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Archived soil samples (1937-1999) and historic air quality data from the Los Angeles Basin were used for reconstructing the record of change between atmospheric NO(x) loads, soil delta(15)N values and the diversity of arbuscular mycorrhizae (AM), which are ubiquitous plant-fungus mutualists that control plant community productivity. A tripling of atmospheric NO(x) loads between 1937 and the 1970s was paralleled by soil nitrogen enrichment (delta(15)N = 3.18). From 1975 onwards, atmospheric NO(x) declined, but soils became nitrogen saturated (delta(15) N = -4 and NO(3)-nitrogen = 171mgkg(-1)). The shifts in the AM community followed 28 years of atmospheric nitrogen enrichment and coincided with the onset of soil...
Seasonal dynamics of arbuscular mycorrhizal (AM) colonization of Sporobolus wrightii and AM fungal communities were assessed at four riparian sites in south-east Arizona which represented upper terrace or lower floodplain habitats and perennial or intermittent river reaches. Colonization was co-ordinated with growth/reproductive stages of plants at three sites with higher levels from February to May when plants were primarily vegetative and lower levels in September and December during seed set and onset of dormancy. Fifteen species of AM fungi were associated with S. wrightii, includingGlomus , Acaulospora, Paraglomus and Archaeospora species. Species richness ranged from 9 to 13 AM fungal species per site. Published...
Invasive exotic weeds pose one of the earth's most pressing environmental problems. Although many invaders completely eliminate native plant species from some communities, ecologists know little about the mechanisms by which these exotics competitively exclude other species. Mycorrhizal fungi radically alter competitive interactions between plants within natural communities, and a recent study has shown that arbuscular mycorrhizal (AM) fungi provide a substantial competitive advantage to spotted knapweed, Centaurea maculosa, a noxious perennial plant that has spread throughout much of the native prairie in the northwestern U.S. Here we present evidence that this advantage is potentially due to mycorrhizally mediated...
We assessed species composition, richness and abundance of understory vegetation, as well as arbuscular mycorrhizal (AM) inoculum potential on the San Francisco Peaks, tallest mountains in Arizona, crossing a steep, south-facing elevational gradient. These mountains have a high conservation value due to their rare habitats but previous vegetation studies have been limited. Because mature trees in the Pinaceae do not form associations with AM fungi, there may be more variation in plant community and AM fungal associations in coniferous forest than in ecosystems where all species associate with AM fungi. Differences in species composition between forest types reflected differences in the historical disturbance regimes....
Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with the root systems of most plant species. These mutualisms regulate nutrient exchange in the plant?soil interface and might influence the way in which plants respond to increasing atmospheric CO2. In other experiments, mycorrhizal responses to elevated CO2 have been variable, so in this study we test the hypothesis that different genera of AM fungi differ in their response, and in turn alter the plant's response, to elevated CO2. Four species from three genera of AM fungi were tested. Artemisia tridentata Nutt. seedlings were inoculated with either Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, Acaulospora sp. or Scutellospora...
We examined plant community responses to interactions between arbuscular mycorrhizal (AM) fungi and availability of atmospheric CO2 and soil N. Communities of 14 plant species were grown in mesocosms containing living or killed AM fungal inoculum, ambient or elevated atmospheric CO2 and low or enriched soil N. After one growing season, significantly different plant communities existed in the different treatments. Plant species richness was lowest in +N mesocosms and highest in +AM + CO2 mesocosms. At ambient CO2, AM fungi reduced richness but at elevated CO2 they increased it. This was caused by changes in mortality rates of several C3 forbs and may suggest that CO2 enrichment ameliorates the carbon cost of some...
Arbuscular mycorrhizal (AM) fungi are integral components of grasslands because most plants are associated with interconnected networks of AM hyphae. Mycorrhizae generally facilitate plant uptake of nutrients from the soil. However, mycorrhizal associations are known to vary in their mutualistic function, and there is currently no metric that links AM functioning with fungal colonization of roots. Mycorrhizal structures differ in their physiological and ecological functioning, so changes in AM allocation to intraradical (inside roots) and extraradical (in soil) structures may signal shifts in mycorrhizal function. We hypothesize that the functional equilibrium model applies to AM fungi and that fertilization should...