Consequences of inoculation with native arbuscular mycorrhizal fungi for root colonization and survival of <Emphasis Type="Italic">Artemisia tridentata</Emphasis> ssp. <Emphasis Type="Italic">wyomingensis</Emphasis> seedlings after transplanting

In arid environments, the propagule density of arbuscular mycorrhizal fungi (AMF) may limit the extent of the plant–AMF symbiosis. Inoculation of seedlings with AMF could alleviate this problem, but the success of this practice largely depends on the ability of the inoculum to multiply and colonize the growing root system after transplanting. These phenomena were investigated in Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) seedlings inoculated with native AMF. Seedlings were first grown in a greenhouse in soil without AMF (non-inoculated seedlings) or with AMF (inoculated seedlings). In spring and fall, 3-month-old seedlings were transplanted outdoors to 24-L pots containing soil from a sagebrush habitat (spring and fall mesocosm experiments) or to a recently burned sagebrush habitat (spring and fall field experiments). Five or 8 months after transplanting, colonization was about twofold higher in inoculated than non-inoculated seedlings, except for the spring field experiment. In the mesocosm experiments, inoculation increased survival during the summer by 24 % (p?=?0.011). In the field experiments, increased AMF colonization was associated with increases in survival during cold and dry periods; 1 year after transplanting, survival of inoculated seedlings was 27 % higher than that of non-inoculated ones (p?<?0.001). To investigate possible mechanisms by which AMF increased survival, we analyzed water use efficiency (WUE) based on foliar ¹³C/¹²C isotope ratios (δ ¹³C). A positive correlation between AMF colonization and δ ¹³C values was observed in the spring mesocosm experiment. In contrast, inoculation did not affect the δ ¹³C values of fall transplanted seedlings that were collected the subsequent spring. The effectiveness of AMF inoculation on enhancing colonization and reducing seedling mortality varied among the different experiments, but average effects were estimated by meta-analyses. Several months after transplanting, average AMF colonization was in proportion 84 % higher in inoculated than non-inoculated seedlings (p?=?0.0042), while the average risk of seedling mortality was 42 % lower in inoculated than non-inoculated seedlings (p?=?0.047). These results indicate that inoculation can increase AMF colonization over the background levels occurring in the soil, leading to higher rates of survival.     

Life-history strategies of arbuscular mycorrhizal fungi determine succession into roots of Rosmarinus officinalis L., a characteristic woody perennial plant species from Mediterranean ecosystems

Aim

Few studies have analyzed life-history strategies of arbuscular mycorrhizal fungi (AMF), in terms of the different propagule types they produce, and their ability to colonize new seedlings. The aim was to assess whether life-history strategies influence AMF successional dynamics and assemblages.

Methods

Rosemary (Rosmarinus officinalis L.) seedlings, grown in a mesocosm system, were colonized by either the AMF hyphae coming from a living rosemary plant, or from spores germinating in soil. The AMF community established in the plantlets was monitored every 3 months during 2 years, using terminal restriction fragment length polymorphism of genes coding for rDNA.

Results

The two different sources of AMF propagules resulted in a different initial community colonizing rosemary roots. AMF propagating from hyphae attached to living mycorrhizal-roots seemed to colonize faster and were season-dependent. AMF taxa originating from soil-borne propagules were most frequent over time and exhibit the dominant colonization strategy in this system. The evolution of the AMF community also revealed different strategies in succession.

Conclusions

AMF associated with rosemary evidenced contrasting life-history strategies in terms of source of inoculum for new colonization and hence survival. The observed successional dynamics of AMF have implications for understanding the ecological processes in Mediterranean environments and seasonality of colonization processes.     

Effects of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia spec.) on soil chemical properties in a mixed deciduous forest

Background and aims

We investigated the genetic diversity of arbuscular mycorrhizal fungi (AMF) in soils and the roots of Phalaris aquatica L., Trifolium subterraneum L., and Hordeum leporinum Link growing in limed and unlimed soil, the influence of lime application on AMF colonization and the relationship between AMF diversity and soil chemical properties.

