The heterogeneity of humus profiles and earthworm communities in a virgin beech forest

Thirty sites, encompassing a range of soil and vegetation conditions in the biological reserve of La Tillaie (Fontainebleau Forest, France) were investigated in April 1992. Beech (Fagus sylvatica L.) was the dominant tree species, with several developmental phases forming the forest patchwork. Sessile oak [Quercus petraea (Mattus.) Liebl.] was present but only as old relictual individuals. Gaps in the canopy cover were abundant, mostly caused by wind storms 2 years previously. The next most recent storm was 25 years before, resulting in distinct patches of full-grown trees. Humus profiles were classified and compared with the distribution of earthworm communities, canopy cover, and soil types. Geomorphology was responsible for the main part of the observed variation. Absence of lime in the substrate and direct contact with a sandstone stratum near the ground surface was associated with the absence of earthworms and the appearance of an OH horizon (moder humus). Elsewhere, earthworms were present and humus profiles did not display any OH horizon (mull or mull-like moder humus), but species composition was variable and strongly influenced by the thickness of the superficial sand deposit overlying limestone. On a thick (1 m or more) sandy substrate earthworm communities were dominated by epigeic species together with the anecic Lumbricus terrestris L. The species richness was higher on a shallower sandy substrate (50 cm) where lime was more accessible to tree roots and burrowing animals. The influence of the forest cycle of beech was visible in the latter case (covering most of the area), with an increase in the thickness of the OL and OF horizons and a decrease in endogeic earthworm populations during the phase of intense growth of beech. This fall in burrowing activity was apparent in gaps created by wind storms and fungal diseases within mature stands as early as 2 years after the fall of the trees.     

Ecology of soil springtails (Collembola, Insecta) from pine woods and Rhododendron shrublands in the Central and Eastern Pyrenees (North Spain)

The collembological composition of samples from the Central and Western Pyrenees (Northern Spain) was studied. Soils from two biotopes (pine forest and Rhododendron shrub) were studied in Nuria and Vallibierna, using different diversity indices and multivariate analyses. Ten species were found that were endemic to the Iberian Peninsula. Three of these are exclusive to the Pyrenees: Ceratophysella elegans, Hypogastrura dasiensis and Protachorutes pyrenaeus. The greatest diversity was observed in the soils of Rhododendron, above all at Nuria. Collembola were most poorly represented in the pine forest of Vallibierna, where the endemic Hypogastrura meridionalis was the dominant species. Multivariate analyses indicated that the latter species characterizes this pine forest and separates it from all other biotopes studied. The evenness (E) was most pronounced in Nuria, where Folsomia manolachei was the characteristic species.     

Interactions between tree seedling roots and humus forms in the control of soil C and N cycling

The hypothesis that roots enhance soil-N turnover in humified soil organic matter (SOM) (mull) but not in lignified SOM (mor) was tested in a study involving the growth of eight species of tree seedlings on the two contrasting humus forms. After 12 and 22 weeks of seedling growth, soil-CO₂ efflux was measured with (1) growing seedlings, and after 22 weeks, with (2) roots only, shoots excised, and (3) with roots removed and soils amended with different rates of glucose. Indices of C-flux and of soil available-C were derived and compared to plant-N uptake, extractable soil mineral-N, anaerobically mineralized soil-N, N bioavailability to Agrostis grass following harvest of seedlings, and to seedling fine root C-chemistry. Significant soil x species interactions were found for total soil-CO₂ efflux, root-dependent CO₂, soil available-C and microbial biomass. In all cases, roots were important contributors to C-cycling in the mull soil but not in the mor soil. C was more limiting in the mor than in the mull microbial community. Plant-N uptake and the mineral-N pool was greater in the mor soil, reflecting that soil's higher specific N-supplying capacity (N-mineralized:CO₂). Seedlings decreased the mineral-N pool in both soils, but the presence of roots increased N-mineralization in the mull soil and decreased N-mineralization in the mor soil. Significant positive relationships were observed in the mull soil only between soil respiration and plant N uptake at mid-season, and between soil respiration and N-mineralization at late-season. Birch root activity in the mull soil was greater than that of all other seedlings and this observation is discussed with respect to the autecology of birch. Soil respiration correlated with the non-polar extract content but not the lignin:N ratio of fine roots. Results suggest that root-released C in mull SOM is sufficient to relieve energy limitation to soil microbes and allow them to access appreciable amounts of soil-N, whereas ligninolytic activity, which may ultimately control soil-N turnover in mor SOM, is not increased by rhizodeposition.     

