Effects Of Plant Species Richness Research Articles

Aphid biological control in arable crops via flower strips: The predominant role of food resources over diversity effects

Abstract Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. In agroecosystems, flower strips can be sown to promote biodiversity and associated services, but their plant composition is poorly considered from a functional diversity perspective so as to promote multitrophic interactions. In a field experiment, aphid biological control was compared across contrasting flower strip mixtures, over a 4‐year arable crop rotation. The effects of plants providing food resources, that is nectar and legumes supporting alternative hosts and prey, and the effects of plant species richness and functional dispersion were investigated on the biological control of aphid populations. In general, increases in the percentage of plant cover providing nectar and alternative prey (Fabaceae) to natural enemies increased predator–prey ratios and aphid parasitism and decreased aphid population growth rates. These effects however depended on the crop species. Species richness and the functional dispersion of traits involved in plant–arthropod interactions were of lesser importance, and the directions of their effects were crop‐specific. Synthesis and applications. These findings provide useful insight for designing perennial plant mixtures for creating or restoring habitats supporting aphid regulation. It is not adequate to sow any mixture containing simply flowering plants. Plant mixtures should comprise a large proportion of plant species supporting alternative prey, like legumes, and species producing nectar being easily accessible to natural enemies (corollas with nondeep nectar). To be efficient over a crop rotation, with aphids being present at different seasons, these nectar resources should be provided throughout the year thanks to a diversity of plant flowering periods.

Positive plant diversity effects on soil microbial drought resistance are linked to variation in labile carbon and microbial community structure

Abstract Biodiversity loss and drought are substantially altering both above‐ and below‐ground terrestrial ecosystem functioning, but mechanistic understanding of plant diversity effects on the drought resistance of soil microbial biomass remains limited. We designed a mesocosm experiment to examine drought resistance of soil microbial biomass along a plant species richness gradient (five plant species richness levels based on old‐field communities). We calculated resistance of microbial biomass to drought and recorded key below‐ground properties which may influence microbial resistance to drought (i.e. microbial diversity, microbial community structure, soil carbon stocks and root biomass). Plant species richness had a positive effect on microbial resistance to drought. Variation in microbial resistance to drought was linked to properties of the fungal community in ambient soil (Shannon diversity, arbuscular mycorrhizal fungal richness and abundance) but not soil bacterial diversity. Moreover, microbial resistance to drought increased with increasing root biomass and dissolved organic carbon recorded under ambient conditions. These results highlight the importance of plant diversity for microbial biomass stability in our old‐field study system with implications for biogeochemical cycling, and suggest that indirect effects of plant species richness on labile soil carbon and soil fungi may drive resistance of soil microbial biomass to drought. Read the free Plain Language Summary for this article on the Journal blog.

Conservation-relevant plant species indicate arthropod richness across trophic levels: Habitat quality is more important than habitat amount

The massive declines in terrestrial arthropods reported across Europe call for effective methods to monitor and promote biodiversity in human-dominated landscapes. Previous studies vary in their support for the suitability of plants as indicators of arthropod diversity, while the potential of subsets of conservation-relevant plant species to estimate arthropod richness remains to be tested. Moreover, the relative importance of plant species richness compared to other factors driving arthropod richness, such as land-use intensity, habitat amount and landscape configuration, is poorly understood. We conducted a multi-scale field study in Southern Germany, sampling vascular plants and terrestrial arthropods in four local land-use types (forest, grassland, arable field, settlement) across large-scale gradients of climate and land-use intensity. We obtained an extensive arthropod dataset using Malaise traps as sampling method and DNA metabarcoding for species identification. We compared the correlation of three sets of plant species richness (total, red-listed and biotope-indicator plants) with arthropod richness, including different trophic and taxonomic groups. Using mixed-effect models, we assessed the partial effects of plant species richness, habitat amount and landscape configuration on local arthropod richness while controlling for climate and land-use effects, and explored the environmental drivers of plant species richness. Arthropod species numbers of all trophic groups strongly responded to species numbers of plants that indicate protected habitats, while red-listed plant species richness was a key determinant for the richness of red-listed arthropods and butterflies. In most cases, plant species richness and temperature were stronger drivers of arthropod richness than the amount of surrounding semi-natural habitat and landscape configuration. While total plant species richness was highest in settlements, the richness of biotope-indicator plants was highest in forests and positively influenced by the amount of semi-natural habitat and edge density. The number of red-listed plant species increased with edge density at the landscape scale but was independent of habitat amount. We conclude that the richness of conservation-relevant plant species provides a powerful indicator of arthropod diversity, and underpins the potential of such plant lists for monitoring habitat quality. Our study highlights the importance of openings in forests for conservation of plants and arthropods as well as of preserving and restoring fragments of high-quality biotopes in agricultural and urban areas where the amount of semi-natural habitat is limited.

