Benjamin Z. Houlton

Agricultural fertilizers are the main global source of ammonia emissions, which harm human health and reduce farmers' profits. An analysis using big data and machine learning reveals that locally optimized fertilizer-management and tillage practices could slash ammonia emissions from rice, wheat and maize cultivation by up to 38%.

Crop production is a large source of atmospheric ammonia (NH 3), which poses risks to air quality, human health and ecosystems 1, 2, 3, 4, 5. However, estimating global NH 3 emissions from croplands is subject to uncertainties because of data limitations, thereby limiting the accurate identification of mitigation options and efficacy 4, 5. Here we develop a machine learning model for generating crop-specific and spatially explicit NH 3 emission factors globally (5-arcmin resolution) based on a compiled dataset of field observations. We show that global NH 3 emissions from rice, wheat and maize fields in 2018 were 4.3±1.0 Tg N yr− 1, lower than previous estimates that did not fully consider fertilizer management practices 6, 7, 8, 9. Furthermore, spatially optimizing fertilizer management, as guided by the machine learning model, has the potential to reduce the NH 3 emissions by about 38%(1.6±0.4 Tg N yr− 1 …

Scientifically verifiable, durable, and scalable carbon dioxide removal (CDR) technologies are essential to reducing atmospheric CO2 concentrations and avoiding the most dangerous impacts of climate change this century. Within the nature-based solution portfolios, the soil system provides promising CDR and sequestration potential, including in both organic and inorganic forms at time scales that reflect durable removals (Smith et al., 2023)—those that exceed 100 years or longer. Soil organic carbon (SOC) and inorganic carbon (SIC) collectively preserve more than eight times as much carbon as does vegetation. Their changes determine the magnitudes of soil carbon sequestration and have profound impacts on the global carbon cycle. A critical challenge is to grow the total amount of carbon in soil pools in a way that is scientifically verifiable and scalable to the billions of tons of CDR needed to stabilize and …

Global estimates of the size, distribution, and vulnerability of soil inorganic carbon (SIC) remain largely unquantified. By compiling 223,593 field-based measurements and developing machine-learning models, we report that global soils store 2305 ± 636 (±1 SD) billion tonnes of carbon as SIC over the top 2-meter depth. Under future scenarios, soil acidification associated with nitrogen additions to terrestrial ecosystems will reduce global SIC (0.3 meters) up to 23 billion tonnes of carbon over the next 30 years, with India and China being the most affected. Our synthesis of present-day land-water carbon inventories and inland-water carbonate chemistry reveals that at least 1.13 ± 0.33 billion tonnes of inorganic carbon is lost to inland-waters through soils annually, resulting in large but overlooked impacts on atmospheric and hydrospheric carbon dynamics.

In their commentary, Xiao et al.[1] cautioned that the conclusions on the critical role of microbial carbon use efficiency (CUE) in global soil organic carbon (SOC) storage in the paper by Tao et al.[2] might be too simplistic. TheyclaimedthatTaoetal.’sstudylacked mechanistic consideration of SOC formation and excluded important data sets. Xiao et al. brought up important points, which can be largely reconciled with our findings by understanding the differences in expressing processes in empirical studies and in models.Mechanistic understanding of complex processes from empirical research is usually translated into mathematical models with some level of simplification. For example, processes involved in SOC stabilization and persistence, as brought up by Xiao et al., were considered using the model and evaluated together with microbial CUE for their relative importance to global SOC storage in Tao et al.[2]. The …

Understanding the formation and stabilization mechanisms of soil organic carbon (SOC) is important for managing land carbon (C) and mitigating climate change. Tao et al. 1 reported that microbial C use efficiency (CUE) is the primary determinant of global SOC storage and that the relative impact of plant C inputs on SOC is minor. Although soil microbes undoubtedly play an important role in SOC cycling, we are concerned about the robustness of the approach taken by Tao et al. 1. The potential biases in their analyses may lead to misleading, model-dependent results.An important piece of evidence in support of an empirical relationship between CUE and SOC stems from a meta-analysis based on 132 paired CUE and SOC measurements. Tao et al. 1 applied a linear mixed-effects model to this dataset that included CUE, mean annual temperature (MAT), soil depth and random effects and explained 55% of the …

