Evolution of plant functional strategies

Photo Credit

USDA figure by Robert Heckman

Selection on two leaf functional traits promotes correlated functional syndromes based on data from sites in Texas, Missouri, and Michigan.

Integrated plant functional strategies arise via selection on trait combinations and genes that encode multiple traits.

Trade-offs occur when traits that confer an advantage in one environment also confer a disadvantage, either in the same or a different environment. Considering trade-offs is important because they often limit the ability of plants to respond to novel conditions, which may reduce their performance or their ability to provide ecosystem services. One such trade-off—the leaf economics spectrum—results from differences in resource availability. In high resource environments, plants typically possess short-lived leaves with low structural costs and high nutrient content, while in low resource environments, plants often have long-lived leaves with high structural costs and low nutrient content.

Despite strong evidence for the presence of the leaf economics spectrum at broad geographic and taxonomic scales, few studies have examined how this spectrum evolves. In a dominant warm-season tallgrass species, switchgrass, we show that leaf economics strategies could evolve through a combination of mechanisms: pairs of leaf economics traits (photosynthetic rate and nitrogen content) may be coded by the same genes and selection for particular, advantageous trait combinations (e.g., low nitrogen concentration and high leaf structural costs) and against other, deleterious combinations. Moreover, selection on leaf economics traits can differ geographically—near switchgrass’s southern range limit where growing seasons are long, a slow-return on investment strategy with high leaf structural costs was favored; further north, where growing seasons are shorter, a quick-return on investment strategy with high nitrogen concentration and low leaf structural costs strategies was favored. Together, these evolutionary causes can promote the evolution of distinct leaf economics strategies within different varieties of switchgrass.

Understanding how these leaf economics strategies have evolved geographically will improve our ability to select plant varieties that thrive in different environments and help promote management of productive grasslands that can provide necessary ecosystem services.