Effects of plant species richness on the structure of plant-bird interaction networks along a 3000-m elevational gradient in subtropical forests

Ecological community diversity and structure has implications for bird seed-dispersal networks that change with environmental conditions and plant species richness along elevational gradients. In this study, we examined how plant-bird interactions change with plant species richness at both the network and species level, along a 3000-m elevational gradient in a subtropical forest ecosystem. At the network level, Shannon diversity interactions (H2) decreased consistently with elevation, with a concomitant decrease in network specialization (H2′), likely due to lower plant and bird species richness at higher elevations. At the species level, the number of effective partners for both plants and birds decreased with increasing elevation, while the degree of specialization of both plants and birds on their partners increased with elevation. Specifically, we found a unimodal pattern where the effective partners of both birds and plants initially increased and then decreased with plant species richness. Furthermore, we found an inverted unimodal relationship between the degree of specialization and plant species richness, where the degree of specialization between birds and plants initially decreased and then increased with plant species richness. This study provides the first empirical evidence that changes in plant species richness with elevation can affect plant-bird interaction networks in subtropical forests.

Functional and phylogenetic relationships link predators to plant diversity via trophic and non-trophic pathways.

Human-induced biodiversity loss negatively affects ecosystem function, but the interactive effects of biodiversity change across trophic levels remain insufficiently understood. We sampled arboreal spiders and lepidopteran larvae across seasons in 2 years in a subtropical tree diversity experiment, and then disentangled the links between tree diversity and arthropod predator diversity by deconstructing the pathways among multiple components of diversity (taxonomic, phylogenetic and functional) with structural equation models. We found that herbivores were major mediators of plant species richness effects on abundance, species richness, functional and phylogenetic diversity of predators, while phylogenetic, functional and structural diversity of trees were also important mediators of this process. However, the strength and direction differed between functional, structural and phylogenetic diversity effects, indicating different underlying mechanisms for predator community assembly. Abundance and multiple diversity components of predators were consistently affected by tree functional diversity, indicating that the variation in structure and environment caused by plant functional composition might play key roles in predator community assembly. Our study highlights the importance of an integrated approach based on multiple biodiversity components in understanding the consequences of biodiversity loss in multitrophic communities.

Plant diversity and functional identity alter ant occurrence and activity in experimental grasslands

AbstractIncreasing plant species richness has been shown to positively affect the diversity of a range of other organisms, both above‐ and belowground. Although ants have a multitude of interactions with other organisms through their role as predators and mutualists, ants are a taxon that has rarely been investigated in studies of biodiversity effects. Ants are known to respond to changes in microclimatic conditions such as temperature and humidity, and these microclimatic conditions are known to be affected by vegetation characteristics such as standing biomass, which in turn can be affected by plant diversity. We investigated the effects of plant species richness (1–60), the number of plant functional groups (FGs; 1–4), and the presence of particular FGs on the occurrence and activity of ants, in the context of a grassland biodiversity experiment. Ant abundance, estimated as the mean number of workers in pitfall traps, and the number of colonies within plots, but not ant species richness, were negatively affected by plant species richness, and also by the identity of plant FGs, particularly legumes (negative effects) and grasses (positive effects). Statistical approaches showed that these effects were largely mediated by biotic (aboveground plant biomass: negative effect) and abiotic variables (soil temperature: positive effect). Notably, ant activity, measured as the mean number of workers foraging on baits and with a disproportionate dominance of a single species (Lasius niger), showed a more complex pattern, where plant species richness and number of FGs interacted to explain differential attractiveness to different resources (represented by sugar and tuna baits), likely representing current nutritional requirements for ants. Similarly, increasing soil temperature increased the level of ant activity, indicating that abiotic factors might impose thermal constraints on ectotherms inhabiting temperate grasslands. Our results indicate that a higher number of plant species and higher plant biomass had a negative effect on ants in experimental grasslands. Understanding the responses of an ecologically important group such as ants will allow us to infer the effects that biodiversity loss could have on animal‐mediated ecosystem processes.

