ABSTRACT
This chapter discusses the natural abundance levels of nitrogen (N) in terrestrial vascular plants. Soil research has traditionally focused on amounts of N. Chemical analytical methods (e.g. various types of digestions and colorimetric techniques) were developed in order to quantify the amounts of N. The central difficulty in designing experiments for the interpretation of N lies in the persistence of simultaneously occurring multiple isotopic N sources. Many of the processes which physically or chemically transform N also change the sources and sinks of N. Whole plant experiments can be conducted in a number of growth media under varying amounts of experimental control and designed to answer different questions at different scales. If N-enrichment is not used, treatment effects can be magnified by using a hydroponic system of growth in which the external concentration of N is large, relative to the plants’ usual growth conditions.
