Earthworm Pontoscolex Corethrurus Research Articles

Fourteen-year field experiment reveals neutral effects of N and P deposition on abundance and stoichiometric traits of the earthworm Pontoscolex corethrurus in tropical plantations

The afforestation of tropical forests plays an important role in mitigating climate change. Exploring the impacts of nitrogen (N) and phosphorus (P) deposition on earthworm communities is significant for understanding the contributions of tropical forests to global change. A 14-year field experiment simulating N and P deposition at a station with 50-year-old tropical plantations was conducted. We found that the pantropical widespread exotic earthworm species Pontoscolex corethrurus was dominant, and it did not respond to exogenous N input. Moreover, P addition only increased the abundance of P. corethrurus after 14 years. Similarly, neither N addition nor P addition changed the stoichiometric traits of P. corethrurus. However, over the past decade, the abundance, biomass, and carbon (C), N, and P concentrations in the tissues of P. corethrurus have increased. A strong positive correlation between P. corethrurus population size and soil gram-negative (G−) bacteria biomass was observed, suggesting that P. corethrurus may benefit from the soil bacterial channel. This study ascertained that non-natural tropical lands may be resistant to N and P deposition in terms of earthworm related belowground processes, which would be helpful for fully understanding plant-soil biota feedback and their contributions to tropical plantation development and the mitigation of global climate change.

Vigna unguiculata: a productive option in the face of climate change?

Faced with the challenges of extreme climatic events and increasing food demand, cowpea farming offers a viable option for generating grains and foliage while aiding soil preservation. This research aimed to evaluate the impact of diverse organic fertilizers and plastic mulches on cowpea yields and soil macrofauna. A completely randomized block design was employed, with a factorial arrangement of 3 × 3 + 1, encompassing plastic mulch (3.5 mm) color (white, black, and blue), organic fertilizer (compost of chicken manure-agricultural soil-dolomite, island guano, and cattle manure compost), as well as a control (without synthetic mulch and organic fertilization). The study evaluated soil temperature, plant height, area biomass, foliar macronutrients, yield, and soil macrofauna. The findings demonstrate that soil temperature varies based on the color of the plastic mulch. It was observed that using organic fertilizers resulted in significantly taller plants than the control group, with fresh and dry biomass weight also being significantly greater (p<0.05) for cattle manure compost compared to the other treatments. Furthermore, the use of plastic mulches had an impact on soil macrofauna. Cowpea displayed resistance to low soil fertility and fluctuations in soil temperature ranging from <35°C to >40°C. However, high precipitation during the fruiting and harvesting seasons significantly impacted grain yields. Organic fertilizers produced noticeable variances (p<0.05) in the aerial biomass weight of cowpeas, particularly cattle manure compost. The data, indicates that soil macrofauna, like the earthworm Pontoscolex corethrurus, improved the availability of N, P, and K to the plant during the reproductive stage. Plastic mulches and organic fertilizers were linked to an increase in earthworm weights, specifically P. corethrurus. Additionally, plastic mulches served as a physical barrier against ants and bugs.

Effects of the tropical endogeic earthworm Pontoscolex corethrurus on the horizontal dispersal of soil nematodes

Free-living nematodes are key organisms that greatly enhance plant growth and nutrient uptake. In contrast, plant-parasitic nematodes are considered a major pest group in agriculture. The effect of nematodes, either positive or negative, on plant productivity depends on their ability to disperse in soils. Understanding the dispersal process of nematodes is therefore crucial but is still poorly documented. The aim of this study was to examine the effects of the endogeic tropical earthworm Pontoscolex corethrurus on the horizontal dispersal of nematodes in Ferralsols in Madagascar. A microcosm experiment was conducted under controlled laboratory conditions. Two factors modulating dispersion were studied: (i) the earthworm density with three modalities (without, five or ten individuals) and (ii) the duration of the experiment with two modalities (four and eight weeks). The results showed that P. corethrurus favored the horizontal dispersal of nematodes. This is mainly a dispersal mechanism through the earthworm casts that they deposit in the soil or on the soil surface during their movements. The total abundance of dispersed nematodes increased with the earthworm density and the duration of the experiment. Cephalobidae dominated the trophic structure of the dispersed nematodes, similar to the original populations. However, the original populations had a higher taxonomic diversity than the dispersed nematode communities. These results indicate that P. corethrurus, through dispersion, influences the spatial and temporal distribution, abundance and structure of nematode communities in the soil.

