Mycorrhizal associations in the rain forest of South Cameroon

Mycorrhizal associations of important tree species were investigated within the research area of the Tropenbos Cameroon Programme (TCP), situated on the western portion of the Atlantic Biafrean forest of south Cameroon. Ninety-seven tree species of economic, social, and ecological importance, and three lianas were selected in three sites that differed in altitude, soil clay content, and soil pH. In each site plots were laid out in undisturbed forest. In each plot, seedlings, saplings, juvenile, and mature trees were identified to species level and counted; girth at breast height measured and basal area calculated; root samples were taken and examined for mycorrhizal type and extent of mycorrhizal colonization.

All 100 species investigated were mycorrhizal. Tree of 74 species formed exclusively arbuscular mycorrhizas (AM); 23 trees and three Gnetum species formed ectomycorrhizas (ECM). Five of these ECM plants also harbored AM structures. Extent of mycorrhizal root colonization showed large differences for various AM trees; however, colonization of more than half of these trees was less than 25%. Colonization of ECM trees was often higher than 75%. The contribution of ECM trees to basal area varied between 19 and 35%. ECM trees often occurred in small to large clumps. In sustainable forest management plans, existing ECM forest clumps should be given special conservation value.     

孟加拉国Dinajpur农林复合区内不同树种和作物种中丛枝菌根分布和孢子群落多样性的研究

从孟加拉国Dinajpur地区采集了不同农林复合区内树种和作物种,对采集植物的丛枝菌根多样性进行了研究.在3个取样地采集了18种植物的根和根际土,取样地和被采取植物分别为：取样地Dashmail为黄豆树 （Albizia procera Benth.）、小指椒 （Capsicum frutescens L）、姜黄（Curcuma domestica Vahl）、印度黄檀 （Dalbergia sissoo Roxb.） 和大叶桃花心木（Swietenia macrophylla）5种植物; 取样地Kantaji为姜黄（C.Domestica）、印度檀 （D.Sissoo）、赤桉 （Eucalyptus camaldulensis Dehnn.）、石梓（Gmelina arborea （Roxb） DC） 和水稻 （Oryza sativa L.） 5种植物; 取样地Ramsagar为姜黄（C.Domestica）, 印度檀 （D.Sissoo）, Litchi chinensis Sonn.和水稻.在取样地Dashmail,植物丛枝的分布范围在36%-79%,其中分布最高的是小指椒,达到79%,而C.Domestica仅占36%.取样地 Kantaji丛枝的分布范围在33%-70%之间,其中分布最高的是石梓,达到79%,而O.Sativa分布最低,仅36%.取样地 Ramsagar丛枝的分布范围在35%-70%之间,印度檀丛枝分布在该地最高, 达70%,而水稻丛枝在该地的分布最小,仅35%.在采样地Dashmail,每100克干土中所含采样植物丛枝菌根孢子群落54-140个;孢子群落最多的是印度檀（140/100g dry soil）,最低的是姜黄（C.Domestica） （40/100g dry soil）.在采样地Kantaji,孢子群落在63-221/100g dry soil,石梓具有的群落最高,为221/100g dry soil;印度檀为63/100g dry soil.在采样地Ramsagar, 所具有的最高和最低群落分别是 160/100g dry soil （D.Sissoo）和69/100g dry soil（L.Chinensis）.土壤Ph值与土壤中丛枝分布和菌根孢子群落无显著相关性.Simpson多样性指数和Shannon多样性指数在取样地Kantaji 的印度檀土壤中最高;而在取样地Ramsagar的水稻土壤中最低.研究表明孟加拉国Dinajpur地区丛枝菌根的存在、树种和作物种中的营养性质、丛枝菌根的必要性和贡献以及复合农林植物生长与丛枝?     

