Time and terpenoids : Experimental and data-intensive investigations into temporal ecology and phytochemistry

Time and terpenoids mediate interactions between plants and their environment. Time has increasingly been recognized as a source of variability in ecological interactions. Despite known temporal variability in natural systems, ecological experiments often evaluate treatment effects at a single moment or as the aggregation of many moments in a community. I hypothesize that both treatment timing (i.e., when we apply a change to a system) and observation timing (i.e., when we measure a response) will affect the responses measured in herbivory experiments. Studying the interactions between Solidago altissima and insects and pathogens in in situ and common garden experiments, I evaluate how the timing and frequency of herbivory, as well as the timing of observations, affects estimations of plant growth and community responses. Feeding by Slaterocoris sp. (Hemiptera: Miridae) variably impacted subsequent chewing herbivory, pathogen damage, and plant height; pathogen damage was generally reduced in mirid-fed plants until the final observation date, and plant height was reduced in mirid-fed plants at all observation dates. In a second experiment, I found that late-timed jasmonic acid sprays significantly reduced chewing herbivory damage at the first observation, but not ten days later. Multiple sprays had cumulative effects on pathogen susceptibility, depending on spray timing.Terpenoids are the most diverse group of phytochemicals, yet identifying macro-scale trends in their diversity across environmental gradients and phylogeny has lagged due to limitations in cross-study synthesis and the logistical constraints of analyzing plant tissues at a global scale. Through a meta-analysis of studies on more than 200 plant species, I tested how terpenoid diversity varies across a gradient of two climate variables—mean annual temperature and annual precipitation—and if plant species that are more closely related produce more similar terpenoid profiles. I focused on two easily detectable superclasses of terpenoids, monoterpenoids and sesquiterpenoids. Both compound richness and structural alpha-diversity increased with increasing annual precipitation. I also found that more different temperature and precipitation regimes are associated with increasingly distinct terpenoid profiles. These patterns may be explained by the physicochemical properties that govern terpenoid release from plant tissue, including stomatal conductance, but further mechanistic investigations are needed. More closely related species produced more similar terpenoid profiles but less similar chemical substructures than more distantly related species. These phylogenetic patterns may be explained by plants sharing evolutionary history that constrains the overall terpenoid profile. Closely related species may also differentiate themselves through chemical substructures that govern other organisms’ structurally specific perception to compounds. Assembling large, detailed trait databases is imperative for the advancement of testing macroecological and macroevolutionary hypotheses, and most plant trait databases are assembled around morphological and life history traits that can be measured readily across many plant species. Phytochemicals have gone largely overlooked in the generation of these databases because the methods for detection, identification, and reporting vary widely across investigators and focal groups of chemicals. To lay a foundation for the development of global, quantitative, and methodologically detailed phytochemical databases, I present terpr v1.0.0, a database of plant monoterpenoids and sesquiterpenoids from 1127 studies containing 5107 samples from 1178 plant species, constituting 1852 unique identified monoterpenoids and sesquiterpenoids. I collected 86 features, including table indices, for each study, and present the database for further investigation into the patterns of terpenoid diversity, identification of valuable natural products, and best methodological practices.