The role of arbuscular mycorrhizal fungi and glomalin in soil aggregation: comparing effects of five plant species

Soil aggregation and soil structure are fundamental properties of natural and managed ecosystems. However, most of our knowledge on the role of plant species in soil aggregation is derived from work in agroecosystems or with agriculturally important plants. Here we examined the effects of five plant species on soil aggregate water stability. The five species (three grasses, one forb, and a legume) were from the same natural grassland, and were grown in monoculture plots in the field. Our first goal was to test if productivity-related or species-specific factors would prevail in determining soil aggregation. We also tested what the relative importance of the soil protein glomalin (produced by arbuscular mycorrhizal fungi, AMF) in soil aggregation is, compared to other factors, including AMF hyphal and root length and percent plant cover. We found significant differences in soil aggregate water stability (1–2 mm size class) for the five plant species examined, and corresponding differences in plant cover, root weight and length, AMF soil hyphal length, and glomalin concentrations. A structural equation modeling approach (path analysis) was used to distinguish direct from indirect effects of factors on soil aggregation based on covariance structures. Root length, soil glomalin, and percent cover contributed equally strong paths to water-stable aggregation. The direct effect of glomalin was much stronger than the direct effect of AMF hyphae themselves, suggesting that this protein is involved in a very important hypha-mediated mechanism of soil aggregate stabilization, at least for the 1–2-mm size class of aggregates.     

Seasonality of arbuscular mycorrhizal hyphae and glomalin in a western Montana grassland

In order to more fully understand the basic biology of arbuscular mycorrhizal fungi (AMF), and their role in natural ecosystems, it is necessary to document seasonal changes of various aspects of the life history of these fungi. Due to their unique position at the root-soil interface, AMF have been described as `keystone mutualists' in ecosystems. Despite the importance of AMF in ecosystems, few studies exist that examine the seasonality of external hyphae and their exuded products (e.g. glomalin), the AMF variables directly related to ecosystem function through their contributions to soil aggregation. This study examined seasonal dynamics of several soil variables, with a specific interest in the seasonality of external hyphae and glomalin, a glycoprotein produced by AMF, which is correlated with soil aggregate stability. Here we measured glomalin concentrations and external AMF and non-AMF hyphal length, as well as soil moisture, percent fungal root colonization (AMF and non-AMF), and root length in soil in an intermountain grassland in western Montana over one growing season (13 time points). Of the glomalin pools and hyphal lengths measured, significant seasonal changes occurred for total glomalin (TG; 24.5% change), immunoreactive easily extractable glomalin (IREEG; 53.8% change), and AM hyphal length (107% change). Prior studies on glomalin in natural systems have not considered seasonal effects. The small seasonal change in glomalin pools lends further support to the hypothesis that glomalin is relatively stable in soils, and suggests that one-time sampling may be sufficient to satisfactorily capture this response variable. However, the generality of this observation has yet to be tested in a wider range of ecosystems.     

丛枝菌根真菌产球囊霉素研究进展

球囊霉素（Glomalin）是由丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）产生的一种含金属离子的糖蛋白,由于丛枝菌根真菌在自然和人工陆生生态系统中广泛分布,丛枝菌根真菌在生态系统中的生态学功能一直是菌根生物学研究中诱人的问题。自1996年球囊霉素被发现以来,球囊霉素在土壤生态系统中的生态学功能、生态学地位日益受到重视。本文对球囊霉素作为土壤主要有机源和超级胶的功能作了简介,综述了球囊霉素的研究现状,并对其研究前景作了展望。     

Root Biomass Dynamics Under Experimental Warming and Doubled Precipitation in a Tallgrass Prairie

