Organic carbon decomposition rates with depth under an agroforestry system in a calcareous soil

Dr Rémi Cardinael1,2,3, Dr Tiphaine Chevallier2, Dr Bertrand Guenet4, Dr Cyril Girardin5, MSc Thomas Cozzi3, Valérie Pouteau5, Dr Claire Chenu3

1Cirad – UR AIDA, Montpellier, France, 2IRD – UMR Eco&Sols, Montpellier, France, 3AgroParisTech – UMR Ecosys, Thiverval-Grignon, France, 4CNRS – LSCE, Gif-sur-Yvette, France, 5INRA – UMR Ecosys, Thiverval-Grignon, France

Soil inorganic carbon (SIC) in the form of carbonates is found in a large part of soils, especially in arid and semi-arid environments. Despite their important distribution at the global scale, the organic carbon dynamic has been poorly investigated in these soils due to the complexity of measurement and of the processes involved. It requires the removal of carbonates by acid dissolution or the use of natural isotopes to discriminate the carbon originating from the soil organic carbon (SOC) than the one from the carbonates. We incubated soil samples, coming from an 18-year-old agroforestry system (both tree row and alley) and an adjacent agricultural plot established in the South of France, during 44 days. Soil samples were taken at four different depths: 0-10, 10-30, 70-100 and 160-180 cm. Total CO2 emissions, the isotopic composition (δ13C, ‰) of the CO2 and microbial biomass were measured. The contribution of SIC-derived CO2 represented about 20% in the topsoil and 60% in the subsoil of the total soil CO2 emissions. The SOC-derived CO2, or heterotrophic soil respiration, was higher in the topsoil, but the decomposition rates (day-1) remained stable with depth, suggesting that only the size of the labile carbon pool was modified with depth. Subsoil organic carbon seems to be as prone to decomposition as surface organic carbon. No difference in CO2 emissions was found between the agroforestry and the control plot, except in the tree row at 0-10 cm where the carbon content and microbial biomass were higher, but the decomposition remained lower. Our results suggest that the measurement of soil respiration in calcareous soils could be overestimated if the isotopic signature of the CO2 is not taken into account. It also advocates more in-depth studies on dissolution-precipitation processes and their impact on CO2 emissions in these soils.


Biography:

Professor of Soil Science at AgroParisTech

N and P co-limitation of carbon turnover in a clayey loam very deep subsoil

Ms Leanne Peixoto1, Jørgen Eivind  Olesen1, Dr Jim  Rasmussen1, Dr Lars  Elsgaard1

1Aarhus University, Department of Agroecology, Tjele, Denmark

The growth of deep-rooted crops within agricultural soils has the potential to increase carbon deposition within deep subsoil layers potentially mitigating climate change. The growth of these deep-rooted crops and subsequent availability of both labile C substrates and nutrients such as nitrogen (N), phosphorus (P), and/or sulfur (S) have the potential to influence both C turnover and stability within deep subsoil layers. The present study utilized intact soil samples obtained from 5-6 m to study the effects of nutrient limitations for microbial C turnover when glucose or an artificial root exudate (ARE) mixture, and supplementary nutrients (N-P-S) were introduced as different treatments to deep subsoil samples during a 10-week incubation study. Our results document that C substrates alone are not the only drivers in C turnover, although significant differences between the addition of only C substrates were documented with the addition of only glucose compared to the addition of the ARE mixture. Such differences were interpreted as a partial alleviation of the N limitation due to the N-containing amino acid, L-arginine within the ARE mixture, but differences are also a likely a response to the diversity of compounds within the ARE mixture. Furthermore, we found potential effects of a co-limitation of N and P on C turnover in these deep subsoil samples to depths of 5-6 m, far exceeding depths from previous studies. As such, based on the co-limitation of N and P as observed within this study, it is important to know the N and P status of subsoils to predict the fate of organic C in deep soils as the production of microbial residues is based on the coupling of these nutrients to meet the stoichiometric microbial demand. Hence, managements removing such limitations could facilitate the stability and long-term storage of C in deep subsoil.


Biography:

“I am a PhD Student at Aarhus University at the Department of Agroecology within the Climate and Water section. The main aim of the project is to investigate the potential for long-term soil carbon storage in subsoil from deep rooted crops by quantifying the effect of deep rooted crops on soil carbon stocks, and improving our understanding of the factors controlling deposition and decomposition of carbon in deep soil layers.”

