Influence of arbuscular mycorrhizal fungi on soil structure and aggregate stability of a vertisol

The influence of arbuscular mycorrhizal (AM) fungi on aggregate stability of a semi-arid Indian vertisol was studied in a pot experiment in which Sorghum bicolor (L.) was grown as test plant for 10 weeks. Pasteurized soil inoculated with AM fungi was studied with pasteurized and unpasteurized soils as references. A part of the soil in each pot was placed in nylon mesh bags to separate effects of roots and hyphae. The sorghum plants were planted outside the mesh bags which permitted AM hyphae to enter while excluding roots. Aggregate stability of the soil was determined by wet-sieving and turbidimetric measurements. Development of the AM fungi was quantified as colonized root length and external hyphal length. Soil exposed to growth of roots and hyphae (outside mesh bags) showed aggregates with larger geometric mean diameter (GMD) in pasteurized soil inoculated with AM fungi than in pasteurized uninoculated soil. There was no significant difference in GMD of the inoculated, pasteurized soil and the unpasteurized soil. No significant effects of inoculation or plant growth were found in pasteurized soil exposed to hyphal growth only (inside the mesh bags). However, the unpasteurized soil had significantly higher GMD than the pasteurized soil, irrespective of plants and inoculum. Turbidimetric measurements of soil exposed to roots and hyphae (outside mesh bags) showed the highest aggregate stability for the inoculated pasteurized soil. These results demonstrate that AM fungi contribute to the stabilization of soil aggregates in a vertisol, and that the effect is significant after only one growing season. The effect was associated with both AM hyphae and the stimulation of root growth by AM fungi. The contribution from plant roots and AM hyphae to aggregate stability of different size fractions is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

不同丛枝菌根真菌侵染对土壤结构的影响

为了定量化比较研究接种丛枝菌根真菌后,根际、菌根际和菌丝际土壤结构的变化,采用四室分根装置,比较中性紫色土接种不同AM真菌后,菌根际、根际、菌丝际和非根际土壤平均重量直径(MWD)、几何平均直径(GMD)和大于0.25mm团聚体总量(R_0.25)的变化。结果表明:接种3个菌种后菌丝际EEG和有机质含量均呈高于菌根际的趋势。菌丝密度和易提取球囊霉素相关蛋白(EEG)与MWD、GMD和R_0.25呈显著正相关,菌根际和菌丝际土壤水稳性R_0.25与菌丝密度显著正相关,相关系数分别为0.777和0.671。接种G. mosseae的菌根际土壤R_0.25值显著高于其它分室土壤,而接种G.etunicatum的菌丝际土壤R_0.25值显著高于其它分室土壤。试验结果在一定程度上说明不同菌种对土壤结构均有不同程度的影响,反映了丛枝菌根真菌生态功能的多样性。     

Arbuscular Mycorrhizas, Microbial Communities, Nutrient Availability, and Soil Aggregates in Organic Tomato Production

Effects of arbuscular mycorrhzal (AM) fungi on plant growth and nutrition are well-known, but their effects on the wider soil biota are less clear. This is in part due to difficulties with establishing appropriate non-mycorrhizal controls in the field. Here we present results of a field experiment using a new approach to overcome this problem. A previously well-characterized mycorrhizal defective tomato mutant (rmc) and its mycorrhizal wildtype progenitor (76R MYC+) were grown at an organic fresh market tomato farm (Yolo County, CA). At the time of planting, root in-growth cores amended with different levels of N and P, were installed between experimental plants to study localized effects of mycorrhizal and non-mycorrhizal tomato roots on soil ecology. Whilst fruit yield and vegetative production of the two genotypes were very similar at harvest, there were large positive effects of colonization of roots by AM fungi on plant nutrient contents, especially P and Zn. The presence of roots colonized by AM fungi also resulted in improved aggregate stability by increasing the fraction of small macroaggregates, but only when N was added. Effects on the wider soil community including nematodes, fungal biomass as indicated by ergosterol, microbial biomass C, and phospholipid fatty acid (PLFA) profiles were less pronounced. Taken together, these data show that AM fungi provide important ecosystem functions in terms of plant nutrition and aggregate stability, but that a change in this one functional group had only a small effect on the wider soil biota. This indicates a high degree of stability in soil communities of this organic farm.     

