The effects of feeding byOniscus asellus (Isopoda) on nutrient cycling in an incubated hardwood forest soil

Summary Oniscus asellus produced changes in the nutrients leached from Oie and Oa horizons of a hardwood forest soil. Soil with isopods lost more K⁺ (54%) from the Oie horizon and more Ca²⁺ (25%), Mg²⁺ (40%), and water-extractable S (23%) from the Oa horizon than soil without isopods. In contrast, soils with isopods lost less Ca²⁺ (39076) from the Oie horizon and less dissolved C-bonded S (33%) from the Oa horizon than soil without isopods. In addition, the Oia and Oa horizons exhibited different nutrient dynamics. When isopods were present, the Oa horizon leachates accumulated more Na⁺ K⁺, Ca²⁺, Mg²⁺, NO₃ ^– , water-soluble SO₄ ^2–, and dissolved C-bonded S, and the Oie horizon retained more of these nutrients. The type of leaching solution also had a major effect on nutrients. Leaching with a simulated soil solution resulted in smaller nutrient losses for K⁺ and Mg²⁺ in both horizons and for Na⁺, Ca²⁺, and NO₃ ^– in the Oa horizon than leaching with distilled water.     

Site of leaf origin affects how mixed litter decomposes

Recent studies have demonstrated that mass loss, nutrient dynamics, and decomposer associations in leaf litter from a given plant species can differ when leaves of that species decay alone compared to when they decay mixed with other species’ leaves. Results of litter-mix experiments have been variable, however, making predictions of decomposition in mixtures difficult. It is not known, for example, whether interactions among litter types in litter mixes are similar across sites, even for litter mixtures containing the same plant species. To address this issue, we used reciprocal transplants of litter in compartmentalized litterbags to study decomposition of equal-mass litter mixtures of sugar maple (Acer saccharum Marshall) and red oak (Quercus rubra L.) at four forest sites in northwestern Connecticut. These species differ significantly in litter quality. Red oak always has higher lignin concentrations than maple, and here C:N is lower in oak leaves and litter, a pattern often observed when oak coexists with maple. Overall, we observed less mass loss and lower N accumulation in sugar maple and red oak litter mixtures than we predicted from observed dynamics in single-species litterbags. Whether these differences were significant or not depended on the site of origin of the leaves (P<0.02), but there was no significant interaction between sites of decay and the differences in observed and predicted decomposition (P>0.2) . Mixing of leaf litter types could have significant impacts on nutrient cycling in forests, but the extent of the impacts can vary among sites and depends on the origin of mixed leaves even when the species composition of mixes is constant.     

Fragmentation of leaf litter by a natural population of the millipede Julus scandinavius (Latzel 1884)

Summary The rate and degree of fragmentation of leaf litter by Julus scandinavius in a Sycamore/ash wood in Cheshire, England, were determined from the ratio of surface area of the leaf diet consumed by all individuals of each instar during the period when they were present on the surface area of leaf materials in the faecal pellets. Generally, the rate of fragmentation of leaf litter decreased in the series young instars sexed immature instars mature instars. The total degree of increase in the fragmentation of leaf litter by the population was 72×10⁶.     

Leaf litter selection by detritivore and geophagous earthworms

Summary Litterbag experiments with 10 different kinds of leaf litter showed that detritivore (Lumbricus species) and geophagous (Aporrectodea species) earthworms prefer certain litter types over others, since different numbers of worms were found below the litter after 50–52 days of exposure in a pasture. The detritivores preferred Fraxinus, Tilia, and predecomposed Ulmus and Fagus litter to Fagus litter and paper, while geophages preferred Tilia litter to Alnus and Ulmus litter, so that the two groups of earthworms showed different preferences. The detritivores seemed to be more selective than the geophages. The palatability of the litter was examined in relation to the C: N ratio, the lignin concentration and the initial and final polyphenol concentration. The numbers of detritivores were significantly correlated with the C: N ratio and the final polyphenol concentration, so that selection of litter seems to be related to palatability. The numbers of geophages were not significantly correlated with any of the parameters for palatability. The disappearance of litter after 50–52 days appeared to be due to detritivore activity, since the numbers found below the litter were positively and significantly correlated with the litter disappearance. There was no significant correlation with geophage activity. This indicates that detritivores use litter as food, and therefore influence the composition of the litter layer.     