Whether nitrogen (N) availability will limit plant growth and removal of atmospheric CO2 by the terrestrial biosphere this century is controversial. Studies have suggested that N could progressively limit plant growth, as trees and soils accumulate N in slowly cycling biomass pools in response to increases in carbon sequestration. However, a question remains over whether longer‐term (decadal to century) feedbacks between climate, CO2 and plant N uptake could emerge to reduce ecosystem‐level N limitations. The symbioses between plants and microbes can help plants to acquire N from the soil or from the atmosphere via biological N2 fixation—the pathway through which N can be rapidly brought into ecosystems and thereby partially or completely alleviate N limitation on plant productivity. Here we present measurements of plant N isotope composition (δ15N) in a peat core that dates to 15,000 cal. year BP to …

More frequent and severe droughts are driving increased forest mortality around the globe. We urgently need to describe and predict how drought affects forest carbon cycling and identify thresholds of environmental stress that trigger ecosystem collapse. Quantifying the effects of drought at an ecosystem level is complex because dynamic climate–plant relationships can cause rapid and/or prolonged shifts in carbon balance. We employ the CARbon DAta MOdel fraMework (CARDAMOM) to investigate legacy effects of drought on forest carbon pools and fluxes. Our Bayesian model‐data fusion approach uses tower observed meteorological forcing and carbon fluxes to determine the response and sensitivity of aboveground and belowground ecological processes associated with the 2012–2015 California drought. Our study area is a mid‐montane mixed conifer forest in the Southern Sierras. CARDAMOM …

In the accompanying Comment, He et al. argue that the determinant role of microbial carbon use efficiency in global soil organic carbon (SOC) storage shown in Tao et al. (2023) was overestimated because carbon inputs were neglected in our data analysis while they suggest that our model-based analysis could be biased and model-dependent. Their argument is based on a different choice of independent variables in the data analysis and a sensitivity analysis of two process-based models other than that used in our study. We agree that both carbon inputs and outputs (as mediated by microbial processes) matter when predicting SOC storage - the question is their relative contributions. While we encourage further studies to examine how the evaluation of the relative importance of CUE to global SOC storage may vary with different model structures, He et al.'s claims about Tao et al. (2023) need to be taken as an alternative, unproven hypothesis until empirical data support their specific parameterization. Here we show that an additional literature assessment of global data does not support He et al.'s argument, in contrast to our study, and that further study on this topic is essential.

Most climate mitigation scenarios point to a combination of GHG emission reductions and CO2 removal for avoiding the most dangerous climate change impacts this century. The global food system is responsible for ~1/3 of GHG emissions and thus plays an important role in reaching emission targets. Consumers, technology innovation, industry, and agricultural practices offer various degrees of opportunity to reduce emissions and remove CO2. However, a question remains as to whether food system transformation can achieve net negative emissions (i.e., where GHG sinks exceed sources sector wide) and what the capacity of the different levers may be. We use a global food system model to explore the influence of consumer choice, climate-smart agro-industrial technologies, and food waste reductions for achieving net negative emissions for the year 2050. We analyze an array of scenarios under the conditions of full yield gap closures and caloric demands in a world with 10 billion people. Our results reveal a high-end capacity of 33 gigatonnes of net negative emissions per annum via complete food system transformation, which assumes full global deployment of behavioral-, management- and technology-based interventions. The most promising technologies for achieving net negative emissions include hydrogen-powered fertilizer production, livestock feeds, organic and inorganic soil amendments, agroforestry, and sustainable seafood harvesting practices. On the consumer side, adopting flexitarian diets cannot achieve full decarbonization of the food system but has the potential to increase the magnitude of net negative emissions when …

Nitrogen dioxide (NO2) plays a pivotal role in the production of secondary pollutants, most importantly ozone (O3) and particulate matter. Regulatory controls have greatly reduced NO2 in cities, where most of the surface monitoring occurs, but the change in rural environments is less certain. Here, we present summertime (June–September) spatio-temporal patterns of NO2 concentrations using satellite and ground observations across California from 2009–2020, quantifying the differences in NO2 trends for five distinct land cover classes: urban, forests, croplands, scrublands (shrublands, savannas, and grasslands), and barren (minimally vegetated) lands. Over urban environments, NO2 columns exhibited continued but weakening downward trends (−3.7 ± 0.3%a−1), which agree fairly well with contemporaneous trends estimated from the surface air quality network (−4.5 ± 0.5%a−1). In rural (i.e., non-urban) parts of …

The Editors of the Global Biogeochemical Cycles express their appreciation to those who served as peer reviewers for the journal in 2022.

