bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tree species diversity increases fine root productivity through increased soil volume filling
Authors: Brassard Brian W. , Chen Han Y. H. , Cavard Xavier , Laganière Jérôme , Reich Peter B. , Bergeron Yves , Paré David , Yuan Zhiyou 
Published: May 2013

Summary

Although fine roots (< 2 mm in diameter) account for a major share of the production of terrestrial ecosystems, diversity effects on fine root productivity and their mechanisms remain unclear.

We hypothesized that: (i) fine root productivity increases with tree species diversity, (ii) higher fine root productivity is a result of greater soil volume filling due to species‐specific patterns of root placement and proliferation, and (iii) differences in fine root productivity and soil volume filling associated with tree species diversity are more pronounced in summer when plants are physiologically active and demand for water and nutrients is at its greatest.

We investigated the effects of tree species diversity on fine root productivity and soil volume filling of boreal forest stands that have grown naturally for 85 years on similar sites.

Annual fine root production was 19–83% higher in evenly mixed‐ than single‐species‐dominated stands, and increased with tree species evenness, but not tree species richness. Fine root biomass was higher in evenly mixed‐ than single‐species‐dominated stands in summer months, but not in spring or fall. Higher fine root productivity in evenly mixed‐ than single‐species‐dominated stands was realized by filling more soil volume horizontally and vertically in the forest floor in the mixtures of deep‐ and shallow‐rooted species vs. the deeper mineral soil in the mixtures of deep‐rooted species.

Synthesis. Our results provide some of the first direct evidence for below‐ground species complementarity in heterogeneous natural forests, by demonstrating that tree species evenness increases fine root productivity by filling/exploiting the soil environment more completely in space and time, driven by differences in the inherent rooting traits of the component species and variations of root growth within species.
Novel chemical weapon of an exotic macroalga inhibits recruitment of native competitors in the invaded range
Authors: Svensson J. Robin , Nylund Göran M. , Cervin Gunnar , Toth Gunilla B. , Pavia Henrik 
Published: May 2013

Summary
Allelopathy is an important non‐resource interaction in terrestrial plant communities that may affect invasions by non‐indigenous plants. The ‘novel weapons hypothesis’ (NWH) predicts that non‐indigenous plants will become invasive if they have allelopathic compounds that assemblages in the new range are not adapted to. Recently, the non‐indigenous, chemically rich macroalga Bonnemaisonia hamifera (Hariot) has become one of the most abundant filamentous red algae in Scandinavian waters.
We used B. hamifera to specifically test the aspect of the NWH that concerns invasion success based on novel allelochemicals in the invaded range. Allelopathic interactions were tested through effects on the growth rate of adult native macroalgae in co‐cultures with B. hamifera and through the settlement success of native macroalgal propagules and microalgae on surfaces coated with 1,1,3,3‐tetrabromo‐2‐heptanone. We also investigated whether 1,1,3,3‐tetrabromo‐2‐heptanone can be transferred from B. hamifera to its native host algae, as a means of pre‐emptive competition.
The settlement of native macroalgal propagules and microalgae was strongly inhibited on surfaces coated with 1,1,3,3‐tetrabromo‐2‐heptanone at ecologically relevant concentrations, but there were no effects of adult B. hamifera on growth rates of adults of the six native naturally co‐occurring species. The compound was shown to be transferred from B. hamifera to the surface of its native host algae at inhibitory concentrations in both laboratory and field experiments.
By inhibiting the settlement of propagules on its thallus and on surrounding surfaces, B. hamifera achieves a competitive advantage over native macroalgae, a finding that parallels previous reports on soil‐ and litter‐mediated allelopathic interactions among vascular plants. Because competition for available substrata in marine benthic systems is intense, the ability to reserve space may be vital for B. hamifera's successful invasion. This is the first example of an allelopathic compound that can be transferred by direct contact from an exotic to a native species, with an active and unaltered function.
Synthesis. Our results clearly show that the main secondary metabolite of the invasive red alga B. hamifera has strong allelopathic effects towards native competitors, suggesting that its novel chemical weapon is important for the highly successful invasion of new ranges.
Hydrological consequences of declining land use and elevated CO2 in alpine grassland
Authors: Inauen Nicole , Körner Christian , Hiltbrunner Erika 
Published: May 2013

Summary

Large areas of alpine pastures and meadows currently face declining land use or abandonment, which leads to tall‐grass transition ecosystems with higher leaf area index (LAI), potentially increased evapotranspiration (ET) and thus, reduced water yield. Elevated atmospheric CO2, on the other hand, is known to reduce stomata opening and hence, leaf‐level transpiration, which may translate into higher soil moisture and enhanced total runoff. Here, we quantify these opposing effects of global change on the water balance of alpine grassland in a field experiment in the Swiss Alps (2440 m a.s.l.).