Removing subordinate species in a biodiversity experiment to mimic observational field studies

AbstractBackgroundPositive effects of plant species richness on community biomass in biodiversity experiments are often stronger than those from observational field studies. This may be because experiments are initiated with randomly assembled species compositions whereas field communities have experienced filtering.MethodsWe compared aboveground biomass production of randomly assembled communities of 2–16 species (controls) with experimentally filtered communities from which subordinate species were removed, resulting in removal communities of 1–8 species.ResultsRemoval communities had (1) 12.6% higher biomass than control communities from which they were derived, that is, with double species richness and (2) 32.0% higher biomass than control communities of equal richness. These differences were maintained along the richness gradient. The increased productivity of removal communities was paralleled by increased species evenness and complementarity.ConclusionsResult (1) indicates that subordinate species can reduce community biomass production, suggesting a possible explanation for why the most diverse field communities sometimes do not have the highest productivity. Result (2) suggests that if a community of S species has been derived by filtering from a pool of 2S randomly chosen species it is more productive than a community derived from a pool of S randomly chosen species without filtering.

Plant diversity and soil properties regulate the microbial community of monsoon evergreen broad-leaved forest under different intensities of woodland use

A key aspect of global forest management, woodland use intensity (WUI) greatly affects the composition and diversity of soil microbial communities, thereby affecting multiple ecosystem functions and services. However, the effects of WUI on soil microbial community composition and enzymatic activities remains unclear. The effects of anthropomorphic alterations to a natural monsoon evergreen broad-leaved forest in terms of the composition and diversity of soil fungal and bacterial communities, was investigated at a site in Yunnan Province, Southwest China. Soil microbial communities were assessed under four levels of disturbance with increasing levels of WUI: (i) none, undisturbed forest (control), (ii) light, naturally-regenerated Pinus kesiya Royle ex Gordon forest, (iii) intermediate, shrub and grassland communities formed through grazing, and (iv) severe, continuously managed coffee (Coffea arabica L.) plantations. With increasing WUI, the diversity of soil fungal and bacterial communities increased, while similarities in community composition decreased for fungi but increased for bacteria. Among fungal functional guilds, ectomycorrhizal fungi decreased significantly with increasing WUI, whereas saprotrophic fungi (undefined, wood, and soil saprotrophs) increased significantly. The species richness of woody plants remarkably affected fungal functional guilds. Ectomycorrhizal fungi interacted in a synergistic manner with the fungal network structure. Significantly affecting microorganismal network structure, WUI increases led to more homogeneous networks with less integration within modules within the microbial community. The WUI strongly altered hub identity and module composition in the microbial community. According to structural equation models, WUI had direct positive effects on soil fungal community composition via its effects on plant species richness. The diversity of bacterial and fungal communities and composition of bacterial communities were jointly regulated by the indirect effects of plant species richness and soil nutrients (including enzyme activity). Deterministic processes largely determined the composition of soil fungal and bacterial communities. This study highlights the importance of maintaining the diversity of soil fungal and bacterial communities despite changes in woodland use to sustain ecosystem functions. These results can be used to develop management practices in subtropical forests and help sustain plant and soil microbial diversity at levels sufficient to maintain long-term ecosystem function and services.

Do details matter? Disentangling the processes related to plant species interactions in two grassland models of different complexity

Biogeochemical models of vegetation dynamics could potentially be used to complement empirical studies on the effect of plant species richness. A key precondition is the simulation of species coexistence. While community scale models regularly incorporate respective processes, models at the field or landscape scale used for larger scale assessments, require additional model development. However, it is unclear how the particular process description within these models affects simulations of species performance and resulting ecosystem functions.We compare simulations of two grassland models of different complexity for monocultures and two-species mixtures in a grassland experiment in Jena, Germany. By providing an in-depth analysis of the models’ process descriptions, we evaluate their ability to simulate the response of different species, their interactions and their joint performance to drought and mowing.Both models simulated similar average above-ground biomass (AGB) but showed different intra-annual variability. Generally, the models had difficulties representing a balanced species composition in multiple species mixtures and competition for space was the main driver of community composition in both models. The resulting communities were dominated by the more competitive species, while the weak competitor was only marginally present in most mixtures independent of drought and mowing. The competitive strength which we derived from the calibrated parameter sets of the species differed between the models and the agreement on which species dominate specific mixtures was mixed. While both models simulated reduced soil water content and above-ground biomass in response to drought, the strength and duration of these responses differed. Despite these differences, simulated species interactions were barely affected, and strong competitors remained dominant. Mowing had opposing effects on the competition for space in the models, which could be attributed to the different representations of plants in the two models.The models selected for the comparison are two representatives for local- and large-scale applications and use widely applied approaches for which our comparison highlighted strengths and weaknesses. To enable the investigated models (and those with similar complexity) to simulate coexistence of multiple species, niche differentiation needs to be improved. This requires a stricter separation of access to different resources and improved representation of different ecological strategies for which community scale models that are able to simulate coexistence may be an inspiration. Our approach may serve as an example for other modellers looking for ways to identify important model processes for further model development in the context of species interaction.

