Spatial patterns of total and available N and P at alpine treeline

Background and aims

Vegetation can have direct and indirect effects on soil nutrients. To test the effects of trees on soils, we examined the patterns of soil nutrients and nutrient ratios at two spatial scales: at sites spanning the alpine tundra/subalpine forest ecotone (ecotone scale), and beneath and beyond individual tree canopies within the transitional krummholz zone (tree scale).

Methods

Soils were collected and analyzed for total carbon (C), nitrogen (N), and phosphorus (P) as well as available N and P on Niwot Ridge in the Colorado Rocky Mountains.

Results

Total C, N, and P were higher in the krummholz zone than the forest or tundra. Available P was also greatest in the krummholz zone while available N increased from the forest to the tundra. Throughout the krummholz zone, total soil nutrients and available P were higher downwind compared to upwind of trees.

Conclusions

The krummholz zone in general, and downwind of krummholz trees in particular, are zones of nutrient accumulation. This pattern indicates that the indirect effects of trees on soils are more important than the direct effects. The higher N:P ratios in the tundra suggest nutrient dynamics differ from the lower elevation sites. We propose that evaluating soil N and P simultaneously in soils may provide a robust assay of ecosystem nutrient limitation.     

Changes in N and C concentrations,soil acidity and P availability in tropical mixed acacia and eucalypt plantations on a nutrient-poor sandy soil

Background and aims

The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation.

Methods

Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees.

Results

N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand.

Conclusions

The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves.     

Soil nutrient patchiness and plant genotypes interact on the production potential and decomposition of root and shoot litter: evidence from short-term laboratory experiments with Triticum aestivum

Aims

The purpose of this study was to test the hypotheses that soil nutrient patchiness can differentially benefit the decomposition of root and shoot litters and that this facilitation depends on plant genotypes.

Methods

We grew 15 cultivars (i.e. genotypes) of winter wheat (Triticum aestivum L.) under uniform and patchy soil nutrients, and contrasted their biomass and the subsequent mass, carbon (C) and nitrogen (N) dynamics of their root and shoot litters.

Results

Under equal amounts of nutrients, patchy distribution increased root biomass and had no effects on shoot biomass and C:N ratios of roots and shoots. Roots and shoots decomposed more rapidly in patchy nutrients than in uniform nutrients, and reductions in root and shoot C:N ratios with decomposition were greater in patchy nutrients than uniform nutrients. Soil nutrient patchiness facilitated shoot decomposition more than root decomposition. The changes in C:N ratios with decomposition were correlated with initial C:N ratios of litter, regardless of roots or shoots. Litter potential yield, quality and decomposition were also affected by T. aestivum cultivars and their interactions with nutrient patchiness.

Conclusions

Soil nutrient patchiness can enhance C and N cycling and this effect depends strongly on genotypes of T. aestivum. Soil nutrient heterogeneity in plant communities also can enhance diversity in litter decomposition and associated biochemical and biological dynamics in the soil.     

Contrasting nitrogen and phosphorus dynamics across an elevational gradient for subarctic tundra heath and meadow vegetation

Aims

This study explores soil nutrient cycling processes and microbial properties for two contrasting vegetation types along an elevational gradient in subarctic tundra to improve our understanding of how temperature influences nutrient availability in an ecosystem predicted to be sensitive to global warming.

Methods

We measured total amino acid (Amino-N), mineral nitrogen (N) and phosphorus (P) concentrations, in situ net N and P mineralization, net Amino-N consumption, and microbial biomass C, N and P in both heath and meadow soils across an elevational gradient near Abisko, Sweden.

Results

For the meadow, NH₄ ⁺ concentrations and net N mineralization were highest at high elevations and microbial properties showed variable responses; these variables were largely unresponsive to elevation for the heath. Amino-N concentrations sometimes showed a tendency to increase with elevation and net Amino-N consumption was often unresponsive to elevation. Overall, PO₄-P concentrations decreased with elevation and net P immobilization mostly occurred at lower elevations; these effects were strongest for the heath.

Conclusions

Our results reveal that elevation-associated changes in temperature can have contrasting effects on the cycling of N and P in subarctic soils, and that the strength and direction of these effects depend strongly on dominant vegetation type.     

