•Soil organic carbon storage should be differentiated from soil organic carbon sequestration.•Methods to estimate the carbon sequestration potential of a soil need to be developed and compared.•Soil ...organic carbon storage potential of agricultural practices need re-assessment.•More exploratory levers to increase soil organic carbon storage are related to soil biota.
Recent initiatives, such as the United Nations declaring 2015 as the International Year of Soils and the French « 4 per 1000 » initiative call attention on soils and on the importance of maintaining and increasing soil organic matter stocks for soil fertility and food security, and for climate change adaptation and mitigation. We stress that soil organic carbon storage (i.e. an increase of soil organic carbon stocks) should be clearly differentiated from soil organic carbon sequestration, as the latter assumes a net removal of atmospheric CO2. Implementing management options that allow increasing soil organic carbon stocks at the local scale raises several questions, which are discussed in this article: how can we increase SOC stocks, at which rate and for how long; where do we prioritize SOC storage; how do we estimate the potential gain in C and which agricultural practices should we implement? We show that knowledge and tools are available to answer many of these questions, while further research remains necessary for others. A range of agricultural practices would require a re-assessment of their potential to store C and a better understanding of the underlying processes, such as no tillage and conservation agriculture, irrigation, practices increasing below ground inputs, organic amendments, and N fertilization. The vision emerging from the literature, showing the prominent role of soil microorganisms in the stabilization of soil organic matter, draw the attention to more exploratory potential levers, through changes in microbial physiology or soil biodiversity induced by agricultural practices, that require in-depth research.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
First‐order organic matter decomposition models are used within most Earth System Models (ESMs) to project future global carbon cycling; these models have been criticized for not accurately ...representing mechanisms of soil organic carbon (SOC) stabilization and SOC response to climate change. New soil biogeochemical models have been developed, but their evaluation is limited to observations from laboratory incubations or few field experiments. Given the global scope of ESMs, a comprehensive evaluation of such models is essential using in situ observations of a wide range of SOC stocks over large spatial scales before their introduction to ESMs. In this study, we collected a set of in situ observations of SOC, litterfall and soil properties from 206 sites covering different forest and soil types in Europe and China. These data were used to calibrate the model MIMICS (The MIcrobial‐MIneral Carbon Stabilization model), which we compared to the widely used first‐order model CENTURY. We show that, compared to CENTURY, MIMICS more accurately estimates forest SOC concentrations and the sensitivities of SOC to variation in soil temperature, clay content and litter input. The ratios of microbial biomass to total SOC predicted by MIMICS agree well with independent observations from globally distributed forest sites. By testing different hypotheses regarding (using alternative process representations) the physicochemical constraints on SOC deprotection and microbial turnover in MIMICS, the errors of simulated SOC concentrations across sites were further decreased. We show that MIMICS can resolve the dominant mechanisms of SOC decomposition and stabilization and that it can be a reliable tool for predictions of terrestrial SOC dynamics under future climate change. It also allows us to evaluate at large scale the rapidly evolving understanding of SOC formation and stabilization based on laboratory and limited filed observation.
