Growth and Arbuscular Mycorrhizal Fungal Colonization of Two Prairie Grasses Grown in Soil from Restorations of Three Ages

I compared growth and arbuscular mycorrhizal fungal (AMF) colonization of two prairie grasses (Wild rye [Elymus canadensis] and Little bluestem [Schizachyrium scoparium]), an early‐ and a late‐dominating species in prairie restorations, respectively, grown in soil from restored prairies of differing age, soil characteristics, and site history. There were no consistent patterns between restoration age and soil inorganic nutrients or organic matter. The oldest restoration site had higher soil mycorrhizal inoculum potential (MIP) than 2‐ and 12‐year‐old restorations. However, MIP did not translate into actual colonization for two species grown in soils from the three restorations, nor did MIP relate to phosphorus availability. There were significant differences in root mass and colonization among Wild rye plants but not among Little bluestem plants grown in soils from the three restorations. Wild rye grown in 2‐year‐old restoration soil had significantly higher AMF colonization than when it was grown in soils from the 12‐ and 17‐year‐old restorations. Wild rye grown in 2‐year‐old restoration soil also had higher colonization than Little bluestem grown in 2‐ and 12‐year‐old restoration soils. Little bluestem had no significant correlations between shoot biomass, root biomass or colonization, and concentrations of soil P, total N, or N:P. However, for Wild rye, total soil N was positively correlated with root mass and negatively correlated with colonization, suggesting that in this species, mycorrhizae may affect N availability. Collectively, these results suggest that soil properties unrelated to restoration age were important in determining differences in growth and AMF colonization of two species of prairie grasses.     

Local soil,but not commercial AMF inoculum,increases native and non‐native grass growth at a mine restoration site

Soil communities are often degraded in mined sites, and facilitating the recovery of soil mutualists such as arbuscular mycorrhizal fungi (AMF) may assist with the restoration of native plants. At a grassland mine restoration site, I compared a commercial AMF inoculum with soil collected from beneath native grasses as a source of inoculum, as well as a control treatment. Field plots were broadcast‐inoculated and seeded with native grasses, and biomass of native and non‐native species was measured in three consecutive years. In addition, greenhouse‐grown seedlings of a native bunchgrass (Stipa pulchra) were inoculated with similar treatments, transplanted into the field, and assessed after 18 months. When broadcast inoculation was used, the local soil inoculum tended to increase non‐native grass biomass, and marginally decreased non‐native forb biomass in the second year of study, but did not significantly affect native grass biomass. Broadcast commercial inoculum had no detectable effects on biomass of any plant group. Stipa pulchra transplants had greater N content and mycorrhizal colonization, and marginally higher shoot mass and K content, when pre‐inoculated with local soil (relative to controls). Pre‐inoculation with commercial AMF increased AMF colonization of the S. pulchra transplants, but did not significantly affect biomass or nutrient content. The findings indicate that at this site, the use of local soil as an inoculum had greater effects on native and non‐native plants than the commercial product used. In order to substantially increase native grass performance, inoculation of transplanted plugs may be one potential strategy.     

Mycorrhizal suppression alters plant productivity and forb establishment in a grass-dominated prairie restoration

A fundamental goal of restoration is the re-establishment of plant diversity representative of native vegetation. However, many prairie restorations or Conservation Reserve Program sites have been seeded with warm-season grasses, leading to grass-dominated, low-diversity restorations not representative of native grasslands. These dominant grasses are strongly mycotrophic, while many subordinate forb species appear to be less dependent on mycorrhizal symbiosis. Therefore, manipulating arbuscular mycorrhizal fungi (AMF) may be useful in promoting establishment and growth of forb species in grass-dominated prairie restorations. To assess the potential role of mycorrhizae in affecting the productivity and community composition of restored tallgrass prairie, we conducted a 4-year field experiment on an 8-year-old grassland restoration at the Konza Prairie in northeastern Kansas, USA. At the initiation of our study, seeds of 12 forb species varying in degree of mycorrhizal dependence were added to established grass-dominated plots. Replicate plots were treated bi-weekly with a soil drench of fungicide (Topsin-M^®) over four growing seasons and compared to non-treated control plots to assess the role of AMF in affecting plant species composition, productivity, leaf tissue quality, and diversity in restored tallgrass prairie. Topsin applications successfully reduced mycorrhizal colonization of grass roots to approximately 60–80% relative to roots in control plots. Four years of mycorrhizal suppression reduced productivity of the dominant grasses and increased plant species richness and diversity. These results highlight the importance of mycorrhizae as mediators of plant productivity and community dynamics in restored tallgrass prairie and indicate that temporarily suppressing AMF decreases productivity of the dominant C4 grasses and allows for establishment of seeded forb species.     

