Farming in the city: How does the urban atmospheric environment influence vegetable crop physiology?

Background/Question/Methods

The recent growth of urban agriculture in the US has led to an increase in the area of agroecosystems within urban ecosystems. While rural agroecosystems are well-studied, little scientific knowledge exists regarding their urban counterparts. The objective of this study is to characterize plant physiological response across six experimental agroecosystems located along an urban to rural latitudinal transect in the greater Chicago metropolitan region. Fourteen cultivars of seven crop plant species are grown in uniform soil mixtures at each site to isolate urban atmospheric effects on plant physiology. Weather towers equipped with micrometeorological (temperature, relative humidity, light intensity, and wind speed and direction) and pollution (CO₂ and O₃) sensors continuously collect data at each site to help explain variability in physiological responses across sites. Plant physiology data collected includes leaf area index, relative growth rate, plant architecture, biomass partitioning, and fruit yield and quality. Data is analyzed with generalized linear mixed models to assess the influence of site-years on individual response variables and partial least squares regression analysis to understand relationships among microclimatic factors, pollutants, and plant responses.

Results/Conclusions

Preliminary data indicate that urban sites were between 1 (daytime) and 4°C (nighttime) warmer than rural sites. Warmer temperatures in the urban agroecosystems coincided with increases in ambient CO₂ between 20 and 40 ppm. Ozone flux (up to 600 ppb) and VPD were also greatest in the most urban agroecosystems (e.g., those nearest downtown Chicago). Plant productivity tended to increase at urban sites (especially for Brassicaceae spp.), but two species were more productive at the most rural site (Allium cepa and Beta vulgaris). Growth of two cultivars of Phaseolus vulgaris with differential susceptibility to ozone was variable among sites, but interveinal chlorosis, early senescence, and reduced productivity of the ozone susceptible cultivar was consistent across all sites. Proximity to urban forests and built structures reduced light intensity within some urban and peri-urban agroecosystems resulting in reduced plant productivity across most species and cultivars. The influence of urban atmospheric factors on plants in the urban agroecosystem was significant, but not consistent across cultivars, species, or plant families. Through further study, we aim to identify predictable trends in urban plant physiological response that will inform crop selection and management for urban and peri-urban farmers.