Host taxonomy determines the composition, structure, and diversity of the earthworm cast microbiome under homogenous feeding conditions

Host evolutionary history is a key factor shaping the earthworm cast microbiome, although its effect can be shadowed by the earthworm's diet. To untangle dietary from taxon effects, we raised nine earthworm species on a uniform diet of cow manure and compared cast microbiome across species while controlling for diet. Our results showed that, under controlled laboratory conditions, earthworm microbiomes are species-specific, more diverse than that of the controlled diet, and mainly comprised of native bacteria (i.e., not acquired from the diet). Furthermore, diet has a medium to large convergence effect on microbiome composition since earthworms shared 16 to 74% of their bacterial amplicon sequence variants (ASV). The inter-species core microbiome included 10 ASVs, while their intra-species core microbiomes were larger and varied in ASV richness (24-48%) and sequence abundance across earthworm species. This specificity in core microbiomes and variable degree of similarity in bacterial composition suggest that phylosymbiosis could determine earthworm microbiome assembly. However, lack of congruence between the earthworm phylogeny and the microbiome dendrogram suggests that a consistent diet fed over several generations may have weakened potential phylosymbiotic effects. Thus, cast microbiome assembly in earthworms seem to be the result of an interplay among host phylogeny and diet.

Composition, Structure and Diversity of Soil Bacterial Communities before, during and after Transit through the Gut of the Earthworm Aporrectodea caliginosa

Earthworms heavily modify the soil microbiome as it passes throughout their guts. However, there are no detailed studies describing changes in the composition, structure and diversity of soil microbiomes during gut transit and once they are released back to the soil as casts. To address this knowledge gap, we used 16S rRNA next-generation sequencing to characterize the microbiomes of soil, gut and casts from the earthworm Aporrectodea caliginosa. We also studied whether these three microbiomes are clearly distinct in composition or can be merged into metacommunities. A large proportion of bacteria was unique to each microbiome—soil (82%), gut (89%) and casts (75%), which indicates that the soil microbiome is greatly modified during gut transit. The three microbiomes also differed in alpha diversity, which peaked during gut transit and decreased in casts. Furthermore, gut transit also modified the structure of the soil microbiome, which clustered away from those of the earthworm gut and cast samples. However, this clustering pattern was not supported by metacommunity analysis, which indicated that soil and gut samples make up one metacommunity and cast samples another. These results have important implications for understanding the dynamics of soil microbial communities and nutrient cycles.

Bacterial Succession during Vermicomposting of Silver Wattle (Acacia dealbata Link)

Vermicomposting is the process of organic waste degradation through interactions between earthworms and microbes. A variety of organic wastes can be vermicomposted, producing a nutrient-rich final product that can be used as a soil biofertilizer. Giving the prolific invasive nature of the Australian silver wattle Acacia dealbata Link in Europe, it is important to find alternatives for its sustainable use. However, optimization of vermicomposting needs further comprehension of the fundamental microbial processes. Here, we characterized bacterial succession during the vermicomposting of silver wattle during 56 days using the earthworm species Eisenia andrei. We observed significant differences in α- and β-diversity between fresh silver wattle (day 0) and days 14 and 28, while the bacterial community seemed more stable between days 28 and 56. Accordingly, during the first 28 days, a higher number of taxa experienced significant changes in relative abundance. A microbiome core composed of 10 amplicon sequence variants was identified during the vermicomposting of silver wattle (days 14 to 56). Finally, predicted functional profiles of genes involved in cellulose metabolism, nitrification, and salicylic acid also changed significantly during vermicomposting. This study, hence, provides detailed insights of the bacterial succession occurring during vermicomposting of the silver wattle and the characteristics of its final product as a sustainable plant biofertilizer.

Gut microbiome and telomere length in gull hatchlings

In many animals, recent evidence indicates that the gut microbiome may be acquired during early development, with possible consequences on newborns' health. Thus, it has been hypothesized that a healthy microbiome protects telomeres and genomic integrity against cellular stress. However, the link between the early acquired microbiome and telomere dynamics has not hitherto been investigated. In birds, this link may also be potentially modulated by the transfer of maternal glucocorticoids, since these substances dysregulate microbiome composition during postnatal development. Here, we examined the effect of the interplay between the microbiome and stress hormones on the telomere length of yellow-legged gull hatchlings by using a field experiment in which we manipulated the corticosterone content in eggs. We found that the hatchling telomere length was related to microbiome composition, but this relationship was not affected by the corticosterone treatment. Hatchlings with a microbiome dominated by potential commensal bacteria (i.e. Catellicoccus and Cetobacterium) had larger telomeres, suggesting that an early establishment of the species-specific microbiome during development may have important consequences on offspring health and survival.

