Saturday, 15 July 2006

The Role of Arbuscular Mycorrhizal Fungi in Aggregate Stability and Soil Carbon and Nitrogen Storage in Tallgrass Prairie.

Gail Wilson and Charles Rice. Kansas State Univ, Dept of Biology, 214 Bushnell Hall, Manhattan, KS 66506

Arbuscular Mycorrhizal (AM) fungi are integral components of grasslands because most grassland plants are associated with interconnected networks of AM hyphae. Mycorrhizae generally facilitate plant uptake of mineral nutrients. Consequently, nitrogen (N) enrichment may alter plant allocation belowground to roots and mycorrhizae as well as AM fungal allocation to internal (intraradical) and external (extraradical) structures that function in supplying mineral nutrients to plants. Changes in symbiotic activity and AM allocation to intraradical and extraradical structures is important because a reduction in extraradical hyphal networks is likely to impact soil structure, soil carbon and nitrogen storage, and soil food webs. The objectives of this research were to examine the long-term (17 yrs) effects of N enrichment coupled with important tallgrass prairie management practices (annual burning and mowing) on mycorrhizal symbiosis, soil aggregation, and soil C and N storage. To further investigate the role of AM fungi in soil aggregate stability, we also examined long-term effects (6 yrs) of fungicide applications (AM fungal suppression) in native tallgrass prairie soils. Nitrogen enrichment increased the colonization and extraradical hyphae of mycorrhizal fungi and these increases were strongly correlated to increases in water-stable soil macroaggregates, as well as the amount of C and N stored in the soil and into soil aggregates. Suppression of the symbiosis (via fungicide applications) resulted in a large and significant decrease in hyphal networks resulting in a loss of water-stable macroaggregates (Fig 1). The loss of macroaggregates decreased the physical protection of C resulting in a subsequent reduction of the C storage in the soil. The data presented in this study provide strong evidence that soil structure and stability, as well as enhancement of soil sequestration of C and organic N, are largely mediated by AM hyphae.

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