Soil microbiome and carbon under the A (horizon)

Dr Charles Rice1, Dr. Marcos  Sarto1, mr. Carlos Pires1, Mr. James Lin1

1Kansas State University, Manhattan, United States

Central USA was dominated by tallgrass prairie across a large precipitation gradient broadly representative of both current and future precipitation regimes. Much of the prairie is now under cultivation. Much research has focused on the role of the soil microbiome in the global C cycle, given soils can serve as a sink or source of greenhouse gases. These microbial functions are strongly influenced by microbial resource limitations and available moisture. Microbes also influence soil structure. Soil aggregation mediates soil chemical, physical, and biological properties and improves soil quality and sustainability. Identifying drivers of the long-term persistence of soil organic C represents another challenge for projecting future interactions between soil properties, water, and soil microbial behavior.  The aim of this study was to investigate the soil biophysical properties across a precipitation gradient with different land uses.  Soil profiles were sampled to 1m for soil C and N, aggregate structure, and microbial community composition by phospholipid fatty acid (PLFA) analysis. Microbial biomass C (MBC) in the native prairie and agriculture were not significantly affected by the precipitation gradient.  Large aggregates (>2 mm) were higher in the native prairie at central> west and east. Large aggregates (>2 mm) were higher in the native prairie relative to agriculture.

Total PLFA was higher in the native prairie with greater precipitation. Total PLFA was higher in the native prairie relative to agriculture.  Higher AMF content was found under greater precipitation regime in all land uses. The aggregate structure was highly correlated to fungal and mycorrhizal fungi biomass. Relations with C, depth, and microbial community composition are being explored.


Biography:

Charles (Chuck) Rice is a University Distinguished Professor and holds the Vanier University Professorship at Kansas State University.  He is a Professor of Soil Microbiology in the Department of Agronomy.

Compacted and suppressed: physical constraints of soil microbial response to carbon supply in the subsoil

Dr Yui Osanai1, Dr Oliver Knox1, A/Prof Brian Wilson1,2

1University Of New England, Armidale, Australia, 2NSW Office of Environment and Heritage, Armidale, Australia

Recent studies highlight the importance of dissolved organic carbon (DOC) in soil carbon (C) dynamics through microbial processes. Both the quantity and spatial accessibility of DOC influence the relative importance of microbial processes compared with physical processes. However, the extent to which microbial activity responds to DOC and differences in physical condition through the soil profile remain largely unknown. Here, we conducted a laboratory incubation to quantify microbial respiration responses to DOC in the topsoil (0–30 cm) and the subsoil (30–100 cm) along a simulated soil compaction gradient (disturbed, no adjustment, slightly compacted and compacted), using the soils collected from cotton-based cropping systems under different tillage and rotational managements. Preliminary analysis showed that basal respiration decreased in response to compaction, but increased following disturbance in both topsoil and subsoil. DOC addition increased microbial respiration. However, the response differed between the physical treatments and soil profiles. Both disturbance and compaction resulted in reduced respiration, with a greater reduction observed in the topsoil than the subsoil. When adjusted for field bulk density, the estimated respiration responses to DOC showed much larger responses in the topsoil than the subsoil and in maximum tillage than minimum tillage systems. These results suggest that under field conditions, subsoil respiration will be lower than that of the topsoil due to both physical and substrate constraints. The contrasting effect of disturbance on basal and DOC-induced respiration also suggests that there is a complex interplay between physical and biological processes in regulating C fluxes. Our study demonstrates that soil physical conditions modulate microbial responses to substrate availability, and that agricultural practices that affect physical conditions can have a significant impact on C dynamics and sequestration in agricultural soils.


Biography:

Yui is a postdoctoral research fellow at University of New England. She is interested in the regulation of the C and N cycles in terrestrial ecosystems in the context of environmental changes. In particular, her research focuses on the interactions and feedback between plants, soil and soil microbial communities and how changes in the environment may directly or indirectly impact the interactions between them to influence soil processes and nutrient availability, and their consequences for plant productivity.