Deployment of wind energy is an essential renewable energy source that mitigates climate change and reduces air pollution [1]. Over the last several decades, wind energy development has increased worldwide, expanding from 20 to 900 GW (gigawatt) during 2001–2022 [1]. Nonetheless, researchers have identified unintended consequences of wind energy on microclimate via turbine-altered surface-atmosphere exchanges of energy, momentum, mass, and trace gases [2, 3]. Based on multi-source observations and models, researchers also have drawn some conclusions that wind farms could warm the land surface, especially at night, at regional and continental scales [4, 5]. Consequently, altered microclimates at wind farms may affect vegetation productivity and carbon sequestration, two critically important ecosystem services related to carbon dynamics; however, such potential impacts and driving mechanisms remain poorly understood [6]. Wind energy deployment is increasing globally to meet carbon neutrality goals, with upscaling of onshore wind power capacity projected to grow from 542 GW in 2018 to 1787 and 5044 GW by 2030 and 2050, respectively [7]. Increased demand for wind energy deployment may lead to much larger wind farms in open, expansive landscapes [7]. In turn, a large array of geographically clustered wind turbines could collectively modify local microclimate and amplify turbine-atmosphere interactions, which, if large enough, may produce detectable impacts on ecosystem dynamics. Thus, identifying and quantifying the potential impacts of wind farms on carbonrelated ecosystem services may facilitate …

Soils store more carbon than other terrestrial ecosystems,. How soil organic carbon (SOC) forms and persists remains uncertain,, which makes it challenging to understand how it will respond to climatic change,. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss, –. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways,,, , –, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes,. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved,,. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data …

The current generation of biogeochemical models produce large uncertainty in carbon-climate feedback projections. Structural differences in these models have been identified as a major source of inter-model uncertainties when simulating soil organic carbon (SOC) dynamics worldwide. However, parameterization could also play a role, particularly when common observational data are used to constrain model simulations. Here we demonstrate the critical role of observational data in reducing model-based uncertainty in global estimates of SOC. We applied the PROcess-guided deep learning and DAta-driven modeling (PRODA) approach to constrain both a microbial implicit model based on first-order kinetics (i.e., Community Land Model version 5, CLM5) and a microbial explicit model based on Michaelis-Menten kinetics (i.e., CarbOn cycle and Microbial PArtitioning Soil model, COMPAS) with >50,000 globally distributed SOC vertical profiles. Overall, the two constrained models predicted similar carbon transfer efficiency, baseline decomposition rate, and environmental effects on carbon fluxes. These converged model components contributed to similar SOC patterns simulated by the two structurally different biogeochemical models. Carbon input allocation and vertical transport were less constrained by SOC profile data and require other data sets to constrain. Moreover, after being constrained by SOC observations, the Michaelis constant in COMPAS tends to be much larger than its corresponding substrate concentration in SOC decomposition. Thus, the Michaelis-Menten kinetics in the COMPAS model can be approximated by multiplicative …

Denitrification and leaching nitrogen (N) losses are poorly constrained in Earth System Models (ESMs). Here, we produce a global map of natural soil 15N abundance and quantify soil denitrification N loss for global natural ecosystems using an isotope-benchmarking method. We show an overestimation of denitrification by almost two times in the 13 ESMs of the Sixth Phase Coupled Model Intercomparison Project (CMIP6, 73 ± 31 Tg N yr−1), compared with our estimate of 38 ± 11 Tg N yr−1, which is rooted in isotope mass balance. Moreover, we find a negative correlation between the sensitivity of plant production to rising carbon dioxide (CO2) concentration and denitrification in boreal regions, revealing that overestimated denitrification in ESMs would translate to an exaggeration of N limitation on the responses of plant growth to elevated CO2. Our study highlights the need of improving the …

Enhanced weathering of soil-applied crushed silicate rocks may remove substantial atmospheric carbon dioxide; however, field testing of this negative emission technology is lacking. Models have suggested that enhanced weathering could, in principle, remove billions of tons of CO 2 each year across global croplands, but methodological limitations have hindered direct measurement of CO 2 sequestration via crushed rock amendments in agriculture. Further questions remain concerning the efficacy of this technology in arid climates. Here we provide direct evidence of rapid CO 2 removal via enhanced weathering in soil pore water samples from a corn (Zea mays L.) cropping system in California. From December through February, during an extreme drought in our study region, we demonstrate a 2.6 to 2.9-fold increase in in situ bicarbonate alkalinity in response to additions of metabasalt and olivine fines. We …

