AN ECOLOGICAL FRAMEWORK FOR WEED POPULATION DYNAMICS AND CROP COMPETITION UNDER A CHANGING CLIMATE: PARTHENIUM HYSTEROPHORUS AS A MODEL SPECIES

The overarching goal of this project is to study the effects of climate change on global populations of parthenium (Parthenium hysterophorus) through the lens of ecological feedback between the soil, weeds, and crops. This projectwill provide ecological insights into the adaptation of global parthenium biotypes (i.e., US, Australia, India, Israel) to climate change by 1) uncovering climate interactions driving aboveground and belowground weed-crop competition in a growth chamber study, 2) identifying adaptive weedy traits in irrigated/dryland cropping systems replicated across five global field environments, and 3) link ecological and climate data to population dynamics models to predict risk of range expansion for US agriculture.In addition to guiding the management of parthenium, this projectwill produce general insights into the direct and indirect effects of climate change on invasive agricultural weeds. To this end, this project hasthe following three objectives:Objective 1. Assess the interactive effects of climatic factors on parthenium growth, below-ground interactions, and competition against C3 and C4 crops. The interactive effectsof temperature, moisture, CO2 concentration, and parthenium population (four global populations) on weed and crop morphology, physiology, and yield will be evaluated in a growth chamber experiment. We will also extract allelopathic compounds and conduct microbial analyses to investigate the relationship between allelopathy and microbial activity, including its response to climate change and its effect on crop growth.Objective 2. Investigate how drought modifies parthenium competition against C3 and C4 crops in representative global cropping systems. A common garden experiment will evaluate morphological variation and weedy traits across four global parthenium populations in competition with regionally important C3 and C4 crops grown under dryland and irrigated conditions at five field sites in four representative countries.Objective 3. Incorporate ecological knowledge into existing population dynamics models to improve predictions about climate-driven range expansion across agricultural landscapes. We will use our experimental data to build upon existing population dynamics models, applying ecological knowledge about the nexus of climate change, range expansion, and weed plasticity to better predict threats to US and global cropping systems.