Vesicular-arbuscular mycorrhizae in tropical sedges of southern India

Twenty-four species of sedges (representing six genera) from different vegetation types in Western Ghats, South India, were examined for vesicular-arbuscular mycorrhizal (VAM) associations. All the sedges had VAM fungal infections with hyphae and vesicles, but arbuscules were observed only in 42% of the total species. The VAM fungal colonization varied considerably between species, ranging from 9 to 62%. Root colonization was positively and negatively correlated with root diameter and root hair length, respectively. The number of VAM fungal spores in the rhizosphere varied from 5 to 86 g^-1 soil. No significant relationship was found between spore numbers or root colonization and either soil pH or moisture. Four Glomus spp., one Acaulospora sp., one Sclerocystis spp., and one Gigaspora sp. were identified among the VAM fungal spores. The results reflect a high incidence of VAM in sedges occurring in Western Ghats and emphasize the need to assess the VAM status of plant species from different ecosystems to understand their mycorrhizal status.     

巴西大西洋森林中巴西松地面根部显示丛枝菌根真菌高定殖率和多样性

Almost 30 different arbuscularmycorrhizal fungi (AMF)species, distributed in different genera such as Glomus, Acaulospora,Scutellospora,Entrophospora,Ambispora,Kuklospora,Gigaspora,and Archeospora, have been identified in the root zone of Araucaria angustifolia, known as Brazil Pine. During our AMF survey in this ecosystem, our attention was called to the presence of many superficially growing Araucaria roots. Our hypothesis was that these roots were colonized with AMF because of the presence of AMF spores in organic material aboveground. Samples of these superficial roots and the organic substrate they were growing on were evaluated for their mycorrhizal status. DNA was extracted from the AMF colonized superficial roots and submitted to polymerase chain reaction (PCR) amplification using the NS31-AM1 primer pair, followed by cloning and sequencing. We found that the root colonization percentages were between 31% and 52%, and the number of AMF spores in the substrate ranged from 27 to 164 spores per 50 g dry substrate.The phylogenetic analyses and tree construction using maximum parsimony (MP) and neighbor-joining (NJ) methods identified 13 different species of the phylum Glomeromycota belonging to the genera Glomus, Funneliformis, Rhizophagus, Gigaspora, Acaulospora,and Archaeospora, and five isolates were identified only at the genus level. To our knowledge, this is the first report on Araucaria angustifolia with roots growing aboveground, producing runner roots that develop on dead tree trunks and organic material. The higher colonization of the aboveground roots than those commonly found in belowground Araucaria roots suggests that they may present active metabolic uptakeof nutrients.     

Arbuscular mycorrhizal fungi associated with wild forage plants in typical steppe of eastern Inner Mongolia

A preliminary investigation was conducted on the arbuscular mycorrhizal (AM) status of the dominant and common wild forage plants in typical steppe of eastern Inner Mongolia, a major semi-arid grassland region in China. Fifty-four wild forage plant species were collected and examined, and 27 of these were colonized by AM fungi. Some plants belonging to families that are presumed to lack mycorrhizas (Cyperaceae, Caryophyllaceae and Chenopodiaceae) were also found to be mycorrhizal. Higher proportions of arbuscular mycorrhizal plants were found in perennial (56.1%) and monocotyledonous (64.7%) forage species. However, neither percentage of root length colonized nor spore density varied significantly between the two life forms or cotyledon types. Twenty-seven species belonging to 7 genera of AM fungi were identified in total according to the morphological characteristics of the spores from field soil and trap cultures, and the results indicate that Glomus was the dominant AM genus and Glomus geosporum (Nicolson & Gerdemann) Walker and Glomus mosseae (Nicolson & Gerdemann) Gerdemann & Trappe were the dominant species in field soil and trap cultures, respectively. Glomus intraradices Schenck & Smith, Glomus etunicatum Becher & Gerdemann, Glomus claroideum Schenk & Smith emend Walker & Vestberg, Glomus clarum Nicolson & Schenck and Scutellospora callospora (Nicolson & Gerdemann) Walker & Sanders also occurred with high frequencies.     