Temporal Dynamics of Bacterial Communities in a Pilot-Scale Vermireactor Fed with Distilled Grape Marc

Vermicomposting has been found as a profitable approach to dispose of and treat large quantities of raw grape marc. However, less information is available with regard to its efficiency for treating distillery winery byproducts, even though distillation has been widely used as a way to economically valorize grape marc. As such, we sought to characterize the compositional and functional changes in bacterial communities during vermicomposting of distilled grape marc by using 16S rRNA high-throughput sequencing. Samples were collected at the initiation of vermicomposting and at days 14, 21, 28, 35 and 42. There were significant changes (p < 0.0001) in the bacterial community composition of distilled grape marc after 14 days of vermicomposting that were accompanied by twofold increases in bacterial richness and diversity from a taxonomic and phylogenetic perspective. This was followed by significant increases in functional diversity of the bacterial community, including metabolic capacity, lignin and cellulose metabolism, and salicylic acid synthesis. These findings indicate that the most striking compositional and functional bacterial community changes took place during the active phase of the process. They also pinpoint functional attributes that may be related to the potential beneficial effects of distilled grape marc vermicompost when applied on soil and plants.

Changes in the composition and function of bacterial communities during vermicomposting may explain beneficial properties of vermicompost

Vermicomposting is the process by which organic waste is broken down through the synergistic actions of earthworms and microbial communities. Although vermicomposting has been shown to effectively reduce organic biomass and generate high-quality fertilizer for plants, little is known about the bacterial communities that are involved in this decomposition process. Since optimization of vermicomposting for commercial use necessitates additional knowledge of the underlying biological processes, this study sought to characterize the bacterial succession involved in the vermicomposting of Scotch broom (Cytisus scoparius), a leguminous shrub that has become invasive around the world with consequences for the dynamics and productivity of the ecosystems they occupy. Scotch broom was processed in a pilot-scale vermireactor for 91 days with the earthworm species Eisenia andrei. Samples were taken at the initiation of vermicomposting, and days 14, 42 and 91, representing both active and mature stages of vermicomposting. Significant changes (P < 0.0001) in the bacterial community composition (richness and evenness) were observed throughout the process. Increases in taxonomic diversity were accompanied by increases in functional diversity of the bacterial community, including metabolic capacity, streptomycin and salicylic acid synthesis, and nitrification. These results highlight the role of bacterial succession during the vermicomposting process and provide evidence of microbial functions that may explain the beneficial effects of vermicompost on soil and plants.

Multigene phylogeny reveals a new Iranian earthworm genus (Lumbricidae: Philomontanus) with three new species

Lumbricidae taxonomy is vastly restricted by the morphological simplicity of earthworms and their lack of complex appendices. This has led to confusing results in the Lumbricidae classifications, which in turn, has hindered our ability to identify and assign new and cryptic species to the family. Here we propose the addition of a new Lumbricidae genus from the Zagros and Elburz Mountains of Iran, i.e. Philomontanus gen. nov, including three new species. Our taxonomic inferences were based on the phylogenetic analysis of two nuclear gene regions (28S rDNA and 18S rDNA) and 11 mitochondrial gene regions (16S rDNA, 12S rDNA, NADH dehydrogenase I, cytochrome oxidase subunits I and II and tRNAs Asn, Asp, Val, Leu, Ala and Ser). Philomontanus gen. nov comprises the earthworm species Philomontanus sarii sp. nov., Philomontanus mahmoudi sp. nov. and Philomontanus baloutchi sp. nov. These three species are morphologically similar to each other with only a few characters separating them (e.g. size, pigmentation and position of clitellum). Our findings support the adoption of an integrative approach including molecular information (e.g., DNA sequences) to aid earthworm classification and develop a robust taxonomy.