Methods

The sampling was conducted on a long-term liming experimental site, established in 1992, in which lime was applied every 6 years to maintain soil pH (in CaCl₂) at 5.5 in the 0–10 cm soil depth. Polymerase chain reaction, cloning and sequencing techniques were used to investigate the diversity of AMF.

Results

Altogether, 438 AMF sequences from a total of 480 clones were obtained. Sequences of phylotypes Aca/Scu were detected exclusively in soil, while Glomus sp. (GlGr Ab) and an uncultured Glomus (UnGlGr A) were detected only in plant roots. Glomus mosseae (GlGr Aa) was the dominant AMF in the pastures examined; however, the proportion of G. mosseae was negatively correlated with soil pH, exchangeable Ca and available P. Generally, diversity of the AMF phylotypes was greater in the bulk unlimed soil and plants from this treatment when compared to the limed treatments.

Conclusions

Long-term lime application changed soil nutrient availability and increased AMF colonization, but decreased AMF phylotype diversity, implying that soil chemistry may determine the distribution of AMF in acid soils. Future studies are required to explore the functions of these AMF groups and select the most efficient AMF for sustainable farming in acid soils.     

Chemistry and Microbial Functional Diversity Differences in Biofuel Crop and Grassland Soils in Multiple Geographies

We obtained soil samples from geographically diverse switchgrass (Panicum virgatum L.) and sorghum (Sorghum bicolor L.) crop sites and from nearby reference grasslands and compared their edaphic properties, microbial gene diversity and abundance, and active microbial biomass content. We hypothesized that soils under switchgrass, a perennial, would be more similar to reference grassland soils than sorghum, an annual crop. Sorghum crop soils had significantly higher NO₃ ^? -N, NH₄ ⁺ -N, SO₄ ^2? -S, and Cu levels than grassland soils. In contrast, few significant differences in soil chemistry were observed between switchgrass crop and grassland soils. Active bacterial biomass was significantly lower in sorghum soils than switchgrass soils. Using GeoChip 4.0 functional gene arrays, we observed that microbial gene diversity was significantly lower in sorghum soils than grassland soils. Gene diversity at sorghum locations was negatively correlated with NO₃ ^? -N, NH₄ ⁺ -N, and SO₄ ^2? -S in C and N cycling microbial gene categories. Microbial gene diversity at switchgrass sites varied among geographic locations, but crop and grassland sites tended to be similar. Microbial gene abundance did not differ between sorghum crop and grassland soils, but was generally lower in switchgrass crop soils compared to grassland soils. Our results suggest that switchgrass has fewer adverse impacts on microbial soil ecosystem services than cultivation of an annual biofuel crop such as sorghum. Multi-year, multi-disciplinary regional studies comparing these and additional annual and perennial biofuel crop and grassland soils are recommended to help define sustainable crop production and soil ecosystem service practices.     

Plant-soil feedbacks between invasive shrubs and native forest understory species lead to shifts in the abundance of mycorrhizal fungi

Aims

Non-native shrubs are important invaders of the Eastern Deciduous Forest, dramatically altering forest structure and functioning. Study of invasion mechanisms in this system has emphasized aboveground processes, and plant-soil feedbacks are relatively unexplored as a mechanism of shrub dominance. We tested whether plant-soil feedback in this habitat is affected by competition and whether arbuscular mycorrhizal fungi (AMF) are involved in plant-soil feedback.

Methods

We used a standard two-phase plant-soil feedback experiment run concurrently for each of three invasive shrub species, measuring feedback effects on AMF colonization, aboveground biomass, and the responses of native plant species in greenhouse mesocosms.

