Trees on farms and their contribution to soil fertility parameters in Badessa, eastern Ethiopia

Surface (0–15 cm) and subsurface (30–45 cm) soil samples from under canopy, edge of canopy and away from canopy of isolated Cordia africana Lam. and Croton macrostachyus Del. trees and their leaves were examined to investigate leaf nutrient content, root biomass and the contribution of trees on farms to soil fertility parameters in Badessa area, eastern Ethiopia. Leaves of C. macrostachyus had 20% higher P and 25% lower K contents than those of C. africana. The studied species had comparable leaf N content. Both species produced shallow lateral roots that extended beyond the canopy zone. Typically, higher fine root biomass was observed in the surface soils than the subsurface soils. Both species did not affect soil organic C, pH and cation exchange capacity. Surface and subsurface soils under tree canopies had 22–26 and 12–17% higher N, respectively, than the corresponding soils away from tree canopies. Surface soil available P under tree canopies was 34–50% higher than the corresponding soil away from canopies. Available P content of subsurface soil was improved only under C. africana canopy. The available P of surface soil under C. macrostachyus canopy was more than double that for C. africana. Trees of both species increased underneath surface and subsurface exchangeable K by 18–46% compared with the corresponding controls. In conclusion, C. macrostachyus and C. africana trees on farms keep soil nutrient high via protection against leaching, translocation of nutrients from deeper to the surface layer and accumulation of litter, which create a temporary nutrient pool in the surface soils under their canopies.     

Reproduction and growth of three deep-burrowing earthworms (Lumbricidae) in laboratory culture in order to assess production for soil restoration

Laboratory experiments were conducted to examine the growth and reproduction of three deep-burrowing lumbricids, Aporrectodea longa, Lumbricus terrestris, and Octolasion cyaneum. The reproductive output was recorded as 18.8, 38.0, and 32.3 cocoons per worm per year for A. longa, L. terrestris, and O. cyaneum, respectively. For the same species, maturity was reached at a mean mass of 3.9, 5.0 and 2.4 g, within 3 months from the hatchling stage by L. terrestris and within 4 months by the other two species. The hatching success of cocoons at 15 and 20°C was within the range of 70–80% for each species, except A. longa at the higher temperature, where a viability of 47% was recorded. Twenty percent of viable O. cyaneum cocoons produced twin hatchlings, compared with only one percent for A. longa and L. terrestris. A combination of these results suggests that a complete life-cycle for each species could be achieved within 6 months (L. terrestris and A. longa) or 7–8 months (O. cyaneum). Each species has particular life-cycle strategies that would aid survival and colonisation, under field conditions, if inoculated into restored soils.     

Diversity of potential microbial parasites colonizing sclerotia of Macrophomina phaseolina in soil

The colonization of Macrophomina phaseolina sclerotia by microbial parasites was evaluated in unsterilized field soil at different levels of soil moisture (0,-5, and-10 kPa) and temperature (20, 30, and 40°C). The maximum colonization of sclerotia was recorded in soil held at-5 or-10 kPa at 30–40°C. Trichoderma harzianum isolate 25–92 and Pseudomonas fluorescens isolate 4–92 were recorded as potential sclerotial parasites, and they significantly (P=0.05) reduced the germination of sclerotia by 60–63%. Cells of P. fluorescens and buffer-washed conidia of T. harzianum were completely agglutinated at 28°C with crude agglutinin of M. phaseolina. The ability of different antagonists to parasitize the sclerotia were correlated with the agglutination ability of the antagonists.     

