Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soi... more Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N2O production. However, in the literature, there are numerous reports of net negative fluxes of N2O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise.Net N2O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N2O consumption. This fits in with denitrification as the responsible process, reducing N2O to N2. However, it has also been reported that nitrifiers consume N2O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N2O consumption, ranging from low to high temperat...
The objective of this work was to assess the effects of conventional tillage and of different dir... more The objective of this work was to assess the effects of conventional tillage and of different direct seeding mulch-based cropping systems (DMC) on soil nematofauna characteristics. The long-term field experiment was carried out in the highlands of Madagascar on an andic Dystrustept soil. Soil samples were taken once a year during three successive years (14 to 16 years after installation of the treatments) from a 0-5-cm soil layer of a conventional tillage system and of three kinds of DMC: direct seeding on mulch from rotation soybean-maize residues; direct seeding of maize-maize rotation on living mulch of silverleaf (Desmodium uncinatum); direct seeding of bean (Phaseolus vulgaris)-soybean rotation on living mulch of kikuyu grass (Pennisetum clandestinum). The samples were compared with samples from natural fallows. The soil nematofauna, characterized by the abundance of different trophic groups and indices (MI, maturity index; EI and SI, enrichment and structure indices), allowed ...
Acacia holosericea seedlings were planted in 1-l pots filled with a soil collected from an Austra... more Acacia holosericea seedlings were planted in 1-l pots filled with a soil collected from an Australian Acacia plantation in Southern Senegal. After 6 months of culture, mycorrhizosphere soil, roots, galls induced by root-knot nematodes and Rhizobium nodules were sampled from each pot. The diversity of this bacterial group was characterized by siderotyping (pyoverdine IsoElectric Focusing (IEF) analysis) and by restriction fragment length polymorphism (RFLP). The effect of these isolates on the establishment of the ectomycorrhizal symbiosis between an Australian Acacia (A. holosericea) and Pisolithus sp. strain IR100 was studied. In the mycorrhizosphere soil, the population of fluorescent pseudomonads was represented by strains of two different siderovars (groups of bacterial strains presenting an identical pyoverdine^IEF pattern): siderovar 1 (74%) and siderovar 2 (26%). The siderotyping of the isolates around galls of the root-knot nematodes revealed three siderovars (40% from siderovar 1, 40% from siderovar 2 and about 15% from siderovar 3). RFLP of 16S rDNA divided the isolates into four different groups with MspI, two with HhaI and two with HaeIII endonucleases. The establishment of the ectomycorrhizal symbiosis with A. holosericea was promoted by 14 bacterial strains isolated from the mycorrhizosphere soil, three isolates from the roots and four from the galls. Shoot biomass of A. holosericea seedlings was stimulated by eight bacterial isolates from soil, six isolates from galls and seven from roots. These mycorrhiza helper bacteria could have a great ecological importance in tropical areas through the reforestation programs.
Pasteuria penetrans, a bacterial parasite of plantparasitic nematodes, is used to control root-kn... more Pasteuria penetrans, a bacterial parasite of plantparasitic nematodes, is used to control root-knot nematode Meloidogyne spp. populations in vegetable crops. But its efficiency is variable, mostly because of the patchy distribution of the bacteria in arable fields. As the infective P. penetrans are non-motile bacteria in soil, abiotic soil factors can affect the bacteria-nematode relationships. An epidemiological study, conducted in a vegetable field, showed that abiotic factors such as irrigation, soil water holding capacity and texture, affected the efficiency of P. penetrans. A correspondence analysis between these abiotic factors and the density of P. penetrans spores in the soil, and the proportion of Meloidogyne javanica juveniles infected by the bacteria, revealed that irrigation affected directly the distribution of the spores in soil pores related to their passive transport by water flow. Laboratory experiments conducted on the passive transport of spores confirmed that intensive irrigation leached the spores down the soil profile and decreased the percentage of infected Meloidogyne juveniles.