Results

Lonicera maackii and Ligustrum vulgare reduced AMF colonization of native roots, both with legacy effects (prior growth in soil) and direct effects (current growth in soil). Elaeagnus umbellata grown with natives left a legacy of increased AMF colonization of native communities.

Conclusions

Our results suggest that woody invasive species can alter the AMF associations of native plants even after the invasive is no longer present. Such consequences merit study with other native species and where environmental factors, such as light availability, might be expected to compound the effects of changes in AMF.     

The relationship between the diversity of arbuscular mycorrhizal fungi and grazing in a meadow steppe

Aims

To study the relationship between changes in soil properties and plant community characters produced by grazing in a meadow steppe grassland and the composition and diversity of spore-producing arbuscular mycorrhizal fungi (AMF).

Methods

A field survey was carried out in a meadow steppe area with a gradient of grazing pressures (a site with four grazing intensities and a reserve closed to grazing). The AMF community composition (characterized by spore abundance) and diversity, the vegetation characters and soil properties were measured, and root colonization by AMF was assessed.

Results

AMF diversity (richness and evenness) was higher under light to moderate grazing pressure and declined under intense grazing pressures. Results of multiple regressions indicated that soil electrical conductivity was highly associated with AMF diversity. The variation in AMF diversity was partially associated to the density of tillers of the dominant grass (Leymus chinensis), the above and below-ground biomass and the richness of the plant community.

Conclusions

We propose that the relationship between plants and AMF is altered by environmental stress (salinity) which is in turn influenced by animal grazing. Direct and indirect interactions between vegetation, soil properties, and AMF community need to be elucidated to improve our ability to manage these communities.     

Signal effects of the lectin from the associative nitrogen-fixing bacterium Azospirillum brasilense Sp7 in bacterial–plant root interactions

Aims

We compared the degree of arbuscular mycorrhizal fungi (AMF) colonization on an invasive, Triadica sebifera, and two native, Baccharis halimifolia and Morella cerifera, woody species that occur in coastal Mississippi, USA. Specifically, we investigated how the degree of colonization affects growth of these species and assessed potential allelopathic effects of T. sebifera on the two native species.

Methods

A field study and a greenhouse experiment were used to determine the degree of AMF colonization on focal woody species. Seedling growth of these species was compared between active (fungicide untreated) and AMF-suppressed (fungicide treated) soils in the greenhouse experiment. In a second greenhouse experiment, we tested the potential allelopathic effects of T. sebifera on the native species by growing the natives in soils from T. sebifera invaded or uninvaded regions, with and without activated carbon (AC).

Results

The invasive species, Triadica sebifera, exhibited a higher degree of AMF colonization compared to the native species and significantly higher total biomass in active soils compared to AMF-suppressed soils. Seedling biomass and AMF colonization of native B. halimifolia and M. cerifera did not differ between T. sebifera invaded and uninvaded soils, irrespective of the application of AC.

Conclusions

Results suggest that invasive T. sebifera benefits from the presence of AMF, which might facilitate establishment of this invader. Results also suggest that allelopathy is not a likely mechanism of T. sebifera invasion in coastal transition ecosystems. A higher degree of AMF colonization, relative to native co-occurring species, may partly explain the successful invasion of T. sebifera into coastal plant communities of the southeastern USA.     