The earthworm population of a winter cereal field and its effects on soil and nitrogen turnover

The earthworm population in a winter cereal field in Ireland was studied over a 3-year-period and its effects on soil and N turnover were assessed. The mean annual population density was 346–471 individuals m^-2 and the mean biomass was 56.9–61.2 g m^-2. Twelve species were recorded, the most abundant being Allolobophora chlorotica followed by Aporrectodea caliginosa, and 242 mg at 5°C to 713 mg at 10°C in the case of juvenile Lumbricus terrestris. Gut contents (dry mass of soil) comprised 6.7–15.5% of the A. caliginosa live mass, and 9.7–14.7% of the Lumbricus terrestris mass. Annual soil egestion by the field population was estimated as 18–22 kg m^-2. Tissue production ranged from 81.7 to 218.5 g m^-2, while N turnover resulting from mortality was calculated as 1.5–3.9 g m^-2 depending on the year and the method of calculation. Earthworms were estimated to contribute an additional 3.4–4.1 g mineral N to the soil through excretion, mucus production, and soil ingestion. Independent estimates of N output via mucus and excretion derived from ¹⁵N laboratory studies with Lumbricus terrestris were 2.9–3.6 g m^-2 year^-1.     

Leaf-litter consumption and assimilation by juveniles of Lumbricus terrestris L. (Oligochaeta,Lumbricidae) under different environmental conditions

Summary The rate of consumption of dandelion leaves per g earthworm dry weight per week was described by non-linear functions of soil temperature, soil water potential, and food availability. The optimum temperature and soil water potential for food consumption are about 22°C and-7 kPa, respectively. Zero consumption occurred at about-40 kPa. Food consumption increased with greater food availability, but only up to 1.05 (dandelion) and 1.23 (grass) g dry weight per g earthworm dry weight per week at 15°C. A general consumption function to account for all three environmental factors is given. The assimilation rate per g earthworm dry weight per week was defined as the sum of the growth rate and the maintenance rate. Maintenance was calculated according to respiratory measurements reported previously, whereas growth was measured. High temperatures and limiting environmental conditions, such as a low food availability and a low soil water potential, led to an increase in the assimilation efficiency of Lumbricus terrestris. At-7 kPa and 15°C, L. terrestris assimilated 55 and 43% of the ingested dandelion if 0.25 and 1.0 g dry weight of food was available per g earthworm dry weight per week, respectively. it is concluded that L. terrestris has a strong, direct effect on the decomposition of highly palatable plant materials.     

入侵植物豚草与本地植物马唐对土壤肥力与酶活性影响的比较

通过同质园试验比较研究了外来入侵植物豚草与本地植物马唐对土壤肥力及3大类酶活性的影响.结果表明: 与本地植物及空白对照相比, 豚草显著提高了入侵地的土壤有效养分含量, 特别是有效钾含量是空白对照区和本地植物马唐区的3.6倍和1.3倍.与空白对照区和本地植物马唐种植区相比, 豚草种植区的土壤酶活性亦显著提高.外来入侵植物豚草在入侵地形成新的关系过程中, 比本地植物马唐能更快地提高土壤有效养分含量及酶活性, 从而实现较短时间内通过提高土壤肥力, 形成对自身生长有利的土壤环境来帮助其竞争入侵.     

Potassium uptake of rye-grass (Lolium perenne) and red clover (Trifolium pratense) as related to root parameters

Summary Rye-grass (Lolium perenne) is known to be a strong competitor to red clover (Trifolium pratense) for soil K⁺ under conditions of low K availability in the soil. The objective of this study was to clarify whether this competitive behaviour of the two species can be explained by root morphology. Total K⁺ uptake ofL. perenne andT. pratense was studied under field conditions in relation to root fresh weight, root density, root cation exchange capacity, root surface and root length. The soil was an Alfisol, Udalf. All root parameters, when calculated per unit soil surface (M²), were higher inL. perenne than inT. pratense. In addition,L. perenne had longer root hairs and a denser root hair system thanT. pratense. The greatest difference in root morphology between species was root length, withL. perenne roots averaging 4–6 times longer than those ofT. pratense.Significant correlations were found between the total K⁺ uptake and all root parameters examined, with highest correlationsforroot fresh weight (r,0.92***T. pratense; 0.94***L. perenne) and root length (r, 0.91***T. pratense;r, 0.93***L. perenne). Potassium uptake per unit root fresh weight, root surface and root length were all significantly higher forT. pratense than for L. perenne. Differences in the rate of K⁺ uptake between species were particularly high when expressed per unit root length. Because of its greater root length and surface area,L. perenne can take up more soil K⁺ thanT. pratense, particularly where there is a low K^– supply in the soil. Under such conditionsL. perenne will be a particularly strong competitor toT. pratense.     

