Diversity Of Natural Communities Research Articles

Microplastics and cadmium affect invasion success by altering complementarity and selection effects in native community

The diversity-invasibility hypothesis predicts that native plant communities with high biodiversity should be more resistant to invasion than low biodiversity communities. However, observational studies have found that there is often a positive relationship between native community diversity and invasibility. Pollutants were not tested for their potential to cause this positive relationship. Here, we established native communities with three levels of diversity (1, 2 and 4 species) and introduced an invasive plant [Symphyotrichum subulatum (Michx.) G. L. Nesom] to test the effects of different pollutant treatments (i.e., unpolluted control, microplastics (MPs) alone, cadmium (Cd) alone, and their combination) on the relationship between native community diversity and community invasibility. Our results indicate that different MPs and Cd treatments altered the invasibility of native communities, but this effect may depend on the type of pollutant. MPs single treatment reduced invasion success, and the degree of reduction increased with increasing native community diversity (Diversity 2: - 14.1 %; Diversity 4: - 63.1 %). Cd single treatment increased the aboveground biomass of invasive plants (+ 40.2 %) and invasion success. The presence of MPs inhibited the contribution of Cd to invasion success. Furthermore, we found that the complementarity and selection effects of the native community were negatively correlated with invasion success, and their relative contributions to invasion success also depended on the pollutant type. We found new evidence of how pollutants affect the relationship between native community diversity and habitat invasibility, which provides new perspectives for understanding and managing biological invasions in the context of environmental pollution. This may contribute to promoting the conservation of biodiversity, especially in ecologically sensitive and polluted areas.

High immigration rates critical for establishing emigration-driven diversity in microbial communities

Unraveling the mechanisms governing the diversity of ecological communities is a central goal in ecology. Although microbial dispersal constitutes an important ecological process, the effect of dispersal on microbial diversity is poorly understood. Here, we sought to fill this gap by combining a generalized Lotka-Volterra model with experimental investigations. Our model showed that emigration increases the diversity of the community when the immigration rate crosses a defined threshold, which we identified as Ineutral. We also found that at high immigration rates, emigration weakens the relative abundance of fast-growing species and thus enhances the mass effect and increases the diversity. We experimentally confirmed this finding using co-cultures of 20 bacterial strains isolated from the soil. Our model further showed that Ineutral decreases with the increase of species pool size, growth rate, and interspecies interaction. Our work deepens the understanding of the effects of dispersal on the diversity of natural communities.

Soil nutrient limitation and natural enemies promote the establishment of alien species in native communities.

The invasion of alien plant species threatens the composition and diversity of native communities. However, the invasiveness of alien plants and the resilience of native communities are dependent on the interactions between biotic and abiotic factors, such as natural enemies and nutrient availability. In our study, we simulated the invasion of nine invasive plant species into native plant communities using two levels of nutrient availability and suppression of natural enemies. We evaluated the effect of biotic and abiotic factors on the response of alien target species and the resistance of native communities to invasion. The results showed that the presence of enemies (enemy release) increased the biomass proportion of alien plants while decreasing that of native communities in the absence of nutrient addition. Furthermore, we also found that the negative effect of enemy suppression on the evenness of the native community and the root-to-shoot ratio of alien target species was greatest under nutrient addition. Therefore, nutrient-poor and natural enemies might promote the invasive success of alien species in native communities, whereas nutrient addition and enemy suppression can better enhance the resistance of native plant communities to invasion.

Testing the links between bird diversity, alien species and disturbance within a human‐modified landscape