Diversity, structure and sources of bacterial communities in earthworm cocoons

Animals start interactions with the bacteria that will constitute their microbiomes at embryonic stage. After mating, earthworms produce cocoons externally which will be colonized with bacteria from their parents and the environment. Due to the key role bacterial symbionts play on earthworm fitness, it is important to study bacterial colonization during cocoon formation. Here we describe the cocoon microbiome of the earthworms Eisenia andrei and E. fetida, which included 275 and 176 bacterial species, respectively. They were dominated by three vertically-transmitted symbionts, Microbacteriaceae, Verminephrobacter and Ca. Nephrothrix, which accounted for 88% and 66% of the sequences respectively. Verminephrobacter and Ca. Nephrothrix showed a high rate of sequence variation, suggesting that they could be biparentally acquired during mating. The other bacterial species inhabiting the cocoons came from the bedding, where they accounted for a small fraction of the diversity (27% and 7% of bacterial species for E. andrei and E. fetida bedding). Hence, earthworm cocoon microbiome includes a large fraction of the vertically-transmitted symbionts and a minor fraction, but more diverse, horizontally and non-randomly acquired from the environment. These data suggest that horizontally-transmitted bacteria to cocoons may play an important role in the adaptation of earthworms to new environments or diets.

Glucocorticoids modulate gastrointestinal microbiome in a wild bird

It has recently been hypothesized that stress exposure (e.g. via glucocorticoid secretion) may dysregulate the bacterial gut microbiome, a crucial 'organ' in animal health. However, whether stress exposure (e.g. via glucocorticoid secretion) affects the bacterial gut microbiome of natural populations is unknown. We have experimentally altered the basal glucocorticoid level (corticosterone implants) in a wild avian species, the yellow-legged gull Larus michahellis, to assess its effects on the gastrointestinal microbiota. Our results suggest underrepresentation of several microbial taxa in the corticosterone-implanted birds. Importantly, such reduction included potentially pathogenic avian bacteria (e.g. Mycoplasma and Microvirga) and also some commensal taxa that may be beneficial for birds (e.g. Firmicutes). Our findings clearly demonstrate a close link between microbiome communities and glucocorticoid levels in natural populations. Furthermore, they suggest a beneficial effect of stress in reducing the risk of infection that should be explored in future studies.

Underground evolution: new roots for the old tree of lumbricid earthworms

Earthworms belonging to the family Lumbricidae are extremely abundant in terrestrial temperate regions. They affect soil properties and nutrient cycling, thus shaping plant community composition and aboveground food webs. Some lumbricids are also model organisms in ecology and toxicology. Despite the intense research efforts dedicated to lumbricids over the last 130years, the evolutionary relationships and taxonomic classification of these organisms are still subject to great debate. Resolution of their systematics is hampered by the structural simplicity of the earthworm body plan and the existence of cryptic species. We sampled 160 earthworm specimens belonging to 84 lumbricid species (28 genera) and 22 Lumbricoidea outgroups, sequenced two nuclear genes, four mitochondrial genes and seven mitochondrial tRNAs and examined 22 morphological characters. We then applied a combination of phylogenetic methods to generate the first robust genus-level phylogeny of the Lumbricidae. Our results show that the current Lumbricidae classification and the underlying hypotheses of character evolution must be revised. Our chronogram suggests that lumbricids emerged in the Lower Cretaceous in the holarctic region and that their diversification has been driven by tectonic processes (e.g. Laurasia split) and geographical isolation. Our chronogram and character reconstruction analysis reveal that spermathecae number does not follow a gradual pattern of reduction and that parthenogenesis arose from sexual relatives multiple times in the group; the same analysis also indicates that both epigeic and anecic earthworms evolved from endogeic ancestors. These findings emphasize the strong and multiple changes to which morphological and ecological characters are subjected, challenging the hypothesis of character stasis in Lumbricidae.