There is an increasing food demand with growing population and limited land for agriculture. Conventional agriculture with nitrogen (N) fertilizer applications, however, is a key source of ammonia (NH3) emissions that cause severe haze pollution and impair human health. Organic and conservation agricultural (OCA) practices are thereby recommended to address these dual challenges; however, whether OCA provides cobenefits for both air quality and crop productivity is controversial. Here, we perform a meta-analysis and machine learning algorithm with data from China, a global hotspot for agricultural NH3 emissions, to quantify the effects of OCA on NH3 emissions, crop yields and nitrogen use efficiency (NUE). We find that the effects of OCA depend on soil and climate conditions, and the 40–60% substitution of synthetic fertilizers with livestock manure achieves the maximum cobenefits of enhanced crop …

Long‐term carbon (C) sequestration in terrestrial vegetation and soil is mediated by soil nitrogen (N) supply. Afforestation is regarded as a global‐scale solution to climate change; thus, resolving the role of N in either facilitating or reducing the long‐term C benefits of this practice has essential implications to maximize its C sink potential. The impacts of afforestation on soil C, N, and their stoichiometric ratio have been widely explored but what regulates these impacts remains unclear at regional and global scales. In this study, we conducted an intensive field sampling investigation including 610 pairs of afforested and control plots in northern China and extensively compiled a global data set containing 211 afforested‐control pairs worldwide to evaluate responses of soil N concentrations and C:N ratios to afforestation and further explored their major regulator. We identified a soil N threshold, the inflection point …

Recent analysis by the IPCC suggests that, across an array of scenarios, both GHG emissions reductions and various degrees of carbon removal will be required to achieve climate stabilization at a level that avoids the most dangerous climate changes in the future. Among a large number of options in the realm of natural climate solutions, atmospheric carbon dioxide removal (CDR) via enhanced silicate weathering (EW) in global working lands could, in theory, achieve billions of tons of CO2 removal each year. Despite such potential, however, scientific verification and field testing of this technology are still in need of significant advancement. Increasing the number of EW field trials can be aided by formal presentation of effective study designs and methodological approaches to quantifying CO2 removal. In particular, EW studies in working lands require interdisciplinary “convergence” research that links low temperature geochemistry and agronomy. Here, drawing on geologic and agronomic literature, as well as demonstration-scale research on quantifying EW, we provide an overview of (1) existing literature on EW experimentation as a CO2 removal technique, (2) agronomic and geologic approaches to studying EW in field settings, (3) the scientific bases and tradeoffs behind various techniques for quantifying CO2 removal and other relevant methodologies, and (4) the attributes of effective stakeholder engagement for translating scientific research in action. In doing so, we provide a guide for establishing interdisciplinary EW field trials, thereby advancing the verification of atmospheric CO2 in working lands through the convergence of …

Enhanced rock weathering (ERW) is a climate change mitigation technology that has been proposed to capture inorganic carbon (C) in soils and catalyze negative C emissions at large scales. ERW involves the application of finely crushed silicate rock minerals to soils to increase the weathering rate and maximize soil as a natural, long-term CO2 sink. It is currently unknown if, and to what degree, ERW may influence soil health and C storage. Co-deployment of inorganic and organic amendments, such as compost and biochar, may also impact the ability of soils to sequester C, but those potential synergies have not yet been explored. In addition to soil C pools, greenhouse gas (GHG) emissions represent key C budget components needed to quantify the net movement of C and nitrogen (N) in or out of a system. Southern California croplands represent significant sources of GHG emissions and undergo frequent …

Mitigating livestock-related nitrous oxide (N2O) emissions is key for China to meet its 2060 carbon neutrality target. Here we present a comprehensive analysis of the magnitude, spatiotemporal variation and drivers of Chinese livestock N2O emissions from 1978 to 2017. We developed scenarios to explore emissions mitigation potential and associated marginal abatement costs and social benefits. The average growth rate of China’s livestock N2O emissions increased by 4.6% per year through 2006, falling sharply over 2007–2015 and gradually declining in 2017 due to a slowdown in population and meat-consumption growth rates. We estimate the technical mitigation potential of livestock N2O emissions in 2030 to be 7–21% (or 23.1–70.9 Gg N2O), with implementation costs of US$5.5 billion to US$6.0 billion. Priority regions for intervention were identified in the North China Plain, Northeast Plain and Lianghu …

Nitrogen oxides (NOx, the sum of nitric oxide (NO) and N dioxide (NO2)) emissions and deposition have increased markedly over the past several decades, resulting in many adverse outcomes in both terrestrial and oceanic environments. However, because the microbial NOx emissions have been substantially underestimated on the land and unconstrained in the ocean, the global microbial NOx emissions and their importance relative to the known fossil-fuel NOx emissions remain unclear. Here we complied data on stable N isotopes of nitrate in atmospheric particulates over the land and ocean to ground-truth estimates of NOx emissions worldwide. By considering the N isotope effect of NOx transformations to particulate nitrate combined with dominant NOx emissions in the land (coal combustion, oil combustion, biomass burning and microbial N cycle) and ocean (oil combustion, microbial N cycle), we …

The Editors of the Global Biogeochemical Cycles express their appreciation to those who served as peer reviewers for the journal in 2021.

