Elsevier

Geoderma

Volume 367, 15 May 2020, 114230
Geoderma

Crops for increasing soil organic carbon stocks – A global meta analysis

https://doi.org/10.1016/j.geoderma.2020.114230Get rights and content

Highlights

  • 227 trials from different experiments based on C isotopic labeling are considered.

  • The highest plant C stocks were found for maize.

  • Wheat had with 23% the highest C translocation to soil.

  • “Superior carbon” crops could help mitigating against climate change.

Abstract

Quantifying the ability of plants to store atmospheric inorganic carbon (C) in their biomass and ultimately in the soil as organic C for long duration is crucial for climate change mitigation and soil fertility improvement. While many independent studies have been performed on the transfer of atmospheric C to soils for single crop types, the objective of this study was to compare the ability of crops, which are most commonly found worldwide, to transfer C to soils, and the associated controlling factors. We performed a meta-analysis of 227 research trials, which had reported C fluxes from plant to soil for different crops. On average, crops assimilated 4.5 Mg C ha−1 yr−1 from the atmosphere with values between 1.7 Mg C ha−1 yr−1, for barley (Hordeum vulgare) and 5.2 Mg C ha−1 yr−1 for maize (Zea mays). Sixty-one percent (61%) of the assimilated C was allocated to shoots, 20% to roots, 7% to soils while 12% was respired back into the atmosphere as autotrophic respiration by plants. Maize and ryegrass (Lolium perenne) had the greatest allocation to the soil (1.0 Mg C ha−1 yr−1 or 19% total assimilation), followed by wheat (Triticum aestivum). 0.8 Mg C ha−1 yr−1, 23%) and rice (Oryza Sativa, 0.7 Mg C ha−1 yr−1, 20%). Carbon allocation to the soil positively correlated to C allocation to roots (r = 0.33, P < 0.05), while correlations between shoot and root biomass on the one hand and C allocation to shoots on the other hand were not significant. The question on the long-term stability of the C transferred to soils remains unanswered.

Introduction

In 2015, 192 countries ratified the Paris Agreement at COP21 in Paris to limit the rise of global air temperature to 2°C above pre-industrial levels by the end of this century (Minasny et al., 2017). At that occasion, the 4 per mille Initiative: Soils for food security and climate (4p1000) was launched by the French government with the aspiration to transfer atmospheric carbon (C) to soils for a net increase in soil organic carbon (SOC) stocks (also termed soil carbon sequestration, e.g. Chenu et al., 2019) by 0.4% per year (Minasny et al., 2017). The Initiative envisaged that atmospheric C sequestration into soils would yield spillover benefits such as a reduction in the global temperature, improved soil fertility; favorable soil structure, high soil biodiversity, and reduced risk of soil erosion will accrue (Lal, 2016) to sustain higher crop productivity.

However, some practices proposed by Paustian et al. (2016) to meet the 4p1000 objectives, such as reduced tillage and land use conversion, are subjects of debate. For example, it has been argued that reduced tillage only cause redistribution of SOC within the soil profile with no net gain (Dimassi et al., 2014, Haddaway et al., 2017), while land use conversion from cropland to grassland or forest can have negative implications for SOC stocks and food security. Furthermore, there is a high tendency to rely on best agronomic practices for increasing SOC stocks, while neglecting the effects of plants despite abundant evidence that genetic variation, especially in root traits, influences C allocation in terrestrial ecosystems (Warembourg et al., 2003).

