Subordinate Plant Research Articles

Invasion alters plant and mycorrhizal communities in an alpine tussock grassland.

Plant invasions are impacting alpine zones, altering key mutualisms that affect ecosystem functions. Plant-mycorrhizal associations are sensitive to invasion, but previous studies have been limited in the types of mycorrhizas examined. Consequently, little is known about how invaders that host rarer types of mycorrhizas may affect community and ecosystem properties. We studied invasion by an ericoid mycorrhizal host plant (Calluna vulgaris L., heather) in alpine tussock grasslands in New Zealand. We investigate the effects of increasing C. vulgaris density on the plant and soil microbial community and on mycorrhization in the dominant native species (Chionochloa rubra Z., red tussock), an arbuscular mycorrhizal host. We show that variation in plant community composition was primarily driven by invader density. High invader densities were associated with reductions in C. rubra diameter and in the cover, richness and diversity of the subordinate plant community. Belowground, we show that higher invader densities were associated with lower rates of mycorrhization in C. rubra and higher proportional abundance of the fungal lipid biomarker 18:2ω6 but had little effect on total microbial biomass, which may suggest increased ericoid mycorrhizal and fine root biomass in high C. vulgaris density stands. Our data suggest that disruption of native plant-arbuscular mycorrhizal networks may contribute to the competitive success of C. vulgaris, and that the dramatic decline of C. rubra with invasion reflects its relatively high mycorrhizal dependence. By exploring invasion of a plant with a less common mycorrhizal type, our study expands knowledge of the ecosystem consequences of biological invasions.

A Link between Species Abundance and Plant Strategies for Semi-Natural Dry Grasslands.

Due of the potential of species to determine ecosystem properties, it is important to understand how species abundance influences community assembly. Using vegetation surveys on 35 dry grasslands in north-east Slovenia, we defined dominant (8) and subordinate (61) plant species. They were compared on 14 traits to test for differences in community-weighted mean (CWM) and functional diversity (FD). We found that dominants and subordinates differed strongly in their functional traits. Dominants showed higher leaf dry matter content and a more pronounced stress tolerance strategy and were all clonal with a large proportion of species with rhizomes and a rich bud bank, while other species showed a higher specific leaf area, a longer flowering period and more ruderals. For most traits, FD was higher in subordinates. Our results suggest that dominants drive community structure by limited susceptibility to non-competitive processes. Dominants may have positive effects on subordinates by mitigating environmental stressors. Subordinates are able to assemble together by being dissimilar and use different fine-scale niches that are engineered and homogenised by dominants. Our results show that there are fundamental differences in the relative importance of ecological processes between dominant and subordinate plants in species-rich grasslands, which is also important for their conservational management.

Development of an output management model for a branch of an engineering corporation

The model of output control in a corporation, carried out by its top manager (Chief), is considered. The head of the branch of the corporation (Head) controls the subordinate plant headed by the Director. A corporation’s branch output is affected by random external influences. The Head knows exactly the maximum possible volume of outsourcing production at the branch level. But he does not know the maximum possible volume of production (potential) in the plant. The Adviser helps the Head to eliminate this uncertainty. For his part, the Director knows exactly plant’s potential. At the same time, the Chief does not know this potential, nor the possibilities of outsourcing. Thus, the Head can manipulate branch output to influence the decisions of the Chief in order to increase his own promotion. Therefore, the Chief needs to learn how to control the Head in order to maximize branch output. Similarly, the Director can manipulate plant’s output to influence the Head’s decisions about his own denomination. Therefore, the Head needs to control the Director in order to increase plant’s output. A complex control mechanism has been found, in which total branch output is maximal. The use of such a mechanism is illustrated by the example of the modernization of freight railway platforms.

