Articles | Volume 14, issue 6
Research article
28 Mar 2017
Research article |  | 28 Mar 2017

Estimating global nitrous oxide emissions by lichens and bryophytes with a process-based productivity model

Philipp Porada, Ulrich Pöschl, Axel Kleidon, Christian Beer, and Bettina Weber

Abstract. Nitrous oxide is a strong greenhouse gas and atmospheric ozone-depleting agent which is largely emitted by soils. Recently, lichens and bryophytes have also been shown to release significant amounts of nitrous oxide. This finding relies on ecosystem-scale estimates of net primary productivity of lichens and bryophytes, which are converted to nitrous oxide emissions by empirical relationships between productivity and respiration, as well as between respiration and nitrous oxide release. Here we obtain an alternative estimate of nitrous oxide emissions which is based on a global process-based non-vascular vegetation model of lichens and bryophytes. The model quantifies photosynthesis and respiration of lichens and bryophytes directly as a function of environmental conditions, such as light and temperature. Nitrous oxide emissions are then derived from simulated respiration assuming a fixed relationship between the two fluxes. This approach yields a global estimate of 0.27 (0.19–0.35) (Tg N2O) year−1 released by lichens and bryophytes. This is lower than previous estimates but corresponds to about 50 % of the atmospheric deposition of nitrous oxide into the oceans or 25 % of the atmospheric deposition on land. Uncertainty in our simulated estimate results from large variation in emission rates due to both physiological differences between species and spatial heterogeneity of climatic conditions. To constrain our predictions, combined online gas exchange measurements of respiration and nitrous oxide emissions may be helpful.

Short summary
Lichens and bryophytes have been shown to release nitrous oxide, which is a strong greenhouse gas and atmospheric ozone-depleting agent. Here we apply a process-based computer model of lichens and bryophytes at the global scale, to estimate growth and respiration of the organisms. By relating respiration to nitrous oxide release, we simulate global nitrous oxide emissions of 0.27 (0.19–0.35) Tg yr−1. Moreover, we quantify different sources of uncertainty in nitrous oxide emission rates.
Final-revised paper