Spatial variation of earthworm communities and soil organic carbon in temperate agroforestry

Dr Rémi Cardinael1,2,3, Dr Kevin Hoeffner4, Pr Claire Chenu3, Dr Tiphaine Chevallier2, Camille Béral5, Antoine Dewisme4, Dr Daniel Cluzeau4

1Cirad – UR AIDA, Montpellier, France, 2IRD – UMR Eco&Sols, Montpellier, France, 3AgroParisTech – UMR Ecosys, Thiverval-Grignon, France, 4Univ-Rennes – UMR Ecobio, Rennes, France, 5Agroof, Anduze, France

The aim of this study was to assess how soil organic C (SOC) stocks and earthworm communities were modified in agroforestry systems compared to treeless control plots, and within the agroforestry plots (tree rows vs alleys). We used a network of 13 silvoarable agroforestry sites in France along a North/South gradient. Total earthworm abundance and biomass were significantly higher in the tree rows than in the control plots, but were not modified in the alleys compared to the control plots. Earthworm species richness, Shannon index, and species evenness were significantly higher in the tree rows than in the alleys. Total abundance of epigeic, epi-anecic, strict anecic and endogeic was higher in the tree rows. Surprisingly, earthworm individual weight was significantly lower in the tree rows than in the alleys and in the control plots. SOC stocks were significantly higher in the tree rows compared to the control plots across all sites. Despite higher SOC stocks in the tree rows, the amount of available C per earthworm individual was lower compared to the control. The absence of disturbance (no tillage, no fertilizers, no pesticides) in the tree rows rather than increased SOC stocks therefore seems to be the main factor explaining the increased total abundance, biomass, and diversity of earthworms. The observed differences in earthworm communities between tree rows and alleys may lead to modified and spatially structured SOC dynamics within agroforestry plots.


Biography:

Professor of Soil Science at AgroParisTech

Mutual interactions between decaying plant litter, soil microorganisms and mineral particles, controlled by soil texture

Ms Kristina Witzgall1, Ms Alix Vidal1, Mr Steffen Schweizer1, Ms Valerie  Pouteau2, Ms Claire Chenu2, Mr David Schubert3, Ms Juliane Hirte4, Mr Carsten Müller1

1TU München, Lehrstuhl für Bodenkunde, Technische Universität München, Freising-Weihenstephan, Germany, 2UMR Ecosys, AgroTechParis, Batiment EGER, Thiverval Grignon, France, 3TU München, Freising-Weihenstephan, Germany, 4Plant-Soil Interaction Group, Division Agroecology and Environment, Agroscope, Zurich, Switzerland

Soil texture and microorganisms are key drivers controlling the fate of organic matter (OM) from decaying plant litter and thus soil organic matter (SOM) stabilization. A better understanding of mutual interactions between microbial litter decay and soil structure formation controlled by different soil texture remains challenging. We monitored the fate of litter-derived compounds (using 13C isotopic enrichment) from decaying litter (maize leaves) to microorganisms and soil in two differently textured soils (sand and loam). We incubated the two soils with litter mixed in the top layer in microcosms for three months with regular CO2 and 13CO2 measurements. Using a physical soil fractionation scheme, we assessed the fate of the litter-derived OM as free and occluded particulate organic matter (POM) as well as mineral associated OM (MOM) together with the effects of the different textures on the microbial communities using PLFA. The POM and MOM fractions were analyzed with respect to mass distribution, C, N and 13C contents, as well as the chemical composition using 13C-CPMAS NMR spectroscopy. We could clearly demonstrate higher contents of OM in the mineral associated fractions of the sandy textured soil in contrast to the loamy textured soil, where instead higher OM contents were detected in the POM fractions. Thus we show a distinct negative effect of the clay content on MOM, while clay sustains a high level of OM stored as POM. The 13C measurements showed higher enrichment in almost all fractions in the sandy textured soil compared to the loamy soil. The PLFA analysis revealed a coherent pattern between the textures, where microbial activity increased in the top layers and the community structure remained similar in both treatments. This interdisciplinary approach, where biogeochemical and microbiological methods were combined, gave insights in the interactions between decaying plant litter, microorganisms, and soil minerals.