我国南方桉树人工林菌根合成及其多样性研究(英文)

对我国南方部分地区桉树人工林菌根真菌资源和菌根类型进行了调查 .对采自广东、云南 15个桉树林地的根系样品进行了显微观察 ,结果证实了在自然土壤中桉树能形成不同类型的菌根 ,检查的根样在不同程度上均有菌根菌的感染 .其中 ,有 4个人工林的根系样品AM感染率在 50 %以上 ,另有 4个根样ECM感染根段长超过 50m .调查发现林分年龄大小对菌根形成及菌根类型有一定的影响 ,表现在幼林及过熟林菌根感染率均较低 ,而 4～ 7年生按树林菌根感染率相对较高 ,在同一根系上AM与ECM菌间存在一定的竞争性 .在菌根菌资源方面 ,从总体上来说 ,我国南方菌根菌资源较少 ,尤其是ECM菌 .调查结果表明 ,我国南方桉树人工林根际土壤中有AM菌 2 8种 ,隶属于 4个属 ,其中以球囊霉属真菌最多 ,占 6 4 % ;地球囊霉在所采集的土样中出现的频度最高 .南方 15个桉树人工林中发现有 17种ECM菌 ,隶属 10个属 ,其中彩色豆马勃、多根硬皮马勃、光硬皮马勃等菌种在两广地区许多桉林中较常见 ,云南地区则多以黄须腹菌、硬皮马勃等菌较多 .这些ECM菌通常生长于松树林中 ,能否与引进的桉属树种形成较好的菌根还有待于进一步研究 .本文对自然条件下混合菌根的形成及真菌间的竞争关系进行了讨论     

Growth response of <Emphasis Type="Italic">Acacia mangium</Emphasis> Willd. seedlings to arbuscular mycorrhizal fungi and four isolates of the ectomycorrhizal fungus <Emphasis Type="Italic">Pisolithus tinctorius</Emphasis> (Pers.) Coker and Couch

Some Acacia mangium Willd. plantations in Asia grow poorly due to low soil fertility and the absence of compatible mycorrhizal fungi. This legume tree can be colonized by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi but inoculation is not routinely practiced. This study aimed to compare the effectiveness of AM fungi and four isolates of the ECM fungus Pisolithus tinctorius (Pers.) Coker and Couch (Pt) in promoting growth of A. mangium seedlings under glasshouse conditions. AM inoculants were: Glomus etunicatum, G. fasciculatum, G. macrocarpum and Gigaspora margarita and mixed species extracted from rhizosphere soil of a Populus stand in Suwon (AMKFRI), and Carex (AMM6) and Populus (AMM7) growing in mine tailings in Korea. Pisolithus isolates were from Philippines (PtPhil) and Korea (PtKFRI, PtMKACC, PtKACC). Generally, ECM fungi promoted height and diameter growth of A. mangium more than the AM inoculants. The Korean Pisolithus increased plant dry weight by 122–145%, mixed AM inoculants by 61–97%, and Glomus and Gigaspora by 45–72% over the control. PtKACC gave the highest root colonization and promoted the highest growth and concentration of most nutrients. Mycorrhizal root colonization was positively correlated with plant dry weight, Na, Fe and Cu concentrations and N, P, K, Ca, Na, Fe and Cu contents. In conclusion, the results provide strong evidence for benefits of mycorrhizal inoculation on A. mangium seedlings under glasshouse conditions. The Korean Pisolithus isolates (particularly PtKACC), and two AM fungi (AMKFRI and AMM6) are potential mycorrhizal inoculants but their effectiveness and persistence should be determined on degraded lands in tropical countries where A. mangium is being planted for rehabilitation.     