Coarse woody debris modifies surface soils of degraded temperate eucalypt woodlands

Aims

Reintroductions of coarse woody debris (CWD) to Australia’s temperate eucalypt woodlands have been proposed to address the paucity of CWD in these landscapes. This study aimed to quantify the effects of CWD on surface soils.

Methods

Values of C, N, C:N, P, NO₃ ^?, NH₄ ⁺, pH and electrical conductivity (EC) were measured adjacent to, and at reference distances from CWD. Soils were measured at depths of 0–1 cm, 1–3 cm and 3–5 cm for 12 individual CWD samples of varying decay classes and diameters. A linear mixed model was used to test the effects of the presence of CWD, soil depth and CWD decay class and diameter.

Results

Significantly larger values for C, N, C:N, P, NO₃ ^?, EC, and significantly smaller values for pH were found adjacent to CWD. The greatest impact of CWD was on the upper most surface soil. CWD decay class and diameter had little influence on the measured soil characteristics.

Conclusion

This is the first quantitative determination of the effects of eucalypt CWD on woodland soils in Australia. The effect of added CWD is rapid, occurring after just 2 years. The results suggest that the effects are due to the structural properties of CWD.     

Biocrusts control the nitrogen dynamics and microbial functional diversity of semi-arid soils in response to nutrient additions

Aims

Human activities are causing imbalances in the nutrient cycles in natural ecosystems. However, we have limited knowledge of how these changes will affect the soil microbial functional diversity and the nitrogen (N) cycle in drylands, the biggest biome on Earth. Communities dominated by lichens, mosses and cyanobacteria (biocrusts) influence multiple processes from the N cycle such as N fixation and mineralization rates. We evaluated how biocrusts modulate the effects of different N, carbon (C) and phosphorus (P) additions on theN availability, the dominance of different available N forms and the microbial functional diversity in dryland soils.

Methods

Soil samples from bare ground (BG) and biocrust-dominated areas were gathered from the center of Spain and incubated during seven or 21 days under different combinations of N, C and P additions (N, C, P, N?+?C, N?+?P, P?+?C, and C?+?N?+?P).

Results

The relative dominance of dissolved organic N (DON) and the microbial functional diversity were higher in biocrust than in BG microsites when C or P were added. Changes in the C to N ratio, more than N availability, seem to modulate N transformation processes in the soils studied. In general, biocrusts increased the resilience to N impacts (N, C?+?N, N?+?P, C?+?N?+?P) of the total available N, ammonium, nitrate and DON when C was present.

Conclusions

Our results suggest that biocrusts may buffer the effects of changes in nutrient ratios on microbial functional diversity and DON dominance in dryland soils. Thus, these organisms may have an important role in increasing the resilience of the N cycle to imbalances in C, N and P derived from human activities.     

Fragmentation modulates the strong impact of habitat quality and plant cover on fertility and microbial activity of semiarid gypsum soils

Background and aims

Plant-soil interactions are a crucial component of ecosystem functioning. However, most global change studies focus on plant communities, with information on soil properties and performance being scarce. Our goal was to assess the individual and joint effect of habitat heterogeneity and three global change drivers (fragmentation, loss of habitat quality and climate change) on nutrient availability and soil microbial activity in Mediterranean gypsum soils.

Methods

We collected soil samples from an experimental field site from large/small fragments, with high/low habitat quality, subjected to two levels of water availability (dry/mesic) and from two microhabitats (under the canopy of shrubs and in the open). We analyzed nutrient concentrations (C, N and P) and enzymatic activities (?-glucosidase, urease and acid phosphatase).

Results

C, N, P content, ?-glucosidase, urease and acid phosphatase activities were higher under the canopy than in the open and in high- than in poor- habitat quality sites. These differences were exacerbated in small fragments.

Conclusions

The strong interdependence between plant and soil was modulated by fragmentation in the Mediterranean gypsum soils studied. Drought did not exert a direct negative effect on soil properties, although the effect might arise under more intense drought or under drought taking place at times of the year different from those explored here. Results highlight the importance of considering several drivers simultaneously to forecast realistic ecosystem responses to global change.     