Diversity of arbuscular mycorrhizal fungi associated with desert ephemerals in plant communities of Junggar Basin,northwest China

Colonization by and diversity of arbuscular mycorrhizal (AM) fungi associated with five common ephemerals, Eremopyrum orientale (L.) Jaub. et Spach., Gagea sacculifera Regel., Plantago minuta Pall., Tragopogon kasahstanicus S. Nikit., and Trigonella arcuata C. A. Mey. were investigated in four typical desert plant communities in Junggar Basin, northwest China. All five ephemerals examined were found to be colonized and formed typical arbuscules or vesicles. The proportion of root length colonized ranged from 2 to 85% with an average of 19%. Spore density in soil near the roots of different ephemerals varied from 1 to 120 spores per 20 ml soil, with an average value of 33 spores. Species richness averaged 8.8 AM fungal species in soil near the roots and ranged from 2 to 21. Fifty-four AM fungal taxa belonging to the genera Acaulospora, Archaeospora, Entrophospora, Glomus and Paraglomus were isolated and identified from soil around the roots. Glomus was the dominant AM fungal genus with a frequency of 100% and relative abundance of 82.6%. The AM fungal species with the highest frequency of occurrence was Glomus aggregatum with a frequency of 75%. G. microaggregatum was present in the highest relative abundance (16%). G. sacculifera, P. minuta and T. arcuata formed Arum-type mycorrhizas. Arbuscular mycorrhizal fungi are ubiquitous and Arum-type mycorrhizas are especially prevalent in these important desert communities used for grazing and traditional medicine.     

Mycological characteristics of the cultural layer of a medieval settlement on soddy calcareous soils

The difference between fungal communities in the cultural layer of a medieval settlement and in the background soddy calcareous soil is shown. In the cultural layer, the portion of spores, especially large spores (d > 6 μm), in the total fungal biomass is increased, whereas the portion of mycelium, especially with a thickness of > 4 μm, is decreased. The species composition of micromycetes in the cultural layer is also transformed; species from the Aspergillus and Fusarium genera predominate. The frequency and diversity of Penicillium representatives decreases, whereas the fungal species from the Phoma, Doratomyces, Geomyces, and Verticillium genera, which are not typical of the background soil horizons, increases. The diversity of the minor fungal species also increases in the cultural layer. An increased content of keratin-decomposing soil fungi is found in the cultural layer. It is argued that the use of the entire set of these characteristics makes it possible to perform mycological indication of the parts of the cultural layer that served different purposes (ancient streets, house floors, backing of the walls, etc.) within the settlement.     

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.     

Distribution of arbuscular mycorrhizal fungi spores in soils of smallholder agroforestry and monocultural coffee systems in southwestern Ethiopia

Arbuscular mycorrhizal fungi (AMF) are associated with the root system of coffee (Coffea arabica L.) plants, but their distribution in smallholder agroforestry and monocultural coffee systems is not well known. This study investigates the spatial distribution of AMF spores in a field study in southwestern Ethiopia. Soil samples from different depths (0–50 cm) were collected under the tree canopies of Acacia abyssinica, Albizia gummifera, Ficus sur, Ficus vasta and randomly selected unshaded coffee plants at different sampling points (canopy base, radius, edge and outside canopy). Significantly higher AMF spore densities were recorded at canopy bases and at 0–30 cm soil depth. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus and Acaulospora dominating. Sampling points, sites and depths, shade tree species and shade tree/coffee plant age affected AMF spore density. Agroforestry practices including the use of leguminous shade trees effectively maintained AMF numbers in soils even at depth compared with unshaded coffee plants (monocultures).     

Evaluation of the effects of spores and their heat-treated residues from different Bacillus strains on the initial growth of rice plants

This study evaluated the effects of the spores and their heat-treated residues from different strains of Bacillus species (B. pumilus, B. altitudinis, and B. megaterium) on the early growth of paddy rice cultivars, including Hitomebore (short-grain japonica rice), Takanari (high-yielding indica rice), and two new lines, TULK-143-6 and LTAT-29. The spores of seven Bacillus strains positively affected Hitomebore root growth, while, the root volume of TULK-143-6 with inoculation of B. pumilus TUAT1 and JM52, and root length and root surface area of LTAT-29 with inoculation of B. megaterium MAFF301694 were increased significantly. In contrast with Hitomebore, Takanari root growth was significantly inhibited by the spores of six Bacillus strains. Surprisingly, inoculations with the spore residues from all tested Bacillus strains increased the root dry weight of Hitomebore, with the effects of four bacterial strains being significant. Furthermore, there were more Bacillus spores than vegetative cells at different time points during the initial rice growth stage, and most plant samples mainly consisted of Bacillus spores. Thus, the spores of Bacillus species likely promote rice root development.     