Contrasting nitrogen cycling between herbaceous wetland and terrestrial ecosystems inferred from plant and soil nitrogen isotopes across China

Abstract Understanding nitrogen (N) cycling in different ecosystems is crucial to predicting and mitigating the global effects of altered N inputs. Although wetlands have always been assumed to differ largely from terrestrial ecosystems in N cycling, evidence from direct comparison from the field along wide environmental gradients is lacking. Here, we hypothesized strong coupling of plant and soil δ15N in terrestrial ecosystems due to lower N inputs and losses but weak coupling of plant and soil δ15N in wetlands because of higher N inputs and losses. We performed a large‐scale field investigation on 26 pairs of herbaceous wetland and terrestrial sites across China covering 21 degrees of latitude and determined natural abundance of nitrogen isotopes (δ15N) in soils and leaves of 346 dominant and subordinate plant species. We analysed the relationships between leaf and soil δ15N and their drivers including plant functional types in these two types of ecosystems. Plant functional types including mycorrhizal type and N2‐fixing status had consistently significant influences on leaf δ15N in herbaceous wetland and terrestrial ecosystems. Leaf δ15N increased significantly with soil δ15N within and across mycorrhizal types in both ecosystems, and, as hypothesized, the relationships were stronger and steeper in terrestrial than in wetland ecosystems. Moreover, leaf and soil δ15N were positively and significantly correlated within both N2‐fixers and non‐N2‐fixers in terrestrial ecosystems and within only non‐N2‐fixers in wetlands. At the community level, we also found more highly significant relationships between leaf and soil δ15N in terrestrial than in wetland ecosystems. Besides plant functional types, climatic and soil factors contributed to the variation in leaf δ15N in both ecosystems. Synthesis. Weaker relationships between plant and soil δ15N in wetlands at species and community levels support the hypothesis that larger N inputs and losses lead to weaker coupling in the plant–soil systems in wetlands than in terrestrial ecosystems. This provides strong evidence from a large spatial scale for contrasting N cycling in these two types of ecosystems regardless of plant functional type in terms of nutrient uptake strategy. Our findings add to our predictive power of ecosystem N dynamics under environmental changes, for example, land‐use changes and elevated N inputs.

Frenemy at the gate: Invasion by Pheidole megacephala facilitates a competitively subordinate plant ant in Kenya

Biological invasions can lead to the reassembly of communities and understanding and predicting the impacts of exotic species on community structure and functioning are a key challenge in ecology. We investigated the impact of a predatory species of invasive ant, Pheidole megacephala, on the structure and function of a foundational mutualism between Acacia drepanolobium and its associated acacia-ant community in an East African savanna. Invasion by P. megacephala was associated with the extirpation of three extrafloral nectar-dependent Crematogaster acacia ant species and strong increases in the abundance of a competitively subordinate and locally rare acacia ant species, Tetraponera penzigi, which does not depend on host plant nectar. Using a combination of long-term monitoring of invasion dynamics, observations and experiments, we demonstrate that P. megacephala directly and indirectly facilitates T. penzigi by reducing the abundance of T. penzigi's competitors (Crematogaster spp.), imposing recruitment limitation on these competitors, and generating a landscape of low-reward host plants that favor colonization and establishment by the strongly dispersing T. penzigi. Seasonal variation in use of host plants by P. megacephala may further increase the persistence of T. penzigi colonies in invaded habitat. The persistence of the T. penzigi-A. drepanolobium symbiosis in invaded areas afforded host plants some protection against herbivory by elephants (Loxodonta africana), a key browser that reduces tree cover. However, elephant damage on T. penzigi-occupied trees was higher in invaded than in uninvaded areas, likely owing to reduced T. penzigi colony size in invaded habitats. Our results reveal the mechanisms underlying the disruption of this mutualism and suggest that P. megacephala invasion may drive long-term declines in tree cover, despite the partial persistence of the ant-acacia symbiosis in invaded areas.