干旱条件下AM真菌对植物生长和土壤水稳定性团聚体的影响

采用分室培养系统,模拟正常水分和干旱胁迫两种环境条件,探讨不同丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)对紫花苜蓿(Medicago sativa L.)生长和土壤水稳性团聚体的影响.试验条件下,Glomus intraradices对苜蓿根系的侵染率均显著高于Acaulospora scrobiculata和Diversispora spurcum接种处理.正常水分条件下,供试AM真菌均能显著提高植株生物量及磷浓度.干旱胁迫显著抑制了植株生长和菌根共生体发育,总体上菌根共生体对植株生长没有明显影响,接种D.spurcum甚至趋于降低植株生物量;同时,仅有G.intraradices显著提高了植株磷浓度.AM真菌主要影响到＞2mm的水稳性团聚体数量,以G.intraradices作用效果最为显著.在菌丝室中,G.intraradices显著提高了总球囊霉素含量.研究表明AM真菌对土壤大团聚体形成具有积极作用,而菌根效应因土壤水分条件和不同菌种而异,干旱胁迫下仅有G.intraradices对土壤结构和植物生长表现出显著积极作用.在应用菌根技术治理退化土壤时,需要选用抗逆性强共生效率高的菌株,对于不同AM真菌抗逆性差异的生物学与遗传学基础尚需进一步研究.     

球囊霉素相关土壤蛋白的分布及环境功能研究进展

球囊霉素相关土壤蛋白(GRSP)是由丛枝菌根真菌(AMF)在土壤中产生的一种糖蛋白,其在土壤中大量存在,可分为总球囊霉素、易提取球囊霉素、免疫反应性总球囊霉素、免疫反应性易提取球囊霉素.土地利用方式、施肥条件、AMF及宿主类型、外界环境条件等均会影响土壤中GRSP的含量及分布.GRSP能改善土壤团聚体的水稳定性、降低陆地生态系统土壤中CO₂排放、促进土壤中碳贮存、降低土壤中重金属的有效性、减弱重金属的植物毒害.GRSP的提取及定量表征技术仍是限制人们深入了解其在土壤中分布及环境功能的瓶颈.今后有关GRSP的研究应重视以蛋白及其编码该蛋白的基因为基础,阐释GRSP在土壤生态系统中的分子生物学作用及机制,以及GRSP对土壤中有机污染物环境行为的影响.     

