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MASS LOSS AND NITROGEN DYNAMICS DURING THE DECOMPOSITION OF A N-LABELED N2-FIXING EPOPHYTIC LICHEN, LOBARIA OREGANA (TUCK.) MULL. ARG.
Holub*, S M. AND Lajtha. MASS LOSS AND NITROGEN DYNAMICS DURING THE DECOMPOSITION OF A N-LABELED N2-FIXING EPOPHYTIC LICHEN, LOBARIA OREGANA (TUCK.) MULL. ARG. CANADIAN JOURNAL OF BOTANY 81:698-705, (2003).
We studied mass loss and nitrogen dynamics during fall and spring initiated decomposition of an N2-fixing epiphytic lichen, Lobaria oregana (Tuck.) Mull. Arg. using 15N. We developed a method of labeling lichens with 15N that involved spraying lichen material with a nutrient solution containing 15N-enriched ammonium. Through the first six months of sampling, lichens placed in the field during the spring had a smaller decay constant (k=1.24 yr-1) than the lichens placed in the field during the fall (k=3.1 yr-1). However, both spring and fall lichen samples were decomposed beyond recognition after one year. Patterns in exogenous N uptake, gross N loss relative to net N loss, and N concentration did not differ by season. Both spring and fall lichens took up N from the surrounding environment during decay while simultaneously losing N to the environment. The N concentration in both lichen additions increased during decay to a peak of around 2.8% N, equal to a C to N of 16, and then began to fall. This indicates that early in decay net immobilization occurred in the lichen, but was followed by net mineralization in later stages of decay.