Invasive ectomycorrhizal fungi can disperse in the absence of their known vectors

Positive interactions between non-native species can accelerate their invasion rate and exacerbate their impacts. This has been shown for non-native mammals that disperse invasive ectomycorrhizal fungi (EMF), in turn facilitating the invasion of non-native tree species. Mammal-mediated dispersion is assumed to be the main mechanism of EMF long distance dispersal, being particularly critical for truffle-like EMF species. We asked whether the absence of non-native mammals is an obstacle for Pinaceae invasion given the lack of invasive EMF being dispersed. We studied EMF species colonization and Pseudotsuga menziesii (Douglas-fir) trees’ growth in soil from mainland sites where non-native mammals are highly abundant, and lake islets in which they have been historically absent. Contrary to what we expected, we found invasive EMF, including truffle-like species, in sites where invasive mammals have been historically absent. Douglas-fir trees grew equally well and had the same EMF colonization in soil from mainland and islets. Alternative mechanisms of EMF dispersal, such as saltation, bird dispersal, or human dispersal, can be involved in their arrival to native stands. The presence of invasive EMF makes native sites vulnerable to Pinaceae invasion, even in the absence of mammalian dispersers.     

Reduced risk for positive soil-feedback on seedling regeneration by invasive trees on a very nutrient-poor soil in Seychelles

Invasive plants sometimes alter habitat conditions so as to promote further invasion, either by the same or by other non-native species. Such positive feedbacks often occur because the non-native species increases soil fertility, thereby favouring recruitment of non-native seedlings. This has been demonstrated in nitrogen-poor habitats invaded by nitrogen-fixing species, but it is unclear whether similar processes operate in habitats limited by phosphorus and other nutrients. I compared the growth of seedlings of Cinnamomum verum, an abundant invasive tree on phosphorus-poor soils in the Seychelles, in soils taken from beneath different tree species. I expected that soil phosphorus availability would be higher beneath stands of C. verum than beneath stands of either the native Northea hornei or the non-native nitrogen-fixing species, Falcataria moluccana. I therefore predicted that C. verum seedlings would grow faster in soil taken from beneath C. verum trees than in soil taken from beneath either of the other two species. To test this hypothesis, I performed a bioassay experiment with seedlings of C. verum grown in soils from stands of C. verum, F. moluccana and N. hornei. Different nutrient treatments (control, plus phosphorus (P), plus nitrogen (N), plus N and P, and plus complete fertilizer) were applied to investigate how nutrient availabilities modulate the effects of the trees. In the control treatment without added nutrients, there was a weak tendency for seedlings to perform better in the soils from beneath invasive than native trees. However, seedling growth in soils from beneath invasive species was markedly higher following the addition of phosphorus in the case of the F. moluccana soil, and complete fertilizer in the case of the C. verum soil. These results indicate that on very nutrient-poor soils, a low supply of nutrients other than N may reduce the risk of a soil-feedback by invasive trees on seedling regeneration.     

Competitive effects of the invasive shrub,Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings

Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests.     

亚热带典型树种根毛特征及其与共生真菌的关系

根毛和共生真菌增加了吸收面积,提高了植物获取磷等土壤资源的能力。由于野外原位观测根表微观结构较为困难,吸收细根、根毛、共生真菌如何相互作用并适应土壤资源供应,缺乏相应的数据和理论。该研究以受磷限制的亚热带森林为对象,选取了21种典型树种,定量了根毛存在情况、属性变异,分析了根毛形态特征与共生真菌侵染率、吸收细根功能属性之间的关系,探讨了根表结构对低磷土壤的响应和适应格局。结果表明:1)在亚热带森林根毛不是普遍存在的, 21个树种中仅发现7个树种存有根毛, 4个为丛枝菌根(AM)树种, 3个为外生菌根(ECM)树种。其中,马尾松(Pinus massoniana)根毛出现率最高,为86%;2)菌根类型是理解根-根毛-共生真菌关系的关键,AM树种根毛密度与共生真菌侵染率正相关,但ECM树种根毛直径与共生真菌侵染率负相关; 3) AM树种根毛长度和根毛直径、ECM树种根毛出现率与土壤有效磷含量呈负相关关系。该研究揭示了不同菌根类型树种根毛-共生真菌-根属性的格局及相互作用,为精细理解养分获取策略奠定了基础。     