Biography:

Kristina Witzgall, born 1992 in Lund, Sweden.

  • 2016-2019 M.Sc. Sustainable Resource Management, Technical University of Munich, Germany
  • 2018 Internship, Bavarian State Research Centre for Agriculture, Germany
  • 2017-2018 Student Research Assistant, Technical University of Munich, Germany
  • 2016-2017 Student Representative, Technical University of Munich, Germany
  • 2011-2015 B.Sc. Environmental Sciences, Lund University, Sweden

Soil amino acids on association converted to peptide-polypeptide and protein part of humic molecules during humification process

Dr Sanjib Kar1

1University Of Calcutta, Kolkata, India

The aim of this study were  to find out the fate of amino acid on  humification processes  in soil. For this study humic acid were extracted from  jalpaiguri  forest soil and treated with eleven different amino acids with or without clay. It was observed that cation exchange capacity and    electric potential decreases  with time whereas  N content, molecular weight and % aromiticity of humic molecule increase with time. Infrared and C13 nuclear magnetic resonance spectra established that various groups of amino acids react with each other converted to peptide ,poly-peptide   and finally  protein part  in humic  molecule. Carbon % , N % and protein content of humic molecules increase from 55.4  –  57.1, 3.5 – 4 and 13.575  – 24.725   mgg-1respectively within one year reaction . From this study it is clear that amino acids in soil on association converted to peptide –polypeptide and protein and that became a part of humic molecules during humification process.

Soil organic matter mineralization by earthworms: A meta-analysis

Dr Patricia Garnier1, Dr. Mickael Hedde2, Dr David Makowski3, Dr Michel Bertrand3

1INRA, UMR Ecosys, Thiverval Grignon, France, 2INRA, Eco&Sol, Montpellier, France, 3INRA, UMR Agronomie, Thiverval Grignon, France

In most of soil organic matter models, the action of macroorganisms such as earthworms (EWs) is not represented. In order to build a model simulating the effect of EWs on the mineralization of soil organic matter (SOM), we used a statistical model based on a meta-analysis approach that allows taking into account the main experimental results of the selected literature. First, a database was built using the following steps: literature review, selection of references, data extraction, build a table of the input variables and finally choice of the response variable. Second, several statistical models (programmed in R-language) were tested with the experimental data set between the carbon mineralization response variable and the various explanatory variables selected. The results of the database show that there is an increase in carbon mineralization with the presence of earthworms and also that the effect of earthworms varies greatly between studies. To describe the effect of time, random-effect models are better than fixed-effect models and therefore this indicates that inter-study variability must be taken into account. The cubic model is better than the linear and quadratic models. Among the explanatory variables other than time, only the density makes it possible to improve the model. Thus an equation is proposed to calculate the effect of earthworms on soil carbon mineralization using a cubic model for time and linear for the density.


Biography:

Dr Patricia Garnier is a senior researcher at INRA, UMR EcoSys, Grignon, France. She was awarded a Ph.D. in soil science in 1996, from the University of Nancy in France.  She then worked as a post-doc at Cornell University, USA. She has authored or co-authored 63 articles in international peer-reviewed journals. Her main research activity concerns the modelling of soil processes like water transport, organic matter transformation, soil structure dynamic, organic contaminant movement… She has been in charge of several large research projects including international exchanges with China, Germany, etc…She is the leader of the national ANR project Soil µ3D (2015-2018) dealing with the modelling of organic matter on soil pores. She has also been leader of several other French national projects.