Microniches harbor distinct bacterial communities at the soil-plant-earthworm interface

Earthworms modify soil physicochemical properties and microbial communities, although their effect on different soil microniches is unclear. Here, we aimed to elucidate the effect of the geophagous earthworm Pontoscolex corethrurus on bacterial communities in the bulk soil, rhizosphere and rhizoplane of two cultivated Coffea species. In addition, we assessed the similarity of the earthworm bacterial microbiome (anterior and posterior intestine and casts) with the soil bacterial communities. We implemented a mesocosm experiment with four treatments: 1) Coffea arabica with earthworms; 2) C. arabica without earthworms; 3) Coffea canephora with earthworms; 4) C. canephora without earthworms. We used 16S rDNA amplicon sequencing to study bacterial communities associated with soil microniches and P. corethrurus intestine content and casts. Our findings show that rhizoplane bacterial communities were markedly distinct from those of the bulk and rhizosphere soils, regardless of the coffee species or the presence of earthworms. Nonetheless, P. corethrurus influenced bacterial community composition and structure in the different soil microniches, at the phylum and genus levels. Strong differences were observed in bacterial community structure and diversity between soil and earthworm gut and cast samples, which suggests that the P. corethrurus gut bacterial microbiome is not predominantly derived from the surrounding soil. Bacterial communities from the anterior and posterior gut sections were dominated by different bacterial taxa than those in the casts. Our study is the first one to demonstrate earthworm-induced shifts in rhizoplane-associated bacterial communities and emphasizes the need to consider the earthworm gut as a complex environment with a specific bacterial community.

Synergy of the Tropical Earthworm Pontoscolex corethrurus and Oil Palm Bagasse in the Removal of Heavy Crude Oil.

The tropical endogeic earthworm Pontoscolex corethrurus, a non-standard species used in ecotoxicity, has been found in crude oil-contaminated habitats. We estimated the removal of total hydrocarbons from heavy crude "Maya" oil on an artificially contaminated soil with a median lethal concentration of P. corethrurus and an addition of oil palm bagasse. P. corethrurus had a high survival rate, and the addition of oil palm bagasse led to a greater growth and an increase in abundance of bacteria and fungi. The activity of P. corethrurus and the nutritional quality of oil palm bagasse had a significant impact on the removal of a larger amount of petroleum hydrocarbons from contaminated soil. We concluded that the endogeic earthworm P. corethrurus and oil palm bagasse acted synergistically to achieve a more effective removal of total petroleum hydrocarbons from soil. These results show the potential for using P. corethrurus to remove, either directly or indirectly, crude oil from soil.

Heavy Metal Levels and Potential Ecological Risks Assessed at an Agroecosystem Site in Tropical Region

The concentrations and distribution of thirteen metals and metalloids were investigated in soils, sediments, and two biological matrices (the fish Clarias gariepisnis and the earthworm Pontoscolex corethrurus) from the CECOMAF agroecosystem, in Kinshasa, Democratic Republic of the Congo, in order to assess the impact of anthropogenic activities. The results revealed high concentrations of heavy metals, such as Cu, Zn, As, Cd, Pb, and Hg all above values recommended by sediment quality guidelines and their probable effect levels on biota. According to the calculated Enrichment Factor, soil and sediments ranked from moderately to heavily polluted by Cu, Zn, Cd, Pb and Hg. The Contamination Degree and other ecological risk indices indicated very high contamination and very high ecological risks posed by Cd and Hg, respectively. The Geoaccumulation Index indicated that current metal concentrations in the agroecosystem originated from anthropogenic activities, while the Spearman correlation matrix values indicated that Hg could originate from different sources and pathways than the other metals. It was concluded that metals from unchecked anthropogenic activities have negatively impacted agricultural activities and fish production at the CECOMAF agroecosystem. Action to reduce the contamination level and the ecological risks by remediating and preventing metal pollution in the CECOMAF agroecosystem site is recommended.