Gall-inducing arthropods in a Neotropical savanna area in the EPA of Rio Pandeiros (Bonito de Minas, MG, Brazil): effects of plant species richness and super-host abundance

Several plant-related factors can influence the diversity of gall-inducing species communities. In the present study we performed an inventory of gall-inducing arthropods and we tested if the plant species richness and the abundance of super-host plants (Copaifera oblongifolia) influenced positively in the diversity of gall-inducing arthropod species. The study was realized in an area of Neotropical savanna (cerrado sensu stricto) in the Environmental Protection Area (EPA) of Rio Pandeiros, Minas Gerais, Brazil. Host-plant species and gall-inducing arthropods were sampled in 18 10 × 10 m plots distributed in the vegetation. In total we found 40 arthropod gall morphotypes, distributed on 17 botanical families and 29 plant species. Cecidomyiidae (Diptera) induced the most arthropod galls (85%), and the plant family Fabaceae had the greatest richness of gall morphotypes (16). The plant species Copaifera oblongifolia and Andira humilis (Fabaceae) were the most important host species with five and three morphotypes, respectively. Galling species richness was not affected by none of explanatory variables (plant species richness and abundance of super-host plants). On the other hand, galling species per plant species was negatively affected by plant species richness and positively affected by abundance of super-host plants. This is the first study of arthropod-induced galls conducted in EPA of Rio Pandeiros, Brazil. Our results corroborate previous studies that highlight the importance of super-host plants for galling arthropod diversity on a local scale.

The biodiversity - N cycle relationship: a 15N tracer experiment with soil from plant mixtures of varying diversity to model N pool sizes and transformation rates

We conducted a 15N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity experiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH4+ and NO3− in soil solution, and exchangeable NH4+) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH4+ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO3− immobilization, adsorption of NH4+) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH4+ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH4+ pool, gross N mineralization, and NH4+ immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples.

Dilution effect of plant diversity on infectious diseases: latitudinal trend and biological context dependence

Biodiversity is thought to help regulate the impacts of disease through the dilution effect, where biodiversity among potential host species helps limit the impacts of pathogens. However, our knowledge is fragmentary about the direction and magnitude of the effects of plant species richness on disease impact. Here, we gathered data from 145 comparisons presented in 21 papers to conduct a systematic meta‐analysis on the effect of plant species richness on aboveground plant disease impact. We estimated the effect size using Pearson's correlation coefficient (r) with Fisher's z‐transformation. We evaluated how the magnitude of effect size varies between systems, including ecosystem type (grassland versus forest), pathogen taxon (virus versus fungus), study design (observational versus manipulative), parasite life history (biotroph versus necrotroph) and kinds of symptoms associated with the disease. We also tested whether there was a latitudinal trend of the effect size. We found there was a significant overall dilution effect in plant communities, but the magnitude varied among systems. Studies based on manipulative experiments and those in grassland ecosystems showed a significant dilution effect, as did both viral and fungal pathogens. Furthermore, obligate biotrophic pathogens but not necrotrophs showed a significant dilution effect. Diseases with different kinds of symptom manifestation differed, but not in a consistent pattern to the life history of the pathogens. The dilution effect was notably stronger at lower latitudes in the mid‐temperate region than at higher latitudes. This latitudinal trend existed in forest ecosystems, both observational and manipulative experiments, and necrotrophs. Dilution effects occur prevalently in plant communities, although the magnitude depends on ecosystem type, pathogen life history and kinds of symptoms associated with the disease. In conclusion, this study shows the importance of preserving the biodiversity of plants for maintaining ecosystem health.

