Explanations for nitrogen decline

Olff, Han; Aerts, Rien; Bobbink, Roland; Cornelissen, Johannes H. C.; Erisman, Jan Willem; Galloway, James N.; Sutton, Mark A.; Vries, Franciska T. de; Wamelink, G.W.W.; Wardle, David A.

doi:10.1126/science.abq7575

Cited by 11 publications

(6 citation statements)

References 11 publications

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“…Mycorrhizal fungi are known to retain the heavier 15 N atom and pass the depleted N onto the plant (Hobbie and Högberg, 2012) resulting in lower δ 15 N values in plant tissues. Finally, a counter-argument to the PNL explanation for declining δ 15 N values is that the total amount and δ 15 N signature of anthropogenic N deposition has declined for approximately three to four decades (Olff et al, 2022). However, we note that the decline in δ 15 N we observed in our wood data started at least one decade prior to peak atmospheric N deposition rates in Sweden, which occurred in the early 1980s (Lajtha and Jones, 2013;Ferm et al, 2019).…”

Section: Mean Temporal Response Of Wood Traitscontrasting

confidence: 50%

Forest inventory tree core archive reveals changes in boreal wood traits over seven decades

Bassett,

Östlund,

Gundale

et al. 2024

Preprint

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Boreal forests play an important role in the global carbon cycle (C), and there is increasing interest in understanding how they react to environmental changes, including nitrogen (N) and water limitations, which may influence future forest growth and C storage. Utilizing tree cores archived by the Swedish National Forest Inventory, we measured stemwood traits, including stable N and C isotope composition, which provides information on N availability and water stress, respectively, as well as N and C content, and the C/N ratio over the period 1950–2017 in two central Swedish counties, Jämtland and Västernorrland, covering an area of ca. 55,000 sq. km (n = 1038). We tested the hypothesis that wood traits change over time and that temporal patterns would vary depending on alternative dendrochronological reconstruction methods, i.e. the established standard “single tree method” (STM) or a conceptually stronger “multiple tree method” (MTM). Averaged across all MTMs, our data showed that all five wood traits for Picea abies and Pinus sylvestris changed over time. Wood δ15N declined strongly, indicating progressive nitrogen limitation. The decline in δ13C followed the known atmospheric δ13CO2 signal, indicating there was no change in water stress. In addition, wood N increased significantly, while C and C/N ratios declined over time. Furthermore, wood trait patterns sometimes differed between dendrochronological methods. The most prominent difference was for δ15N, where the slope was much shallower for the STM compared to MTMs for both species, indicating that mobiity of contemporary N is problematic when the STM is used, leading to much less sensitivity to detect historical signals. Our study shows strong temporal changes in boreal wood traits and also indicates that the field of dendroecology should adopt new methods and archival protocols for studying highly mobile element cycles, such as nitrogen, which are critical for understanding environmental change in high latitude ecosystems.

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Section: Mean Temporal Response Of Wood Traitscontrasting

confidence: 50%

Forest inventory tree core archive reveals changes in boreal wood traits over seven decades

Bassett,

Östlund,

Gundale

et al. 2024

Preprint

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“…We also used a version of the toy model to evaluate changes in δ 15 N because a decline in 15 N was used as evidence for declining N availability by Mason et al (2022a), and this was an area of disagreement between Mason et al (2022a,b) and Olff et al (2022). Publications by Vitousek et al (2021) and Burnett et al (2022) evaluated δ 15 N in soils and plants (respectively) across this broad precipitation gradient (285-3240 mm/year) in an unpolluted region on the Simulated effects of increasing temperature on the NPP of a non-N-fixing plant and on N availability (calculated as described in the legend of Fig.…”

Section: Resultsmentioning

confidence: 99%

“…This suggestion is controversial. A response by Olff et al (2022) suggested that air quality regulations could have decreased N availability in recent decades, and that some of the evidence summarized by Mason et al (2022a) for decreasing N availability (particularly the declining δ 15 N in tree rings, lake sediments, and plant tissues) could reflect a changed mixture of 15 N sources reaching downwind ecosystems. Mason et al (2022b) responded that the decline in N availability began well before air quality regulations took effect, and that any change in the mixture of 15 N sources would have to be unrealistically large to have the effects that Olff et al (2022) suggested.…”