Adaptation of plant‐mycorrhizal interactions to moisture availability in prairie restoration

The strength and direction of plant response to inoculation with arbuscular mycorrhizal fungi (AM fungi) is dependent on both abiotic and biotic contexts, often generating patterns of AM fungal mediation of plant adaptation. However, knowledge of plant‐community level effects of these interactions in grassland restoration is limited. We conducted a field inoculation experiment by inoculating five plant species native to a drier prairie and five plant species native to a moister prairie with mycorrhizal fungal communities from each prairie type. Species were paired by genus or family to account for phylogenetic effects. The inoculated plants were transplanted to study plots seeded with a restoration seed mix. Plots were manipulated to create either moister or drier conditions similar to environments of the plant species and mycorrhizal communities. In both transplanted and seeded plant species, we found that only drier prairie‐range species benefited from moisture‐regime matched AM fungal inoculum. Other seeded prairie plant species demonstrated a negative response to inoculation, likely due to the earlier successional stage of these species. Additionally, nonseeded plants benefited from inoculation in different ways: native nonseeded plants had highest cover with drier prairie inoculum in drier conditions, while nonnative plants had highest cover with moister prairie‐origin inoculum. These results suggest that use of local AM fungi may be particularly important in restorations at drier sites, even at relatively small differences in moisture availability. Further, specific knowledge of relative responsiveness of seeded plant species and nonseeded plant species to AM fungal inoculation will be useful in planning restorations.     

Inoculation with native soil improves seedling survival and reduces non-native reinvasion in a grassland restoration

Losses of grasslands have been largely attributed to widespread land-use changes, such as conversion to row-crop agriculture. The remaining tallgrass prairie faces further losses due to biological invasions by non-native plant species, often with resultant ecosystem degradation. Of critical concern for conservation, restoration of native grasslands has been met with little success following eradication of non-native plants. In addition to the direct and indirect effects of non-native invasive plants on beneficial soil microbes, management practices targeting invasive species may also negatively affect subsequent restoration efforts. To assess mechanisms limiting germination and survival of native species and to improve native species establishment, we established six replicate plots of each of the following four treatments: (1) inoculated with freshly collected prairie soil with native seeds; (2) inoculated with steam-pasteurized soil with native seeds; (3) noninoculated with native seeds; or (4) noninoculated/nonseeded control. Inoculation with whole soil did not improve seed germination; however, addition of whole soil significantly improved native species survival, compared to pasteurized soil or noninoculated treatments. Inoculation with whole soil significantly decreased reestablishment of non-native invasive Bothriochloa bladhii (Caucasian bluestem); at the end of the growing season, plots receiving whole soil consisted of approximately 30% B. bladhii cover, compared to approximately 80% in plots receiving no soil inoculum. Our results suggest invasion and eradication efforts negatively affect arbuscular mycorrhizal hyphal and spore abundances and soil aggregate stability, and inoculation with locally adapted soil microbial communities can improve metrics of restoration success, including plant species richness and diversity, while decreasing reinvasion by non-native species.     

Assessment of Natural Mycorrhizal Potential in a Desertified Semiarid Ecosystem

A survey of the natural mycorrhizal potential has been carried out in a representative area of a desertified semiarid ecosystem in the southeast of Spain. Many indigenous plants from the field site were mycorrhizal, including the dominant Anthyllis cytisoides, which had high levels of colonization by arbuscular mycorrhizal fungi (AMF). Low numbers of AMF spores were present in the soil, although a range of species, including Scutellospora calospora, Glomus coronatum, Glomus constrictum, and several Acaulospora species, was represented. Soil infectivities, as determined by a soil dilution method, were similar for most plants tested but were significantly lower for Anthyllis cytisoides. Nevertheless, when a less disruptive method to determine soil infectivity was used, the importance of the mycelial network in maintaining the infectivity of soil under perennial shrubs, such as Anthyllis cytisoides, was highlighted. Seasonal variations in the mycorrhizal infectivity showed that it was higher towards the end of the summer period than in midwinter. In screening trials in a greenhouse, the indigenous AMF did not significantly improve the growth of plants compared with that of noninoculated controls. Augmentation of the soil with an inoculum of Glomus intraradices resulted in improved growth of Anthyllis cytisoides in both sterile and nonsterile conditions, in contrast to results obtained following inoculation with Glomus mosseae or another Glomus sp. Our findings suggest that the indigenous inoculum levels of AMF are inadequate to support an extensive revegetation program in the absence of an additional mycorrhizal inoculum.     