Evidence for progressive phosphorus limitation over long-term ecosystem development: Examination of a biogeochemical paradigm

Aims

To test predictions of ecosystem theory for changes in P cycling over primary succession, we determined soil phosphorus (P) in labile, primary mineral, organic, and occluded forms along a chronosequence of five wave cut terraces known as the “Ecological Staircase”. The Ecological Staircase terraces (T1-T5) transition naturally from fertile native coastal forests in California, USA, to diminutive pygmy vegetation over the span of?>?500,000 years of pedogenesis.

Methods

Soil P fractions were quantified to a depth of 40 cm on T1-T5 using a modified Hedley P fractionation procedure.

Results

Overall results confirmed the Walker and Syers Model of Phosphorus Transformations During Pedogenesis: total P declined from youngest (194 mg/kg P) to oldest (127 mg/kg P) sites; primary-mineral P decreased sharply from T1 to older sites; and occluded P dominated P pools at the oldest pygmy sites (T3-T5). In addition, foliar P concentrations declined markedly in the pygmy forest, and N/P of vegetation (T1: 6.03, T5: 14.4) and N/P_organic of mineral soils (T1: 6.10, T5: 25.3) increased significantly over time.

Conclusions

Results point to P as the primary limiting nutrient in the pygmy forest, exemplifying the terminal steady-state of ecosystem retrogression that underlies the persistence of this unique ecosystem.     

Increased availability of phosphorus after drying and rewetting of a grassland soil: processes and plant use

Aims

Drying and rewetting (DRW) often increases soil phosphorus (P) availability. Our aims were to elucidate underlying processes and assess potential plant uptake of released P.

Methods

Using a grassland soil with low available and high microbial P as a model, we studied the contributions of microbial and physicochemical processes to P release by determining DRW effects on i) C:P ratios of nutrient pulses in fresh and sterilized soils, ii) aggregate stability and iii) P forms released upon soil dispersion. Use of the P pulse by maize was examined in a bioassay and a split-root experiment.

Results

The strong P pulse after DRW was larger than that observed for C. Experiments with sterilized soil pointed to a non-microbial contribution to the pulse for P, but not for C. Aggregate disruption after DRW occurred due to slaking, and this released molybdate-reactive and -unreactive P. Maize benefitted from the P pulse only in the bioassay, i.e. when planted after the DRW cycle.

Conclusions

The majority of C and P released upon DRW originated from the microbial biomass, but for P release, physicochemical processes were also important. In the field, the released P would only be available to drought-resistant plants.     

Amending soils of different texture with six compost types: impact on soil nutrient availability, plant growth and nutrient uptake

Background

Composts with different feedstocks may have differential effects on soil properties and plant growth which, may be further modulated by soil texture.

Materials and methods

In a 77-day pot experiment in the glasshouse, we investigated the effect of a single application as mulch of six types of composts derived from different starting feedstocks in two soils (13% and 46% clay, referred to as S13 and S46) on soil physical, chemical and biological properties, plant growth and nutrient uptake. Composts were placed as 2.5?cm thick mulch layer on the soil surface and wheat plants were grown and harvested at 42?days and at 77?days (grain filling).

Results

Composts differed in total and available N and P and particle size with C1, C3, C4 and C5 being fine-textured, whereas C2 and C6 were coarse-textured. Compost addition as mulch increased soil total organic C and EC, but had no effect on pH. In all treatments, cumulative soil respiration was higher in S13 than in S46 and was increased by compost addition with the greatest increase with C2 and C6. Compared to the unamended soil, most compost mulches (except C2) increased macroaggregate stability. Compost mulches significantly increased available P and N in both soils, except for C2. Compost mulches increased available N up to 6-fold in both soils with the strongest increase by C5. Most composts also increased wheat growth and shoot P and N concentrations with the greatest effect on plant N concentration by C5 and on plant P concentration by C4. However, C2 decreased shoot N and P concentrations compared to the unamended soil. Most compost mulches (except C2) increased mycorrhizal colonization by up to 50% compared to the unamended soil.

Conclusions

Fine-textured compost mulches generally had a greater effect on soil properties and plant growth than coarse-textured composts. Despite distinct differences between the soils with respect to clay content, TOC and available P, the effect of the compost mulches on soil and plant properties was quite similar.     

