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Initial nutrient status of ecosystems influences mycorrhizal responses to nitrogen additions along a Hawaiian chronosequence.
Treseder, Kathleen1, Allen, Michael2, Vitousek, Peter3, 1 2 3
ABSTRACT- The hypothesis that increased availability of N in the soil will reduce mycorrhizal growth has frequently been tested in field experiments, but with inconsistent results. In addition, recent studies have indicated that N deposition may alter the community composition of arbuscular mycorrhizal fungi. We examined the possibility that the initial nutrient status of an ecosystem may determine effects of N additions on the growth of arbuscular mycorrhizal (AM) fungi, and assessed responses of individual AM genera through immunofluorescent labeling. AM hyphal biomass was measured in control-, N-, and P-fertilized plots along a soil fertility gradient in Hawaii that included N-limited, fertile, and P-limited sites. Nitrogen fertilization significantly increased hyphal lengths in the N-limited site from 3.5- to 5.5-mm/g soil (P < 0.02), but had no effect in the fertile and P-limited sites where N was relatively abundant. Across treatments, hyphal lengths were lowest in the P-limited site (P < 0.03). The presence of the AM genus Scutellospora dropped significantly with N-fertilization (P < 0.02), while the incidence of Glomus species was significantly higher in the fertile site then the N-limited site (P < 0.04). Gigaspora and Acaulospora did not vary significantly among sites or treatments. Our results suggest that the nutrient status of ecosystems may be a predictor of effects of N deposition on AM growth, and that differences in dynamics of individual AM genera may contribute to these effects.
KEY WORDS: arbuscular mycorrhizal fungi, Hawaiian chronosequence, nitrogen, immunofluorescent labeling