森林植物多样性、树种重要值与土壤理化性质对球囊霉素相关土壤蛋白的影响

球囊霉素相关土壤蛋白(glomalin-related soil protein, GRSP)在土壤物理结构调节和土壤碳库稳定性中发挥着重要作用,但植物多样性和优势种如何影响GRSP还缺乏系统性研究。本研究依托东北林业大学哈尔滨实验林场的72块样地, 对1 m深土壤剖面分5层采样, 测定土壤易提取球囊霉素(easily extractable GRSP, EEG)、总提取球囊霉素(total GRSP, TG)及土壤理化性质, 并同时计算植物多样性指数及优势种重要值(importance value, IV), 进一步通过相关分析和冗余排序分析判断影响GRSP的主要因素与贡献。结果表明: (1)在整个土壤剖面上均表现为TG和EEG与土壤有机碳(SOC)正相关, 在部分土层深度与全氮(total nitrogen, TN)和含水量(moisture content, MC)正相关, 而与电导率(electrical conductivity, EC)和pH值负相关。(2)部分土层TG和EEG与黑皮油松(Pinus tabuliformis var. mukdensis)、樟子松(P. sylvestris var. mongolica)、胡桃楸(Juglans mandshurica)、黄檗(Phellodendron amurense)、榆树(Ulmus pumila)优势种重要值显著相关, 表现为黑皮油松重要值越高, 而黄檗、榆树重要值越小, 越有利于EEG的积累, 并且伴随EEG-C/SOC (EEG中C占SOC比例)增加、EEG/TG增大; 群落中胡桃楸、黄檗、榆树更有利于TG积累, 黑皮油松、落叶松(Larix gmelinii)、樟子松不利于TG的积累。(3)植物Simpson指数、Shannon-Wiener指数、物种丰富度与EEG、TG、EEG/TG无显著相关性, 而与EEG-C/SOC、EEG-N/TN (EEG中N占TN的比例)、TG-C/SOC (TG中C占SOC比例)、TG-N/TN (TG中N占TN的比例)显著负相关; 土壤EEG/TG和EEG-N/TN与植物均匀度指数显著正相关, 在1 m土壤不同土层趋势类似。(4)方差分解分析表明: 生物因子对GRSP变化的解释率是20.2%, 土壤理化因子解释率为7.8%, 而生物因子中植物优势种重要值的解释率最大(16.4%), 而植物物种多样性指数解释率仅为0.4%。冗余排序发现常绿针叶树种(黑皮油松和樟子松)越多且阔叶树种越少时, GRSP含量和GRSP对土壤碳氮的贡献越高(P < 0.01), 其机制可能与树种菌根类型有关: 外生菌根树种重要值与TG显著负相关, 丛枝菌根树种重要值与TG显著正相关。本研究解析了植物物种多样性对GRSP含量的重要影响, 并强调未来土壤管理和评估可以通过调整优势物种而不是树种多样性来促进GRSP积累。     

Effects of Common Mycorrhizal Network on Plant Carbohydrates and Soil Properties in Trifoliate Orange–White Clover Association

Common mycorrhizal network (CMN) allows nutrients and signals to pass between two or more plants. In this study, trifoliate orange (Poncirus trifoliata) and white clover (Trifolium repens) were planted in a two-compartmented rootbox, separated by a 37–μm nylon mesh and then inoculated with an arbuscular mycorrhizal fungus (AMF), Diversispora spurca. Inoculation with D. spurca resulted in formation of a CMN between trifoliate orange and white clover, whilst the best AM colonization occurred in the donor trifoliate orange–receptor white clover association. In the trifoliate orange–white clover association, the mycorrhizal colonization of receptor plant by extraradical hyphae originated from the donor plant significantly increased shoot and root fresh weight and chlorophyll concentration of the receptor plant. Enzymatic activity of soil β-glucoside hydrolase, protease, acid and neutral phosphatase, water-stable aggregate percentage at 2–4 and 0.5–1 mm size, and mean weight diameter in the rhizosphere of the receptor plant also increased. The hyphae of CMN released more easily-extractable glomalin-related soil protein and total glomalin-related soil protein into the receptor rhizosphere, which represented a significantly positive correlation with aggregate stability. AMF inoculation exhibited diverse changes in leaf and root sucrose concentration in the donor plant, and AM colonization by CMN conferred a significant increase of root glucose in the receptor plant. These results suggested that CMN formed in the trifoliate orange–white clover association, and root AM colonization by CMN promoted plant growth, root glucose accumulation, and rhizospheric soil properties in the receptor plant.     

The proliferation of fungal hyphae in soils supporting mycorrhizal and non-mycorrhizal plants

This study investigated the impact of mycorrhizal plants, non-mycorrhizal plants and soil organic matter on the relative abundance of soil hyphae perceived to belong to indigenous arbuscular mycorrhizal (AM) plants. The mycorrhizal plants corn (Zea mays L.) and barley (Hordeum vulgare L.) and a non-mycorrhizal plant, canola (Brassica napus L.), were grown in unsterilized soil in pots inoculated with mycorrhizal corn root fragments. The abundance of hyphae was measured after 5 weeks and the response of fungal growth to the addition of corn residues in the absence of plants was assessed. The abundance of hyphae was higher in the presence of the mycorrhizal plants than in the other treatments. AM hyphae present under mycorrhizal plants accounted for more than 83% of the measured hyphae. The levels of root colonization of 32% in corn and 27% in barley confirmed the mycorrhizal status of the experimental plants. Only a few points of entry were observed in canola, the non-host plant. The percentage of mycorrhizal colonization was positively related (R ²?=?0.85) to the abundance of soil hyphae, indicating that AM hyphae were the major component of the soil hyphae in the presence of mycorrhizal plants in this study.     