Rates of ET and deep seepage (percolation water) of four alpine grassland types (dominated by Agrostis, Nardus, Carex or forbs) were measured using intact monoliths in 51 weighing lysimeters. A part of the monoliths was clipped to simulate sheep grazing during three seasons (2008–2010). Another set was exposed to elevated CO2 (580 ppm) using free‐air CO2 enrichment (FACE) during the 2009 growing season.

Simulated grazing reduced bright day ET by on average −12% across all years, with the most pronounced effects in the high‐stature swards. Correspondingly, the higher biomass and LAI in unclipped grassland lowered the seasonal sum of deep seepage by −13% in a drier summer (2009) and by −5% in a rather wet summer (2010) compared to clipped swards.

CO2 enrichment reduced ET in all grassland types by −3 to −7%, increased δ18O in foliage and enhanced soil moisture, but not deep seepage. Hence, future CO2 slightly counteracts the land use effects at canopy level, however, not in terms of water yield.

Synthesis. Our results indicate that both grazing and elevated CO2 are mitigating the effects of dry spells on alpine vegetation. The net effect of the continuous decline in the land use and of elevated CO2 is negative for catchment water yield and thus, for potential hydroelectric power production. Although these economic ‘costs’ are rather moderate per hectare of alpine grassland, sums are substantial when scaled to the vast areas potentially affected in the Alps. These calculated ‘costs’ attribute economic value to the eco‐hydrological benefits of land care at these high elevations.
Plant functional effects on ecosystem services
Authors: Lavorel Sandra 
Published: May 2013

Summary

The prominent new place of ecosystem services in environmental policy, land management and land planning requires that the best ecological knowledge be applied to ecosystem service quantification. Given strong evidence that functional diversity underpins the delivery of key ecosystem services, assessments of these services may progress rapidly using a trait‐based approach.

The trait‐based approach shows promising results, especially for plant trait effects on primary production and some processes associated with carbon and nitrogen cycling in grasslands. However, there is a need to extend the proof of concept for a wider range of ecosystems and ecosystem services and to incorporate not only the functional characteristics of plants but those of other organisms with which plants interact for the provision of ecosystem services.

The five papers in this Special Feature illustrate how some of the key conceptual and methodological challenges can be resolved, and provide a range of case studies across three continents. Relevant plant functional traits depict different axes of variation including stature, the leaf economics spectrum, and associated or independent variations in root or stem traits. The application of the trait approach to ecosystem processes underpinned by interactions between plants and other biota is illustrated for soil micro‐organisms and granivorous invertebrates. There is strong evidence for the biomass ratio hypothesis (i.e. prevalent effects of the traits of dominant species through the community‐weighted mean), along with less prevalent and more complex effects of heterogeneous trait values between species (i.e. functional divergence).

Synthesis. Together, the five papers in this Special Feature illustrate how trait‐based approaches may help elucidate the complexity of ecological mechanisms operating in the field to determine ecosystem service delivery. To address scientific and management questions about the provision of multiple services, progress is needed in understanding how functional trade‐offs and synergies within organisms scale up to interactions between ecosystem services. Service‐oriented ecosystem management within the context of global change, or ecological restoration, remains a major challenge, but trait‐based understanding opens new avenues towards more generic, integrated approaches.
What happens when ants fail at plant defence?Cordia nodosadynamically adjusts its investment in both direct and indirect resistance traits in response to herbivore damage
Authors: Frederickson Megan E. , Ravenscraft Alison , Arcila Hernández Lina M. , Booth Gregory , Astudillo Viviana , Miller Gabriel A. 
Published: May 2013