Bulk and rhizosphere soil properties under two Coffea species influenced by the earthworm Pontoscolex corethrurus

Rhizosphere processes are critical for nutrient cycling, maintaining soil quality and sustaining plant growth and productivity. However, our understanding of the interplay between plant roots and other soil ecosystem engineers such as earthworms is still limited. Our objective was to determine the influence of Pontoscolex corethrurus, a common endogeic earthworm, on the bulk and rhizosphere soil chemical properties and on the growth of two economically important coffee species. A six-month mesocosm experiment was implemented to grow Coffea arabica and C. canephora with and without earthworms. We measured plant growth variables (height, stem thickness, number of leaves, leaf area, biomass and chemical composition) and soil physico-chemical parameters in both the rhizosphere and bulk soils. We found that soil properties significantly differed among soil zones (bulk vs. rhizosphere). Contents of total P, H, Ca, C/N ratio and CEC were consistently larger in the bulk soil than in the rhizosphere, while C, N and Mg contents were highest in the rhizosphere soil. Although the presence of earthworms had little effect on plant growth, their influence on plant and soil nutrient contents was stronger and highly dependent on coffee species. In C. arabica, earthworms reduced the depletion of Na and Ca in the rhizosphere, but promoted the accumulation of available P and possibly accelerated plant N uptake in that of C. canephora. These differences may be explained by the indirect effect of earthworms on nutrient dynamics, likely mediated by induced shifts in the rhizosphere microbial community. Our findings contribute to the understanding of nutrient dynamics in the rhizosphere of two coffee species, revealing a complex influence of earthworms in rhizosphere processes, and call for a further understanding of the microbe-mediated impact of earthworms in the rhizosphere of C. arabica and C. canephora.

A Comparative Study on Earthworm Biodiversity & Species Habitat-Relationship of Hilly and Plain Areas of Sirohi District of Rajasthan, India

Extensive surveys of earthworm diversity were done in different habitats of plain and hilly areas of Sirohi district of Rajasthan, India. Earthworms differed in their ecomorphological characteristics and relative abundances in different habitats. A total twelve species of earthworms Pontoscolex corethrurus, Amynthas morrisi, Lampito mauritii, Metaphire posthuma, Megascolex konkanensis, Metaphire houlleti, Perionyx sansibaricus, Polypheretima elongata, Ocnerodrilus occidentalis, Dichogaster bolaui, Octochaetona beatrix and Gordiodrilus sp. were recorded from hilly and plain areas. Among these, ten species were found from plain area and nine from hilly area. Five earthworm species (M. konkanensis, M. houlleti, P. elongata, O. beatrix, Gordiodrilus sp.) were recorded for the first-time from Rajasthan. The plain area species P. elongata, O. beatrix and Gordiodrilus sp. were replaced by M. konkanensis and M. houlleti in hilly region. This showed the habitat preferences of earthworm species. Few species were present in a particular habitat of plain area, but they were absent in the same type of habitat in hilly area. The relative density, frequency and species diversity index of earthworm species differed in different habitats and areas. Earthworm diversity exhibited differing species-habitat relationship in hilly and plain areas. These findings may be utilized for eco-restoration of degraded land in similar habitats.

Does rice breeding affect the ability of plants to interact with earthworms in nutrient-depleted Ferralsols?

Agroecology is based on the optimization of ecological processes occurring in agrosystems, especially by improving beneficial interactions among organisms. Recent studies have provided evidence that the ability of plants to interact with free-living soil organisms can be influenced by plant breeding. The upland rice breeding programme in the Highlands of Madagascar aims to develop cultivars that are adapted to local climatic, soil fertility and pest constraints. However, it is still unknown whether this genetic improvement alters rice cultivar abilities to interact with free-living soil plant-mutualistic organisms such as earthworms. We assessed in mesocosms the response of six upland rice cultivars commonly used by farmers in the Highlands of Madagascar to the presence of the endogeic earthworm Pontoscolex corethrurus. Plant nutrition and growth-related traits were measured after eight weeks of growth. These traits were significantly improved in the presence of P. corethrurus for all cultivars compared to the control treatment. However, the magnitudes of earthworm effects on plant traits were strongly variable and were dependent on specific rice cultivars. Agronomic and phylogenetic distance matrices were computed using agronomic data and available phylogenetic data of the rice cultivars. We did not detect significant correlations between cultivar responses to earthworm inoculation and agronomic or phylogenetic distances. Our results suggest that (i) the ability of rice to exploit beneficial interactions involving free-living soil organisms is influenced by its genetic background, but (ii) the loss of earthworm-interactive abilities of rice crops is independent of the genetic distance among cultivars and breeders' agronomic criteria. Our findings are significant for attempts to use rice cultivars that optimize plant-soil interactions within agroecological practices and highlight the need to integrate free-living soil partners as life-long plant partners in future strategies for plant breeding.