Introduced alien species are associated with lower taxonomic, functional and phylogenetic diversity of native communities and negative impacts on ecosystem functioning. This is particularly evident in habitats where human disturbance may favour alien species, posing an additional stressor on native communities. Following the community resistance hypothesis (higher diversity promotes higher resistance to invasion), we predicted: 1) higher taxonomic, functional and phylogenetic diversity (TD, FD and PD respectively) in non‐invaded bird communities (i.e. no alien bird species); and 2) higher diversity and resistance to invasion in less human‐disturbed areas. We surveyed bird communities in a modified Mediterranean landscape subject to varying levels of human disturbance. We tested whether TD, FD and PD were significantly different between non‐invaded and invaded bird communities, and assessed the effect of land classes (forest, agriculture, urban), landscape composition and heterogeneity on these metrics. We found that non‐invaded communities retained higher TD and FD, but not PD, than invaded communities. Alien birds occupied marginal niches in invaded communities, and did not fully compensate for the taxonomic and functional diversity loss caused by the absence of native species. These results were consistent across different land classes, suggesting weak environmental filtering of communities. Generally, less human‐modified and more heterogeneous areas supported higher TD regardless of the presence of alien species. FD and PD of invaded communities decreased with increases in human‐modified areas, whereas non‐invaded communities were not affected. Our results suggest that even within a human‐modified landscape, invaded community diversity is more affected by, and thus has a lower resilience to, disturbance. Restoring and protecting natural habitats within human‐modified landscapes is likely to increase the resilience of native species.

Herbivore and native plant diversity synergistically resist alien plant invasion regardless of nutrient conditions

Alien plant invasion success can be inhibited by two key biotic factors: native herbivores and plant diversity. However, few studies have experimentally tested whether these factors interact to synergistically resist invasion success, especially factoring in changing global environments (e.g. nutrient enrichment). Here we tested how the synergy between native herbivores and plant diversity affects alien plant invasion success in various nutrient conditions. For this purpose, we exposed alien plant species in pot-mesocosms to different levels of native plant diversity (4 vs. 8 species), native generalist herbivores, and high and low soil nutrient levels. We found that generalist herbivores preferred alien plants to native plants, inhibiting invasion success in a native community. This inhibition was amplified by highly diverse native communities. Further, the amplified effect between herbivory and native plant diversity was independent of nutrient conditions. Our results suggest that a higher diversity of native communities can strengthen the resistance of native generalist herbivores to alien plant invasions by enhancing herbivory tolerance. The synergistic effect remains in force in nutrient-enriched habitats that are always invaded by alien plant species. Our results shed light on the effective control of plant invasions using multi-trophic means, even in the face of future global changes.

Macroscale analyses suggest invasive plant impacts depend more on the composition of invading plants than on environmental context

AbstractAimNative biodiversity is threatened by the spread of non‐native invasive species. Many studies demonstrate that invasions reduce local biodiversity but we lack an understanding of how impacts vary across environments at the macroscale. Using ~11,500 vegetation surveys from ecosystems across the United States, we quantified how the relationship between non‐native plant cover and native plant diversity varied across different compositions of invading plants (measured by non‐native plant richness and evenness) and environmental contexts (measured by productivity and human activity).LocationContinental United States.Time PeriodSurveys from 1990s‐present.Major Taxa StudiedTerrestrial plant communities.MethodsWe fit mixed effects models to understand how native plant richness, diversity and evenness varied with non‐native cover. We tested how this relationship varied when non‐native cover interacted with non‐native plant richness and evenness, and with productivity and human activity.ResultsAcross the United States, communities with greater cover of non‐native plants had lower native plant richness and diversity but higher evenness, suggesting rare native plants can be lost while dominant plants decline in abundance. The relationship between non‐native cover and native community diversity varied with non‐native plant richness and evenness but was not associated with productivity and human activity. Negative associations were strongest in areas with low non‐native richness and evenness, characterizing plant communities that were invaded by a dominant non‐native plant.Main ConclusionsNon‐native plant cover provides a first approximation of invasion impacts on native community diversity, but the magnitude of impact depended on non‐native plant richness and evenness. Relationships between non‐native cover and native diversity were consistent in strength across continental scale gradients of productivity and human activity. Therefore, at the macroscale, invasive plant impacts on native plant communities likely depend more on the characteristics of the invading plants, that is the presence of a dominant invader, than on the environmental context.

