Effects of Epigeic Earthworms on Decomposition of Wheat Straw and Nutrient Cycling in Agricultural Soils in a Reclaimed Salinity Area:A Microcosm Study

Earthworms,one of the most important macroinvertebrates in terrestrial ecosystems of temperate zones,exert important influences on soil functions.A laboratory microcosm study was conducted to evaluate the influence of the earthworm Eisenia fetida on wheat straw decomposition and nutrient cycling in an agricultural soil in a reclaimed salinity area of the North China Plain.Each microcosm was simulated by thoroughly mixing wheat straw into the soil and incubated for 120 d with earthworms added at 3 different densities as treatments:control with no earthworms,regular density(RD)with two earthworms,and increased density(ID)with six earthworms.The results showed that there was no depletion of carbon and nitrogen pools in the presence of the earthworms.Basal soil respiration rates and metabolic quotient increased with the increase in earthworm density during the initial and middle part of the incubation period.In contrast,concentrations of microbial biomass carbon and microbial biomass quotient decreased in the presence of earthworms.Earthworm activity stimulated the transfer of microbial biomass carbon to dissolved organic carbon and could lead to a smaller,but more metabolically active microbial biomass.Concentrations of inorganic nitrogen and NO₃^--N increased significantly with the increase in earthworm density at the end of the incubation(P<0.05),resulting in a large pool of inorganic nitrogen available for plant uptake.Cumulative net nitrogen mineralization rates were three times higher in the ID treatment than the RD treatment.     

真菌群落沿气候梯度与植物凋落物分解之间的关系研究

The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning. The spatiotemporal changes in the composition and dynamics of litter fungal community along a climate gradient ranging from arid desert to humid-Mediterranean regions in Israel was examined using wheat straw litter bags placed at four selected sites along the climate gradient, arid, semi-arid, Mediterranean, and humid-Mediterranean sites. Litter samples were collected over a two-year decomposition period to evaluate litter weight loss, moisture, C：N ratio, fungal composition, and isolate density. The litter decomposition rate was found to be the highest during the first year of the study at the Mediterranean and arid sites. Although the Shannon-Wiener index values of the fungal communities in the litter samples were the highest at the humid-Mediterranean site, the number of fungal species was not significantly different between the four study sites. Different fungal groups were found to be related to different study sites： Basidiomycota, Mucoromycotina, and teleomorphic Ascomycota were associated with the humid-Mediterranean site, while Coelomycetes were mostly affected by the arid site. Our results indicate that climate factors play an important role in determining the structure of saprotrophic fungal communities in the decomposing litter and in mediating plant litter decomposition processes.     

川西3种亚高山针叶林的养分和凋落物格局分析

Investigations were conducted to quantify litterfall, and litter and nutrient accumulation in forest floor, and to acquire information on litter decomposition and nitrogen and phosphorus release patterns in three different subalpine coniferous forests, a plantation （P1）, a secondary forest （SF）, and a primitive forest （PF）, in western Sichuan, China. The litter trap method was used to evaluate litterfall with the litterbag method being utilized for litter decomposition. Seasonal patterns of litterfall were similar in the three forests, with two peaks occurring in September-November and March-May. The plantation revealed an annual litterfall of 4.38 x 103 kg ha-1, which was similar to those of SF and PF, but P1 had a lower mass loss rate and a higher C/N ratio. The C/N ratio may be a sound predictor for the decomposition differences. N concentrations of leaf litter in both the secondary forest and primitive forest increased first and then decreased, and the percentages of their final/initial values were 108.9% and 99.9%, respectively. P concentration in the three forests increased by the end of the study. The results of litterfall and decomposition indicated that in the plantation the potential to provide nutrients for soil organic matter was similar to those of SF and PF; however, its slower decomposition rate could result in a somewhat transient accumulation of litter in the forest floor.     