Mycorrhizal fungi maintain plant community stability by mitigating the negative effects of nitrogen deposition on subordinate species in Central Asia

AbstractQuestionsPlant community stability is threatened by increasing numbers of simultaneously changing factors such as increased precipitation and nitrogen (N) deposition. Despite the pivotal roles of arbuscular mycorrhizal fungi (AMF) for plant community dynamics, only few studies have paid attention to their roles in maintaining plant community stability under global change. We therefore assessed the interactive effects of a realistic N deposition and AMF on plant community temporal stability under future increased precipitation scenarios.LocationGurbantunggut desert, China.MethodsWe conducted a four‐year field experiment simulating a realistic N deposition and with/without AMF treatments in one typical ephemeral plant community, dynamically monitoring the changes in plant community biomass and composition.ResultsWe found that suppression of AMF significantly reduced Shannon–Wiener diversity and evenness while the realistic N deposition only marginally reduced the Shannon–Wiener diversity. Suppression of AMF and increased N deposition highly increased the species turnover. Particularly, the stability of subordinate plant species significantly correlated to the community‐level stability. AMF were able to buffer the negative effects of increased N deposition on plant community diversity, to maintain community‐level stability.ConclusionsOur study supports the subordinate insurance hypothesis, highlighting the considerable roles of subordinate plant species in maintaining community stability. Furthermore, our results indicate the joint roles of AMF and N deposition in regulating plant community stability, and point to the importance of taking AMF and the realistic N deposition into account for understanding the responses of community stability to multiple global change scenarios.

Along with intraspecific functional trait variation, individual performance is key to resolving community assembly processes

Abstract Species contributing high proportions to community biomass strongly influence ecosystem processes within the community. Studies have shown that dominant species may serve as nurse plants, helping to ensure biomass stability of the subordinate species under stress conditions. The question is widely debated as to whether either niche differentiation or neutral processes drive the net outcome of plant interactions within a subordinate plant community. To answer this question, requires precise estimates of individual variation in functional traits and performance. In a 5‐year mesocosm experiment, the functional responses of a subordinate plant community to the removal of the dominant species were evaluated across two drought‐stress scenarios. Small‐scale (i.e. large pots) wetland communities were constructed comprising one dominant species Carex elata and three subordinate species. Removal of the dominant species allowed evaluation of the net effects of drought and interspecific interactions. We estimated the functional divergences for three traits (SLA, leaf dry matter content and allocation to height growth) and compared these with performance differences quantified individually. This enabled distinctions to be made between deterministic (i.e. niche differentiation) and neutral processes driving the drought response of the subordinate community. We showed that the dominant species decreased relative performance differences within the subordinate plant community under conditions of permanent drought stress. These changes were associated with the convergence of traits related to resource acquisition and growth. The dominant species equalized species performance differences by supressing relatively drought‐tolerant species with low competitive ability and by supporting the less drought‐tolerant species with relatively high competitive ability. Meanwhile, under conditions of inter‐annual drought, the subordinate species likely coexisted due to differentiation in resource‐use strategies and the interaction with the dominant species. Inclusion of individual variation in performance with a functional trait approach provides valuable insights into the processes structuring plant communities. Ours is the first study to provide evidence that subordinate species exposed to drought may coexist via neutral processes arising from their interactions with the dominant species, leading to functional convergence of traits associated with the trade‐off between stress tolerance and competitive ability. A free Plain Language Summary can be found within the Supporting Information of this article.

Six-year removal of co-dominant grasses alleviated competitive pressure on subdominant grasses but dominant shrub removal had neutral effects in a subalpine ecosystem

