Mycorrhizal relationships in bottomland hardwood forests of the southern United States

Mycorrhizae are important in the functioning of forest ecosystems worldwide, and play a critical role in water uptake, nutrient acquisition, and prevention of feeder root disease. The majority of mycorrhizal research has been conducted on upland sites, especially in coniferous ecosystems and in commercial agricultural production. However, the maintenance and restoration of bottomland hardwood (BLH) forest ecosystems in the southern United States is of increasing concern. Both ectomycorrhizae and endomycorrhizae are present in BLH forests, although the dominance of one or the other type depends primarily on both the tree species and the hydrologic regime. Ectomycorrhizae tend to be more sensitive to flooding, while endomycorrhizal infection can be present even in permanently flooded soils. The mycorrhizae of sweetgum (Liquidambar styraciflua), green ash (Fraxinus pennsylvanica), and the oaks (Quercus spp.) have been studied most due to their economic importance.Considerable work is still needed to better understand mycorrhizal relationships in BLH ecosystems and associated trees, both with respect to infectivity and nutrient cycling. Such information may be necessary for restoration of BLH forests on old agricultural fields, or to maintain the productivity of BLH forests after harvest. This paper summarizes studies on mycorrhizae relationships in BLH forests and suggests future work necessary for understanding the role mycorrhizae can have in managing these ecosystems.