长期保护性耕作对丛枝菌根真菌多样性的影响

为了明确我国北方干旱地区长期保护性耕作以及深松对丛枝菌根真菌(AMF)多样性的影响,笔者于2014年在山西省临汾市连续22年实施保护性耕作的长期定位试验基地,针对免耕覆盖(NTS)、深松免耕覆盖(SNTS)及传统耕作(TT)3种处理方式,进行了不同耕作条件下土壤AMF物种丰度、孢子密度、Shannon多样性指数以及AMF侵染率等因素的比较研究。结果显示,长期保护性耕作(NTS和SNTS)共分离鉴定出AMF 7属9种,其中根孢囊霉属(Rhizophagus)和斗管囊霉属(Funneliformis)各2种,球囊霉属(Glomus)、近明球囊霉属(Claroideoglomus)、无梗囊霉属(Acaulospora)、硬囊霉属(Sclerocystis)和隔球囊霉属(Septoglomus)各1种;而传统耕作(TT)共分离鉴定出AMF 6属8种,没有检测到无梗囊霉属。NTS、SNTS和TT处理在不同土层的AMF优势种基本一致,0~40 cm土层为摩西斗管囊霉(Fu.mosseae)和变形球囊霉(G.versiforme),40~80 cm土层为摩西斗管囊霉、变形球囊霉和聚丛根孢囊霉(Rh.aggregatum),80~120 cm土层为聚丛根孢囊霉,120 cm土层以下只有NTS和SNTS处理中存在聚丛根孢囊霉,说明保护性耕作措施促进了AMF向土壤深层发展。NTS和SNTS处理在同一土层的AMF物种丰度、孢子密度和Shannon多样性指数均高于TT处理,SNTS处理高于NTS处理。同一耕作措施不同土层的AMF物种丰度、孢子密度和Shannon多样性指数均随土层加深而逐渐降低;NTS和SNTS处理在小麦各生育期的丛枝侵染率和孢子密度均高于TT处理;各处理在小麦拔节期的AMF侵染率最高,分别为14.9%、16.1%和10.6%,而在收获期的土壤孢子密度最高,分别为111.7个·(100g)~(-1)、125.0个·(100g)~(-1)和90.3个·(100g)~(-1)。研究认为,长期免耕覆盖、尤其深松免耕覆盖,提高了AMF多样性。该研究结果可为中国北方旱作农田生态系统中AMF自然潜力的充分发挥,以及保护性耕作技术的合理应用提供科学依据。     

Gram-negative bacterial flora on the root surface of wheat (Triticum aestivum) grown under different soil conditions

We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson's test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

拉萨温性草原土壤原生动物群落对不同放牧强度的响应

探究土壤原生动物对拉萨河谷温性草原不同放牧强度的响应，可以动态监测草原生态系统的环境变化，为保护青藏高原草原生态环境提供科学依据。本研究选取5年围封的温性草原进行为期3年的放牧试验，于2018年9月采取不同放牧强度下的土壤样品进行土壤原生动物培养和鉴定（非淹没培养法、活体观察法）。结果表明：供试样地共鉴定出土壤原生动物46属，隶属于2门、12纲、21目和36科；不同放牧强度下的土壤原生动物主要类群为旋毛纲（Spirotrichea）；不同放牧强度下土壤原生动物多样性指数（H、E、C、M）无显著差异（P>0.05）；Jaccard相似性指数在极不相似到中等不相似之间；样地B3（禁牧）单独聚为一类，说明其空间异质性较大；全氮是影响土壤原生动物分布的主要环境因子，土壤湿度、速效钾、电导率等环境因子共同影响不同放牧强度下土壤原生动物物种组成和分布。     