Changes in respiration rate and some physicochemical properties of soil during gut transit through Allolobophora molleri (Lumbricidae,Oligochaeta)

Summary Some physicochemical and biological measurements were carried out on the gut content and casts of Allolobophora molleri, an earthworm which lives in humid soils of Northern Spain. In the anterior part of the gut, water (22% of moist weight of soil) and soluble organic matter (27.4%) had been added to the ingested soil and pH had increased from 5.75 to 7.0. The amount of water-soluble compounds decreased sharply in the middle and posterior parts of the gut and were hardly detectable in control soil or casts. The average O₂ consumption, measured at 28° and 21°C, indicated respectively 2.75-to 12-fold increases in microbial respiration in the gut content compared to the non-ingested soil. These results extend the hypothesis of a mutualistic digestion in earthworms previously proposed for tropical endogeic species.     

Effect of low root temperature on symbiotic nitrogen fixation and competitive nodulation of Onobrychis viciifolia (sainfoin) by strains of arctic and temperate rhizobia

Summary Symbiotic effectiveness and competitive nodulation of the temperate forage legume sainfoin (Onobrychis viciifolia cv. Melrose) by two strains of arctic rhizobia (from Astragalus or Oxytropis sp.) and two strains of temperate rhizobia (from sainfoin) were evaluated at temperatures of 9, 12, or 15°C for roots and 20°C (day) and 15°C (night) for shoots. The inocula consisted of effective individual or paired arctic and temperate strains which were identified on the basis of differential growth. At 9°C, the arctic strains were generally more competitive than the temperate strains, whereas at the highest temperature tested, the converse was apparent. Symbiotic effectiveness (shoot dry weight, nitrogenase activity, and number of nodules) was similarly affected by root temperature, except that at 15°C the arctic strains were generally as effective as the temperate strains. The marked interaction between temperature and strain on competitiveness or on effectiveness indicates symbiotic adaptation of the arctic rhizobia to low temperatures. On the basis of these data we suggest that the use of selected, cold-adapted rhizobia in sainfoin inoculants may be beneficial in temperate regions where low soil temperatures occur early in the growing season.Contribution no. 413 and 1334 of the Agriculture Canada Sainte-Foy Research Station and Plant Research Centre, respectively     

Evaluation of some phosphoroamides as soil urease inhibitors

Summary The effectiveness of six phosphoroamides for retardation of urea hydrolysis in soils was studied by determining the effects of 10 g g^–1 soil of each compound on the amounts of urea hydrolyzed when soils treated with urea were incubated at 10°, 20°, 30°, and 40°C for 3, 7, and 14 days. The phosphoroamides used wereN-(diaminophosphinyl)-cyclohexylamine,N-benzyl-N-methyl phosphoric triamide, diethyl phosphoric triamide, trichloroethyl phosphorodiamidate, dimethyl phosphoric triamide, andN-butyl phosphorothioic triamide [N-(n-butyl) thiophosphoric triamide]. The soils used were selected to obtain a range in properties, and the effects of the six phosphoroamides studied were compared with those of two compounds known to be among the most effective compounds thus far proposed for retardation of urea hydrolysis in soils (phenylphosphorodiamidate and hydroquinone). The data obtained showed that all six of the phosphoroamides evaluated compared favorably with hydroquinone as soil urease inhibitors and that two of them [N-butyl phosphorothioic triamide andN-(diaminophosphinyl)-cyclohexylamine] were superior to phenylphosphorodiamidate for retardation of urea hydrolysis in soils at 20°, 30°, or 40°C.     