Growth of celery (Apium graveolens L.) in the red-yellow podzolic soils as inoculated by earthworms Pontoscolex corethrurus

In this study, the inoculation effect of earthworms Pontoscolex corethrurus on celery growth (Apium graveolens L.) has been carried out in red-yellow podzolic (RYP) soils. The research studied in a pot experiment using a completely randomized design (CRD) with 6 (six) treatments and 3 (three) replications. One-pot consists of 4 (four) plants. The treatments carried out were as follows: I0 (without inoculum of earthworm), I1 (inoculum of 5 earthworms pot-1), I2 (inoculum of 10 earthworms pot-1), I3 (inoculum of 15 earthworms pot-1), I4 (inoculum of 10 earthworms pot-1) and I5 (inoculum of 25 earthworms pot-1). Observation parameters were the number of tillers clumps-1, fresh biomass clumps-1 (g clump-1), and root volume (mL). The observations were statistically analyzed using variance (one-way ANOVA) and followed by the Duncan Multiple Range Test (DMRT) with a level of 5%. Treatment I5 gave the best results on celery crop in all parameters, i.e., 20.33 tillers per hill; fresh biomass per clump 113.93 g; and a root volume of 10 mL. The results showed that earthworms' inoculation into RYP soils significantly affected all parameters. There was also an increase in pH in each treatment that was inoculated with earthworms.

Earthworm Inoculation Improves Upland Rice Crop Yield and Other Agrosystem Services in Madagascar

The effects of earthworm inoculation and cropping systems on upland rice systems were examined over a four-year period in the Highlands of Madagascar. Each year, endogeic earthworms Pontoscolex corethrurus (Rhinodrilidae) were inoculated (EW+) at a density of 75 ind m−2 or were not inoculated (EW0). Inoculation was tested in three cropping systems: conservation agriculture (CA) and traditional tillage with or without residues restitution. Soil and plant properties were measured during the first three years while soil biological properties were assessed at the fourth year. At the end of the experiment, earthworm density was three-fold higher in EW+ than in EW0, demonstrating the success of the inoculation. Earthworm density was more important in CA than in tillage systems. Earthworm inoculation had higher significant effects on soil and plant properties than cropping systems. Earthworm inoculation had positive effects on soil macroaggregation (+43%), aboveground biomass (+27%), rice grain yield (+45%), and N grain amount (+43%). Intensifying earthworm activity in field conditions to meet the challenge of ecological transition is supported by our study.

Effects of the earthworm Pontoscolex corethrurus on rice P nutrition and plant-available soil P in a tropical Ferralsol

We conducted a greenhouse experiment in mesocosms for 28 days to assess the effects of the endogeic earthworm Pontoscolex corethrurus on plant-available soil phosphorus (P) and rice ( Oryza sativa ) P nutrition in a Malagasy Ferralsol. To assess plant-available soil P, we determined the L-value by measuring the specific activity of P taken up from the soil by rice and by applying the isotopic dilution principle. Despite earthworm mortality, P. corethrurus significantly increased rice shoot biomass (+26%) and P nutrition (+65%), confirming that the soil used for the experiment was P-deficient. The L-value also markedly increased from 6.8 ± 0.9 to 14.2 ± 1.3 mg P mesocosm −1 in the presence of P. corethrurus . We estimated that the orthophosphate ions released due to earthworm mortality contributed to 30% of the L-value increase. We attributed the remaining 70% increase to the solubilization of native soil P during its transit through the digestive tract. Thereafter, we discussed the sources of uncertainty associated with the L-value calculation and their utilization to assess earthworm effects on P availability in further studies. • We assessed the effects of P. corethrurus ( Ponto ) on plant-available soil P. • Ponto increased rice shoot biomass (+26%) and P nutrition (+65%). • The L -value raised from 6.8 (±0.9) to 14.2 (±1.3) mg P cosm −1 in presence of Ponto . • The P release due to Ponto mortality contributes to 30% of the L -value increase. • The relevance of using L -value in earthworm inoculation experiments is discussed.

