Urbanization impacts on red maple (Acer rubrum L..) in deciduous forests embedded in cities

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University of Delaware
The urban forest should be viewed as living ‘public health’ and an environment ‘bio-recording’ infrastructure in urban environments. This infrastructure is extremely vital to achieving ‘greener’ cities, as the globe becomes more urbanized. However, plant data supporting urban plants as environmental mitigating infrastructures are sparse, inconsistent, and not long-term in approach. Moreover, the lack of data on the physiology, biochemistry, morphology, and long-term stress adaptation of plants in urban environment is a current gap in urban plant-ecology research. Cities are a natural ‘open lab’, and city size can be a proxy for multiple co-occurring impacts on plants that determine productivity and acclimation to better assess plant effectiveness. The FoRests Among Managed Ecosystem (FRAME) network was used to investigate urbanization (e.g., city size) impacts on the physio-biochemistry and morphology of red maple (Acer rubrum L.) in urban forests in a small (Newark, DE) and large (Philadelphia, PA) city. In addition, a manipulated field experiment was used to decipher above- and below-ground urbanization impacts on the physio-morphology of red maple (A. rubrum) saplings in urban forests. I measured health indicating pigments, nutrient ions, stress signaling metabolites, and morphological traits that can integrate multiple stress impacts and provide insight into urban forest trees’ ability to effectively mitigate urban conditions. I found greater chlorophyll, free amino acids and spermine, nutrient ions (N, P, K), and stomatal size in red maples in Philadelphia forests relative to Newark forests suggesting these traits are good indicators and integrators of multiple co-occurring stress impacts on plant growth, productivity, and acclimation in the large city. The results indicate cities as a surrogate and red maple as a biomonitor for urbanization impacts can be a good model system to study urban plant physiology and long-term stress mitigation-adaptation. The findings showing greater physio-biochemical and morphological response in the large city suggest theoretical models that do not account for physiological acclimation are overestimating deciduous forest tree mitigating potential in urban environments. ☐ Keywords: Acclimation, Acer rubrum L., Amino acids, Biomonitor, Chlorophyll, City size, Heavy metal, Nitrogen deposition, Nutrients, Polyamine, Stomate size, Subcanopy soil, Urban forests, Urban heat island, Urbanization