Trees in urban environments are often severely stressed by poor quality soils. We investigated the potential for mulch and fertilization to enhance the health of trees growing in a highly disturbed, inverted subsoil profile as measured by their effects on growth, foliar phenolic compounds and insect resistance of Betula papyrifera (Marsh) in a controlled field study. Trees in topsoil grew faster than those in subsoil. However, these faster growing trees had lower concentrations of foliar phenolic compounds, and were less resistant to key defoliating insect pests including Malacosoma disstria (Hübner), Orgyia leucostigma (J.E. Smith), Datana ministra (Drury), and Hyphantria cunea (Drury) as noted by their higher growth rates. Fertilization of subsoil plots did increase tree growth but it also decreased concentrations of foliar phenolics and resistance to fall webworm. There was a strong negative correlation between aboveground growth and foliar phenolic concentrations, consistent with a postulated physiological trade-off between growth and secondary metabolism. Fertilization also decreased resistance of trees in subsoil to Hyphantria cunea, but had no effects on other defoliators. Fertilization had no effect on growth or insects resistance of trees in topsoil. We find little evidence that fertilization or mulch can do much to ameliorate disturbed soils, at least after one year. Contrary to conventional wisdom, fertilization also did not increase insect resistance of trees in poor soils.
Species 1: Lepidoptera Arctiidae Hyphantria cunea (fall webworm)
Species 2: Lepidoptera Lymantriidae Orgyia leucostigma (white-marked tussock moth)
Species 3: Lepidoptera Lasiocampidae Malacosoma disstria (forest tent caterpillar)
Keywords: chemical defense
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