The ‘stress-gradient hypothesis’ predicts increasing facilitative interactions with increasing environmental stress, but it remains unclear if the prevailing type of interaction (i.e. facilitative or competitive) between dominant and subordinate plant species occurring in harsh environments is dependent on the plant functional type. In addition, most plant-species removal experiments in grasslands are short-term (1–2 years), which may imprecisely reflect transient effects arising from methodological limitations. We conducted a dominant species removal experiment in a subalpine ecosystem, containing a mosaic of grass-dominated and shrub-dominated community patches, both of which are common in the subalpine zone of the Qinghai-Tibetan Plateau. We examined the direction and magnitude of the effects of three co-dominant grass and a dominant shrub species on subordinate species richness and biomass over a 6-year period. Removal of the dominant grass species alleviated their competitive pressure on subdominant grasses, which resulted in similar total and grass biomass detected in the final year of the study. By contrast, shrub removal showed no effects on its subordinate species biomass. Furthermore, neither the removal of the dominant shrubs nor the grasses altered their respective subordinate species richness. Thus, in subalpine ecosystems that experience harsh environmental conditions, our results showed that the direction of interactive effects of dominant plant species on subordinate species may be dependent on the plant functional type and are not necessarily facilitative. Furthermore, we showed that longer-term plant-removal experiment observations may be required to better determine the effects of species removal for this subalpine and other montane ecosystem(s).

Optimal solutions for an automatic control system for medium capacity power supply facilities using renewable energy sources

Introduction: extensive logistics costs (including long distance transportation and high fuel prices) and a high cost of electric energy, generated by diesel power plants, are the main problem of power supply to consumers by off-grid power systems. The author unlocks the potential of hybrid power systems using renewable energy sources and saving expensive fuel. The author offers the analysis of automatic control systems capable of improving the efficiency of subordinate power plant elements.Methods: the author provides a classification of wind-diesel power plants and describes their performance pro rata to the share of wind energy consumption. The author has also compiled a set of specifications applicable to the technological solutions of wind-driven power plants. He also formulates the principles underlying an intelligent automatic control system for off-grid power supply facilities. This system served as the basis for a software and hardware module designed and developed for an intelligent power conversion/control/distribution system. The author provides diagrams of (1) electrical circuits of a software and hardware module for an intelligent power conversion/control/distribution system, and (2) the operation of an off-grid power supply package using renewable energy sources and controlled by the power conversion/control/distribution system. The author analyzes the primary and secondary sources of power in an off-grid power supply facility and describes principles of their operation within a software and hardware module.Results and discussions: the author offers a methodology of intelligent control over off-grid power supply facilities within the framework of the project for development of a wind-diesel power plant in thevillage ofAmderma. The author describes the results of incorporation of a wind-diesel power plant into the power supply facility operating in the permafrost environment of the Arctic region.Conclusion: presently,Russia has pre-conditions in place capable of boosting the development of power supply technologies using hybrid facilities comprising renewable energy sources. The implementation of such off-grid power supply facilities, controlled by newly designed software and hardware modules designated for an intelligent power conversion/ control/distribution system optimizes electric power generation and consumption modes and substantially reduces fuel consumption by diesel power plants.

Separating effects of soil microorganisms and nematodes on plant community dynamics

AimsSoil food webs include multiple groups of organisms that each can favor or repress particular plant species in a plant community. This study explores how microbes and nematodes alter the temporal dynamics of specific plant species and functional groups (i.e. grasses and forbs) in mixed grassland communities.MethodsWe extracted communities of nematodes and microorganisms from natural grassland soil and inoculated them, separately and in combination, into containers filled with sterilized grassland soil to examine how these groups of soil organisms influence the compositional dynamics of a diverse grassland plant community consisting of 12 species.ResultsAddition of soil microorganisms altered the composition of the plant community by enhancing forb species and promoting evenness, but these effects took time to develop and became significant only 6 months after inoculation. Addition of soil nematodes showed faster effects and reduced plant community evenness via suppressing several subordinate plant species. The nematode community was dominated by root-feeding nematodes that were less abundant when microorganisms were present, indicating a potential inhibitory effect of microorganisms on plant-feeding nematodes.ConclusionsOur results show that soil microorganisms and nematodes may differ in the magnitude and direction of their effects on the compositional dynamics of plant communities in natural grasslands, and that these effects may operate at different timespans. This study highlights the complexity of plant-soil biotic interactions and the importance to explore these interactions at multiple temporal scales.

Phylogenetic, functional, and taxonomic richness have both positive and negative effects on ecosystem multifunctionality.

