Effect of transportation, storage and revival on nitrogen fixation measurements using arctic bryophyte and lichen samples
P. A. HAGGE, E. K. KING-DOONAN, F. M. LUTZONI, J. M. MIADLIKOWSKA, N. M. CASSAR
Division of Earth and Climate Sciences, Nicholas School of the Environment, Duke University, 9 Circuit Drive, Durham, NC 27708, USA

Acetylene Reduction Assay (ARA) measurements of biological nitrogen fixation (BNF) using high-latitude cryptogams generally are made in laboratories with samples that have been desiccated in the field and rehydrated under simulated natural conditions. However, it’s unclear how accurately laboratory measurements reflect the in situ BNF capacity of diazotrophs associated with lichens and bryophytes. Using ARACAS, a field-deployable method of ARA developed in our lab with 1000 times the sensitivity of traditional ARAs, we measured BNF capacity in fresh (within 8 hours of collection) cryptogam samples representing nearly two dozen genera on Svalbard. We then repeated these measurements using the same samples revived under simulated natural conditions in a growth chamber at Duke University. Among samples that fixed under both fresh and revived conditions, we found fresh lichen BNF rates were higher than revived rates, while fresh and revived bryophyte rates were largely the same. We also found that more lichens and fewer bryophytes fixed revived than fresh. These results suggest that lichen BNF rates are more variable than bryophyte rates between in situ and laboratory measurements, possibly due to changes in water content or stress from desiccation/rehydration, and should be accounted for when upscaling laboratory BNF measurements to Arctic-wide estimates.