Human-induced climate change is expected to increase both the frequency and severity of extreme climate events, but their ecological impacts on root dynamics are poorly understood. We conducted a 1-year pulse warming and precipitation experiment in a tallgrass prairie in Oklahoma, USA to examine responses of root dynamics. We collected data in the pre-treatment year of 2002, imposed four treatments (control, 4°C warming, doubled precipitation, and warming plus doubled precipitation) in 2003, and observed post-treatment effects in 2004. Root biomass dynamics (for example, root growth and death) were measured using sequential coring and ingrowth coring methods. Treatment effects were not significant on standing root biomass in 2003, although root growth rate was significantly higher in the warmed than control plots. However, in the post-treatment year, the warmed plots had significantly lower standing root biomass than the controls, likely resulting from increased root death rate. Root death rate was significantly lower in the doubled precipitation and warmed plus doubled precipitation plots than that in the warmed plots in 2004. The root:shoot ratio showed similar responses to the post-treatments as standing root biomass, whereas aboveground biomass changed relatively little, indicating that roots were more sensitive to lagged effects than aboveground biomass. Our results demonstrate that root growth and death rates are highly sensitive to extreme climate events and lagged effects of extreme climate on root dynamics are important in assessing terrestrial carbon-cycle feedbacks to climate change.     

Spatio-temporal dynamics of arbuscular mycorrhizal fungi associated with glomalin-related soil protein and soil enzymes in different managed semiarid steppes

Temporal and spatial patterns of arbuscular mycorrhizal fungi (AMF) and glomalin and soil enzyme activities were investigated in different managed semiarid steppes located in Inner Mongolia, North China. Soils were sampled in a depth up to 30 cm from non-grazed, overgrazed, and naturally restored steppes from June to September. Roots of Leymus chinense (Trin.) Tzvel. and Stipagrandis P. Smirn. were also collected over the same period. Results showed that overgrazing significantly decreased the total mycorrhizal colonization of S. grandis; total colonization of L. chinensis roots was not significantly different in the three managed steppes. Nineteen AMF species belonging to six genera were isolated. Funneliformis and Glomus were dominant genera in all three steppes. Spore density and species richness were mainly influenced by an interaction between plant growth stage and management system (P?P?相似文献   

Does percent root length colonization and soil hyphal length reflect the extent of colonization for all AMF?

Percent root length colonization may not be an appropriate measure of root colonization by arbuscular mycorrhizal fungi (AMF) in all cases. We suggest that AMF will differ in how well percent root length colonization measures the amount of AMF colonization in the root due to differences among AMF in hyphal structure and hyphal aggregation. Although soil hyphal length accounts for hyphal density, we suggest that it does not consider differences in hyphal structure in measurements of external colonization and thus might also misrepresent the true amount of AMF in the soil. To test these suggestions, we measured and compared percent root length colonization and soil hyphal length with root ergosterol and soil ergosterol, respectively, for 21 different species of AMF from three families in a greenhouse experiment. Percent root length colonization predicted intra-radical colonization best for Glomaceae and Acaulosporaceae isolates, while soil hyphal length best represented soil ergosterol for Gigasporaceae isolates. The results show that conventional methods for estimating AMF colonization are not universal for all AMF. Caution is advised when drawing inferences for different groups of AMF.     

高寒灌丛生长季土壤转化酶与脲酶活性对增温和植物去除的响应

对青藏高原东缘窄叶鲜卑花土壤转化酶与脲酶活性对增温(0.6～1.3 ℃)和植物去除的响应进行研究,以了解气候变暖和植被干扰对高寒灌丛生长季不同时期土壤生态过程的影响.结果表明: 增温在整个生长季节使去除/不去除植物处理土壤转化酶活性显著增加了3.7%～13.3%.增温除在生长季末期对不去除植物处理土壤脲酶活性影响不显著以外,在其他时期使去除/不去除植物处理土壤脲酶活性显著增加10.8%～56.3%.去除植物处理对土壤转化酶与脲酶活性的影响因增温与生长季节而存在显著差异.去除植物显著降低了不增温样方生长季初期和末期与增温样方整个生长季节土壤转化酶活性,而没有显著影响生长季中期不增温样方土壤转化酶活性.去除植物仅在生长季末期使不增温样方土壤脲酶活性显著降低了10.5%;而在增温样方,去除植物仅在生长季初期和中期使土壤脲酶活性显著降低16.0%～18.7%.以上结果有利于全面认识高寒灌丛生态系统土壤碳氮循环过程.     