Plant response to biochar,compost, and mycorrhizal fungal amendments in post‐mine sandpits

Extreme growing conditions inhibit restoration in sandpit mines. Co‐amendment of soil conditioners such as biochar, compost, and arbuscular mycorrhizal fungi (AMF) may alleviate these stresses and lead to a more successful restoration. We conducted a multiyear restoration experiment in a sandpit in Southern Ontario, Canada, following industrial‐scale grassland restoration protocols. The sandpit substrate was sand with low carbon (C) and nutrients. We tested the effect of biochar, compost, and AMF inoculum in two experiments (plant plugs vs. seed application). In the plant plug trial, we investigated the treatment effects on the growth of eight grassland plant species and colonization of plant roots by AMF over two growing seasons. We found that co‐amending soils with compost plus biochar (20 T/ha + 10 T/ha) was more beneficial than other amendment combinations. Amendments including AMF were not more beneficial to plant growth than those without AMF. In the seed application trial, direct inoculation of AMF in the field combined with high compost addition (20 T/ha or 40 T/ha) resulted in the highest plant cover compared to other treatment combinations. Our results indicate that co‐amending sandpit substrates with biochar, compost, and AMF are practical restoration tools that enhance grassland restoration.     

Mycorrhizae and succession in plantings of beachgrass in sand dunes

A survey of arbuscular mycorrhizal fungi (AMF), arbuscular mycorrhizae (AM), and hyphal networks of AMF was carried out in sand dune sites of different successional stages in the Province Lands Area of Cape Cod National Seashore, Massachusetts. The study focused on large-scale plantings (each of 12–20 ha) of American beachgrass (Ammophila breviligulata) aged 0–7 yr and five adjacent natural dune areas. Sample sites ranged in vegetative cover from barren to forested. Spores of 17 species of AMF were recovered from the dunes. Over the successional sequence, there were increases in the richness and spore populations of the AMF community, the extent of colonization of A. breviligulata roots, and the mycorrhizal inoculum potential of the soil. Unvegetated sites lacked propagules of AMF, but roots of planted culms of A. breviligulata (which carried propagules of AMF) became mycorrhizal in <1 yr after planting. Spores were recovered from previously AMF-free sites that had been planted with beachgrass for 47 wk, and five species of AMF sporulated in sites <6 yr old. Significant hyphal networks were not present in any of the planted areas (<6 yr old at the time of sampling), but did occur in natural areas. The rate of invasion of areas planted to A. breviligulata by later successional plant species may in part depend upon the establishment of a vigorous network of hyphae of AMF in a site.     

Relationship of seed source and arbuscular mycorrhizal fungi inoculum type to growth and colonization of big bluestem (Andropogon gerardii)

Big bluestem (Andropogon gerardii) is a key grass of tallgrass prairies and is commonly included in restoration projects. In many cases, it has been found to benefit significantly from arbuscular mycorrhizal (AM) fungi, however results have varied under non-sterile soil conditions. This study investigated the effects of two types of AM fungi inoculum (commercial and prairie) on growth and root colonization of big bluestem from five different seed sources grown in non-sterile soils. Seed sources were collected from five remnant prairies in the Tallgrass Prairie Peninsula located in the Midwestern United States. Growth of big bluestem and root length colonized by AM fungi was highly variable among seed source treatments. Overall, percentage of root length colonized by AM fungi was positively correlated with the total dry weight of plants, and plants that received inoculum generally grew better than those that did not receive inoculum. Inoculum treatment affected both big bluestem growth and percentage root length colonized and there was an interaction between seed source and inoculum treatment relative to colonization. Root colonization responses were not significantly different between the prairie and commercial inoculum types, although there was a significant response between plants that received additional inoculum as opposed to no additional inoculum. Seed sources from Ohio and Illinois had the highest biomasses and greatest percentage of root length colonized while plants from Wisconsin and Missouri grew poorly and had low root colonization. These results demonstrate the importance of considering both seed source and inoculum type before the incorporation of AM inoculum to prairie restoration projects.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

AMF components from a microbial inoculum fail to colonize roots and lack soil persistence in an arable maize field