Crop rotation diversity changes soil organic matter composition and microbial function in corn- and wheat-based systems

Dr Bobbi Helgason1, Dr Jennifer  Town2, Mr Kehinde Adams1, Dr Edward Gregorich3

1University Of Saskatchewan, Saskatoon, Canada, 2Agriculture and Agri-Food Canada, Saskatoon, Canada, 3Agriculture and Agri-Food Canada, Ottawa, Canada

Sustainable cropping systems rely on diverse crop rotations to maintain balanced fertility and critical soil functions, including organic matter turnover. We evaluated soils from two long-term field experiments comparing continuous cereals with cereals in diverse crop rotations. The first is a humid corn-based system (Ontario, Canada) and the second is a semi-arid wheat-based system (Saskatchewan, Canada), both of which have exhibited a yield boost of at least 20% in the cereals grown in diverse rotations. Using multiple indicators of soil function and DNA amplicon-based microbial community profiling we found significant differences in soil organic matter composition and microbial community structure and activity. Effects of diverse crop rotations were greater in the corn vs. wheat system, with bigger changes in the relative abundances of different bacterial and fungal taxa, extracellular enzyme activities and available nutrient concentrations. Soil organic matter characterization showed an accumulation of lignin, increased syringyl:vanillin ratio and greater mineralizable C in continuous wheat and corn but no difference in amino sugar content, indicating that there was faster turnover of recent plant C inputs in the diverse rotations but no differences in microbial necromass accumulation. A soil incubation study using ¹³C labelled corn and wheat residues to track the microbial decomposition of residue C revealed differences in active decomposers between rotation treatments. Similar to our field survey, these rotation-induced differences were greater in the corn compared to the wheat system. We hypothesize that this is due to moisture stress being a stronger determinant of microbial decomposer community structure and function than residue quality in the semi-arid climate. Our work demonstrates that changes in residue quality, realized through crop rotation, impact soil organic matter composition and soil function and explicitly considers microbial functions as both causative and indicative of changing soil fertility and organic matter dynamics.


Biography:

Bobbi Helgason is a soil microbial ecologist whose research program focusses on how soil bacteria and fungi affect soil function and plant growth, with a focus on agroecosystems. Her research program focusses on how soil microorganisms interact with climate and agricultural management practices to affect soil functioning and crop productivity. Her work combines field and laboratory research using leading edge methodologies in microbial ecology, stable isotope probing, and soil energetics to link microbial abundance, community structure and activity with soil biogeochemical processes and plant-microbe interactions

Mineral regulations on microbial necromass accumulation efficiency in soils

Miss Yue Cai1,2, Ms Tian Ma1,2, Miss Yiyun Wang1,2, Dr Juan Jia1, Dr Yufu Jia1, Dr Xiaojuan Feng1,2

1Institute Of Botany, Chinese Academy Of Sciences, Beijing, China, 2University of Chinese Academy of Sciences, Beijing, China

Soil microbes are known to play a key role in transforming labile organic carbon (OC) into relatively stable soil carbon in the form of microbial necromass. However, the efficiency of microbial necromass accumulation relative to labile OC mineralization remains under-investigated, which has vital implications for soil carbon sequestration. Here we construct artificial soils based on fructose, a common microbial inoculum and inorganic matrices with varying contents of clay and mineralogy to examine mineral regulations on microbial necromass accrual versus mineralization. By measuring microbial biomass and necromass (indicated by amino sugars) relative to respiration, we compare microbial carbon use efficiency (CUE) and amino sugar accumulation efficiency (AAE) throughout the 116-day incubation. We find that while clay promotes microbial consumption of labile OC (fructose), it enhances the rate as well as efficiency of microbial necromass accumulation without affecting CUE. On the contrary, ferrihydrite decreases CUE and AAE and promotes fructose preservation via inhibiting microbial growth. Hence, microbial necromass accrual is more efficient in clay-rich soils while labile OC is better preserved in soils containing ferrihydrite. Collectively, our findings suggest that the accrual efficiency of microbial carbon heavily depends on its preservation other than growth efficiency and is mediated by soil mineral content as well as composition. Parameters depicting microbial carbon preservation such as AAE warrant further study for modelling and managing the formation of microbial derived stable soil OC.


Biography:

Yue Cai is a 5th-year Ph.D. student at the Institute of Botany, Chinese Academy of Sciences. She mainly investigates mineral and microbial effects on soil organic carbon sequestration. She has published one first-authored paper in the Journal of Geophysical Research: Biogeosciences and has another first-authored paper under review in Biogeochemistry.