Increased temperature and precipitation interact to affect root production,mortality, and turnover in a temperate steppe: implications for ecosystem C cycling

Fine root production and turnover play important roles in regulating carbon (C) cycling in terrestrial ecosystems. In order to examine effects of climate change on root production and turnover, a field experiment with increased temperature and precipitation had been conducted in a semiarid temperate steppe in northern China since April 2005. Experimental warming decreased annual root production, mortality, and mean standing crop by 10.3%, 12.1%, 7.0%, respectively, while root turnover was not affected in 2006 and 2007 by the warming. Annual root production and turnover was 5.9% and 10.3% greater in the elevated than ambient precipitation plots. Changes in root production and mortality in response to increased temperature and precipitation could be largely attributed to the changes in gross ecosystem productivity (GEP) and belowground/aboveground C allocation. There were significant interactive effects of warming and increased precipitation on root productivity, mortality, and standing crop. Experimental warming had positive and negative effects on the three root variables (root production, mortality, standing crop) under ambient and increased precipitation, respectively. Increased precipitation stimulated and suppressed the three root variables in the unwarmed and warmed subplots, respectively. The positive dependence of soil respiration and ecosystem respiration upon root productivity and mortality highlights the important role of root dynamics in ecosystem C cycling. The nonadditive effects of increased temperature and precipitation on root productivity, mortality, and standing crop observed in this study are critical for model projections of climate–ecosystem feedbacks. These findings indicate that carbon allocation is a focal point for future research and that results from single factor experiments should be treated with caution because of factor interactions.     

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.     

Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: results from long-term field experiments

We examined the role of arbuscular mycorrhizal fungi (AMF) in ecosystems using soil aggregate stability and C and N storage as representative ecosystem processes. We utilized a wide gradient in AMF abundance, obtained through long-term (17 and 6 years) large-scale field manipulations. Burning and N-fertilization increased soil AMF hyphae, glomalin-related soil protein (GRSP) pools and water-stable macroaggregates while fungicide applications reduced AMF hyphae, GRSP and water-stable macroaggregates. We found that AMF abundance was a surprisingly dominant factor explaining the vast majority of variability in soil aggregation. This experimental field study, involving long-term diverse management practices of native multispecies prairie communities, invariably showed a close positive correlation between AMF hyphal abundance and soil aggregation, and C and N sequestration. This highly significant linear correlation suggests there are serious consequences to the loss of AMF from ecosystems.     

Mycorrhizal influence on protein and lipid of durum wheat grown at different soil phosphorus levels

 Root colonization by arbuscular mycorrhizal fungi (AMF) may affect protein and lipid composition of plants by altering P nutrition or by eliciting other metabolic responses in the host plant. This study was conducted to determine the effects of an AMF and soil P on seed protein and lipid contents and yield of two genotypes of durum wheat (Triticum durum L.). Plants were grown in a greenhouse using soil: sand mixes with different levels of P, and with or without the AMF Glomus mosseae [(Nicol. and Gerd.) Gerd. and Trappe]. Percentage AMF root colonization decreased as P added to soil increased. The wheat genotype CR057 had higher AMF root colonization but lower seed P and protein concentrations than CR006. Without added soil P, protein concentration was significantly lower and lipid concentration and seed dry weight higher in arbuscular mycorrhizal (AM) than in nonAM plants. Seed lipid and protein contents were highly correlated with P content of plants. In nonAM plants, seed lipid and protein contents were low with no added soil P and did not differ with added soil P. Seed protein/lipid (Pro/L) concentration ratios of AM plants were higher than those of nonAM plants only when no P was added to the soil. The data indicate different patterns of seed P accumulation and different relationships between seed P and protein and lipid in AM and nonAM plants. Thus, both the presence and degree of AMF root colonization affected seed lipid metabolism in these durum wheat genotypes. Accepted: 18 May 1999     