Mountain beech seedling responses to removal of below-ground competition and fertiliser addition

We examine the height growth, diameter growth and below-ground allocation responses of mountain beech (Nothofagus solandri var. cliffortioides) seedlings to the experimental removal of root competition through root trenching and the addition of fertiliser within relatively intact-canopied mountain beech forest in the Craigieburn Range, Canterbury. Trenching and trenching combined with fertiliser increased relative height and diameter growth of mountain beech seedlings above that of controls. Trenching and trenching combined with fertiliser also increased the root:shoot biomass ratio of seedlings above that of controls suggesting rapid root proliferation to maximise short-term nutrient uptake. Our results are consistent with an increasing number of studies that show that on infertile soils under intact canopies seedlings of ‘apparent’ light-demanding species can respond to the removal of root competition. Because New Zealand indigenous forests usually occur on infertile soils, we conclude that root competition may be particularly important.     

What happens to the mycorrhizal communities of native and exotic seedlings when Pseudotsuga menziesii invades Nothofagaceae forests in Patagonia,Argentina?

Pseudotsuga menziesii is one of the most widely planted conifers in the Patagonian Andes of Argentina, having invading characteristics that are broadly reported. We studied the mycorrhizal status of seedlings along six Nothofagaceae + P. menziesii invasion matrices to investigate their role in the invasive process, according to these hypothesis: a) The abundance and richness of EM will be higher in seedlings grown in their own soil; b) In the presence of native EM inoculum, the invasive plant will be associated with generalist mycorrhizae (EM and/or AM), c) AM associations will be more abundant in P. menziesii seedlings grown in Interface or native forest soils, d) Mycorrhizal community differences between treatments will alter host fitness (growth and nutritional parameters). Seedlings from Nothofagus dombeyi, N. antarctica, Lophozonia alpina, L. obliqua and Pseudotsuga menziesii were set up in a soil-bioassay that included soils from non-invaded Nothofagaceae forests, pure P. menziesii plantations, and the interface between both. Pseudotsuga menziesii seedlings showed a decreasing, although never null, ectomycorrhizal (EM) colonization pattern from plantations to non-invaded forests, mainly with exotic EM species. Hebeloma mesophaeum and Wilcoxina sp. 1, two EM species with cosmopolitan distribution, were found to be shared by both tree species. Hebeloma hiemale and Wilcoxina sp. 1, common mycorrhizal partners of P. menziesii in Patagonia although not registered from Nothofagaceae forest, were found to be associated with N. antarctica, being the first report for both fungal species. Pseudotsuga menziesii seedlings showed the ability to form different arbuscular mycorrhiza (AM) colonization types (Paris-, Arum-, Both- and Intermediate-types) depending on the treatments, with significantly higher presence of Intermediate-type in the Interface treatment, where colonization was low. The shared EM species and the presence of different AM colonization types imply enhanced possibilities for invasive P. menziesii seedlings establishment and development. Seedling features and EM colonization rates evidenced that P. menziesii invasion could produce maladaptation (defined as a relative decline in host fitness due to altered mycorrhizal communities from native settings) of mycorrhizal communities, seriously injuring native ecosystem.     

两种光强下木质藤本与树木幼苗的竞争关系

 为了探讨木质藤本和树木幼苗的相互作用关系,对两种光强(4%和35%的光强)、4种竞争处理下(全竞争、地上竞争、地下竞争和无竞争),一种 需光木质藤本(刺果藤(Byttneria grandifolia))和3个树种(耐荫种：五桠果木姜子(Litsea dilleniifolia)和绒毛番龙眼(Pometia tomentosa);需光种：羊蹄甲(Bauhinia variegata))幼苗的地上部分和地下部分的竞争关系进行了研究。结果表明：木质藤本的竞争显著影响 着3种树木幼苗的光合能力、形态特征和生长,但生长环境的不同光强影响地上部分竞争和地下部分竞争的相对强度。在低光下,地上部分竞争 比地下部分竞争对3种树木幼苗的相对生长速率(Relative growth rate,RGR)和光合能力造成更大的影响;而高光下,地下竞争对树木幼苗的 生长有更强的抑制作用。不同的竞争处理和光强对树木幼苗的生物量积累造成显著的影响。光强对3种树种的比叶面积(Specific leaf area, SLA)和叶面积比(Leaf area ratio,LAR)有显著的抑制作用,但竞争只对需光的羊蹄甲的SLA和LAR有显著影响。不同的光照和竞争处理之间, 同种植物表现出不同的表型特征。由于竞争的影响,苗木在形态上较为矮小、叶片数目较少、叶面积减小,但是长细比改变较少 。     