PHYSIOLOGICAL EFFECTS OF PROFENOFOS INSECTICIDE TOWARDS CONSUMPTION RATE 6 AND ASSIMILATION EFFICIENCY OF COW – DUNG BY EARTHWORMS 7 PONTOSCOLE CORETHRURUS FR. MULL

The purpose of this research is to determined the effect of insecticide profenofos to the rate of consumption and assimilation efficiency of cow- dung by earthworms Pontoscolex corethrurus Fr. Mull. This research used Completely Randomized Design with 6 treatments and 5 repetition. Treatments that was given to sample are the insecticide profenofos with concentration of 0 % (control); 0.1%; 0.2 %; 0.3 %; 0.4 %; 0.5 %. Data analysis was using Varians Analysis. If there was real difference then data analysis continued with The Duncan Test on level of confidence of 95%. The results of this research show us that several concentration of insecticide carbaryl have the real effect to the average of consumption rate and the efficiency of absorption. The lowest average of consumption rate on earthworm Pontoscolex corethrurus Fr.Mull is on concentration of 0.5 % (0.23 ± 0.02 mg/g day) and the highest average of consumption 26 rate on earthworm Pontoscolex corethrurus Fr. Mull is on concentration of 0% (control) (2.53 ± 0.05 mg/g day). The lowest average of approach digestyon earthworm Pontoscolex corethrurus is on concentration of 0 % (control) (40.78 28 ± 2.56 %) and the highest average of digestion earth worm Pontoscolex corethrurus Fr.Mull is on concentration of 0.5 % 29 (70.76 ± 3.67 %).

Earthworms negate the adverse effect of arbuscular mycorrhizae on living bacterial biomass and bacterial necromass accumulation in a subtropical soil

Earthworms and arbuscular mycorrhizal fungi (AMF) have substantial individual effects on the supply and absorption of soil nutrients in terrestrial ecosystems. How their interactions regulate the soil living microbial community and microbial necromass accumulation remains unknown. We hypothesized that the effect of their interaction on the microbial community and necromass accumulation may relate to their controls on status of soil N and P. We conducted a greenhouse experiment manipulating the AMF Rhizophagus intraradices and the earthworm Pontoscolex corethrurus in microcosms planted with a fern Dicranopteris dichotoma. Phospholipid fatty acids and amino sugars were used to indicate the living microbial community and necromass accumulation, respectively. The AMF consistently reduced the biomass of bacterial groups and the concentration of total amino sugars, glucosamine and muramic acid, in the absence of earthworms, but had no effect in their presence. The earthworms increased the concentration of soil total dissolved N, water-soluble N and water-soluble P, and the activity of β–1,4–N-acetylglucosaminidase and phosphatase, and the amount of P in total plant biomass. Redundancy analysis showed that the bacterial biomass was positively correlated with most soil labile N indices and negatively correlated with the amount of N in total plant biomass. Pearson correlation revealed that the bacterial nutritional stress indicator Sat/Mono was negatively correlated with soil NH4+ concentration and positively correlated with the amount of N in total plant biomass. The results suggested that earthworms might negate the suppression effect of AMF on bacterial abundance and necromass accumulation by alleviating AMF-induced N deficiency.

Interactive effect of glyphosate-based herbicides and organic soil layer thickness on growth and reproduction of the tropical earthworm Pontoscolex corethrurus (Müller, 1857)

Glyphosate-based herbicides (GBHs) have negative effects on the fitness parameters of earthworms; however, these effects may vary from one commercial product to another and between different recommended doses. Additionally, frequent applications of GBHs may decrease the thickness of the topsoil layer due to increased soil erosion through vegetation reduction. To investigate the effects of frequent applications of GBHs, and their interactive effect on the performance of P. corethrurus, we performed a two-factor experiment exposing in vitro the earthworm to two commercial GBHs (factor I, FAENA FUERTE (FF, Monsanto Co.) and GLYFOS (GLY, Cheminova Co., with three levels)) and soil thickness (factor II, with two levels); having six treatments in total, each with four replicates. Both herbicides were applied at their recommended doses; a total of 11 times at intervals of 14 days in soil layers 2.5 and 5 cm deep. Earthworm biomass and cocoon production were measured every 12 days for 168 days. Application of GLY resulted in significant biomass decreases of between 51 ± 11.54% (here and further S.E. is provided) and 100 ± 0.00% compared to a control. For FF, the final biomass decreased significantly by between 19 ± 7.33% and 24 ± 8.44% at both doses, independently of soil thickness. Additionally, a significant biomass reduction of 41 ± 7.93% was detected when soil thickness was low at highest dose. At a soil depth of 5 cm, GLY significantly decreased cocoon production by between 69 ± 7.86% and 83 ± 10.53% at each dose compared to the control. In contrast, the different doses of FF did not affect the number of cocoons produced, although there was a significant decrease of 72 ± 7.18% when the soil layer was reduced. The growth rate increased significantly under exposure to both GBH at all tested doses. Our results suggest that cumulative doses of GLY are more detrimental for P. corethrurus than those of FF and that soil thickness may help buffer some of the negative effects of GBHs. In order to reduce negative impacts on earthworms in the field, we therefore suggest maintaining the topsoil layer thickness and adjusting the doses of GBHs to the lowest end of the recommended range.