Biodiversity encompasses multiple attributes such as the richness and abundance of species (taxonomic diversity), the presence of different evolutionary lineages (phylogenetic diversity), and the variety of growth forms and resource use strategies (functional diversity). These biodiversity attributes do not necessarily relate to each other and may have contrasting effects on ecosystem functioning. However, how they simultaneously influence the provision of multiple ecosystem functions related to carbon, nitrogen, and phosphorus cycling (multifunctionality) remains unknown. We evaluated the effects of the taxonomic, phylogenetic, and functional attributes of dominant (mass ratio effects) and subordinate (richness effect) plant species on the multifunctionality of 123 drylands from six continents. Our results highlight the importance of the phylogenetic and functional attributes of subordinate species as key drivers of multifunctionality. In addition to a higher taxonomic richness, we found that simultaneously increasing the richness of early diverging lineages and the functional redundancy between species increased multifunctionality. In contrast, the richness of most recent evolutionary lineages and the functional and phylogenetic attributes of dominant plant species (mass ratio effects) were weakly correlated with multifunctionality. However, they were important drivers of individual nutrient cycles. By identifying which biodiversity attributes contribute the most to multifunctionality, our results can guide restoration efforts aiming to maximize either multifunctionality or particular nutrient cycles, a critical step to combat dryland desertification worldwide.

Competition for microsites during recruitment in semiarid annual plant communities.

The concept of microsites for recruitment is central to plant ecology, but it is unclear whether these sites are abstract constructs or real entities. I hypothesize that, in generally microsite-limited communities, microsites comprise a limiting physical resource for which different species compete. I tested this hypothesis on winter-annual communities on biocrust in the semiarid Northern Negev of Israel, in which most species are microsite-limited, while the dominant grass (Stipa capensis) has overcome this limitation by efficient microsite acquisition and a lack of secondary seed dormancy. I tested whether the dominant suppresses the subordinate species, collectively, during recruitment, rather than during growth. To this end, I conducted a field experiment with three blocks of six plots (6m×6m) with two treatments - mowing in spring 2006 (intershrub, intershrub+shrub patches, and none) and shrub-patch removal (0% or 50% of the patches). I collected data from four seed traps per plot before spring 2007 and from five plant samples per plot at the end of spring. Mowing significantly reduced both seed and plant density of the dominant species, reflecting seed-limited recruitment, and increased subordinate plant density by competitive release. Multiple regressions of per-plant and per-gram effects and responses showed that competition was a direct effect of the dominant's density. Total and per-group biomass was proportional to density, implying density-independent per capita growth. Subordinate species number also increased with their density, due to the sample-size effect. These findings indicate that the seed-limited dominant diffusely suppresses the subordinates during recruitment, supporting the microsite competition hypothesis. The shift from growth resources to microsites extends the role of inter-specific competition along productivity and disturbance gradients, and highlights the asymmetric relationship between the two kinds of competition, as microsite competition is only observable if initial abundances are not overshadowed by density-dependent growth and mortality. The findings also demonstrate that (1) lacking secondary seed dormancy is an evolutionarily stable strategy in dryland annuals, alongside seed dormancy in microsite-limited species, and (2) biomass removal (e.g., by herbivory) increases small-scale biodiversity, enhancing the sustainability of dryland grazing, but without compensatory growth.

The balance of canopy and soil effects determines intraspecific differences in foundation species’ effects on associated plants

