Nitrous oxide and methane emissions from cryptogamic covers

Abstract

Cryptogamic covers, which comprise some of the oldest forms of terrestrial life on Earth (Lenton & Huntingford, ), have recently been found to fix large amounts of nitrogen and carbon dioxide from the atmosphere (Elbert etal., ). Here we show that they are also greenhouse gas sources with large nitrous oxide (N2O) and small methane (CH4) emissions. Whilst N2O emission rates varied with temperature, humidity, and N deposition, an almost constant ratio with respect to respiratory CO2 emissions was observed for numerous lichens and bryophytes. We employed this ratio together with respiration data to calculate global and regional N2O emissions. If our laboratory measurements are typical for lichens and bryophytes living on ground and plant surfaces and scaled on a global basis, we estimate a N2O source strength of 0.32-0.59 Tg year(-1) for the global N2O emissions from cryptogamic covers. Thus, our emission estimate might account for 4-9% of the global N2O budget from natural terrestrial sources. In a wide range of arid and forested regions, cryptogamic covers appear to be the dominant source of N2O. We suggest that greenhouse gas emissions associated with this source might increase in the course of global change due to higher temperatures and enhanced nitrogen deposition

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

“…Absolute values of N 2 O release estimated by Lenhart et al (2015) were highest for lichens and bryophytes living on the ground in the boreal zone and for epiphytic lichens and bryophytes in the humid tropics. The relative contributions of lichens and bryophytes to total ecosystem N 2 O emissions, however, were highest in desert and tundra biomes, due to the low emissions by other vegetation and the soil there.…”

“…Furthermore, Lenhart et al (2015) showed that a large variety of lichen and bryophyte species release nitrous oxide (N 2 O). They estimated that the organisms emit a total value of 0.45 (0.32-0.59) (Tg N 2 O) year −1 at the global scale, which corresponds to 4-9 % of natural terrestrial N 2 O emissions (Zhuang et al, 2012).…”

“…The estimate by Lenhart et al (2015) is derived from measuring emissions of N 2 O by the organisms in the laboratory under a range of environmental conditions. All lichen and bryophyte species analysed by Lenhart et al (2015) showed release of N 2 O. Lichens and bryophytes were shown to utilize 15 N labelled NO − 3 but not NH + 4 , indicating that N 2 O is likely formed during denitrification.…”

Pan-Eurasian Experiment (PEEX): towards a holistic understanding of the feedbacks and interactions in the land–atmosphere–ocean–society continuum in the northern Eurasian region

“…However, most of the atmospheric nitrogen is in the form of inert N 2 , which is unavailable most for plants and microbes, and can only be assimilated into terrestrial ecosystems through biological N 2 fixation (Canfield et al, 2010). Only cryptogamic covers and certain organisms living in symbiosis with plants are capable of nitrogen fixation, making nitrogen the main growth-limiting nutrient in terrestrial ecosystems (Elbert et al, 2012;Lenhart et al, 2015). Human perturbations to the natural nitrogen cycle have, however, significantly increased the availability of nitrogen in the environment (Fig.…”

Revisiting chlorophyll extraction methods in biological soil crusts – methodology for determination of chlorophyll a and chlorophyll a + b as compared to previous methods

“…It has been shown that biocrusts play significant functional roles in the desert ecosystems (Eldridge and Greene, 1994;Evans and Belnap, 1999;Lan et al, 2011), as they stabilize the soil surface 5 and reduce erosion by wind and water (Zhao et al, 2014;Belnap et al, 2014;Belnap and Büdel, 2016), they contribute to soil fertility through carbon and nitrogen fixation (Elbert et al, 2012;Sancho et al, 2016;Barger et al, 2016;Brankatschk et al, 2013), and they positively affect water retention and distribution in drylands (Rodriguez-Caballero et al, 2014;Chamizo et al, 2016). Biocrusts and their organisms have been shown to also release gaseous nitrogen compounds, as nitrous acid (Lenhart et al, 2015), nitric oxide and nitrous oxide into the atmosphere Meusel et al, 2017). Biocrusts 10 are composed of photosynthesizing cyanobacteria, algae, lichens, and bryophytes plus decomposers, i.e.…”