Forest fire may disrupt plant–microbial feedbacks

Plant–microbial feedbacks are important drivers of plant community structure and dynamics. These feedbacks are driven by the variable modification of soil microbial communities by different plant species. However, other factors besides plant species can influence soil communities and potentially interact with plant–microbial feedbacks. We tested for plant–microbial feedbacks in two Eucalyptus species, E. globulus and E. obliqua, and the influence of forest fire on these feedbacks. We collected soils from beneath mature trees of both species within native forest stands on the Forestier Peninsula, Tasmania, Australia, that had or had not been burnt by a recent forest fire. These soils were subsequently used to inoculate seedlings of both species in a glasshouse experiment. We hypothesized that (i) eucalypt seedlings would respond differently to inoculation with conspecific versus heterospecific soils (i.e., exhibit plant–microbial feedbacks) and (ii) these feedbacks would be removed by forest fire. For each species, linear mixed effects models tested for differences in seedling survival and biomass in response to inoculation with conspecific versus heterospecific soils that had been collected from either unburnt or burnt stands. Eucalyptus globulus displayed a response consistent with a positive plant–microbial feedback, where seedlings performed better when inoculated with conspecific versus heterospecific soils. However, this effect was only present when seedlings were inoculated with unburnt soils, suggesting that fire removed the positive effect of E. globulus inoculum. These findings show that external environmental factors can interact with plant–microbial feedbacks, with possible implications for plant community structure and dynamics.     

Soil moisture effects on gross nitrification differ between adjacent grassland and forested soils in central Alberta, Canada

Background and aims

Changes in soil moisture availability seasonally and as a result of climatic variability would influence soil nitrogen (N) cycling in different land use systems. This study aimed to understand mechanisms of soil moisture availability on gross N transformation rates.

Methods

A laboratory incubation experiment was conducted to evaluate the effects of soil moisture content (65 vs. 100% water holding capacity, WHC) on gross N transformation rates using the ¹⁵N tracing technique (calculated by the numerical model FLUAZ) in adjacent grassland and forest soils in central Alberta, Canada.

Results

Gross N mineralization and gross NH ₄ ⁺ immobilization rates were not influenced by soil moisture content for both soils. Gross nitrification rates were greater at 100 than at 65% WHC only in the forest soil. Denitrification rates during the 9 days of incubation were 2.47 and 4.91 mg N kg^-1 soil d^-1 in the grassland and forest soils, respectively, at 100% WHC, but were not different from zero at 65% WHC. In the forest soil, both the ratio of gross nitrification to gross NH ₄ ⁺ immobilization rates (N/IA) and cumulative N₂O emission were lower in the 65 than in the 100% WHC treatment, while in the grassland soil, the N/IA ratio was similar between the two soil moisture content treatments but cumulative N₂O emission was lower at 65% WHC.

Conclusions

The effect of soil moisture content on gross nitrification rates differ between forest and grassland soils and decreasing soil moisture content from 100 to 65% WHC reduced N₂O emissions in both soils.     

Elevated CO2 enhances the growth of hybrid larch F1 (Larix gmelinii var. japonica × L. kaempferi) seedlings and changes its biomass allocation

Key message

Elevated CO ₂ enhances the photosynthesis and growth of hybrid larch F ₁ seedlings. However, elevated CO ₂ -induced change of tree shape may have risk to the other environmental stresses.

Abstract

The hybrid larch F₁ (Larix gmelinii var. japonica × L. kaempferi) is one of the most promising species for timber production as well as absorption of atmospheric CO₂. To assess the ability of this species in the future high CO₂ environment, we investigated the growth and photosynthetic response of hybrid larch F₁ seedlings to elevated CO₂ concentration. Three-year-old seedlings of hybrid larch F₁ were grown on fertile brown forest soil or infertile volcanic ash soil, and exposed to 500 μmol mol^?1 CO₂ in a free-air CO₂ enrichment system located in northern Japan for two growing seasons. Regardless of soil type, the exposure to elevated CO₂ did not affect photosynthetic traits in the first and second growing seasons; a higher net photosynthetic rate was maintained under elevated CO₂. Growth of the seedlings under elevated CO₂ was greater than that under ambient CO₂. We found that elevated CO₂ induced a change in the shape of seedlings: small roots, slender-shaped stems and long-shoots. These results suggest that elevated CO₂ stimulates the growth of hybrid larch F₁, although the change in tree shape may increase the risk of other stresses, such as strong winds, heavy snow, and nutrient deficiency.     

