PARENT SESSION
Oral Session #35: Carbon and Nitrogen Cycling.
Presiding: D. Rothstein
Tuesday, August 6. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.

The relationship between carbon and nitrogen in New Zealand lichens.

Thomas, Michael^*,1, Galloway, David², Farnden, Kevin³, ¹ Mesa Community College, Mesa, Arizona² LandCare Research New Zealand Ltd., Dunedin, New Zealand³ University of Otago, Dunedin, New Zealand

ABSTRACT- Carbon (C) and nitrogen (N) are linked in ecosystem development and function. N is the most common limiting factor in terrestrial ecosystems. Understanding C/N interactions in an ecosystem is fundamental to understanding ecosystem mechanics. New inputs of N from natural sources result primarily from dinitrogen-reduction by organisms utilizing nitrogenase. Most nitrogenase activity in terrestrial ecosystems occurs by way of Rhizobium-leguminous symbioses. In New Zealand the abundance of native legumes is extremely low. However, NZ has a robust flora of cyanobacterial lichens, which also utilize nitrogenase. Using mass spectrometry, we examined C/N abundances in a variety of NZ lichens, as well as the major isotopic fractions of C/N. We found a significant relationship between the C content and ¹³C values. This relationship was particularly strong when samples were isolated based on the nature of the primary photobiont (either a chlorophyte or a cyanobacteria). Searching further, we combined the C/N data with morphological, anatomical and growth habit information and performed a Principle Component Analysis. The largest three principle components accounted for approximately 85% of the variation observed. When we plotted those values in three dimensions, the resulting graph shows a spiral continuum rather than the expected clusterings of data points. The implication is that a combination of factors influences the quality and quantity of C/N in lichens, and that the results of these influences may be predictable.

KEY WORDS: carbon, nitrogen, lichens, PCA