Pasture trees in tropical México: the effect of soil nutrients on seedling growth

Environment and seedling community under isolated trees in pastures are different from those in the open pasture. The effect of the pasture trees on the soil nutrients and on the seedling growth were investigated. Seven isolated trees and eight plots were selected in two pastures of 12-yr and 32-yr old derived from a lowland rain forest with nutrient-rich soil at Los Tuxtlas, Mexico. The soil concentrations of total N, P Bray, K+, Na+, Ca2+ and Mg2+, plus others physical and chemical characteristics, were compared between the pasture trees and the open-pasture. An experiment was done to test the hypothesis that soil from under the pasture trees was better for seedling growth than soil from the open pasture. Seedlings of two native tree species and two domesticated species were grown in soil from the two different sites in a shade-house. The dry weight of the shoot and root/shoot ratio were compared. Only total N, P and Na+ differed slightly in concentrations between the sites, but did not promote more seedling biomass. It seems that the soil at this location is sufficiently nutrient-rich even in the open pastures and over-ride any effect of the pasture trees on nutrient availability.     

Above- and below-ground competition between the liana <Emphasis Type="Italic">Acacia kamerunensis</Emphasis> and tree seedlings in contrasting light environments

Proliferation of lianas in canopy gaps can restrict tree regeneration in tropical forests through competition. Liana effects may differ between tree species, depending on tree requirements for above- and below-ground resources. We conducted an experiment in a shade house over 12 months to test the effect of light (7 and 27% external irradiance) on the competitive interactions between seedlings of one liana species and three tree species and the contribution of both above- and below-ground competition. Seedlings of the liana Acacia kamerunensis were grown with tree seedlings differing in shade tolerance: Nauclea diderrichii (Pioneer), Khaya anthotheca (Non-Pioneer Light Demander) and Garcinia afzelii (Non-Pioneer Shade Bearer). Trees were grown in four competition treatments with the liana: no competition, root competition, shoot competition and root and shoot competition. Both root and root–shoot competition significantly reduced relative growth rates in all three tree species. After one year, root–shoot competition reduced growth in biomass to 58% of those (all species) grown in no competition. The root competition treatment had a more important contribution in the effect of the liana on tree growth. Tree seedlings did not respond to competition with the liana by altering their patterns of biomass allocation. Although irradiance had a great effect on tree growth and allocation of biomass, the interaction between competition treatments and irradiance was not significant. Nauclea diderrichii, the tree species which responded most to the effects of competition, showed signs of being pot-bound, the stress of which may have augmented the competition effects. The understanding of the interaction of above- and below-ground competition between lianas and trees and its moderation by the light environment is important for a proper appreciation of the influence of lianas on tropical forest regeneration.     

No evidence of spatial root system segregation and elevated fine root biomass in multi-species temperate broad-leaved forests

Differences in spatial rooting patterns among coexisting species have been recognized as an important mechanism for generating biodiversity effects on ecosystem functioning. However, it is not yet clear whether complementarity in root space exploration is a universal characteristic of multi-species woody communities. In a temperate broad-leaved forest with a mosaic of species-poor and species-rich stands, we tested two hypotheses related to putative below-ground ‘overyielding’ in more diverse forests, (1) that species mixture results in a partial spatial segregation of the fine root systems of different species, and (2) that stand fine root biomass increases with tree species diversity. We investigated 12 stands either with one, three, or five dominant tree species (4 replicate stands each) under similar soil and climate conditions for stand fine root biomass and spatial root segregation in vertical and horizontal direction in the soil. Fine roots of different tree species were identified using a morphological key based on differences in colour, periderm surface structure, and branching patterns. In species-poor and species-rich stands, and in all tree species present, fine root density (biomass per soil volume) decreased exponentially with soil depth at very similar rates. Stand fine root biomass in the densely rooted upper soil (0–40 cm depth) was not significantly different between stands with 1, 3 or 5 dominant tree species. We conclude that ‘below-ground overyielding’ in terms of higher fine root biomasses in species-rich stands as compared to monospecific ones does not occur in these broad-leaved forests which most likely results from a missing complementarity in vertical rooting patterns of the present tree species.     