甘肃天水浅表层滑坡易发区滑坡分布与植被根系特征

为探究甘肃天水浅表层滑坡易发区滑坡分布特征与植被的关系，选取典型滑坡区域和典型植被类型进行研究。油松、华山松、日本落叶松和锐齿槲栎为研究区内典型乔木类型，针对种间根系分布特征和力学特性展开研究。首先，通过无人机获取区域不同植被类型分布，统计得到不同林分类型下的滑坡密度；其次，通过剖面法调查0—100 cm土层深度内的根系数量与直径分布，进行了单根抗拉试验测得抗拉强度，并分层量化为根系附加黏聚力；最后，结合林分调查结果和岩土体力学性质，计算不同植被类型边坡在不同水分条件下和坡度下的安全系数。结果表明：（1）在滑坡高密度区和滑坡低密度区，油松×华山松林地的滑坡密度均高于日本落叶松×锐齿槲栎林地；（2）锐齿槲栎根系数量、分布深度和单根抗拉强度显著高于油松、华山松和日本落叶松，其根系垂直分布深度超过100 cm，抗拉强度最大可达（32.551±7.551） MPa，0—100 cm土层深度内提供的平均附加黏聚力达9.364 kPa；（3）当岩土体处于饱和的极端降水条件时，油松、华山松、日本落叶松对坡体稳定的作用效果为负，而锐齿槲栎能有效加固边坡，在当地具有防治浅表层滑坡的良好功能。     

Diversity of halophytes and identification of arbuscular mycorrhizal fungi colonising their roots in an abandoned and sustained part of Sečovlje salterns

Sečovlje salterns are an important protected area of biotic diversity in the Mediterranean. They represent an extreme environment with high salinity and drought that severely influence the growth of organisms. In the present study, diversity of plant halophytes and their mycorrhizal status were screened at eight different locations, which were mostly dikes and salt ponds, and which were deliberately selected for their distinct properties (e.g. soil salinity ranging from 105 to 2627 μS cm⁻¹, vegetation type and management practice of the salterns).Twelve different halophytic plant species were recorded, of which eleven are designated as vulnerable. With few exceptions, they were found at the abandoned (Fontanigge) and sustained (Lera) locations of the Sečovlje salterns, distributed according to their tolerance to the salinity and waterlogging. The highest diversity of halophytes was listed at Fontanigge, in the abandoned, periodically flooded and gradually overgrown salt ponds. All of the examined species were colonised with either arbuscular mycorrhizal fungi (AMF) and/or dark septate endophytes (DSEs). High levels of colonisation were however detected only for species belonging to the Asteraceae and Plantaginaceae families. Higher root colonisation frequencies were generally seen for plants growing in the abandoned parts, when compared to the managed parts, whereas there was little correlation of the colonisation parameters with physicochemical parameters of rhizospheric soil properties.Molecular analysis by temporal temperature gradient gel electrophoresis (TTGE) of roots of halophytic plant species with confirmed AMF colonisation (arbuscules present) revealed the occurrence of at least six different AMF species, related to Glomus geosporum, Glomus caledonium and Glomus intraradices, and to different Glomus sp. clades and the Diversispora clade. This is to the best of our knowledge the first report of AMF and DSE mycorrhizal status of most of the halophyte plant species examined and of the brother scale identification of AMF species based on molecular analyses of roots of diverse halophytes from high saline environments.     

Species composition of arbuscular mycorrhizal fungi in two mountain meadows with differing management types and levels of plant biodiversity

Species composition of arbuscular mycorrhizal fungi (AMF) was analysed in two differently managed mountain grasslands in Thuringia (Germany). Arbuscular mycorrhizal fungi were studied in the roots of 18 dominant plant species from a total of 56 (32%). Additionally, spores of AMF were isolated from soil samples. Arbuscular mycorrhizal fungi species composition was analysed based on 96 sequences of the internal transcribed spacer of the nuclear ribosomal DNA, 72 originated from mycorrhizal roots, and 24 originated from AMF spores. Phylogenetic analyses revealed a total of 19 AMF species representing all genera of the Glomeromycota except Scutellospora and Pacispora. Despite a different farming intensity, resulting in remarkable differences concerning their plant species diversity (27 against 43 plant species), the diversity of AMF was found to be similar with 11 species on the intensively farmed meadow and ten species on the extensively farmed one. Nevertheless, species composition between both sites was clearly different. It thus seems likely that the AMF species composition, but not necessarily the species number, is related to above ground plant biodiversity in the system under study.     