Earthworm functional groups are related to denitrifier activity in riparian soils

Riparian buffers, located in the transition zone between terrestrial and aquatic ecosystems, are a hotspot for nitrogen (N) removal through denitrification. Earthworms are abundant in riparian buffers and may enhance denitrification. This study investigated earthworm demographics of three earthworm functional groups (anecic, epigeic, and endogeic) and denitrifier activity in temporarily flooded and non-flooded riparian soils from April to October 2012 in southern Quebec, Canada. Nine earthworm species, mostly endogeic, were found in the temporarily flooded soil, while only six earthworm species were found in the non-flooded soil. On average, there were 11.7 times more earthworms with 12.4 times greater biomass (P<0.05) found in the temporarily flooded soil than in the non-flooded soil. The denitrification enzyme activity (DEA) was of similar magnitude in temporarily flooded and non-flooded soils, with temporal variation associated with rainfall patterns. Endogeic earthworm biomass was positively correlated (P<0.05) with DEA, while epigeic earthworm biomass was positively correlated (P<0.05) with 16S rRNA gene copies and nosZ gene copies from bacteria, indicating an association between earthworm functional groups and denitrifier activity in riparian soils. Stepwise multiple regressions showed that DEA in riparian soils could be predicted using soil moisture, inorganic N concentration, and earthworm functional groups, suggesting that endogeic and epigeic earthworms contributed to denitrifier activity in riparian soils.     

Fluoride-induced changes in chemical properties and microbial activity of mull,moder and mor soils

Summary Fluoride-induced changes of chemical properties and microbial activities in humus soils were investigated in 12-week lysimeter experiments. The mull soil showed the highest F-adsorption capacity, in which 94% of the fluoride added was retained after addition of 4.5 mg F/cm² as NaF. The moder and mor soils only adsorbed 52% and 41%, respectively. F-additions induced leaching of organic matter, Fe, Al and P and increases in soil pH in the moder and mor. In contrast no Al, Fe and P was leached from the mull and only minor amounts of organic matter dissolved after a single application of 4.5 mg F/cm². Treatments with NaF up to 3700 mg F/kg did not significantly reduce respiration in any of the humus forms. Dehydrogenase, alkaline phosphatase and arylsulfatase activities as well as nitrification were inhibited at much lower F-additions in the moder and mor soils. A significant decrease in ammonification was observed in the moder. In contrast, microbial processes in the mull soil were not inhibited. This is due to its high adsorption capacity and the relatively low toxicity of F-ions. According to computations using GEOCHEM, the F-ion was the most abundant species in mull lysimeter leachates. Leachates of moder and mor soils contained mainly AIF-complexes (90%–99%). The lack of any effects from NaF treatment on soil respiration is attributed to the observed positive effects, e.g. dissolution of organic matter, desorption of P and increases in soil pH.     

Über Sorption und Wirkung von Blei auf die biologische Aktivität terrestrischer Humusformen

Lead sorption and effect of lead pollution on biological activity of different types of humus forms Effects of Pb(NO₃)₂ on biological activity (e. g. respiration and enzyme activity) of mull, moder and mor soils were investigated under controlled laboratory conditions. Lead sorption capacity of investigated humus forms decreased in the order mull > moder > mor. Soil respiration was inhibited after addition of 10 mg Pb/g soil at lead concentrations > 1 μg Pb/ml of soil solutions of the mor and moder profiles. Highly significant positive regression coefficients were obtained for decreases in soil respiration and decreases in dehydrogenase-, phosphatase- and arylsulfatase activities of O-horizons. It is assumed that minor enzymatic acitivities after lead addition result from its effect on enzyme producing organisms. After additions of 200 mg Pb/g soil biological activities of investigated humus layers were also affected by a marked increase of acidity of soil solutions. This ?secondary”? effect was also obtained using Ca(NO₃)₂ in pollution experiments.     