Section: Introductionmentioning

confidence: 99%

Has nitrogen availability decreased over much of the land surface in the past century? A model-based analysis

Vitousek,

Cen,

Groffman

2024

Biogeochemistry

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A recent publication (Mason et al. in Science 376:261, 2022a) suggested that nitrogen (N) availability has declined as a consequence of multiple ongoing components of anthropogenic global change. This suggestion is controversial, because human alteration of the global N cycle is substantial and has driven much-increased fixation of N globally. We used a simple model that has been validated across a climate gradient in Hawai ‘i to test the possibility of a widespread decline in N availability, the evidence supporting it, and the possible mechanisms underlying it. This analysis showed that a decrease in δ15N is not sufficient evidence for a decline in N availability, because δ15N in ecosystems reflects both the isotope ratios in inputs of N to the ecosystem AND fractionation of N isotopes as N cycles, with enrichment of the residual N in the ecosystem caused by greater losses of N by the fractionating pathways that are more important in N-rich sites. However, there is other evidence for declining N availability that is independent of 15N and that suggests a widespread decline in N availability. We evaluated whether and how components of anthropogenic global change could cause declining N availability. Earlier work had demonstrated that both increases in the variability of precipitation due to climate change and ecosystem-level disturbance could drive uncontrollable losses of N that reduce N availability and could cause persistent N limitation at equilibrium. Here we modelled climate-change-driven increases in temperature and increasing atmospheric concentrations of CO2. We show that increasing atmospheric CO2 concentrations can drive non-equilibrium decreases in N availability and cause the development of N limitation, while the effects of increased temperature appear to be relatively small and short-lived. These environmental changes may cause reductions in N availability over the vast areas of Earth that are not affected by high rates of atmospheric deposition and/or N enrichment associated with urban and agricultural land use.

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“…Soil nitrogen (N) cycling is a fundamental component of terrestrial biogeochemistry, yet the mechanisms controlling it remain unclear (Addiscott & Brookes, 2002; Hiltbrunner et al., 2019; Hungate et al., 2003; Olff et al., 2022). The stable N isotopic signature (δ 15 N) of soil reflects soil N input–output balance (Högberg, 1997; Robinson, 2001), where higher δ 15 N values suggest a more open (leaky) N cycling and lower δ 15 N values indicate a more close (conservative) N cycling (Mason et al., 2022; Peters et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Global evidence for joint effects of multiple natural and anthropogenic drivers on soil nitrogen cycling

Zhang,

Cheng,

Terrer

et al. 2024

Global Change Biology

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Global soil nitrogen (N) cycling remains poorly understood due to its complex driving mechanisms. Here, we present a comprehensive analysis of global soil δ15N, a stable isotopic signature indicative of the N input–output balance, using a machine‐learning approach on 10,676 observations from 2670 sites. Our findings reveal prevalent joint effects of climatic conditions, plant N‐use strategies, soil properties, and other natural and anthropogenic forcings on global soil δ15N. The joint effects of multiple drivers govern the latitudinal distribution of soil δ15N, with more rapid N cycling at lower latitudes than at higher latitudes. In contrast to previous climate‐focused models, our data‐driven model more accurately simulates spatial changes in global soil δ15N, highlighting the need to consider the joint effects of multiple drivers to estimate the Earth's N budget. These insights contribute to the reconciliation of discordances among empirical, theoretical, and modeling studies on soil N cycling, as well as sustainable N management.

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Explanations for nitrogen decline

Cited by 11 publications

References 11 publications

Forest inventory tree core archive reveals changes in boreal wood traits over seven decades

Forest inventory tree core archive reveals changes in boreal wood traits over seven decades

Has nitrogen availability decreased over much of the land surface in the past century? A model-based analysis

Global evidence for joint effects of multiple natural and anthropogenic drivers on soil nitrogen cycling

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