Assessing the mechanisms and impacts of shrub invasion in forests: A meta‐analysis

Abstract The encroachment of invasive shrubs in forest understories can have detrimental effects on native plant recruitment. As a result, removal of invasive species is a common practice although long‐lasting success is rare. In order to effectively conserve and manage invaded forests, it is crucial to understand the mechanisms that drive shrub invasion, that is, high propagule pressure, low native resistance and exploitation of empty niches. To gain a deeper understanding of the invasion process in forest ecosystems we conducted a meta‐analysis of the work done in this topic. We collected data on invasive species and native community performance, and on the abiotic conditions of forest understories under low and high levels of shrub invasion. We analysed data from 124 articles that yielded 377 unique observations. Our results revealed that while invader performance did not vary by the mechanism of invasion, the impact on the native community was significantly detrimental when invasion occurred via low biotic resistance, and only marginally significant via propagule pressure. Invasive species performance was associated with increases in light availability, but not with other resources (soil water or nutrients). When assessing impact on native performance as a function of invasive performance, results were again only significant under the low biotic resistance mechanism. Lastly, impacts were stronger when invasion took place by a single invader. Synthesis and applications. Taken together, these results suggest that restoration efforts should focus on (i) increasing the presence of strong native competitors or functionally diverse native communities, (ii) decreasing sources of invasive shrub propagules while keeping the canopies closed when invasion occurs via high propagule pressure, (iii) avoiding management techniques that degrade or diminish canopy cover and (iv) prioritizing management of forest understories dominated by particularly impactful invasive shrubs.

Functional traits of both specific alien species and receptive community but not community diversity determined the invasion success under biotic and abiotic conditions

Abstract Biodiversity can provide some resistance to alien species in some cases, but not in others. The observed paradoxical results may be related to several reasons, including variations in abiotic and/or biotic conditions, alien species characteristics and the fact that the species number cannot adequately reflect native community diversity. A comprehensive study that incorporates these elements is lacking. We constructed invasion systems using nine alien plant species and 12 native communities, composed of two diversity levels (three vs. six species), under different nitrogen (N) and arbuscular mycorrhiza fungi (AMF) inoculation conditions. We used this fully crossed factorial experiment, that is, N (low vs. high) × native community diversity (three vs. six species) × AMF (with vs. without), to systematically explore the invasion success in native communities. We found that the species number of native community did not affect invasion success under any of the N or AMF conditions. The effects of N enrichment and AMF inoculation on invasion were not consistent between alien species and native communities based on their phenotypic plasticity of functional traits in response to N enrichment and AMF inoculation. Specifically, the changing of invasion in response to N enrichment and AMF inoculation was associated with the plasticity of plant height and root mass fraction that reflects the competitiveness for the acquisition of light and soil resources. Our results that species number did not capture well the resistance of the native community suggested that the simple expression of species richness is not realistic to describe the invasion resistance of the community. Additionally, the association between functional traits of both alien species and native communities and invasion success suggested that changes in competitive advantage and resource acquisition strategy are more important in explaining changes in invasive success in different N and AMF conditions. Future studies are needed to explore invasion success by systematically considering the characteristics of invasive species and the native community, and the specific abiotic and biotic conditions. Using functional traits may help advance our understanding of plant invasion in broad circumstances and shed light on a generalized framework of biological invasion. Read the free Plain Language Summary for this article on the Journal blog.

Mitigating buffelgrass invasion through simulated targeted grazing: understanding restoration potential in a variable precipitation regime

The potential for targeted grazing for restoration through the removal of invasive species represents an effective tool for practitioners. This study examines the impact of targeted grazing across highly variable precipitation on buffelgrass, a widely introduced African grass that often escapes cultivation. We simulated targeted grazing, overgrazing, and no grazing by clipping at two intensities and not clipping in a third treatment. We did this in plots with buffelgrass invasion and documented buffelgrass size and reproduction, as well as native plant community diversity. Additionally, as a further proxy for grazing, we tracked root allocation by buffelgrass in mowed and unmowed plots for 25 months while documenting large variability in precipitation. We found that targeted grazing reduced the negative impact of buffelgrass on the native community; on the other hand, overgrazing reduced the native community diversity. Precipitation interacted with simulated grazing such that buffelgrass subjected to grazing was less tolerant to drought and future simulated herbivory after rains returned. Long‐term targeted grazing may lead to reductions in buffelgrass that allow the restoration of the native plant community, which benefits the biodiversity of flora and fauna, and supports multiple uses of rangelands.

