Levels Of Plant Species Richness Research Articles

Nitrogen Addition and Heterotroph Exclusion Affected Plant Species Diversity-Biomass Relationship by Affecting Plant Functional Traits.

(1) Background: Heterotrophs can affect plant biomass and alter species diversity-productivity relationships. However, these studies were conducted in systems with a low nitrogen (N) availability, and it is unclear how heterotroph removal affects the relationship between plant species diversity and productivity in different N habitats. (2) Methods: Three typical understory herbaceous plants were selected to assemble the plant species diversity (three plant species richness levels (1, 2, and 3) and seven plant species compositions), and the control, insecticide, fungicide, and all removal treatments were performed at each plant species diversity level in systems with or without N addition treatments. (3) Results: In systems without N addition, the insecticide treatment increased the plant aboveground biomass, total biomass, and leaf area, while the fungicide treatment reduced the plant belowground biomass, root length, and root tip number; the presence of Bidens pilosa increased the plant aboveground biomass. Similarly, the presence of Bletilla striata increased the plant belowground biomass and root diameter under each heterotroph removal treatment. In systems with N addition, all removal treatments reduced the plant belowground biomass and increased the plant leaf area; the presence of B. pilosa significantly increased the plant aboveground biomass, total biomass, and root length under each heterotroph removal treatment. The presence of B. striata significantly increased the plant belowground biomass and leaf area under insecticide and fungicide treatments. (4) Conclusions: Heterotroph removal alters the plant species diversity-biomass relationship by affecting the plant functional traits in systems with different N availabilities. The impact of biodiversity at different trophic levels on ecosystem functioning should be considered under the background of global change.

Relationships between ecosystem functions vary among years and plots and are driven by plant species richness

Ecosystem management aims at providing many ecosystem services simultaneously. Such ecosystem service multifunctionality can be limited by tradeoffs and increased by synergies among the underlying ecosystem functions (EF), which need to be understood to develop targeted management. Previous studies found differences in the correlation between EFs. We hypothesised that correlations between EFs are variable even under the controlled conditions of a field experiment and that seasonal and annual variation, plant species richness, and plot identity (identity effects of plots, such as the presence and proportion of functional groups) are drivers of these correlations. We used data on 31 EFs related to plants, consumers, and physical soil properties that were measured over 5 to 19 years, up to three times per year, in a temperate grassland experiment with 80 different plots, constituting six sown plant species richness levels (1, 2, 4, 8, 16, 60 species). We found that correlations between pairs of EFs were variable, and correlations between two particular EFs could range from weak to strong or negative to positive correlations among the repeated measurements. To determine the drivers of pairwise EF correlations, the covariance between EFs was partitioned into contributions from species richness, plot identity, and time (including years and seasons). We found that most of the covariance for synergies was explained by species richness (26.5%), whereas for tradeoffs, most covariance was explained by plot identity (29.5%). Additionally, some EF pairs were more affected by differences among years and seasons, showing a higher temporal variation. Therefore, correlations between two EFs from single measurements are insufficient to draw conclusions on tradeoffs and synergies. Consequently, pairs of EFs need to be measured repeatedly under different conditions to describe their relationships with more certainty and be able to derive recommendations for the management of grasslands.

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.

The structure of root-associated fungal communities is related to the long-term effects of plant diversity on productivity.

Root-associated fungi could play a role in determining both the positive relationship between plant diversity and productivity in experimental grasslands, and its strengthening over time. This hypothesis assumes that specialized pathogenic and mutualistic fungal communities gradually assemble over time, enhancing plant growth more in species-rich than in species-poor plots. To test this hypothesis, we used high-throughput amplicon sequencing to characterize root-associated fungal communities in experimental grasslands of 1 and 15 years of age with varying levels of plant species richness. Specifically, we tested whether the relationship between fungal communities and plant richness and productivity becomes stronger with the age of the experimental plots. Our results showed that fungal diversity increased with plant diversity, but this relationship weakened rather than strengthened over the two time points. Contrastingly, fungal community composition showed increasing associations with plant diversity over time, suggesting a gradual build-up of specific fungal assemblages. Analyses of different fungal guilds showed that these changes were particularly marked in pathogenic fungi, whose shifts in relative abundance are consistent with the pathogen dilution hypothesis in diverse plant communities. Our results suggest that root-associated fungal pathogens play more specific roles in determining the diversity-productivity relationship than other root-associated plant symbionts.