Soil microbial activity and nutrient dynamics with soil depth, under mixed tree species environmental plantings in NSW, Australia

Ms Apsara Amarasinghe1, Mrs Christine  Fyfe1, Dr Oliver  Knox1, Associate Professor Lisa  Bruyn1, Associate Professor Paul Kristiansen1, Associate Professor Brian  Wilson1

1School of Environmental and Rural Sciences, Faculty of Science Agriculture Business and Law, University of New England, Armidale, Australia

The impacts of mixed tree species environmental plantings on soil biology is an emerging topic. A pilot study was conducted to determine the variability of microbial activity, total soil organic carbon (C), nitrogen (N) and available phosphorus (P) under Eucalyptus camaldulensis and Acacia pendula used for mixed tree species environmental plantings in NSW. A 13 year old tree planting was selected from a chronosequence of established environmental plantings near Gunnedah, NSW. Soil samples were taken from both inside and outside the tree canopy at depths of: 0–5 cm, 5–10 cm, 10-20 cm, 20-30 cm and 30-50 cm. The soil was tested for heterotrophic respiration (MicroRespTM), total C and N (LECO), and available P (Colwell).

For both tree species, greater microbial activity was observed at: 0-5 and 5-10 cm soil depths compared with the deeper soil layers (20-50 cm). Further, both basal and substrate induced (glucose) respiration rates were higher under the tree canopy compared with outside the tree canopy by 3% and 12%, respectively. Basal respiration rate was significantly higher under E. camaldulensis canopy compared to A. pendula canopy at the 5-10 cm soil depth, however, at 30-50 cm, this result was reversed for the two tree species. For both tree species, C, N and P significantly decreased with depth up to 20 cm. However, no significant difference were detected between 20-30 cm and 30-50 cm. Further, C, N and P contents were lower under the E. camaldulensis canopy than outside whereas, those were not different under and outside of A. Pendula canopy. Under A. pendula the C, N and P were higher than under E. camaldulensis, however, the differences were significant only for total N. Furthermore, microbial respiration was positively correlated with C, N and P. These results suggest trees in environmental plantings do have positive impacts on soil microbial activity and enhance soil nutrient status.

 

Key Words: Available Phosphorous, Environmental plantings, Microbial respiration, Soil organic carbon, Total nitrogen


Biography:

Apsara Amarasinghe is a UNE PhD candidate. She completed her Bachelor of Science (Agric) in 2010 and Master of Philosophy in 2017 at Wayamba University of Sri Lanka. Further she has completed a Postgraduate diploma in 2017 at University of Colombo Sri Lanka. She is a Lecturer at Wayamba University of Sri Lanka and obtained International Postgraduate Research Award (IPRA) to carry out her PhD at University of New England. Her PhD is one component of a larger project funded by the Environmental Trust NSW for “Soil biodiversity benefits from environmental plantings”.

 

Beyond the Rhizosphere: Microbial potential in sub- and bulk vertosols

Ms Katherine Polain1, Dr Oliver Knox1, Dr Nina Siebers3, Associate Professor Brian Wilson1,2

1Department of Agronomy and Soil Science, University Of New England, Armidale, Australia, 2Science Division, NSW Office of Environment and Heritage, University of New England, Armidale, Australia, 3Institute for Bio- and Geosciences (Agrosphere), Jülich Forschungszentrum, Jülich, Germany

The continuation of sustainable agricultural practice, despite climate change and an increasing human population, presents a global challenge requiring approaches that push beyond the boundaries of current research. One solution may reside within our soil microbial communities. Australian cotton (Gossypium hirsutum) is predominantly grown in vertosols, dynamic soils that can move nutrients from the soil surface into the sub-soil and from rhizosphere to bulk soil. Whilst cultivation of crop rotations may improve soil properties, the potential impact on microbial communities in response to this regime, remains unexplored.

 

Our work assessed and compared microbial activity (using respiration incubations) and biomass (via substrate induced respiration), in the top- (0-30 cm) and sub- (30-100 cm) soils of continuous cotton (CC) and cotton-maize (CM) rotations at three time points (pre-, in- and post-crop) for two growing seasons, sampling in the plant line, but not targeting the rhizosphere. In addition, we used a δ18OP-HCl stable isotope method to gauge the long-term impact of crop rotation on sub-soil microbial activity.