Abstract The impact of plant–plant interactions on species diversity patterns has been broadly addressed in stressful environments, such as alpine ecosystems, where foundation species promote species richness by creating habitat for other species. However, foundation species with contrasting phenotypes might modify the microhabitat differently, which would alter the subordinate community composition, and coincide with distinct feedback effects of those subordinate species on the foundation species. However, the precise interaction mechanisms that facilitate species are not fully understood, especially the relative contribution of above‐ and below‐ground compartments of foundation species to subordinate species and the potential feedbacks they receive. We explored whether two contrasted canopy phenotypes (tight and loose) of the shrub Cytisus galianoi differed in their effects on the microhabitat and on subordinate plant community composition in a dry subalpine system. We also experimentally distinguished the relative contribution of above‐ (canopy) and below‐ground (soil) effects of C. galianoi on the most frequent subordinate species, Festuca indigesta, as well as the reciprocal effects of F. indigesta on C. galianoi. We performed observational and manipulative experiments to assess the influence of phenotypic differences of the shrub on understorey microhabitat and subordinate plant community composition. Reciprocal effects were assessed by removing either F. indigesta from the understorey of the two shrub phenotypes or the C. galianoi canopy from the immediate vicinity of F. indigesta. The two C. galianoi phenotypes differed in mean values of functional traits (like stem density or plant height), modified their understorey microhabitats differently and hosted distinct subordinate communities. Loose phenotypes had more positive effects on community composition and diversity than tight phenotypes. In addition, tight phenotypes simultaneously showed both more positive above‐ground and more negative below‐ground effects on F. indigesta than loose phenotypes. There were no significant feedback effects of F. indigesta on C. galianoi. The two phenotypes of the foundation species C. galianoi showed contrasting effects on the subordinate plant community: Compared to the tight phenotype, the loose phenotype had higher associated species diversity and reduced reciprocal interaction intensities above‐ and below‐ground with the subordinate species F. indigesta. This highlights the impact of phenotypic variation for plant interactions and community‐level diversity. A plain language summary is available for this article.

Plant endophytes and arbuscular mycorrhizal fungi alter plant competition

AbstractIn nature, grasses simultaneously establish multiple symbiotic associations with endophytic fungi and arbuscular mycorrhizal fungi (AMF). The effect of these multiple interactions on competitive interactions between plants remains poorly understood.In this study, we tested whether endophytes andAMF(Glomus mosseaeorGlomus etunicatum) alter plant competition between a subordinate plant species that associates with both symbionts (Achnatherum sibiricum) and a dominant plant species,Stipa grandis, that only associates with one symbiont (AMF). And we hypothesized that endophytes can facilitate the coexistence of the subordinate plant species (A. sibiricum) and the dominant plant species (S. grandis).The results demonstrated that endophyte infection significantly enhanced the competitive ability of the subordinate plant species compared to the dominant plant species. The effects ofAMFon plant competition were variable and depended on the identity of theAMFspecies.Glomus etunicatumgaveA. sibiricumplants a higher competitive ability, whileG. mosseaegaveS. grandisa higher competitive ability. Simultaneous infections of both endophytes andAMFinA. sibiricumalso altered the competitive relationships withS. grandis.In conclusion, these results suggest that endophytic fungi can facilitate the coexistence of a subordinate plant species with a dominant plant species. Moreover, endophytes could not only affect the competitive ability of the host plant directly but also indirectly by interacting with differentAMFto change the growth of competing plant species.Aplain language summaryis available for this article.

Herbivory and presence of a dominant competitor interactively affect salt marsh plant diversity

AbstractQuestionDo herbivory and the presence of a dominant grass competitor interactively affect herbaceous communities and assembly rules in a SW Atlantic salt marsh?LocationUpper salt marsh, Mar Chiquita coastal lagoon, Argentina.MethodsWe performed a field factorial experiment over 4 yr to evaluate the separate and interactive effects of (1) herbivory and (2) competition with the dominant grass species (i.e. Spartina densiflora) on the salt marsh subordinate plant community. The factorial design includes dominant grass removal and herbivory manipulation.ResultsOur results show that herbivory and presence of the dominant competitor interactively affect subordinate plant cover and diversity. Results further indicate that, in the presence of the dominant competitor, patch‐to‐patch variation in subordinate species composition is lower than expected at random, a result consistent with the expected outcomes of deterministic exclusion following light competition. Removal of the dominant grass nevertheless led to patch‐to‐patch dissimilarity in subordinate species composition, far from the dissimilarity expected at random, indicating increased importance of deterministic processes that drive communities to diverge.ConclusionOur results show that the conditional effect of herbivory on plant diversity can be determined by the presence of a single plant species. Dominant plant species, in addition, may not only affect plant species diversity by determining the number and identity of subordinate species in a given patch (i.e. α‐diversity) but also by affecting spatial variability through habitat homogenization.