Earthworm burrowing behaviour in 2D terraria with single- and multi-species assemblages

Experiments were performed in 2D terraria to investigate the burrowing behaviour of different earthworm species from various ecological categories in single- and multi-species assemblages. The burrowing behaviour was quantified using image analysis software during a 2-week period. Terraria were found to reveal realistic impressions of the burrowing behaviour of various species according to the ecological classification of Bouché into epigeic, endogeic and anecic species. Results of the study also permit the recommending of classifying various earthworms as intermediate species, e.g. Aporrectodea longa as endo-anecic and Lumbricus rubellus as epi-endogeic. Burrowing activity of endogeic species was significantly reduced in multi-species compositions compared to single-species treatments. Moreover, burrowing activity of Octolasion tyrtaeum was significantly reduced in the presence of Lumbricus terrestris compared to the specific single treatment. This endogeic species profited from the burrowing behaviour, e.g. bioturbation, of L. terrestris, and as such this is circumstantial evidence for commensalism (species interaction, in which one partner benefits while the other is unaffected) between anecic and endogeic earthworm species. Simultaneous burrowing activity of a combined assemblage of both endogeic species, Aporrectodea caliginosa and O. tyrtaeum, was also significantly reduced compared with the particular single treatments. Thus, this seems likely to be a response of interspecific competition and trophic niche separation between endogeic species.     

Chemical characterization and decomposition of organic matter from two contrasting grassland soil profiles

Particle size fractions of soils from the surface 6 cm of two adjacent grassland plots which, as a result of different fertilizer treatments since 1897, have either a mor or a mull humus form were analysed using solid-state ¹³C nuclear magnetic resonance spectroscopy and fractionation of organic N by steam distillation. In the mor humus soil, which had received 180 kg (NH⁴)²SO⁴ ha^?1 annually and was pH 4.3, there was more C and N in the larger particle size fractions than in the mull humus soil (pH 5.8). The NMR spectra of correspondingly sized soil fractions were similar for both soils. The intensities of NMR signals between 0 and 40 ppm (alkyl-C) and between 160 and 200 ppm (carbonyl-C) increased with decreasing particle size. The intensities of the NMR signals between 60 and 90 ppm (0-alkyl-C) and between 90 and 110 ppm (acetal- and ketal-C) decreased with increasing particle size. Comparison of the NMR spectra of the >2000 um fractions from both soils with those of dried grass litter from the same plots indicated the exclusive plant origin of the C in the largest size fraction of the soils. NMR resonances between 40 and 60 ppm were attributed to alkyl-amino-C because their intensities agreed with the amino-N determinations obtained during organic N fractionation. During incubation in soil microcosms, the larger sized fractions decomposed more rapidly than the smaller fractions. However, all the correspondingly sized particle fractions from the two soils decomposed at the same rate except the >2000 pm fractions. The largest size fraction from the mor humus soil decomposed faster than that from the mull humus soil. This difference in decomposition rate could not be attributed to differences in the chemical composition of the >2000 pm fraction.     

Changes in the earthworm community of an acidophilous lowland beech forest during a stand rotation

The study examines humus profile development during a chronosequence consisting of four beech forest growth stages, and particularly the role of some components of soil fauna (lumbricid oligochaetes) on humus morphogenesis. An experimental site was set up in a lowland beech forest (Fougères state forest, eastern Brittany, France) to carry out a chronosequence analysis. This lowland beech forest is acidophilous, managed as an even-aged beech stand. The dominant tree species is beech (Fagus sylvatica L.). Samples were taken twice a year, from autumn 1997 to spring 2000 inclusive. Earthworms were caught after watering with formalin solutions. Only five species were found: three epigeic (litter-dwellers): Dendrobaena octaedra, D. rubida tenuis, Eisenia eiseni; one epi-anecic (litter/soil-dweller): Lumbricus rubellus; one endogeic (soil-dweller): Allolobophora caliginosa. D. octaedra is dominant in the four plots at densities ranging from 41 ind·m^–2 (88 % of total earthworm population) to 12.4 ind·m^–2 (99 % of total). Species richness and abundance are low in accordance with a moder humus form typical of acid soil conditions. Results are discussed according to plot heterogeneity, stand age, seasonal variations and functional diversity.     