Spatially explicit phylogeographical reconstruction sheds light on the history of the forest cover in the Congo Basin

AbstractAimThe impact of Pleistocene climatic oscillations on the biodiversity of African tropical rain forests remains poorly understood, and the Congo Basin is particularly understudied. We aim to elucidate how Pleistocene climatic oscillations shaped lowland tropical rain forests by investigating the intraspecific diversity and evolutionary history of a widespread tree species.LocationGuineo‐Congolian rain forest, Central Africa.TaxonStaudtia kamerunensis Warb. (Myristicaceae).MethodsWe used genome skimming combined with maximum likelihood and Bayesian inference to infer the plastid phylogeny. We estimated the time of speciation and differentiation, genetic diversity, and we employed a continuous phylogeographical approach to infer the dispersal history of its plastid lineages.ResultsWe sequenced an average of 5,827,783 reads per sample, and the reconstructed reference plastome had a mean depth of 73.3. We identified five plastid lineages that diverged during the Early or Middle Pleistocene and are parapatric, suggesting past population fragmentation. Four lineages are endemic to Lower Guinea, and one spans the Congo Basin. We found contrasting patterns of expansion in the two regions, with a rapid and recent range expansion of the Congolian lineage in the last 200,000 years, while the spread of the Lower Guinean lineages was substantially slower.Main conclusionThe contrasting demographic histories between eastern and western lineages, associated with contrasted levels of plant species richness and rates of endemism, suggest that forest cover was more stable in Lower Guinea during the Late Pleistocene than in Congolia, where the biodiversity might have been eroded before the forest re‐expanded in the Congo basin. This study illustrates how a continuous phylogeographical inference approach, mostly applied so far for inferring the spread of fast‐evolving pathogens over months or years, can provide new insights to reconstruct the dispersal history of tropical tree species over thousands or millions of years.

Effects of plant species diversity on nematode community composition and diversity in a long-term biodiversity experiment

Diversity loss has been shown to change the soil community; however, little is known about long-term consequences and underlying mechanisms. Here, we investigated how nematode communities are affected by plant species richness and whether this is driven by resource quantity or quality in 15-year-old plant communities of a long-term grassland biodiversity experiment. We extracted nematodes from 93 experimental plots differing in plant species richness, and measured above- and belowground plant biomass production and soil organic carbon concentrations (Corg) as proxies for resource quantity, as well as C/Nleaf ratio and specific root length (SRL) as proxies for resource quality. We found that nematode community composition and diversity significantly differed among plant species richness levels. This was mostly due to positive plant diversity effects on the abundance and genus richness of bacterial-feeding, omnivorous, and predatory nematodes, which benefited from higher shoot mass and soil Corg in species-rich plant communities, suggesting control via resource quantity. In contrast, plant-feeding nematodes were negatively influenced by shoot mass, probably due to higher top–down control by predators, and were positively related to SRL and C/Nleaf, indicating control via resource quality. The decrease of the grazing pressure ratio (plant feeders per root mass) with plant species richness indicated a higher accumulation of plant-feeding nematodes in species-poor plant communities. Our results, therefore, support the hypothesis that soil-borne pathogens accumulate in low-diversity communities over time, while soil mutualists (bacterial-feeding, omnivorous, predatory nematodes) increase in abundance and richness in high-diversity plant communities, which may contribute to the widely-observed positive plant diversity–productivity relationship.