Edaphic influences of ophiolitic substrates on vegetation in the Western Italian Alps

Background and aims

Soils derived from serpentinite (serpentine soils) often have low macronutrient concentrations, exceedingly low Ca:Mg molar ratios and high heavy metal concentrations, typically resulting in sparse vegetative cover. This combined suite of edaphic stresses is referred to as the “serpentine syndrome.” Although several plant community-level studies have been conducted to identify the most important edaphic factor limiting plant growth on serpentine, the primary factor identified has often varied by plant community and local climate. Few studies to date have been conducted in serpentine plant communities of alpine or boreal climates. The goal of our study was to determine the primary limiting edaphic factors on plant community species composition and productivity (cover) in the alpine and boreal climate of the Western Alps, Italy.

Methods

Soil properties and vegetation composition were analyzed for several sites underlain by serpentinite, gabbro, and calc-schist substrates and correlated using direct and indirect statistical methods.

Results

Boreal forest soils were well-developed and tended to have low pH throughout the soil profile resulting in high Ni availability. Alpine soils, in comparison, were less developed. The distinct serpentine plant communities of the Western Alps are most strongly correlated with high levels of bioavailable Ni associated with low soil pH. Other factors such as macronutrient deficiency, low Ca:Mg molar ratio and drought appear to be less important.

Conclusions

The strong ecological influence of Ni is caused by environmental conditions which increase metal mobilization.     

Coupled soil-availability and tree-limitation nutritional shifts induced by N deposition: insights from N to P relationships in Abies pinsapo forests

Background and aims

Interacting effects of atmospheric N deposition on the degree to which tree demand for other nutrients is met by soil supply has seldom been explored in Mediterranean-type ecosystems. We hypothesized that patterns for the relative availability of N and P in soils will be matched by variations in process rates related to soil organic P cycling and by shifts from N to P limitation of tree growth.

Methods

We examined N/P relationships in Mediterranean-fir (Abies pinsapo) forests from two nearby regions differing in N deposition levels.

Results

N pools and transformation rates and the contribution of organic fractions to the labile P pool in soils showed increasing trends toward the pollution source. Phosphomonoesterase activity (PME) in bulk soils, root PME per unit biomass (but not per unit soil volume) and biomass accumulation in P-fertilized root-in-growth cores incubated in situ were also the highest at the sites receiving elevated N deposition, indicating P limitation. In contrast, forest stands in the region farther from the pollutant source were N-limited (preferential root growth in N-rich soil microsites) and showed lower PME activities and higher total fine root biomass.

Conclusions

In the forests under elevated N deposition, higher values for an overall indicator of soil N status matched with indications of an accelerated soil organic P subcycle and P-limitation of tree growth.     

Increasing phosphorus limitation along three successional forests in southern China

Background and Aims

Phosphorus (P) is commonly one of most limiting nutrients in tropical and subtropical forests, but whether P limitation would be exacerbated during forest succession remains unclear.

Methods

Soil phosphatase activity is often used as an indicator of P limitation. Here we examined soil acid phosphatase activity (APA) underneath tree species in pine forest (PF), mixed pine and broadleaf forest (MF) and monsoon evergreen broadleaf forest (MEBF) which represented the early, middle and late successional stages of subtropical forests in China, respectively. We also analyzed other indicators of P status (soil available P and N and P stoichiometry of the tree species).

Results

APA or APA per unit soil organic carbon under tree species was relatively low in the early successional forest. Different from PF and MF, soil available P beneath the tree species was lower than in the bulk soils in MEBF. Soil APA was closely related to N:P ratios of tree species across all three forests.

Conclusions

Our results imply that P limitation increases during forest succession at our site. The dominant tree species with low soil APAs in MEBF are likely more P-limited than other tree species.     