荒漠北沙柳根系丛枝菌根真菌和黑隔内生真菌定殖状况

为利用土壤共生真菌资源促进荒漠植被恢复和生态重建, 分别于2013年6月、8月和10月, 从内蒙古元上都地区采集北沙柳(Salix psammophila)根围0-10、10-20、20-30、30-40和40-50 cm共5个土层的土壤样品, 系统研究了丛枝菌根真菌(AMF)和黑隔内生真菌(DSE)的时空分布及其与土壤因子的相关性。结果表明: AMF和DSE的平均定殖率分别为77%和84%, 说明北沙柳根系能与这两类真菌形成良好的共生关系。AMF和DSE的分布和定殖具有明显的时空异质性, 并与土壤因子密切相关。AMF和DSE的平均定殖率均表现为10月> 8月> 6月。土壤深度对AMF和DSE的定殖率有显著影响, AMF和DSE定殖率的最大值分别在0-20 cm和0-10 cm土层。双因子方差分析表明, 月份和土层对AMF和DSE的定殖率以及土壤因子具有显著的交互效应。主成分分析表明, 土壤湿度、pH值、碱性磷酸酶、易提取球囊霉素是内蒙古荒漠环境中AMF和DSE定殖的主要影响因子。     

Soil mycorrhizal and nematode diversity vary in response to bioenergy crop identity and fertilization

The mandate by the Energy Independence and Security Act of 2007 to increase renewable fuel production in the USA has resulted in extensive research into the sustainability of perennial bioenergy crops such as switchgrass (Panicum virgatum) and miscanthus (Miscanthus× giganteus). Perennial grassland crops have been shown to support greater aboveground biodiversity and ecosystem function than annual crops. However, management considerations, such as what crop to plant or whether to use fertilizer, may alter belowground diversity and ecosystem functioning associated with these grasslands as well. In this study, we compared crop type (switchgrass or miscanthus) and nitrogen fertilization effects on arbuscular mycorrhizal fungal (AMF) and soil nematode abundance, activity, and diversity in a long‐term experiment. We quantified AMF root colonization, AMF extra‐radical hyphal length, soil glomalin concentrations, AMF richness and diversity, plant‐parasitic nematode abundance, and nematode family richness and diversity in each treatment. Mycorrhizal activity and diversity were higher with switchgrass than with miscanthus, leading to higher potential soil carbon contributions via increased hyphal growth and glomalin production. Plant‐parasitic nematode (PPN) abundance was 2.3 ×  higher in miscanthus plots compared to switchgrass, mostly due to increases in dagger nematodes (Xiphinema). The higher PPN abundance in miscanthus may be a consequence of lower AMF in this species, as AMF can provide protection against PPN through a variety of mechanisms. Nitrogen fertilization had minor negative effects on AMF and nematode diversity associated with these crops. Overall, we found that crop type and fertilizer application associated with perennial bioenergy cropping systems can have detectable effects on the diversity and composition of soil communities, which may have important consequences for the ecosystem services provided by these systems.     

石油污染土壤中不同人工林木根际丛枝菌根真菌与球囊霉素的研究

以陕西延长县石油污染区常见的13种人工种植林木为材料,测定了各人工种植林木根际丛枝菌根(AM)真菌发育状况、污染土壤的理化性质、土壤酶活性和球囊霉素含量,探讨AM真菌在石油污染土壤生态修复中的作用。结果表明,13种林木均能形成AM,其定殖率平均为63.2%,孢子密度平均为1.93个.g-1干土,其中受污染程度最低的柠条AM真菌定殖率和孢子密度最高,分别为91.6%和4.73个.g-1干土;毛白杨、狼牙刺和刺槐的根际土壤养分(有机碳、碱解氮、速效磷)含量相对较高;各种人工种植林木的根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性随根际土壤石油烃污染浓度的增加而明显升高,其中刺槐、狼牙刺和酸枣根际土壤的过氧化氢酶和多酚氧化酶活性都较高,同时这3种林木的球囊霉素含量也较高。因此,林木根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性可以作为石油污染的敏感指标。     