紫茎泽兰叶片凋落物对入侵地4 种草本植物的化感作用

为了明确紫茎泽兰叶片凋落物对入侵地草本植物的化感作用, 研究了不同浓度紫茎泽兰叶片凋落物水提液对入侵地草本植物多年生黑麦草、白三叶、辣子草和紫花苜蓿种子萌发和幼苗生长的影响, 同时结合土培试验研究了叶片凋落物在入侵地土壤中的化感作用。结果表明, 除多年生黑麦草外, 水提液对其他3 种草本植物种子萌发均产生了显著的化感抑制作用, 且水提液的浓度越高抑制效果越强; 低浓度水提液对紫花苜蓿和辣子草的幼苗生长存在显著化感促进作用, 高浓度的水提液对除多年生黑麦草外的其他3 种植物幼苗的生长存在显著化感抑制作用, 水提液对多年生黑麦草幼苗生长的影响不显著; 土壤中按照50 g·kg^-1的比例添加叶片凋落物后, 显著抑制了白三叶的生长, 而添加活性炭后, 白三叶的单株生物量相对于未添加活性炭的处理增加71.25%, 进一步证实叶片凋落物在土壤中的化感抑制作用。这说明外来入侵植物紫茎泽兰可能通过其叶片凋落物在入侵地土壤中降解, 释放化感物质, 抑制伴生植物的种子萌发和幼苗生长, 为自身创造有利的生长环境, 实现其成功入侵和扩张。     

不同氮源对三倍体毛白杨落叶分解的影响

为探索加快毛白杨落叶分解的途径, 采取室内培养的方法研究了添加铵态氮、硝态氮及混合氮对三倍体毛白杨落叶分解速度和主要营养元素释放的影响。结果表明, 添加氮源对三倍体毛白杨落叶分解有一定的促进作用, 不同氮源之间差异显著。140 d后, 施加铵态氮、混合氮和硝态氮的落叶分解率分别为46.0%、30.0%和28.8%, 而对照为27.4%, 处理间差异显著; Olson指数方程拟合结果表明,施加铵态氮、混合氮和硝态氮后落叶分解50%和95%所需时间分别为175 d、316 d、301 d和781 d、1 238 d、1 627 d,比对照分别缩短49.7%、9.2%、13.5%和52.0%、23.9%、14.1%。同时, 添加氮源后对落叶中N、P、K元素的释放影响有所不同, 其中对K元素的释放基本没有产生影响, 随着分解的进行, 不同处理落叶中K元素浓度逐渐降低。但添加氮源对N、P元素的释放产生了显著影响, 与对照相比, 添加氮源缩短了N、P释放的富集时间, 降低了富集的幅度;N、P的富集时间均从对照的21 d缩短到处理的7 d; N的富集幅度从对照为初始浓度的1.94倍降低到处理为初始浓度的1.32~1.56倍, P的富集幅度从对照为初始浓度的2.98倍降低到处理为初始浓度的1.70~2.26倍。因此添加氮源加快了落叶的分解速度,促进了落叶中N、P的释放, 有利于加快养分循环, 提高立地生产力。     

Carbon dioxide emissions of soils under pure and mixed stands of beech and spruce, affected by decomposing foliage litter mixtures

Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO₂ concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO₂ emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO₂ emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO₂ effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO₂-C m⁻² h⁻¹). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the O_i - and O_e horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO₂ efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.     

The fate of condensed tannins during litter consumption by soil animals

Condensed tannins (CT) can strongly affect litter decomposition, but their fate during the decomposition process, in particular as influenced by detritivore consumption, is not well understood. We tested the hypothesis that litter CT are reduced by the gut passage of two functionally distinct detritivores of Mediterranean forests, the millipede Glomeris marginata, and the land snail Pomatias elegans, as a fixed proportion of initial litter CT, but more so in Pomatias since snails are known to have a more efficient enzymatic capacity. Contrary to our hypothesis, both detritivore species reduced litter CT to near zero in their faecal pellets irrespective of the wide range in initial leaf litter CT concentrations of 9-188 mg g⁻¹ d m among three Mediterranean tree species (Pistacia terebinthus, Quercus ilex, Alnus glutinosa) and different decomposition stages of their litter. The almost complete disappearance of CT even from some litter types highly concentrated in CT, due to either degradation by gut microorganism or complexation of CT into insoluble high molecular weight structures, suggests a high “de-tanning” efficiency across functionally distinct detritivore species. The transformation of CT-rich litter into virtually CT-free faecal pellets by detritivores might be highly relevant for the subsequent decomposition process in ecosystems with a high macrofauna abundance and CT-rich plant species such as Mediterranean forests.     