通过纯培养蛋白质组学跟踪研究石油污染的土壤上微生物群落的变化

Hydrocarbon contamination may affect the soil microbial community, in terms of both diversity and function. A laboratory experiment was set-up, with a semi-arid control soil and the same soil but artificially contaminated with diesel oil, to follow changes in the dominant species of the microbial community in the hydrocarbon-polluted soil via proteomics. Analysis of the proteins extracted from enriched cultures growing in Luria-Bertani (LB) media showed a change in the microbial community. The majority of the proteins were related to glycolysis pathways, structural or protein synthesis. The results showed a relative increase in the complexity of the soil microbial community with hydrocarbon contamination, especially after 15 days of incubation. Species such as Ralstonia solanacearum, Synechococcus elongatus and different Clostridium sp. were adapted to contamination, not appearing in the control soil, although Bacillus sp. dominated the growing in LB in any of the treatments. We conclude that the identification of microbial species in soil extracts by culture-dependent proteomics is able to partially explain the changes in the diversity of the soil microbial community in hydrocarbon polluted semi-arid soils, but this information is much more limited than that provided by molecular methods.     

Earthworm populations are stable in temperate agricultural soils receiving wood-based biochar

The application of decomposable organic residues such as manure and crop litter is generally beneficial to earthworms. There is an emerging interest in applying biochar, a carbonaceous product of pyrolysis, to temperate agricultural soils. The slow decomposition rate of biochar, which also contains ash and combustion byproducts, could be detrimental to earthworms. The objective of this study was to describe the earthworm populations in biochar-amended soils on a dairy farm in the St. Francis River watershed, Quebec, Canada. Earthworms were collected from replicated field plots under cereal production. Site A received three wood-based biochar types at two application rates(5 and 10 t ha~(-1) biochar) plus an unamended control, while Site B received wood-based biochar(7.5 t ha~(-1) biochar), dairy cattle slurry(10 t ha~(-1) manure), or a combination of the biochar and manure rates plus an unamended control. Earthworms were collected by hand sorting and formaldehyde expulsion from soil pits. Three species, Aporrectodea turgida, Aporrectodea tuberculata, and Lumbricus rubellus, were found at the sites, and Aporrectodea was the dominant genus. Biochar sources, rates, and application with dairy slurry did not affect the earthworm population, which had 52–218 individuals m~(-2) in 2010 and 4–96 individuals m~(-2) in 2011. The seasonal variation in earthworm population may be due to flooding in the spring of 2011, which apparently interfered with earthworm reproduction. The similarity in earthworm abundance and biomass in plots with and without wood-based biochar leads to the conclusion that earthworm populations are stable in biochar-amended soils in this cold, humid temperate region.     

红吼猴粪便沉积物对表层土壤的影响

The short-term influence of dung deposition and the further redistribution of dung by dung beetles were studied under a resting place of the red howler monkey (Alouatta seniculus) living in tropical rainforests of South America. Monkey dung was experimentally clumped on the field in a place used by troops of howler monkeys for resting in the Nouragues Reserve Station, French Guiana. Dung-treated plots were sampled serially over three weeks and compared with controls located in their immediate vicinity. The composition of the soil matrix (top 10 cm) was studied in successive microlayers using an optical method. Under the influence of dung beetle activity, the topsoil became more homogeneous by losing its litter, its content in earthworm faeces increased in the course of time, and surface mineral deposits were penetrated by roots. The results were interpreted in the light of present knowledge on the effects of soil animal activity on plant growth and survival of seedlings.     

内盖夫荒漠中小型土壤节肢动物群落的时空变化

Desert ecosystems are characterized by sparse vegetation that affects both abiotic parameters and soil biota along the soil profile.This study was conducted in 2010–2011 in a loess plain in the northern Negev Desert highlands, Israel, to test two main hypotheses:1) the abundance and diversity of microarthropods would vary seasonally in the top 30-cm soil layer, but would be relatively stable at soil depths between 30 and 50 cm and 2) soil microarthropods would be more abundant in soils under shrubs with large litter accumulations than under shrubs with less litter or bare soil. Soil samples were collected each season from the 0–50 cm profile at10-cm intervals under the canopies of Hammada scoparia and Zygophyllum dumosum and from the bare interspaces between them.Soil moisture and soil organic carbon in the top 30-cm layers varied seasonally, but there was little variation in the soil layers deeper than 30 cm. Soil mites were most abundant in the top 30-cm soil layer in autumn and winter, with the highest number of families found in winter. There were no differences in soil microarthropod abundance attributable to the presence or absence of shrubs of either species. The microarthropod communities of the microhabitats studied consisted of Acari, Psocoptera, and Collembola. The Acari were mostly identified to the family level and were dominated by Oribatida(55%) and Prostigmata(41%) in all seasons and microhabitats, while the psocopterans were most abundant in summer. These results are opposite to those obtained in other studies in similar xeric environments. Moreover, our findings were not in line with our hypothesis that a better microhabitat played a major role in microarthropod community composition, diversity, and density.     