海拔梯度变化对中亚热带黄山松土壤微生物生物量和群落结构的影响

全球变暖对陆地生态系统造成一系列生态问题,使这些问题将随着全球平均气温的升高而进一步加剧。海拔梯度变化是研究气候变暖对陆地生态系统影响的一种重要手段。目前为止利用海拔梯度对微生物影响的研究尚未定论,其主要原因是忽略了植被类型的影响。因此,以中亚热带戴云山的3个海拔(1300、1450、1600 m)的黄山松(Pinus taiwanensis)林为研究对象,探究沿海拔梯度的变化,森林土壤微生物生物量和微生物群落结构的响应变化。结果表明:土壤碳氮磷养分(SOC、TN、TP)、微生物生物量氮(MBN)、微生物生物量磷(MBP)和丛枝菌根真菌(AMF)、革兰氏阴性菌(GN)、真菌(Fungi)、总磷脂脂肪酸(T_(PLFA)),细菌∶真菌(F∶B)均随海拔升高显著下降,而革兰氏阳性菌∶革兰氏阴性菌(GP∶GN)随海拔升高呈相反的趋势。冗余分析(RDA)表明,温度(T)和可溶性有机氮(DON)是影响微生物群落结构的最重要的环境因子。研究表明:与1600 m海拔相比,1300 m海拔温度较高,土壤有机质矿化作用较强,土壤速效养分及微生物生物量随之增加,从而提高(Fungi)、细菌(Bacteria)等。因此,未来气候变暖将通过改变土壤碳氮磷养分来影响本区域微生物群落组成结构。这对进一步深入了解气候变化对山地生态系统土壤养分循环过程具有重要意义。     

干旱胁迫下AM真菌对矿区土壤改良与玉米生长的影响

以神东矿区塌陷区退化土壤为供试基质,以玉米为宿主植物,研究在干旱胁迫下,丛枝菌根真菌(arbuscular mycorrhizalfungi)对玉米生长和养分吸收的影响,以及对矿区退化土壤的改良作用.结果表明:干旱胁迫下,接种AMF显著提高了玉米根系侵染率和生物量,玉米叶片相对含水量和叶色值明显高于对照组;接种组玉米地上部分磷、氮、钙和根系部分磷、钾、钙含量显著增加;接种AMF后,玉米根际土壤总球囊霉素和易提取球囊霉素含量分别增加了36.2％和33％,且根际土壤中有机质含量显著增加.由此可见,接种AMF促进了玉米对矿质养分的吸收,缓解了干旱造成的玉米生长的不利影响,提高了根际土壤中有机质含量,对矿区退化土壤改良有重要意义.     

N-P fertilization did not reduce AMF abundance or diversity but alter AMF composition in an alpine grassland infested by a root hemiparasitic plant

Fertilization has been shown to have suppressive effects on arbuscular mycorrhizal fungi (AMF) and root hemiparasites separately in numerous investigations, but its effects on AMF in the presence of root hemiparasites remain untested. In view of the contrasting nutritional effects of AMF and root hemiparasites on host plants, we tested the hypothesis that fertilization may not show strong suppressive effects on AMF when a plant community was infested by abundant hemiparasitic plants. Plants and soil samples were collected from experimental field plots in Bayanbulak Grassland, where N and P fertilizers had been applied for three continuous years for control against a spreading root hemiparasite, Pedicularis kansuensis. Shoot and root biomass of each plant functional group were determined. Root AMF colonization levels, soil spore abundance, and extraradical hyphae length density were measured for three soil depths (0-10 cm, 10-20 cm, 20-30 cm). Partial 18S rRNA gene sequencing was used to detect AMF diversity and community composition. In addition, we analyzed the relationship between relative abundance of different AMF genera and environmental factors using Spearman's correlation method. In contrast to suppressive effects reported by many previous studies, fertilization showed no significant effects on AMF root colonization or AMF species diversity in the soil. Instead, a marked increase in soil spore abundance and extraradical hyphae length density were observed. However, fertilization altered relative abundance and AMF composition in the soil. Our results support the hypothesis that fertilization does not significantly influence the abundance and diversity of AMF in a plant community infested by P. kansuensis.     