Microbial explicit decomposition models have been developed to replace the conventional first‐order model used in most Earth System Models, but their evaluation was limited to observations from laboratory incubations or few field experiments. A comprehensive evaluation of these models is essential using large‐scale in situ observations. We found that, compared to first‐order decomposition model, microbial explicit model more accurately estimates SOC concentrations, microbe/SOC ratio, SOC composition and the sensitivities of SOC stock to changed climate, litter input and soil properties. We support to replace the first‐order decomposition model used in existing Earth System Models with microbial explicit model.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Soil mineral phases strongly influence soil organic carbon (SOC) dynamics. Clay-size particles have been recognized as protecting SOC from microbial decomposition. Among clay-size minerals, ...phyllosilicates (clay minerals) have been shown to efficiently protect SOC. There is an important variety of phyllosilicate types present in soils which have contrasting surface properties (specific surface area, charge density). Although these differing surface properties should influence their ability in protecting SOC, this has not been clearly established yet. Publications comparing the ability of the different phyllosilicates to protect SOC are reviewed in this study. Relatively few studies dealing with the link between phyllosilicate mineralogy and SOC protection exist. The few existing studies have followed different methodologies and are based on various analytical techniques, such that direct comparisons among them are difficult. More problematic, they provide different conclusions. Indeed, if experiments conducted in suspension using pure clay phases and recent meta-analyses suggest that phyllosilicate mineralogy has a significant importance for SOC stabilization and SOC stock response to land-use change, these results are not clearly corroborated by studies conducted on a reduced number of soils. The recent technical developments which allow improving both quantitative and qualitative descriptions of the soil clay mineral assemblages, together with nanoscale investigations of phyllosilicate/OM interactions, offer exciting perspectives for determining more accurately the efficiency of the different phyllosilicate types in SOC protection. Such information may provide a much clearer understanding of the impact of phyllosilicate mineralogy on SOC dynamics in the coming years.
•We reviewed studies comparing the impact of phyllosilicate type on SOC protection•2:1 phyllosilicates are the most efficient according to studies conducted in suspension•Case studies conducted in soils did not univocally support such a conclusion•More data obtained using accurate protocols are needed to conclude•Developing visualization methods will bring new and important insights
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Soil carbon dynamics is strongly controlled by depth globally, with increasingly slow dynamics found at depth. The mechanistic basis remains however controversial, limiting our ability to predict ...carbon cycle-climate feedbacks. Here we combine radiocarbon and thermal analyses with long-term incubations in absence/presence of continuously
C/
C-labelled plants to show that bioenergetic constraints of decomposers consistently drive the depth-dependency of soil carbon dynamics over a range of mineral reactivity contexts. The slow dynamics of subsoil carbon is tightly related to both its low energy density and high activation energy of decomposition, leading to an unfavourable 'return-on-energy-investment' for decomposers. We also observe strong acceleration of millennia-old subsoil carbon decomposition induced by roots ('rhizosphere priming'), showing that sufficient supply of energy by roots is able to alleviate the strong energy limitation of decomposition. These findings demonstrate that subsoil carbon persistence results from its poor energy quality together with the lack of energy supply by roots due to their low density at depth.
The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the ...response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 226-year-old carbon. Our results support the previously suggested idea7 that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Parent material can deeply influence soil organic matter (SOM) stocks. In this study we tested the hypotheses that parent material had an effect on SOM concentrations and stocks and that this effect ...may be explained by the influence of soil parent material on basic soil parameters. However, as the factors known to influence SOM stocks such as land use and climate frequently co-vary with geology, testing the influence on SOM stocks of the factor “soil parent material” alone is challenging.
To properly test our hypotheses, we studied SOM stocks of forest and cropland soils in a small landscape (17km2) of the Paris basin (France), i.e. with an homogeneous climate. We collected topsoil samples (0–30cm) in 50 forest and cropland plots, located in five geological contexts: loess deposit, mudstone, grainstone, chalk and calcareous clay deposits. Basic soil parameters (texture, pH, CaCO3 concentration) and SOM stocks to 30cm depth (organic C and total N) were determined on the 50 soil samples.
Organic C and total N concentrations and stocks in topsoils (0–30cm) were much higher in forests than in cultivated soils (38.1 (±12.8) vs. 19.0 (±4.7)gCkg−1 soil and 83.4 (±19.8) vs 48.9 (±9.9)tCha−1 for SOC concentrations and stocks respectively). The influence of land-use on organic C and total N concentrations and stocks was modulated by parent material (significant interactions between land-use and parent material, p<0.05 for concentrations and stocks). Indeed, the difference in organic C and total N concentrations and stocks in topsoils (0–30cm) was much lower for soils developed on loess deposits.