Carbon sequestration into soils is influenced by equilibrium C carrying capacity of the soil, the vegetation it supports and the attendant climatic factors (Gupta and Rao, 1994, Lal, 2004). Plants play a pivotal role in the global C cycle because more than 10% of the carbon dioxide (CO2) in the atmosphere is recycled through photosynthesis (Raich and Potter, 1995). After photosynthesis, plants deposit organic C into the soil via exudation and biomass C incorporation into the soil and a net increase in the soil C stocks is realized when the amount of C deposits are higher than C losses through microbial decomposition and root respiration (Fearnside and Barbosa, 1998). Plant C is either incorporated as structural C, released as exudates or respired as CO2 (Ostle et al., 2003). These processes vary with crops’ genetic characteristics, leading to potential differences in C fluxes to soils (Kuzyakov and Domanski 2000). Yet there is little empirical analysis on how crops differ in their ability to enhance SOC stocks (Wegener et al., 2015). The first step for assessing the ability of crops to sequester C in terrestrial ecosystems lies in the evaluation of the C fluxes to the different pools: shoots, roots and soil.

There have been concerted efforts to understand C fluxes in the plant/soil system (e.g. Remus and Augustin, 2016, Studer et al., 2014). Carbon fluxes are commonly estimated by measuring changes in SOC stocks over time (e.g. Hemminga et al., 1996). However, this method lacks precision when little changes in SOC stocks occur and is unable to distinguish between the preexistent and “new” SOC (e.g. Remus and Augustin, 2016). Isotopic C labeling, where C 12 atoms are replaced with either C 13 or 14 atoms, facilitate the quantification of C fluxes from atmosphere to soil through plants (Studer et al., 2014). Based on C labelling, it has been reported that plants transfer from 30 to 50% of their photosynthetic C below ground (Buyanovsky and Wagner, 1997). Furthermore, C labelling has proven that the translocation of C to roots may occur immediately after C assimilation in leaves with up to 10% of the photosynthetic C being detected in roots within 2 h (Kaštovská and Šantrůčková, 2007).

Carbon assimilated by plants is allocated to above ground (shoots and reproductive organs) and below ground (roots) biomass depending on plant genetic constitution (de Neergaard and Gorissen 2004), plant growth pattern, environmental conditions and interactions among these factors (Rangel-Castro et al., 2005). However, it is the root C fluxes, which are particularly important for increasing SOC stocks because root tissues and/or root exudates are in immediate contact with the decomposer community and the mineral phase, thus leading to lower mineralization rates as compared to shoot-derived C (Rasse et al., 2005). Labile C inputs such as those derived from above ground biomass are potentially easily decomposed, leading to losses of the total plant C stock of 15–45% in case of perennial plants and 27–60% in annuals (e.g. Warembourg and Paul, 1977).

Several compilations of individual studies have been performed to identify the trends in SOC dynamics (e.g., Guo and Gifford, 2002). From Guo and Gifford (2002), we learn that the conversion of natural vegetation to cropland is detrimental to SOC stocks with a worldwide average loss in the 0–0.3 m soil layer of 42% from native forest and of 59% from grassland. From this meta-study we also learn that afforestation of cropland can increase SOC stocks by as much as 50%, with Laganière et al. (2010) indicating greatest increase by using broadleaf tree species as compared to coniferous species. Meta-studies on land management impact on SOC stocks have also been performed. Poeplau and Don (2015), using 139 plots worldwide, showed the potential of cover crops to increase SOC stocks in the first 0.2 m of the soil to be 0.32 ± 0.08 Mg C ha−1 yr−1 or about 0.5% or 5p1000. The study by Ugarte et al. (2014), using data from 55 peer-reviewed studies, showed a 9% average increase of SOC stocks in the 0–0.3 m layer using diversified crop rotations and conservation systems as compared to the conventional controls, a result confirmed by Alison et al. (2017). The increase was 32% by using a combination of chemical and organic fertilization (Han et al., 2016) as compared to no fertilization. Shi et al. (2018) pointed to an 18% increase in SOC stocks using agroforestry under subtropical climate. All these studies considered the soil to a depth of 0.3 m.

While several individual studies worldwide have been published on the fluxes of atmospheric C to soils on one or several crops, these data have not been synthesized yet and the global trends are still unknown. This study aimed at compiling multiple trials across the world that quantified C fluxes from the atmosphere to the soil during the growing cycle using C labelling. The hypothesis behind this study is that some crops might be more efficient than others to build SOC and might thus be promoted.

