon isotope ratios discriminated C3 from C4 grasses (K >1, P< 0.05). Within the broadleaves, forbs had higher % boron and % potassium (0< K< 1, P< 0.05) than legumes. Legumes had higher % nitrogen than other taxa (K >1, P< 0.05).
Our analyses demonstrate that tissue chemistry traits had stronger power to discriminate plant phylogeny and functional groups than did most classic leaf traits. The species in this experiment appear differentiated in their biogeochemical niche, perhaps including their abilities to compete for soil nutrients. In effect, increasing species richness assembles a greater breadth of tissue chemical traits, providing the functional diversity that influenced ecosystem processes. Tissue chemical levels, termed the plant elementome, was a powerful approach to capture functional and phylogenetic biodiversity
