Urban, suburban, and rural environments may differ in many factors that affect growth and survival of organisms, including temperature, abiotic and biotic soil conditions, and frequency of human disturbance. What do such differences mean for plant populations, and species that interact with plants? This study explored the association between urbanization and the density, phenology, and foliar fungal pathogen infections of common herbaceous plants in the metropolitan area of St. Louis, Missouri, USA. Specifically, we studied Plantago lanceolata and Plantago rugelii and their powdery mildew pathogens. These species are ideal for investigating effects of urbanization, because they are abundant in human-disturbed habitats, and the genus Plantago features in studies of plant ecology and plant-pathogen interactions worldwide. We performed monthly surveys of these plants in two 0.5 x 15 m belt transects, plus censuses of 50 randomly selected plants outside the transects, in each of 21 sites from June-October 2019. The sites (primarily city and county parks) span > 60 km along an urbanization gradient from urban downtown St. Louis to rural Shaw Nature Reserve. We assessed how the abundance and spatial distribution, stage of flower development, and powdery mildew infection of the focal plants changed through time across the urbanization gradient. We asked questions including: (1) does rate of flower development differ between urban, suburban, and rural sites and (2) do powdery mildew epidemics begin earlier in the season and reach higher peak infection prevalence in urban than rural areas?
Results/Conclusions
Our preliminary analyses show that rates of flowering and seed development were overall much higher for Plantago rugelii than P. lanceolata. Within each species, the proportion of plants at a given stage of flower development varied strongly with time, and less dramatically between habitat types. Plantago rugelii in urban and suburban sites became infected with powdery mildew significantly earlier in the summer season than P. rugelii in rural sites. Powdery mildew infection prevalence on P. lanceolata was overall very low, so urban-suburban-rural contrasts could not be evaluated. This study is significant because little research has been published on the impact of urbanization on plant diseases, and it is important to begin filling this major gap in our knowledge of human impact on the environment. Ongoing work involves developing computational methods for digital image analysis of photos taken of 0.5 x 0.5 m quadrats along the belt transects in the field sites, to aid in future studies of this and similar systems.