Genetic evidence of multiple introductions and mixed reproductive strategy in the peregrine earthworm Pontoscolex corethrurus

Pontoscolex corethrurus is a well-known invasive earthworm in tropical zone which is believed to have originated from the Guayana Shield in South America and was described as parthenogenetic. A recent phylogenetic study revealed four cryptic species in the P. corethrurus complex (L1, L2, L3 and L4), among them L1 was particularly widespread and was proposed as P. corethrurus sensu stricto. Here, our aims were to investigate the genetic variation of P. corethrurus L1 in its presumed native and introduced ranges and to examine its reproductive strategy. An extensive dataset of 478 cytochrome oxidase I gene (COI) sequences, obtained in specimens sampled all around the world, revealed a weak COI haplotype diversity with one major haplotype (H1) present in 76% of the specimens. Analyses of the genetic variation of 12 L1 populations were done using both nuclear (226 AFLP profiles) and mitochondrial (269 COI sequences) genetic information. The high AFLP genotype diversity at the worldwide scale and the fact that no genotype was shared among populations, allowed to reject the ‘super-clone’ invasion hypothesis. Moreover, a similar level of mean genetic diversity indices were observed between the introduced and native ranges, a pattern explained by a history of multiple introductions of specimens from different parts of the world. At last, occurrence of identical AFLPs genotypes (i.e. clones) in several population confirmed asexual reproduction, but recombination was also revealed by gametic equilibrium analysis in some populations suggesting that P. corethrurus L1 may have a mixed reproductive strategy.

Disturbance intensity overwhelms propagule pressure and litter resource in controlling the success of Pontoscolex corethrurus invasion in the tropics

The mechanisms by which exotic earthworms invade new habitats are largely unknown. Previous research concluded that factors including habitat disturbance, propagule pressure and variation in the litter resource may significantly drive the establishment of exotic earthworms, however, these studies did not conduct manipulative experiments to compare the effects of these three factors. To fill this knowledge gap, we established a moderate disturbance experiment and a severe disturbance experiment in a tropical natural forest (Xishuangbanna, China) with the exotic earthworm Pontoscolex corethrurus. The former mesocosm experiment manipulated disturbance (no disturbance vs moderate disturbance) and propagule pressure as the independent factors, while the latter mesocosm experiment manipulated propagule pressure and litter resource (difference in quality and diversity) as the independent factors that affect the establishment of P. corethrurus. In the moderate disturbance experiment: disturbance and propagule pressure did not affect the final population size of P. corethrurus, i.e., populations in all treatments declined to the same size at the end of the experiment. In the severe disturbance experiment: the population size of P. corethrurus increased in all treatments, with larger population size observed under the treatments with higher propagule pressure; litter treatments with a higher C/N ratio slightly increased the population biomass. In conclusion, our results showed that disturbance (severe vs no or moderate disturbance) overwhelmed the effects of propagule pressure and litter resource on the establishment of P. corethrurus. We suggest that the protection of tropical natural forests from severe disturbance, e.g., slash-and-burn deforestation, is the key means to prevent earthworm invasion.