 

Our results highlight that, regardless of crop rotation, sub-soil microbial activity does not significantly (P = 0.11) differ from top-soil, with sub-soil microorganisms contributing 46% to the overall profile activity. Sub-soil microbial activity only differed (P = 0.03) when cotton was in-crop, resulting in a decrease in activity. Microbial biomass was different (P = 0.00) between both soil depth and crop rotation, with sub-soils contributing 37% to the profile’s microbial biomass. The long term implementation of rotations found CC system promoting microbial activity down the entire profile, in comparison to CM (P = 0.01) . Our work emphasises the importance of considering soils beyond the surface as a significant amount of activity and, to a lesser extent, biomass is occurring below 30 cm, with crop rotation and establishment significantly influencing microbial properties beyond the crop rhizosphere.


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!

Effect of pesticides on earthworm population dynamics in two ecologically different land use systems of Uttarakhand, India

Ms Rashi Miglani1, Dr Satpal Singh Bisht2

1Kumaun University, Nainital, India, 2Kumaun University, Nainital, India

Earthworms Density and Soil Organic Matter are the two prime aspects of soil ecology which include dynamics of soil properties in terms of nutrients porosity aeration water holding capacity humification and distribution, dispersal and decomposition of soil organic matter generated from various sources. The external inputs in agricultural lands such as fertilizers, and pesticides are likely to increase crop production but it comes at the cost of soil degradation. Earthworm population creates nutrient rich biocover but high precision of pesticides application and exhaustive rotation of pesticides in soil disturbs dynamics of earthworms population. To parameterize the toxic effect of pesticides on earthworm an acute toxicity test of Chemical (Emamectin Benzoate) was performed using a contact filter paper method proposed by OECD (Organization for Economic and Cooperative Development) testing guideline 2016 and earthworm population dynamics were studied for two consecutive years in two different land use systems. In contact filter test the worms were exposed to different concentration of insecticide for 48 h and mortality was recorded and LC50 for Emamectin benzoate i.e. 22.90 μg/cm2 found to be very toxic to earthworm Metaphire posthuma.

Keywords: LC50, Emamectin benzoate, Population Dynamics, Insecticides


Biography:

Bio to come

Impacts of aridity on soil organic matter and microbial communities using phospholipid fatty acid techniques

Mrs Athina Puccini1, Dr Mark Farrell1

1CSIRO Agriculture and Food, Urrbrae, Australia

Recent work has clearly established that by looking at the dynamic of climate change, climate gradients, and the vegetation community structure, there are multiple and interactive impacts on Soil Organic Matter (SOM) and the microbial communities living within it. This study examined soil samples taken from 42 sites within a transect that was established under the Terrestrial Ecosystem Research Network (TERN) that runs for 900 km from Cape Jervis in the south to north of the Flinders Ranges in central South Australia. Microbial communities were analysed for community structure using PLFA analysis to provide robust information on functional microbial community structure at time of sampling. Beyond microbial measurements, comprehensive analysis of soil biogeochemistry including litter and soil organic matter chemistry by NMR was conducted. Combined with vegetation community structure and climatic information, this data was then analysed to understand the strengths of relationships between vegetation, climatic, soil and microbial variability along the transect. Litter was more degraded with an increase in rainfall, therefore climate is a major driver and has a significant relationship with litter alkyl/O-alkyl (A/OA) ratio (r = 0.436, P = 0.039). There was also a significant relationship between litter and SOM chemistry (Litter x SOM) (ρ = 0.224, P =0.014) showing a statistically significant relationship between both. In examining relationships between all the variables and the PLFA data, SOM chemistry was most closely related (ρ = 0.447). Further integration of NMR and PLFA data will allow us to link the microbial communities to climate and SOM.


Biography:

Athina Puccini has 18 years of research laboratory experience in the field of soil biogeochemistry and ecology within CSIROs Agriculture and Food, located on the Waite Campus in Adelaide. She possesses strong analytical capabilities delivering within experimental research projects on SOM characterisation through key analytical expertise in fractionation and NMR. Most recently focussing on the quantification of biomarkers using isotopic GC-MS analysis.

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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