水稻土中外源铅和苄嘧磺隆交互作用对碳源矿化的影响

Little information is available on the interactive effects of inorganic and organic pollutants on carbon utilization by soil microorganisms.This study examined the effects of two common soil pollutants,lead (Pb) and bensulfuron-methyl herbicide (BSM),on decomposition of an adscititious carbon source (¹⁴C-glucose).Two contrasting paddy soils,a silty clay soil and a clay loam soil,were incubated with different concentrations and combinations of pollutants for 60 days.Orthogonal rotatable central composite design was adopted to design the combinations of the pollutant concentrations so that rate response curves could be derived.Rapid decomposition of ¹⁴C-glucose occurred in the first three days for both soils where no Pb or BSM was added (control).Overall,63%-64% of the added ¹⁴C-glucose was decomposed in the control over the 60-day incubation.The addition of Pb or BSM significantly decreased the decomposition of ¹⁴C-glucose during the first week but increased the decomposition thereafter;as a result,the percentages of ¹⁴C-glucose decomposed (57%-77%) over the 60-day period were similar to or higher than those of the control.Application of the pollutants in combination did not further inhibit decomposition compared with the control.Overall,decomposition rates were lower in the silty clay soil than in the clay loam soil,which was related to the soil texture,cation exchange capacity,and pH.The relationship between the decomposition rates and the pollutants could be well characterized by the quadratic regression orthogonal rotation model.The initial antagonistic effects of the pollutants followed by the synergistic effects on microbial activity might result from changes of the concentrations of the pollutants.     

中国亚热带两种竹林凋落物输入量、凋落物分解和养分释放动态

Bamboos are one of the fast-growing and multiple use species in the world, and thus bamboo forests/plantations play an important role in C sequestration at regional and global levels. We studied aboveground litterfall, litter decomposition and nutrient dynamics for two years in two subtropical bamboo ecosystems in Southwest China so as to test the hypothesis that litter quality determine the rate and nutrient dynamics during decomposition of different litter fractions. Mean annual total aboveground litter production ranged from 494 to 434 g m-2 in two bamboo stands （P stand, dominated by Pleioblastus amarus and H stand, hybrid bamboo dominated by Bambusa pervariabilis x Dendrocalamopsis daii）. Bulk （-80%） of litter production was contributed by leaf litter in two stands followed by twigs and sheathes. Different litter fractions represented considerable variations in the rates of mass loss and nutrient release. Variation of the mass remaining after 2 years of decomposition was significantly explained by initial C/N ratio and initial P concentration. Initial concentrations of N, P, Ca, and Mg explained 57.9%, 95.0%, 99.8% and 98.1%, respectively, of the variations of these elements mass remaining after 2 years of decomposition. The patterns of nutrient dynamics and the final amount remaining were mainly determined by their initial litter substrate quality in tl~ese two subtropical bamboo plantations.     

Influence of drying and ageing on the stabilization of earthworm (Lumbricidae) casts

The influence of drying and ageing on the stabilization of casts produced by the endoge′ic earthworm, Aporrectodea rosea, from a soil, which was hard-setting and low in organic matter, were investigated in the laboratory. Casts and uningested soil were aged-most for up to 32 days, dried for up to 21 days, or subjected to different wetting and drying cycles over 30 days. The dispersion index of aged-moist casts decreased from 0.40 to 0.25 over 32 days, while dispersion index of dried casts decreased from 0.40 to 0.01 over 21 days. The dispersion index of air-dried casts was not significantly increased by five cycles of wetting and drying. The dispersion index of dried casts was not significantly less than that of dried soil. In soils wetter than a matric potential of approximately –35kPa, stabilization of casts was probably due to a combination of cohesion of soil particles, age-hardening and growth of microorganisms. However, in soils drier than –35kPa, cementation was probably the major mechanism of stabilization. The addition of wheat straw to the soil prior to ingestion by earthworms increased dispersion from aged-moist casts, but did not influence dispersion from dried casts. The addition of wheat straw decreased the number of air-dried casts which slaked severely. The concentration of soluble carbohydrate decreased with dispersion index as casts and uningested soil were each dried. This suggested that soluble carbohydrate may have been denatured with or without being bonded to soil particles during drying. Received: 7 May 1996     