Interspecific facilitation favors rare species establishment and reduces performance disparities among adults

AbstractQuestionsA variety of mechanisms sustain diversity in natural communities as a result of ecological interactions between organisms. Competition has been studied extensively in the context of species maintenance, but facilitation is often conceptualized as simply reducing competition between functionally different species, which tends to decline throughout the plants' life span. Here we explore how interspecific facilitation may sustain diversity throughout the species' life by avoiding the extinction of locally rare species at juvenile stages and reducing performance disparities between neighbors of differing species at mature stages.MethodsTo do so, we measured whether rarer species relied more on facilitation than abundant ones in semiarid shrubland in southeast Spain. A mechanistic explanation of this relationship was subsequently tested by correlating rarity with the species' affinity to a particularly edaphic stressful environment. Finally, we assessed whether growing associated with neighbors in vegetation patches shaped by facilitation could balance performance disparities between species when they become adults.ResultsWe show that facilitation (i) favors the rare species, which, in addition, tend to be those with low affinity to the stressful environment, and (ii) reduces the performance dissimilarities among plants growing associated within multispecific vegetation patches compared to plants growing alone.ConclusionsThese facilitative effects, beyond the reduction of competition between functionally similar species, might ensure positive and long‐lasting effects of biotic interactions, implying a more critical role for facilitation in preserving biodiversity than previously thought.

Phagotrophic Protists Modulate Copper Resistance of the Bacterial Community in Soil.

Protist predation is a crucial biotic driver modulating bacterial populations and functional traits. Previous studies using pure cultures have demonstrated that bacteria with copper (Cu) resistance exhibited fitness advantages over Cu-sensitive bacteria under the pressure of protist predation. However, the impact of diverse natural communities of protist grazers on bacterial Cu resistance in natural environments remains unknown. Here, we characterized the communities of phagotrophic protists in long-term Cu-contaminated soils and deciphered their potential ecological impacts on bacterial Cu resistance. Long-term field Cu pollution increased the relative abundances of most of the phagotrophic lineages in Cercozoa and Amoebozoa but reduced the relative abundance of Ciliophora. After accounting for soil properties and Cu pollution, phagotrophs were consistently identified as the most important predictor of the Cu-resistant (CuR) bacterial community. Phagotrophs positively contributed to the abundance of a Cu resistance gene (copA) through influencing the cumulative relative abundance of Cu-resistant and -sensitive ecological clusters. Microcosm experiments further confirmed the promotion effect of protist predation on bacterial Cu resistance. Our results indicate that the selection by protist predation can have a strong impact on the CuR bacterial community, which broadens our understanding of the ecological function of soil phagotrophic protists.

Host phylogeny and functional traits differentiate gut microbiomes in a diverse natural community of small mammals.

Differences in the bacterial communities inhabiting mammalian gut microbiomes tend to reflect the phylogenetic relatedness of their hosts, a pattern dubbed phylosymbiosis. Although most research on this pattern has compared the gut microbiomes of host species across biomes, understanding the evolutionary and ecological processes that generate phylosymbiosis requires comparisons across phylogenetic scales and under similar ecological conditions. We analysed the gut microbiomes of 14 sympatric small mammal species in a semi-arid African savanna, hypothesizing that there would be a strong phylosymbiotic pattern associated with differences in their body sizes and diets. Consistent with phylosymbiosis, microbiome dissimilarity increased with phylogenetic distance among hosts, ranging from congeneric sets of mice and hares that did not differ significantly in microbiome composition to species from different taxonomic orders that had almost no gut bacteria in common. While phylosymbiosis was detected among just the 11 species of rodents, it was substantially weaker at this scale than in comparisons involving all 14 species together. In contrast, microbiome diversity and composition were generally more strongly correlated with body size, dietary breadth, and dietary overlap in comparisons restricted to rodents than in those including all lineages. The starkest divides in microbiome composition thus reflected the broad evolutionary divergence of hosts, regardless of body size or diet, while subtler microbiome differences reflected variation in ecologically important traits of closely related hosts. Strong phylosymbiotic patterns arose deep in the phylogeny, and ecological filters that promote functional differentiation of cooccurring host species may disrupt or obscure this pattern near the tips.