Section snippets

Meta analysis

The study is a meta-analysis based on data collated from isotopic C enrichment experiments conducted across the world. The data was obtained from peer-reviewed journal articles published between 1985 and 2016. The journal articles were obtained from academic databases (Google Scholar, Refseek, Science Direct, SciFinder, Scopus, Springer Link and Web of Science) using key words and phrases, singly and/or in combination, such as “isotopic pulse labelling”, “C allocation”, “plant carbon

Variability in C allocation to plant parts

Table 4 presents the statistics of biomass and C allocation to the different plant parts from the field and greenhouse trials. As shown by the statistical t test (Table 4), there was no significant differences between field and greenhouse trials for all study variables, except for root biomass (Rb), which was about two times higher under field conditions than in greenhouses (36 vs 16 Mg C ha−1).

The average C allocation to shoots ranged from 0.20 Mg C ha−1 yr−1 recorded by for barley in the

Soil texture

Fig. 5 shows the variations in C allocation in response to soil clay content. For clayey soils, the mean C allocation to shoots was 2.36 ± 0.23 Mg C ha−1 yr−1 (Fig. 5a), which was 13% lower than that of loam textured soils (2.70 ± 0.25 Mg C ha−1 yr−1) with the widest variability (values between 0.5 and 4.6 Mg C ha−1 yr−1). There was a decrease in root C allocation from clayey and loamy (1.30 ± 0.13; 1.36 ± 0.16 Mg C ha−1 yr−1) to sandy soils (0.91 Mg C ha−1 yr−1) (Fig. 5b). In contrast, soil

The impact of crop species on C assimilation from atmosphere to shoots and roots

The wide variations in atmospheric C allocation to shoots from 0.4 to 5.6 Mg C ha−1 yr−1 was expected and is likely to result from variable environmental conditions, plant growth patterns and internal metabolism which are under genetic control (Warembourg et al., 2003). Maize exhibited a significantly higher assimilation of atmospheric C into shoots than ryegrass, which confirmed previous reports by Pausch and Kuzyakov, 2017, Atkinson et al., 2014. The differences in shoot C fluxes among annual

Conclusions

Three main conclusions can be drawn from this study of 227 research trials worldwide investigating atmospheric C allocation to crop shoots, roots and to the soil:

  • (i)

    Only a small fraction (about 7%) of the plant assimilated C is found in the soil after harvest with wheat showing the highest proportion (23%), followed by rice (20%), and maize and ryegrass with 19%;

  • (ii)

    The transfer of atmospheric C to the soil was highest for maize (1.00 Mg C ha−1 yr−1) followed by ryegrass (0.95 Mg C ha−1 yr−1), rice

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (83)

  • J. Fan et al.

    Root distribution by depth for temperate agricultural crops

    Field Crops Res.

    (2016)
  • Y. Fang et al.

    In situ assessment of new carbon and nitrogen assimilation and allocation in contrastingly managed dryland wheat crop–soil systems

    Agric. Ecosyst. Environ.

    (2016)
  • P.M. Fearnside et al.

    Soil carbon changes from conversion of forest to pasture in Brazilian Amazonia

    For. Ecol. Manage.

    (1998)
  • B. Huang et al.

    Root respiration and carbohydrate status of two wheat genotypes in response to hypoxia

    Ann. Bot.

    (1995)
  • R. Lal

    Soil carbon sequestration to mitigate climate change

    Geoderma

    (2004)
  • Y. Li et al.

    Comparison of methane production potential, biodegradability, and kinetics of different organic substrates

    Bioresour. Technol.

    (2013)
  • I. Mathew et al.

    What crop type for atmospheric carbon sequestration: results from a global data analysis

    Agric. Ecosyst. Environ.