Arbuscular mycorrhizal fungi (AMF) are root obligate biotrophs that provide the host with nutrients and pathogen protection, in exchange of photosynthetic products. A decline in AMF diversity can reduce the overall benefit for host plants. A sustainable strategy to re-establish AMF diversity is to supply the target soil with AMF inoculants. After inoculation, it is essential to verify whether the inoculants successfully colonize the host plant and persist, and if the resident AMF community is affected. The AMF components of a microbial inoculum (including other saprotrophs) that was applied to maize were identified and traced in field by 454-pyrosequencing of the partial rRNA 18S gene. In addition, mycorrhizal colonization and plant biomass were monitored in inoculated and non-inoculated maize. The inoculated AMF taxa failed to colonize roots and lacked soil persistence. Nevertheless, the inoculation process reduced species dominance and increased diversity in the pre-existing AMF community. No differences were seen between mycorrhizal colonization in treated and control maize. We suggest that the slightly significant increase in treated plant biomass was potentially due to (i) marginally colonizing inoculated AMF that remained unseen and other saprotroph inoculants applied and/or (ii) the effect of inoculation on the pre-existing AMF community in treated maize roots.     

Are two strategies better than one? Manipulation of seed density and soil community in an experimental prairie restoration

Restoration practitioners have a variety of practices to choose from when designing a restoration, and different strategies may address different goals. Knowledge of how to best use multiple strategies could improve restoration outcomes. Here, we examine two commonly suggested strategies in a single tallgrass prairie restoration experiment: increased forb sowing density and prairie soil inoculation. We designed a study with two different forb seeding densities. Within these densities, we transplanted seedlings into 1‐m² plots that had been grown in either a whole prairie soil inoculum or sterilized prairie soil. After 4 years, we found positive effects of both high forb sowing density and inoculation treatments on the ratio of seeded to nonseeded plant cover in these plots, and negative effects of both treatments on nonseeded plant diversity. No effects of either treatment were seen on seeded plant diversity. Each strategy also affected the plant community in different ways: high forb sowing density increased seeded forb richness and decreased native nonseeded plant cover, while inoculation decreased non‐native cover, and tended to increase average successional stage of the community. These effects on restoration outcome were typically independent of each other, with the result that plots with both manipulations had the most positive effects on restoration outcomes. We thus advocate the combined use of these restoration strategies, and further studies which focus on both seeding and soil community manipulation in restoration.     

Forest reclamation of fly ash deposit: a field study on appraisal of mycorrhizal inoculation

An extensive field trial was established on a fly ash deposit (1) to evaluate whether the inoculation with arbuscular mycorrhizal fungi (AMF) and/or ectomycorrhizal fungi (EcMF) improves growth and survival of 13 planted tree species and (2) to trace the inoculated mycorrhizal fungi in tree roots after one growing season. Molecular methods were applied to characterize AMF and EcMF entering the studied system (inocula, native soil, and roots of nursery seedlings). Biometric parameters and mortality of the trees were recorded and the presence of AMF and EcMF in sampled trees was determined both microscopically and genetically. Mycorrhizal inoculation did not improve survival or growth of any tree species. Most AMF‐host and all EcMF‐host seedlings were highly precolonized already from the nursery. An abundant and diverse AMF community was also found in the field soil. The AMF inoculum taxa partially overlapped with AMF in the native soil and in the precolonized roots. After one season, the only two inoculum‐unique AMF taxa were detected in host species non‐precolonized or only partially precolonized from the nursery. The components of EcMF inoculum were not detected in any sampled tree. After the season, the ectomycorrhizal hosts maintained most of their original EcMF taxa gathered in nursery, some tree species were additionally colonized by EcMF probably originating from the soil. Our results show considerable self‐restoration potential of nature on the target site. Mycorrhizal inoculation thus did not bring any conclusive advantage to the planted trees and seems superfluous for reclamation practice on the fly ash deposit.     