Correlation between earthworms and plant litter decomposition in a tropical wet forest of Puerto Rico

Earthworms are recognized to play an important role in the decomposition of organic materials. To test the use of earthworms as an indicator of plant litter decomposition, we examined the abundance and biomass of earthworms in relation to plant litter decomposition in a tropical wet forest of Puerto Rico. We collected earthworms at 0–0.1 m and 0.1–0.25 m soil depths from upland and riparian sites that represent the natural variation in soils and decomposition rates within the forest. Earthworms were hand-sorted and weighed for both fresh and dry biomass. Earthworms were dominated by the exotic endogeic species Pontoscolex corethrurus Müller; they were more abundant, and had higher biomasses in the upland than in riparian sites of the forest. Plant leaf litter decomposed faster in the upland than riparian sites. We found that earthworm abundance in the upper 0.1 m of the soil profile positively correlated with decomposition rate of plant leaf litter. Ground litter removal had no effect on the abundance or biomass of endogeic earthworms. Our data suggest that earthworms can be used to predict decomposition rates of plant litter in the tropical wet forest, and that the decomposition of aboveground plant litter has little influence on the abundance and biomass of endogeic earthworms.     

Competition between invasive earthworms (Amynthas corticis, Megascolecidae) and native North American millipedes (Pseudopolydesmus erasus, Polydesmidae): Effects on carbon cycling and soil structure

Invasive earthworms can have significant impacts on C dynamics through their feeding, burrowing, and casting activities, including the protection of C in microaggregates and alteration of soil respiration. European earthworm invasion is known to affect soil micro- and mesofauna, but little is known about impacts of invasive earthworms on other soil macrofauna. Asian earthworms (Amynthas spp.) are increasingly being reported in the southern Appalachian Mountains in southeastern North America. This region is home to a diverse assemblage of native millipedes, many of which share niches with earthworm species. This situation indicates potential for earthworm-millipede competition in areas subject to Amynthas invasion.In a laboratory microcosm experiment, we used two ¹³C enriched food sources (red oak, Quercus rubra, and eastern hemlock, Tsuga canadensis) to assess food preferences of millipedes (Pseudopolydesmus erasus), to determine the effects of millipedes and earthworms (Amynthas corticis) on soil structure, and to ascertain the nature and extent of the interactions between earthworms and millipedes. Millipedes consumed both litter species and preferred red oak litter over eastern hemlock litter. Mortality and growth of millipedes were not affected by earthworm presence during the course of the experiment, but millipedes assimilated much less litter-derived C when earthworms were present.Fauna and litter treatments had significant effects on soil respiration. Millipedes alone reduced CO₂ efflux from microcosms relative to no fauna controls, whereas earthworms alone and together with millipedes increased respiration, relative to the no fauna treatment. CO₂ derived from fresh litter was repressed by the presence of macrofauna. The presence of red oak litter increased CO₂ efflux considerably, compared to hemlock litter treatments.Millipedes, earthworms, and both together reduced particulate organic matter. Additionally, earthworms created significant shifts in soil aggregates from the 2000-250 and 250-53 μm fractions to the >2000 μm size class. Earthworm-induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Earthworms translocated litter-derived C to soil throughout the microcosm.Our results suggest that invasion of ecosystems by A. corticis in the southern Appalachian Mountains is unlikely to be limited by litter species and these earthworms are likely to compete directly for food resources with native millipedes. Widespread invasion could cause a net loss of C due to increased respiration rates, but this may be offset by C protected in water-stable soil aggregates.     