In tropical ecosystems, termite mound soils constitute an important soil compartment covering aro... more In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites ( Cubitermes niokoloensis ) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revea...
Tropical sandy soils (or upper sandy horizons of tropical soils) have diverse physical and chemic... more Tropical sandy soils (or upper sandy horizons of tropical soils) have diverse physical and chemical constraints: poor structural stability (making soils sensitive to crusting, and compaction), poor nutrient holding capacity and low cation exchange capacity. In these soils, in which the clay content is low (3 to 15% by mass), organic matter is the main determinant of fertility, nutrient storage, aggregate stability, microbial and enzymatic activities. However, cultural practices or land uses aimed at increasing organic matter stocks have a minor impact if compared with the potential storage of organic matter in clayey soils. Nevertheless, this stock increase is possible in sandy soils and is mainly linked with the increase of the "vegetal debris" functional pool. Like organic matter, the abundance, activity, and diversity of soil biota are largely dependent upon land management. In these soils, biotic interactions such as termites-microorganisms or nematodesmicroorganisms modify nutrient fluxes, N mineralization being higher in soil-feeding termite mounds or in the presence of bacterial feeding nematodes. Moreover, the management of organic residues represents a means to control the activity of soil microorganisms and the structure of nematode and other fauna populations. An adequate management of organic matter (through fallows, improved fallows, pastures, external organic inputs) through its consequences on soil biofunctioning, largely determines the agronomic (plant production) and environmental (carbon sequestration) potentials of sandy soils. In the present paper, we provide information on the biofunctioning in sandy soils, i.e., interactions existing between organic matter, biological activities (termites, earthworms, nematodes, microorganisms) and physical soil properties, in natural and cropped ecosystems. Data mainly originate from experiments and measurements from West (Senegal, Burkina Faso, Ivory Coast) and East (Kenya) Africa.
2015 was the United Nations International Year of Soils and, for the first time, soils and the li... more 2015 was the United Nations International Year of Soils and, for the first time, soils and the life within them were in the spotlight globally. An international group of experts and scientists from the European Commission’s Joint Research Centre (JRC), in close collaboration with colleagues from the Commission’s Directorate-General for the Environment and the Global Soil Biodiversity Initiative, have produced the first ever Global Soil Biodiversity Atlas. Soils are vital for human survival and underpin many sectors of our economy. It is estimated that 99% of the world’s food comes from the terrestrial environment. But soils are also home to over a quarter of global biodiversity. Millions of soil-dwelling organisms promote essential ecosystem services – from plant growth to food production. They support biodiversity, benefit human health, promote the regulation of nutrient cycles that in turn influence climate, and represent an unexplored capital of natural sources. Our knowledge of ...
Environment promotes environmentally sound practices globally and in its own activities. This pub... more Environment promotes environmentally sound practices globally and in its own activities. This publication is printed on 100% recycled paper, using vegetable-based inks and other ecofriendly practices. Our distribution policy aims to reduce UN Environment's carbon footprint. About the International Resource Panel The International Resource Panel (IRP), a global scientific panel hosted by the United Nations Environment Programme, was created in 2007 to contribute to a better understanding of sustainable development from a natural resources perspective. It provides science-based policy options on how to decouple economic growth from environmental degradation while enhancing human well-being. With more than 20 scientific publications, the work of the panel has shed light on growing environmental challenges related to natural resources, their socioeconomic implications and potential new pathways towards their sustainable management. What is an IRP think piece? An IRP think piece is a technical or policy paper based on IRP scientific studies and assessments and other relevant literature. It is not a full study and assessment but a collection of science-based reflections, which may catalyze the generation of new scientific knowledge and highlight critical topics to be considered in policy discourse.