While SOC concentration was significantly correlated to soil clay concentration for both cropland (r2=0.36, p<0.001) and forest (r2=0.44, p<0.001), there was no significant relation between SOC stocks and soil clay stocks for forest soil (p=0.11) and a significant but highly scattered positive correlation between SOC and clay stocks in cropland soils (r2=0.20, p=0.02). No significant relation between pH or CaCO3 and SOC stocks was observed. Our results therefore revealed that soil parent material can significantly influence topsoil (0–30cm) organic C and N stocks but that more research is needed to understand how soil parent material influences SOM stocks as it cannot be simply explained by basic soil physico-chemical parameters (clay and carbonate concentrations or stocks, pH). Overall, our results suggest that a good knowledge of the geology is needed to better constrain SOC stocks as well as SOC stocks evolution in a changing environment from landscape to global scale.
•SOM stocks in the top 30cm are controlled by parent material in forest soils.•SOM stock differences between forest and cropland are influenced by parent material.•SOM stocks were weakly correlated to clay contents or stocks.•Geology should be considered to better predict SOC and N stock evolutions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Taxon identification is an important step in many plant ecological studies. Its efficiency and reproducibility might greatly benefit from partly automating this task. Image-based identification ...systems exist, but mostly rely on hand-crafted algorithms to extract sets of features chosen a priori to identify species of selected taxa. In consequence, such systems are restricted to these taxa and additionally require involving experts that provide taxonomical knowledge for developing such customized systems. The aim of this study was to develop a deep learning system to learn discriminative features from leaf images along with a classifier for species identification of plants. By comparing our results with customized systems like LeafSnap we can show that learning the features by a convolutional neural network (CNN) can provide better feature representation for leaf images compared to hand-crafted features.
We developed LeafNet, a CNN-based plant identification system. For evaluation, we utilized the publicly available LeafSnap, Flavia and Foliage datasets.
Evaluating the recognition accuracies of LeafNet on the LeafSnap, Flavia and Foliage datasets reveals a better performance of LeafNet compared to hand-crafted customized systems.
Given the overall species diversity of plants, the goal of a complete automatisation of visual plant species identification is unlikely to be met solely by continually gathering assemblies of customized, specialized and hand-crafted (and therefore expensive) identification systems. Deep Learning CNN approaches offer a self-learning state-of-the-art alternative that allows adaption to different taxa just by presenting new training data instead of developing new software systems.
•LeafNet is a plant identification system based on convolutional neural networks.•We used images of leaves to train and evaluate LeafNet on three datasets.•We achieved a better performance compared to hand-crafted customized systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Conversion to no-till (NT) is usually associated to increased soil organic carbon (SOC) stocks in comparison to inversion tillage (IT). However, an important and unexplained variability in the ...changes in SOC with NT adoption exists, which impedes accurate prediction of its potential for C sequestration. We performed a meta-analysis with pedo-climatic and crop factors observed to influence SOC storage under NT at local and regional scales, in order to determine those better explaining this variability at a global scale. We studied SOC stocks (0–30 cm) in an equivalent soil mass, climatic and soil characteristics in 92 NT–IT paired cases. A sub-base with the 35 pairs providing C inputs was used to test their effect. Greater SOC stocks were observed with NT, with a smaller difference than often described (6.7%, i.e. 3.4 Mg C ha−1). Crop C inputs differences was the only factor significantly and positively related to SOC stock differences between NT and IT, explaining 30% of their variability. The variability in SOC storage induced by NT conversion seems largely related to the variability of the crop production response. Changes at the agro-ecosystem level, not only in soil, should be considered when assessing the potential of NT for C sequestration.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Grain legumes in crop rotations can benefit sandy soil structure in the short-term.•The effect is however species- and management-dependent.•SOC storage was not affected in the short-term with grain ...legumes included in rotation.