Morphological and molecular characterization of arbuscular mycorrhizal fungal communities inhabiting the roots and the soil of saffron (Crocus sativus L.) under different agricultural management practices

Crocus sativus L. cultivation is expanding to areas with low soil fertility, where mycorrhizal fungi are supposed to be essential for plants growth and ecosystems functioning. Agricultural practices applied under these conditions should lead to good saffron productivity and quality. Our objective was to study the density and diversity of mycorrhizal fungi populations associated with saffron grown in Taliouine (Morocco) under different agricultural management practices (fertilization type, age and plantation method). Morpho-anatomical studies identified rhizospheric mycorrhizal spores and assessed root colonization by arbuscular mycorrhizal fungi (AMF). Molecular identification of AMF was realized by sequencing the Large Subunit (LSU) rDNA gene region. Among the eleven species of AMF spores identified, Funneliformis and Rhizoglomus species were the most abundant (> 35%). Modern saffron plantation showed higher roots colonization rates (mycorrhization intensity (100%) and frequency (51.6%)), while in traditional plantations lower mycorrhization frequency values were found (17.4%). LSU sequencing identified five AMF genera and three unknown genomic groups, whereas Shannon diversity index indicated that AMF community composition changed significantly according to plantation age and fertilization type. Our results contribute to a better knowledge of saffron AMF communities and open new perspectives for a rational utilization of the agricultural practices for organic saffron production.     

长期定位施肥对丛枝菌根真菌多样性的影响

Diversity of arbuscular mycorrhizal fungi (AMF) was investigated in a field that had received long-term fixed ferti-lization (LFF) for 26 years.There were a total of 12 treatments in triplicates with different amounts of manure,urea,calcium phosphate,and potassium chloride.Rhizosphere soil samples of maize and wheat grown in the experimental field in Shandong Province,China,were collected in September 2003 and May 2004,respectively.Arbuscular mycorrhizal fungal spores were isolated and identified using morphological characters.Mycorrhizal colonization percentage,spore density (SD),species richness (SR),relative abundance (RA),and Shannon-Weiner index (SWI) were determined.Nineteen recognized species of AMF belonging to 5 genera were identified.Long-term fixed fertilization significantly influenced colonization percentage,SR,SD,and species diversity of AMF.The adaptability of AMF to soil fertility was different among species.Species richness and SD of AMF in maize and wheat rhizosphere soils were the highest in the nonferti-lization treatment (control) and lowest in the high manure + high nitrogen treatment (M₂N₂).The SWI decreased as the fertilization level increased except in the low manure treatment (M₁) on maize.Compared with the other treatments,Treatment M₂N₂ significantly reduced SD of Glomus,and the high manure + low nitrogen treatment (M₂N₁) significantly retarded sporulation of Scutellospora.Manure treatments stimulated sporulation of Glomus mosseae.Spore density of G.mosseae was higher in the high nitrogen + phosphorus + potassium treatment (N₂PK) than in the high nitrogen + phosphorus treatment (N₂P) and the high nitrogen + potassium treatment (N₂K).The SD of S.pellucida was higher in Treatment N₂K than Treatments N₂PK and N₂P.In conclusion,long-term fixed fertilization,especially with high levels of manure and N,decreased SR,SD,and colonization and changed the species composition of AMF.     