A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types... more A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types of biogenic structures: earthworm casts and crop sheetings built by two fungus-growing termites (Ancistrotermes guineensis and Odontotermes nilensis) and compared to the neighbouring soil in a mango orchard in the This region of Senegal. A principal component analysis shows clearly that the biogenic structures were differentiated from the neigbhouring soils in their content of organic components. The amino sugar contents of biogenic structures were 3-5 times higher than those measured in soil. In these structures, an increase in the contents of phenols and proteins was also observed. In contrast, their physical and chemical characteristics (texture, cationic exchanges capacity) were little different from those of the soil with the exception of their much lower waterretention capacity. Differences were also noted between the biogenic structures: the structures built by the two species of termite show more similarities with each other than with the casts. This result was confirmed by a similarity dendrogram which was used to graduate oppositions between samples. Casts were different from termite sheetings primarily in their C and N contents which were twice as high. Conversely, the contents of proteins in termite sheetings were higher than those measured in casts. Altogether, the results suggest that, in the biogenic structures, the organic content is stored and protected from mineralization.
Bacterial-feeding nematodes constitute one of the primary grazers of soil bacteria. We investigat... more Bacterial-feeding nematodes constitute one of the primary grazers of soil bacteria. We investigated the effects of selective grazing of a representative nematode (Zeldia punctata, Cephalobidae) on nematode life history and population biology and on the soil microbial community. Firstly, we measured (i) the effect of five different bacterial strains on the nematode life cycle using petri dishes and (ii) the impact of bacterial inoculation on nematode population growth in a soil microcosm. Selection of the five bacterial strains was based on morphology, cell-wall characteristics and mucus production. Z. punctata development was strongly affected by the type of bacteria ingested, independent of experimental design. Bacterial cell-wall characteristics seemed to directly affect Z. punctata development since high nematode densities were only reached with gram-negative strains (Pseudomonas monteilii and Methylobacterium nodulans). In petri dishes, the filamentous organisms (Actinomyces sp.) and mucus-producing bacteria (Bradyrhizobium sp.) led to the least reproduction. Duration of the various nematode life phases (egg, juvenile, reproductive stage and non-reproductive stage) was significantly affected by the bacterial food source. Total life span varied from 12.5 days (Bradyrhizobium sp.) to 40 days (Pseudomonas monteilii). Secondly, we monitored the influence of Z. punctata on the indigenous soil microbial community in the presence or absence of a maize plantlet. Nematode inoculation led to an increase in bacterial activity (as measured by alkaline phosphatase activity) but did not significantly influence bacterial biomass. The genetic fingerprint (DGGE) of soil bacteria was more influenced by plant presence than by nematode inoculation. Nematode activity has important repercussions on N flux in the soil since inoculation of Z. punctata in the absence of plants resulted in a net increase of N mineralization (2 mg N per pot) while a decrease of mineral N (0.5 mg N per pot) was observed in the absence of the nematodes, due to bacterial immobilization. This study underscores the close relationship between selective bacterial grazing and nematode development. Nevertheless, the impact of nematode grazing on the overall soil microbial community seems to primarily affect microbial activity and relative dominance rather than microbial diversity.
Current Plant Science and Biotechnology in Agriculture, 2008
A potential solution to land degradation is to promote the utilization, regeneration, and plantin... more A potential solution to land degradation is to promote the utilization, regeneration, and planting of the native legume tree, Acacia senegal, which is the main species in the world producing the internationally traded gum-arabic. This tree species is very important for the livelihoods of many rural populations and has potential for wider use. Sarr et al. (2005a) assessed the rhizobial
International Journal of Biological and Chemical Sciences, 2013
Une typologie des palmeraies villageoises du département du Plateau au sud-est du Bénin a été éta... more Une typologie des palmeraies villageoises du département du Plateau au sud-est du Bénin a été établie à travers : i) une étude cartographique de la couverture pédologique et d'occupation des sols, ii) des entretiens semi-structurés en assemblée générale avec des groupes de producteurs choisis de façon aléatoire dans chaque commune, iii) des entretiens semi-structurés individuels avec quatre vingt dix producteurs dont les palmeraies sont installées sur les terres de barre et étudiées par une analyse factorielle des correspondances multiples. Les terres de barre sont les sols les plus plantés avec le palmier à huile et Adja-Ouèrè et Sakété constituent les communes de grosse production. Les palmeraies du département présentent i) des caractéristiques très peu variables : la densité de plantation, le précédent cultural, les pratiques d'association des cultures vivrières et d'utilisation des engrais et ii) des caractéristiques variables et spécifiques : la restitution des sous-produits de transformation et le recyclage des feuilles d'élagage des palmiers. Parmi les cinq modalités de gestion des feuilles d'élagage identifiées, l'exportation des feuilles est une pratique dominante dans le département. Sur les terres de barre, on retrouve quatre types de palmeraies qui se différencient par la superficie, les pratiques culturales et l'âge des palmeraies.