The effect of disturbance by Phellinus weirii on decomposition and nutrient mineralization in a Tsuga mertensiana forest

Summary Microbial biomass in the upper 7 cm of soil and needle decomposition on the forest floor were measured seasonally for 10 months in a mountain hemlock (Tsuga mertensiana) old-growth forest and in a regrowth forest after Phellinus weirii, a root-rot pathogen infection, had caused disturbance. The microbial biomass was higher in the old-growth forest soil than in the regrowth forest soil. However, T. mertensiana needle decomposition rates were higher in the regrowth than in the old-growth forest. Total N, Ca, Fe, Cu, and Zn concentrations in needles increased during the 1st year of decomposition in both the old and the regrowth forests, but P, K, Mg, Mn, and B concentrations decreased. N, P, K, Mg, Cu, and Zn concentrations were lower in regrowth than in old-growth decomposing needles. During mineralization, needles in the regrowth forests released more N, P, and K as a result of higher needle decomposition rates. Our results suggest that higher needle decomposition rates increased the mineralization of N, P, and K, which may lead to increased soil fertility and faster tree growth rates in the regrowth forest.     

Influence of microarthropod abundance and climatic factors on weight loss and mineral nutrient contents of Eucalyptus leaf litter during decomposition

Summary Densities of the different taxa of microarthropods per gram of litter in litter bags varied widely from the rainy to the dry season. Collembola and Acarina constituted more than 86% of the total microarthropods, and occurred in significantly greater numbers in the coarse-mesh bags than the fine-mesh bags. There were no fauna in the litter of suspended bags. The average weight loss was greater in the coarse-mesh bags (50.4%) than in the fine-mesh bags (44.5%), and the suspended bags (7.4%). Similarly, the concentrations of N and Ca were greater in the litter of coarse-mesh bags compared to that of the fine-mesh bags. In contrast, the concentrations of P and K were comparatively lower in coarse-mesh bags. The mass loss of litter showed a negative linear correlation with the total Collembola and with litter temperature. The N concentrations in the litter in both the mesh bags showed negative correlations with the abundance of total Collembola, and with that of Lepidocyrtus sp. and Sminthuridae, and rainfall. The N concentration in the litter in the coarse-mesh bags was positively correlated with the total number of arthropods but, surprisingly, was negatively correlated with the total number of Acarina. The concentration of Ca showed negative correlations with rainfall and litter moisture only. The P concentration showed positive correlations with total Collembola, with Lepidocyrtus sp. and Sminthuridae in both the mesh bags, with rainfall in the fine-mesh bags, and with total microarthropods in the coarse-mesh bags.     

Earthworm effects on the use of C sources by microorganisms: Non-linear response to temperature alteration

A microcosm was used to study the effect of the endogeic earthworm Aporrectodea caliginosa (Savigny) on the use of C by microorganisms in a calcareous beech forest soil and its dependence on temperature (5–25%C). Inclusion of ¹⁴C-labelled beech leaf litter made it possible to differentiate between C use by litter-colonizing microflora and by autochthonous soil microflora. The effect of temperature on the soil microbial biomass ¹²C was confined to a significant increase at 15 and 20°C. The size of the ¹⁴C-labelled microbial biomass, in contrast, was positively correlated with temperature. The ¹²C mineralization increased exponentially with temperature. The relationship between ¹⁴C mineralization and temperature, in contrast, followed a logistic curve. Significant main effects of A. caliginosa were confined to ¹²C mineralization, reflecting an increase in ¹²CO₂–C production in the earthworm treatments. The earthworm effects on ¹²CO₂–C production and on ¹⁴C incorporation of the microflora were not linear. The effect of A. caliginosa on ¹²CO₂–C production was most pronouned at intermediate temperatures. It is concluded that temperature alterations affect the microbial use of different C sources in different ways and that the temperature effects can be significantly modified by endogeic earthworms.     