Earthworm Pontoscolex corethrurus stimulated soil CO2 emission by enhancing substrate availability rather than changing microbiota community structure

Earthworms may regulate carbon (C) mineralization through a top-down process by altering microbiota community and/or a bottom-up process by providing basic conditions such as mineralizable substrates. However, these two roles performed by earthworms have not been separately quantified. Here, we focused on how the pantropical widespread earthworm, Pontoscolex corethrurus, affected CO2 emission by changing soil microbiota community and substrate availability in infertile subtropical soils. Two experiments were performed. Firstly, we conducted a 3-year field experiment wherein P. corethrurus population was manipulated by electrical shocking. The two treatments were earthworm reduction (ER) and earthworm addition (EA). Thereby, we tried to understand CO2 emission pattern through the earthworm-induced changes in soil microbiota community and C-related enzyme activities in field plots. Secondly, a cross-soil inoculation microcosm experiment was conducted to partition the contributions of earthworm-regulated microbiota community and substrate quality to CO2 emission. The four treatments were 1) autoclaved ER soil + ER microbiota, 2) autoclaved EA soil + ER microbiota, 3) autoclaved ER soil + EA microbiota, and 4) autoclaved EA soil + EA microbiota. We found that, in the field experiment, earthworm addition changed soil microbiota community structure, but increased CO2 emission despite decreasing soil β-glucosidase activity by 12%. In the cross-inoculation experiment, the β-glucosidase activity and CO2 emission (1-day incubation) in EA soils was 65.5% and 35.5% greater than that in the ER soils, respectively; the cumulative CO2 emission (30-day incubation) in EA soils was also significantly greater than that in ER soils. However, no significant effects of microbiota inoculation on soil CO2 emissions were observed. These results suggested that the earthworm-enhanced substrate availability, rather than the earthworm-induced changing in the microbiota community structure and enzymatic activities, played a key role in C mineralization. This study implies that P. corethrurus occupies a “bottom niche” in infertile subtropical soils.

The presence of earthworm Pontoscolex corethrurus rather than organic matter sources indirectly controls N2O flux in tropical plantation soils

Both organic matter status and earthworm activity may affect the microbial-mediated N2O production in tropical plantations which contribute greatly to the global N2O emission. The representative pantropical earthworm Pontoscolex corethrurus was likely to be increasingly dominant in degraded lands due to intensified disturbances such as understory removal and soil erosion. We noticed that the relatively fertile surface soil plays key roles in fueling both microbes and earthworms. Therefore, we hypothesized that N2O production was stimulated most by earthworm P. corethrurus in less-disturbed tropical plantations where the surface soil layer was conserved. To determine the effect of organic matter sources and P. corethrurus activity on N2O flux in tropical plantation soils, a field mesocosm experiment including four organic treatments with and without earthworms was then conducted. In plant-free mesocosms, mineral soils (60–80 cm layer) received four organic matter treatments: no organic matter (CK), non-fragmented fallen leaves (NL), partially fragmented leaves (PL) and surface soil containing decomposed litter (0–5 cm, SS), which were used to simulate different levels of disturbance-mediated resource depletion. We found that although the population of P. corethrurus declined with the intensity of food resource limitation, mostly P. corethrurus stimulated N2O flux, but occasionally reduced N2O flux in the organic matter-depleted control soils. In contrast, organic matter sources did not exert significant effects on N2O flux. This study indicates that, although the disturbance-induced changes in organic matter supply altered earthworm population size, the presence of P. corethrurus rather than organic matter sources is the determinant of N2O flux in the studied tropical soils. Although the occasionally negative earthworm effects on N2O flux brings uncertainty, the population size-independent positive earthworm effect on N2O flux may simplify the modeling of earthworm contributions to greenhouse gas fluxes.

¿La lombriz de tierra favorece la supervivencia y el crecimiento de plántulas de Abies religiosa(Kunth) Schltdl. & Cham. en vivero?

Introduction: In nurseries, irrigation inside plastic bags contributes to soil compaction, affecting plant growth. Objective: To evaluate the effect of the earthworm Pontoscolex corethrurus Muller on the survival and growth of Abies religiosa (Kunth) Schltdl. & Cham. plants and on soil compaction in a nursery. Materials and methods: The plants were subjected to three treatments (adult earthworm, two juvenile earthworms and no earthworms) in plastic bags (250 cc, 400 gauge) with 25 replicates. One year later, the height, cover, number of primary and secondary branches and biomass production (root, stems and branches) of the plants were recorded and soil compaction evaluated. Results and discussion: The earthworm promoted an increase of 28 % in height and 44 % in root dry matter production (P 0.05) in all three treatments. Compaction was significantly lower (48 %, P Conclusion: P. corethrurus has the potential to improve the quality of plants grown in plastic bags in forest nurseries.