Earthworm management in tropical agroecosystems

The effects of earthworms on soil structure and the resulting physical properties in natural or cultivated systems were studied in different sites of the Macrofauna project. Four main results were obtained from these experiments : (1) In kaolinitic soils (Lamto, Manaus, Yurimaguas), irrespective of clay content, andogeic earthworms play a major role in soil structure formation and maintenance, while in smectitic soils (Martinique), the effects of earthworms on soil structure formation and maintenance are not as clear. In the Vertisols of Martinique, the effect of roots and organic materials seem predominant in soil structure development and earthworms play a secondary role. (2) Endogeic earthworm species have different effects on soil properties. Large earthworms such as #Pontoscolex corethrurus or #Millsonia anomala egest large and compact casts. They increase the proportion of large aggregates in soil and the bulk density ; they are called "compacting species". Conversely, small earthworm species such as eudrilid worms feed at least partly on large compact casts and egest smaller and fragile aggregates. They decrease the proportion of large aggregates in soil and the bulk density ; they are called "decompacting species". The effects of "compacting species" on soil structure formation seem to be linked to the presence of organic residues at the soil surface. In agroecosystems of Yurimaguas (Peru), the intense activity of #P. corethrurus$ and the coalescence of surface casts lead to the formation of a compact surfacecrust with impedes water infiltration in the absence of organic residues, but a favourable macroaggregate structure develops in the presence of organic residues and leguminous mulch. (3) The introduction of earthworms in agroecosystems changes soil physical properties and especially water retention and infiltration... (D'après résumé d'auteur

Earthworm management in tropical agroecosystems

Data of 145 and 69 earthworm communities from managed and natural ecosystems, respectively, of four continents and 15 tropical countries were analysed. The aim of the study was to separate the influence of phylogenetic, environmental and agricultural factors on the structure of earthworm communities in agroecosystems, and to evaluate their relative importance in the whole soil macrofauna community. Earthworms comprise 40-90% of macrofaunal biomass in most ecosystems except for annually cropped systems. Three major conclusions were drawn from the analysis of community structure (regional analysis) : (i) crops were, independently of region, characterized by a loss of native species and by the dominance of exotic endogeics ; (ii) pastures were highly heterogenous in terms of native or exotic species dominance ; (iii) native species survived better in management ecosystems of India and Africa than in Mexico-Central America. Local analysis in selected countries indicated that, as a general rule, the intensity of agricultural practices is negatively correlated with the amount of native species and the total abundance and biomass of earthworms ; the only exception was found in the conversion of savannas to pastures, in Colombian llanos. (Résumé d'auteur

Earthworm management in tropical agroecosystems

Collaborative research in the Macrofauna project has enabled development of some techniques that presently are at different stages of advancement, from promising pilot experiments (tomato production and inoculation in plant nursery bags at Yurimaguas and in India) to the fully developed technique of massive worm production and biofertilization of tea gardens in Tamil Nadu (India) (patent deposited). Failures have also helped to gain better insight into the potential feasibility of techniques that had been considered in the objectives of this project. Endogeic earthworms (#Pontoscolex corethrurus$) may be produced in large quantities, i.e.about 12000 worms (1.6-2.8 kg live wt)/m2/year in specific culture beds using either sawdust (Yurimaguas, Peru) or a mixture of high and low quality materials (Tamil Nadu, India) mixed into soil as substrates. Cost of production of 1 kg of earthworm biomass through bed culture is about 3.6 Euro, much lower than the cost of hand collection of worms from pastures/grasslands where these species are abundant (6-125 Euro depending on the cost of labour and earthworm density). The theorical value of an active earthworm community with an average biomass of 400 kg live wt has been estimated at 1400 Euro, the price that it would cost to reintroduce an equivalent biomass produced in our culture units, indicating the cost of land restoration. Direct inoculation of earthworms in the field to improve production may only affect plant growth positively if a large biomass (greater than 30 g live wt/m2) is inoculated from the beginning. An alternative may be to concentrate the inoculum in small areas regularly distributed across the field... (D'après résumé d'auteur

Earthworm management in tropical agroecosystems

Ecological and demographic parameters of 26 species of native and exotic earthworms species common in tropical agroecosystems, with large environmental tolerance and/or extended distribution were investigated. Principal component analysis (PCA) isolated four groups : (i) large native endogeic and anecic species (16-32 g individual fresh wt) with long generation time (2-4 years), low fecundity (0.5-3.1 cocoons/year/adult) and one hatchling per cocoon ; (ii) medium size species (1.2-6 g) endogeic mesohumic, with intermediate fecundity (1.3-45 cocoons/year/adult) ; (iii) small species (0.17-1.25 g f.w.) mainly endogeic polyhumic, with short generation time (3-7 months), intermediate fecundity (10-68 cocoons/year/adult) and one hatchling per cocoon ; and (iv) generally small (80-150 mg f.w.) species mainly exotic and epigeic, with short generation time (1-3 months), very high fecundity (50-350 cocoons/year/adult) and up to three hatchlings per cocoon. Casts may be either large globular or small granular. The selective investigations of large organic particles and small mineral particles (clays) concentrates total organic matter in the casts. There is an intense mineralization rate of nitrogen in the casts (6-29% of organic N), exotic worms seeming to be less efficient than natives at mineralizing N. The mineral phosphorus content of casts is always at least 30% higher than in the non-ingested soil. All these worms ingest daily, on average, three times their own weight of soil at the adult stage (1-9) and much more when juvenile ; up to 1000 Mg dry soil/ha may transit yearly through earthworm guts. (Résumé d'auteur

Indicadores de qualidade do solo em sistemas de cultivo orgânico e convencional no semi-árido Cearense.