Organic manure input not benefit for inorganic carbon accumulation in semiarid cropland

Prof. Shulan Zhang1, Miss Wenjing Yang1

1Northwest A&f University, Yangling, China

Understanding soil carbon dynamics affected by agricultural practices in dryland ecosystems is helpful in mitigating climate change. This study investigated the responses in soil organic carbon (SOC) and inorganic carbon (SIC) distribution and storage in 3 m depth of soil profiles under long-term applications of chemical fertilizers (NPK) and organic manure plus NPK fertilizers (MNPK) in a loess soil in northwest China. The SOC contents decreased with increasing soil depth. The fertilizer treatments significantly enhanced the SOC concentrations at the top 20 cm depth as compared with the control (CK, no nutrient put). The amount of SOC to the depth of 100 cm in the MNPK-treated soil was significantly higher than those in the CK- and NPK-treated soils. The SIC contents showed higher values at deeper layers than at the top layers of the soil profiles. Application of MNPK significantly increased the SIC contents at the 60–140 cm depth but decreased the SIC contents at the 180–300 cm layer. Correspondingly, the SIC storage to the depth of 100 cm was significantly higher under the MNPK treatment than under the CK and NPK treatments. However, the amounts of SIC to the depth of 300 cm were not significantly different among treatments. It is concluded that manure application enhanced both SOC and SIC accumulation at top one-meter depth, but not three-meter depth.


Biography:

Shulan Zhang, born on the 9th of November 1966 in Inner Mongolia, China. Currently she is a professor at College of Natural Resources and Environment, Northwest A&F University, China. Her research is long-term effects of fertilization on crop productivity, nutrient use efficiency and soil carbon sequestration.

 

Changes in microbial biomass, community composition and diversity, and functioning with soil depth in two alpine ecosystems on the Tibetan Plateau

Tianle Xu1, Xiao Chen1, Yanhui Hou1, Ying Chen1, Biao Zhu1

1Peking University, , China

Microbial communities play an important regulating role in soil carbon and nutrient cycling in terrestrial ecosystems. Most studies on microbial communities and biogeochemical cycling focus on surface soils (0-20 cm). However, relatively little is known about how structure and functioning of microbial communities shift with depth in a soil profile, which is crucial to understand biogeochemical cycling in deep soils. Here, we combined a number of complimentary techniques to investigate the microbial biomass, community composition and diversity, and potential functioning along soil profile (0-70 cm) in two contrasting alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Results showed that microbial biomass (MBC, MBN or PLFA) and fungi:bacteria ratio all declined greatly with depth, while the ratio of Gram-positive to Gram-negative bacteria increased with depth. Microbial community composition, by PLFA or DNA sequencing (archaea, bacteria or fungi), showed remarkable differences among different soil layers. Microbial community diversity (OTU number) also changed with depth – both bacteria and fungi richness declined with depth, while archaea richness showed the opposite trend. The co-occurrence network analysis further showed that surface soil microbes were more connected and interacted among each other compared to deep soil microbes. Moreover, total enzyme activities (per gram soil) declined with depth, while specific enzyme activities (per gram MBC) did not change with depth. Potential C mineralization rate decreased with depth, while net N mineralization rate was higher at deep soils than at surface soils. We also detected shifts in some functional guilds of bacteria (based on faprotax database) and fungi (based on FUNGuild database) with depth in both ecosystems. Taken together, we detected dramatic shifts in biomass, community composition and diversity, and potential functioning of microbial communities with soil depth, which may have important implications for driving soil organic matter dynamics along soil profile in alpine ecosystems.


Biography:

Tianle is a postdoctor in Peking University. His work focuses on soil microbial community structure and function, especially the influence of soil microbes on soil organic carbon dynamics in grassland ecosystem. He also works on microbiogeography, and explored the key predictors of fungi and arbuscular mycorrhizal fungi communities across a 5000-km transect in northern China. Tianle have published 10 papers as first author or co-author.

Evaluation of dissolved organic carbon stabilisation in soils using δ13C isotopic signature

Mrs. Kakali Roy1, Dr. Brian Wilson1,2, Dr. S.M.F. Rabbi3, Katherine Polain1

1University Of New England, Faculty of Science, Agriculture, Business and Law, Armidale, Australia, 2NSW Office of Environment and Heritage, PO Box U221, Armidale, Australia, 3University of Sydney, Camden, Australia

Carbon storage in the soil is believed to be an effective way to sequester atmospheric carbon and abate the impact of climate change.  Water soluble carbon in the soil can be adsorbed and stabilised on the clay surfaces.  The mechanisms of translocation and stabilisation in this way are complex and require detailed investigation. The sorption and stabilisation of dissolved organic carbon (DOC) is dependent on the DOC concentration, clay content and mineralogy of the soil.  We undertook a batch sorption experiment using DOC extracted from a C4 plant to explore the sorption of the added DOC in three soils (i.e. Dermosol, Chromosol and Ferrosol) with contrasting mineralogy. The concentration and isotopic signature of soluble and adsorbed carbon were determined, and the maximum sorption capacity of the soils were modelled.  Initial DOC concentration and soil mineralogy both had significant effects on the DOC sorption and our results have significance for the long-term storage of carbon in soils, particularly in the deeper, clay rich horizons.