Using digital polymerase chain reaction to characterize microbial communities in wetland mesocosm soils under different vegetation and seasonal nutrient loadings

Constructed wetlands are multi-functional systems that can effectively store and transform pollutants primarily through natural processes. However, the removal of nitrogen pollutant by wetlands is highly variable, likely due to a combination of factors such as plant species-specific assimilation behavior, the effects of soil microbial diversity, and variable nitrogen inputs. In this study, the effects of plant species richness (i.e., number of plant species in a system) and seasonal nutrient loading (i.e., nitrogen fertilization) on the microbial community responsible for regulating nitrogen turnover in wetland mesocosm soils was investigated. Digital polymerase chain reaction was used to quantify bacterial abundance. Principal component analysis was employed to identify dominant patterns within the data, and resampling-based analysis of variance was used to assess statistical significance of any observed differences caused by fertilization, season, and/or plant species richness. Results indicated that fertilization or season, which was convolved with fertilization, was the dominant factor influencing the microbial community in the study environment. The effects of plant species richness were more nuanced. Its greater richness significantly impacted the abundance of only a subset of bacterial groups (i.e., the ammonia oxidizing bacteria, Nitrospira spp. of nitrite-oxidizing bacteria, and comammox, but not the denitrifying bacteria).

Insect and plant traits drive local and landscape effects on herbivory in grassland fragments

AbstractHerbivory is one of the most important antagonistic insect–plant interactions and can be influenced by factors at local and landscape scales. Landscape fragmentation may reduce herbivory directly (i.e., decreasing abundance and species richness of herbivores), but also indirectly increase herbivory (i.e., releasing herbivores from top‐down control). At a local scale, reduced plant diversity may enhance herbivory through lessened associated resistance, while resource availability (i.e., higher vegetation height and cover) may promote herbivory. Few studies have simultaneously considered the influence of local and landscape variables on insect herbivory. We evaluate effects of landscape (fragment size, connectivity, and arable land percentage) and local factors (plant cover and height and plant species richness) on insect herbivory in fragmented calcareous grasslands. Further, we ask whether these effects depend on feeding traits of herbivores (chewers vs. suckers) and habitat specialization of plants (specialists vs. generalists). Results show that herbivory was best explained by models including variables at both local and landscape scales. However, local factors were more important than landscape variables. Herbivory was in all cases positively related to height of herbs (i.e., taller and more heterogeneous food resources), whereas the effect of plant species richness varied with feeding traits of herbivores. Herbivory by chewers, which are commonly more generalist feeders, was negatively affected by plant species richness, supporting the idea of associated plant resistance. In contrast, herbivory by suckers, which tend to be more specialized, increased with plant richness. Although there was little influence of landscape scale, herbivory on specialist plants was significantly higher in smaller grasslands probably as a consequence of herbivore release from natural enemies. Functional redundancy among herbivore species would allow to maintain overall herbivory in fragmented calcareous grasslands. This study highlights the need to consider different herbivore and plant traits for a better understanding of herbivory responses to local and landscape factors.

Soil Microbial Restoration Strategies for Promoting Climate‐Ready Prairie Ecosystems

Tractable practices for soil microbial restoration in tallgrass prairies reclaimed from agriculture are a critical gap in traditional ecological restoration. Long-term fertilization and tilling permanently alter soil bacterial and fungal communities, requiring microbe-targeted restoration methods to improve belowground ecosystem services and carbon storage in newly restored prairies. These techniques are particularly important when restoring for climate-ready ecosystems, adapted to altered temperature regimes. To approach these issues, we conducted a multi-factorial greenhouse experiment to test the effects of plant species richness, soil amendment and elevated temperature on soil microbial diversity, growth, and function. Treatments consisted of three seedlings of one plant species (Andropogon gerardii) or one seedling each of three plant species (A. gerardii, Echinacea pallida, Coreopsis lanceolata). Soil amendments included cellulose addition, inoculation with a microbial community collected from an undisturbed remnant prairie, and a control. We assessed microbial communities using extracellular enzyme assays, Illumina sequencing of the bacterial 16S rRNA gene, predicted bacterial metabolic pathways from sequence data and phospholipid fatty acid analysis (PLFA), which includes both bacterial and fungal lipid abundances. Our results indicate that addition of cellulose selects for slow-growing bacterial taxa (Verrucomicrobia) and fungi at ambient temperature. However, at elevated temperature, selection for slow-growing bacterial taxa is enhanced, while selection for fungi is lost, indicating temperature sensitivity among fungi. Cellulose addition was a more effective means of altering soil community composition than addition of microbial communities harvested from a remnant prairie. Soil water content was typically higher in the A. gerardii treatment alone, regardless of temperature, but at ambient temperature only, predicted metagenomics pathways for bacterial carbon metabolism were more abundant with A. gerardii. In summary, these results from a mesocosm test case indicate that adding cellulose to newly restored soil and increasing the abundance of C4 grasses, such as A. gerardii, can select for microbial communities adapted for slow growth and carbon storage. Further testing is required to determine if these approaches yield the same results in a field-level experiment.