Stress and subsidy effects of seagrass wrack duration, frequency, and magnitude on salt marsh community structure.

Environmental perturbations can strongly affect community processes and ecosystem functions by acting primarily as a subsidy that increases productivity, a stress that decreases productivity, or both, with the predominant effect potentially shifting from subsidy to stress as the overall intensity of the perturbation increases. While perturbations are often considered along a single axis of intensity, they consist of multiple components (e.g., magnitude, frequency, and duration) that may not have equivalent stress and/or subsidy effects. Thus, different combinations of perturbation components may elicit community and ecosystem responses that differ in strength and/or direction (i.e., stress or subsidy) even if they reflect a similar overall perturbation intensity. To assess the independent and interactive effects of perturbation components, we experimentally manipulated the magnitude, frequency, and duration of wrack deposition, a common stress-subsidy in a variety of coastal systems. The effects of wrack perturbation on salt marsh community and ecosystem properties were assessed both in the short-term (at the end of a 12-week experimental manipulation) and long-term (6 months after the end of the experiment). In the short-term, plants and associated benthic invertebrates exhibited primarily stress-based responses to wrack perturbation. The extent of these stress effects on density of the dominant plant Spartina alterniflora, total plant percent cover, invertebrate abundance, and sediment oxygen availability were largely determined by perturbation duration. Yet, higher nitrogen content of Spartina, which indicates a subsidy effect of wrack, was influenced primarily by perturbation magnitude in the short-term. In the longer term, perturbation magnitude determined the extent of both stress and subsidy effects of wrack perturbation, with lower subordinate plant percent cover and snail density, and higher Spartina nitrogen content in high wrack biomass treatments. However, stress effects on the marsh community were generally less pronounced 6 months after the wrack perturbation, indicating capacity for recovery. Our results demonstrate that individual perturbation components can determine the degree to which its effects on the community elicit primarily stress- and/or subsidy-based responses. Further, the nature and extent of stress-subsidy effects can change over time, depending on species' relative ability to tolerate and/or recover from perturbation.

Differential effects of dominant and subordinate plant species on the establishment success of target species in a grassland restoration experiment

AbstractQuestionsWe investigated how the establishment of sown target species for ecological restoration is affected by the early introduction of either dominant or subordinate species during the assembly of a restored topsoil‐stripped, nutrient‐poor grassland. Do dominant or subordinate species exert different priority effects on either wanted target species or unwanted pioneer species? If priority effects are detected, are these exerted via niche preemption or niche modification mechanisms? Are the resulting patterns of species establishment related to differences in functional trait composition?LocationMeerdaal forest, Oud‐Heverlee, Belgium.MethodsA 2‐yr field experiment on a topsoil‐stripped site of 8.5 ha was carried out. We manipulated the early arrival of dominant and subordinate species. The ‘dominant species’ set consisted of three generalist grass species, and the ‘subordinate species’ set consisted of nine species of forbs and graminoids that often occur in nutrient‐poor grasslands. After 4 wk, we sowed nine target species for ecological restoration. We recorded plant species cover during 2 yr. We used repeated measures ANOVA to test for effects of time (2013, 2014) and treatment (dominant, subordinate and control) on plant species richness, evenness, cover, functional diversity and species and trait composition dissimilarity.ResultsBoth dominant and subordinate species successfully suppressed undesirable early colonizing species. Dominants did not exert priority effects on target species. However, subordinate species exerted strong priority effects via niche preemption, and suppressed their establishment of target species.ConclusionsManipulating the arrival order of dominant species has potential as a restoration tool that can allow restoration practitioners to enhance the establishment success of target species for restoration. We suggest that seed mixtures for restoration should contain dominant species, because they will not affect the establishment of subordinate (target) species, but will impede the establishment of unwanted pioneer and ruderal species. We also demonstrate that implementing trait‐based measures in restoration projects can help to adequately predict assembly processes.

