Mycorrhizal Responses to Anthropogenic Nitrogen Enrichment in Urban and Rural Woodlands (03-DG-11244225-124)

This project studied the effects of increased nitrogen concentrations in soils.

We examined the effects of nitrogen (N) enrichment from human activities, such as agriculture and autos, on soils, plants, and mycorrhizae -- a soil fungus-plant root symbiosis that facilitates the uptake of nutrients -- in 11 urban and rural oak woodlands. Patterns of soil NO3 paralleled those of NOx air pollution and wet deposition; the impact of N from agricultural fertilizer drift was small. An increase in soil N resulted in a proportional increase in plant growth and leaf N content. The aboveground sporocarp (mushroom), and belowground root tip and spore communities, demonstrated that shifts in fungal composition were linked primarily to soil N: Pstatus, and secondarily to soil NO3 concentration. An increase in soil N: P was correspondent with increases in fungal diversity, and vice versa. High N soils also contained many pathogenic fungi and mycorrhizae that were less effective at acquiring nutrients and water for their host. Mycorrhizal fungi from high quality (low N) sites increased plant growth, productivity, and nutrient status. The addition of carbon (as chips + sawdust) reduced soil N levels, and was accompanied by an increase in plant productivity and diversity, and a reduction in weedy plant abundance.

The specific project objectives were to:

1.Determine how increasing soil N levels (a calculated consequence of anthropogenic N deposition) will affect soil nutrient availability, and mycorrhizal biodiversity and productivity in oak and maple communities in metropolitan Chicago; and

2.Evaluate the potential roles of mycorrhizae and enhanced soil organic in ameliorating the negative consequences of N enrichment.

To address these objectives, the project was initially divided into four work plans:

Work plan 1: Soils: the quantification of N, as the availability of ammonium (NH4) and nitrate (NO3), and carbon (C) pools in soil. We also quantified soil pH, and concentrations of magnesium (Mg), calcium (Ca), and potassium (K).

Work plan 2: Biodiversity: the investigation of biodiversity in mycorrhizae, and identification of key indicator species of ecosystem N enrichment.

Work plan 3: Bioassay: the the evaluation of the growth response and foliar N content of mycorrhizal-dependent species in soils from each study site as a measure of site N enrichment.

Work plan 4: Restoration: the evaluation of the interactive effects of mycorrhizal fungi from high or low N soils on the survival and growth of oak seedlings planted into N-enriched soils.

An additional two work plans were added to the research program:

Work plan 5: Carbon additions: evaluation of the effect of sawdust alone, wood chips alone, or sawdust + chips on plant productivity and diversity in N-enriched soils.

Work plan 6: Interactions between mycorrhizal and non-mycorrhizal fungi on plant growth: the evaluation of the feedbacks between mycorrhizal and non-mycorrhizal fungi (from sites that differed in soil N) on the abundance, growth and function of plants.

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