Seasonal carbon allocation to arbuscular mycorrhizal fungi assessed by microscopic examination, stable isotope probing and fatty acid analysis

Background and Aim

Climate change models are limited by lack of baseline data, in particular carbon (C) allocation to – and dynamics within – soil microbial communities. We quantified seasonal C-assimilation and allocation by plants, and assessed how well this corresponds with intraradical arbuscular mycorrhizal fungal (AMF) storage and structural lipids (16:1ω5 NLFA and PLFA, respectively), as well as microscopic assessments of AMF root colonization.

Methods

Coastal Hypochoeris radicata plants were labeled with ¹³CO₂ in February, July and October, and ¹³C-allocation to fine roots and NLFA 16:1ω5, as well as overall lipid contents and AM colonization were quantified.

Results

C-allocation to fine roots and AMF storage lipids differed seasonally and mirrored plant C-assimilation, whereas AMF structural lipids and AM colonization showed no seasonal variation, and root colonization exceeded 80 % throughout the year. Molecular analyzes of the large subunit rDNA gene indicated no seasonal AMF community shifts.

Conclusions

Plants allocated C to AMF even at temperatures close to freezing, and fungal structures persisted in roots during times of low C-allocation. The lack of seasonal differences in PLFA and AM colonization indicates that NLFA analyses should be used to estimate fungal C-status. The implication of our findings for AM function is discussed.     

Soil-mediated local adaptation alters seedling survival and performance

Background and aims

Soils can act as agents of natural selection, causing differential fitness among genotypes and/or families of the same plant species, especially when soils have extreme physical or chemical properties. More subtle changes in soils, such as variation in microbial communities, may also act as agents of selection. We hypothesized that variation in soil properties within a single river drainage can be a selective gradient, driving local adaptation in plants.

Methods

Using seeds collected from individual genotypes of Populus angustifolia James and soils collected from underneath the same trees, we use a reciprocal transplant design to test whether seedlings would be locally adapted to their parental soil type.

Results

We found three patterns: 1. Soils from beneath individual genotypes varied in pH, soil texture, nutrient content, microbial biomass and the physiological status of microorganisms. 2. Seedlings grown in local soils experienced 2.5-fold greater survival than seedlings planted in non-local soils. 3. Using a composite of height, number of leaves and leaf area to measure plant growth, seedlings grew ～17.5% larger in their local soil than in non-local soil.

Conclusions

These data support the hypothesis that variation in soils across subtle gradients can act as an important selective agent, causing differential fitness and local adaptation in plants.     

Mycorrhiza alters the profile of root hairs in trifoliate orange

Root hairs and arbuscular mycorrhiza (AM) coexist in root systems for nutrient and water absorption, but the relation between AM and root hairs is poorly known. A pot study was performed to evaluate the effects of four different AM fungi (AMF), namely, Claroideoglomus etunicatum, Diversispora versiformis, Funneliformis mosseae, and Rhizophagus intraradices on root hair development in trifoliate orange (Poncirus trifoliata) seedlings grown in sand. Mycorrhizal seedlings showed significantly higher root hair density than non-mycorrhizal seedlings, irrespective of AMF species. AMF inoculation generally significantly decreased root hair length in the first- and second-order lateral roots but increased it in the third- and fourth-order lateral roots. AMF colonization induced diverse responses in root hair diameter of different order lateral roots. Considerably greater concentrations of phosphorus (P), nitric oxide (NO), glucose, sucrose, indole-3-acetic acid (IAA), and methyl jasmonate (MeJA) were found in roots of AM seedlings than in non-AM seedlings. Levels of P, NO, carbohydrates, IAA, and MeJA in roots were correlated with AM formation and root hair development. These results suggest that AMF could alter the profile of root hairs in trifoliate orange through modulation of physiological activities. F. mosseae, which had the greatest positive effects, could represent an efficient AM fungus for increasing fruit yields or decreasing fertilizer inputs in citrus production.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

Importance of native arbuscular mycorrhizal inoculation in the halophyte Asteriscus maritimus for successful establishment and growth under saline conditions

Background and aims

The biological restoration of saline habitats could be achieved by using halophyte plant species together with adapted arbuscular mycorrhizal fungi (AMF). An interesting plant to be used in restoration of saline environments, Asteriscus maritimus, is highly mycotrophic. The aim of this study was to assess the effectiveness of native and allochthonous AMF to enhance the establishment and growth of the halophyte A. maritimus under saline conditions.