Page 291. Chapter 24 THE NEMATOPHAGOUS FUNGI HELPER BACTERIA (NHB): A NEW DIMENSION FOR THE BIOLO... more Page 291. Chapter 24 THE NEMATOPHAGOUS FUNGI HELPER BACTERIA (NHB): A NEW DIMENSION FOR THE BIOLOGICAL CONTROL OF ROOT KNOT NEMATODES BY TRAPPING FUNGI R. Duponnois1, JL Chotte1 ...
... It was silty clay (36% clay, 50% silt, 14% sand), with 22.1 g C kg −1 , 2.3 g N kg −1 , and a... more ... It was silty clay (36% clay, 50% silt, 14% sand), with 22.1 g C kg −1 , 2.3 g N kg −1 , and a pH of 8.9. The experimental site was a plot (65 m width, 83 m length) at the experimental station of Sidi Ahmed Essaleh in North-West Tunisia (35°43′N,/8°35′E, alt. ...
Lessons learned from Long-term Soil Fertility Management Experiments in Africa, 2012
Soil fertility decline is increasingly leading to reduced food production worldwide. Over 70% of ... more Soil fertility decline is increasingly leading to reduced food production worldwide. Over 70% of small holder farmers in the central highlands of Kenya are using crop manure, animal wastes and inorganic fertilizers to increase their farms’ fertility and subsequent productivity. The dilemma with these practices is that less is known on the impact of these resources on the below ground biodiversity particularly the microbial communities which play a key role in determining soil quality. A study was carried out on a 32 year old long-term trial in Kabete, Kenya. These soils were treated with organic (maize stover at 10 t ha−, farmyard manure at 10 t ha−) and inorganic fertilizers (120 kg N, 52.8 kg P plus farmyard manure at 10 t ha−1 (N2P2 + FYM), 120 kg N, 52.8 kg P plus maize stover at 10 t ha−1 (N2P2 + R), 120 kg N, 52.8 kg P (N2P2), and a control (Nil and fallow) for over 30 years. We examined 16S rRNA gene and 28S rRNA gene fingerprints of bacterial and fungal communities, respectively, by PCR amplification and denaturing gradient gel electrophoresis (PCR-DGGE) separation. Bacterial community structure and diversity were negatively affected by N2P2, as evidenced by changes in the PCR-DGGE banding patterns. Bacterial community structure in the N2P2-treated soil was more closely related to the bacterial structure in the untreated soil (fallow and Nil) than that in soils treated with a combination of inorganic and organic or inorganic fertilizers alone. For the fungal community the negative effect of N2P2 alone was not as adverse as for the bacterial community structure since the soils treated with N2P2 were closely related to those treated with N2P2 + FYM and N2P2 + maize stover. However, soils treated with organic inputs clustered away from soils amended with inorganic inputs. Organic inputs had a positive effect on both fungal and bacterial community structures with or without chemical fertilizers. Results from this study suggested that bacterial and fungal community structure was closely related to agro-ecosystem management practices conducted for over the past 30 years.
Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soi... more Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N2O production. However, in the literature, there are numerous reports of net negative fluxes of N2O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise.Net N2O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N2O consumption. This fits in with denitrification as the responsible process, reducing N2O to N2. However, it has also been reported that nitrifiers consume N2O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N2O consumption, ranging from low to high temperat...
The objective of this work was to assess the effects of conventional tillage and of different dir... more The objective of this work was to assess the effects of conventional tillage and of different direct seeding mulch-based cropping systems (DMC) on soil nematofauna characteristics. The long-term field experiment was carried out in the highlands of Madagascar on an andic Dystrustept soil. Soil samples were taken once a year during three successive years (14 to 16 years after installation of the treatments) from a 0-5-cm soil layer of a conventional tillage system and of three kinds of DMC: direct seeding on mulch from rotation soybean-maize residues; direct seeding of maize-maize rotation on living mulch of silverleaf (Desmodium uncinatum); direct seeding of bean (Phaseolus vulgaris)-soybean rotation on living mulch of kikuyu grass (Pennisetum clandestinum). The samples were compared with samples from natural fallows. The soil nematofauna, characterized by the abundance of different trophic groups and indices (MI, maturity index; EI and SI, enrichment and structure indices), allowed ...
Acacia holosericea seedlings were planted in 1-l pots filled with a soil collected from an Austra... more Acacia holosericea seedlings were planted in 1-l pots filled with a soil collected from an Australian Acacia plantation in Southern Senegal. After 6 months of culture, mycorrhizosphere soil, roots, galls induced by root-knot nematodes and Rhizobium nodules were sampled from each pot. The diversity of this bacterial group was characterized by siderotyping (pyoverdine IsoElectric Focusing (IEF) analysis) and by restriction fragment length polymorphism (RFLP). The effect of these isolates on the establishment of the ectomycorrhizal symbiosis between an Australian Acacia (A. holosericea) and Pisolithus sp. strain IR100 was studied. In the mycorrhizosphere soil, the population of fluorescent pseudomonads was represented by strains of two different siderovars (groups of bacterial strains presenting an identical pyoverdine^IEF pattern): siderovar 1 (74%) and siderovar 2 (26%). The siderotyping of the isolates around galls of the root-knot nematodes revealed three siderovars (40% from siderovar 1, 40% from siderovar 2 and about 15% from siderovar 3). RFLP of 16S rDNA divided the isolates into four different groups with MspI, two with HhaI and two with HaeIII endonucleases. The establishment of the ectomycorrhizal symbiosis with A. holosericea was promoted by 14 bacterial strains isolated from the mycorrhizosphere soil, three isolates from the roots and four from the galls. Shoot biomass of A. holosericea seedlings was stimulated by eight bacterial isolates from soil, six isolates from galls and seven from roots. These mycorrhiza helper bacteria could have a great ecological importance in tropical areas through the reforestation programs.
Pasteuria penetrans, a bacterial parasite of plantparasitic nematodes, is used to control root-kn... more Pasteuria penetrans, a bacterial parasite of plantparasitic nematodes, is used to control root-knot nematode Meloidogyne spp. populations in vegetable crops. But its efficiency is variable, mostly because of the patchy distribution of the bacteria in arable fields. As the infective P. penetrans are non-motile bacteria in soil, abiotic soil factors can affect the bacteria-nematode relationships. An epidemiological study, conducted in a vegetable field, showed that abiotic factors such as irrigation, soil water holding capacity and texture, affected the efficiency of P. penetrans. A correspondence analysis between these abiotic factors and the density of P. penetrans spores in the soil, and the proportion of Meloidogyne javanica juveniles infected by the bacteria, revealed that irrigation affected directly the distribution of the spores in soil pores related to their passive transport by water flow. Laboratory experiments conducted on the passive transport of spores confirmed that intensive irrigation leached the spores down the soil profile and decreased the percentage of infected Meloidogyne juveniles.