Using priority effects to manipulate competitive relationships in restoration

AbstractRestoration success is often hampered by the failure of less dominant competitors to establish. An emerging literature on priority effects suggests the manipulation of community assembly as a useful technique to help overcome these difficulties by altering competitive relationships. We present data from a set of four priority experiments, carried out at each of three sites in restoration settings in California grasslands. These data, combined with patterns summarized from the literature, indicate that both short‐term priority (1–3 weeks) and long‐term priority (1 year) can profoundly shift interspecific relationships and benefit otherwise subordinate plant species, but that these effects are sometimes transitory, asymmetric, and contingent on environmental conditions and species composition. Restoration interventions that can produce priority effects include staggered planting times, weed control, seed pre‐germination, plug planting, and spatial aggregation. Such interventions are likely to be at least initially effective, but their strength and persistence can differ considerably across systems in space and time. Further research may help identify the conditions that maximize the strength and persistence of priority effects in restoration settings.

Subordinate plant species moderate drought effects on earthworm communities in grasslands

Loss of plant diversity resulting from forecasted drought events is likely to alter soil functioning and affect earthworm communities. Plant-soil interactions are expected to play an important role in mediating climate change effects on soil decomposers. In this study, we test above-belowground linkages after drought by focusing on the effects of subordinate plant species on earthworm communities. Using a combination of subordinate species removal and experimental drought, we show that subordinate species, when present, increased in biomass after drought and induced an increase in total earthworm biomass. These effects were thought to be associated with the maintenance of food quantity and quality (e.g. nitrogen-rich litter) in relation to subordinate species. In support to this hypothesis, we found a positive correlation between the abundance of juvenile earthworms and plant community biomass hence litter quantity, and between the total biomass of earthworms and the abundance of subordinate species. Anecic earthworms were the most benefited by the presence of subordinate species under drought, especially Lumbricus terrestris, which was significantly correlated to the biomass of the nitrogen-rich subordinate species Veronica chamaedrys. Results of a multiple factor analysis (MFA) also highlighted positive associations between earthworm and subordinate species, independently of the drought treatment. Our study highlights how climate change, in this case reduced summer rainfall, can influence plant functional groups, with cascading effects on earthworms. It is therefore crucial, considering forecasted climate change, to understand these processes in order to better predict ecosystem responses and to adapt grassland management.

Contribution of co-occurring shrub species to community richness and phylogenetic diversity along an environmental gradient

In alpine environments facilitator species buffer environmental extremes while building up soil resources above that of open areas. These modulating effects are critical for the persistence of species out of their optimal range and contribute to increase community-level plant species richness and phylogenetic diversity. We analyzed the effects of seven potential facilitator species with contrasting morphologies on subordinate plant species along a crossed environmental gradient, linking such effects to canopy effects. We also used these patches consisting of multiple shrub species to evaluate the effects of the whole shrub community on species richness and phylogenetic diversity, and whether such shrub community effects differed along the gradient. We used ecological and phylogenetic data of alpine plant communities along two altitudinal gradients on opposing aspects of the Sierra Nevada Mountains (Spain). As expected, shrubs buffered harsh abiotic conditions by decreasing mean temperatures and increasing relative humidity with regard to open areas. Composition of subordinate plant communities differed among shrubs and among sites, and correlated with relative humidity along the gradient pointing to the dependence of subordinate species on micro-environments created by shrubs. There were a variety of shrub effects on overall plant abundance and richness depending on shrub identity. In the most extreme sites we recorded generally positive effects of the shrub community, which promoted whole-community species richness and phylogenetic diversity despite species-specific effects ranging from clearly negative to positive. Our data therefore show that the effect of different shrub species on plant community richness and phylogenetic diversity is not redundant, as every shrub species may host unique communities, thereby affecting the structure and composition of the whole community.