Induced plant defensive traits in ecosystems: The consequences of genes and nutrients in Solidago altissima

Background/Question/Methods

Recently, scientists have become very interested in connecting genetic material to ecosystem processes through plant traits (e.g. genes to ecosystems). However, genetic effects are modified by interactions with the environment that can change phenotypic expression of key traits thus altering the impact on ecosystem processes. If phenotypes are quite plastic than the environment may be a better predictor of the impact of plants on ecosystem processes than genotype. I examined this question by measuring induced defensive traits (tolerance and resistance) in nine genotypes of Solidago altissima along a four level nutrient gradient. Individuals of Melanoplus femurrubrum, a dominant old field grasshopper species, were used to induce defensive traits and measure differential plant resistance through bioassays.

Results/Conclusions

In general, S. altissima exhibited highest induced resistance to herbivores at the highest nutrient level. In contrast, plants in low nutrient environments exhibited the highest tolerance of herbivory. Resistant and tolerant plants tended to associate with different suites of plant functional traits (leaf toughness, nutrient content etc.) and have different effects on herbivore stoichiometric ratios. Because plant and animal stoichiometry are a major determinant of decomposition dynamics in ecosystems, these divergent, plastic trait responses to herbivory may feedback to create heterogeneity in nutrient context and thus impact future plant/herbivore interactions. In this system, it is clear that both genes and environment play strong roles in mediating ecosystem process. However, it is a challenge to understand how these individual plant responses scale within real ecosystems that are characterized by spatially clumped genotypes and nutrient environments across the landscape. Preliminary results from a multi-year field mesocosm experiment designed to explicitly test this question demonstrate that clumping of differential plant induction across landscapes may drive changes to ecosystem processes such as nutrient cycling and decomposition.