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The response of mycorrhizal fungi to long-term fertilization of an oak savanna.
Avis, Peter1, Charvat, Iris1, McLaughlin, David1, Reich, Peter1, 1
ABSTRACT- Mycorrhizal fungi depend on the availability of two essential resources: soil nutrients and root carbohydrates. However, MF vary in 1) ability to acquire soil nutrients; 2) growth on different levels of soil nutrients; 3) trade of nutrients to host-plant; and 4) response to changes in host plant allocation to the roots. Therefore, events such as fertilization that change soil nutrient and root carbohydrate availability should dramatically alter the composition of MF communities and their ecosystem function. The response of MF communities in an oak savanna subject to long-term field fertilization is being examined to address this question. Arbuscular mycorrhizae and ectomycorrhizal fungi (EMF) are measured by root colonization and inoculum bioassays. EMF community composition is also determined by fruitbody surveys, morphotyping and molecular analyses. N mineralization is assessed as an indicator of N availability. Below-ground allocation by plants is assessed by looking at fine root biomass, productivity, and carbohydrate content. Results indicate that fertilization increases N mineralization and decreases fine root biomass. In addition, the abundance of AMF declines as does the presence of their host plants. However, it is not clear how EMF respond -- fertilization decreases the abundance and diversity of fruitbodies but not EMF colonization. RFLP and morphotype analyses suggest the EMF communities differ among the treatments. Future experiments will examine the functional differences of these different EMF communities.
KEY WORDS: arbuscular mycorrhizae, ectomycorrhizae, fertilization