Methods

We studied the symbiotic effectiveness of four AMF strains (three native fungal isolates from a saline soil and one allochthonous, from collection) in A. maritimus subjected to increasing salinity stress. We measured plant physiological parameters by which AMF may ameliorate the detrimental effects of salinity stress.

Results

A. maritimus plants showed a high mycorrhizal dependency, even in absence of salt stress. Plants inoculated with native AMF had higher shoot dry weight, efficiency of photosystem II, stomatal conductance and accumulation of glutathione than those inoculated with the collection AMF at the highest level of salinity. Moreover, at this salt level, only 30 % of A. maritimus plants inoculated with the collection AMF survived, while with the three native AMF, the rate of survival was 100 %.

Conclusions

Results points out the importance of native AMF inoculation in the establishment, survival and growth of A. maritimus plants. Inoculation with these native AMF enhanced A. maritimus salt tolerance by increasing efficiency of photosystem II, stomatal conductance and glutathione content and by reducing oxidative damage. Thus, the use of adequate native AMF inocula could be a critical issue for success in recovering saline degraded areas.     

Mycorrhizal benefits on native plants of the Caatinga,a Brazilian dry tropical forest

In the terrestrial ecosystems, soil is an important component, characterized by holding high diversity of microorganisms which play a key role for productivity and vegetal composition. The group of symbionts microorganisms stands out for contributing directly to the growth and plant nutrition, and among them, the arbuscular mycorrhizal fungi form one of the oldest and well established associations. In order to increase the knowledge and contribute for further research with AMF and plants of Caatinga, in this review we compile data from previous studies on the effects of symbiosis between arbuscular mycorrhizal fungi (AMF) and plants of the Caatinga, a type of dry tropical forest found in the northeast of Brazil. These studies collected data under various experimental conditions, emphasizing fungal efficiency and host responsiveness in soils with varied fertility. From our analysis we conclude that in general the symbiotic efficiency on these plants depends on many factors, such as the plant-fungi combination, fertility and soil type. Furthermore, in leguminosae the impact of a joint inoculation with nitrogen fixing bacteria must be taken into account. Claroideoglomus etunicatum was the most tested AMF species benefiting almost all plants tested. Approximately 30 plant species were studied regarding possible benefits provided by AMF and of these only Hymenea courbaril and Aspidosperma pyrifolium did not respond to mycorrhization. Higher efficiency of the mycorrhizal symbiosis can be obtained in soils with low P levels, emphasizing the essential role of these microorganisms in the growth and survival of plant species from the Caatinga biome.     

Effects of arbuscular mycorrhizal inoculation on the growth,zinc distribution and photosynthesis of two citrus cultivars grown in low-zinc soil

Key message

‘Newhall’ and ‘Ponkan’ citrus cultivars grafted on trifoliate orange with mycorrhization by Glomus intraradices displayed different responses to low-Zn, and the optimal growth of ‘Newhall’ was more fungal inoculation dependent.