Ant-induced soil modification and its effect on plant below-ground biomass

Lasius flavus is a dominant mound-building ant species of temperate grasslands that significantly modifies soil parameters. These modifications are usually the result of workers’ activities such as food accumulation and nest construction. An alternative hypothesis that could explain changes in soil is colony founding in areas of higher soil fertility.In our study we investigated several soil parameters sampled in 10 ant nests and adjacent (control) plots in mountain grassland in Slovakia. The alternative hypothesis was tested by comparing occupied and abandoned mounds. While we found increased concentrations of available P and K in the nests, concentrations of total C, total N, Ca²⁺ and Mg²⁺ were lower there. We propose that differences found between the soil of nests and control plots are entirely a product of ant activity during mound occupancy and not due to initial soil differences during nest establishment. This was confirmed by the comparison of occupied and abandoned nests in which the soil fertility of abandoned nests was similar to conditions in the surrounding soil.Along with the modification of soil chemistry, we recorded changes in soil physical properties and the vertical distribution of nutrients. Ant nests were characterized by the dominance of 0.02–0.1 mm particles and lower bulk density. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased and bulk density increased with depth. Root biomass followed the vertical pattern observed with nutrients: in control plots, most roots were concentrated in the uppermost layer (0–3 cm), whereas they were evenly distributed along the vertical gradient in the nests. We also found that rhizome internodes of Agrostis capillaris were thinner and longer in plants from the mounds. Changes in soil physical properties, vertical distribution of nutrients and root biomass in the nests are most probably a consequence of mounding and soil mixing (bioturbation), which has been less reported on in ant-soil studies.     

Characterisation of the three-dimensional structure of earthworm burrow systems using image analysis and mathematical morphology

The aim of this work was to exemplify the specific contribution of both two- and three-dimensional (3D) X-ray computed tomography to characterise earthworm burrow systems. To achieve this purpose we used 3D mathematical morphology operators to characterise burrow systems resulting from the activity of an anecic ( Aporrectodea nocturna), and an endogeic species ( Allolobophora chlorotica), when both species were introduced either separately or together into artificial soil cores. Images of these soil cores were obtained using a medical X-ray tomography scanner. Three-dimensional reconstructions of burrow systems were obtained using a specifically developed segmentation algorithm. To study the differences between burrow systems, a set of classical tools of mathematical morphology (granulometries) were used. So-called granulometries based on different structuring elements clearly separated the different burrow systems. They enabled us to show that burrows made by the anecic species were fatter, longer, more vertical, more continuous but less sinuous than burrows of the endogeic species. The granulometry transform of the soil matrix showed that burrows made by A. nocturna were more evenly distributed than those of A. chlorotica. Although a good discrimination was possible when only one species was introduced into the soil cores, it was not possible to separate burrows of the two species from each other in cases where species were introduced into the same soil core. This limitation, partly due to the insufficient spatial resolution of the medical scanner, precluded the use of the morphological operators to study putative interactions between the two species     

Effects of soil compaction and arbuscular mycorrhiza on corn (Zea mays L.) nutrient uptake

Soil compaction is of great importance, due to its adverse effects on plant growth and the environment. Mechanical methods to control soil compaction may not be economically and environmentally friendly. Hence, we designed experiments to test the hypothesis that use of plant symbiotic fungi, arbuscular mycorrhiza (AM) may alleviate the stressful effects of soil compaction on corn (Zea mays L.) growth through enhancing nutrient uptake. AM continuously interact with other soil microorganisms and its original diversity may also be important in determining the ability of the fungi to cope with the stresses. Hence, the objectives were: (1) to determine the effects of soil compaction on corn nutrient uptake in unsterilized (S1) and sterilized (S2) soils, and (2) to determine if inoculation of corn with different species of AM with different origins can enhance corn nutrient uptake in a compacted soil. Using 2 kg weights, soils (from the field topsoil) of 10 kg pots were compacted at three and four levels (C1, C2, C3 and C4) (C1 = non-compacted control) in the first and second experiment, respectively. Corn (cv. 704) seeds were planted in each pot and were inoculated with different AM treatments including control (M1), Iranian Glomus mosseae (M2), Iranian G. etunicatum (M3), and Canadian G. mosseae, received from GINCO (Glomales In Vitro Collection), Canada (M4). Corn leaf nutrient uptake of N, P, K, Fe, Mn, Zn and Cu were determined. Higher levels of compaction reduced corn nutrient uptake, however different species of AM and soil sterilization significantly increased it. The highest increase in nutrient uptake was related to P (60%) and Fe (58%) due to treatment M4S2C3. Although it seems that M3 and M4 may be the most effective species on corn nutrient uptake in a compacted soil, M2 increased nutrient uptake under conditions (C3 and C4 in unsterilized soil) where the other species did not. Through increasing nutrient uptake AM can alleviate the stressful effects of soil compaction on corn growth.     