Plant diversity effects on plant longevity and their relationships to population stability in experimental grasslands

Abstract Identifying to what degree inherent characteristics of plant species and their variation in response to their environment regulate the temporal stability of plant populations is important to understand patterns of species coexistence and the stability of ecosystems. Longevity is a key characteristic of plant life history and an important component of demographic storage, but age is usually unknown for herbaceous species. In a 12‐year‐old biodiversity experiment (Jena Experiment) comprising 80 grassland communities with six levels of plant species richness (1, 2, 4, 8, 16 and 60 species) and four levels of functional groups richness (1, 2, 3 and 4 functional groups), we studied populations of 38 dicotyledonous forb species (N = 1,683 plant individuals). The sampled individuals represented three plant functional groups (legumes, small herbs and tall herbs) and two different growth forms (species with long‐lived primary roots and clonal species with rhizomes/stolons). We assessed the age of plant individuals by means of growth ring analysis and related the age of plant populations to their temporal stability in terms of peak biomass production. On average, plant species richness did not affect the mean age of the populations or the maximum age of individuals found in a population. Age of herbs with taproots increased and age of herbs with clonal growth decreased with increasing species richness, cancelling out each other when growth forms were analysed together. Mean population age was lowest for small herbs and highest for tall herbs, while legumes had an intermediate population age. Herbs with a taproot were on average older than herbs with a rhizome. Across all species‐richness levels, populations with older individuals were more stable in terms of biomass production over time. Synthesis. Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species.

The invasive tree, Ailanthus altissima, impacts understory nativity, not seedbank nativity

Ailanthus altissima, the invasive forest tree commonly known as the tree-of-heaven, has been associated with decreased levels of plant species richness and native species diversity. However, this relationship with resident plants has been inconsistently found and the tree’s influence on the seedbank has yet to be studied. To further understand the long-term impact of this tree, ten paired invaded-uninvaded sites were identified in Virginia, USA in a variety of different-aged stands. The herbaceous and woody understories for each plot were inventoried and soil samples were collected and grown out for 34 weeks in a greenhouse. All plants were identified to the most detailed taxonomic level possible. In total, 35 woody understory species, 62 herbaceous understory taxa, and 77 seedbank taxa were identified. The relationship between A. altissima presence and i) the proportion of individual plants that are native, ii) the proportion of species that are native, iii) the native diversity, and iv) the nonnative diversity were analyzed. In addition, models including the invasion age were also considered. We show that A. altissima invasions were associated with a decrease in the proportion of native plants and species in the understory, but not in the seedbank. Nonnative woody diversity also increased with A. altissima presence. Additionally, the impact on the nativity of the woody understory became more extreme over time. We end by discussing the benefits of both managing A. altissima invasions early to limit its overall impact and including the management of other nonnative plants in A. altissima restoration plans.

Connectivity assessment and prioritization of urban grasslands as a helpful tool for effective management of urban ecosystem services.

Urban grasslands are usually managed as short-cut lawns and have limited biodiversity. Urban grasslands with low-intensity management are species rich and can perform numerous ecosystem services, but they are not accepted by citizens everywhere. Further, increasing and/or maintaining a relatively high level of plant species richness in an urban environment is limited by restricted plant dispersal. In this study, we examined the connectivity of urban grasslands and prioritized the grassland patches with regard to their role in connectivity in an urban landscape. We used high-resolution data from a land use system to map grassland patches in Wrocław city, Silesia, southwest Poland, Central Europe, and applied a graph theory approach to assess their connectivity and prioritization. We next constructed a model for several dispersal distance thresholds (2, 20, 44, 100, and 1000 m), reflecting plants with differing dispersal potential. Our results revealed low connectivity of urban grassland patches, especially for plants with low dispersal ability (2-20 m). The priority of patches was correlated with their area for all dispersal distance thresholds. Most of the large patches important to overall connectivity were located in urban peripheries, while in the city center, connectivity was more restricted and grassland area per capita was the lowest. The presence of a river created a corridor, allowing plants to migrate along watercourse, but it also created a barrier dividing the system. The results suggest that increasing the plant species richness in urban grasslands in the city center requires seed addition.

