Monitoring Forest Health as Nitrogen Levels Rise
Soil biology and chemistry can be seriously damaged by acid rain. Created when sulfur dioxide and nitrogen oxide from fossil fuel combustion and other sources mix with precipitation, acid rain harms plants in several ways: it leaches calcium from the soil, depriving plants of a key nutrient, and it dissolves aluminum-rich minerals, freeing the metal to poison plants. Acid rain, along with other factors such as prolonged application of nitrogen fertilizer, can also raise nitrogen levels in plants, soils and soil microbes (such as bacteria). Acid rain has affected forested ecosystems in parts of northeastern United States and Europe, with far-reaching effects on plants, animals and groundwater quality.
While nitrogen is an essential component of plant growth and healthy foliage development, it’s possible to have too much of a good thing. Excess nitrogen can cause dehydration, reduce root growth, and change the competitive relationships between different tree species. It can also cause waste materials to accumulate in leaves, which can make trees shed their leaves earlier than usual.
Northern Research Station scientists are finding out how higher nitrogen levels in plants, soil and soil microbes affect forest productivity. More specifically, we are trying to find out how higher nitrogen levels affect the relationship between photosynthesis and nitrogen assimilation. At the Harvard Forest in western Massachusetts, scientists are applying ammonium nitrate to the ecosystem. In the Bear Brook watershed in eastern Maine, we are applying ammonium sulfate, which contains both nitrogen and sulfur. At both sites, we are researching the effects on soil microbes and on several tree types, including American beech, sugar maple, red oak, red pine and red spruce.
Because changes in trees’ cellular functions and metabolites (the substances needed to maintain life) often occur before stress or disease symptoms become visible to the naked eye, this research may help scientists predict overall tree and ecosystem health.
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- Rakesh Minocha, US Forest Service Northern Research Station, Senior Supervisory Plant Physiologist
- Stephanie Long, US Forest Service Northern Research Station, Biological Sciences Technician and Lab Manager
- Subhash C. Minocha, University of New Hampshire, Biological Sciences Department
- University of New Hampshire, Department of Natural Resources and the Environment
- Ivan Fernandez, University of Maine, School of Forest Resources
- Last modified: March 19, 2019