Microbial inoculation influences arbuscular mycorrhizal fungi community structure and nutrient dynamics in temperate tree restoration

Soil microbial communities have a profound influence on soil chemical processes and subsequently influence tree nutrition and growth. This study examined how the addition of a commercial inoculum or forest‐collected soils influenced nitrogen (N) and phosphorus (P) dynamics, soil microbial community structure, and growth in Liriodendron tulipifera and Prunus serotina tree saplings. Inoculation method was an important determinant of arbuscular mycorrhizal fungi (AMF) community structure in both species and altered soil N dynamics in Prunus and soil P dynamics in Liriodendron. Prunus saplings receiving whole forest soil transfers had a higher rhizosphere soil carbon/nitrogen ratio and ammonia content at the end of the first growing season when compared to unmanipulated control saplings. Inoculation with whole forest soil transfers resulted in increased inorganic phosphorus in Liriodendron rhizosphere soils. The number of AMF terminal restriction fragments was significantly greater in rhizosphere soils of Liriodendron saplings inoculated with whole forest soil transfers and Prunus saplings receiving either inoculum source than control saplings. Forest soil inoculation also increased AMF colonization and suppressed stem elongation in Liriodendron after 16 months; conversely, Prunus AMF colonization was unchanged and stem elongation was significantly greater when saplings were inoculated with whole forest soil transfers. Longer term monitoring of tree response to inoculation will be essential to assess whether early costs of AMF colonization may provide long‐term benefits. This study provides insight into how practitioners can use microbial inoculation to alter AMF community structure and functioning, subsequently influencing tree growth and nutrient cycling during the restoration of degraded lands.     

Changes in arbuscular mycorrhizal fungal communities along a river delta island in northeastern Brazil

Arbuscular mycorrhizal fungi (AMF) play a key role in the maintenance of the balance of terrestrial ecosystems, but little is known about the biogeography of these fungi, especially on tropical islands. This study aims to compare AMF community structure along a transect crossing a fluvial-marine island and relate these communities with soil and vegetation parameters to shed light on the forces driving AMF community structure on a local scale. We tested the hypothesis that the composition of AMF communities changes across the island, even within short distances among sites, in response to differences in edaphic characteristics and vegetation physiognomies. We sampled roots and soils in five different natural and degraded habitats: preserved mangrove forest (MF), degraded mangrove forest (MD), natural Restinga forest (RF), and two regeneration Restinga forests (RR1 and RR2) on Ilha da Restinga, northeastern Brazil. We determined the mycorrhizal colonization rate and AMF community structure based on morphological spore identification. The island soils were sandy with pH varying from acid to neutral; higher levels of organic matter were registered in RF and lower in MF; other chemical and physical soil attributes differed along the habitat types on the island. In total, 22 AMF species were identified, without any difference in species richness. However, the diversity and composition of AMF communities, spore abundance per families, and mycorrhizal colonization were statistically different among the habitats. The composition of AMF communities was strongly related to soil characteristics, especially the sum of exchangeable bases. Our results indicate that the different habitat types have diverse AMF communities even within short distances among habitats. In conclusion, islands with high spatial heterogeneity in soil parameters and diverse vegetation are potential refuges for the diversity conservation of AM fungi.     

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.     

Bare soil cover and arbuscular mycorrhizal community in the first montane forest restoration in Central Argentina

Soil erosion affects extensive areas worldwide and must be urgently reduced promoting plant cover and beneficial microorganisms associated with plants, including arbuscular mycorrhizal fungi (AMF). In mountain environments, plant cover is difficult to enhance due to harsh conditions during the dry season and steep slopes. Our objective was to evaluate the percentage of the soil surface covered by plants and the AMF community associated with trees 12.5 years after planting during forest restoration efforts in microsites at different levels of soil degradation. The study was performed in the first montane forest restoration initiative of Central Argentina, where one of the trials consisted of planting Polylepis australis saplings at microsites with different levels of soil degradation: high, intermediate, and low. After 12.5 years, percentage of bare soil cover was significantly reduced by 36 and 37% in the high and intermediate degradation microsites, respectively. Low degradation microsites were initially very low in bare soil and did not significantly change. Mycorrhizal colonization, hyphae, vesicles, arbuscules, AMF diversity, and community structure were similar among microsite types. Percentage of hyphal entry points was higher at microsites with low degradation, number of spores was higher in high and intermediate degradation, and species richness was higher in high degradation. Acaulospora and Glomus were the most abundant genera in all microsites. We conclude that even in the most degraded microsites around 2.8% of the bare soil is covered by vegetation each year and that the arbuscular mycorrhizal community is highly tolerant and adapted to soils with different disturbance types.     