An earthworm riddle: systematics and phylogeography of the Spanish lumbricid Postandrilus

Background

As currently defined, the genus Postandrilus Qui and Bouché, 1998, (Lumbricidae) includes six earthworm species, five occurring in Majorca (Baleares Islands, western Mediterranean) and another in Galicia (NW Spain). This disjunct and restricted distribution raises some interesting phylogeographic questions: (1) Is Postandrilus distribution the result of the separation of the Baleares-Kabylies (BK) microplate from the proto-Iberian Peninsula in the Late Oligocene (30–28 Mya) – vicariant hypothesis? (2) Did Postandrilus diversify in Spain and then colonize the Baleares during the Messinian salinity crisis (MSC) 5.96–5.33 Mya – dispersal hypothesis? (3) Is the distribution the result of a two-step process – vicariance with subsequent dispersal?

Methodology/Principal Findings

To answer these questions and assess Postandrilus evolutionary relationships and systematics, we collected all of the six Postandrilus species (46 specimens – 16 locations) and used Aporrectodea morenoe and three Prosellodrilus and two Cataladrilus species as the outgroup. Regions of the nuclear 28S rDNA and mitochondrial 16S rDNA, 12S rDNA, ND1, COII and tRNA genes (4,666 bp) were sequenced and analyzed using maximum likelihood and Bayesian methods of phylogenetic and divergence time estimation. The resulting trees revealed six new Postandrilus species in Majorca that clustered with the other five species already described. This Majorcan clade was sister to an Iberian clade including A. morenoe (outgroup) and Postandrilus bertae. Our phylogeny and divergence time estimates indicated that the split between the Iberian and Majorcan Postandrilus clades took place 30.1 Mya, in concordance with the break of the BK microplate from the proto-Iberian Peninsula, and that the present Majorcan clade diversified 5.7 Mya, during the MSC.

Conclusions

Postandrilus is highly diverse including multiple cryptic species in Majorca. The genus is not monophyletic and invalid as currently defined. Postandrilus is of vicariant origin and its radiation began in the Late Oligocene.

Selective reduction of the pathogenic load of cow manure in an industrial-scale continuous-feeding vermireactor

Vermicomposting is a suitable technology for processing different wastes, to produce a valuable end product (vermicompost). However, the pathogenic load of the waste must be greatly reduced in order to prevent risks to human health. Although Eisenia andrei may reduce the levels of several pathogens, the feasibility of vermicomposting, with regard to pathogen reduction, has not been tested on an industrial scale. This work studied whether vermicomposting in a continuous feeding vermireactor, is able to reduce the pathogenic load of cow manure. The effect of E. andrei on pathogens depended on the type of pathogen; thus, levels of Clostridium, total coliforms and Enterobacteria were not modified, but levels of faecal enterococci, faecal coliforms and Escherichia coli were reduced to acceptable levels. Pathogens could have maintained their levels in continuous feeding vermireactors, as fresh layers of manure are added to the top, which allows the vertical spread of pathogens through leaching.

Changes in microbial community structure and function during vermicomposting of pig slurry

Most studies investigating the effects of earthworms on microorganisms have focused on the changes before and after vermicomposting rather than those that occur throughout the process. In the present study, we designed continuous feeding reactors in which new layers of pig slurry (1.5 and 3 kg) were added sequentially to form an age gradient inside the reactors in order to evaluate the impact of the earthworm species Eisenia fetida on microbial community structure and function. The activity of earthworms greatly reduced the bacterial and fungal biomass and microbial diversity relative to the control values. However, the pronounced presence of earthworms in the younger layers stimulated microbial activity and as such increased carbon mineralization probably due to the fact that the microorganisms may have been less resource-limited as a result of earthworm activity, as indicated by the ratio of monounsaturated to saturated PLFAs.

Earthworm effects without earthworms: inoculation of raw organic matter with worm-worked substrates alters microbial community functioning

BACKGROUND

Earthworms are key organisms in organic matter decomposition because of the interactions they establish with soil microorganisms. They enhance decomposition rates through the joint action of direct effects (i.e. effects due to direct earthworm activity such as digestion, burrowing, etc) and indirect effects (i.e. effects derived from earthworm activities such as cast ageing). Here we test whether indirect earthworm effects affect microbial community functioning in the substrate, as when earthworms are present (i. e., direct effects).