Effect of earthworm addition on soil nitrogen availability,microbial biomass and litter decomposition in mesocosms

The aim of the study was to determine the effect of adding two tropical earthworm species, Rhinodrilus contortus and Pontoscolex corethrurus, to mesocosms on the availability of mineral N (NH₄ ⁺ and NO₃ ^– concentrations), soil microbial biomass (bio-N), and the decomposition rates of three contrasting leaf litter species, in a glasshouse experiment. The mesocosms were filled with forest soil and covered with a layer of leaf litter differing in nutritional quality: (1) Hevea brasiliensis (C/N=27); (2) Carapa guianensis (C/N=32); (3) Vismia sp., the dominant tree species in the second growth forest (control, C/N= 42); and, (4) a mixture of the former three leaf species, in equal proportions (C/N=34). At the end of the 97-day experiment, the soil mineral N concentrations, bio-N, and leaf litter weight loss were determined. Both earthworm species showed significant effects on the concentrations of soil NO₃ ^– (p<0.01) and NH₄ ⁺ (p<0.05). Bio-N was always greater in the mesocosms with earthworms (especially with R. contortus) and in the mesocosms with leaf litter of H. brasiliensis (6 µg N g^–1 soil), the faster decomposing species, than in the other treatments (0.1–1.6 µg N g^–1). Thus, earthworm activity increased soil mineral-N concentrations, possibly due to the consumption of soil microbial biomass, which can speed turnover and mineralization of microbial tissues. No significant differences in decomposition rate were found between the mesocosms with and without earthworms, suggesting that experiments lasting longer are needed to determine the effect of earthworms on litter decomposition rates.     

Decomposition and mineralization of energy crop residues governed by earthworms

Energy crops are increasingly cultivated in agricultural management systems world-wide. A substitution of food crops (e.g. cereals) by energy crops may generally alter the biological activity and litter decomposition in soil due to their varying structural and chemical composition and subsequently modify soil functioning. A soil microcosm experiment was performed to assess the decomposition and microbial mineralization of different energy crop residues in soil compared to a food crop, with or without earthworms. Residues of the energy crops winter rape (Brassica napus), maize (Zea mays), miscanthus (Miscanthus giganteus) and the food crop oat (Avena sativa) were each provided as food source for a mixed earthworm population, each consisting of one individual of Lumbricus terrestris, Aporrectodea caliginosa, and Octolasion tyrtaeum. After 6 weeks, the rate of litter loss from the soil surface, earthworm biomass, microbial biomass-C and -N, microbial activity, and enzyme activities were determined. The results emphasized, that litter loss and microbial parameters were predominantly promoted by earthworms and were additionally influenced by the varying structural and chemical composition of the different litter. Litter decay by earthworms was highest in N-rich maize litter treatment (C-N ratio 34.8) and lowest in the case of miscanthus litter (C-N ratio 134.4). As a consequence, the microbial biomass and basal respiration in soils with maize litter were higher, relative to other litter types. MBC-MBN ratio in soil increased when earthworms were present, indicating N competition between earthworms and microorganisms. Furthermore, enzyme activities responded in different ways on the varying types of litter and earthworm activity. Enzymes involved in the N-cycle decreased and those involved in the C-cycle tended to increase in the presence of earthworms, when litter with high C-N ratio was provided as a food source. Especially in the miscanthus treatments, less N might remain for enzymatic degradation, indicating that N competition between earthworms and microorganisms may vary between different litter types. Especially, an expansion of miscanthus in agricultural management systems might result in a reduced microbial activity and a higher N deficit for microorganisms in soil.     

Understory vegetation,soil structure and soil invertebrates in Congolese eucalypt plantations,with special reference to the invasive plant Chromolaena odorata and earthworm populations

Earthworm relationships with vegetation have received extensive attention, and earthworm density has been shown to be related to vegetation types or plant species. However, the factors involved are rarely known. In Congo, we studied the effect of Chromolaena odorata (L) R.M. King & H. Robinson, which invades eucalypt plantations, on soil invertebrates, especially earthworms. In order to investigate relationships between vegetation cover and soil invertebrates, four understory species, including C. odorata, were studied. Also, comparisons were made between plots invaded by C. odorata and plots free from it. The addition of leaf litter on experimental plots was made in order to check its influence. Plant remains were observed in the digestive tract of earthworms. An increased earthworm density was observed under C. odorata. The leaf litter and roots of this species had low lignin/N ratio. The size of leaf fragments found in the digestive tract of the earthworms, and the lack of short-term effect of experimentally added leaf litter, suggested that litter quality could influence earthworm through their feeding on fine particulate top soil organic matter. The amount of soil aggregates, in the size classes that fitted the size range of earthworm casts, was increased under C. odorata. More field experiments are needed to establish a causal effect in the relationships observed between earthworm density and C. odorata. If so, the major drawbacks, such as water and nutrient competition, resulting from C. odorata overrunning the plantations, could be somewhat offset by its positive effects through soil improvement.     