In tropical ecosystems, termite mound soils constitute an important soil compartment covering aro... more In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites ( Cubitermes niokoloensis ) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revea...
Tropical sandy soils (or upper sandy horizons of tropical soils) have diverse physical and chemic... more Tropical sandy soils (or upper sandy horizons of tropical soils) have diverse physical and chemical constraints: poor structural stability (making soils sensitive to crusting, and compaction), poor nutrient holding capacity and low cation exchange capacity. In these soils, in which the clay content is low (3 to 15% by mass), organic matter is the main determinant of fertility, nutrient storage, aggregate stability, microbial and enzymatic activities. However, cultural practices or land uses aimed at increasing organic matter stocks have a minor impact if compared with the potential storage of organic matter in clayey soils. Nevertheless, this stock increase is possible in sandy soils and is mainly linked with the increase of the "vegetal debris" functional pool. Like organic matter, the abundance, activity, and diversity of soil biota are largely dependent upon land management. In these soils, biotic interactions such as termites-microorganisms or nematodesmicroorganisms modify nutrient fluxes, N mineralization being higher in soil-feeding termite mounds or in the presence of bacterial feeding nematodes. Moreover, the management of organic residues represents a means to control the activity of soil microorganisms and the structure of nematode and other fauna populations. An adequate management of organic matter (through fallows, improved fallows, pastures, external organic inputs) through its consequences on soil biofunctioning, largely determines the agronomic (plant production) and environmental (carbon sequestration) potentials of sandy soils. In the present paper, we provide information on the biofunctioning in sandy soils, i.e., interactions existing between organic matter, biological activities (termites, earthworms, nematodes, microorganisms) and physical soil properties, in natural and cropped ecosystems. Data mainly originate from experiments and measurements from West (Senegal, Burkina Faso, Ivory Coast) and East (Kenya) Africa.
2015 was the United Nations International Year of Soils and, for the first time, soils and the li... more 2015 was the United Nations International Year of Soils and, for the first time, soils and the life within them were in the spotlight globally. An international group of experts and scientists from the European Commission’s Joint Research Centre (JRC), in close collaboration with colleagues from the Commission’s Directorate-General for the Environment and the Global Soil Biodiversity Initiative, have produced the first ever Global Soil Biodiversity Atlas. Soils are vital for human survival and underpin many sectors of our economy. It is estimated that 99% of the world’s food comes from the terrestrial environment. But soils are also home to over a quarter of global biodiversity. Millions of soil-dwelling organisms promote essential ecosystem services – from plant growth to food production. They support biodiversity, benefit human health, promote the regulation of nutrient cycles that in turn influence climate, and represent an unexplored capital of natural sources. Our knowledge of ...
Environment promotes environmentally sound practices globally and in its own activities. This pub... more Environment promotes environmentally sound practices globally and in its own activities. This publication is printed on 100% recycled paper, using vegetable-based inks and other ecofriendly practices. Our distribution policy aims to reduce UN Environment's carbon footprint. About the International Resource Panel The International Resource Panel (IRP), a global scientific panel hosted by the United Nations Environment Programme, was created in 2007 to contribute to a better understanding of sustainable development from a natural resources perspective. It provides science-based policy options on how to decouple economic growth from environmental degradation while enhancing human well-being. With more than 20 scientific publications, the work of the panel has shed light on growing environmental challenges related to natural resources, their socioeconomic implications and potential new pathways towards their sustainable management. What is an IRP think piece? An IRP think piece is a technical or policy paper based on IRP scientific studies and assessments and other relevant literature. It is not a full study and assessment but a collection of science-based reflections, which may catalyze the generation of new scientific knowledge and highlight critical topics to be considered in policy discourse.