Source of mycorrhizal inoculum influences growth of Faidherbia albida seedlings

Poor land use management and practice inhibit the growth and establishment of tree seedlings in dryland areas.We assessed arbuscular mycorrhizal fungi(AM)status of Faidherbia albida(Del.)A.Chev.trees grown on different land uses.We quantified the growth and nutrient uptake of F.albida seedlings inoculated with AM from different sources.These efforts were based on soil and fine root samples from the rhizosphere soils of F.albida trees.AM root colonization was determined using the gridline intersect method.Spores were extracted by the wet sieving and decanting method and identified to genus level.The seedling experiment had a completely randomized onefactorial design with four treatments and five replications.Faidherbida albida seedlings were grown in a greenhouse.All in situ F.albida trees were colonized by AM fungi.AM root colonization of F.albida trees was significantly higher(P<0.0086)in area exclosures than on lands used for grazing or cultivation.Spore abundance was significantly higher(P<0.0014)in area exclosures followed by cultivated land and grazing land.Glomus was the dominant genus in all land-uses.AM-inoculated F.albida seedlings grew better(P<0.05)than non-inoculated controls.Seedlings inoculated with AM from area exclosure had significantly(P<0.05)higher growth and nutrient uptake than those inoculated with AM from grazing and cultivated land.This emphasizes the importance of the native soil AM potential for better establishment of seedlings to achieve optimum plant growth improvement and assist in rehabilitation of degraded arid lands.     

Arbuscular mycorrhizas and performance of Polylepis australis trees in relation to livestock density

Polylepis australis trees endemic to Argentina dominate the canopy of subtropical high altitude forests. Here, livestock rearing is the main economic activity and is suspect of the low performance of P. australis trees through direct and indirect effects which could include the reduction in arbuscular mycorrhizal fungi (AMF) and their benefit to trees. To elucidate the role of AMF, we compare plant performance indicators, arbuscular mycorrhizal (AM) colonization and AMF communities in 20 trees distributed in two areas of central Argentina which differed in livestock grazing intensity. The area with high livestock density presented more soil degradation and trees with a lower overall plant performance than the area with reduced livestock density. The AM colonization values of P. australis were considerably higher than reported for other tree species and the area with high livestock density had a lower proportion of arbuscules and higher proportion of hyphae, while vesicles and AM colonization – all structure considered together – did not differ between areas. Overall AMF spore number and of most species when considered separately was significantly higher in the area with high livestock density, suggesting a high tolerance and adaptation of AMF to livestock. We conclude that a reduction in livestock improves the performance of P. australis, that this improvement could be mediated by an increase in the proportion of arbuscules, but there does not appear to be any limitation in AM colonization or AMF spore number which could otherwise be limiting forest restoration.     

Arbuscular mycorrhizal associations in Boswellia papyrifera (frankincense-tree) dominated dry deciduous woodlands of Northern Ethiopia

This study assessed the arbuscular mycorrhizal (AM) status of Boswellia papyrifera (frankincense-tree) dominated dry deciduous woodlands in relation to season, management and soil depth in Ethiopia. We studied 43 woody species in 52 plots in three areas. All woody species were colonized by AM fungi, with average root colonization being relatively low (16.6% – ranging from 0% to 95%). Mean spore abundance ranged from 8 to 69 spores 100 g⁻¹ of dry soil. Glomus was the dominant genus in all study sites. Season had a strong effect on root colonization and spore abundance. While spore abundance was higher (P < 0.001) in the dry season in all three study sites, root colonization showed a more variable response. Root colonization was reduced in the dry season in the site that was least subject to stress, but increased in the dry season in the harshest sites. Management in the form of exclosures (that exclude grazing) had a positive effect on spore abundance in one of the two sites considered. Spore abundance did not significantly differ (P = 0.17) between the two soil depths. Our results show that in this arid region all trees are mycorrhizal. This has profound consequences for rehabilitation efforts of such dry deciduous woodlands: underground processes are vital for understanding species adaptation to pulsed resource availability and deserve increasing attention.     