A model of algal‐virus population dynamics reveals underlying controls on material transfer

AbstractThe influence of viruses on nutrient cycles and energy transfer in aquatic systems is important, yet still being determined. We developed a dynamic model to capture the population dynamics of algal hosts and their viruses. The model was fitted to literature data of population dynamics during laboratory one‐step infection experiments. Model parameters that underlie population dynamics were quantified in diverse algal groups, covering 7 different algal classes, 14 different host genera, and 32 different virus genotypes. The hypothesis that trade‐offs exist between traits that underlie population dynamics was evaluated. We report a possible virus size‐dependent trade‐off between the rate at which viruses can initiate infection, and the efficiency of carbon transfer from hosts to viruses upon lysis. We hypothesize that slower rates of infection in large viruses, due to slower rates of molecular diffusion, are compensated by enhanced utilization of host resources. Our approach provides a quantitative trait‐framework for understanding and quantifying virus activity in diverse natural communities.

The Healthy Native Youth Implementation Toolbox: Using Implementation Mapping to adapt an online decision support system to promote culturally-relevant sexual health education for American Indian and Alaska Native youth.

American Indian and Alaska Native (AI/AN) youth experience serious disparities in sexual and reproductive health, including the highest teen birth rate among racial/ethnic groups, and disproportionate rates of sexually transmitted infections (STI), including HIV. A growing number of evidence-based programs (EBPs) that integrate the strengths and cultural teachings of Native communities exist. Yet, multiple factors, including lack of trained personnel, limited resources, and geographic isolation, may hinder their adoption and implementation. Innovative implementation strategies that facilitate the adoption and implementation of sexual health EBPs in Native communities may help reduce these disparities. We applied Implementation Mapping, a systematic planning framework that utilizes theory, empirical evidence, and community input, to adapt a theory-based, online decision support system, iCHAMPSS (CHoosing And Maintaining Effective Programs for Sex Education in Schools), to support underlying dissemination and implementation processes unique to Native communities. We used an iterative design process, incorporating input from Native practitioners and academicians, to ensure that the adapted decision support system reflects cultural identification, community values, and experiences. Grounded in diffusion of innovations, organizational stage theory, and social cognitive theory, the Healthy Native Youth Implementation Toolbox supports Native practitioners through five phases (Gather, Choose, Prepare, Implement, and Grow) to adopt, implement, and maintain a culturally-relevant, age-appropriate sexual health EBP. The Toolbox provides tools, ready-to-use templates, and guidance to plan, implement, and grow a culturally-relevant adolescent health program with their Tribe or community. Hosted within the Healthy Native Youth website (www.healthynativeyouth.org), the Toolbox comprises: (1) a curriculum portal with access to 15 culturally-relevant, age-appropriate evidence-based health promotion programs for AI/AN youth; (2) a "resource library" comprising 20+ support tools, templates, and links to external resources, and (3) "stories from the field" comprising testimonials from experienced Native educators, who have implemented sexual health programs. There is a continued need to design, test, and evaluate D&I strategies that are relevant to Native communities. The Healthy Native Youth Implementation Toolbox contributes to the dissemination and implementation of evidence-based, culturally-relevant sexual health education programs in diverse Native communities. Implementation Mapping provided a systematic approach to guide the adaptation process and integrate community voice with the ultimate goal of enhancing sexual health equity among AI/AN youth.

The effects of fire, climate, and species composition on longleaf pine stand structure and growth rates across diverse natural communities in Florida