METHODOLOGY/PRINCIPAL FINDINGS

To address these questions we inoculated fresh organic matter (pig manure) with worm-worked substrates (vermicompost) produced by three different earthworm species. Two doses of each vermicompost were used (2.5 and 10%). We hypothesized that the presence of worm-worked material in the fresh organic matter will result in an inoculum of different microorganisms and nutrients. This inoculum should interact with microbial communities in fresh organic matter, thus promoting modifications similar to those found when earthworms are present. Inoculation of worm-worked substrates provoked significant increases in microbial biomass and enzyme activities (β-glucosidase, cellulase, phosphatase and protease). These indirect effects were similar to, although lower than, those obtained in pig manure with earthworms (direct and indirect earthworm effects). In general, the effects were not dose-dependent, suggesting the existence of a threshold at which they were triggered.

CONCLUSION/SIGNIFICANCE

Our data reveal that the relationships between earthworms and microorganisms are far from being understood, and suggest the existence of several positive feedbacks during earthworm activity as a result of the interactions between direct and indirect effects, since their combination produces stronger modifications to microbial biomass and enzyme activity.

Substrate-induced respiration as a measure of microbial biomass in vermicomposting studies

Here it is evaluated the relationship between substrate-induced respiration (SIR) and microbial biomass C (C(mic), estimated by chloroform fumigation-extraction) in order to establish SIR as a quick technique to determine microbial biomass in vermicomposting processes. For this, there were designed continuous feeding reactors in which new layers of manure were added sequentially to form an age gradient inside the reactors. Six reactors were set up with and without earthworms (three reactors per treatment). In reactors, with and without earthworms, values of C(mic) and SIR ranged from 1690 to 42,900 microg g(-1)dw and from 43 to 2300 microg CO(2) h(-1)g(-1)dw, respectively. SIR was significantly related to C(mic) (r=0.63, P<0.0001). It is proposed an equation to convert SIR values into C(mic), SIR (microg CO(2) h(-1)g(-1)dw)=25.97+0.04 C(mic) (microg g(-1)dw) which will be useful for comparison between studies which used different techniques for determining microbial biomass.

Occupational isolation among general practitioners in Finland

BACKGROUND

It is proposed that isolation in general practice is one of the factors that leads to work-related stress and the low attraction of this work. In Finland, 71% of physicians who worked or had worked in a primary health care centre agreed with the statement 'working as a doctor in a health centre is too often isolated work'.

AIMS

To gain a deeper understanding of this feeling and to find out which factors constitute it.

METHODS

A qualitative in-depth interview study of 32 physicians working in a primary health care centre in Finland. Qualitative analysis of transcribed verbatim interviews using a constant comparison method.

RESULTS

The main components of isolation were making decisions alone, lack of collaboration with other workers in the health centre and secondary care specialists, not being a part of the work community and lack of mentoring at work.

CONCLUSIONS

Enabling flexible teamwork and social and professional support networks are the key issues in solving the problem of occupational isolation in general practice.

Reduction of total coliform numbers during vermicomposting is caused by short-term direct effects of earthworms on microorganisms and depends on the dose of application of pig slurry

During vermicomposting of organic waste, the interactions between epigeic earthworms and the detrital microbial community lead to decreases in the abundance of some potentially pathogenic microorganisms. Despite its importance, little is known about the mechanisms involved and the factors that affect the intensity of this effect. In the present study, we carried out three experiments to test the effect of the earthworm Eisenia fetida on total coliform numbers in pig slurry. We firstly applied low and high doses (1.5 and 3 kg, respectively) of pig slurry to small scale vermireactors with and without earthworms. We found that E. fetida significantly reduced total coliform numbers after 2 weeks, but only in the low dose vermireactors. In a subsequent feeding experiment in mesocosms, we observed that the coliform population was reduced by 98% after passage through the earthworms' guts, which suggests that digestive processes in the gut of E. fetida are the main factors involved in the decrease in total coliforms observed in the low dose vermireactors. Decreases in total coliform numbers were not related to decreases in bacterial biomass, which indicates a specific negative effect of earthworms on the coliforms. In the third experiment, we tested the indirect effect of earthworms on total coliforms by inoculating pig slurry with either 2 or 10% vermicompost. The addition of vermicompost did not affect the number of coliforms either after 15, 30 or 60 days, which supports the idea that this bacterial group is more affected by the passage through the gut of E. fetida than by interactions with the earthworm-shaped microbial community.