Arbuscular mycorrhizal fungi in the rhizosphere of Macaranga denticulata Muell. Arg., and their effect on the host plant

A fallow enriching tree, Macaranga denticulata Muell. Arg., has been shown to increase rice yield in a rotational shifting cultivation system in northern Thailand through increased accumulation of mineral nutrients. As arbuscular mycorrhizal (AM) fungi may play an important role in nutrient accumulation, AM fungi in the rhizosphere of M. denticulata and the effects of the indigenous soil inoculum on the host plant were investigated. The diversity and abundance of AM fungi were documented for the rhizosphere of M. denticulata in the field for two years. Based on morphology, 29 species of AM fungi were found in the rhizosphere of M. denticulata growing in farmers’ fields. Root colonization ranged from 63.5 to 81.5% in the first year and 68.7 to 79.9% in the second year of study. The highest spore density was observed at the end of the wet season. The effects of indigenous soil inoculum, and N and P fertilizers on the host plant were investigated in pots for four months. Inoculation with soil-containing AM fungi strongly increased plant growth and nutrient contents when P was limiting but N was applied. Application of N and P together strongly depressed root colonization and spore density of AM fungi, whereas applying them separately had much less effect. AM fungi may play an important role in nutrient accumulation in M. denticulata-rich fallow and thus in nutrient cycling that is beneficial to the maintenance of upland rice yield and sustainability of the rotational shifting cultivation system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tree species as hosts for arbuscular mycorrhizal and dark septate endophyte fungi

A survey of 35 tree species(belonging to 28 genera in 19 families) in Aliyar,South India was carried out to ascertain their arbuscular mycorrhizal(AM) and dark septate endophyte(DSE) fungal status.All the tree species examined had AM association.AM and DSE colonization is reported for the first time in 20 and 14 species respectively.Cooccurrence of AM and DSE was observed in 14(40%) tree species.The extent of DSE colonization was inversely related to the extent of AM fungal colonization.Six tree species had Arum-type,18 had intermediatetype and 11 had typical Paris-type AM morphology.AM fungal spore morphotypes belonging to 11 species in two genera were isolated from the rhizosphere soil.AM fungal spore numbers were not related to the extent of AM colonization and Glomus dominated spore diversity.AM association individually and along with DSE were found respectively in the 63% and 44% of the economically important tree species.The occurrence of AM and DSE fungal association in economically important indigenous tree species indicates the possibility of exploiting this association in future conservation programmes of these species.     

Arbuscular mycorrhizal associations in different forest tree species of Hazarikhil forest of Chittagong, Bangladesh

Biodiversity of arbuscular mycorrhizal (AM) colonization and AM fungal spores were studied in the roots and rhizosphere soils of Acacia catechu (L.f). Wild., A. mangium Willd, Anthocephala cadamba Miq., Artocarpus chaplasha Roxb., Chickrassia tabularis A. Juss., Swietenia macrophylla King., Tectona grandis L. from plantations; Albizia procera (Roxb.) Benth., A. falcataria L., Alstonia scholaris (L.) R. Br., Aphanamixis polystachya (Wall.) Parker., Hydnocarpus kurzii (King.) Warb., Heynea trijuga Roxb., Lagerstroemia speciosa (L.) Pers., Messua ferrea Linn., Podocarpus nerifolia Don., Swintonia floribunda Griff., Syzygium fruticosum (Roxb.) DC., S. grandis (Wt.) Wal. from forest and nursery seedlings of A. polystachya, A. chaplasha, Gmelina arborea Roxb. and S. cuminii (L.) Skeels from Hazarikhil forest, Chittagong of Bangladesh. Roots were stained in aniline blue and rhizosphere soils were assessed by wet sieving and decanting methods. The range of AM colonization varied significantly from 10%-73% in the plantations samples. Maximum colonization was observed in A. mangium (73%) and minimum colonization was observed in C. tabularis (10%). Vesicular colonization was recorded 15%-67% in five plantation tree species. The highest was in A. cadamba (67%) and the lowest was in T. grandis; A. chaplasha and C. tabularis showed no vesicular colonization. Arbuscular colonization was recorded 12%-60% in four plantation tree species. The highest was in A. mangium (60%) and the lowest was in A. cadamba. Roots of Artocarpus chaplasha, C. tabularis and T. grandis showed no arbuscular colonization. Among 12 forest tree species, nine tree species showed AM colonization. The highest was in A. falcataria (62%) and the lowest was in S. fruticosum (10%). Significant variation in vesicular colonization was recorded in seven forest tree species. The highest was in H. trijuga (52%) and the lowest was in L. speciosa (18%). Hydnocarpus kurzii, M. ferrea, P. nerifolia S. fruticosum and S. grandis showed no vesicular colonization. Arbuscular colonization was recorded in seven forest tree species. The highest was in A. falcataria (60%) and the lowest was in A. procera (10%). All the nursery seedlings showed AM colonization and the range was 10%-73%. Vesicules were recorded in G. arborea (40%) and S. cumini (40%). Arbuscular colonization was recorded in G. arborea (100%) and S. cumini (100%). Spore population was recorded 77-432/100 g dry soils, 80-276/100 g dry soils, and 75-153/100g dry soils in plantation, forest and nursery, respectively. Glomus and Acaulospora were dominant genera among the six AM fungi recorded. Significantly positive correlation was observed between AM colonization and AM fungal spore population in Hazarikhil plantation tree species, forest tree species and nursery tree seedlings. The present study showed the biodiversity of root colonization and AM fungi are active in nutrient cycling, survivals and seedling establishment of the plants in the Hazarikhil forest, plantation and nursery.     