A recent study suggests that the optimal temperature for symbiotic nitrogen fixation rates exceeds the plant’s preferred growth temperature in laboratory conditions. A few degrees of warming could thereby increase or decrease nitrogen fixation rates, depending on the optimal rate among species.

Achieving net negative emissions to combat climate change depends on energy decarbonization and the removal of atmospheric CO2. Soil-based strategies can both reduce greenhouse gas emissions and enhance the removal of atmospheric CO2 into inorganic and organic forms. However it is uncertain to what extent soil carbon strategies, particularly for inorganic carbon sequestration, are viable and impactful pathways in California for helping to achieve the states aggressive climate change mitigation goal of carbon neutrality by 2045. Here we quantify the range in the carbon sequestration potentials of soil conservation (ie, compost, reduced tillage, cover crop) and enhanced silicate rock weathering (ERW) practices that build soil carbon at varying extents of implementation areas (50% or 100% of private and 100% of all ownerships) in cultivated, grassland, savanna, and woodland in California under …

Anthropogenic nitrogen deposition is widely considered to increase CO2 sequestration by land plants on a global scale. Here, we demonstrate that bedrock nitrogen weathering contributes significantly more to nitrogen‐carbon interactions than anthropogenic nitrogen deposition. This working hypothesis is based on the introduction of empirical results into a global biogeochemical simulation model over the time period of the mid‐1800s to the end of the 21st century. Our findings suggest that rock nitrogen inputs have contributed roughly 2–11 times more to plant CO2 capture than nitrogen deposition inputs since pre‐industrial times. Climate change projections based on RCP 8.5 show that rock nitrogen inputs and biological nitrogen fixation contribute 2–5 times more to terrestrial carbon uptake than anthropogenic nitrogen deposition though year 2101. Future responses of rock N inputs on plant CO2 capture rates …

Soil carbon (C) sequestration in agricultural working lands via soil amendments and management practices is considered a relatively well‐tested and affordable approach for removing CO2 from the atmosphere. Carbon farming provides useful benefits for soil health, biomass production, and crop resilience, but the effects of different soil C sequestration approaches on the nitrogen (N) cycle remain controversial. While some C farming practices have been shown to reduce N fertilizer use in some cases, C farming could also impose an unwanted “N penalty” through which soil C gains can only be maintained with additional N inputs, thereby increasing N losses to the environment. We systematically reviewed meta‐analysis studies on the impacts of C farming on N cycling in agroecosystems and estimated the cumulative effect of several C farming practices on N cycling. We found that, on average, combined C …

California's push to incentivize sustainable, climate-friendly agronomic practices emphasizes the need for verification of proposed soil management practices and their effects. In particular, soil amendments used to sequester carbon have been promoted as a climate mitigation strategy, however field-scale testing is limited. Here we examine the effects of crushed silicate minerals, compost, and biochar amendments on yields over the first two years of a row crop experiment. Soil amendments were applied in fall 2019 at three California sites located in Davis, Los Banos, and the Imperial Valley. These sites span a geographical transect of neutral to basic California agricultural soils. Field corn (Zea mays) was planted at each site between February and April 2020 and harvested between June and September 2020, when aboveground biomass and grain yield were collected from each plot. We also collected …

Human activities have increased reactive nitrogen (Nr) input to terrestrial ecosystems compared with the pre-industrial era. However, the fate of such Nr input remains uncertain, leading to missing sink of the global nitrogen budget. By synthesizing records of Nr burial in sediments from 303 lakes worldwide, here we show that 9.6 ± 1.1 Tg N year−1 (Tg = 1012 g) accumulated in inland water sediments from 2000 to 2010, accounting for 3%–5% of global Nr input to the land from combined natural and anthropogenic pathways. The recent Nr burial flux doubles pre-industrial estimates, and Nr burial rate significantly increases with global increases in human population and air temperature. Sediment ratios of C:N decrease after 1950 while N:P ratios increase over time due to increasingly elevated Nr burial and other related processes in lakes. These findings imply that Nr burial in lakes is overlooked as an important …