全灭菌环境下蚯蚓和堆肥对土壤五氯酚老化过程的影响

通过全灭菌环境下的土壤五氯酚（PCP）污染模拟实验,分别测定水提取态、乙醇提取态、腐殖质固定态以及蚯蚓生物累积态PCP的变化,研究添加两种不同蚯蚓品种（赤子爱胜蚓和壮尾环毛蚓）和堆肥对土壤PCP老化过程的影响。结果显示,在42d的培养期内,水提取态PCP在全灭菌土壤对照和添加灭菌堆肥的处理中随时间推移逐渐下降,存在明显的老化效应。在蚯蚓处理中,水提取态PCP呈现先下降后上升的趋势,说明蚯蚓促进土壤PCP的解吸附,这主要与蚯蚓的生物扰动作用以及调节土壤pH趋向中性的作用直接相关。培养结束时,蚯蚓能够有效促进土壤PCP向腐殖质固定态转化,并进一步促进PCP的去除,这与蚯蚓提高土壤腐殖质的含量,促进PCP的化学还原转化作用以及蚯蚓自身对PCP的消解作用有关。壮尾环毛蚓比赤子爱胜蚓更能有效促进PCP的转化与去除,这与两者的生活习性不同有关。灭菌堆肥对全灭菌土壤PCP向其他形态转化的影响不显著。     

Earthworms in New Zealand sheep- and dairy-grazed pastures with focus on anecic Aporrectodea longa

Earthworms play an important role as primary decomposers in the incorporation and initial mixing of plant litter. This study explored the response of earthworms to increasing fertiliser inputs, pasture production and livestock numbers (and their influence on food availability and soil physical condition) on six different managements in sheep-grazed and fifteen different managements in dairy-grazed pastures in a variety of New Zealand soils.Native earthworms were only found in some low-fertility pastures. Accidentally introduced peregrine earthworms, when present, dominate pasture soils. Of these, endogeic earthworms dominated the earthworm community and were positively associated with soil types with higher bulk densities. Peregrine anecic earthworms were absent from most hill-country sheep-grazed pastures, however in more fertile and productive dairy-grazed pastures they reached a biomass of up to 2370 kg ha^?1. Only anecic earthworms showed a positive response to the increasing pressures associated with higher potential dry matter inputs and liveweight loadings of grazing livestock on soil, while epigeic earthworms declined. The positive response of anecic earthworms probably reflects the combined effect of the increase in food resources, including dung and plant litter, available on the soil surface, and their lower susceptibility to livestock treading pressure. Anecic species may be a suitable substitute for incorporation of surface litter in those soils where livestock treading limits epigeic earthworm populations.This study confirmed previous observations of limited distribution of the introduced Aporrectodea longa in pastoral hill-country soils in the North Island, and their near absolute absence from the South Island of New Zealand. This would suggest that large areas of New Zealand pastoral farmed soils could benefit from the introduction of anecic species from other parts of New Zealand which already contain A. longa.     

Inter- and intra-specific interactions of Lumbricus rubellus (Hoffmeister, 1843) and Octolasion lacteum (Örley, 1881) (Lumbricidae) and the implication for C cycling