<Emphasis Type="Italic">Acer rubrum</Emphasis> (red maple) growth is negatively affected by soil from forest stands dominated by its invasive congener (<Emphasis Type="Italic">Acer platanoides</Emphasis>, Norway maple)

Invasive species continue to alter the plant communities of the eastern United States. To better understand the mechanisms and characteristics associated with invasive success, we studied competition between two Acer species. In a greenhouse, we tested (1) the effect of forest soil type (beneath an invasive and native stand) on seedling growth of the invasive Acer platanoides (Norway maple) and native A. rubrum (red maple), and the (2) effects of full (above- and below-ground) and partial inter-specific competition on species growth. We found A. rubrum growth was negatively affected by soil from the invaded stand, as it had lower above-ground (32%) and below-ground (26%) biomass, and number of leaves (20%) than in the native soil. The root:shoot resource allocations of A. platanoides depended on soil type, as it had 14% greater root:shoot mass allocation in the native soil; this ability to change root:shoot allocation may be contributing to the ecological success of the species. Widely published as having a large ecological amplitude, A. rubrum may be a useful species for ecological restoration where A. platanoides has been present, but the impacts of A. platanoides on soil functioning and subsequent plant interactions must be addressed before protocols for native reintroductions are improved and implemented.     

Influence of Invasive Tree Kill Rates on Native and Invasive Plant Establishment in a Hawaiian Forest

Fire tree (Morella faya) has invaded extensive areas of wet and mesic forest on the Island of Hawai’i, forming nearly monospecific stands. Our objective was to identify a method of controlling M. faya, which would allow native plants to establish while minimizing establishment by invasive plants. Treatments (logging all trees, trees left standing but girdled, and incremental girdling over 20 months) were selected to kill M. faya stands at different rates, thereby creating different conditions for species establishment. Leaf litter was either removed or left in place; seeds and seedlings of three native pioneer species, three native forest species, and three alien invasive species were then added to determine their ability to establish. Native pioneer species established best in the log and girdle treatments, whereas seedling emergence of native forest species was higher in the girdle and incremental girdle treatments. Seedlings of invasive species emerged faster than the natives, but each of them responded differently to the stand treatments. Leaf litter reduced seedling emergence for all species, with small‐seeded species (<1 mg/seed) affected most under low light conditions. No single method eliminated all invaders, but girdling of M. faya provided suitable conditions for most native species. If combined with selective removal of the most disruptive alien species and native seed additions, girdling could be an effective general strategy for restoring native forests that have been overwhelmed by woody invaders.     

Differing interactions between an introduced beetle and a resident root nematode mediated by an invasive plant and its native congener

Interactions between above- and below-ground herbivores play an important role in shaping plant competition and invasion, while the effects of non-native species invasions on above- and below-ground interactions remain unexplored. In this study, we report the interactions between an above-ground introduced beetle and a resident root nematode hosted by an invasive plant or its native congener with a laboratory bioassay and a greenhouse experiment in Wuhan, China. Nematode infections decreased beetle food conversion rates and larval biomass on the native plant, and increased beetle food conversion rates with no detectable impact on the larval biomass on the invasive plant. Beetle defoliation decreased nematode egg production on both the native and invasive plants. The interactions of the introduced beetle and the nematode were different by the invasive and native plants, which suggests that invasive plants and their introduced herbivores have the potential to alter above- and below-ground interactions and affect associated community members, which may in turn affect invasion processes and the safety of classical biocontrol practices.     