Effect of arbuscular mycorrhizal fungi inoculation on root traits and root volatile organic compound emissions of Sorghum bicolor

Volatile organic compounds (VOCs) emitted by plant roots have important functions that can influence the rhizospheric environment. The aim of this study was to examine the effects of arbuscular mycorrhizal (AM) fungi on the profile of root VOCs. Sorghum (Sorghum bicolor) plants were grown in pots inoculated with either Glomus mosseae or Glomus intraradices, which formed mycorrhiza with the roots. Control plants were grown in pots inoculated with sterile inoculum and did not form mycorrhiza. Forty-four VOCs were determined using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). Alkanes were the most abundant type of VOCs emitted by both mycorrhizal and non-mycorrhizal plants. Both the quantity and type of volatiles were dramatically altered by the presence of AM fungi, and these changes had species specificity. Compared with non-mycorrhizal plants, mycorrhizal plants emitted more alcohols, alkenes, ethers and acids but fewer linear-alkanes. The AM fungi also influenced the morphological traits of the host roots. The total root length and specific root length of mycorrhizal plants were significantly greater than those of non-mycorrhizal plants; however, both the incidence and length of root-hair were dramatically decreased. Our findings confirm that AM fungi can alter the profile of VOCs emitted by roots as well as the root morphology of sorghum plants, indicating that AM fungi have the potential to help plants adapt to and alter soil environments.     

Mycorrhizal fungi influence plant and soil functions and interactions

Potted soybean (Glycine max (L.) Merr.) plants were grown in P-fertilized (+P) or low-P soil (-P), or colonized in -P soil by one of the arbuscular mycorrhizal (AM) fungi Glomus etunicatum (Ge), Glomus mosseae (Gm), or Gigaspora rosea (Gr). Treatment effects on plant development, on the soil microflora, and on the status of water-stable soil aggregates (WSA) were evaluated for all 5 treatments or for the 3 AM treatments alone. Dry weights of the AM plants, as a group, were half-way between the dry weights of the +P and -P plants, but within the AM group, Gm plants had the highest pod dry weights and pod/stem and root/stem ratios and the lowest specific root lengths, while Ge plants had high stem dry weights and were highly nodulated. High reproductive development and coarse roots in the Gm plants were associated with the most extensive growth of AM soil hyphae (km pot-1: Gm, 20; Gr, 12; Ge, 8), while nodulation was inversely related with AM-colonized root length. The soils colonized by AM fungi had significantly higher levels of WSA (size classes 1 to 2 and 2 to 4 mm), and within the larger size class, Gm soils had the highest percentage of WSA. Proliferation (plate counts) of Gram positive (G+) and Gram negative (G-) bacteria, Arthrobacter sp. (G+), and Pseudomonas sp. (G-) was greatest in the -P soils, but the bacterial populations of the +P and the AM soils were generally not significantly different. There were, however, differences among the AM treatments, where Gm soils had the lowest G- bacterial populations, while Ge soils had the highest populations of both G+ and G- bacteria. Correlations between plant and soil traits indicated that interactions within the plant-soil system were mediated by the AM fungi.     