Occurrence and intensity of wild boar disturbances, effects on the physical and chemical soil properties of alpine grasslands

Background and aims

Physical and chemical soil properties determine local plant conditions and resources, affecting plants’ ability to respond to disturbances. In alpine grasslands, wild boar disturbances occur at different intensities, what may affect differently their soil properties. Alpine soils from five contrasted plant communities were explored within and outside disturbances, accounting for an overall and community scale effect. Additionally, we analysed the effect of disturbance intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Methods

Soils were analyzed for physical (bulk density, moisture content and electrical conductivity), and chemical properties (pH, total N and C, oxidizable C, C:N ratio, available K, P, Ca²⁺, Na⁺ and Mg²⁺). Resin bags were used to compare the effect of the disturbance occurrence and intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Results

Bulk density, total N and NO₃ ^--N concentration were significantly higher in disturbed areas, while soil moisture, C:N, NH₄ ⁺-N, Na⁺, Mg²⁺ and Ca²⁺ concentrations were significantly lower. However, low disturbance intensity reduced NO₃ ^--N and increased NH₄ ⁺-N concentrations.

Conclusions

Wild boar occurrence and intensity strongly alter physical and chemical conditions of alpine soils, increasing soil compaction, and altering the availability of N forms. These changes may affect most plant species, thus affecting the structure and dynamics of alpine plant communities.     

Comparative analysis of basidiomycetous laccase genes in forest soils reveals differences at the cDNA and DNA levels

Aims

This study was undertaken to investigate laccase-containing basidiomycete communities at the cDNA and DNA levels and to assess the influences of vegetation and soil types on the basidiomycete communities in forest soils.

Materials and methods

Soil samples were collected from the upper soil layers of two typical subtropical forests (a broad-leaved forest developed in Karst limestone soil and an artificial coniferous forest with Pinus massoniana in red soil) in China. The basidiomycete communities were characterized by cloning and sequencing of the laccase genes at both the cDNA and DNA levels. Compositions of lignin monomers were determined by gas chromatography–mass spectrometry.

Results

Most of the laccase genes obtained in this study were new, highlighting the research gap of this functional group. The trends of the basidiomycetous laccase gene diversity among the upper soil layers of the two forests were consistent between the cDNA and DNA levels. The Agaricales had high activity because they dominated all the tested soils. However, the total basidiomycete communities reflected at the cDNA and DNA levels were significantly different due to the presence of some quiescent basidiomycetous groups. Almost all of the lignin components were decomposed from the O to the A layers in the two forests, and laccases produced by Agaricales were likely responsible for the decomposition of guaiacyl monomers. Both vegetation and soil types had great influences on the active laccase-containing basidiomycete communities, primarily via the pH, C/N, and the contents of lignin monomers.

Conclusions

The cDNA- and DNA-level approaches presented good consistency of diversities but different compositions of laccase-containing basidiomycete communities, thus emphasizing the importance of focusing on laccase genes at the cDNA level in future studies. It is the quality but not the quantity of SOM to determine the diversity and composition of the active laccase-containing basidiomycete communities.     

A closeup study of early beech litter decomposition: potential drivers and microbial interactions on a changing substrate

Aims

Litter decomposition and subsequent nutrient release play a major role in forest carbon and nutrient cycling. To elucidate how soluble or bulk nutrient ratios affect the decomposition process of beech (Fagus sylvatica L.) litter, we conducted a microcosm experiment over an 8 week period. Specifically, we investigated leaf-litter from four Austrian forested sites, which varied in elemental composition (C:N:P ratio). Our aim was to gain a mechanistic understanding of early decomposition processes and to determine microbial community changes.

Methods

We measured initial litter chemistry, microbial activity in terms of respiration (CO₂), litter mass loss, microbial biomass C and N (C_mic and N_mic), non purgeable organic carbon (NPOC), total dissolved nitrogen (TDN), NH₄ ⁺, NO₃ ^- and microbial community composition (phospholipid fatty acids – PLFAs).

Results

At the beginning of the experiment microbial biomass increased and pools of inorganic nitrogen (N) decreased, followed by an increase in fungal PLFAs. Sites higher in NPOC:TDN (C:N of non purgeable organic C and total dissolved N), K and Mn showed higher respiration.

Conclusions

The C:N ratio of the dissolved pool, rather than the quantity of N, was the major driver of decomposition rates. We saw dynamic changes in the microbial community from the beginning through the termination of the experiment.     