Earthworms are important engineering species of many terrestrial ecosystems as they play a significant role in regulating C turnover. The effects of earthworms on moderating C decomposition processes differ across species and with interactions between species, which is not fully understood. We carried out an experiment to study the interactions of Lumbricus rubellus and Octolasion lacteum, and their effects on soil respiration. Laboratory mesocosms were set up using tulip poplar (Liriodendron tulipifera) leaf litter and varying densities of earthworms in single and combined species treatments. CO₂ efflux rate was used as an indicator of C decomposition rates, and measured with CO₂ sensors every five days over one month. L. rubellus induced higher leaf consumption rate and higher CO₂ efflux than O. lacteum; meanwhile O. lacteum grew more than L. rubellus. Both litter consumption rate and growth rate of earthworms decreased with increasing earthworm density. Soil CO₂ efflux increased with increasing earthworm density (from ∼1-2 μg CO₂ g⁻¹ hr⁻¹ with no earthworms to ∼ 4 μg CO₂ g⁻¹ hr⁻¹ with 8 earthworms). Combining the two species had a synergistic effect on leaf litter consumption, and neutralizing effects on soil respiration. The data suggest that the strength of intra- and inter-specific interactions among earthworm ecological groups varies at different absolute and relative densities, leading to altered leaf litter decomposition and C cycling.     

Effects of different land use on soil chemical properties, decomposition rate and earthworm communities in tropical Mexico

The effects of land use on soil chemical properties were evaluated, and earthworm communities and the decomposition rate of three typical land use systems in tropical Mexico, namely banana plantations (B), agroforestry systems (AF) and a successional forest (S) were compared.The study was carried out from November 2005 to April 2006. A completely randomized sampling design was established in six sites (B1, B2, AF1, AF2, S1 and S2). Soil properties and chemical characteristics (texture, pH, organic carbon (Corg), nutrients, and available Zn and Mn), earthworm communities and the decomposition of Bravaisia integerrima and Musa acuminata litter were analyzed over a period of 8 weeks.All soils were loamy clays with a medium to high content of nutrients. Three principal clusters were generated with the soil chemical properties: a first cluster for forest soils with high Corg and Ntot and low available Zn content, a second cluster for AF1 and a third cluster for B1, B2 and A2.The decomposition of B. integerrima litter was significantly faster (half-life time: 1.8 (AF2)–3.1 (B1) weeks) than that of M. acuminata (4.1 (AF2)–5.8 (S2) weeks). However, the decomposition rates did not differ significantly among the different sites.The greatest earthworm diversities were observed in AF2 and B1. Native species were dominant in the forest soils, whereas exotic species dominated in AF and in the banana plantations. The abundance and biomass of certain earthworm species were correlated to physical and chemical soil parameters. However, litter decomposition rates were not correlated with any of the soil physical–chemical parameters.While none of the land use systems studied led to a decrease in nutrient status, earthworm biodiversity and abundance, or in litter decomposition rate, they did result in a change in earthworm species composition.     

Can the invasive earthworm,Amynthas agrestis,be controlled with prescribed fire?

Biological invasions are one of the most significant global-scale problems caused by human activities. Earthworms function as ecosystem engineers in soil ecosystems because their feeding and burrowing activities fundamentally change the physical and biological characteristics of the soils they inhabit. As a result of this “engineering,” earthworm invasions can have significant effects on soil physical, chemical and biological properties. The species Amynthas agrestis (family Megascolecidae) was introduced to the United States from Asia, and has expanded its distribution range to include relatively undisturbed forests. Here, to clarify life history traits, we reared individuals under seven different conditions of food provision using litter, fragmented litter and soil, and also analyzed the stable isotope ratios of field-collected specimens to investigate their food resources in the field. Second, we examined whether prescribed fire can be used to manage invasive earthworms. We constructed eight experimental plots, each with 100 individuals of A. agrestis each, and burned half of the plots. The feeding experiment showed that the earthworms in units containing soil and some form of organic matter (litter and/or fragmented litter) produced many cocoons, indicating that litter and fragmented litter are important food resources for them. Stable isotope analyses also supported this result. During the experimental fires, average soil temperature at 5 cm depth increased by only 7.7 °C (average maximum of 32.2 °C). Litter mass was significantly reduced by the fires. Although numbers of A. agrestis and cocoons recovered from burned and unburned plots were not different, the viability of cocoons was significantly lower in burned plots. Fire may also reduce the survival rate of juveniles in the next year by depriving them of their preferred food resource. Most native earthworms in the United States live in the soil, while many invasive ones live in the litter layer and soil surface. Therefore, prescribed fire could be a viable tool for control of invasive earthworms without negatively impacting native earthworm populations.