黄土丘陵区主要植物根系对土壤有机质和团聚体的影响

植物根系是植物与土壤进行物质交换的通道,在土壤侵蚀严重、生态脆弱的黄土丘陵区,深入认识根系对土壤物理化学性质的影响具有重要意义。选取了白羊草(Bothriochloa ischaemum)、苔草(Carex lanceolata)、茭蒿(Artemisia leucophylla)、铁杆蒿(Artemisia sacrorum)、狼牙刺(Sophora viciifolia)、柠条(Caragana intermedia)6种植物作为研究对象,取0—10,10—20,20—30,30—40,40—50,50—60 cm土层根系和土样,分析不同土层各物种根长密度、根表面积密度、平均根直径、土壤有机质(SOM)、土壤容重以及各级水稳性团聚体重量百分含量。结果表明:所研究植物根系以细根为主。在0—20 cm土层中,白羊草、苔草根长密度显著大于其余植物(P0.05),表现为苔草白羊草铁杆蒿茭蒿狼牙刺柠条,平均根直径则相反。根系能不同程度地增加SOM含量,SOM含量与根系平均直径和根系表面积密度呈极显著的正相关关系(P0.01)。在土壤剖面上,水稳性团聚体重量百分含量明显减少的是白羊草、苔草和铁杆蒿样地,水稳性团聚体重量百分含量随土层深度变化不明显的是茭蒿、狼牙刺和柠条样地。根表面积、根长密度能够显著增加0.5～2 mm水稳性团聚体重量百分含量(P0.05),说明根系能够使小粒径团粒凝聚成更大粒径的土壤团粒。根系能够提高土壤有机质含量,增加中等粒径团聚体含量,改善土壤结构,提高土壤稳定性,对增加土壤抗蚀性起到重要作用。     

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.     

Ecology of soil microflora and mycorrhizal symbionts in degraded forests at two altitudes

Summary Microbial populations were estimated in four different forest stands at different regenerational stages, two each at higher and lower altitudes. The fungal and bacterial populations showed marked seasonal variations at both altitudes. Quantitatively, the bacterial population was higher than the fungal population. Although 25 fungal species were isolated at the lower altitude, only 15 were obtained at the higher altitude. Penicillium chrysogenum and Trichoderma viride were dominant at the lower and higher altitudes, respectively. In the more degraded forest stand at the lower altitude both the fungal and the bacterial population showed a significant positive correlation with organic C (r=0.658 and 0.735, respectively), whereas in the less degraded forest stand there was a significant correlation only between the fungal population and organic C (r=0.835). At the higher altitude, however, a highly significant correlation (P<0.05) was observed between the fungal population, soil moisture and organic C in both the forest stands. Disturbance to the soil and vegetation adversely affected the microbial population, and also affected endogonaceous spores. At the lower altitude, plants in the more degraded forest stand were more mycotrophic compared to those in the less degraded stand. The level of mycorrhizal infection showed a highly positive correlation with soil moisture, organic C, total N, and available P. The spore population, however, was correlated negatively with these parameters. Three different endogonaceous genera, Glomus, Gigaspora, and Acaulospora, were identified during the course of investigation. Glomus, however, was dominant.     

Infection potential of farm soils as mycorrhizal inocula for Leucaena leucocephala

A greenhouse experiment was conducted to assess the arbuscular mycorrhizal (AM) fungi inoculum potential for Leucaena leucocephala in a range of nutrient-depleted farm soils in western Kenya. Leucaena was grown in 12 uninoculated farm soils with pH 5.0–6.7, with or without rock P and farmyard manure. Root infection, nodulation, and shoot and root weight were determined 25, 46, and 69 days after planting. Spore concentrations in the farm soils at the start of the experiment ranged from 44 to 126 live spores per 100 g dry soil with 6–10 species per soil, principally Scutellospora spp. and Acaulospora spp. Nodulation was absent or poor in all soils, indicating the need for rhizobial inoculation of species belonging to the leucaena crossinoculation group in this agrosystem. Rock-P alone increased final shoot dry weight by a factor of 1.4, manure alone by 1.8, and rock-P plus manure by 1.9, compared with no ameliorant. Root infection with AM fungi was detected in all soils 25 days after planting and increased linearly in the different farm soils to values of 33–65% 69 days after planting. Soil pH and root infection 25 days after planting accounted for much of the variation in final shoot weight among soils with no amelioront (87%). As early root infection increased from 20 to 40% at soil pH 5.0, the predicted final shoot dry weight was doubled, and the response to ameliorants was reduced by two-thirds. The growth responses to increased infection became smaller as pH increased from 5.0 to 6.5.