A qualidade do solo pode mudar com o passar do tempo, em decorrência de eventos naturais ou ações antrópicas. A adoção de práticas de cultivo orgânico reduz o revolvimento do solo, favorecendo a recuperação de suas propriedades físicas e químicas. Este trabalho teve como objetivo comparar propriedades físicas,químicas e biológicas de solos cultivados com algodão em bases orgânicas e no sistema convencional, assim como identificar as que possam ser utilizadas como indicadores de qualidade do solo. Selecionaram-se seis áreas submetidas ao cultivo orgânico e três ao cultivo convencional para coleta de amostras de solo deformadas e indeformadas, nas camadas de 0–10, 10–20 e 20–30 cm. Técnicas de estatística univariada e multivariada foram utilizadas para análise dos dados. Os resultados mostraram que os indicadores físicos e químicos testados individualmente não foram sensíveis para diferenciar as áreas sob sistema de cultivo orgânico daquelas sob cultivo convencional. No entanto, a aplicação de técnicas de análise multivariada – no caso, componentes principais e a discriminante de Anderson – permitiu a distinção entre algumas áreas cultivadas sob cultivo orgânico comparativamente às convencionais, até mesmo as que estavam em transição.Dos indicadores biológicos, a fauna edáfica mostrou-se mais precisa na avaliação da qualidade do solo, distinguindo de forma satisfatória as áreas sob sistema de cultivo orgânico das que estavam sob sistema convencional

Influence of Olfactory Epithelium on Mitral/Tufted Cell Dendritic Outgrowth

Stereotypical connections between olfactory sensory neuron axons and mitral cell dendrites in the olfactory bulb establish the first synaptic relay for olfactory perception. While mechanisms of olfactory sensory axon targeting are reported, molecular regulation of mitral cell dendritic growth and refinement are unclear. During embryonic development, mitral cell dendritic distribution overlaps with olfactory sensory axon terminals in the olfactory bulb. In this study, we investigate whether olfactory sensory neurons in the olfactory epithelium influence mitral cell dendritic outgrowth in vitro. We report a soluble trophic activity in the olfactory epithelium conditioned medium which promotes mitral/tufted cell neurite outgrowth. While the trophic activity is present in both embryonic and postnatal olfactory epithelia, only embryonic but not postnatal mitral/tufted cells respond to this activity. We show that BMP2, 5 and 7 promote mitral/tufted cells neurite outgrowth. However, the BMP antagonist, Noggin, fails to neutralize the olfactory epithelium derived neurite growth promoting activity. We provide evidence that olfactory epithelium derived activity is a protein factor with molecular weight between 50–100 kD. We also observed that Follistatin can effectively neutralize the olfactory epithelium derived activity, suggesting that TGF-beta family proteins are involved to promote mitral/tufted dendritic elaboration

DLK1 Is a Somato-Dendritic Protein Expressed in Hypothalamic Arginine-Vasopressin and Oxytocin Neurons

Delta-Like 1 Homolog, Dlk1, is a paternally imprinted gene encoding a transmembrane protein involved in the differentiation of several cell types. After birth, Dlk1 expression decreases substantially in all tissues except endocrine glands. Dlk1 deletion in mice results in pre-natal and post-natal growth deficiency, mild obesity, facial abnormalities, and abnormal skeletal development, suggesting involvement of Dlk1 in perinatal survival, normal growth and homeostasis of fat deposition. A neuroendocrine function has also been suggested for DLK1 but never characterised. To evaluate the neuroendocrine function of DLK1, we first characterised Dlk1 expression in mouse hypothalamus and then studied post-natal variations of the hypothalamic expression. Western Blot analysis of adult mouse hypothalamus protein extracts showed that Dlk1 was expressed almost exclusively as a soluble protein produced by cleavage of the extracellular domain. Immunohistochemistry showed neuronal DLK1 expression in the suprachiasmatic (SCN), supraoptic (SON), paraventricular (PVN), arcuate (ARC), dorsomedial (DMN) and lateral hypothalamic (LH) nuclei. DLK1 was expressed in the dendrites and perikarya of arginine-vasopressin neurons in PVN, SCN and SON and in oxytocin neurons in PVN and SON. These findings suggest a role for DLK1 in the post-natal development of hypothalamic functions, most notably those regulated by the arginine-vasopressin and oxytocin systems