Changes in bacterial numbers and microbial activity of pig slurry during gut transit of epigeic and anecic earthworms

In soils, organic matter decomposition and stabilization largely occur as a result of microbial activity, although when present, earthworms are important drivers of the processes through their interactions with microflora which begin during organic matter digestion by earthworms. Here, we studied the effects of gut transit on the number of bacteria and the microbial activity in pig slurry, using three epigeic (Eisenia fetida, Eisenia andrei, Eudrilus eugeniae) and one anecic (Octodrilus complanatus) species of earthworm. Bacterial counts revealed that the effect of gut transit on microbes differed depending on the earthworm species. Thus, no changes in the number of bacteria were found in the gut contents of E. fetida and E. eugeniae, whereas large decreases were recorded in those of O. complanatus and E. andrei (2.7 and 1.3 times, respectively). We suggest that, unlike in the three epigeic earthworm species, microorganisms are preferentially utilized by O. complanatus to meet its nutrient requirements, because of its limited digestive capacity. Despite the decrease in bacterial numbers, there were no differences in the gut contents of the four earthworm species or undigested pig slurry in terms of dehydrogenase activity. Therefore, we suggest that after gut transit in the four earthworm species under study the potential microbial degradation of pig slurry remains unaltered.

Microbial and nutrient stabilization of two animal manures after the transit through the gut of the earthworm Eisenia fetida (Savigny, 1826)

Here we studied how the transit through the gut of the earthworm Eisenia fetida affects the microbial and nutrient stabilization of pig and cow manure, by analyzing fresh casts. Earthworms reduced the pools of dissolved organic C and N in casts from both types of manure, as wells as mineral N. Microbial biomass was enhanced only in casts from pig manure and did not change in casts from cow manure, and fungal populations only raised in casts from cow manure. Earthworms reduced microbial activity in casts from cow manure and did not modify in casts from pig slurry. Enzyme activities in casts also depended on the manure ingested; there were no changes in dehydrogenase and beta-glucosidase activities, whereas acid and alkaline phosphatases increased. The results indicate that the first stage in vermicomposting of pig and cow manure by E. fetida, i.e. casting, produced a microbial stabilization decreasing the activity of microorganisms; this stabilization occurred despite of the increase in microbial biomass. The strong reduction in nutrient pools of manures may be the responsible of this contradiction. These changes will influence the dynamics of the organic matter degradation by reducing forms of C and N available to microorganisms and hence restricting their growth and multiplication. Nevertheless, casts were also characterized by an increased enzyme potential that might lead to a further thorough degradation of pig and cow manure.

Optimizing vermicomposting of animal wastes: effects of rate of manure application on carbon loss and microbial stabilization

Vermicomposting is the process whereby organic residues are broken down by earthworms and microorganisms. Addition of manure has been shown to be of critical importance and determines most of the changes that take place during vermicomposting. Here, we study how the rate of manure applied affects microbial biomass and activity and carbon losses. For this, we designed continuous feeding reactors in which new layers of manure were added sequentially to form an age gradient inside the reactors. We compared two application rates of pig slurry (1.5 and 3 kg) and set up six reactors for each one; half of the 12 reactors initially contained a population of 500 earthworms (Eisenia fetida). We found that earthworms increased microbial biomass and were more active in reactors fed with 3 kg of slurry. However, the differential rates of respiration were not reflected in C losses. The results thus showed that loss of C was not affected by the rate of pig slurry applied. We conclude that despite the strong effect that the rate of manure has on microbe-earthworm relationships, it did not affect carbon losses. We therefore recommend the use of low application rates of manure when the objective is the microbial stabilization of the residue.

Eisenia fetida (Oligochaeta: Lumbricidae) modifies the structure and physiological capabilities of microbial communities improving carbon mineralization during vermicomposting of pig manure

