Vegetable crop response and insect prevalence in urban agroecosystems
Urban agriculture is a growing land use, but little is known about how vegetable crops and insect communities respond to the unique suite of biophysical characteristics in urban agroecosystems. The objective of this study is to characterize ecological responses of vegetable crops and agriculturally important arthropods in agroecosystems located along an urban to rural latitudinal transect in greater Chicago, IL. Two 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, wind speed and direction) and gas (CO2, O3) sensors continuously monitor each site. Data for crop growth, yield, and quality are collected along with arthropod abundance and community composition. Data is analyzed with generalized linear mixed models to assess the influence of site-years on individual ecosystem response variables and partial least squares regression analysis to understand complex relationships among microclimatic factors, atmospheric gases, and ecosystem responses.
After two years of data collection, crop biomass and yield is trending higher at urban sites, with up to a three-fold increase in Brassica spp. Growing degree day accumulation appears to be the major driver of crop response, although light interception and ozone (AOT40) explain variation in production. Yield is reduced in peri-urban sites where incident light is lower due to increased tree canopy. Soluble solids (Brix°) in Brassica oleracea were 30% lower at one peri-urban site, but brix readings did not differ across sites for any other species. Total phenolics, antioxidant capacity, and carotenoid content assays are ongoing; early results show Brassica oleracea total phenolics were 26% lower at a rural site where plants suffered cold damage, all other sites were similar. Insect pest species Helicoverpa zea and Ostrinia nubilalis were only present at rural sites, whereas abundance of Trichoplusia ni and Pieris rapae were greatest at the most urban sites. Insect sticky traps had highest counts in the rural environment, with orders Diptera and Lepidoptera driving differences. Insect damage from aphids was mainly at an urban site near a large urban farm. Micrometeorological measures drove plant responses while fruit quality does not seem affected; some pest insect species were reduced while other species increased in the rural to urban gradient.