Effects of tillage method and fallow frequency on leaf spotting diseases of spring wheat in the semiarid Canadian prairies

Leaf spotting diseases of wheat (Triticum spp.) are widespread in western Canada. Because these diseases are residue-borne, they are expected to be affected by changes in the quality and quantity of crop residues. A field study was conducted to determine the effects of summerfallow and tillage practices on leaf spotting diseases of spring wheat (T. aestivum L.) in the semiarid area of the western Canadian prairies. Leaf spot severity was greater in wheat grown after fallow than in continuous wheat when these systems were managed using either cultivator- or zero-tillage methods. Disease severity in wheat after fallow was similar in all three tillage methods: cultivator-, reduced-, and zero-tillage. Pyrenophora tritici-repentis (Died.) Drechs. (tan spot) was the pathogen most commonly isolated from lesioned leaf tissue. Crop residues collected in the spring of 1995 and 1996 from cultivator- and zero-tillage treatments were examined for the presence and density of fungal infective structures. The density of mature and immature structures, especially of P. tritici-repentis, was greater in residues from two years previous than in those from the previous growing season. Most of the residues in the continuous wheat system were from the previous crop. The apparent lower amount of initial inoculum available in a continuous wheat system than in wheat grown after fallow would explain the higher leaf spotting severity in the latter system. In addition, lower levels of infective structures on residues were found in wheat after fallow in zero- rather than in cultivator-tillage. However, similar disease levels in cultivator- and zero-tillage treatments suggest that the more favourable microclimate for disease development in a zero-tillage system might have compensated for the lower amounts of residue-borne inoculum.     

The influence of slug (Arion rufus) mucus and cast material addition on microbial biomass,respiration, and nutrient cycling in beech leaf litter

We investigated the effects of slug (Arion rufus L.) mucus and cast material on litter decomposition, nutrient mobilization, and microbial activity in two laboratory experiments: (1) Slug mucus and cast material was added to beech leaf litter (Fagus sylvatica L.), and leaching of N and P and CO₂ production in microcosm systems were measured during 77 days of incubation; (2) mucus was added to beech leaf litter, and basal respiration, microbial biomass (substrate-induced respiration), specific respiration (qO₂), microbial growth ability after C, CN, CP, and CNP amendment, and lag time (time between CNP addition and start of exponential increase in respiration rate) were measured during 120 days of incubation. Leaching of N and P from beech leaf litter was significantly increased in treatments with mucus or faecal material of A. rufus. Following day 3, slug mucus increased nitrification processes. Mucus addition to beech leaf litter also increased basal respiration and microbial biomass significantly. In contrast, specific respiration was not significantly affected by mucus addition, and generally declined until day 60 but then increased until day 120. Nutrient amendments indicated that between days 1 and 30, N was available for microbial growth in litter with mucus but not in control litter. Generally, the lag time in beech leaf litter with added mucus was shorter than in control litter. Lag times generally increased with age, indicating dominance of slow-growing microbial populations at later stages as a consequence of depletion of easily available C resources and nutrients. We conclude that C, N, and P cycling is accelerated by slug activity.     

Dominant effects of litter substrate quality on the difference between leaf and root decomposition process above- and belowground

Initial decomposition rates, changes in organic chemical components (acid-insoluble fraction, holocellulose, polyphenols, soluble carbohydrates) and nutrient dynamics (K, Mg, Ca, P, N) were examined for fine roots and leaves of Japanese cypress (Chamaecyparis obtusa). Litterbag experiments designed to evaluate the relative effects of litter type and position of litter supply in the soil were carried out, considering that root and leaf litter typically occupy different locations and have different substrate qualities. Litterbags of roots and leaves were placed at two positions (on the soil surface and in the humus layer), and collected every 3 months over one year. The mass loss rate and N release were slower during root decomposition in the humus layer than during leaf decomposition on the soil surface. These differences between root and leaf decomposition were mainly caused by the litter type, and the effect of the position on decomposition was relatively small. Root litter was less influenced by position related effects, such as differences in humidity, than leaf litter, and this recalcitrant trait to environmental effects may be responsible for the slower mass loss rate and N release in root decomposition. The results of the present study suggest that fine roots are persistent in the soil and serve an important role in N retention in forest ecosystems because of their litter substrate quality.     