Although microorganisms are largely responsible for organic matter decomposition, earthworms may also affect the rates of decomposition directly by feeding on and digesting organic matter and microorganisms, or indirectly affect them through their interactions with the microorganisms, basically involving stimulation or depression of the microbial populations. We tested the general hypothesis that microbial populations, and especially fungi, are enhanced by earthworm activity, and also whether earthworms are able to modify the biodiversity of microbial populations, and its relation to the function of the system. In addition, we examined the metabolic quotient and the effect of labile organic C to assess the relationships between earthworm and microbes. We found that decomposition of pig manure has two stages characterized by the presence or absence of earthworms. Thus, the presence of earthworms was related with increases in overall microbial biomass and activity, which decreased when earthworms left the substrate; the same pattern was observed for fungi. Furthermore, earthworms modified the physiological profiles of microbial communities of pig manure, increasing the diversity of substrates utilized. In addition, earthworms promoted a more efficient use of energy of microbial communities, as the metabolic quotient showed. The rate of carbon loss was almost twice where earthworms were present, revealing faster decomposition. Our data match with the recent findings that to maintain essential processes the functional properties of present species are at least as important as the number of species per se. This is in accordance with the "insurance hypothesis," which states that a large number of species is probably essential for maintaining stable processes in changing environments, as the presence of earthworms would have promoted in pig manure.

Earthworms strongly modify microbial biomass and activity triggering enzymatic activities during vermicomposting independently of the application rates of pig slurry

We studied the relationships between earthworm activity, microbial biomass and the activation and dynamics of several enzyme activities. We carried out an experiment in which low and high rates (1.5 and 3 kg respectively) of pig slurry were applied to small scale reactors with and without earthworms. We found that extracellular enzyme activity increased with rate of pig slurry. In both rates of pig slurry applied, the presence of earthworms in young layers stimulated microbial growth which decreased once earthworms left the slurry and the layers aged. This increase was related to the initial activation of the microbial enzymes studied as correlations between microbial biomass and enzymes showed, which indicated an increase of intracellular enzyme activity. In the aged slurry, the pattern of activity of the four enzymes assayed depended on the rate of pig slurry applied. Thus, in low rate reactors, enzymatic activity through layers appeared to be related to microbial biomass, but in high rate reactors the activity of enzymes was more or less continuous. Further, these differences in overall enzyme activity agree with the variation found in extracellular enzyme activity suggesting certain dependence on substrate availability.

Life cycle of the earthworm Octodrilus complanatus (Oligochaeta, Lumbricidae)

The earthworm Octodrilus complanatus (Dugès, 1828) is a large-sized species often found in grasslands and pastures, with a wide distribution area in Europe and North Africa. In order to determine the characteristics of its life cycle, earthworms of this species were cultured from hatching until they reached maturity. Development rates, cocoon production, and incubation period were recorded under controlled conditions. On average, individuals of O. complanatus reared in isolation from hatching reached maturity at day 150 and body weight at maturity ranged between 6 and 8 g. The cocoon incubation period was 66 days, and only one individual hatched from each cocoon, with a mean hatchability of 55%. Reproductive rate showed by O. complanatus after mating was of 52 cocoons per earthworm per year. The results showed that the life cycle of O. complanatus was characterized by both low growth rates and low fecundity. Specific features in life history traits of O. complanatus were compared with those of species of the genus Octodrilus and other related earthworms.

Microbial biomass governs enzyme activity decay during aging of worm-worked substrates through vermicomposting

Vermicomposting is the biooxidation and stabilization of organic matter involving the joint action of earthworms and microorganisms, thereby turning wastes into a valuable soil amendment called vermicompost. Studies have focused on the changes in the type of substrates available before and after vermicomposting, but little is known on how these changes take place, especially those changes related with maturation of vermicompost. This study investigated the effects of aging on the microbiological properties of fresh vermicompost produced from pig slurry by analyzing the substrate after the earthworms had left it. We incubated 16-wk-old vermicompost and sampled it after 15, 30, 45, and 60 d analyzing microbial biomass and activity (assessed as microbial biomass N and basal respiration respectively) and four enzymatic activities (beta-glucosidase, cellulase, protease, and alkaline phosphatase). Aging of vermicompost resulted in decreases of microbial biomass and activity. Three of the four enzymes analyzed also showed decrease. An initial increase followed by a rapid decrease in alkaline phosphatase was also recorded. High and significant correlations between microbial biomass and beta-glucosidase (r = 0.62, P < 0.001), cellulase (r = 0.56, P < 0.01), and protease (r = 0.82, P < 0.001) were found. Results suggest that there may be two steps involved in the aging dynamics of vermicompost with regards to extracellular enzyme activity; the first step was characterized by a decrease in microbial populations, which resulted in a reduction in the synthesis of new enzymes. The second step was the degradation of the pool of remaining enzymes. This dynamic does not seem to be affected by earthworms because similar decaying patterns of microbial biomass and activity were found in substrate where earthworms were present.

