Mycorrhizal dynamics under CO2 and nitrogen enrichment.
Garcia, Maria *,1, Ovasapyan, Tatevik1, Finzi, Adrien 2, Treseder, Kathleen1, 1 University of California, Irvine, Irvine, CA2 Duke University, Durham, NC
ABSTRACT- We tested the hypothesis that elevated atmospheric CO2 would increase the prevalence of mycorrhizal fungi, because plant investment in mycorrhizal fungi should increase if soil nutrients become limiting. Likewise, mycorrhizal abundance should decline under N fertilization. At four dates between December 2004 and November 2005, soil was collected from fertilized and unfertilized sectors within replicate rings of the Duke FACE experiment. CO2 fumigation began in summer of 1996, and N fertilization in spring of 2005. CO2 enrichment significantly increased colonization of roots by ectomycorrhizal fungi, from 34 ±2% root length in ambient plots to 43 ±2% in enriched plots. We found no effect of CO2 or nitrogen fertilization on root colonization by arbuscular mycorrhizal (AM) fungi (average: 43% root length), hyphal length of AM fungi (average: 1.2 m g-1 soil), or glomalin (average: 7.7 mg g-1 soil). Radiocarbon signatures indicated that glomalin residence times were approximately 7 ±2 years in this site (14C = 107 ±5.1), so this glycoprotein could constitute a long-lived sink of nutrients. Neither elevated CO2 nor nitrogen fertilization altered ECM production of -N-acetylglucosaminidase (NAG) or glycine aminopeptidase (GAP), which break down chitin and proteins, respectively. Moreover, ECM-produced enzymes might only contribute to a small fraction (0 to 1.5%) of chitin and protein degradation in the soil. Our CO2 hypothesis was supported with respect to ECM fungi, but not AM fungi. The general lack of response to nitrogen may be due to the short duration of the fertilization treatment at the time of sample collection.
Key words: mycorrhizal fungus, enriched carbon dioxide, enriched nitrogen
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