Plant diversity improves the effluent quality and stability of floating constructed wetlands under increased ammonium/nitrate ratio in influent

The major targets of constructed wetlands (CWs) during wastewater treatment include achieving high-quality effluent and maintaining stable effluent quality. Plant species diversity can increase nitrogen (N) removal efficiency and improve effluent quality by decreasing the effluent N concentrations, including nitrate (NO3−-N), ammonium (NH4+-N) and total inorganic nitrogen (TIN) concentrations in CWs. However, the effect of plant diversity on the stability of effluent quality in response to perturbation in the form of an increased NH4+/NO3− ratio in influent has not been studied. This study conducted a microcosm experiment and assembled four plant species richness levels (1, 2, 3 and 4) and 15 species compositions by using 90 simulated CW microcosms to investigate the effect of plant diversity on the effluent N concentrations and their stability with an increase in the influent NH4+/NO3− ratio from 0:100 to 33:67 in the later stage of the experiment. The results showed that (1) plant species richness maintained a positive effect on effluent quality under an increased influent NH4+/NO3− ratio; (2) high species richness enhanced the stability of effluent water quality; (3) the presence of Phragmites australis in the community decreased the effluent TIN concentration and improved its stability under perturbation; and (4) the presence of Typha latifolia had a positive effect on N removal efficiency under perturbation. The establishment of communities with high plant species richness and proper species (such as P. australis) could simultaneously improve the effluent quality and stability in CWs for treating wastewater with increased NH4+/NO3− ratio.

Environmental and evolutionary drivers of diversity patterns in the tea family (Theaceae s.s.) across China.

Subtropical forest is recognized as an important global vegetation type with high levels of plant species richness. However, the mechanisms underlying its diversity remain poorly understood. Here, we assessed the roles of environmental drivers and evolutionary dynamics (time‐for‐speciation and diversification rate) in shaping species richness patterns across China for a major subtropical plant group, the tea family (Theaceae s.s.) (145 species), at several taxonomic scales. To this end, we assessed the relationships between species richness, key environmental variables (minimum temperature of the coldest month, mean annual precipitation, soil pH), and phylogenetic assemblage structure (net related index) by using non‐spatial and spatial linear models. We found that species richness is significantly related to environmental variables, especially soil pH, which is negatively related to species richness both across the whole family and within the major tribe Theeae (116 species). Family‐level species richness is unrelated to phylogenetic structure, whereas species richness in tribe Theeae was related to phylogenetic structure with U‐shaped relationship, a more complex relation than predicted by the time‐for‐speciation or diversification rate hypotheses. Overall, these results suggest that both environmental and evolutionary factors play important roles in shaping species richness patterns within this subtropical plant family across China, with the latter mainly important at fine taxonomic scales. Most surprisingly, our findings show that soils can play a key role in shaping macro‐scale diversity patterns, contrary to often‐stated assumptions.

Plant diversity enhances the natural attenuation of polycyclic aromatic compounds (PAHs and oxygenated PAHs) in grassland soils

Increasing plant species richness stimulates microbial activity in soil, which might favor biodegradation of polycyclic aromatic compounds (PACs). To explore the relationship between plant community composition and PACs in grassland soils (Fluvisols exposed to an urban atmosphere), we determined the concentrations of 29 polycyclic aromatic hydrocarbons (PAHs) and 15 oxygenated PAHs (OPAHs) in topsoils of 80 plots of a grassland biodiversity experiment. The plots included different levels of plant species richness (1, 2, 4, 8, 16, 60 species) and 1–4 plant functional groups (grasses, small herbs, tall herbs, and legumes) in a randomized block design. The concentrations (ng g−1) of ∑29PAHs and ∑15OPAHs in the soils were 271–2407 and 57–329, respectively. Concentrations of 16 (out of 44) PACs and ∑29PAHs decreased significantly with increasing plant species richness, after accounting for the effects of block and initial soil organic C concentration (ANCOVA, p < 0.05). Microbial turnover as the mechanism underlying this relationship was supported by the findings that (i) the regression of the concentrations of PAH with >4 aromatic rings on plant species richness yielded slopes that were negatively correlated with their octanol-water partitioning coefficients, (ii) two OPAHs accumulated in soils with higher plant species richness, and (iii) higher plant species richness increased four OPAH/parent-PAH ratios. Accordingly, structural equation modeling indicated that the higher concentration of 1,2-acenaphthenequinone (a metabolite of acenaphthene) and the higher 1,2-acenaphthenequinone/acenaphthene and 1-indanone/fluorene ratios in plots with higher plant species richness were partly explained by higher soil microbial biomass on plots with higher plant species richness. We conclude that higher plant species richness can be used to enhance biodegradation of aged PACs in soil. We however caution that OPAHs (some of which are more toxic than their related PAHs) might accumulate in soils during such a plant-assisted remediation process.