The longleaf pine (Pinus palustris) savanna is an endangered ecosystem within a global biodiversity hotspot. However, most studies of longleaf habitats have not considered their distinct structure and function among unique communities, which are critical for developing appropriate management strategies. We aim to assess how differences in climate, fire, and species composition interact and relate to longleaf pine densities and growth rates in distinct communities. We surveyed longleaf pine stand structure (density by size and age classes) and estimated growth rates using 516 tree cores across 5 community types (69 plots, each ≤ 160 m2). Surveys covered the range of longleaf pine in Florida, USA, including the southernmost extent of the species range, and included all communities where longleaf are dominant (sandhill, upland pine, and mesic, wet, and scrubby flatwoods). We used an NMDS ordination to classify communities by species composition. We used linear mixed-effects models to examine the effect of community type on longleaf pine density and growth rates and then used recursive partitioning and regression tree analyses to identify how climate, fire, and species composition affect density and growth rates. We found that stand structure and species composition were different across communities, with upland pine being the most species rich and having the highest density of mature trees, whereas growth rates were not statistically different across communities. Across communities, unique interactions between climate, fire, and species composition, resulted in differences in stand structure and growth rates. In general, tree and grass stage densities were best predicted by species composition and fire rather than by climate, whereas growth rates were best predicted by climate. Having included the southernmost extent of longleafs range we show that longleaf growth rates increased with higher temperatures, but this effect is reversed in dry conditions. Our results suggest that longleaf growth rates across its range will be more sensitive to current and future climate change than longleaf population density. Furthermore, while controlling competition from hardwoods has been a focus of longleaf restoration, our results suggest that species that facilitate longleaf establishment may be equally important in restoring and managing these habitats. Managers should design and apply regional and community specific plans that take into account relationships between fire and associated species composition under a changing climate, which will influence strand structure and tree growth differently in different communities.

Disentangling structural and functional responses of native versus alien communities by canonical ordination analyses and variation partitioning with multiple matrices

Freshwaters are under accelerated human pressure, and mollusk communities are among its most sensitive, threatened, and valuable components. To the best of our knowledge, the overall effects of damming, environment, space, time, and invasive alien mollusk species, on structural and functional responses of native mollusk communities were not yet compared. Using historical information and recent data from a river, we aimed to investigate and disentangle these effects and evaluate the differences in structural and functional responses of natives and alien invasives to the same predictors. Variation partitioning showed that alien species were as important predictors as were environmental factors and time in explaining species composition of native freshwater mollusk communities. Aliens were more independent of environmental conditions than natives and responded to different drivers, partially explaining their invasion success. The increased abundance of some alien gastropods was positively related to taxonomic diversity, while certain alien bivalves were negatively associated with the functional diversity of native communities. We introduce a cumulative variation partitioning with multiple response (native and alien) and predictor matrices, along with a diagram to show their relations, advocating for a conceptual shift in future community ecology, from “variables to matrices” and from “multivariate analyses to multi-matrix statistical modeling”.

Prey naiveté alters the balance of consumptive and non‐consumptive predator effects and shapes trophic cascades in freshwater plankton

Predators drive trophic cascades by reducing prey biomass and altering prey traits, selecting for prey that exhibit constitutive and induced anti‐predator defenses that decrease susceptibility to consumption. These defense traits are often costly, generating a tradeoff between consumptive (CEs) and non‐consumptive predator effects (NCEs). The ecological and evolutionary experience that prey share with a given predator may determine their position along this tradeoff curve, affecting the nature and strength of top–down control of ecosystems. Conceptual models predict that predator‐experienced prey suffer greater NCEs than predator–naive prey, which suffer stronger CEs and total predator effects (CEs + NCEs), but this has not been tested in diverse prey communities. We tested these predictions by comparing the effects of predation (CEs + NCEs) and predation risk (NCEs only) of planktivorous fish on food web structure in pond mesocosms with diverse natural communities of either predator‐naive or predator‐experienced zooplankton. Contrary to expectations, top–down control of zooplankton and phytoplankton biomass was strengthened by prey community experience: in systems with experienced relative to naive zooplankton communities both predation risk (NCEs only) and predation (CEs + NCEs) had stronger effects on zooplankton prey biomass and trophic cascades were twice as strong. These results show that the ecological and evolutionary experience of diverse prey communities alters the balance of consumptive and non‐consumptive predator effects and influences trophic cascade strength.

Phenotypic plasticity of light use favors a plant invader in nitrogen-enriched ecosystems.

