Geology Reports⌕ Search
Home/Archive/USGS

USGS · 70031179

Rainfall limit of the N cycle on Earth

Stephanie A. Ewing·Greg Michalski·Mark Thiemens·R.C. Quinn·J. L. Macalady·S. Kohl·Scott D. Wankel·Carol Kendall·Christopher P McKay·Ronald Amundson
View original source ↗Export metadata ↓

Abstract

In most climates on Earth, biological processes control soil N. In the Atacama Desert of Chile, aridity severely limits biology, and soils accumulate atmospheric NO 3 − . We examined this apparent transformation of the soil N cycle using a series of ancient Atacama Desert soils (>2 My) that vary in rainfall (21 to <2 mm yr −1 ). With decreasing rainfall, soil organic C decreases to 0.3 kg C m −2 and biological activity becomes minimal, while soil NO 3 − and organic N increase to 4 kg N m −2 and 1.4 kg N m −2 , respectively. Atmospheric NO 3 − (Δ 17 O = 23.0‰) increases from 39% to 80% of total soil NO 3 − as rainfall decreases. These soils capture the transition from a steady state, biologically mediated soil N cycle to a dominantly abiotic, transient state of slowly accumulating atmospheric N. This transition suggests that oxidized soil N may be present in an even more arid and abiotic environment: Mars.

Explore related subjects

Global Biogeochemical CyclesArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Stephanie A. Ewing, Greg Michalski, Mark Thiemens, R.C. Quinn, J. L. Macalady, S. Kohl, Scott D. Wankel, Carol Kendall, Christopher P McKay, Ronald Amundson. 2007-08-08. Rainfall limit of the N cycle on Earth. https://doi.org/10.1029/2006gb002838

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Blind spots in our understanding of the tropical nitrogen cycle

Understanding environmental controls on tropical nitrogen (N) cycling is critical for projecting flux rates and modeling ecosystem responses to rising CO 2 . Here, we ask whether geographic bias in field sampling may shape our understanding of N cycling by failing to capture the breadth of environmental heterogeneity within the tropics. We mapped empirical sampling locations of two major ecosystem N inputs and outputs—biological nitrogen fixation and denitrification—paired with a wide range of variables thought to influence N cycling. Both single and multi-variate analyses revealed that sampling density is greater in productive, wet, fertile, warmer tropical ecosystems with low seasonality—areas expected to have higher process rates—but biased away from spatially extensive biomes which may have high process rate variability and thus higher uncertainty. Even within tropical broadleaf forests, sampling is biased toward sites with unusually high soil fertility (N and phosphorus), potentially skewing biome-wide averages. Although some geographically undersampled regions share environmental characteristics with well-studied sites, others are unique, compromising inference from existing data. Finally, we find that while sampled field locations capture the range of N cycle process means/variances predicted by an ensemble of terrestrial biosphere models, this may be the result of circularity in model parameters and driving data rather than true coverage, including overrepresentation of forest plant functional types that may be parameterized from a small subset of sites. Data coverage expansion into areas with novel environmental conditions and higher uncertainty could be used to assess and improve model parameterization, as well as test general hypotheses.

Global Biogeochemical Cycles↗
USGS2026

Global carbon investment in terrestrial biological nitrogen fixation

Biological nitrogen (N) fixation (BNF) provides the N needed to produce proteins and other biological building blocks, helping feed humanity and mitigate climate change. Due to its high energetic cost compared to other forms of N acquisition, biotic investment in BNF indicates N limitation. Globally gridded BNF flux data provide an opportunity to determine the energetic investment in BNF across ecosystems, which would help reconcile conflicting indicators of N limitation. Here, we use a new BNF synthesis to quantify the relative importance of BNF in different N-fixing niches, in different biomes, and across the globe by calculating the fraction of net primary productivity (NPP) invested in BNF and the fraction of plant N acquisition provided by BNF. Larger fractions of non-agricultural NPP were invested in BNF in less-productive, higher-latitude biomes. This pattern was driven by biocrusts and mosses. Similarly, non-agricultural symbiotic N-fixing plants invested relatively more of their own NPP in BNF in less-productive, higher-latitude biomes. This symbiotic plant pattern was driven by shrubs and herbs, overriding the opposite pattern in trees. Symbiotic plants also acquired a higher fraction of their N from BNF at higher latitudes and in less productive biomes. Investments in symbiotic BNF were 10× higher in agricultural (2.9% of NPP) versus natural (0.29%) biomes, providing 26% versus 3.1% of ecosystem-scale plant N acquisition. These results support the paradigm of strong N limitation at higher latitudes, help understand the rarity of N-fixing trees at higher latitudes, underscore the dominance of human activity, and inform terrestrial biosphere models.

Global Biogeochemical Cycles↗
USGS2026

Erosional and hydrological controls on the age and thermochemical stability of particulate organic carbon in an Arctic river

Understanding the mechanisms that drive the mobilization and fate of organic carbon (OC) in Arctic landscapes is important for modeling the feedbacks among permafrost thaw, carbon cycling, and climate change. While significant progress has been made toward measuring in situ OC decomposition in permafrost soils and bulk particulate organic carbon (POC) export from Arctic rivers, few studies have distinguished the source and lability of POC across Arctic landscapes, limiting our ability to predict whether mobilized POC will be oxidized to CO 2 and CH 4 or buried in downstream depositional environments. This study uses ramped pyrolysis/oxidation radiocarbon (RPO- 14 C) analyses to investigate spatial and temporal variations in the thermochemical stability and radiocarbon content of fluvial POC during downstream transport from mountains to the coast in the Canning River (North Slope, Alaska). Fluvial POC in the headwaters is predominantly comprised of high activation energy, thermally recalcitrant petrogenic OC (OC petro ) derived from shale bedrock. Moving into the foothills and low-relief coastal plains, river bank erosion primarily drives mobilization of labile, low activation energy, soil-derived OC (OC soil ). Fluvial POC in mountainous upstream reaches consisted of ∼70% OC petro and just ∼30% OC soil , while POC in the downstream coastal plain reaches comprised ∼85% OC soil and ∼15% OC petro . The high relative lability of POC exported to the coast indicates high susceptibility to oxidation and microbial decomposition, which could enhance CO 2 release as the Arctic hydrologic cycle intensifies. However, the persistence of refractory OC petro in the suspended load indicates the potential for long-term burial of rock organic carbon in marine sediments.

Alaska↗