Eisenia fetida (Oligochaeta, Lumbricidae) activates fungal growth, triggering cellulose decomposition during vermicomposting

Cellulose is the most abundant polymer in nature and constitutes a large pool of carbon for microorganisms, the main agents responsible for soil organic matter decomposition. Cellulolysis occurs as the result of the combined action of fungi and bacteria with different requirements. Earthworms influence decomposition indirectly by affecting microbial population structure and dynamics and also directly because the guts of some species possess cellulolytic activity. Here we assess whether the earthworm Eisenia fetida (Savigny 1826) digests cellulose directly (i.e., with its associated gut microbiota) and also whether the effects of E. fetida on microbial biomass and activity lead to a change in the equilibrium between fungi and bacteria. By enhancing fungal communities, E. fetida would presumably trigger more efficient cellulose decomposition. To evaluate the role of E. fetida in cellulose decomposition, we carried out an experiment in which pig slurry, a microbial-rich substrate, was treated in small-scale vermireactors with and without earthworms. The presence of earthworms in vermireactors significantly increased the rate of cellulose decomposition (0.43 and 0.26% cellulose loss day(-1), with and without earthworms, respectively). However, the direct contribution of E. fetida to degradation of cellulose was not significant, although its presence increased microbial biomass (C(mic)) and enzyme activity (cellulase and beta-glucosidase). Surprisingly, as fungi may be part of the diet of earthworms, the activity of E. fetida triggered fungal growth during vermicomposting. We suggest that this activation is a key step leading to more intense and efficient cellulolysis during vermicomposting of organic wastes.

Seasonal population dynamics of Eisenia fetida (Savigny, 1826) (Oligochaeta, Lumbricidae) in the field

In order to assess the response of epigeic earthworms to seasonal changes we monitored the population dynamics of Eisenia fetida (Oligochaeta, Lumbricidae) in a manure heap in the field during a year. Earthworms were hand-sorted from five 0.25 x 0.25 x 0.20 m blocks around the heap in November (autumn) 1999 and in January (winter), April (spring) and August (summer) 2000 to determine earthworm population dynamics. Earthworms of each block were classified into different age classes: mature, preclitellate, juvenile, hatchling and cocoon, and afterwards counted and weighed. Seasonality had a strong effect on the density, biomass and reproductive activity of the population. The population of E. fetida was characterized by a high density of individuals and the predominance of mature individuals throughout the year. Maximum density, mating activity and size of cocoons were achieved in spring, but there were not changes in the number of cocoons per mature earthworm throughout the year. Unexpectedly, the smallest cocoons were produced in winter by the largest individuals. These results suggest that E. fetida is able to allocate resources to growth and/or reproduction in response to environmental fluctuations.

Quercus pollen season dynamics in the Iberian peninsula: response to meteorological parameters and possible consequences of climate change

The main characteristics of the Quercus pollination season were studied in 14 different localities of the Iberian Peninsula from 1992-2004. Results show that Quercus flowering season has tended to start earlier in recent years, probably due to the increased temperatures in the pre-flowering period, detected at study sites over the second half of the 20th century. A Growing Degree Days forecasting model was used, together with future meteorological data forecast using the Regional Climate Model developed by the Hadley Meteorological Centre, in order to determine the expected advance in the start of Quercus pollination in future years. At each study site, airborne pollen curves presented a similar pattern in all study years, with different peaks over the season attributable in many cases to the presence of several species. High pollen concentrations were recorded, particularly at Mediterranean sites. This study also proposes forecasting models to predict both daily pollen values and annual pollen emission. All models were externally validated using data for 2001 and 2004, with acceptable results. Finally, the impact of the highly-likely climate change on Iberian Quercus pollen concentration values was studied by applying RCM meteorological data for different future years, 2025, 2050, 2075 and 2099. Results indicate that under a doubled CO(2) scenario at the end of the 21st century Quercus pollination season could start on average one month earlier and airborne pollen concentrations will increase by 50 % with respect to current levels, with higher values in Mediterranean inland areas.