SummaryAnts provide variable protection against herbivores to ant‐plants (i.e. myrmecophytes and myrmecophiles). The ways in which ant‐plants dynamically adjust both their direct (chemical and physical) and indirect (biotic) defences in response to varying levels of herbivory are not well understood.We experimentally generated a broad range of ant‐attendance levels and herbivory pressures in a tropical myrmecophyte,Cordia nodosa,which allowed exploration of the inducibility of and interactions between direct and indirect resistance traits.In response to increased herbivory, host plants encouraged indirect (biotic) defence by increasing domatium volume, regardless of whether ants were present on the plant. When ants were present, larger domatia housed more workers, which in turn decreased herbivory on adjacent leaves.Independent of the presence of ants, plants responded to increased herbivory by inducing both chemical (phenolics) and structural (leaf toughness, trichomes) resistance traits; these traits were associated with reduced palatability to a folivorous beetle.Synthesis. Our results show that both direct and indirect defences are inducible inC. nodosa, which suggests thatC. nodosamay retain direct defences as insurance against varying levels of protection from its ant bodyguards. Thus, the predictions of optimal defence theory are not violated: althoughC. nodosainvests in multiple forms of defence, they are not redundant.
Initial density affects biomass–density and allometric relationships in self‐thinning populations of Fagopyrum esculentum
Authors: Li Lei , Weiner Jacob , Zhou Daowei , Huang Yingxin , Sheng Lianxi 
Published: May 2013

Summary

The form and generality of the biomass–density relationship, especially during self‐thinning of crowded stands, have been intensively debated in recent years. All models of self‐thinning assume that the trajectory is independent of the initial pre‐thinning density, so populations differing in initial density can be analysed together. As plant allometry is a determinant of the self‐thinning trajectory, and competition alters plants' allometric growth, initial density may have consequences for the self‐thinning trajectory.

To ask whether initial density can influence allometric relationships and the biomass–density trajectory, we grew Fagopyrum esculentum populations at three high densities and measured shoot biomass, density and the height and diameter of individual plants at six harvests.

Initial density did not affect the slope of the log biomass–log density relationship, but there was a clear and significant effect on the intercept. Populations sown at higher densities had significantly more biomass at a given density of survivors.

If the data for all densities and harvests are analysed together, the log biomass–log density relationship is linear with a slope of −0.377, which is consistent with the predictions of Metabolic Scaling Theory. If the independent variable initial density is included as a factor, the estimated slope of the log B–log N relationship is much steeper and consistent with the classical ‘Self‐thinning Rule’.

The position of the self‐thinning trajectory is determined in part by the biomass density: the relationship between mass and volume. Initial density could affect this by altering allometric growth in a way that influences architectural compactness. An alternative hypothesis is that competition at higher initial density is more size symmetric, which has been shown to reduce growth and mortality.

Synthesis. The self‐thinning trajectory is not always independent of initial population density. Interpopulation scaling patterns, even within one species, do not reflect processes within populations, and this conflation lies behind much of the current debate about size–density relationships in plant populations and communities. Interactions among plants and allometry are more important than internal physiological scaling mechanisms in determining the self‐thinning trajectory of crowded stands.
Evolution of fast‐growing and more resistant phenotypes in introduced common mullein (Verbascum thapsus)
Authors: Kumschick Sabrina , Hufbauer Ruth A. , Alba Christina , Blumenthal Dana M. 
Published: May 2013

Summary

Species introduced into areas outside of their native range face novel biotic and abiotic conditions, which probably impose novel selection pressures. Adaptation to these new conditions may increase the ability of introduced species to establish and spread. Like many other introduced plant populations, introduced genotypes of common mullein (Verbascum thapsus) are more successful in their introduced than in their native range, with increased growth and fecundity. These differences appear to be at least partly genetically based. The most successful introduced populations also grow in an environment that is drier and has fewer competitors than native populations. It is not known, however, whether differences between native and introduced mullein populations are related to these environmental differences between ranges.

We used a common garden experiment with 23 native and 27 introduced populations of common mullein to test whether common mullein in the introduced range exhibits evolutionary shifts with respect to responses to competition, drought stress and nitrogen (N) stress. We also used choice experiments to learn whether introduced mullein is more or less resistant to a generalist herbivore than native mullein.

Without competition, introduced genotypes grew larger than native genotypes under high resource availability (control) and N stress, but not water stress. Survival, however, was increased in native populations under competition and N stress. The introduced genotypes also had a lower root:shoot ratio than the native genotypes. With competition, introduced genotypes grew larger than native genotypes across all treatments, with that difference being significant under N stress. The introduced genotypes were also more resistant to a generalist herbivore.