Microbial oxidation of organic compounds produces organic and inorganic acids in soil, and these ligands and proton sources drive the weathering of soil minerals. Understanding the linkages between these biological and chemical processes has stimulated research on technologies to accelerate the rate of a C stabilization associated with weathering minerals, especially in highly disturbed agricultural soils. One approach involves applying organic and inorganic amendments together (eg, compost, biochar, pulverized rock) to induce a synergistic effect via microbial and chemical mechanisms. However, it is unclear if a co-application of organic amendment appreciably enhances the weathering of mineral amendments and C accumulation. Also, the surface of weathering minerals can provide reactive binding sites for secondary mineral formation or metal co-precipitation with dissolved organic C, thus coating the …

While controls over the Earth's climate system have undergone rigorous hypothesis-testing since the 1800s, questions over the scientific consensus of the role of human activities in modern climate change continue to arise in public settings. We update previous efforts to quantify the scientific consensus on climate change by searching the recent literature for papers sceptical of anthropogenic-caused global warming. From a dataset of 88125 climate-related papers published since 2012, when this question was last addressed comprehensively, we examine a randomized subset of 3000 such publications. We also use a second sample-weighted approach that was specifically biased with keywords to help identify any sceptical peer-reviewed papers in the whole dataset. We identify four sceptical papers out of the sub-set of 3000, as evidenced by abstracts that were rated as implicitly or explicitly sceptical of human …

Soil amendments are commonly used in agricultural soils to improve soil biogeochemistry and increase crop yield. Some soil amendments may also facilitate soil organic and inorganic carbon sequestration, though the full extent of carbon sequestration and its dependence on soil minerals and microbial associations remains uncertain. To determine the role of mineral and microbial amendments on soil biogeochemistry, crop performance, and carbon sequestration, we tested the effect of two soil amendments-a combined inoculum of bacteria (Bacillus) and fungi (Trichoderma), and a powdered basalt coated in a humic acid-on soil biogeochemistry (ie, nutrient cycling, organic and inorganic carbon sequestration) and crop performance (ie, nutrient use efficiency and yield) on a 1-acre corn plot at Cornells AgriTech campus in Geneva, NY. The basalt amendment was designed to rapidly dissolve in soils, adding …

Carbon use efficiency—the proportion of substrate carbon that is converted to microbial biomass—is an important control on many ecosystem properties including carbon sequestration and nutrient cycling. Although CUE varies widely across terrestrial ecosystems, a coherent understanding of edaphic controls on CUE is lacking, thereby limiting the accuracy of global carbon models. The objective of this study was to determine how microbial CUE changes with long-term soil development and nutrient availability. Soil was collected across the chronosequence and fertility gradient at Jug Handle State Natural Reserve (the “Ecological Staircase”) in Mendocino County, CA. These soils exhibit a range in pH (3.29–6.59), litter quantity and quality (litter C:N, 32–70), and clay content (14.13–87.30%), while other factors such as modern-day climate, potential biota, and parent material are common to all sites. CUE …

The social cost of nitrous oxide does not account for stratospheric ozone depletion. Doing so could increase its value by 20%. Links between nitrous oxide and other nitrogen pollution impacts could make mitigation even more compelling.

Lindsay Hornstein, Dobbs Ferry High SchoolF. Garrett Boudinot and Benjamin Houlton, Dept of Ecology and EvolutionaryBiology, Cornell UniversityAssessing the permanence and performance of enhanced weathering for carbonsequestration using geospatial modelling Enhanced silicate rock weathering (ERW) has the potential to drive carbon dioxideremoval (CDR) across a wide range of landscapes, including croplands, through theconversion of atmospheric CO2 to the water-soluble bicarbonate (HCO3) or solidmineral carbonate (eg, CaCO3) in soils and soil waters. While models and trials havedemonstrated the capacity for ERW to sequester carbon, potentially at a gigatonne-scale globally, questions remain regarding the downstream fate and permanence ofcarbon following conversion to bicarbonate and carbonate. Integratinggeospatial mapping, field data from ERW trials in New York, and existing …

To stave off world hunger, humanity manipulated and unbalanced the nitrogen cycle. Today's excess fixed nitrogen is a global pollutant, of which our food system is a primary driver. Yet, food insecurity remains a global concern. In this Voices, food-system experts offer insights into the challenge of the sustainable management of nitrogen.

