Nitrogen cycling in desert biological soil crusts across biogeographic regions in the Southwestern United States

Abstract

Biological soil crusts (BSCs) are thought to be important in the fertility of arid lands as gateways for carbon (C) and nitrogen (N). Studies on the Colorado Plateau have shown that an incomplete internal N cycle operates in BSCs that results in significant exports of dissolved organic N, ammonia and nitrate into the bulk soil through percolating water, thus mechanistically explaining their role as a N gateway. It is not known if this pattern is found in other arid regions. To examine this, we measured rates of major biogeochemical N-transformations in a variety of BSCs collected from the Colorado Plateau and the Mojave, Sonoran and Chihuahuan Deserts. Dinitrogen fixation and aerobic ammonia oxidation were prominent transformations at all sites. We found anaerobic ammonia oxidation (anammox) rates to be below the detection limit in all cases, and at least 50-fold smaller than rates of N 2 -fixation, making it an irrelevant process for these BSCs. Heterotrophic denitrification was also of little consequence for the flow of N, with rates at least an order of magnitude smaller than those of N 2 -fixation. Thus we could confirm that despite the demonstrable differences in microbial community composition and soil material, BSCs from major biogeographic regions in arid North America displayed a remarkably consistent pattern of internal N cycling. The implications for arid land fertility drawn from previous studies in the Colorado Plateau appear applicable to BSCs across other arid regions of the Southwestern United States.

Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

“…Each sample was collected in dry state in a plastic petri dish (diameter 5.5. cm, height 1 cm), sealed and stored in the dark at room temperature until further analysis (storage time less than 15 weeks). Storage of biocrust samples under dry and dark conditions at room temperature is the most widely spread method and has been used in many other studies on N cycling in which samples have been stored even up to 6 months before measurements were performed (Abed et al, 2013;Strauss et al, 2012;Johnson et al, 2007;Brankatschk et al, 2013).…”

“…Globally it has been estimated that 100-290 Tg (N) yr −1 is fixed biologically (Cleveland et al, 1999), of which 49 Tg yr −1 (17-49 %) is fixed by cryptogamic covers, which comprise biocrusts, but also other microbially dominated biomes, like lichen and bryophyte communities occurring on soil, rocks and plants in boreal and tropical regions (Elbert et al, 2012). Studies have suggested that nitrogen cycling in soil (N 2 fixation, nitrification, denitrification) and hence reactive nitrogen emission (NO, N 2 O, HONO) is often enhanced by well-established biocrusts, especially by dark cyanobacteria (Cleveland et al, 1999;Elbert et al, 2012;Belnap, 2002;Barger et al, 2013;Johnson et al, 2005;Abed et al, 2013;Strauss et al, 2012;Weber et al, 2015). However, much of the molecular biology and chemistry that is important for atmosphere-land interactions likely occurs just below the crust (that is visible at the surface).…”

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

“…Measurements of N 2 O emissions by lichens and bryophytes, too, show considerable variation. Regarding biological soil crusts, several studies analysed denitrification rates to be negligible (Johnson et al, 2007;Strauss et al, 2012), and N 2 O production was calculated to constitute only 3-4 % of the N fixation rate (Barger et al, 2013). Other studies, however, described high denitrification rates that either increased (Brankatschk et al, 2013) or decreased with advancing crust development (Abed et al, 2013).…”

Species identity of biocrust-forming lichens drives the response of soil nitrogen cycle to altered precipitation frequency and nitrogen amendment

“…Biocrusts are important to the stability and productivity of dryland ecosystems where plants are typically sparse (Eldridge and Greene, 1994;Belnap et al, 2008;Lindo and Gonzalez, 2010;Zelikova et al, 2012). Previous studies have demonstrated that biocrusts play crucial roles in mediating key processes of N turnover, such as N fixation, nitrification and denitrification (Belnap, 2003;Johnson et al, 2007;Strauss et al, 2012;Abed et al, 2013;DelgadoBaquerizo et al, 2013c;Kidron et al, 2015). Much less, however, is known about the importance of biocrusts on the diversity and abundance of particular microbial communities such as those related to N processes.…”