Elevated carbon dioxide and irrigation effects on water stable aggregates in a Sorghum field: a possible role for arbuscular mycorrhizal fungi

While soil biota and processes are becoming increasingly appreciated as important parameters for consideration in global change studies, the fundamental characteristic of soil structure is a neglected area of research. In a sorghum [Sorghum bicolor (L.) Moench] field experiment in which CO₂[supplied using free‐air CO₂ enrichment (FACE) technology] was crossed factorially with an irrigation treatment, soil aggregate (1–2 mm) water stability increased in response to elevated CO₂. Aggregate water stability was increased by 40% and 20% in response to CO₂, at ample and limited water supply treatments, respectively. Soil hyphal lengths of arbuscular mycorrhizal fungi (AMF) increased strongly (with a threefold increase in the dry treatment) in response to CO₂, and the concentrations of one fraction (easily extractable glomalin, EEG) of the AMF‐produced protein glomalin were also increased. Two fractions of glomalin, and AMF hyphal lengths were all positively correlated with soil aggregate water stability. The present results further support the hypothesis that AMF can become important in global change scenarios. Although in this field study a causal relationship between hyphal length, glomalin and aggregate stability cannot be demonstrated, the present data do suggest that AMF could mediate changes in soil structure under elevated CO₂. This could be of great importance in agricultural systems threatened by erosional soil loss.     

北方两省农牧交错带沙棘根围AM真菌与球囊霉素空间分布

2009年7月在内蒙古和河北两省农牧交错带沙棘(Hippophae rhamnoides L)集中分布区选取3个典型样地,分别从0-10cm、10-20cm、20-30cm、30-40cm和40-50cm土层采集沙棘根围土壤样品,研究了沙棘根围AM真菌与球囊霉素空间分布及与土壤因子的相关性。结果表明,沙棘能与AM真菌形成良好的疆南星型(Arum-type)丛枝菌根。AM真菌定殖率和孢子密度与样地生态条件密切相关。大梁底村和多伦东样地AM真菌不同结构定殖率及孢子密度无明显差别,但均显著高于黄柳条村样地,只在大梁底村发现丛枝定殖;孢子密度在3个样地均随土层加深而降低,不同结构定殖率在大梁底村随土层加深而降低,其他2个样地无明显变化规律;AM真菌最高定殖率和最大孢子密度均出现在0-30cm浅土层。根围土壤总球囊霉素(TEG)和易提取球囊霉素(EEG)含量在3个样地均随土层加深而降低。相关性分析表明,孢子密度与菌丝定殖率、泡囊定殖率和总定殖率极显著正相关。AM真菌菌丝、泡囊和总定殖率与土壤pH值、有机C、碱解N和速效P含量、脲酶和碱性磷酸酶活性极显著正相关,丛枝定殖率与土壤碱解N含量和脲酶活性显著正相关。多元线性回归方程表明,AM真菌不同定殖结构和土壤因子对TEG和EEG含量贡献不同,对于TEG:菌丝>孢子>泡囊;有机C>速效P>酸性磷酸酶>pH值,对于EEG:泡囊>孢子>菌丝;有机C>速效P。结果建议,AM真菌孢子密度、菌丝定殖程度和土壤球囊霉素含量在一定程度上能综合反应土壤AM真菌群落、有机C动态和养分循环进程,可以作为土壤质量及功能评价的新指标进一步深入研究。     

Nitrogen supply affects arbuscular mycorrhizal colonization of Artemisia vulgaris in a phosphate-polluted field site

Root colonization by arbuscular mycorrhizal fungi (AMF) was investigated in industrially polluted grassland characterized by exceptionally high phosphorus levels (up to 120 g kg(-1) soil). Along a pollution-induced nitrogen gradient, soil and tissue element concentrations of Artemisia vulgaris plants and their mycorrhizal status were determined. Additionally, we compared mycorrhization rates and above-ground biomass of A. vulgaris at N-fertilized and control plots in the N-poor area. Despite high soil and tissue P concentrations, plants from N-deficient plots, which were characterized by low tissue N concentrations and N : P ratios, were strongly colonized by AMF, whereas at a plot with comparable P levels, but higher soil and plant N concentrations and N : P ratios, mycorrhization rates were significantly lower. Correlation analyses revealed a negative relationship between percentage root colonization of A. vulgaris by AMF and both tissue N concentration and N : P ratio. Accordingly, in the fertilization experiment, control plants had higher mycorrhization rates than N-fertilized plants, whereas the species attained higher biomass at N-fertilized plots. The results suggest that N deficiency stimulates root colonization by AMF in this extraordinarily P-rich field site.