植物竞争对3种移植树苗生长的影响

在植物幼苗生长过程中,总是受到包括地下根竞争在内的各种竞争影响。植物间的竞争主要同有效光辐射、水分和各种营养相关。当外来植物侵入森林群落时,可能受到群落中其它植物竞争的影响。该文通过移植尾叶桉(Eucalyptus urophylla)、大叶相思(Acacia auriculaeformis)两种外来种和本地种荷木(Schima superba)幼苗,挖沟排除根竞争和砍树创造林窗来排除地上竞争的野外实验,研究植物竞争对幼苗生长的影响。有根竞争时,荷木、尾叶桉和大叶相思幼苗的生物量和净初级生产力均小于没有根竞争时,可见地下根竞争对3种幼苗生长有抑制性影响。尾叶桉、大叶相思和荷木3种幼苗受到的总竞争强度分别是0.357 9、0.338 3和0.198 9,受到的地下根竞争强度则分别是0.104 3、0.053 04和0.118 8,受到的地上竞争强度则分别是0.285 1、0.277 0和0.090 85。尾叶桉和大叶相思两种幼苗受到的总竞争强度间的差异不显著,但都显著大于荷木;3种幼苗受到的地上竞争强度间的差异同总竞争强度情况相似;尾叶桉和荷木两种幼苗受到的地下根竞争强度间的差异不显著,但都显著大于大叶相思。地上竞争对阳性树种尾叶桉和大叶相思两种幼苗的生长影响大,而地下根竞争则对耐阴性强的荷木幼苗影响大。尾叶桉和大叶相思两种外来种幼苗受到的总竞争强度均大于本地种荷木幼苗,这反映了这两种外来树种侵入次生林这样的群落受到竞争影响大。     

The impact of two non-native plant species on native flora performance: potential implications for habitat restoration

Both Impatiens glandulifera and Fallopia japonica are highly invasive plant species that have detrimental impacts on native biodiversity in areas where they invade and form dense monocultures. Both species are weakly dependent on arbuscular mycorrhizal fungi (AMF) for their growth and, therefore, under monotypic stands, the AMF network can become depauperate. We evaluated the impact of I. glandulifera and F. japonica on the performance (expressed as shoot biomass) of three UK native species (Plantago lanceolata, Lotus corniculatus and Trifolium pratense) grown in soil collected from under stands of both invasive plants and compared to plants grown in soil from under stands of the corresponding native vegetation. All native species had a higher percentage colonisation of AMF when grown in uninvaded soil compared to the corresponding invaded soil. P. lanceolata and L. corniculatus had a higher biomass when grown in uninvaded soil compared to corresponding invaded soil indicating an indirect impact from the non-native species. However, for T. pratense there was no difference in biomass between soil types related to I. glandulifera, suggesting that the species is more reliant on rhizobial bacteria. We conclude that simply managing invasive populations of non-native species that are weakly, or non-dependent, on AMF is inadequate for habitat restoration as native plant colonisation and establishment may be hindered by the depleted levels of AMF in the soil below invaded monocultures. We suggest that the reintroduction of native plants to promote AMF proliferation should be incorporated into future management plans for habitats degraded by non-native plant species.     

Impact of invasion of Acer platanoides on canopy structure and understory seedling growth in a hardwood forest in North America

Invasion by exotic plant species is known to affect native communities and ecosystems, but the mechanisms of the impacts are much less understood. In a field study, we examined the effects of a tree invader, Acer platanoides (Norway maple, NM), on canopy structure and seedling growth in the understory of a North American deciduous forest. The experimental site contains a monospecific patch of A. platanoides and a mixed patch of A. platanoides with its native congener, A. rubrum (red maple, RM). In the study, we examined canopy characteristics of three types of trees in the forests, i.e., RM trees in the mixed forest, NM trees in the mixed forest, and NM trees in its monospecific patch. Height growth and biomass production of RM and NM seedlings under intact canopies and newly created gaps of the three types of trees were followed for two growing seasons. We found that removal of half of the canopy from focal trees increased canopy openness and light transmission to the forest floor, but to a greater extent under NM trees than under RM trees. Seedlings of these two Acer species varied greatly in biomass production under canopies of the same type of trees and in their responses to canopy opening. For example, seedlings of the exotic NM grown under the native RM trees in the mixed forests increased biomass production by 102.4% compared to NM seedlings grown under conspecific trees. The native RM seedlings grown under NM trees, however, reduced biomass production by 23.5% compared to those grown under conspecific trees. It was also observed that RM was much more responsive in biomass production to canopy opening than NM. For instance, total seedling biomass increased by 632.2% in RM, but by only 134.6% in NM in response to the newly created gaps. In addition, we found that NM seedlings allocated a greater portion of biomass below-ground as canopy openness increased, whereas the same trend was not observed in RM seedlings. Our results thus demonstrated that invasion of NM significantly altered canopy structure and community dynamics in the hardwood forest. Because the exotic NM seedlings are able to grow well under the native RM trees, but not vice versa, NM will likely expand its distribution in the forests and make it an ever increasingly serious tree invader in its non-native habitats, including North America.     