Distribution of earthworms and influence of soil properties across a successional sand dune ecosystem in NW England

An investigation of earthworms across a sand dune system in NW England examined species distribution and abundance with respect to soil physico-chemical conditions and management. Replicated 0.1 m² quadrats were examined every 50 m along 700 m transects across areas of vegetation succession and samples were then taken every 10 m where earthworms were first encountered. A translocation of Aporrectodea longa assessed the ability of this species to live in soils with a high sand content and laboratory work examined growth, maturation and survival of this species in soils with increasing proportions of sand (0–100%). Nine earthworm species were found on the dunes, but none in yellow dunes where organic matter (OM) content was <1%. Dendrobaena octaedra and Lumbricus rubellus were located 300 m from the strand line in grey dunes with an OM content of 3.9%. Allolobophora chlorotica and Lumbricus castaneus occurred within a wet dune slack at 340 m (OM content 11%). In areas of human disturbance (dune car park), A. longa, Aporrectodea caliginosa and Lumbricus terrestris were present, and in soil below pine trees L. castaneus and L. rubellus were present in litter. Laboratory growth of A. longa demonstrated significant (p < 0.05) increases in growth (2–2.75 g) with 25 and 50% sand compared with 0, 75 and 100% over 24 weeks and a greater rate of maturation. Initial results show earthworm colonisation to be influenced by dune successional stage. Laboratory findings suggested A. longa could exist in higher sand content areas but experimental design needs development. The translocation was unsuccessful. Future investigations could examine soil properties more closely and undertake monitoring on site throughout the year.     

Microbial communities of Lumbricus terrestris L. middens: structure, activity, and changes through time in relation to earthworm presence

Background, aim, and scope  Earthworms make a major contribution to decomposition in ecosystems where they are present, mainly acting in the drilosphere, that is, galleries, burrows, casts, and middens. Earthworm middens are hot-spots of microbial activity and nutrient dynamics and represent a suitable model for studying earthworm-mediated influences on soil microbial communities by alteration of the patch structure of the microbial environment. We studied the structure and activity of the microbial communities in the soil system formed by middens of Lumbricus terrestris and the soil below and surrounding them and the role of earthworms in maintaining these structures through time. Material and methods  We set up an experiment in which middens were either left (control) or removed from their original place (translocated) and left in a nearby area free of earthworm activity for 2 months. After 1 and 2 months we sampled middens, soil below them, and surrounding soil. We analyzed the phospholipid fatty acid (PLFA) profiles and measured respiratory fluxes of CO₂ and CH₄. Results  Microbial communities of middens clearly differed from those of soil below and surrounding soil samples, showing higher bacterial and fungal PLFAs (p < 0.0001 and p < 0.01, respectively); furthermore, changes in microbial communities were stronger in control middens than in translocated middens. Moreover, gram positive and negative bacterial PLFAs were greater in translocated than control middens (p < 0.0001 and p < 0.001, respectively), as well as total organic carbon (p < 0.001). Microbial activity was higher in middens than in soil below and surrounding soil samples both for CO₂ (p < 0.0001) and CH₄ (p < 0.0001). Discussion  Soil bioturbation by the earthworm L. terrestris was strong in their middens, but there was not any effect on soil below and surrounding soil. Microbial communities of middens maintain their biomass and activity when earthworms were not present, whereas they decreased their biomass and increased their activity when earthworms were present. Conclusions  Earthworms strongly enhanced microbial activity measured as CO₂ production in middens, which indicates that there are hot spots for soil microbial dynamics and increasing habitat heterogeneity for soil microorganisms. Moreover, our data strongly support the fact that the impact of this earthworm species in this soil is restricted to their middens and increasing soil heterogeneity. Recommendations and perspectives  Our data indicate that it is not clear if earthworms enhance or depress microbial communities of middens since the microbial activity increased, but did not modify their biomass and this was not dependent on soil organic C content. These results indicate no competence for C pools between this anecic earthworm and microorganisms, which has been found for other earthworm species, mainly endogeics. Conversely, they suggest some type of facilitation due to the release of additional nutrient pools in middens when earthworms are present, through the digestion of middens' material or the addition of casts produced from other food sources.     