Humus forms and metal pollution in soil

Smelters in northern France are a serious source of soil pollution by heavy metals. We have studied a poplar plantation downwind of an active zinc smelter. Three humus profiles were sampled at increasing distance from the smelter, and the thickness of topsoil horizons was measured along a transect. We analysed the vertical distribution of humus components and plant debris to assess the impact of heavy metal pollution on the humus forms and on soil faunal activity. We compared horizons within a profile, humus profiles between them, and traced the recent history of the site. Near the smelter, poplar trees are stunted or dead and the humus form is a mor, with a well‐developed holorganic OM horizon. Here faunal activity is inhibited, so there is little faecal deposition and humification of plant litter. At the distant site poplar grows well and faunal activity is intense, so there are skeletonized leaves and many organo–mineral earthworm and millipede faecal pellets. The humus form is a mull, with a well‐developed hemorganic A horizon. The passage from mor to mull along the transect was abrupt, mor turning to mull at 250 m from the smelter, though there was a progressive decrease in heavy metal deposition. This indicates that there was a threshold (estimated to be 20 000 mg Zn kg^?1) in the resilience of the soil foodweb.     

Earthworms and pH affect communities of nematodes and enchytraeids in forest soil

In northern boreal forests the occurrence of endogeic and anecic earthworms is determined by soil pH. Increasing evidence suggests that large detritivorous soil animals such as earthworms can influence the other components of the decomposer community. To study the effects of earthworms and pH on soil nematode and enchytraeid communities, a factorially designed experiment was conducted with Lumbricus rubellus and/or Aporrectodea caliginosa. Earthworms were added to "mesocosms" containing unlimed (pH 4.8) or limed (pH 6.1) coniferous mor humus with their natural biota of micro-organisms. In the absence of earthworms, nematodes were significantly more abundant in limed than in unlimed humus. Earthworms markedly decreased the numbers of nematodes both in unlimed and limed soils. Earthworm activities eliminated enchytraeids in unlimed soil, but liming improved the survival of some species. It was concluded that liming of soil, either alone or mediated by the earthworm populations, is likely to affect soil nematode and enchytraeid community and mineralisation.     

The impact of earthworms on the abundance of Collembola: improvement of food resources or of habitat?

I assessed the direct influence of earthworm excretions, and the impact of earthworms through their action on the soil structure (increased macroporosity), on the population dynamics of the collembolan species Heteromurus nitidus. The intestinal content of Collembola arising from cultures on different soil types was observed, and two experimental cultures of H. nitidus were run: (1) a culture performed on an inert substrate supplied either with earthworm casts or with soil as food resource, (2) an experiment using microcosms with cores of two humus forms (moder and calcic mull), in the presence or absence of earthworms. The observation of gut contents revealed that H. nitidus feeds on excrements, the composition of which (ratio organic matter/mineral matter) varies according to the humus form where it lived. Slightly aged (10–15 days) organo-mineral casts of earthworms appeared to be a better food than calcic mull aggregates or organic material from moder. Densities of H. nitidus cultured in cores of calcic mull were higher than in moder, except when cores of moder were inhabited by an anecic earthworm for 2 months. The humus form strongly influenced populations of H. nitidus, firstly because densities of predators were higher in moder than in calcic mull, and probably also because of soil macroporosity. It was concluded that earthworms would affect predation on H. nitidus by creating a network of interconnected macropores in which Collembola can move and find shelter.     

HUMUS TYPE DISCRIMINATION USING PATTERN RECOGNITION OF THE MASS SPECTRA OF VOLATILE PYROLYSIS PRODUCTS

Mull and mor humus can be distinguished in freely drained British surface soils by the pyrolysis products derived from whole soil samples. About i milligram of soil is pyrolysed at 770 °C in a Curie point apparatus and a sample of the volatile decomposition products is allowed to enter a low-resolution mass spectrometer. A numerical value (the ‘Discriminator Value’) which will discriminate between the two humus types is then calculated from the spectrum of each sample. This is performed by multiplying the intensity of each mass peak by a weight factor and then summing the weighted intensities up to mass 110 The weight factors are obtained empirically by taking sets of spectra from clearly distinguished mull and mor samples and applying a computerized learning machine procedure. Once obtained, they are relatively easily applied to spectra from other soils. The method places all samples on a numerical scale on which mull types appear positive up to about 20 × 10⁸ and mor types negative down to about -15 × 10³, intermediate types being recognized in about the middle of the range. It is indicated that the most important pyrolysis products active in the discrimination process are the olefin hydrocarbons, particularly ethylene, which are produced in greater abundance from mor humus.     