Plant and nutrient controls on microbial functional characteristics in a tropical Oxisol

Aims

Extracellular enzymes mediate the decomposition of organic matter and the release of plant-available nutrients. Current theory predicts that enzyme production by soil microbes is regulated by the stoichiometric demands of microbial biomass and the complexity of environmental resources, but most experiments ignore the potential effect of alleviated carbon limitation in the rhizosphere. Our objective was to investigate linkages between enzyme activities, soil nutrient availability and plant roots in a tropical Oxisol.

Methods

We conducted a greenhouse experiment using soils from the Luquillo Experimental Forest and seedlings of Tabebuia heterophylla. Planted and unplanted pots were fertilized with different combinations of phosphorus and either mineral nitrogen (ammonia chloride) or a nitrogen-rich organic compound (casein). We measured changes in plant and soil nutrients and five extracellular enzyme activities.

Results

Phosphatase activity declined by 28% in the P and 40% in the complex nitrogen treatment, while N-acetyl glucosaminidase increased 162% in the complex nitrogen treatment. Beta-glucosidase, beta-xylosidase, cellobiohydrolase and N-acetyl glucosaminidase all increased significantly over time in the simple nitrogen treatment (P?<?0.05).

Conclusions

Enzymatic responses support microbial resource allocation theory, that is, the concept that soil microbes regulate enzyme production based on scarcity of resources. However, we did not observe any additional effect of roots on extracellular enzyme activities. Enzymatic C:N, C:P and N:P ratios further support the notion that shifts in microbial stoichiometric demand drive responses to nutrients.     

Positive feedbacks between decomposition and soil nitrogen availability along fertility gradients

Background and aims

We determined the relationship between site N supply and decomposition rates with respect to controls exerted by environment, litter chemistry, and fungal colonization.

Methods

Two reciprocal transplant decomposition experiments were established, one in each of two long-term experiments in oak woodlands in Minnesota, USA: a fire frequency/vegetation gradient, along which soil N availability varies markedly, and a long-term N fertilization experiment. Both experiments used native Quercus ellipsoidalis E.J. Hill and Andropogon gerardii Vitman leaf litter and either root litter or wooden dowels.

Results

Leaf litter decay rates generally increased with soil N availability in both experiments while belowground litter decayed more slowly with increasing soil N. Litter chemistry differed among litter types, and these differences had significant effects on belowground (but not aboveground) decay rates and on aboveground litter N dynamics during decomposition. Fungal colonization of detritus was positively correlated with soil fertility and decay rates.

Conclusions

Higher soil fertility associated with low fire frequency was associated with greater leaf litter production, higher rates of fungal colonization of detritus, more rapid leaf litter decomposition rates, and greater N release in the root litter, all of which likely enhance soil fertility. During decomposition, both greater mass loss and litter N release provide mechanisms through which the plant and decomposer communities provide positive feedbacks to soil fertility as ultimately driven by decreasing fire frequency in N-limited soils and vice versa.     

Fertilization and forb:graminoid ratio affect arbuscular mycorrhiza in seedlings but not adult plants of Plantago lanceolata

Aims

Nutrients play a key role in arbuscular mycorrhizal (AM) symbiosis. We quantified the response of AM symbiosis of seedlings and adult plants of Plantago lanceolata to fertilization under field conditions in managed grasslands differing in nutrient availability and soil moisture.

Methods

The AM symbiosis was measured as the total extent of AM fungal colonization and frequency of arbuscules or vesicles, and as the relative proportions of morphotypes. We further examined the effects of the surrounding vegetation upon AM symbiosis.

Results

Fertilization decreased total AM colonization and relative arbuscular frequency of the whole mycorrhizal community and of Acaulospora and “fine endophyte” morphotypes in seedling roots, but it had no effect upon the mycorrhiza in adult plants. The decline in arbuscular frequency in seedling roots due to fertilization was greater at the sites with higher nutrient availability and lower N:P ratio. Seedlings surrounded by more forbs had a greater total AM colonization and higher vesicular frequency.

Conclusions

Increased nutrient availability in the initial stages of seedling development has a prominent effect upon AM symbiosis development, but these effects seem to diminish over the long term, as evidenced by the results obtained for adult plants and from the limited effects of parameters characterizing long-term nutrient availability.