土著菌根真菌和混生植物对羊草生长和磷营养的影响

植物种间相互作用直接影响植物生长、根系可塑性及养分吸收,而与植物共生的丛枝菌根真菌可以改变植物个体和种间养分资源的分配,具有协调种间竞争的潜力.以我国北方草甸草原建群种羊草(Leymus chinensis)和混生植物紫花苜蓿(Medicago sativa)及独行菜(Lepidium spetalum)为供试植物,通过模拟盆栽试验,研究了土著菌根真菌和混生植物对羊草生长、根系形态及磷营养的影响.试验结果表明,土著菌根真菌能够与羊草及紫花苜蓿形成良好共生,而独行菜根内基本未形成菌根共生结构.土著菌根真菌显著降低了羊草及独行菜的生物量,但促进了紫花苜蓿的生长;混种紫花苜蓿显著促进了羊草的生长,而混种独行菜则显著抑制了羊草的生长.土著菌根真菌对羊草根系形态的影响表现出与植株生物量类似的趋势,但不同混生植物对羊草根系生长均无显著影响.土著菌根真菌和混生植物对羊草植株磷含量均无显著影响.与混生植物相比,羊草具有较高的比根长和磷吸收能力,这也解释了其负向菌根依赖性.研究证实了菌根真菌和植物种间相互作用均是影响草原优势植物生长和根系发育的重要因素,深入研究其交互作用对于科学管理草地生态系统,维持植物群落的稳定性和生态系统生产力具有重要意义.     

植被恢复对黄土区煤矿排土场土壤团聚体特征的影响

目前关于植被恢复对排土场土壤团聚性的影响还不清楚,以植被恢复下黄土区露天煤矿排土场为研究对象,采用湿筛法测定了排土场土壤水稳性团聚体组成,研究了植被恢复类型(草地、灌木)和排土场地形(平台、边坡)对土壤团聚体特征的影响。结果表明:植被恢复促进了排土场水稳性团聚体的形成,平台0—20 cm土层水稳性大团聚体数量(R_(0.25))、平均重量直径(MWD)和几何平均直径(GMD)分别达到31.1%,0.70 mm和0.26 mm,边坡分别达到13.3%,0.37 mm和0.17 mm,均显著高于裸地,分形维数(D)在平台和边坡分别为2.91和2.96,均显著低于裸地;平台土壤团聚性要好于边坡,草地对于平台土壤团聚结构改良效果较好,而灌木对于边坡改良效果较好;排土场土壤有机碳和粘粒含量均与土壤团聚体指标有显著相关性。植被恢复提高了排土场土壤团聚性,植被恢复类型和地形对排土场土壤团聚体特征有显著影响。     

球囊霉素相关土壤蛋白的提取条件

球囊霉素是由丛枝菌根真菌分泌的一种含金属离子的糖蛋白,因被非专一性提取而称为球囊霉素相关土壤蛋白（GRSP）。由于提取条件能影响GRSP的测定值,因此研究了柑橘园土样前期灭菌、离心力和土样质量等3个提取条件对GRSP测定值的影响。结果表明,土样前期灭菌和较高的离心力（15,000′g）均能显著影响GRSP的测定值;在土样质量0.25－1.0g范围内,GRSP的测定值随着土样质量的提高而升高;经过3次和6次的连续提取,总球囊霉素相关土壤蛋白的累积量分别达到理论最大值的66.8%和92.1%以上。研究结果为GRSP测定的标准化提供了依据。     

Changes in soil properties and resistance to concentrated flow across a 25‐year passive restoration chronosequence of grasslands on the Chinese Loess Plateau

Revegetation represents an effective measure for preventing soil erosion on the Loess Plateau. However, the effects of revegetation‐induced changes in soil and root properties on soil resistance to concentrated flow erosion (SRC) remain unclear. This study sampled soils and roots across a 25‐year chronosequence from farmland to grasslands of different ages (3, 7, 10, 18, and 25 years) to quantify variations in soil and root properties (soil bulk density, SBD; soil disintegration rate, SDR; saturated hydraulic conductivity, SHC; organic matter content, OMC; water‐stable aggregate, WSA; mean weight diameter, MWD; root mass density, RMD; root length density, RLD; and root surface area density, RSAD) and their effects on SRC. Farmland and grassland SRCs were obtained using a hydraulic flume. Soil properties and root density gradually improved with restoration time. In terms of the comprehensive soil property index calculated via principal component analysis, grassland values were 0.66 to 1.94 times greater than farmland values. Grassland SRCs increased and gradually stabilized (>18 years) over time and were 1.60 to 8.26 times greater than farmland SRC. SRC improvement was significantly related to increases in OMC, SHC, WSA, and MWD and decreases in SBD and SDR over time. SRC was effectively simulated by the Hill curve of RMD, RLD, and RSAD. SDR, SHC, and RMD (0.5–1.0 mm) affected SRC the most. This study scientifically describes how revegetation improves soil quality and soil resistance to flow erosion, and suggests that vegetations rich in 0.5–1.0 mm roots should be preferred during revegetation.     

