Abstract
We examined potential large-scale controls over the distribution of arbuscular mycorrhizal (AM) fungi and their host plants. Specifically, we tested the hypothesis that AM fungi should be more prevalent in biomes where nutrients are primarily present in mineral, and not organic, forms. Values of percentage root length colonized (%RLC) by AM fungi, AM abundance, and host plant availability were compiled or calculated from published studies to determine biome-level means. Altogether, 151 geographic locations and nine biomes were represented. Percent RLC differed marginally significantly among biomes and was greatest in savannas. AM abundance (defined as total standing root length colonized by AM fungi) varied 63-fold, with lowest values in boreal forests and highest values in temperate grasslands. Biomes did not differ significantly in the percentage of plant species that host AM fungi, averaging 75%. Contrary to the hypothesis, %RLC, AM abundance, and host plant availability were not related to the size, influx, or turnover rate of soil organic matter pools. Instead, AM abundance was positively correlated with standing stocks of fine roots. The global pool of AM biomass within roots might approach 1.4 Pg dry weight. We note that regions harboring the largest stocks of AM fungi are also particularly vulnerable to anthropogenic nitrogen deposition, which could potentially alter global distributions of AM fungi in the near future.
Highlights
Arbuscular mycorrhizal (AM) fungi are recognized as an important, widespread component of most terrestrial ecosystems
Percent RLC, percentage root length colonized by arbuscular mycorrhizal fungi; AM, arbuscular mycorrhizal; SOM, soil organic matter; BNPP, belowground net primary productivity; n.d., not determined. aMean ± 1 SD (n). bProduct of mean community-level % root colonization by AM fungi and live fine root length per biome. cData from Amundson (2001). dIncludes both AM and non-AM plants
Percent RLC, percentage root length colonized by arbuscular mycorrhizal fungi; AM, arbuscular mycorrhizal; SOM, soil organic matter; BNPP, belowground net primary productivity. *P < 0.10, **P < 0.0001
Summary
Arbuscular mycorrhizal (AM) fungi are recognized as an important, widespread component of most terrestrial ecosystems. They receive 3–20% of photosynthate from their host plants (Kucey and Paul 1982; Harris and others 1985; Harris and Paul 1987; Jakobsen and Rosendahl 1990; Finlay and Soderstrom 1992; Johnson and others 2002a, b) in exchange for the transfer of soil-derived nutrients to roots, and in this way influence carbon (C). AM fungi are sensitive to various aspects of global change They often proliferate under elevated atmospheric CO2 and can decline under anthropogenic nitrogen (N) deposition (Jansen and Dighton 1990; Diaz 1996; Hodge 1996; Staddon and Fitter 1998; Rillig and others 2002a; Treseder 2004). Most global change studies of AM fungi are conducted at the ecosystem scale or smaller (Rillig and others 2002a)
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