    (2017)
  • L. Menichetti et al.

    Contribution of roots and amendments to soil carbon accumulation within the soil profile in a long-term field experiment in Sweden

    Agric. Ecosyst. Environ.

    (2015)
  • B. Minasny et al.

    Soil carbon 4 per mille

    Geoderma

    (2017)
  • N. Ostle et al.

    Active microbial RNA turnover in a grassland soil estimated using a 13 CO2 spike

    Soil Biol. Biochem.

    (2003)
  • C. Poeplau et al.

    Carbon sequestration in agricultural soils via cultivation of cover crops – a meta-analysis

    Agric. Ecosyst. Environ.

    (2015)
  • J. Swinnen et al.

    Carbon fluxes in the rhizosphere of winter wheat and spring barley with conventional vs integrated farming

    Soil Biol. Biochem.

    (1995)
  • F.R. Warembourg et al.

    Seasonal transfers of assimilated 14C in grassland: Plant production and turnover soil and plant respiration

    Soil Biol. Biochem.

    (1977)
  • S. Aljazairi et al.

    Carbon and nitrogen allocation and partitioning in traditional and modern wheat genotypes under pre-industrial and future CO2 conditions

    Plant Biol.

    (2015)
  • S.K. Amanullah et al.

    Shoot: root differs in warm season C4-cereals when grown alone in pure and mixed stands under low and high water levels

    Pak. J. Bot.

    (2013)
  • I. Aranjuelo et al.

    13C/12C isotope labeling to study carbon partitioning and dark respiration in cereals subjected to water stress

    Rapid Commun. Mass Spectrom.

    (2009)
  • J.A. Atkinson et al.

    Branching out in roots: uncovering form, function, and regulation

    Plant Physiol.

    (2014)
  • G.A. Buyanovsky et al.
  • D.R. Chaudhary et al.

    Distribution of recently fixed photosynthate in a switchgrass plant-soil system

    Plant Soil Environ.

    (2012)
  • J.R. Davenport et al.

    Carbon partitioning and rhizodeposition in corn and bromegrass

    Can. J. Soil Sci.

    (1988)
  • E.A. Davidson et al.

    Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

    Nature

    (2006)
  • A. de Neergaard et al.

    Carbon allocation to roots, rhizodeposits and soil after pulse labelling: a comparison of white clover (Trifolium repensL.) and perennial ryegrass (Lolium perenne L.)

    Biol. Fertil. Soils

    (2004)
  • G. Domanski et al.

    Carbon flows in the rhizosphere of ryegrass (Lolium perenne)

    J. Plant Nutr. Soil Sci.

    (2001)
  • J. Fernández et al.

    Carbon allocation in a sweet sorghum-soil system using 14C as a tracer

    J. Plant Nutr. Soil Sci.

    (2003)
  • S. Fontaine et al.

    Carbon input to soil may decrease soil carbon content: Carbon input in soil carbon sequestration

    Ecol. Lett.

    (2004)
  • C.P. Giardina et al.

    Warming-related increases in soil CO2 efflux are explained by increased below-ground carbon flux

    Nat. Clim. Change

    (2014)
  • M. Gocke et al.

    Carbonate recrystallization in root-free soil and rhizosphere of Triticum aestivum and Lolium perenne estimated by 14C labeling

    Biogeochemistry

    (2011)
  • P.J. Gregory et al.

    The fate of carbon in pulse-labelled crops of barley and wheat

    Plant Soil

    (1991)
  • L.B. Guo et al.

    Soil carbon stocks and land use change

    Global Change Biol.

    (2002)
  • R.K. Gupta et al.

    Potential of wastelands for sequestering carbon by reforestation

    Curr. Sci.

    (1994)
  • N.R. Haddaway et al.

    How does tillage intensity affect soil organic carbon? a systematic review

    Environ. Evid.

    (2017)
  • Cited by (47)

    View all citing articles on Scopus
    View full text