Eutrophication is believed to promote plant invasion, resulting in high growth performances of invasive plants and, therefore, the great potential for growth-induced intraspecific competition for light. Current hypotheses predict how eutrophication promotes plant invasion but fail to explain how great invasiveness is maintained under eutrophic conditions. In diverse native communities, co-occurring plants of varying sizes can avoid light competition by exploiting light complementarily; however, whether this mechanism applies to intraspecific competition in invasive plant populations remains unknown. Using a 2-year field nitrogen (N)-enrichment experiment on one of the global invasive plants, Spartina alterniflora, we found that the plasticity of light use reduced intraspecific competition and increased biomass production in S. alterniflora. This plasticity effect was enhanced when S. alterniflora had no nutrient limitations. In the N-enrichment treatments, the height difference among S. alterniflora ramets increased as light intensity decreased under the canopy. Compared with ambient N, under N enrichment, shorter individuals increased their light-use efficiency and specific leaf area in response to the reduced light intensity under the canopy. However, such ecophysiological plasticity was not found for taller individuals. Our findings revealed that the light-use plasticity of short individuals can be envisaged as a novel mechanism by which an invasive plant alleviates intraspecific competition and increases its invasiveness, challenging the prevailing perspective that the invasiveness of exotic plants is constrained by intraspecific competition.

Does Commercial Inoculation Promote Arbuscular Mycorrhizal Fungi Invasion?

Interventions with commercial inoculants have the potential to reduce the environmental footprint of agriculture, but their indiscriminate deployment has raised questions on the unintended consequences of microbial invasion. In the absence of explicit empirical reports on arbuscular mycorrhizal fungi (AMF) invasion, we examine the present framework used to define AMF invasion and offer perspectives on the steps needed to avoid the negative impacts of AMF invasion. Although commercial AMF isolates are potential invaders, invasions do not always constitute negative impacts on native community diversity and functions. Instead, the fates of the invading and resident communities are determined by ecological processes such as selection, drift, dispersal, and speciation. Nevertheless, we recommend strategies that reduce overdependence on introduced inoculants, such as adoption management practices that promote the diversity and richness of indigenous AMF communities, and the development of native propagules as a supplement to commercial AMF in applicable areas. Policies and regulations that monitor inoculant value chains from production to application must be put in place to check inoculant quality and composition, as well as the transport of inoculants between geographically distant regions.

Turnover of Lecanoroid Mycobionts and Their Trebouxia Photobionts Along an Elevation Gradient in Bolivia Highlights the Role of Environment in Structuring the Lichen Symbiosis.

Shifts in climate along elevation gradients structure mycobiont–photobiont associations in lichens. We obtained mycobiont (lecanoroid Lecanoraceae) and photobiont (Trebouxia alga) DNA sequences from 89 lichen thalli collected in Bolivia from a ca. 4,700 m elevation gradient encompassing diverse natural communities and environmental conditions. The molecular dataset included six mycobiont loci (ITS, nrLSU, mtSSU, RPB1, RPB2, and MCM7) and two photobiont loci (ITS, rbcL); we designed new primers to amplify Lecanoraceae RPB1 and RPB2 with a nested PCR approach. Mycobionts belonged to Lecanora s.lat., Bryonora, Myriolecis, Protoparmeliopsis, the “Lecanora” polytropa group, and the “L.” saligna group. All of these clades except for Lecanora s.lat. occurred only at high elevation. No single species of Lecanoraceae was present along the entire elevation gradient, and individual clades were restricted to a subset of the gradient. Most Lecanoraceae samples represent species which have not previously been sequenced. Trebouxia clade C, which has not previously been recorded in association with species of Lecanoraceae, predominates at low- to mid-elevation sites. Photobionts from Trebouxia clade I occur at the upper extent of mid-elevation forest and at some open, high-elevation sites, while Trebouxia clades A and S dominate open habitats at high elevation. We did not find Trebouxia clade D. Several putative new species were found in Trebouxia clades A, C, and I. These included one putative species in clade A associated with Myriolecis species growing on limestone at high elevation and a novel lineage sister to the rest of clade C associated with Lecanora on bark in low-elevation grassland. Three different kinds of photobiont switching were observed, with certain mycobiont species associating with Trebouxia from different major clades, species within a major clade, or haplotypes within a species. Lecanoraceae mycobionts and Trebouxia photobionts exhibit species turnover along the elevation gradient, but with each partner having a different elevation threshold at which the community shifts completely. A phylogenetically defined sampling of a single diverse family of lichen-forming fungi may be sufficient to document regional patterns of Trebouxia diversity and distribution.