Effects of Native Plant Species,Mycorrhizal Inoculum,and Mulch on Restoration of Reservoir Sediment Following Dam Removal,Elwha River,Olympic Peninsula,Washington

As dams across the country continue to age, successful restoration of dewatered reservoirs remains a critical factor in decisions regarding dam removal. Freshly exposed reservoir sediment may not support rapid reestablishment of native plant species due to poor fertility or absence of arbuscular mycorrhizal fungi propagules. This field study evaluated treatment effects involving combinations of native plants, mycorrhizal inoculum, and mulch on restoration of dewatered reservoir sediment over 20 months. Most plants, even those uninoculated, became mycorrhizal. In all treatments, sediment pH decreased, as did nitrogen and organic matter, compared to original reservoir sediment, while aggregate stability doubled from original anaerobic sediment. Revegetated plots with mulch had significantly greater vegetation cover and more native volunteer species compared to plots without mulch. The planted mulch treatment also decreased plot runoff tenfold, reducing erosion to the same degree. Indicators suggest that the primary benefit of mulch resulted in increased moisture retention making the planted mulch treatment most successful for restoration of reservoir sediment due to extensive native plant growth, improved soil characteristics, and reduced runoff and erosion compared to nonmulched plots. While results from this plot‐scale study suggest commercial mycorrhizal inoculum is unnecessary since natural inoculum sources sufficiently colonized plants, reservoir‐scale restoration may require creation of additional source areas to encourage rapid reestablishment of native plants and mycorrhizal fungi.     

Effects of Resident Soil Fungi and Land Use History Outweigh Those of Commercial Mycorrhizal Inocula: Testing a Restoration Strategy in Unsterilized Soil

Arbuscular mycorrhizal fungi (AMF) have numerous effects on temperate grassland ecosystems, but prairie restorations are frequently located in sites with depauperate AMF communities. In this greenhouse study, four native species (Schizachyrium scoparium, Elymus canadensis, Monarda punctata, and Aster ericoides) and an invasive grass (Bromus inermis) were grown in unsterilized field soils and treated with two types of commercial AMF inoculum. Inocula were applied at one and two times the manufacturers' suggested rate. Soil was collected from a meadow enrolled in the Conservation Reserve Program (CRP), and from an active agricultural field. Inoculum addition had no effect on biomass or percent colonization by AMF for any grass species, regardless of soil type. Inoculum type significantly affected Aster biomass and percent colonization, although pairwise comparisons of treated individuals and controls were not significant. The overall lack of effectiveness of the commercial inocula may reflect the small number of propagules added, even when used at twice the recommended rate. Higher rates of fungal colonization in all three grasses and increased biomass in the native grasses were observed in individuals grown in the CRP soil. Plants were also colonized by dark septate endophytic fungi; for Schizachyrium, endophyte colonization was significantly greater in tilled than CRP soil. Our results indicate that an existing soil fungal community promotes colonization by AMF more than the addition of commercial inocula, and that soil characteristics associated with land use history significantly affect the growth of native species in a restoration setting.     

Arbuscular mycorrhizal fungi in the tree seedlings of two Australian rain forests: occurrence, colonization, and relationships with plant performance

The roots of rain forest plants are frequently colonized by arbuscular mycorrhizal fungi (AMF) that can promote plant growth in the nutrient poor soils characteristic of these forests. However, recent studies suggest that both the occurrence of AMF on rain forest plants and the dependence of rain forest plants on AMF can be highly variable. We examined the occurrence and levels of AMF colonization of some common seedling species in a tropical and a subtropical rain forest site in Queensland, Australia. We also used a long-term database to compare the growth and mortality rates of seedling species that rarely formed AMF with those that regularly formed AMF. In both forests, more than one-third of the seedling species rarely formed AMF associations, while 40% of species consistently formed AMF in the tropical site compared to 27% in the subtropical site. Consistent patterns of AMF occurrence were observed among plant families at the two sites. Variation among seedling species in AMF occurrence or colonization was not associated with differences in seed mass among species, variation in seedling size and putative age within a species, or lack of AMF inoculum in the soil. Comparisons of four seedling species growing both in the shaded understory and in small canopy gaps revealed an increase in AMF colonization in two of the four species in gaps, suggesting that light limitation partially explains the low occurrence of AMF. Seedling survival was significantly positively associated with seed biomass but not with AMF colonization. Furthermore, seedling species that regularly formed AMF and those that did not had similar rates of growth and survival, suggesting that mycorrhizal and nonmycorrhizal strategies were equivalent in these forests. Furthermore, the high numbers of seedlings that lacked AMF and the overall low rate of seedling growth (the average seedling required 6 years to double its height) suggest that most seedlings did not receive significant indirect benefits from AMF through connection to canopy trees via a common mycorrhizal network.