Mass loss and nitrogen dynamics during the decomposition of a 15N-labeled N2-fixing epiphytic lichen, Lobaria oregana

TL;DR: Fall and spring initiated decomposition of an N2-fixing epiphytic lichen, Lobaria oregana (Tuck.) Mull, was studied using a method of labeling lichens with 15 N for use in a decomposition study that involved spraying lichen material with a nutrient solution containing 15 N-enriched ammonium.

Abstract: 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 15 N. We developed a method of labeling lichens with 15 N for use in a decomposition study that involved spraying lichen material with a nutrient solution containing 15 N-enriched ammonium. Through the first 180 days of sampling, lichens placed in the field during the spring had a smaller decay constant (k = 1.24 year -1 ) than the lichens placed in the field during the fall ( k = 3.1 year -1 ). However, both spring and fall lichen samples were decomposed beyond recognition after 1 year. Patterns in exogenous N uptake and N concen- tration 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 sets of lichen additions increased dur- ing decay to a peak of around 2.8% N, equal t oaCt o Nr atio ofabout 16, and then began to decrease. This indicates that early in decay, net N immobilization occurred in the remaining lichen, but this was followed by net N mineraliza- tion in later stages of decay.