Different earthworm ecological groups interactively impact seedling establishment

There is increasing evidence that direct interactions between earthworms and seeds impact the assembly of plant communities. However, effects of earthworms of different ecological groups and their interactions on plant germination and establishment are little known. We set up a full-factorial greenhouse experiment in order to explore impacts of different ecological groups of earthworms (epigeic, endogeic and anecic) on the establishment of seedlings. The three ecological groups of earthworms affected seedling establishment in an interactive way with the effects varying in time. While anecic earthworms detrimentally affected the number of established seedlings, impacts of epigeic and endogeic species depended on the presence of earthworms belonging to other ecological groups. Impacts of anecic earthworms were more significant and consistent than those of epigeic and endogeic ones pointing to the dominance of the effect of anecic earthworms for seedling establishment. The initial positive effect of the combined presence of epigeic and endogeic earthworms compared to treatments with only endogeic and only anecic earthworms was likely due to the acceleration of seed germination and elevated nutrient availability for seedlings in earthworm casts. By contrast, reduced numbers of seedlings in presence of both epigeic and endogeic earthworms compared to the control treatment might have been due to seedling predation after the litter layer had disappeared. The results extend current knowledge on interactions between earthworms and seeds by showing that, in addition to anecic species, also epigeic and endogeic species influence seedling establishment with their effect depending on the presence of anecic species. Moreover, the results indicate that impacts of earthworms vary with the developmental stage of seedlings highlighting the importance of interactions between earthworms and seeds.     

Earthworm communities in temperate beech wood forest soils affected by liming

To monitor the effects of liming on forest ecosystems, experimental plots were installed in forests in mid-western Germany. In addition to soil chemical indices, earthworm communities were investigated on these plots about 15 years after first lime applications took place. As a “natural reference”, communities were compared to earthworm records that derived from a beech forest on limestone. In the non-acidified plots that had never been limed only epigeic earthworms were detected in small numbers and low species richness. Forest liming caused higher pH and a higher base saturation in the mineral topsoils. To a large extent, epigeic earthworm species seemed to benefit from this and had increased in number and biomass at all three different locations selected for the investigations. The epigeic dominated communities were completed by anecic Lumbricus terrestris that was rarely found in some of the samples from one location and a number of endogeic species that showed a very patchy distribution in limed plots. In contrast to this, the soil of the beech forest on limestone showed a different community composition. It was dominated by endogeic species in abundance and by anecic species in biomass. On limestone the total biomass of earthworms clearly exceeded the biomass values from all other plots. In conclusion, a long-term support of forest earthworm fauna due to liming was detected. This support was mainly effective for epigeic species, but in some cases for endogeic and anecic species, too.     

Earthworm feeding activity and development of the humus profile

Earthworm casts and digestive tract contents were simultaneously examined, using the same methods, in a recently formed humus profile in a mountain spruce forest. Earthworm species had distinct diets and an earthworm foodweb could be distinguished. Lumbricus terrestris and Aporrectodea icterica were distinct from the other species examined: the former to some extent as a litter consumer, and both species because they excavated mineral material which was deposited within new top layers of the mull humus. Aporrectodea nocturna and Aporrectodea caliginosa both had a non-specific soil feeding mode. Most of the species enriched the humus profile with amorphous organic matter finely incorporated within a mineral matrix. Besides different food selection, a network of burrows was produced as a consequence of the different burrowing behaviour of each earthworm species. Received: 2 January 1997     

Polycyclic Aromatic Hydrocarbons Content in Contaminated Forest Soils with Different Humus Types

