Shifts in soil ammonia-oxidizing community maintain the nitrogen stimulation of nitrification across climatic conditions

Anthropogenic nitrogen (N) loading alters soil ammonia-oxidizing archaea (AOA) and bacteria (AOB) abundances, likely leading to substantial changes in soil nitrification. However, the factors and mechanisms determining the responses of soil AOA:AOB and nitrification to N loading are still unclear, making it difficult to predict future changes in soil nitrification. Herein, we synthesize 68 field studies around the world to evaluate the impacts of N loading on soil ammonia oxidizers and nitrification. Across a wide range of biotic and abiotic factors, climate is the most important driver of the responses of AOA:AOB to N loading. Climate does not directly affect the N-stimulation of nitrification, but does so via climate-related shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N-availability and moisture. AOB play a dominant role in affecting nitrification in dry climates, while the impacts from AOA can exceed AOB in humid climates. Together, these results suggest that climate-related shifts in soil ammonia-oxidizing community maintain the N-stimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading

Shifts in soil ammonia-oxidizing community maintain the nitrogen stimulation of nitrification across climatic conditions

© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Anthropogenic nitrogen (N) loading alters soil ammonia-oxidizing archaea (AOA) and bacteria (AOB) abundances, likely leading to substantial changes in soil nitrification. However, the factors and mechanisms determining the responses of soil AOA:AOB and nitrification to N loading are still unclear, making it difficult to predict future changes in soil nitrification. Herein, we synthesize 68 field studies around the world to evaluate the impacts of N loading on soil ammonia oxidizers and nitrification. Across a wide range of biotic and abiotic factors, climate is the most important driver of the responses of AOA:AOB to N loading. Climate does not directly affect the N-stimulation of nitrification, but does so via climate-related shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N-availability and moisture. AOB play a dominant role in affecting nitrification in dry climates, while the impacts from AOA can exceed AOB in humid climates. Together, these results suggest that climate-related shifts in soil ammonia-oxidizing community maintain the N-stimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading.This study was funded by the National Natural Science Foundation of China (32130069). J.C. was funded by EU H2020 Marie Skłodowska-Curie Actions (839806), Aarhus University Research Foundation (AUFF-E-2019-7-1), Danish Independent Research Foundation (1127-00015B), and Nordic Committee of Agriculture and Food Research. K.J.v.G. was funded by the National Environmental Research Council (NE/W001691/1). K.B.B. received funding from the Pioneer Center for Research in Sustainable Agricultural Futures (Land-CRAFT), DNRF grant number P2.Peer reviewe

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

International audienceAbstract Global soil nitrogen (N) cycling remains poorly understood due to its complex driving mechanisms. Here, we present a comprehensive analysis of global soil δ 15 N, 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 δ 15 N. The joint effects of multiple drivers govern the latitudinal distribution of soil δ 15 N, 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 δ 15 N, 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

Ecosystem responses to elevated CO2 governed by plant–soil interactions and the cost of nitrogen acquisition

Land ecosystems sequester on average about a quarter of anthropogenic CO2 emissions. It has been proposed that nitrogen (N) availability will exert an increasingly limiting effect on plants’ ability to store additional carbon (C) under rising CO2, but these mechanisms are not well understood. Here, we review findings from elevated CO2 experiments using a plant economics framework, highlighting how ecosystem responses to elevated CO2 may depend on the costs and benefits of plant interactions with mycorrhizal fungi and symbiotic N-fixing microbes. We found that N-acquisition efficiency is positively correlated with leaf-level photosynthetic capacity and plant growth, and negatively with soil C storage. Plants that associate with ectomycorrhizal fungi and N-fixers may acquire N at a lower cost than plants associated with arbuscular mycorrhizal fungi. However, the additional growth in ectomycorrhizal plants is partly offset by decreases in soil C pools via priming. Collectively, our results indicate that predictive models aimed at quantifying C cycle feedbacks to global change may be improved by treating N as a resource that can be acquired by plants in exchange for energy, with different costs depending on plant interactions with microbial symbionts

Soil carbon storage capacity of drylands under altered fire regimes

Acknowledgements: Funding was provided by the US Department of Agriculture National Institute of Food and Agriculture grant 2018‐67012‐28077 and United Kingdom Research and Innovation G123484 (A.F.A.P.), Gordon and Betty Moore Foundation (R.B.J.) and Lawrence Fellowship LLNL-LDRD Program under project number 21-ERD-045 under the auspices of Department of Energy Contract DE-AC52-07NA27344 (K.G.). The Cedar Creek Long Term Ecological Research programme was funded by National Science Foundation grants DEB-0620652, DEB-1234162, DEB-1831944 and DBI-2021898 (P.B.R. and S.E.H.). Sampling in other sites were funded by the National Park Service and Sequoia Parks Conservancy and South African National Parks.Funder: DEB-0620652, DEB-1234162, DEB-1831944, and DBI-2021898Funder: Gordon and Betty Moore Foundation (Gordon E. and Betty I. Moore Foundation); doi: https://doi.org/10.13039/100000936AbstractThe determinants of fire-driven changes in soil organic carbon (SOC) across broad environmental gradients remains unclear, especially in global drylands. Here we combined datasets and field sampling of fire-manipulation experiments to evaluate where and why fire changes SOC and compared our statistical model to simulations from ecosystem models. Drier ecosystems experienced larger relative changes in SOC than humid ecosystems—in some cases exceeding losses from plant biomass pools—primarily explained by high fire-driven declines in tree biomass inputs in dry ecosystems. Many ecosystem models underestimated the SOC changes in drier ecosystems. Upscaling our statistical model predicted that soils in savannah–grassland regions may have gained 0.64 PgC due to net-declines in burned area over the past approximately two decades. Consequently, ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models.</jats:p

Soil carbon storage capacity of drylands under altered fire regimes

Acknowledgements: Funding was provided by the US Department of Agriculture National Institute of Food and Agriculture grant 2018‐67012‐28077 and United Kingdom Research and Innovation G123484 (A.F.A.P.), Gordon and Betty Moore Foundation (R.B.J.) and Lawrence Fellowship LLNL-LDRD Program under project number 21-ERD-045 under the auspices of Department of Energy Contract DE-AC52-07NA27344 (K.G.). The Cedar Creek Long Term Ecological Research programme was funded by National Science Foundation grants DEB-0620652, DEB-1234162, DEB-1831944 and DBI-2021898 (P.B.R. and S.E.H.). Sampling in other sites were funded by the National Park Service and Sequoia Parks Conservancy and South African National Parks.Funder: DEB-0620652, DEB-1234162, DEB-1831944, and DBI-2021898Funder: Gordon and Betty Moore Foundation (Gordon E. and Betty I. Moore Foundation); doi: https://doi.org/10.13039/100000936The determinants of fire-driven changes in soil organic carbon (SOC) across broad environmental gradients remains unclear, especially in global drylands. Here we combined datasets and field sampling of fire-manipulation experiments to evaluate where and why fire changes SOC and compared our statistical model to simulations from ecosystem models. Drier ecosystems experienced larger relative changes in SOC than humid ecosystems—in some cases exceeding losses from plant biomass pools—primarily explained by high fire-driven declines in tree biomass inputs in dry ecosystems. Many ecosystem models underestimated the SOC changes in drier ecosystems. Upscaling our statistical model predicted that soils in savannah–grassland regions may have gained 0.64 PgC due to net-declines in burned area over the past approximately two decades. Consequently, ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models