Climatic and management drivers of CO2 exchanges by a production crop: Analysis over three successive 4-year crop rotation cycles

Carbon dioxide (CO2) exchanges between crops and the atmosphere are influenced by both climatic and crop management drivers. The investigated crop, situated at the Lonzée Terrestrial Observatory (LTO, candidate ICOS site) in Belgium and managed for more than 70 years using conventional farming practices, was monitored over three complete sugar beet/winter wheat/potato/winter wheat rotation cycles from 2004 to 2016. Continuous eddy-covariance measurements and regular biomass samplings were performed in order to obtain the daily and seasonal Net Ecosystem Exchange (NEE), Gross Primary Productivity (GPP), Total Ecosystem Respiration (TER), Net Primary Productivity (NPP), and Net Biome Production (NBP). Meteorological data and crop management practices were also recorded. Over the 12 years, NEE was negative (-4.34 kg C m-2) but NBP was positive (1.05 kg C m-2), i.e. as soon as carbon exportation by harvest and carbon importation (manure, slimes) are included in the budget, the site behaves as a carbon source. At the crop rotation scale (4 years) it was quite remarkable to observe that NBP was very similar over the three rotations (0.30-0.36 kg C m-2), despite climatic and management differences between years. Crop type impacted carbon exchanges, with sugar beet and winter wheat crops leading to higher net carbon sequestration than seed potato crops. For one given crop, larger growth length and cumulated global radiation drove larger cumulated NEE. Net carbon emissions were observed during intercrops, but growing mustard during these periods reduced their rates and provided carbon residues to the soil. NBP values suggest that one sixth of the total soil organic carbon stock at LTO (6.23 ± 0.16 kg C m-2 in [0, 60] cm) would be lost in 12 years. Large uncertainties (mostly due to biomass measurements) affect NBP estimates, but still, this figure is huge and should encourage cultural practices returning carbon to the soil

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.Peer reviewe

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world\u27s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Description and analysis of a soil heterotrophic respiration model applied to a an agricultural soil.

This work aimed to describe a mechanistic model for soil heterotrophic respiration, to apply it to an agricultural soil and to specify its important parameters, in order to define future research fields. A complete description of the model structure is given. It uses a daily time step and is derived from the CENTURY model. The model was found to be independent from the initial carbon pool contents and an exponential relationship was observed between the order of stabilisation of the different pools and their respective decomposition constants. Literature was scanned to provide a panel of biochemical parameter values (nitrogen, lignin, cellulose and hemicellulose contents) for wheat, sugar beet and potato crops. Large parameter ranges of values were noticed and a lack of information about sugar beet and potato crops drove our choice to work with wheat biochemical parameters later on. An exponential relationship between two parameters linked to the effect of temperature on microbial respiratory activity, respectively Tb and h, was highlighted. For a fixed value of Q10, the values of these two parameters varied in opposite ways. The sensitivity analysis was performed at both short and long terms, mainly on the basis of carbon pool contents. The results were very variable from one pool to another. In both analyses Tb and h appeared to be the most sensitive parameters while some differences between both time spans were noticed, notably because of pool stabilisation dynamics and crop residue types. In the end, the combination of sensitivity values with parameter ranges of values brought us to consider the parameters Tb, h, Nlit (% nitrogen in above-ground residues) and Lignlit (% lignin in above-ground residues) and the forcing variables MBR (root residues quantity) and Litfall (above-ground residues quantity) as the features about which further investigations would be needed. The integration of this mechanistic model into a more complete one, also taking account of autotrophic respiration and CO2 diffusion in soils, is a further goal to achieve.Les objectifs de ce travail étaient de présenter un modèle mécaniste de respiration hétérotrophe du sol, de l’appliquer à un sol agricole et d’en déterminer les paramètres importants pour définir des axes d’investigation futurs. Une description détaillée de la structure et du fonctionnement du modèle utilisé, adoptant un pas de temps de un jour et dérivé de CENTURY, est donnée. L’initialisation du modèle a permis d’affirmer que ce dernier était indépendant des contenus initiaux en carbone dans les différents pools du modèle. De plus, cette étape a montré que l’ordre de stabilisation des différents pools était essentiellement lié aux constantes de décomposition de chacun d’entre eux. Des valeurs de paramètres biochimiques (teneurs en azote, lignine, cellulose et hémicellulose) de cultures de blé, de betterave et de pomme de terre ont été tirées de la littérature et discutées. De larges plages de variation ont été constatées, et un manque d’informations concernant la betterave et la pomme de terre nous a poussés à travailler avec le blé dans la suite du travail. Une relation de forme exponentielle a été mise en évidence entre deux paramètres liés à l’effet de la température sur l’activité respiratoire microbienne, Tb et h. Pour un Q10 fixé, les valeurs de ces deux paramètres évoluaient en sens opposés. Les résultats de l’analyse de sensibilité, menée à court et à long terme sur base du contenu en carbone des pools, étaient très variables d’un pool à l’autre. Tb et h étaient dans les deux cas les paramètres les plus sensibles, tandis que des différences entre le court et le long terme se marquaient notamment à cause de la dynamique de stabilisation des réservoirs et de l’origine des résidus (aériens ou racinaires). Finalement, la combinaison des valeurs de sensibilité avec les plages de variation des différents paramètres a conduit à considérer les paramètres Tb, h, Nlit (% azote résidus aériens) et Lignlit (% lignine résidus aériens) et les variables de forçage MBR (quantité de résidus racinaires) et Litfall (quantité de résidus aériens) comme les éléments qui nécessiteraient le plus d’investigations par la suite. L’intégration de ce modèle dans un ensemble mécaniste plus complet combinant aussi respiration autotrophe et diffusion du CO2 dans les sols est une perspective majeure à l’issue de ce travail