Multiple plant diversity components drive consumer communities across ecosystems

Humans modify ecosystems and biodiversity worldwide, with negative consequences for ecosystem functioning. Promoting plant diversity is increasingly suggested as a mitigation strategy. However, our mechanistic understanding of how plant diversity affects the diversity of heterotrophic consumer communities remains limited. Here, we disentangle the relative importance of key components of plant diversity as drivers of herbivore, predator, and parasitoid species richness in experimental forests and grasslands. We find that plant species richness effects on consumer species richness are consistently positive and mediated by elevated structural and functional diversity of the plant communities. The importance of these diversity components differs across trophic levels and ecosystems, cautioning against ignoring the fundamental ecological complexity of biodiversity effects. Importantly, plant diversity effects on higher trophic-level species richness are in many cases mediated by modifications of consumer abundances. In light of recently reported drastic declines in insect abundances, our study identifies important pathways connecting plant diversity and consumer diversity across ecosystems.

Soil microbial restoration strategies for promoting climate-ready prairie ecosystems.

Tractable practices for soil microbial restoration in tallgrass prairies reclaimed from agriculture are a critical gap in traditional ecological restoration. Long‐term fertilization and tilling permanently alter soil bacterial and fungal communities, requiring microbe‐targeted restoration methods to improve belowground ecosystem services and carbon storage in newly restored prairies. These techniques are particularly important when restoring for climate‐ready ecosystems, adapted to altered temperature regimes. To approach these issues, we conducted a multi‐factorial greenhouse experiment to test the effects of plant species richness, soil amendment and elevated temperature on soil microbial diversity, growth, and function. Treatments consisted of three seedlings of one plant species (Andropogon gerardii) or one seedling each of three plant species (A. gerardii, Echinacea pallida, Coreopsis lanceolata). Soil amendments included cellulose addition, inoculation with a microbial community collected from an undisturbed remnant prairie, and a control. We assessed microbial communities using extracellular enzyme assays, Illumina sequencing of the bacterial 16S rRNA gene, predicted bacterial metabolic pathways from sequence data and phospholipid fatty acid analysis (PLFA), which includes both bacterial and fungal lipid abundances. Our results indicate that addition of cellulose selects for slow‐growing bacterial taxa (Verrucomicrobia) and fungi at ambient temperature. However, at elevated temperature, selection for slow‐growing bacterial taxa is enhanced, while selection for fungi is lost, indicating temperature sensitivity among fungi. Cellulose addition was a more effective means of altering soil community composition than addition of microbial communities harvested from a remnant prairie. Soil water content was typically higher in the A. gerardii treatment alone, regardless of temperature, but at ambient temperature only, predicted metagenomics pathways for bacterial carbon metabolism were more abundant with A. gerardii. In summary, these results from a mesocosm test case indicate that adding cellulose to newly restored soil and increasing the abundance of C4 grasses, such as A. gerardii, can select for microbial communities adapted for slow growth and carbon storage. Further testing is required to determine if these approaches yield the same results in a field‐level experiment.

The oxygen isotope composition of bioavailable phosphate in soil reflects the oxygen isotope composition in soil water driven by plant diversity effects on evaporation

