Wright, C., E.A. Paul, and C.A. Reddy
Presented at the All Scientist Meeting (1996-07-16 to 1996-07-17 )
Soil fungi are a key component of terrestrial ecosystems. They live in both moderate and harsh environments, degrade almost all organic residues and outweigh all other soil microbiota (including bacteria) in both richness of species and biomass. To flourish in diverse environments, soil fungi possess a wide array of degradative capabilities. Consequently, they play a dominant role in soil nutrient cycling and plant nutrition, as well as in the biogeochemical cycling of various elements including carbon © and nitrogen (N). The study of soil fungi is therefore crucial to research in three priority areas of ecology: biodiversity, long term ecological research and global change.Soil basidiomycetes are a group of soil fungi that are responsible for the majority of the degradation of lignocellulose plant residues, soil organic matter and polyaromatic pollutants in soil. Since the combined total of lignocellulose and soil humics represent a major reserve of terrestrial C (i.e. 350-500 pentograms), the soil basidiomycetes therefore play a pivotal role in biogeochemical cycling of C. Soil basidiomycetes are effective at these degradative processes because:Although the importance of basidiomycetes in soils is well recognized, there is little known about the diversity of these organisms. Even less is known about the ecosystem controls that select for basidiomycetous communities. The primary roadblock to the investigation of soil basidiomycetes has been a historic lack of methods to isolate them. Even in the few cases where isolation has been successful, the identification of isolates has been difficult (to impossible). We have addressed these problems by developing techniques and a selective medium which allow, for the first time, the routine isolation of soil basidiomycetes. A combination of particle washing, selective inhibitors and use of a commercially available lignin as the primary C source resulted in the isolation of 67 KBS soil basidiomycetes representing 51 morpho-taxo groups. The majority of these could not be classified utilizing traditional taxonomic characteristics. Therefore, rDNA sequences of the unknown isolates are now being used to generate a phylogenetic tree which includes reference sequences obtained from sequence libraries and databases. While some of the isolates have be placed into known taxonomic groups, many of the isolates appear to be species/genera that have not been previously described.In addition to our isolation methods, we are developing techniques to extract total microbial DNA from soils and selectively amplify informative stretches of basidiomycete rDNA. These amplified sequences will be separated and used for phylogenetic assesment of soil basidiomycetes. This will allow us to study both culturable and nonculturable species.We will use the above techniques to study the diversity soil basidiomycetes inhabiting a range of treatments at the KBS LTER site. We will investigate how the community structure of basidiomycetes in soils is impacted by plant material inputs as well as chemical and physical perturbations. This will be accomplished through: 1) characterization and comparison of the richness of species of soil basidiomycetes; 2) determination of their functional diversity (the richness and heterogeneity of lignin modifying enzymes encoded by soil basidiomycete isolates) and; 3) measurement of the actual decomposition they carry out.Information on species richness and functional diversity will be related to ecosystem processes by integrating the molecular studies with litter exchange experiments. The litter experiments utilize the difference in the 13C signal of corn versus that of deciduous forest leaves (oak and hickory) to measure decomposition. The use of a lignin-humate analog known to be degraded by the lignolytic enzymes of basidiomycetes will further relate the diversity and function data to ecosystem processes. The inclusion of information on basidiomycete populations and function should greatly improve the Century model we use to describe the decomposition rates of forest and agricultural treatments. This study will incorporate the application of molecular based techniques to ecological-ecosystem questions. It will also provide a great deal of fundamental information on an important, previously uncharacterized component of terrestrial ecosystems—the basidiomycetous soil fungi.. The hypotheses we will test include:
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