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.

Floristic and ecological characterization of habitat types on an inselberg in Minas Gerais, southeastern Brazil

ABSTRACT Inselbergs are granitic or gneissic rock outcrops, distributed mainly in tropical and subtropical regions. They are considered terrestrial islands because of their strong spatial and ecological isolation, thus harboring a set of distinct plant communities that differ from the surrounding matrix. In Brazil, inselbergs scattered in the Atlantic Forest contain unusually high levels of plant species richness and endemism. This study aimed to inventory species of vascular plants and to describe the main habitat types found on an inselberg located in the state of Minas Gerais, in southeastern Brazil. A total of 89 species of vascular plants were recorded (belonging to 37 families), of which six were new to science. The richest family was Bromeliaceae (10 spp.), followed by Cyperaceae (seven spp.), Orchidaceae and Poaceae (six spp. each). Life forms were distributed in different proportions between habitats, which suggested distinct microenvironments on the inselberg. In general, habitats under similar environmental stress shared common species and life-form proportions. We argue that floristic inventories are still necessary for the development of conservation strategies and management of the unique vegetation on inselbergs in Brazil.

Responses of Dissimilatory Nitrate Reduction to Ammonium and Denitrification to Plant Presence, Plant Species and Species Richness in Simulated Vertical Flow Constructed Wetlands

This study investigated the effects of plant presence, plant species and their species richness on plant biomass production, pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), denitrification (DNF), dissimilatory NO3 − reduction to ammonium (DNRA) and two associated bacterial community compositions in thirty vertical flow microcosm wetlands fed with the Hoagland solution, where three plant species richness levels (i.e. unvegetated, monocultured and 4-species polycultured treatment, respectively) were established using four macrophytes. Plant presence increased DO and ORP values, as well as the terminal restriction fragment (TRF) richness and Shannon-Weaver index of the DNRA community and also improved both potential DNF and DNRA rates. The microcosms monocultured with Cyperus alternifolius exhibited the greatest DO, ORP, smallest plant biomass parameters and DNF rates among all of the monocultured microcosms, whereas the microcosms monocultured with Canna glauca and Iris pseudacorus harbored the smallest pH, DO, ORP, the greatest plant biomass parameters and DNRA rates. Compared to both unvegetated and monocultured treatments, the 4-species polycultured treatment was effective in increasing both potential DNF and DNRA rates due to the greatest plant biomass parameters as confirmed by the correlation analysis, but was ineffective in terms of changing both DNF and DNRA community compositions.

Plant species richness enhances nitrogen retention in green roof plots.

Vegetated (green) roofs have become common in many cities and are projected to continue to increase in coverage, but little is known about the ecological properties of these engineered ecosystems. In this study, we tested the biodiversity-ecosystem function hypothesis using commercially available green roof trays as replicated plots with varying levels of plant species richness (0, 1, 3, or 6 common green roof species per plot, using plants with different functional characteristics). We estimated accumulated plant biomass near the peak of the first full growing season (July 2013) and measured runoff volume after nearly every rain event from September 2012 to September 2013 (33 events) and runoff fluxes of inorganic nutrients ammonium, nitrate, and phosphate from a subset of 10 events. We found that (1) total plant biomass increased with increasing species richness, (2) green roof plots were effective at reducing storm runoff, with vegetation increasing water retention more than soil-like substrate alone, but there was no significant effect of plant species identity or richness on runoff volume, (3) green roof substrate was a significant source of phosphate, regardless of presence/absence of plants, and (4) dissolved inorganic nitrogen (DIN = nitrate + ammonium) runoff fluxes were different among plant species and decreased significantly with increasing plant species richness. The variation in N retention was positively related to variation in plant biomass. Notably, the increased biomass and N retention with species richness in this engineered ecosystem are similar to patterns observed in published studies from grasslands and other well-studied ecosystems. We suggest that more diverse plantings on vegetated roofs may enhance the retention capacity for reactive nitrogen. This is of importance for the sustained health of vegetated roof ecosystems, which over time often experience nitrogen limitation, and is also relevant for water quality in receiving waters downstream of green roofs.