Legume plants can promote C storage by enhancing the formation and stabilization of soil aggregates that protect soil organic C (SOC) from mineralization. However, this effect can vary with soil biochemical properties, environmental conditions and legume species. This work aimed to test if including grain legumes in rotation with cereals in a sandy acid soil in a Mediterranean climate can enhance aggregation and SOC storage. Triticale (× Triticosecale ‘Alter’ cv.) fodder was monocultivated with and without synthetic-N fertilizer and in rotation either with irrigated cowpeas (Vigna unguiculata’ Fradel’ cv.), rainfed faba beans (Vicia faba ‘Favel’ cv.) or peas (Pisum sativum ‘Grisel’ cv.) in a sandy loam Cambisol for three years. Legume residues were incorporated into the soil after grain harvest. Crop yields and respective organic C inputs were determined. Topsoil (0–20 cm) samples were analyzed for clay-size minerals mineralogy and mass and C distribution in aggregate-size fractions obtained by wet-sieving. SOC stocks were calculated before and after the trial and in non-cultivated controls. Despite differences in C inputs to the soil, SOC storage was not enhanced with legume cultivation. This may be due to the short duration of the experiment or to the low clay content (10%) and very low reactivity of the clay-size minerals (kaolinite-dominated) of the soil, which seem to have weakened SOC protection. However, non-cultivated controls had up to three times higher SOC stocks, indicating that organic C can be stored in this soil under adequate conditions. Nonetheless, a legume-effect on soil aggregation was observed. Introducing irrigated cowpea in the rotation maintained soil structure, as evidenced by a similar macroaggregate (>250 μm, Magg) content to the baseline, which was deteriorated in the fertilized cereal monoculture in the respective site (less Magg than the baseline). Furthermore, including rainfed faba bean in the rotation improved the soil structure (more Magg than the baseline), which was similar to the baseline when pea was used instead or when cereal was monocropped with synthetic N fertilizer. We conclude that including legumes in rotation with cereal can benefit soil structure in the short-term in the studied edaphoclimatic conditions, but these benefits depend on legume species and agricultural management. However, beneficial effects in SOC stock seem not to be attainable in these conditions in such a short period.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•SOC differed in forest soils with similar pH/clay content but different bedrock.•Clay mineralogy differed in sandstone-derived and volcanic soils.•The amounts and quality of SOC may be related to ...mineralogical differences.•Soil parent material could be included as a proxy in SOC model development.
Soil minerals are known to play a major role in soil organic carbon (SOC) stabilization. However, the exact nature of the role is still poorly understood as comparative studies are complicated by the fact that mineralogy usually varies with other important factors such as climate, land-use, texture and acidity. This study investigated naturally-occurring minerals and C storage in nine mature, second-rotation Pinus radiata D. Don forest plantations at a similar development stage and growing under similar climatic conditions, but established on soils derived from three different parent materials: sandstone, basalt and trachyte. We quantified the SOC stocks in the 0–20 cm soil layer, clay-size minerals and metal oxides. The distribution of SOC in labile and mineral-bound fractions and the chemical structure of the SOC were also determined, by CPMAS NMR spectroscopy. For similar tree biomass, mean SOC storage was 2 times higher in the soils derived from basalt and 2.5 times higher in the soils derived from trachyte which were relatively rich in chlorite/vermiculite mixed layers and short-range order aluminium and iron forms, than in the sandstone-derived soils dominated by illite and with no short-range order aluminium. The parent material also affected the major C components of the SOC. Thus, the proportion of aromatic-C forms in the total SOC was higher in the sandstone-derived soil than in the soils of volcanic origin. Furthermore, the proportion of SOC in the mineral-bound fraction was around 30% in the sandstone-derived soil and around 50% in the volcanic soils. We conclude that estimates of ecosystem SOC stocks in acid temperate forest soils should include proxies for clay mineralogy, such as phyllosilicate minerals, contents of Fe and Al (hydr-) oxides and non-crystalline compounds. In addition, we recommend the inclusion of soil parent material as a proxy in models aimed at estimating regional SOC stocks.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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