Abstract Despite the importance of phosphorus (P) for organisms, the contributions of different processes delivering P into the bioavailable pool in soil have not yet been unraveled mainly due to methodological constraints in separating physico-/geochemical from biological processes. Stable O isotope analyses of phosphate might help to disentangle these processes and recent method improvements now allow an application in terrestrial ecosystems. Plant diversity influences not only plant P uptake but also biological P release mechanisms in soil thereby potentially affecting stable isotope ratios of bioavailable P (δ18OPi). We calculated the degree of enzyme-mediated O incorporation into phosphate, determined the contributions of different biological processes (Pi mobilization from soil organic matter, microbial P turnover), and tested for plant diversity effects on δ18O values of phosphate and of soil water as well as on the processes involved in O incorporation. We added 18O-enriched and 18O-depleted water to separated subplots of 27 study sites differing in plant species richness and plant functional group composition. δ18O values of phosphate and soil water were measured before and six days after labeling. We calculated mixing models based on isotope fractionation published so far. The O incorporation factor a reflecting the proportional incorporation of O atoms from labeled water into phosphate molecules under field conditions averaged 0.33 (0.15–0.70). δ18O values of bioavailable phosphate indicated microbial P processing i.e., turnover and subsequent release of P in soil. Plant species richness was related to δ18O values of soil water via evaporation. Because of the complete exchange of O atoms in a phosphate molecule with ambient water during microbial P turnover in soil, plant species richness effects were also visible in δ18O values of bioavailable phosphate. In conclusion, our approach yielded new insights into the role of microorganisms in supplying bioavailable P. For the first time we could show that plant-community induced microclimate shapes δ18O values of bioavailable phosphate in soil indirectly by affecting δ18O values of soil water with which phosphate exchanges O. Therefore, stable O isotope analyses in phosphate represent a useful tool for unraveling complex plant-soil-microorganism interactions in the P cycle.

Fungal Denitrification Activity in Vertical Flow Constructed Wetlands as Impacted by Plant Species Richness, Carbon, Nitrogen and pH Amendments.

To control potential fungal denitrification rate (PFDR) in vertical flow simulated wetlands (VFSW) microcosms, thirty VFSW microcosms were established and planted with three plant species richness levels (i.e. unplanted, monoculture, and four-species polyculture treatment), and effects of carbon, nitrogen and pH amendments on the PFDR were investigated using a room-incubating method. Among seven carbon compounds, sodium citrate, glycerol, glucose and sodium succinate were more effective in enhancing PFDRs. These enhanced effects were dependant on a given species richness level. Sodium nitrite mostly stimulated PFDRs to a greater extent than the other three nitrogen compound amendments at any richness level. Treatments with pH 5.6 or 8.4 had significantly greater PFDRs than the treatment with pH 2.8 in the three species richness levels. However, no effect of plant species richness on the PFDR was observed among any carbon, nitrogen and pH amendments. Current results suggest carbon, nitrogen and pH factors should be considered when mediating fungal denitrification in VFSW microcosms.

Are traditional home gardens in southern Ethiopia heading for extinction? Implications for productivity, plant species richness and food security

While home garden systems are acknowledged for their capacity of supporting a very dense population, the productivity of these systems and their contribution to food security and dietary diversity are poorly quantified. Although several articles document the decrease in species richness in home gardens due to processes of modernization, relatively little attention has been given to how the change in diversity impacted productivity. Five predominant home garden systems identified in a previous study were intensively monitored during 12 months within four districts of Sidama and Gedeo zones of southern Ethiopia. Data from 24 farms were collected on plant species, soil characteristics, crop inputs, field sizes and crop yields and livestock production. The productivity of enset for both food and feed was lowest in Enset-coffee home gardens. Barley and khat yielded significantly more per ha in Khat-based systems than in other ones. Maize and coffee productivity did not differ significantly between home garden types. Overall crop productivity was lowest in the traditional Enset-coffee systems (1820kgDMha−1) and highest in the newly evolved Enset-cereal-vegetable systems (3020DMkgha−1). Energy productivity from food crops was higher in Enset-based systems (43GJha−1) than in other systems whereas revenue was lowest in Enset-based systems (719US$ha−1) and highest in newly evolved Khat-based systems (6817US$ha−1). The rate of N application through compost explained 30% of the variability in kocho standing biomass. The rate of N application in inorganic fertilizer explained 43% and 25% of the variability in khat and barley yield respectively. There was no positive effect of plant species richness on total crop and energy productivity except for the revenue in enset-oriented systems. Khat-based and Enset-cereal-vegetable systems were more food secure than the traditional home gardens, and these newly evolved systems also did not lead to a loss in plant species richness. The modification of traditional home garden systems by introducing the high value cash crop khat and annual cereals in response to farmland constraints and market opportunities enabled smallholders to maintain food security and dietary diversity without jeopardizing plant species richness. With population density expected to continually increase in the region, improvement options tailored to the specific systems are required for sustainable development.