Assessment of earthworm contribution to soil hydrology: a laboratory method to measure water diffusion through burrow walls

The capacity for water diffusion in burrow walls (i.e. the coefficient of sorptivity) either burrowed by Lumbricus terrestris (T-Worm) or artificially created (T-Artificial) was studied through an experimental design in a 2D terrarium. In addition, the soil density of earthworm casts, burrow walls (0–3 mm around the burrow) and the surrounding soil (>3 mm) were measured using the method of petroleum immersion. This study demonstrated that the quantity of water which transits through burrows of L. terrestris in the soil matrix was lower than that transited through soil fractures, due to a reduction of soil porosity in burrow walls (compaction: cast > worms burrow walls > surrounding soil > artificial burrow walls). Earthworm behaviour, in particular burrow reuse with associated cast pressing on walls, could explain the larger burrow wall compaction in earthworm burrows. If water diffusion was lower through the compacted burrows, burrow reuse by the worms makes them more stable (worms would maintain the structure over years) than unused burrows. The present experimental design could be used to test and measure the specific differences between earthworm species in their contributions to water diffusion. Probably, these contributions depend on the presumed related-species behaviours which would determine the degree of burrow wall compaction.     

Influence of fungal-soil water interactions on phytophthora root rot of alfalfa

Summary Phytophthora root rot of alfalfa (Medicago sativa L.) is a serious problem in wet soils. This disease is caused by Phytophthora megasperma f. sp. medicaginis. The influence of soil-water interactions with P. megasperma f. sp. medicaginis and other factors on the severity of phytophthora root rot of mature alfalfa plants (10–12 weeks) was studied in greenhouse experiments. Severe and reproducible root rot was produced by subsurface (3–4 cm) placement of mycelial suspension. Soil saturation 3 days prior to inoculation followed by alternating 3-day wet (soil saturation) and 4-day dry (surface watering once a day) moisture regimes (for 30–40 days following inoculation) resulted in severe root damage.The severity of root rot was greater when the inoculation was done at an ambient temperature of 20°C than at 15°C. Water quality (tap water or deionized distilled water) had no effect on severity of infection. The isolates PT 78-3 (Minnesota) and TN-2 (Maryland) were equally effective in terms of severity of damage.The impact of excess soil water stress (described above) alone on the shoot and root dry weight as well as on shoot symptoms was similar to that of root rot stress. However, root symptoms showed a marked difference. A close examination of root symptoms is highly recommended to differentiate clearly the plant injury due to root rot from that due to excess soil water stress.     

