Effects of Soil Management Practices on Soil Ecology, Tree Carbon Allocation, Insect Resistance and Stress Tolerance in an Inverted Subsoil Profile (03-DG-11244225-428)

This project compared fertilization, mulching and commercial mycorrhizal inoculant on carbon allocation, insect resistance and mychorrhizal associations of paper birch trees growing in two soil types.

We compared effects of fertilization, mulching with composted yard trimmings, and a commercial mycorrhizal inoculant on carbon allocation, insect resistance, and mycorrhizal associations of paper birch (Betula papyrifera) trees growing in either high quality topsoil or an inverted subsoil profile. Fertilization, mulching, and mycorrhizal inoculations had minimal effects on microbial activity and nutrient cycling relative to differences among soil types. Effects of fertilization on tree growth in subsoil were temporary. The most dramatic effect that we observed was rapid physiological acclimation of trees to the subsoil environment, which caused their growth to accelerate such that by the third year their relative growth rate exceeded that of trees in topsoil plots. Physiological acclimation was associated with substantially higherroot: shoot ratios than in topsoil plots, and nearly 100% colonization of roots by native mycorrhizal fungi, which suggests that mycorrhizae are not limited by disturbed urban soils deficient in organic matter and nutrients. We observed no colonization by, or physiological effects of, commercial mycorrhizal inoculations. Contrary to conventional wisdom, fertilization decreased insect resistance of trees growing in extremely nutrient-limited subsoil. These studies suggest that physiological acclimation may be more important than intervention with common soil management practices in the establishment of newly transplanted trees, even in poor quality soils.

Our objective is to quantify effects of fertilization and mulching with composted yard waste on soil organic matter, microbial activity, rates of nutrient cycling, and mycorrhizal associations of paper birch (Betula papyrifera) in an inverted subsoil. We will also examine how these soil processes affect the stress tolerance and insect resistance of birch, by quantifying photosynthesis and stomatal conductance (during periods of favorable soil moisture, and during mid-summer drought, to determine drought stress tolerance), above and below ground carbon allocation, chemical defenses (secondary metabolites), as well as insect growth and survival. Specifically,we will test the following hypotheses:

1.Mulching with composted yard waste will increase tree growth and stress tolerance in highly disturbed soils by increasing soil organic matter, microbial biomass, rates of nutrient cycling, and mycorrhizal associations, without decreasing root growth, secondary metabolism, or insect resistance.

2.Fertilization will increase the insect resistance of trees growing in nutrient deficient subsoil, but decrease insect resistance in fertile topsoil, because of nonlinear effects of nutrient availability on chemical defenses.

3. Fertilization will decrease stress tolerance of trees in both top- and subsoil by decreasing root shoot ratio and mycorrhizal associations.

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