不同套种模式云南核桃丛枝菌根与土壤因子的相关性研究

为探明不同套种模式核桃根际丛枝菌根(AM)与土壤因子之间的相关关系,采用菌根形态学的研究方法,研究了核桃根系中丛枝菌根真菌(AMF)定殖状况和根际土壤中AMF的孢子密度,运用相关分析、主成分分析和通径分析方法,研究了核桃AMF与土壤因子的相关性.结果表明:核桃根系能与AMF形成良好的共生关系,不同套种模式之间核桃根系中...     

Effects of arbuscular mycorrhizal fungi on leaf solutes and root absorption areas of trifoliate orange seedlings under water stress conditions

The effects of the arbuscular mycorrhizal (AM) fungus Glomus mosseae on plant growth, leaf solutes and root absorption area of trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings were studied in potted culture under water stress conditions. Inoculation with G. mosseae increased plant height, stem diameter, leaf area, shoot dry weight, root dry weight and plant dry weight, when the soil water content was 20%, 16% and 12%. AM inoculation also promoted the active and total absorption area of root system and absorption of phosphorus from the rhizosphere, enhanced the content of soluble sugar in leaves and roots, and reduced proline content in leaves. AM seedings had higher plant water use efficiency and higher drought tolerance than non-AM seedlings. Effects of G. mosseae inoculation on trifoliate orange seedlings under 20% and 16% soil water content were more significant than under 12% soil water content. AM infection was severely restrained by 12% soil water content. Thus, effects of AM fungi on plants were probably positively related to the extent of root colonization by AM fungi. The mechanism of AM fungi in enhancing drought resistance of host plants ascribed to greater osmotic adjustment and greater absorption area of root system by AM colonization. __________ Translated from Journal of Plant Physiology and Molecular Biology, 2005, 30(5): 583–588 [译自: 植物生理与分子生物学报, 2005, 30(5): 583–588]     

Arbuscular mycorrhizal association of indigenous agroforestry tree species and their infective potential with maize in the rift valley, Ethiopia

