From Genes to Ecosystems: The Genetic Basis of Condensed Tannins and Their Role in Nutrient Regulation in a Populus Model System.

The influences of condensed tannins (CT) in ecology have long been appreciated in the context of plant-herbivore interactions, but research in the last 20 to 30 years has demonstrated that CT have important ecological consequences beyond trophic dynamics at the level of populations. Moreover, recent advances in genomics have revealed mechanisms and signals for up- or down-regulation of phenylpropanoid pathways and condensed tannin concentrations in plants, as well as putative regions of the genome that are correlated with the expression of CT. These concurrent advances provide the opportunity for a better understanding of the ecological and evolutionary consequences of the expression of CT. Taking a genes-to-ecosystem approach and using Populus spp. as a model system, we examine the diverse ecological effects of CT across above- and belowground processes as well as across terrestrial and aquatic ecosystems. Results to date in Populus highlight the importance of CT in large-scale and long-term ecological processes and demonstrate the following four patterns: 1) CT have little consistent effect on plant-herbivore interactions, excepting organisms utilizing woody tissues (i.e., fungal endophytes and beaver); 2) foliar CT consistently slow rates of leaf litter decomposition (aquatic and terrestrial), alter the composition of heterotrophic soil communities (and some aquatic communities) and reduce nutrient availability in terrestrial ecosystems; 3) large within-plant variation in the expression of CT occurs due to induction of CT by herbivory, ontogenetic stages (i.e., juvenile and mature), and across tissue types (i.e., leaves vs. twigs); and 4) plant-specific tannin structure among species and possibly genotypes may result in varying ecological responses. Taken together these results demonstrate that combining quantitative and molecular genetics techniques with ecological approaches can provide a powerful tool for elucidating the complex biological interactions driven by CT.