Photosynthetic Plant Stress in Urban Vacant Lots

Abstract

The trend of increasing vacant land in many cities in the United States has been considered as an avenue to increase urban greenspace, though soils in vacant lots tend to be poorer quality than rural soils of the same region. Using an Fv/Fm chlorophyll fluorometer to measure general stress, this study seeks to determine whether plants grown in this vacant lot soil experience higher stress than those grown in topsoil, as well as whether heightened competition from nonnatives associated with city plant communities induces stress. This study was executed using 32 experimental raised-bed plots on The University of Maryland, Baltimore County'scampus, each filled with either topsoil or vacant lot fill soil and each assigned to be weeded, unweeded, or left open for colonization. Only dominant species across all these plots were measured. Species studied are native species Eupatorium altissimum, Heliopsis helianthoides, Lespedeza capitada, Monarda punctada, Schizachyrium scoparium, Sorghastrum nutans, Tridens flavus and nonnative species Digitaria sanguinalis, Melilotus officinalus, Plantago lanceolata, Setaria faberi, and Taraxacum officinale. Data was collected pre-dawn at the end of the growing season, from September 20th through October 18th, 2019. The data was analyzed first in bulk, and then separated into native and nonnative species. No significant difference was found between soil types overall (topsoil mean=0.75, fill mean=0.761, p=0.15) , as well as for both native (topsoil mean=0.746, fill mean=0.752, p=0.72) and nonnative species (topsoil mean=0.754, fill mean=0.774, p=0.46). Weeding regime was significant overall (weeded mean=0.738, unweeded mean=0.761, open mean=0.763, p=0.016), but this effect vanished once analyzed at the native (weeded mean=0.767, unweeded mean=0.740, p=0.57) versus nonnative (unweeded mean=0.777, open mean=0.757, p=0.56) level. With no significant effect of urban soil or competition, the difficulty of maintaining high diversity of native species within cities is likely due to other factors, such as functional traits related to dispersal and life history strategy. Native species that can tolerate local soil conditions within cities should be considered for plantings and seedings where they are likely unable to disperse.