Interspecific competition induces asymmetrical rooting profile adjustments in shrub-encroached open oak woodlands

It is recognized that the extent of woody encroachment is increasing worldwide, but less is known concerning the likely altered below-ground structure of co-occurring plants. The aim of this study was to analyze the root system plasticity of three layers of vegetation growing together (trees, shrubs and pasture) and identify potential mechanisms of competition avoidance. Root morphology and distribution of trees, pasture and two contrasting shrub species (deep and shallow rooted) were studied in open oak woodlands of south-western Spain. Soil samples were obtained from paired adjacent plots, with and without shrubs, by taking soil cores to a depth of 3 m. Analysis of tree and pasture root systems in the presence of shrubs revealed significant reductions in root biomass and consistent increases in specific root length. Additionally, root profiles changed substantially, becoming significantly deeper for trees and shallower for pasture. In contrast, both types of shrub increased their root biomass when growing in competition, but without significantly modifying their rooting profile. Shrubs seem to be stronger competitors for below-ground resources than neighboring species. However, trees and pasture show clear plastic responses to shrub presence, irrespective of their rooting patterns, probably to minimize competitive interactions and maximize resource acquisition.     

Does proximity to mature trees influence ectomycorrhizal fungus communities of Douglas-fir seedlings?

The influence of mature trees on colonization of Douglas-fir (Pseudotsuga menziesii) seedlings by ectomycorrhizal fungi (EMF) is not well understood. Here, the EMF communities of seedlings planted near and far from trees are compared with each other, with EMF of seedlings potted in field soils and with EMF of mature trees. Seedlings were planted within 6 m, or beyond 16 m, from residual Douglas-fir trees in recently harvested green-tree retention units in Washington State, USA, or potted in soils gathered from near each residual tree. Mature tree roots were sampled by partly excavating the root system. The EMF communities were assessed by polymerase chain reaction-restriction fragment length polymorphism and sequence analysis of ribosomal RNA genes. Seedlings near trees had higher species richness and diversity of EMF communities compared with seedlings far from trees. The EMF communities of seedlings near trees were more similar to those of mature trees, while seedlings far from trees were more similar to glasshouse seedlings. By enhancing the EMF diversity of seedlings, residual trees may maintain or accelerate the re-establishment of mycorrhizal communities associated with mature forests.     

Role of mycorrhizal networks and tree proximity in ectomycorrhizal colonization of planted seedlings

The importance of mycorrhizal network (MN)-mediated colonization under field conditions between trees and seedlings was investigated. We also determined the combined influences of inoculum source and distance from trees on the ectomycorrhizal (EM) community of seedlings. On six sites, we established trenched plots around 24 residual Pseudotsuga menziesii var. glauca trees and then planted seedlings at four distances (0.5, 1.0, 2.5, and 5.0 m) from the tree into four mesh treatments that served to restrict inoculum access (i.e., planted into mesh bags with 0.5, 35, 250 μm pores or directly into soil). Ectomycorrhizal communities were identified after two growing seasons using morphological and molecular techniques. Mesh treatments had no effect on seedling mycorrhizal colonization, richness, or diversity, suggesting that MN-mediated colonization, was not an essential mechanism by which EM communities were perpetuated to seedlings. Instead, wind-borne and soil inoculum played an important role in seedling colonization. The potential for MNs to form in these forests was not dismissed, however, because trees and seedlings shared 83 % of the abundant EM. Seedlings furthest from trees had a simpler EM community composition and reduced EM richness and diversity compared to seedlings in closer proximity.     

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.