Synthesis: Together, high biomass, strong responses to high water availability and low root:shoot ratio suggest that mullein has evolved a fast‐growing, weedy phenotype in its introduced range rather than adapting to a low‐water environment through increased root growth. Although fast‐growing plants can be more palatable to herbivores, in this case there does not appear to be a trade‐off between growth and defence against a generalist herbivore. Mullein appears to have evolved to be both faster growing and better defended in the introduced range.
Plant apparency, an overlooked driver of associational resistance to insect herbivory
Authors: Castagneyrol Bastien , Giffard Brice , Péré Christelle , Jactel Hervé 
Published: May 2013

Summary

Herbivore regulation is one of the services provided by plant diversity in terrestrial ecosystems. It has been suggested that tree diversity decreases insect herbivory in forests, but recent studies have reported opposite patterns, indicating that tree diversity can trigger associational resistance or susceptibility. The mechanisms underlying the tree diversity–resistance relationship thus remain a matter of debate.

We assessed insect herbivory on pedunculate oak saplings (Quercus robur) in a large‐scale experiment in which we manipulated tree diversity and identity by mixing oaks, birch and pine species.

Tree diversity at the plot scale had no effect on damage due to leaf chewers, but abundance of leaf miners decreased with increasing tree diversity. The magnitude of this associational resistance increased with host dilution, consistent with the ‘resource concentration hypothesis’.

At a smaller scale, we estimated tree apparency as the difference in total height between focal oak saplings and their nearest neighbouring trees. Levels of oak infestation with leaf miners decreased significantly with decreasing tree apparency. As the probability of having taller neighbours increased with tree diversity, notably due to the increase in the proportion of faster growing nonhost trees, such as birches and pines, tree apparency may be seen as a ‘hidden’, sampling effect of tree diversity.

Synthesis. These findings suggest that greater host dilution and lower tree apparency contribute to associational resistance in young trees. They also highlight the importance of taking plant size into account as a covariate, to avoid misleading interpretations about the biodiversity–resistance relationship.
Large herbivores favour species diversity but have mixed impacts on phylogenetic community structure in an African savanna ecosystem
Authors: Yessoufou Kowiyou , Davies T. Jonathan , Maurin Olivier , Kuzmina Maria , Schaefer Hanno , van der Bank Michelle , Savolainen Vincent 
Published: May 2013

Summary

There has been much debate on the impact of large herbivores on biodiversity, especially given that large mammals are becoming locally extinct in many places.

The use of evolutionary information on community structure has typically been limited to evaluating assembly processes, for example, competition or habitat filtering, whereas a lack of long‐term experiments has precluded the test of predictions considering more complex biotic interactions.

Reconstructing the complete phylogeny of the trees and shrubs of the Kruger National Park from DNA data, we tested for phylogenetic signal in antiherbivory traits and compared the phylogenetic structure of communities under various degrees of herbivore pressure using experimental plots spanning several decades.

We show that all antiherbivory traits examined demonstrated weak but significant phylogenetic signal, and that exclusion of large herbivores results in impoverished species diversity in restructured communities. Surprisingly, we also show that reduction in species diversity coupled with community reorganization does not necessarily result in a decrease in phylogenetic diversity, and that community responses to herbivore exclusion depend on initial structure.

Synthesis. Extinction of large mammal herbivores will have cascading effects on plant diversity; however, impacts on plant community structure are contingent on initial conditions. This research has implications for best practice when managing large herbivores and natural habitats.
Uncovering multiscale effects of aridity and biotic interactions on the functional structure of Mediterranean shrublands
Authors: Gross Nicolas , Börger Luca , Soriano‐Morales Sara I. , Le Bagousse‐Pinguet Yoann , Quero José L. , García‐Gómez Miguel , Valencia‐Gómez Enrique , Maestre Fernando T. 
Published: May 2013

Summary

Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact upon plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community‐level patterns of trait divergence or convergence alone.

We used a functional trait‐based and multiscale approach to assess how biotic interactions and aridity determine the functional structure of semi‐arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation.

The shrub species surveyed can be separated along four axes of specialization based on their above‐ground architecture and leaf morphology. Our community scale analysis suggested that the functional structure of semi‐arid communities was clearly non‐random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighbourhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted on the observed changes in the functional diversity of shrubland communities along the aridity gradient.

Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multiscale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient and explained the high functional diversity observed in semi‐arid shrublands. Facilitation affected subordinate and rare species and, thus, may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic trait‐based approaches to study plant community assembly.