Soil carbon (C) sequestration in agricultural working lands (croplands and rangelands) via soil amendments and management practices is considered a relatively well tested and affordable approach for removing CO2 from the atmosphere. Such carbon farming provides useful benefits for soil health, biomass production, and crop resilience, but the effects of different soil C sequestration approaches on nitrogen (N) cycling remains controversial. While some C farming practices have been shown to reduce N fertilizer use, and subsequent N gas emissions, C farming could also impose an unwanted N penalty through which soil C gains can only be maintained with additional N inputs, thereby increasing N losses to the environment. We explored the impact of C farming practices on N gas emissions using three different approaches. First, we systematically reviewed meta-analysis studies on the impacts of C farming on …

Enhanced silicate weathering has been highlighted as a promising carbon sequestration tool in global working lands. A range of studies have suggested a sequestration potential between 0.29 to 18.1 t CO2 ha-1 in cropland soils, though these results are highly uncertain and controversial. Evaluating enhanced weathering as an effective solution for removing atmospheric carbon dioxide at scale is particularly limited by a lack of empirical testing and verification at field scales. Additional uncertainties concern the robustness of silicate rock dust and other soil amendment technologies under conditions of extreme climate change, which threaten the carbon storage potential of soil, especially as precipitation shifts and alters the chemical weathering rates of fine silicate minerals. In November 2020, we installed lysimeters at a five-acre Northern California field trial of irrigated corn (Zea mays) to investigate changes in soil …

Dinitrogen gas (N2) production removes fixed N from the marine biosphere; however, questions remain over the relative influence of microbial processes in determining N2 efflux from coastal sediments. Here, we quantify N2 production processes and controlling factors along a ∼2,500 km continental shelf sediment transect of China via combined molecular and isotopic approaches. We show that denitrification is the dominant pathway of sedimentary N2 production, which is greatly higher than anaerobic ammonium oxidation. N2 production rates by denitrification increase with nosZ gene abundance and decrease with bacterial diversity. The effects of temperature and dissolved oxygen on denitrification are mainly through their influence on biotic factors including functional genes, microbial biomass, and bacterial diversity. The rate of anaerobic ammonium oxidation increases with hzsB gene abundance …

More frequent and severe droughts are driving increased forest mortality around the globe. We urgently need to describe and predict how drought affects carbon uptake, storage and cycling within ecosystems, and identify thresholds of water stress that can trigger ecosystem collapse. However, quantifying the effects of drought at an ecosystem level is complex because dynamic climate-plant relationships can cause rapid and/or prolonged shifts in carbon balance. The CARbon DAta MOdel fraMework (CARDAMOM), a model-data fusion approach, uses meteorological observations to constrain parameters that assess above and below ground carbon and water ecological processes, while also tracking the historical patterns within the ecosystem (ie, a memory function). This can provide an observation-informed, long-term, mechanistic link between drought and forest mortality. We employed CARDAMOM to …

Reactive gaseous nitrogen (Ngr) emissions significantly affect Earth's climate system. Disagreement exists, however, over Ngr contributions to short‐ versus long‐term climate forcing, from local to global scales and among different gaseous forms, including NH3, NOx, and N2O. Here, we provide a comprehensive inventory of Ngr from China's croplands based on a new bottom‐up, mass flow‐based approach integrated with fine‐resolution agricultural activity data and nitrogen emission factors. We demonstrate that China's croplands emit about 8.87 Tg N to the atmosphere in 2014. Across different prefectures, Ngr emission per capita conforms to a “Kuznets curve,” that is, first increases then decreases, along the gradient of increasing urbanization. Ngr emission per gross domestic productivity (GDP) decreases exponentially with increasing urbanization or per capita GDP. Furthermore, climate change impact …

Plant root associations with microbes such as mycorrhizal fungi or N-fixing bacteria enable ecosystems to tap pools of nitrogen (N) that might otherwise be inaccessible, including atmospheric N or N in large soil organic molecules. Such microbially assisted N-foraging strategies may be particularly important in late-successional retrogressive ecosystems where productivity is low and soil nutrients are scarce. Here, we use natural N-stable isotopic composition to constrain pathways of N supplies to different plant functional groups across a well-studied natural soil fertility gradient that includes a highly retrogressive stage. We demonstrate that ectomycorrhizal fungi, ericoid mycorrhizal fungi, and N-fixing bacteria support forest N supplies at all stages of ecosystem succession, from relatively young, N-rich/phosphorus (P)-rich sites, to ancient sites (ca. 500 ky) where both N supplies and P supplies are exceedingly low …

