HR: 0800h
AN: B51A-0183    [Abstracts]
TI: Sequestration of Carbon in Mycorrhizal Fungi Under Nitrogen Fertilization
AU: * Treseder, K K
EM: treseder@uci.edu
AF: University of California Irvine, Dept of Earth System Science, Irvine, CA 92697 United States
AU: Turner, K M
EM: kmturner@uci.edu
AF: Stanford University, Dept of Biological Sciences, Stanford, CA 94305 United States
AB: Mycorrhizal fungi are root symbionts that facilitate plant uptake of soil nutrients in exchange for plant carbohydrates. They grow in almost every terrestrial ecosystem on earth, form relationships with about 80% of plant species, and receive 10 to 20% of the carbon fixed by their host plants. As such, they could potentially sequester a significant amount of carbon in ecosystems. We hypothesized that nitrogen fertilization would decrease carbon storage in mycorrhizal fungi, because plants should reduce investment of carbon in mycorrhizal fungi when nitrogen availability is high. We measured the abundance of two major groups of mycorrhizal fungi, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi, in control and nitrogen-fertilized plots within three boreal ecosystems of inland Alaska. The ecosystems represented different recovery stages following severe fire, and comprised a young site dominated by AM fungi, an old site dominated by ECM fungi, and an intermediate site co-dominated by both groups. Pools of mycorrhizal carbon included root-associated AM and ECM structures, soil-associated AM hyphae, and soil-associated glomalin. Glomalin is a glycoprotein produced only by AM fungi. It is present in the cell walls of AM hyphae, and then is deposited in the soil as the hyphae senesce. Nitrogen significantly altered total mycorrhizal carbon pools, but its effect varied by site (site * N interaction, P = 0.05). Under nitrogen fertilization, mycorrhizal carbon was reduced from 99 to 50 g C m² in the youngest site, was increased from 124 to 203 g C m² in the intermediate-aged site, and remained at 35 g C m² in the oldest site. The changes in total mycorrhizal carbon stocks were driven mostly by changes in glomalin (site * N interaction, P = 0.05), and glomalin stocks were strongly correlated with AM hyphal abundance (P < 0.01). Nevertheless, it is not clear why AM hyphae responded differently to nitrogen fertilization in the different sites. Carbon stocks within root-associated AM structures increased significantly with nitrogen fertilization across all sites (P = 0.001), as did root-associated ECM structures (P = 0.021). The amount of carbon sequestered within living mycorrhizal structures (0.013 to 0.21 g m²), however, was modest compared to that of glomalin (91 g m²). We conclude that allocation by AM fungi to hyphal growth influenced the size of glomalin stocks in the soil, and that nitrogen fertilization altered investment in hyphal growth, with potential consequences for soil carbon storage. However, the nitrogen response was inconsistent among boreal forest ecosystems. An understanding of the mechanisms underlying this variation would improve our ability to predict ecosystem feedbacks to global change.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005