1. Abelson, P. H. 1986. Science 231, 1233.
2. Alexander, I. J. 1983. The significance of ectomycorrhizas in the nitrogen cycle. In Nitrogen as an ecological factor, J. A. Lee et al. (eds), 69–94. Oxford: Blackwell.
3. Alexander, M. 1971. Introduction to soil microbiology, 2nd edn. London: Wiley.
4. Anderson, A. J. and J. Underwood 1959. Trace element deserts. Sci. Am. 213 (1), 97–112.
5. Anderson, J. M. 1981. Ecology for environmental sciences. London: Edward Arnold. (Excellent introductory text.)