Susceptibility and effectiveness of vesicular-arbuscular mycorrhizae in wheat cultivars under different growing conditions

Summary Wheat cultivars assumed to be non-susceptible to vesicular-arbuscular (VA) mycorrhizae became colonized, and this effect persisted under different growth conditions. Colonization of all cultivars was similar regardless of the amount of inoculum and the time interval of inoculation. Different plant growth temperatures and the support given by the culture media, inoculation with different endophytes, and inoculation with sterilized and unsterilized spores affected VA colonization levels, although the level of colonization reached in cv. Champlein was similar to that reached in cv. 7-Cerros under each condition. VA mycorrhizal colonization was also affected by different plant growth conditions. After VA reinoculation, the plant dry weight of Castan and 7-Cerros increased, but not Negrillo and Champlein cultivars. VA mycorrhizae increased the shoot dry weight of 7-Cerros only, but not of Champlein, when grown at 35/24°C, and had no effect on the dry weight of either cultivar grown at 18/12°C and 42/24°C. Inoculation with Glomus mosseae increased the dry weight of the cultivars more than inoculation with G. fasciculatum or G. agregatum. The effect on the plant dry weight was greater in plants grown in soil than in sand/vermiculite pots. Inoculation with sterilized and unsterilized spores of G. mosseae, either in soil pots or in sand/vermiculite tubes, did not increase the plant dry weight. Our results indicate that there was no close relationship between the level of root colonization and the effect on plant growth. The effects of accompanying microorganisms in the VA inoculum on VA mycorrhizal symbiosis are discussed.     

Soil ciliates (Protozoa: Ciliophora) from evergreen rain forests of Australia, South America and Costa Rica: diversity and description of new species

This paper provides, for the first time, comprehensive data on alpha diversity of soil ciliates from evergreen tropical and temperate rain forests. Thirty-three samples were collected in Australia, Tasmania, Amazonia and Costa Rica and analysed with the non-flooded Petri dish method, which reactivates the ciliates’ resting cysts from air-dried samples. The 175 taxa found contained 34 new species, 4 of which are described in this paper, viz. Platyophrya paoletti n. sp., Lamtostyla abdita n. sp., L. granulifera n. sp., and Apoamphisiella tihanyiensis (Gellért and Tamás 1958) n. gen., n. comb. Although this is a considerable number, it is much lower than one would expect. The data would be even more perplexing if the four rich samples (up to 90 species/sample) from the Manaus floodplain were excluded. We then would be confronted with about 90 taxa in 29 samples, of which 13 contained fewer than ten species. A hypothesis is put forward that the non-flooded Petri dish method is inappropriate for studying soil ciliate diversity in evergreen rain forests because most species have a reduced capacity to produce dry-resistant (protective) resting cysts due to the permanent wetness of their habitats. This view is supported by a comparative analysis of a fresh (containing 40 species) and air-dried/rewetted (2 species only) sample from a cloud rain forest near Merida (Venezuela), and the observation that the capacity of soil ciliates to produce resting cysts often dramatically decreases after prolonged laboratory cultivation in liquid media. Direct microscopy of fresh samples seems to be an appropriate alternative because specimens can be easily collected due to their considerable abundance (≥1000 individuals/g wet mass of litter). Received: 8 April 1997     

Differential growth response of Curculigo orchioides to native arbuscular mycorrhizal fungal (AMF) communities varying in number and fungal components

The study reports diversity of arbuscular mycorrhizal fungal (AMF) species in the rhizosphere of an endangered anticancerous herb – Curculigo orchioides Gaertn. in its natural habitat. A total of 18 species of AMF, belonging to three genera (Acaulospora, Glomus and Gigaspora) were recorded, with Glomus microcarpum being the most abundant species type. The AMF species composition across the study sites appeared to be influenced by soil pH rather than soil P and vegetation. Acaulospora laevis spores were restricted to sites where the soil pH was acidic. The effectiveness of these native AMF species on growth performance of C. orchioides plants was compared under experimental conditions. In general, the mycorrhizal plants were superior in most of the evaluated parameters, but the extent to which the growth of mycorrhizal plants was influenced varied with the inocula used. The plants inoculated with mixed consortia containing maximum AMF species richness exhibited improved growth in comparison to consortia containing lower AMF diversity and monospecies cultures. The variable plant responses observed with any two consortia having same species richness in the present study could be due to variable component AMF species and their relative abundance. These results emphasize the need to protect the below-ground diversity of AMF and recommend their usage for restoration practices.