Nutritional hotspots and the secret life of forests

Abstract

The floor of a Douglas-fir forest may be rich in organic matter, but nutrients essential to plant growth are locked within the decomposing needles, leaves, and fallen wood. Before nitrogen, phosphorus, and other nutrients can be cycled back through the forest system, they need to be further broken down into forms accessible to plants. Understanding how nutrients become available to plants has long been of interest in the Pacific Northwest because the productivity of the region’s conifer forests is often thought to be limited by the availability of nitrogen.

In some Douglas-fir forests, a single genus of mat-forming fungi, Piloderma—which has a symbiotic relationship with nearby trees—covers up to 40 percent of the forest floor. These mats, as well as the surrounding forest soil, harbor a diverse suite of microbes. Scientists analyzed samples of mat and non-mat soils from the H.J. Andrews Experimental Forest for biochemical activity linked to nutrient cycling. They found that the presence of the ectomycorrhizal mats enhanced enzyme activity that likely makes soil nitrogen available for plant uptake. The researchers also found chemical compounds in the mat samples that suggests Piloderma helps cycle phosphorus, making it available to plants.

Ectomycorrhizal mat-forming fungi play another essential role in forest ecosystems: The fruiting bodies they produce, such as mushroom or truffles, serve as a major food source for many forest mammals.

Citation

Smith, Jane; Kluber, Laurel; Parks, Noreen. 2014. Nutritional hotspots and the secret life of forests. Science Findings 161. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.