Tree species in agroforestry are important source of inoculum for companion agricultural crops. Agroforestry trees can serve as a source of Arbuscular mycorrhiza (AM) inoculants to intercropped annuals. We studied spore abundance, root colonization of Albizia gummifera (J.F. Gmel.) and Croton macrostachyus (Hochst Ex Del.) trees and their effect on colonization of maize. Soil and root samples were collected from field standing trees from under and outside the canopy of trees and maize crops in the main rainy season. The number of spore count was significantly higher under the canopy of A. gummifera (791/100 g of dry soil) and C. macrostachyus (877/100 g of dry soil) trees than outside the canopy (547 and 588/100 g of dry soil, respectively). The level of root colonization of C. macrostachyus (45 %) was higher than A. gummifera (41 %). Root colonization of maize crops grown under the canopy of A. gummifera and C. macrostachyus trees was significantly higher than outside the canopy (P < 0.001). Maize seedlings grown on non-sterilized soils collected under and outside the canopy of A. gummifera and C. macrostachyus trees recorded higher root colonization, plant height, shoot and root dry weight than grown on sterilized soils (P < 0.001). The percentage of AM colonized roots of Zea mays seedlings was significantly positively correlated with the number of spore counts for field soils. The rhizospheres of indigenous agroforestry perennial species are important source of inoculum for annuals. The integration of perennials and annuals in an agroforestry system enhances the maintenance of soil quality in the tropics.     

Management of ectomycorrhizal symbionts associated to useful exotic tree species to improve reforestation performances in tropical Africa

? The objective of this review was to summarize scientific data on the symbiotic status of exotic tree species useful in tropical Africa, and to update reports about their growth improvement through microbial inoculations, especially ectomycorrhizal symbionts.

? The studies reviewed microbial symbionts associated to exotic tree species belonging to Myrtaceae, Pinaceae, Casuarinaceae and Leguminosae. In their native areas, these trees are associated either with ectomycorrhizal (ECM) fungi (e.g. Pinaceae) or both ECM and arbuscular mycorrhizal (AM) fungi (e.g. Eucalyptus), or sometimes as in Casuarina and Acacia with three coexisting symbionts (nitrogen fixing bacteria, ECM and AM fungi). In their new habitats, using highly efficient mycorrhizal fungi, controlled mycorrhization experiments have pointed out the importance of root symbionts in establishment and growth of exotic tree species such exotic pines or Australian acacias.

? Since the challenge in sylviculture and reforestation was to determine the best compromise between symbiotic compatibility and efficiency of both partners under local soil constraints, further researches have to be encouraged to elucidate the complexity of these tree symbioses in terms of diversity, interaction and effectiveness of their symbiotic partners for their better exploitation in reforestation programmes.

     

不同内外生菌根菌接种对米老排苗期的生长效应

9 mycorrhizal fungi, including 4 ectomycorrhizal fungi (ECMF) and 5 arbuscular mycorrhizal fungi (AMF), were used to explore their effect on seedling growth of Mytilaria laosensis. The study shows that M. laosensis is one of the species with both VAM and ECM. Mycorrhizal infection rate of all ECM inoculation methods reached level 3, and that of AMF infection rate was 88%-93%, of which AM91 became the highest. In different periods, different inoculation treatment expressed different effects on seedling growth. At the end of the experiment, the height, ground diameter, underground dry mass and upper ground dry mass of seedling inoculated with PX0801 and 9006 respectively increased by 71%, 45%, 128%, 184%, and 65%, 54%,150%, 208%, which exhibited the best overall effect. Coinoculated seedlings with AM90036, AM3008 and AM91 had advantages over uninoculated ones in all the tested growth indicators, which suggest to significantly promote the growth of M.laosensis. The results obtained provide reference for mycorrhizal fungi application on M. laosensis.     