Quantifying the dynamic nature of the terrestrial carbon cycle is crucial for mitigating the effects of anthropogenic carbon emissions. While our ability to monitor carbon flux in ecosystems has increasingly advanced over the past few decades, uncertainty remains on the fate, partitioning and residence times of carbon assimilated by plants. Using a model-data fusion approach, the CARbon DAta MOdel fraMework (CARDAMOM) has paved the way for retrieving carbon state and process variables at individual sites and at a global scale. We intend to fill in the spatiotemporal gap and present our findings on the carbon balance of the Southern Sierra Critical Zone Observatory using long-term datasets. In particular, we will highlight key differences in CARDAMOM simulations constrained by satellite and flux tower data to quantify plant carbon allocation, pools and residence times. Measurements from satellites include leaf …

Biological nitrogen fixation (BNF) is the largest nitrogen (N) input pathway in natural terrestrial ecosystems at present, fueling the drawdown of atmospheric CO2 in vegetation and soil on decadal to century time scales. Here, we use a global land‐surface model (CABLE) with three different approaches for estimating the responses of BNF to CO2, climate, and N deposition through Year 2100, particularly the linear versus nonlinear dependence of BNF on C investment and the temperature dependence of BNF. From 1900 to 2100, the cumulative rise in BNF varied from 1.6 to 3.0 Pg N, translating to an increase in terrestrial carbon (C) storage between 33 and 68 Pg C. This range reflects the different approaches used to model BNF (i.e., C‐limited vs. resource optimization approaches), indicating major uncertainties in C‐climate‐N interactions in Earth system model forecasts. The differences among different …

Field-level quantification of carbon (C) sequestration from enhanced rock weathering (ERW) must be robust to assess this technology's potential in agricultural systems or as a tool in C offset programs. Moreover, determining the fate of weathered ions from ERW, particularly if they are lost through runoff or percolation, is essential to evaluating the potential of ERW as a nutrient source for crops. Operating under the umbrella of the Working Lands Innovation Center, I investigate the proportion of soil C stored via ERW that occurs as bicarbonate or carbonate production in a corn cropping system and the fraction of weathered ions that is lost to leaching. The five-acre Northern California field site is characterized by circumneutral pH and young soils (Xerofluvents) and is currently planted with conventionally managed, drip-irrigated corn. Tension-controlled lysimeters were installed in plots amended with meta-basalt alone …

Removing carbon dioxide (CO 2) from the atmosphere in time to avoid the worst impacts of climate change will require large scale carbon (C) sequestration technologies that can be deployed on short time scales. Working lands, such as crop and rangelands, are currently a major source of greenhouse gas emissions but hold enormous potential for decreasing atmospheric CO 2 through enhanced weathering (EW). While the potential for EW remains unrealized, model projections estimate that amending two-thirds of croplands with basalt dust could extract 0.5-4 Pg CO 2 yr-1 by 2100. Even less is known about the potential in rangelands, which cover> 30% of the terrestrial land surface. Conceptual models and field tests of EW will help constrain global estimates and inform where this strategy can be most effective. At the Working Lands Innovation Center, we have developed EW demonstration sites in both crop and …

Soil nitrogen isotope composition (δ15N) is an essential tool for investigating ecosystem nitrogen balances, plant–microbe interactions, ecological niches, animal migration, food origins, and forensics. The advancement of these applications is limited by a lack of robust geospatial models that are capable of capturing variation in soil δ15N (i.e., isotopic landscapes or isoscapes). Due to the complexity of the nitrogen cycle and general scarcity of isotopic information, previous approaches have reconstructed regional to global soil δ15N patterns via highly uncertain linear regression models. Here, we develop a new machine learning approach to ascertain a finer‐scale understanding of geographic differences in soil δ15N, using the South American continent as a test case. We use a robust training set spanning 278 geographic locations across the continent, spanning all major biomes. We tested three different machine …

Nitrogen (N) fertilizer use has simultaneously increased global food production and N losses, resulting in degradation of water quality and climate pollution. A better understanding of N application rates and crop and environmental response is needed to optimize management of agroecosystems. Here we show an orchard agroecosystem with high N use efficiency promoted substantial gains in carbon (C) storage, thereby lowering net global warming potential (GWP). We conducted a 5-year whole-system analysis comparing reduced (224 kg N ha−1 yr−1) and intensive (309 kg N ha−1 yr−1) fertilizer N rates in a California almond orchard. The intensive rate increased net primary productivity (Mg C ha−1) and significantly increased N productivity (kg N ha−1) and net N mineralization (mg N kg−1 soil d−1). Use of 15N tracers demonstrated short and long-term mechanisms of soil N retention. These low organic matter …