Abstract

The effects of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on plant growth, zinc (Zn) concentration and distribution, and photosynthesis were investigated in ‘Newhall’ navel orange (Citrus Sinensis) and ‘Ponkan’ tangerine (Citrus reticulata) grafted on the rootstock trifoliate orange (Poncirus trifoliata) exposed to low-Zn soil. Under the Zn-poor condition, the two cultivars showed similar decreases in growth, levels of leaf chlorophyll, gas exchange parameters, root soluble sugar, and Zn levels in various plant parts; however, the Zn percentage in the roots of ‘Ponkan’ was increased while in ‘Newhall’ it remained stable, indicating ‘Newhall’ may have a higher Zn translocation efficiency from the roots to the scion’s shoots. AM inoculation improved growth, Zn concentrations and photosynthesis in the two cultivars. AM-infected seedlings had lower minimal fluorescence values but higher maximal fluorescence values than non-infected seedlings. In addition, they were more efficient in terms of photosystem II’s (PS II’s) maximal and potential photochemistry. The greater changes appeared in ‘Newhall’, implying AM symbioses could alleviate the negative effects of low-Zn on the PS II reaction center. In addition, AM-infected ‘Newhall’ and ‘Ponkan’ seedlings had higher Zn percentages in the leaves but lower Zn ratios in the roots than non-AM-infected seedlings, especially in the former cultivar. These results indicate that G. intraradices has the potential to enhance the growth and Zn distribution in ‘Newhall’ grafted on trifoliate orange seedlings grown in low-Zn soil in a greenhouse.     

Ectomycorrhizal pre-inoculation of <Emphasis Type="Italic">Pinus hartwegii</Emphasis> and <Emphasis Type="Italic">Abies religiosa</Emphasis> is replaced by native fungi in a temperate forest of central Mexico

Few studies have focused on analyzing the effect of native inoculated ectomycorrhizal (ECM) fungal strains on seedlings under field conditions in temperate forests. However, it is crucial to verify that the positive effects of ECM under nursery conditions also occur in the field, favoring their performance. We evaluated the short-term effect of ECM on three-year-old seedlings of Pinus hartwegii and Abies religiosa in central Mexico by subjecting them to four treatments: inoculation with Inocybe splendens, inoculation with Suillus brevipes (both native strains), inoculation with forest soil, and non-inoculated plants. Percentage of ECM colonization, plant growth (shoot height and stem diameter), and physiological (osmotic potential, stomatal conductance, CO₂ assimilation and water use efficiency) responses were evaluated. We found that these two ECM species were partial (P. hartwegii) or totally (A. religiosa) replaced after one and a half years in the field. P. hartwegii seedlings increased their water use efficiency during the dry season, but in A. religiosa seedlings, a clear strategy for avoiding water stress was not detected. This ECM replacement had a negative effect on the physiological performance Of A. religiosa. Our results emphasize the importance of selecting compatible fungal-host species combinations for nursery inoculation and of using sources of inoculum adapted to the environmental conditions of the transplant site, ensuring root colonization prior to field transplanting to minimize seedling mortality due to water stress.     

Maternal effects and carbohydrate changes of Pinus pinaster after inoculation with Fusarium circinatum

Key message

Carbohydrate differences in offspring as a consequence of maternal effects explain transgenerational tree-pathogen interactions.

Abstract

The expression of disease is increasingly recognised as being influenced by maternal effects, given that environmental conditions experienced by mother trees affect tolerance in offspring. It is hypothesised that plant carbohydrates could mediate transgenerational tree-pathogen interactions. The carbohydrate content of Pinus pinaster seedlings obtained from two contrasting maternal environments was studied and seedlings from the two environments were challenged with Fusarium circinatum. The representative mid-infrared spectra of samples in the range of the carbohydrates diagnosed higher proportion of methylesterified pectic polysaccharides and lower proportion of nonesterified pectic polysaccharides for inoculated than for control seedlings. Total carbohydrate content of seedlings from the unfavourable environment did not differ much from total carbohydrate content of seedlings from the favourable maternal environment. However, glucose was 13 % higher and uronic acids 11 % lower in seedlings from the favourable environment after inoculation in comparison to seedlings from the unfavourable maternal environment which had their carbohydrate contents unaltered after inoculation. It is concluded that plant carbohydrates mediate transgenerational tree-pathogen interactions.