丛枝菌根真菌对在含砷土壤中的云南石梓(Gmelina arborea)生长的影响(英文)

孟加拉东南部土壤中的砷含量很高,不仅威胁人的健康,而且对土壤也有破坏作用。云南石梓(Gmelina arborea)在孟加拉是个快速生长的树种,也是含砷土壤中的潜力树种。研究评价了含砷试验土中丛枝菌根真菌对云南石梓(Gmelina arborea)生长的影响。播种前,四种不同浓度的砷(10mg·kg-1、25mg·kg-1、50mg·kg-1和100mg·kg-1)被加入到试验土中。记录生长参数,如,植物的根、苗鲜重、干重、冠幅径、根长和苗高、根瘤菌和孢子菌群落。菌根植株较非菌根植株生长好。与其它含砷量高的土壤中植株的生长情况相比,在含砷量为10-mg·kg-1的土壤中,菌根植株和菌根生长效果最佳,菌根植株生物量最高。随着砷浓度的增加,种苗生长,根瘤菌和孢子菌群落均明显降低p0.05)。与非菌根植株比较,菌根植株高生长增加了40%,生物量增加了2.4倍。研究表明,根瘤菌接种可以减少有害土壤中的云南石梓(Gmelina arborea)的初生长的影响。     

Growth and reproductive characteristics of the columnar cactus Stenocereus queretaroensis and their relationships with environmental factors and colonization by arbuscular mycorrhizae

Three natural populations of pitayo (Stenocereus queretaroensis (Weber) Buxbaum), a columnar arborescent cactus, were studied in their subtropical environments in western Mexico. All of the sites were characterized by shallow, nutrient-poor soils. Percentage of colonization by arbuscular mycorrhizae (AM) fungi, stem growth, fruit mass, and percentage germination were greater in S. queretaroensis at Autlan, Jalisco (AJ) than at Zacoalco de Torres, Jalisco (ZTJ) or Santa Rosa, Zacatecas (SRZ). The onset of root colonization by arbuscular mycorrhizae during the middle of the summer wet period preceded increases in stem extension rate and stem phosphorus concentration. Based on previous studies of effects of environmental factors on photosynthesis, climatic conditions were more favorable for photosynthesis at AJ than at SRZ and ZTJ, as indicated by the amount of summer rainfall, the amount of light, and the moderate air temperatures that prevailed during the fall and winter seasons. There was a significant positive correlation between stem growth and percentage of total root length colonized by arbuscules of AM fungi for S. queretaroensis at SRZ and AJ, but not at ZTJ. A negative significant correlation was observed between stem growth and maximal and minimal air temperatures at the three study sites. Stem growth was positively related to rainfall only at SRZ, and light was statistically related to stem growth only at ZTJ. Among sites, S. queretaroensis at AJ had the highest carbon gain and greatest AM colonization, creating physiological conditions that led to the highest stem growth, fruit mass and percentage of seed germination.     

Distribution,colonization and diversity of arbuscular mycorrhizal fungi associated with central Himalayan rhododendrons

The objective of the present study was to investigate arbuscular mycorrhizal status of five species of rhododendrons distributed in Kumaun region of the Indian Central Himalaya. Root and rhizosphere soil samples of all the five species of rhododendrons, namely, Rhododendron anthopogon, R. arboreum, R. campanulatum, R. barbatum and R. lepidotum were collected from temperate, sub-alpine to alpine location in altitudinal range from 1500 to 4500 m amsl. The arbuscular mycorrhizal colonization in root samples ranged from 28 to 42%; and maximum and minimum colonization was observed in R. arboreum and R. lepidotum, respectively. The highest number of intraradical vesicles (12.5 ± 2.8 cm⁻¹ root segment) was recorded in R. arboreum and the lowest (7.0 ± 1.7 cm⁻¹ root segment) in R. barbatum; vesicles were not observed in R. lepidotum. Spores were extracted from the rhizosphere soil by wet sieving to perform microscopic identification of the species. The maximum and minimum populations of spores were detected in the rhizosphere soil samples of R. anthopogon (52.0 ± 1.5 spores 25 g⁻¹ soil) and R. lepidotum (32.0 ± 2.5 spore 25 g⁻¹ soil), respectively. Spore populations were found to belong to five genera—Acaulospora, Glomus, Gigaspora, Sclerocystis and Scutellispora; genus Glomus was found to be dominant in the rhizosphere soil samples of all the rhododendron species. The most frequent and abundant species was G. fasciculatum, however, this species was not isolated from the rhizosphere soil of R. barbatum. Finger millet (Eleucine coracana) was used to cultivate the trap culture of arbuscular mycorrhizal fungi to confirm the species identity. Spores of Glomus pustulatum, not detected in the rhizosphere soil, were recovered from the trap culture. Contrary to this, genus Gigaspora, which was present in the rhizosphere soil, did not sporulate in the trap culture. Shannon and Wiener index of diversity and Simpson's index of dominance indicated that the species richness, dominance and diversity of arbuscular mycorrhizal fungi decrease with increasing altitude. In two species of rhododendrons, namely R. campanulatum and R. anthopogon, dark septate mycelium was also observed.     