The combined effects of enhanced UV-B radiation and selenium on growth, chlorophyll fluorescence and ultrastructure in strawberry (Fragaria × ananassa) and barley (Hordeum vulgare) treated in the field

The possible ameliorative effects of selenium (Se) addition to soil on the detrimental effects of enhanced UV-B radiation were tested on strawberry and barley during 4 months of field experiment in Kuopio, Central Finland. Control plants were exposed to ambient levels of UV radiation, using arrays of unenergized lamps. A control for UV-A radiation was also included in the experiment. Added Se, applied as H₂SeO₄, at the level of 0.1 mg kg⁻¹ soil (low dosage) and 1 mg kg⁻¹ soil (high dosage) increased Se concentrations in plants more than 10 and 100 times, respectively. After 4 months of exposure, strawberry and barley plants were harvested for biomass analysis. Chlorophyll fluorescence was measured using the Hansatech FMS2 fluorescence monitoring system. Leaf anatomy and ultrastructure were observed by light and transmission electron microscope. Several effects of UV and Se as well as their interaction were found, mostly for strawberry, but not for barley, indicating species-specific responses. Our results provided evidence that the high Se concentration in soil had no ameliorative effect but increased the sensitivity of strawberry to enhanced UV-B radiation in the field. Under ambient radiation, Se did not alter leaf growth of strawberry, whereas under UV-B radiation, the high Se addition significantly decreased leaf growth. Strawberry runner biomass was affected by the interaction of Se and UV. Under ambient radiation Se did not change dry weight of runners, but in combination with UV-A or UV-B radiation the high Se dosage decreased dry weight of runners by about 30%. Although the high Se concentration positively influenced on quantum efficiency of photosystem II (PSII) in strawberry leaves, it reduced runner biomass, leaf number and ratio of starch to chloroplast area. This suggests that the harmful effects of the high Se dosage on photosynthetic processes occurred as a result of changes in activity or/and biosynthesis of enzymes, rather than alteration of PSII. At the low concentration, Se effects were slight and variable.Although barley leaves accumulated higher Se concentrations than strawberry, there were no apparent changes in their growth, biomass or chlorophyll fluorescence due to Se effect either alone or in combination with UV-B. However, at the ultrastructural level, an enlargement in the peroxisome area was found due to combination of UV radiation with Se, suggesting the activation of antioxidative enzymes, possibly catalase. Decrease in mitochondrial density in barley cells in response to Se might be attributed to alteration of mitochondrial division. Increase in the proportion of cells with cytoplasmic lipid bodies due to combined effect of UV-B and Se indicated the alteration of lipid metabolism and the acceleration of cell senescence in barley. Main UV-B effects were found, mostly at the tissue and ultrastructural level in strawberry, but not in barley, indicating species-specific susceptibility to enhanced UV-B radiation. UV-B-treated strawberry plants developed marginally thinner leaves with reduced ratio of starch to chloroplast area in their cells, suggesting negative influence of UV-B on photosynthetic processes.     

Zinc effects on a soil bacterial flora characterized by fatty acid composition of the isolates

Summary Effects of zinc (zinc chloride) added to a sandy clay loam soil on its bacterial flora were investigated by the study of cellular fatty acid composition of the isolates. The soil amended with glucose (carbon source) and ammonium sulfate (nitrogen source) was incubated in the presence (1.0 mg/g) or absence of zinc for 96 h. Bacterial strains were isolated on albumin agar from the incubated soils every 24 h. Their cellular fatty acid composition was analyzed and the strains were classified according to the percentage distribution pattern of the fatty acid composition.Two and four dominant patterns of the fatty acid composition were obtained in the isolates from the control soil and the soil with zinc added, respectively. They were different from one another. Most of the dominant strains isolated from the soil with added zinc were zinc-tolerant, and it was suggested that the selection for zinc tolerance readily proceeded.     

The effects of earthworms on the demography of annual plant assemblages in a long-term mesocosm experiment

Earthworms have been shown to influence plant growth, survival and fecundity. They can therefore affect plant demography in plant communities changing their composition. A long term mesocosm experiment was set-up to test the effects of an endogeic (Aporrectodea caliginosa) and an anecic (Lumbricus terrestris) earthworm species on assemblages of four species of annuals: one grass (Poa annua), two forbs (Veronica persica and Cerastium glomeratum) and one legume (Trifolium dubium). The number of individuals and the biomass of each species were investigated. A. caliginosa and L. terrestris affected the density of T. dubium at each of the three monitored census dates. The other plant species responded to A. caliginosa and L. terrestris at the second and third generations. The presences of A. caliginosa and L. terrestris reduced the total number of plant individuals from the second to the third generation. At harvest (3rd generation), T. dubium and V. persica had more and larger individuals in the presence of A. caliginosa. When both earthworm species were present, T. dubium had few but larger individuals. Our study confirms that earthworms affect plant demography and plant community structure. Our results also show that accurate prediction of long-term effects of earthworms on plant communities cannot be achieved using results on their short-term effects on plant growth. This is due to the poor understanding of the effects of earthworms on plant resource allocation and demography, and also the possibility that earthworms may exert the opposite effect on the short and long-term availability of nutrients.     