A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types... more A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types of biogenic structures: earthworm casts and crop sheetings built by two fungus-growing termites (Ancistrotermes guineensis and Odontotermes nilensis) and compared to the neighbouring soil in a mango orchard in the This region of Senegal. A principal component analysis shows clearly that the biogenic structures were differentiated from the neigbhouring soils in their content of organic components. The amino sugar contents of biogenic structures were 3-5 times higher than those measured in soil. In these structures, an increase in the contents of phenols and proteins was also observed. In contrast, their physical and chemical characteristics (texture, cationic exchanges capacity) were little different from those of the soil with the exception of their much lower waterretention capacity. Differences were also noted between the biogenic structures: the structures built by the two species of termite show more similarities with each other than with the casts. This result was confirmed by a similarity dendrogram which was used to graduate oppositions between samples. Casts were different from termite sheetings primarily in their C and N contents which were twice as high. Conversely, the contents of proteins in termite sheetings were higher than those measured in casts. Altogether, the results suggest that, in the biogenic structures, the organic content is stored and protected from mineralization.
Bacterial-feeding nematodes constitute one of the primary grazers of soil bacteria. We investigat... more Bacterial-feeding nematodes constitute one of the primary grazers of soil bacteria. We investigated the effects of selective grazing of a representative nematode (Zeldia punctata, Cephalobidae) on nematode life history and population biology and on the soil microbial community. Firstly, we measured (i) the effect of five different bacterial strains on the nematode life cycle using petri dishes and (ii) the impact of bacterial inoculation on nematode population growth in a soil microcosm. Selection of the five bacterial strains was based on morphology, cell-wall characteristics and mucus production. Z. punctata development was strongly affected by the type of bacteria ingested, independent of experimental design. Bacterial cell-wall characteristics seemed to directly affect Z. punctata development since high nematode densities were only reached with gram-negative strains (Pseudomonas monteilii and Methylobacterium nodulans). In petri dishes, the filamentous organisms (Actinomyces sp.) and mucus-producing bacteria (Bradyrhizobium sp.) led to the least reproduction. Duration of the various nematode life phases (egg, juvenile, reproductive stage and non-reproductive stage) was significantly affected by the bacterial food source. Total life span varied from 12.5 days (Bradyrhizobium sp.) to 40 days (Pseudomonas monteilii). Secondly, we monitored the influence of Z. punctata on the indigenous soil microbial community in the presence or absence of a maize plantlet. Nematode inoculation led to an increase in bacterial activity (as measured by alkaline phosphatase activity) but did not significantly influence bacterial biomass. The genetic fingerprint (DGGE) of soil bacteria was more influenced by plant presence than by nematode inoculation. Nematode activity has important repercussions on N flux in the soil since inoculation of Z. punctata in the absence of plants resulted in a net increase of N mineralization (2 mg N per pot) while a decrease of mineral N (0.5 mg N per pot) was observed in the absence of the nematodes, due to bacterial immobilization. This study underscores the close relationship between selective bacterial grazing and nematode development. Nevertheless, the impact of nematode grazing on the overall soil microbial community seems to primarily affect microbial activity and relative dominance rather than microbial diversity.
Current Plant Science and Biotechnology in Agriculture, 2008
A potential solution to land degradation is to promote the utilization, regeneration, and plantin... more A potential solution to land degradation is to promote the utilization, regeneration, and planting of the native legume tree, Acacia senegal, which is the main species in the world producing the internationally traded gum-arabic. This tree species is very important for the livelihoods of many rural populations and has potential for wider use. Sarr et al. (2005a) assessed the rhizobial
International Journal of Biological and Chemical Sciences, 2013
Une typologie des palmeraies villageoises du département du Plateau au sud-est du Bénin a été éta... more Une typologie des palmeraies villageoises du département du Plateau au sud-est du Bénin a été établie à travers : i) une étude cartographique de la couverture pédologique et d'occupation des sols, ii) des entretiens semi-structurés en assemblée générale avec des groupes de producteurs choisis de façon aléatoire dans chaque commune, iii) des entretiens semi-structurés individuels avec quatre vingt dix producteurs dont les palmeraies sont installées sur les terres de barre et étudiées par une analyse factorielle des correspondances multiples. Les terres de barre sont les sols les plus plantés avec le palmier à huile et Adja-Ouèrè et Sakété constituent les communes de grosse production. Les palmeraies du département présentent i) des caractéristiques très peu variables : la densité de plantation, le précédent cultural, les pratiques d'association des cultures vivrières et d'utilisation des engrais et ii) des caractéristiques variables et spécifiques : la restitution des sous-produits de transformation et le recyclage des feuilles d'élagage des palmiers. Parmi les cinq modalités de gestion des feuilles d'élagage identifiées, l'exportation des feuilles est une pratique dominante dans le département. Sur les terres de barre, on retrouve quatre types de palmeraies qui se différencient par la superficie, les pratiques culturales et l'âge des palmeraies.
