You can use these categories to browse browse OneSearch and the bookshelves (4 North) for books on a particular subject.
If you have a specific species that you want to search (fungus, plant, etc.) start with a keywordsearch using the name of your species or family. You may have better luck searching for more general topics and using the index at the back of the book to find your particular organism.
These new books caught my attention; perhaps you will find them useful as well.
Life in the Soil: A Guide for Naturalists and Gardeners - James B. Nardi
Call Number: QH 84.8 .N36 2007
"Nardi takes us deep into the engine room of soil production, exploring and describing the myriad organisms-amoebae, fungi, bacteria, arthropods, etc-that dwell there. A strange, revealing and captivating book."-Mark Cocker, Guardian (Mark Cocker The Guardian 20080207)
Soil Biology Guide - Daniel Dindal
Call Number: QH 84.8 .S632 1990
"A comprehensive study of the biology, taxonomy, and ecology of each of the soil biotic groups. The first chapter presents an ecological approach to soil studies. The remaining 42 chapters provide specific information on each of the taxonomic groupings. Contains illustrated identification keys to each group. Some keys go by functional morphological delineations; others lead the reader to classical identification at family, genus, or species levels. Some incorporate descriptions of new genera and species. Especially useful for the study of mesic, xeric, and hydric terrestrial sites. Includes an extensive bibliography"--from the Publisher