Biography:

Katherine is in her final year as a UNE PhD candidate, investigating the role of soil microorganisms in sub-soil nutrient cycling under rotational cotton crops. Prior to her PhD studies, Katherine worked as a secondary science teacher in both New South Wales and the Northern Territory. Her honours was completed at Charles Darwin University, where she studied the role of microorganisms in the acceleration of acid mine drainage. In addition to her PhD studies, Katherine continues to engage with students and the wider community to promote science education and research, when she is not spending time with her young family!

Does conversion to conservation tillage really increase soil organic carbon stocks in organic arable farming?

Dr Markus Steffens1, Marco Chiodelli Palazzoli1, Fogelina Cuperus2, PD Dr. Axel Don3, Prof. Dr. Andreas  Gattinger4, Sabine Gruber5, Wiepie Haagsma2, Frank Hegewald3, Josefine Peigné6, Franz Schulz4, Prof. Dr. Marcel G. A. van der Heijden7, Laurent Vincent-Caboud6, PD Dr. Martin Wiesmeier8, Raphael Wittwer7, Sabine Zikeli9, Dr. Maike Krauss1

1Research Institute of Organic Agriculture FiBL, Frick, Switzerland, 2Wageningen University & Research, Lelystad, The Netherlands, 3Thünen Institute of Climate-Smart Agriculture, Braunschweig, Germany, 4Justus-Liebig-University Giessen, Chair in Organic Farming with focus on Sustainable Soil Use, Giessen, Germany, 5University of Hohenheim, Institute of Crop Sciences, Stuttgart, Germany, 6ISARA-Lyon, Lyon, France, 7Agroscope, Research Division Agroecology and Environment, Plant-Soil Interactions, Zürich, Switzerland, 8Bavarian State Research Center for Agriculture, Institute for Organic Farming, Soil and Ressource Management, Freising, Germany, 9University of Hohenheim, 9Institute of Crop Science, Coordination for Organic Farming and Consumer Protection, Stuttgart, Germany

Aggravation of weather extremes increases awareness of climate change consequences. Mitigation options are in demand which aim to reduce the atmospheric concentration of greenhouse gases. Amongst others, conversion from ploughing to conservation tillage is argued to increase soil organic carbon (SOC) stocks. Yet, main findings of reviews and meta-analyses comparing SOC stocks between tillage systems show different results: from a significant increase of SOC stocks to the question if there is any effect at all. Reasons are a sampling bias as in many campaigns only topsoil layers are assessed and horizons thickness is not considered adequately, different methods for SOC and bulk density determination, and the comparison of SOC stocks based on equivalent soil masses instead of equal sampling depths.

In order to address these limitations, we initiated the SOCORT consortium (Soil Organic Carbon in Organic Reduced Tillage) – an international network of nine agronomical long-term trials. All trials represent common mixed organic farming systems of the respective region with organic fertilisation and crop rotations including leys. Climatic conditions are similar, but age and soil texture vary (7 to 21 years and sandy to clayey soils). A common sampling campaign was consequently elaborated to answer the question if the combination of conservation tillage and organic farming can really increase SOC stocks. Undisturbed soil cores were taken with driving hammer probes (8 cm in diameter) to a maximum depth of 100 cm. Each core was divided in the increments 0-30, 30-50, 50-70, 70-100 cm. The topsoil layer (0-30 cm) was further divided into the different tillage depths of the respective trial. All samples were analysed in the same laboratory for bulk density, organic carbon content, pH and texture. We compiled the yields for each trial to assess carbon inputs. The SOCORT consortium in combination with the common sampling campaign will entangle the driving factors of carbon sequestration through reduced tillage and add important knowledge on carbon dynamics in agro-ecosystems.


Biography:

Markus Steffens is theme leader for climate and agriculture at the Research Institute of Organic Agriculture FiBL in Switzerland. He received his Ph.D. in soil sciences from the Technische Universität München and did his diploma in applied environmental sciences at Trier University, Germany. Markus’ work is focused on soil organic matter and soil quality in agricultural systems and the application of (imaging) spectroscopic techniques to elucidate the underlying processes.