Plant density can increase invertebrate postdispersal seedpredation in an experimental grassland community.

Janzen–Connell effects are negative effects on the survival of a plant's progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density‐dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species‐specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density‐dependent effects and differing preferences of consumer groups.

Quantifying the diversifying potential of conservation management systems: An evidence-based conceptual model for managing species-rich grasslands

The differential effect of main grassland management types (primarily grazing and mowing) on plant species richness has been discussed in many papers. In-depth investigations, focusing on the effects of particular management attributes (herbage removal intensity, timing, etc.) are less frequent. We propose a new, evidence-based conceptual model for quantifying the specific effects of particular management attributes on the richness and diversity of plant species. The applicability of the model was tested in Central-Hungarian species-rich meadow-steppe grasslands, characterised by different management regimes. Two management attributes involved in this study (herbage removal intensity and spatio-temporal complexity of management regime) significantly affected both the diversity and the plant species richness at a 1m2 spatial scale, whereas management type had a significant effect on species richness only. With regard to the overall variance in species richness, none of the single attributes (without combining with other ones) had considerable explanatory power; for making precise predictions, all the management attributes must have been considered. The “dichotomous effect” of grazing (i.e. both the highest and the lowest levels of plant species richness were observed at pastures) could be quantitatively explained by the model. Grazing at low or medium intensity (less than 0.5 animal unit/ha), with an annually varying rotation sequence of pasture units, led to a much higher, whereas permanent overgrazing resulted in a much lower, level of plant species richness than traditional mowing (conducted once a year during midsummer). Generalisation of the proposed model can be used to predict the potential overall effect of particular management systems on the plant species richness of other grassland types. For the potential overall effect of management, a new term has been introduced: the diversifying potential.

Mediterranean Biomes: Evolution of Their Vegetation, Floras, and Climate

Mediterranean-type ecosystems (MTEs) are located today in southwestern Australia, the Cape Region of South Africa, the Mediterranean Basin, California, and central Chile. These MTEs possess the highest levels of plant species richness in the world outside of the wet tropics. These ecosystems include a variety of vegetation structures that range from the iconic mediterranean-type shrublands to deciduous and evergreen woodlands, evergreen forests, and herblands and grasslands. Sclerophyll vegetation similar to today's mediterranean-type shrublands was already present on oligotrophic soils in the wet and humid climate of the Cretaceous, with fire-adapted Paleogene lineages in southwestern Australia and the Cape Region. The novel mediterranean-type climate (MTC) seasonality present since the middle Miocene has allowed colonization of MTEs from a regional species pool with associated diversification. Fire persistence has been a primary driving factor for speciation in four of the five regions. Understanding the regional patterns of plant species diversity among the MTEs involves complex interactions of geologic and climatic histories for each region as well as ecological factors that have promoted diversification in the Neogene and Quaternary. A critical element of species richness for many MTE lineages has been their ability to speciate and persist at fine spatial scales, with low rates of extinction.

The effects of plant diversity on nitrous oxide emissions in hydroponic microcosms

Previous studies have shown that plant diversity can improve the wastewater purification efficiency of constructed wetlands (CWs), but its effect on the nitrous oxide (N2O) emission in CWs has been unknown. To investigate the effect of plant diversity on the N2O emission, we established four plant species richness levels (each level containing 1, 2, 3 and 4 species, respectively) by using 96 hydroponic microcosms. Results showed that plant species richness enhanced the N2O emission, ranging from 27.1 to 115.4 μg N2O m−2 d−1, and improved nitrate removal (P < 0.001). The presence of Phalaris arundinacea within a given plant community increased the N2O emission (P < 0.001). The presence of Rumex japonicas had no influence on the N2O emissions (P > 0.05), but improved nitrogen removal (P < 0.001). Hence, our study highlights the importance of both plant species richness and species identity in mediating the N2O emission and nitrogen removal in CWs.