Nitrogen Fixation and Leaching of Biological Soil Crust Communities in Mesic Temperate Soils

Abstract

Biological soil crust is composed of lichens, cyanobacteria, green algae, mosses, and fungi. Although crusts are a dominant source of nitrogen (N) in arid ecosystems, this study is among the first to demonstrate their contribution to N availability in xeric temperate habitats. The study site is located in Lucas County of Northwest Ohio. Using an acetylene reduction technique, we demonstrated potential N fixation for these crusts covering sandy, acidic, low N soil. Similar fixation rates were observed for crust whether dominated by moss, lichen, or bare soil. N inputs from biological crusts in northwestern Ohio are comparable to those in arid regions, but contribute substantially less N than by atmospheric deposition. Nitrate and ammonium leaching from the crust layer were quantified using ion exchange resin bags inserted within intact soil cores at 4 cm depth. Leaching of ammonium was greater and nitrate less in lichen than moss crusts or bare soil, and was less than that deposited from atmospheric sources. Therefore, biological crusts in these mesic, temperate soils may be immobilizing excess ammonium and nitrate that would otherwise be leached through the sandy soil. Moreover, automated monitoring of microclimate in the surface 7 cm of soil suggests that moisture and temperature fluctuations in soil are moderated under crust compared to bare soil without crust. We conclude that biological crusts in northwestern Ohio contribute potential N fixation, reduce N leaching, and moderate soil microclimate.

Nitrogen fixation by associative cyanobacteria in the Canadian Arctic.

“…As the primary source of N input in many arid and semi-arid ecosystems, BSCs make an important contribution to the ecosystem N budget. BSCs play an essential role in soil stability and nutrient cycling and contribute significantly to soil fertility (Eldridge, 1998;Issa et al, 2001;Issa et al, 2007;Hu et al, 2003;Veluci et al, 2006). Soil surface structure is altered by BSCs through the creation of a rough surface micro topography, which alters the movement and retention of nutrients by diminishing the impact of surface runoff and wind (Veluci et al, 2006;Housman et al, 2007).…”

“…BSCs play an essential role in soil stability and nutrient cycling and contribute significantly to soil fertility (Eldridge, 1998;Issa et al, 2001;Issa et al, 2007;Hu et al, 2003;Veluci et al, 2006). Soil surface structure is altered by BSCs through the creation of a rough surface micro topography, which alters the movement and retention of nutrients by diminishing the impact of surface runoff and wind (Veluci et al, 2006;Housman et al, 2007). Several studies have found BSCs to have natural abundance 15 N values indicative of fixation of atmospheric sources, higher total and mineralizable N and higher dissolved nitrogenous compounds in porewater compared with adjacent soils (Evans & Ehleringer, 1993;Belnap, 1996;Evans & Belnap, 1999;Smith et al, 2002;Johnson et al, 2005;Marsh et al, 2006).…”

“…Mat-forming lichens in polar ecosystems can retain >80% of NH/ and NO3" deposited in summer rainfall (Crittenden, 1983;. Similarly, atmospheric deposition must pass through BSCs before reaching the underlying soil; therefore crusts may regulate the capture and release of atmospheric N (Hawkes, 2003;Veluci et al, 2006 (Tearle, 1987;Coxson et al, 1992;Wilson & Coxson, 1999). Extracellular polymers secreted from organisms within BSCs can represent a major source of C inputs.…”

“…Several studies have suggested that N-enriched leachate from terricolous cyanolichens contribute labile N to the soil on both a localized scale and can act as a significant N source on a landscape scale (Gunther, 1989;Knowles et al, 2006;Veluci et al, 2006). In environments with N limitation the inputs from N2-fixing lichens can create temporal and spatial variability in the supply of labile N and in turn variation in soil microbial communities (Crittenden, 1983;Millbank & Olsen, 1986;Knowles et al, 2006).…”

Alterations to biological soil crusts with alpine meadow retrogressive succession affect seeds germination of three plant species

“…They can have important impacts on ecological function through physiological or physical processes. For example, BSCs can bind soil particles to protect the surface soil from wind and water erosion (Belnap and Gardner 1993;Eldridge and Leys 2002;Veluci et al 2006;Mazor et al 1996); fix nitrogen (N) and carbon (C) to increase soil nutrients and C storage (Austin et al 2004;Hawkes 2003;Evans and Ehleringer 1993;Lange et al 1994); modify the balance between water run-off and infiltration (Kidron and Yair 1997;Eldridge and Greene 1994); and influence soil roughness. These changes can create a suitable primitive habitat for vascular plant growth, which influence on seed germination and establishment.…”