Alteration of Soil Carbon Pools and Communities of Mycorrhizal Fungi in Chaparral Exposed to Elevated Carbon Dioxide

We examined the effects of atmospheric carbon dioxide (CO₂) enrichment on belowground carbon (C) pools and arbuscular mycorrhizal (AM) fungi in a chaparral community in southern California. Chambers enclosing intact mesocosms dominated by Adenostoma fasciculatum were exposed for 3.5 years to CO₂ levels ranging from 250 to 750 ppm. Pools of total C in bulk soil and in water-stable aggregates (WSA) increased 1.5- and threefold, respectively, between the 250- and 650-ppm treatments. In addition, the abundance of live AM hyphae and spores rose markedly over the same range of CO₂, and the community composition shifted toward dominance by the AM genera Scutellospora and Acaulospora. Net ecosystem exchange of C with the atmosphere declined with CO₂ treatment. It appears that under CO₂ enrichment, extra C was added to the soil via AM fungi. Moreover, AM fungi were predominant in WSA and may shunt C into these aggregates versus bulk soil. Alternatively, C may be retained longer within WSA than within bulk soil. We note that differences between the soil fractions may act as a potential feedback on C cycling between the soil and atmosphere.     

Mycorrhizal colonization status of plant species established in an exposed area following the 2000 eruption of Mt. Usu, Hokkaido, Japan

We investigated the ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) colonization status of plant seedlings that established in areas devastated by the eruption in March 2000 of Mt. Usu, Hokkaido, Japan. In 2005, we estimated the mycorrhizal colonization ratios and frequencies in seedlings of twelve herbaceous and seven woody plant species. Although arbuscular mycorrhizas were found to colonize Equisetum arvense and Polygonum sachalinense, they were presented at very low frequencies and colonization ratios. Other herbaceous plants exhibited higher frequencies of AM associations and either AM and/or ECM fungal associations were observed in all of the woody plant seedlings investigated. The dominant woody plant species (Populus maximowiczii, Salix sachalinensis and Salix hultenii var. angustifolia) associated mainly with ECM fungi and exhibited variable associations with AM fungi. Mycorrhizal associations were common and significant events for plant establishment, even in the early stages of the revegetation process.     

Early Root Herbivory Impairs Arbuscular Mycorrhizal Fungal Colonization and Shifts Defence Allocation in Establishing Plantago lanceolata

Research into plant-mediated indirect interactions between arbuscular mycorrhizal (AM) fungi and insect herbivores has focussed on those between plant shoots and above-ground herbivores, despite the fact that only below-ground herbivores share the same part of the host plant as AM fungi. Using Plantago lanceolata L., we aimed to characterise how early root herbivory by the vine weevil (Otiorhynchus sulcatus F.) affected subsequent colonization by AM fungi (Glomus spp.) and determine how the two affected plant growth and defensive chemistry. We exposed four week old P. lanceolata to root herbivory and AM fungi using a 2×2 factorial design (and quantified subsequent effects on plant biomass and iridoid glycosides (IGs) concentrations. Otiorhynchus sulcatus reduced root growth by c. 64%, whereas plant growth was unaffected by AM fungi. Root herbivory reduced extent of AM fungal colonization (by c. 61%). O. sulcatus did not influence overall IG concentrations, but caused qualitative shifts in root and shoot IGs, specifically increasing the proportion of the more toxic catalpol. These changes may reflect defensive allocation in the plant against further attack. This study demonstrates that very early root herbivory during plant development can shape future patterns of AM fungal colonization and influence defensive allocation in the plant.     