Cultured arbuscular mycorrhizal fungi and native soil inocula improve seedling development of two pioneer trees in the Andean region

The tree species Alnus acuminata and Morella pubescens, native to South America, are candidates for soil quality improvement and afforestation of degraded areas and may serve as nurse trees for later inter-planting of other trees, including native crop trees. Both species not only form symbioses with arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF), but also with N₂-fixing actinobacteria. Because tree seedlings inoculated with appropriate mycorrhizal fungi in the nursery resist transplanting stress better than non-mycorrhizal seedlings, we evaluated for A. acuminata and M. pubescens the potential of inoculation with mycorrhizal fungi for obtaining robust tree seedlings. For the first time, a laboratory-produced mixed AMF inoculum was tested in comparison with native soil from stands of both tree species, which contains AMF and EMF. Seedlings of both tree species reacted positively to both types of inocula and showed an increase in height, root collar diameter and above- and belowground biomass production, although mycorrhizal root colonization was rather low in M. pubescens. After 6 months, biomass was significantly higher for all mycorrhizal treatments when compared to control treatments, whereas aboveground biomass was approximately doubled for most treatments. To test whether mycorrhiza formation positively influences plant performance under reduced water supply the experiment was conducted under two irrigation regimes. There was no strong response to different levels of watering. Overall, application of native soil inoculum improved growth most. It contained sufficient AMF propagules but potentially also other soil microorganisms that synergistically enhance plant growth performance. However, the AMF inoculum pot-produced under controlled conditions was an efficient alternative for better management of A. acuminata and M. pubescens in the nursery, which in the future may be combined with defined EMF and Frankia inocula for improved management practices.     

Mycorrhizal dependency and growth responses of Acacia nilotica and Albizzia lebbeck to inoculation by indigenous AM fungi as influenced by available soil P levels in a semi-arid Alfisol wasteland

A series of available phosphorus (Olsen) levels ranging from 10 to 40 ppm were achieved in a semi-arid soil. The influence of the levels of phosphorus on the symbiotic interaction between two subtropical tree species, Acacia nilotica and Albizzia lebbeck, and a mixed inoculum of indigenous arbuscular mycorrhizal (AM) fungi was evaluated in a greenhouse study. The extent to which the plant species depended on AM fungi for dry matter production decreased as the levels of soil P increased, but the degree of this decrease differed in the two species tested. Acacia nilotica colonized by AM fungi showed a significant increase in shoot P and dry matter at a soil P level of 10 ppm whereas in Albizzia lebbeck, such increase occurred at 20 ppm. Mycorrhizal inoculation response disappeared beyond soil P levels of 25 ppm in Acacia nilotica and 30 ppm in Albizzia lebbeck. Levels of soil P greater than 25 ppm suppressed AM fungus colonization in both species. Soil P levels of 30 and 40 ppm and 40 ppm caused negative mycorrhizal dependencies (MD) in Acacia nilotica and Albizzia lebbeck respectively. Values of MD for both species were negatively correlated with soil P levels. Based on the MD values, regression equations were developed to predict MD for given levels of available P.