The major features of an infestation by the invasive weed legume gorse (Ulex europaeus) on volcanic soils in Hawaii

Gorse (Ulex europaeus) infestation occupies over 4,000 ha of agriculture and conservation lands on the southeastern slope of Mauna Kea on the Island of Hawaii. The aim of this investigation is to identify ecological features associated with this weed invasion by comparing the gorse-infested areas to the surrounding uninfested areas of this landscape. The soils within the gorse infestation are more acidic, resulting in higher levels of KCl-extractable Al and lower levels of Mehlich III-extractable Ca, Mg, Mn, and Zn. Yet, gorse accumulates higher concentrations of Ca, Zn and, Cu than the kikuyu grass (Pennesitum clandestinum), which is ubiquitous throughout the site. The Ca:Al and Mg:Al molar charge ratios of the soils are lowest within the epicenter of the gorse infestation, while the molar ratios are highest in the gorse apical stem tissues. All gorse plants are nodulated and have higher nitrogen contents than the surrounding kikuyu grass. Furthermore, the δ¹⁵N of the gorse stem tissues approaches 0‰, suggesting that nitrogen is being symbiotically fixed from the atmosphere. Characterization of the Bradyrhizobium isolated from gorse nodules shows similarities and distinctions to Bradyrhizobium isolated from the endemic legume koa (Acacia koa) within the same location. Population densities of the indigenous Bradyrhizobium are higher within the gorse rhizosphere than the kikuyu grass. Soil acidification, nutrient depletion, and symbiotic nitrogen fixation distinguish gorse-infested areas from the surrounding uninfested areas. These observations suggest that gorse has a competitive advantage over kikuyu grass under conditions of soil nutrient deficiency.     

The influence of feeding patterns on growth and reproduction of the vermicomposting earthworm Eisenia fetida (Oligochaeta)

Summary Observations in outdoor culture beds indicated that food availability and frequency of feeding influenced worm density. In order to study the role of feeding status on the growth and reproduction of Eisenia fetida, pre-clitellate specimens were kept for 180 days under controlled conditions. A control group was regularly provided with freshly produced cattle manure while the experimental groups were fed only sporadically and at some stage even starved by removing some of the substrate. Worm growth, maturation, and cocoon production were monitored. The role of food availability was highlighted by this study. Both worm growth and cocoon production were correlated closely with the feeding pattern that was followed. This study also showed that freshly produced, urine-free, cattle manure proved an excellent food source provided it was added in such a way as to prevent the development of anaerobic conditions. Regular feeding gave high growth and reproduction rates.     

Seasonal effects of liming,irrigation, and acid precipitation on microbial biomass N in a spruce (Picea abies L.) forest soil

Summary Seasonal effects of liming, irrigation, and acid precipitation on microbial biomass N and some physicochemical properties of different topsoil horizons in a spruce forest (Picea abies L.) were measured throughout one growing season. The highest biomass N was recorded in autumn and spring in the upper soil horizons, while the lowest values were obtained in summer and in deeper horizons. The clearest differences between the different soil treatments were apparent in autumn and in the upper horizons. Liming increased the microbial biomass N from 1.7% of the total N content to 6.8% (Olf₁ layer) and from 1% to 2% of the total N content in the Of₂ layer. The main inorganic-N fraction in the deeper horizons was NO _inf3 ^sup- . An increase in cation exchange capacity was observed down to the Oh layer, while soil pH was only slightly higher in the Olf₁ and Of₂ layers after liming. The effects of irrigation were less marked. The microbial biomass N increased from 1.7% of total N to 4.8% in the Olf₁ layer and from 1% to 2% of total N in the Of₂ layer. In the Olf₁ layer an increase in C mineralization was observed. Acid precipitation decreased the microbial biomass N in the upper horizons from 4.8% of total N to 1.8% in the Olf₁ layer and from 2% to 0.5% in the Of₂ layer. No significant changes in soil pH were observed, but the decrease in cation exchange capacity may result in a decrease in the proton buffering capacity in the near future.