Effect of environmental gradient in coastal vegetation on communities of arbuscular mycorrhizal fungi associated with Ixeris repens (Asteraceae)

The community structure of arbuscular mycorrhizal (AM) fungi associated with Ixeris repens was studied in coastal vegetation near the Tottori sand dunes in Japan. I. repens produces roots from a subterranean stem growing near the soil surface which provides an opportunity to examine the effects of an environmental gradient related to distance from the sea on AM fungal communities at a regular soil depth. Based on partial sequences of the nuclear large subunit ribosomal RNA gene, AM fungi in root samples were divided into 17 phylotypes. Among these, five AM fungal phylotypes in Glomus and Diversispora were dominant near the seaward forefront of the vegetation. Redundancy analysis of the AM fungal community showed significant relationships between the distribution of phylotypes and environmental variables such as distance from the sea, water-soluble sodium in soil, and some coexisting plant species. These results suggest that environmental gradients in the coastal vegetation can be determinants of the AM fungal community.     

The differential behavior of arbuscular mycorrhizal fungi in interaction with Astragalus sinicus L. under salt stress

Three arbuscular mycorrhizal (AM) fungi (Glomus mosseae, Glomus claroideum, and Glomus intraradices) were compared for their root colonizing ability and activity in the root of Astragalus sinicus L. under salt-stressed soil conditions. Mycorrhizal formation, activity of fungal succinate dehydrogenase, and alkaline phosphatase, as well as plant biomass, were evaluated after 7 weeks of plant growth. Increasing the concentration of NaCl in soil generally decreased the dry weight of shoots and roots. Inoculation with AM fungi significantly alleviated inhibitory effect of salt stress. G. intraradices was the most efficient AM fungus compared with the other two fungi in terms of root colonization and enzyme activity. Nested PCR revealed that in root system of plants inoculated with a mix of the three AM fungi and grown under salt stress, the majority of mycorrhizal root fragments were colonized by one or two AM fungi, and some roots were colonized by all the three. Compared to inoculation alone, the frequency of G. mosseae in roots increased in the presence of the other two fungal species and highest level of NaCl, suggesting a synergistic interaction between these fungi under salt stress.     

Availability and function of arbuscular mycorrhizal and ectomycorrhizal fungi during revegetation of dewatered reservoirs left after dam removal

Revegetation following dam removal projects may depend on recovery of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal communities, which perform valuable ecosystem functions. This study assessed the availability and function of AM and EM fungi for plants colonizing dewatered reservoirs following a dam removal project on the Elwha River, Olympic Peninsula, Washington, United States. Availability was assessed via AM fungal spore density in soils and EM root tip colonization of Salix sitchensis (Sitka willow) in an observational field study. The effect of mycorrhizal fungi from 4 sources (reservoir soils, commercial inoculum, and 2 mature plant community soils) on growth and nutrient status of S. sitchensis was quantified in a greenhouse study. AM fungal spores and EM root tips were present in all field samples. In the greenhouse, plants receiving reservoir soil inoculum had only incipient mantle formation, while plants receiving inoculum from mature plant communities had fully formed EM root tips. EM formation corresponded with alleviation of phosphorus stress in plants (lower shoot nitrogen:phosphorus). Thus, revegetating plants have access to AM and EM fungi following dam removal, and EM formation may be especially important for plant P uptake in reservoir soils. However, availability of mycorrhizal fungi declines with distance from established plant communities. Furthermore, EM fungal communities in recently dewatered reservoirs may not be as effective at forming beneficial mycorrhizae as those from mature plant communities. Whole soil inoculum from mature plant communities may be important for the success of revegetating plants and recovery of mycorrhizal fungal communities.