50 Years of contrasted residue management in an agricultural crop: impacts on the soil carbon budget and on heterotrophic respiration.

This study aims to estimate the carbon (C) loss by soil heterotrophic respiration (SHR) in three contrasted residue management treatments (Residue Export, Farm Yard Manure addition and Residue Restitution after harvest) through the establishment of soil C budgets, and to compare these estimations with field SHR measurements. The soil C budgets were calculated in each case on the basis of total soil organic C content and C input data compiled since the beginning of the experiment in Belgium, 50 years ago. SHR fluxes were measured in 2010 and 2011 to compare them with the budget-based estimates and to assess SHR sensitivity to temperature. The comparison suggested that the treatment receiving the largest C input does not necessarily sequestrate the most C or produce the largest CO2 fluxes

Variability of heterotrophic soil respiration in agricultural ecosystems: Analysis at different spatial and temporal scales.

Soil heterotrophic respiration (HR) was studied at different spatial and temporal scales in agricultural ecosystems in Belgium (loamy region). Results from both laboratory and field experiments conducted at short and long timescales were analysed with the aim to better understand the influence of driving variables such as temperature, substrate input quantity and quality on HR. Both empirical and semi-mechanistic models were used in order to help interpret experimental results. Our observations showed that temperature is an important HR driving variable in agricultural ecosystems in temperate regions. HR sensitivity to temperature, characterized by a Q10 differing from 2 in our experiments, was very likely influenced by substrate availability and quality. The impact of these last two factors was however never observed through our measurements. Good agreement between modelled and observed CO2 fluxes in the incubation experiment, where carbon substrate was limited, suggested that temperature played a role both directly (enzymatic response) and indirectly (labile carbon stock depletion) at a relatively short term, and confirmed the hypothesis of occurrence of abiotic fluxes linked to the presence of carbonates in the samples taken from a limed agricultural field. Crop residue management (in both quantity and quality), as characterized by relatively low input levels in our experiment, influenced soil carbon stocks in the long term. However, HR, microbial biomass, labile carbon and metabolic diversity were not affected by the investigated treatments. Besides, results from both soil carbon budgets and short term HR measurements showed that supposedly large differences were likely to be reduced due to the relatively large proportion of root residues, weeds and residues unexported at harvest.La respiration hétérotrophe (RH) du sol a été étudiée à plusieurs échelles spatiales et temporelles dans des écosystèmes agricoles situés en Belgique (région limoneuse). Les résultats d’expériences de laboratoire et de terrain à court et long termes ont été analysés afin de mieux comprendre l’influence de variables conductrices telles que la température, la quantité et la qualité du substrat apporté au sol sur la RH. Des modèles empiriques et semi-mécanistes ont aussi été utilisés afin d’aider à l’interprétation des résultats expérimentaux. Nos observations ont montré que la température s’impose comme une variable conductrice importante de la RH dans les écosystèmes agricoles en région tempérée. La sensibilité de la RH à la température, caractérisée par un Q10 différent de 2 dans nos expériences, a très probablement été influencée par la disponibilité et la qualité du substrat. L’impact de ces deux derniers facteurs n’a toutefois jamais été observé au travers de mesures de laboratoire. Le bon accord entre flux modélisés et observés lors de l’expérience de laboratoire, où le substrat carboné disponible était limitant, a suggéré que la température agissait tant de manière directe (réponse enzymatique) qu’indirecte (réduction des stocks de substrat labile) à relativement court terme, et a confirmé l’hypothèse d’occurrence de flux abiotiques liés à la présence de carbonates dans les échantillons issus d’un sol agricole chaulé. La gestion des résidus de culture (quantité et qualité de ceux-ci), apportés en relativement faible quantité comparé à d’autres études menées sur le sujet, a influencé les stocks de carbone à long terme. Mais n’a pas eu d’impact sur la RH, la biomasse microbienne, le carbone labile et la diversité métabolique. Tant l’établissement d’un bilan carboné de sol à long terme que les mesures de RH à court terme ont par ailleurs montré que les différences apparentes entre traitements étaient probablement réduites en raison d’une relativement grande proportion de résidus racinaires, d’adventices et de résidus non exportables à la récolte