Compacted and suppressed: physical constraints of soil microbial response to carbon supply in the subsoil

Dr Yui Osanai1, Dr Oliver Knox1, A/Prof Brian Wilson1,2

1University Of New England, Armidale, Australia, 2NSW Office of Environment and Heritage, Armidale, Australia

Recent studies highlight the importance of dissolved organic carbon (DOC) in soil carbon (C) dynamics through microbial processes. Both the quantity and spatial accessibility of DOC influence the relative importance of microbial processes compared with physical processes. However, the extent to which microbial activity responds to DOC and differences in physical condition through the soil profile remain largely unknown. Here, we conducted a laboratory incubation to quantify microbial respiration responses to DOC in the topsoil (0–30 cm) and the subsoil (30–100 cm) along a simulated soil compaction gradient (disturbed, no adjustment, slightly compacted and compacted), using the soils collected from cotton-based cropping systems under different tillage and rotational managements. Preliminary analysis showed that basal respiration decreased in response to compaction, but increased following disturbance in both topsoil and subsoil. DOC addition increased microbial respiration. However, the response differed between the physical treatments and soil profiles. Both disturbance and compaction resulted in reduced respiration, with a greater reduction observed in the topsoil than the subsoil. When adjusted for field bulk density, the estimated respiration responses to DOC showed much larger responses in the topsoil than the subsoil and in maximum tillage than minimum tillage systems. These results suggest that under field conditions, subsoil respiration will be lower than that of the topsoil due to both physical and substrate constraints. The contrasting effect of disturbance on basal and DOC-induced respiration also suggests that there is a complex interplay between physical and biological processes in regulating C fluxes. Our study demonstrates that soil physical conditions modulate microbial responses to substrate availability, and that agricultural practices that affect physical conditions can have a significant impact on C dynamics and sequestration in agricultural soils.


Biography: Yui is a postdoctoral research fellow at University of New England. She is interested in the regulation of the C and N cycles in terrestrial ecosystems in the context of environmental changes. In particular, her research focuses on the interactions and feedback between plants, soil and soil microbial communities and how changes in the environment may directly or indirectly impact the interactions between them to influence soil processes and nutrient availability, and their consequences for plant productivity.

Linking soil structure formation and soil organic matter cycling in the rhizosphere

A/Prof. Carsten W. Mueller1

1Technical University of Munich, Freising, Germany

Due to its large interface between soils and plants, the rhizosphere, the volume of soil around living roots directly influenced by root activity, plays a key role in soil formation. Especially the root derived input of organic carbon into the soil matrix triggers a multitude of soil processes. The soil structure formation, i.e. aggregation of solid soil particles into three dimensional clusters, is the key process for the formation of a soil’s pore space and specific surface area, determining the air, water and nutrient balance and thus shaping both plant and microbial habitats. The formation of associations built by the interaction of minerals with organic matter supplied by rhizodeposition or decaying roots together with microbial residues is unique to soils. The high input of organic carbon in the rhizosphere (both from plants and microorganisms) in contrast to root free bulk soil, promotes the formation of micro- and macro-aggregates, and thus the development of a 3D soil structure with positive effects on soil carbon sequestration. As the rhizosphere is a hot spot for organic carbon input and microbial activity, it becomes evident that it also plays a special role for the long term carbon sequestration at greater soil depth. Results from a number of studies will presented on the importance of roots and the rhizosphere on soil organic matter cycling and sequestration. This will reach from using artificial root systems at the lab scale to determine the effect of root exudates on soil aggregate formation and microbial community structures, up to the field scale exploring the major role of roots for soil organic carbon stability.


Biography:

Carsten W. Mueller is currently an Associate Professor at the Technical University of Munich. Following his graduation in Forest science at the Technical University of Dresden, he did his PhD at the Technical University of Munich. After a PostDoc at Pennsylvania State University he became an Assistant Professor at the Technical University of Munich. He is mainly working on the fate of soil organic matter, from the plant input in rhizosphere and detritusphere over microbial transformations to particulate organic matter and mineral-associated organic matter in the soil. Having worked on soils from all continents, currently he especially focuses on soil structure formation and organic matter allocation in the rhizosphere and pristine environments in the Arctic and in Antarctica. In his research he combines quantitative approaches (e.g. density fractionation, elemental and isotopic analyses, lab incubations) with state of the art chemical (GC-MS, NMR spectroscopy) and spectromicroscopic (SEM, NanoSIMS) techniques.

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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