Page 291. Chapter 24 THE NEMATOPHAGOUS FUNGI HELPER BACTERIA (NHB): A NEW DIMENSION FOR THE BIOLO... more Page 291. Chapter 24 THE NEMATOPHAGOUS FUNGI HELPER BACTERIA (NHB): A NEW DIMENSION FOR THE BIOLOGICAL CONTROL OF ROOT KNOT NEMATODES BY TRAPPING FUNGI R. Duponnois1, JL Chotte1 ...
... It was silty clay (36% clay, 50% silt, 14% sand), with 22.1 g C kg −1 , 2.3 g N kg −1 , and a... more ... It was silty clay (36% clay, 50% silt, 14% sand), with 22.1 g C kg −1 , 2.3 g N kg −1 , and a pH of 8.9. The experimental site was a plot (65 m width, 83 m length) at the experimental station of Sidi Ahmed Essaleh in North-West Tunisia (35°43′N,/8°35′E, alt. ...
Lessons learned from Long-term Soil Fertility Management Experiments in Africa, 2012
Soil fertility decline is increasingly leading to reduced food production worldwide. Over 70% of ... more Soil fertility decline is increasingly leading to reduced food production worldwide. Over 70% of small holder farmers in the central highlands of Kenya are using crop manure, animal wastes and inorganic fertilizers to increase their farms’ fertility and subsequent productivity. The dilemma with these practices is that less is known on the impact of these resources on the below ground biodiversity particularly the microbial communities which play a key role in determining soil quality. A study was carried out on a 32 year old long-term trial in Kabete, Kenya. These soils were treated with organic (maize stover at 10 t ha−, farmyard manure at 10 t ha−) and inorganic fertilizers (120 kg N, 52.8 kg P plus farmyard manure at 10 t ha−1 (N2P2 + FYM), 120 kg N, 52.8 kg P plus maize stover at 10 t ha−1 (N2P2 + R), 120 kg N, 52.8 kg P (N2P2), and a control (Nil and fallow) for over 30 years. We examined 16S rRNA gene and 28S rRNA gene fingerprints of bacterial and fungal communities, respectively, by PCR amplification and denaturing gradient gel electrophoresis (PCR-DGGE) separation. Bacterial community structure and diversity were negatively affected by N2P2, as evidenced by changes in the PCR-DGGE banding patterns. Bacterial community structure in the N2P2-treated soil was more closely related to the bacterial structure in the untreated soil (fallow and Nil) than that in soils treated with a combination of inorganic and organic or inorganic fertilizers alone. For the fungal community the negative effect of N2P2 alone was not as adverse as for the bacterial community structure since the soils treated with N2P2 were closely related to those treated with N2P2 + FYM and N2P2 + maize stover. However, soils treated with organic inputs clustered away from soils amended with inorganic inputs. Organic inputs had a positive effect on both fungal and bacterial community structures with or without chemical fertilizers. Results from this study suggested that bacterial and fungal community structure was closely related to agro-ecosystem management practices conducted for over the past 30 years.
Uploads
Papers by J. Chotte