The aim of the study was to determine polycyclic aromatic hydrocarbon (PAH) content in different forest humus types. The investigation was carried out in Chrzanów Forest District in southern Poland. Twenty research plots with different humus types (mor and mull) were selected. The samples for analysis were taken after litter horizons removing from a depth of 0–10 cm (from the Of- and Oh-horizon total or A-horizon). pH, organic carbon and total nitrogen content, base cations, acidity, and heavy metal content were determined. In the natural moisture state, the activity of dehydrogenase was determined. The study included the determination of PAH content. The conducted research confirms strong contamination of study soil by PAHs and heavy metals. Our experiment provided evidence that different forest humus types accumulate different PAH amounts. The highest content of PAHs and heavy metals was recorded in mor humus type. The content of PAHs in forest humus horizon depends on the content and quality of soil organic matter. Weaker degradation of hydrocarbons is associated with lower biological activity of soils. The mull humus type showed lower content of PAHs and at the same time the highest biological activity confirmed by high dehydrogenase activity.     

Earthworm excreta (mucus and urine) affect the distribution of springtails in forest soils

The collembolan species Heteromurus nitidus, exclusively located in soils at pH>5, can be cultured in acidic humus. As this species is attracted to the excreta of earthworms from calcic mull, its distribution is supposed to be determined only indirectly by soil pH through the distribution of earthworms. Higher densities and biomasses of Lumbricidae were observed in a calcic mull (pH 7.8) than in an acidic mull (pH 4.8) and a moder humus (pH 4.2). Choice experiments were performed to compare the attraction of H. nitidus to the mucus-urine mix of five earthworm species from the calcic mull and the acidic mull. H. nitidus was attracted to the excreta of the five species, whatever their ecological category and the humus form from which they originated. The collembolan Heteromurus major, which was indifferent to soil pH, was not attracted to earthworm excreta, which emphasizes the significance of this phenomenon for the distribution of H. nitidus over a pH range. The attraction of H. nitidus to earthworm excreta tended to be weaker and more variable when earthworms originated from acidic mull compared to calcic mull, particularly in the case of Lumbricus terrestris. Increased earthworm density reinforced by better mucus quality and quantity could determine the distribution of H. nitidus according to soil acidity. The only urine compound capable of attracting H. nitidus was NH₃ at a low concentration (0.03 g l^-1). The NH₃ content of the mucus-urine mix which attracted H. nitidus was 0.037 g l^-1, and was therefore responsible, at least partly, for the attraction.     

Selenitadsorption an Waldhumusformen

Adsorption of selenite on different types of forest humus In the present investigation the adsorption of selenite selenium on L-, O-, and A-horizons of the humus forms mull, moder, and mor was studied. Selenite adsorption decreased in the order mull > moder > mor. The organic layers adsorbed nearly the same amount of selenium as the underlying A-horizons. Among the L- and O-layers selenadsorption increased with increasing pH. Amounts of organic carbon, “free” oxides did not influence the adsorption capacity. The Freundlich equation was valid to describe selenite adsorption of all layers under investigation. Additionally the Langmuir equation fitted the adsorption curves of the mull soil and the moder L-horizon. Adsorption experiments using perfusion apparatuses showed microorganismus to incorporate high amounts of selenite under natural conditions.     

Axial and radial pressure exerted by earthworms of different ecological groups

 The aim of this study was to measure the pressures exerted by earthworms during burrowing. For this purpose we developed two methods with which to quantify the axial and radial pressure. The data were recorded with an electronic balance that was connected to a PC. Artificial earthworm burrows were used to standardize the measurements. Plexiglas tubes with diameters ranging from 2 to 6.3 mm which corresponded to the diameter of the earthworms were used. A pin was placed inside the tubes, on which the earthworms exerted a pressure by peristaltic locomotion. Only the maximum values of the pressure measurement were taken into account for evaluation, and the arithmetic mean was calculated. The measurements were conducted with Aporrectodea longa, Lumbricus terrestris, Aporrectodea caliginosa, Octolasion cyaneum, Allolobophora chlorotica, Aporrectodea rosea, Lumbricus rubellus and Dendrobaena octaedra. The species examined were classified into ecological groups. The mean axial pressures exerted by each group were in the order: epigeic (14–25 kPa), endogeic (27–39 kPa) and anecic (46–65 kPa). For the mean radial pressure the order was: epigeic (39–63 kPa), anecic (72–93 kPa) and endogeic (59–195 kPa). It was apparent from the results that radial pressure is the most important pressure with respect to the burrowing activity of earthworms. Received: 28 April 1998