Effects Of Plant Species Diversity Research Articles

A controlled experiment to assess relationships between plant diversity, ecosystem function and planting treatment over a nine year period in constructed freshwater wetlands

Two fundamental questions for wetland restoration science are: how do early management practices affect long term plant species diversity, and how does diversity affect ecological function? Here, we report on a nine year study conducted in six replicate experimental wetland ecosystems designed to shed light on the impact of different planting treatments and nutrient enrichment on plant species diversity and on a variety of indicators of structure and function. Pairs of high- and low-intensity planting treatments were initiated with native seeds and vegetative propagules. In the high-intensity treatment, vegetative propagules that did not establish were replanted in years three and four. An unplanted treatment was seeded through natural recruitment alone. Annual inventories of the presence and percent cover of plant species were used to derive measures of native Shannon–Weaver diversity and the floristic quality assessment index (FQAI). We found that higher plant species diversity was achieved early and was sustained in planted versus unplanted wetlands. However, no differences were evident between high- and low-intensity planting treatments. Although the prevalence of dominant species shifted over time, overall measures of plant diversity did not change between early and later succession in either planted or unplanted treatments. We found no relationships between plant diversity and a variety of direct and indirect measures of ecosystem structure and function, including aquatic community metabolism, aboveground productivity, soil organic matter accumulation and nutrient concentration. Fertilizer was applied in years eight and nine to simulate nutrient loading from agricultural runoff. Plant species diversity had no detectable effects on nutrient uptake rates in response to fertilization. Conversely, fertilization did not measurably alter species diversity in the two years following addition. We conclude that early management efforts were important in achieving a sustained and resilient enhancement in plant species diversity, but that elevated biodiversity resulting from planting did not measurably alter function. We speculate that control of invasive species in all treatment groups during early years of management resulted in high species diversity levels in unplanted as well as planted groups and that species diversity levels in all wetlands were therefore well above levels at which effects of plant species diversity on ecosystem function saturate.

Loss of Plant Species Diversity Reduces Soil Erosion Resistance

In many estuarine areas around the world, the safety of human societies depends on the functioning of embankments (dikes) that provide protection against river floods and storm tides. Vegetation on land-side slopes protects these embankments from erosion by heavy rains or overtopping waves. We carried out a field experiment to investigate the effect of plant species diversity on soil loss through erosion on a simulated dike. The experiment included four diversity treatments (1, 2, 4, and 8 species). In the third year of the experiment, we measured net annual soil loss by measuring erosion losses every 2 weeks. We show that loss of plant species diversity reduces erosion resistance on these slopes: net annual soil loss increased twofold when diversity declines fourfold. The different plant species had strongly diverging effects on soil erosion, both in the single-species and in the multi-species plots. Analysis of the dynamics of the individual species revealed that the main mechanism explaining the strong effects of plant species diversity on soil erosion is the compensation or insurance effect, that is, the capacity of diverse communities to supply species to take over the functions of species that went extinct as a consequence of fluctuating environmental conditions. We conclude that the protection and restoration of diverse plant communities on embankments and other vegetated slopes are essential to minimize soil erosion, and can contribute to greater safety in the most densely populated areas of the world.

Biodiversity effects on nitrate concentrations in soil solution: a Bayesian model

Ecosystems are faced with high rates of species loss which has consequences for their functions and services. To assess the effects of plant species diversity on the nitrogen (N) cycle, we developed a model for monthly mean nitrate (NO3-N) concentrations in soil solution in 0–30 cm mineral soil depth using plant species and functional group richness and functional composition as drivers and assessing the effects of conversion of arable land to grassland, spatially heterogeneous soil properties, and climate. We used monthly mean NO3-N concentrations from 62 plots of a grassland plant diversity experiment from 2003 to 2006. Plant species richness (1–60) and functional group composition (1–4 functional groups: legumes, grasses, non-leguminous tall herbs, non-leguminous small herbs) were manipulated in a factorial design. Plant community composition, time since conversion from arable land to grassland, soil texture, and climate data (precipitation, soil moisture, air and soil temperature) were used to develop one general Bayesian multiple regression model for the 62 plots to allow an in-depth evaluation using the experimental design. The model simulated NO3-N concentrations with an overall Bayesian coefficient of determination of 0.48. The temporal course of NO3-N concentrations was simulated differently well for the individual plots with a maximum plot-specific Nash–Sutcliffe Efficiency of 0.57. The model shows that NO3-N concentrations decrease with species richness, but this relation reverses if more than approx. 25 % of legume species are included in the mixture. Presence of legumes increases and presence of grasses decreases NO3-N concentrations compared to mixtures containing only small and tall herbs. Altogether, our model shows that there is a strong influence of plant community composition on NO3-N concentrations.

PLANT SPECIES DIVERSITY IN RELATION TO CARBON STOCKS AT JANGKOK WATERSHED, LOMBOK ISLAND

ABSTRACT The area around Jangkok watershed has changed, dividing it into some land use systems. This research aimed to study the effect of plant species diversity on C- stocks, and to analyse the characteristics of land use system s based on their similar ity . The observations were carried out on 18 plots representing six land use systems in Jangkok watershed (Lombok Island) i.e. primary forest (PF), disturbed forest (DF), Mahogany - woodlot (MW), candlenut - agroforestry (CA), multistrata - agroforestry (MA), and simple - agroforestry (SA). The species diversity level was measured using Shannon-Weiner diversity index , while C- stocks according to the method of RaCSA ( Rapid Carbon Stock Appraisal ) . Results showed that forest conversion to agricultural land use s reduced the number and density of the species , average w ood density and tree basal area . The PF represented the highest biodiversity index (3.46), while the other land uses were categorised in medium and low. Largest C-stock was found in PF and in (30 years old) of MW average d of 500 Mg ha - 1 , while the lowest was in S A of 68 Mg ha - 1 , while in other land uses wa s 219 Mg ha - 1 . The quantity of C- stock was not related to species diversity and its density , but closely related (p of tree (R 2 =0.84), basal area of all sizes tree (R 2 =0.86), and with the basal area of big trees ( diameter > 30 cm ) (R 2 =0.71). Based on the number and species density, agroforestry system ( MA and CA ) resembled the characteristics of natural forest ( DF and PF ) . /spanEN-GBspan style=

PLANT SPECIES DIVERSITY IN RELATION TO CARBON STOCKS AT JANGKOK WATERSHED, LOMBOK ISLAND

The area around Jangkok watershed has changed, dividing it into some land use systems. This research aimed to study the effect of plant species diversity on C- stocks, and to analyse the characteristics of land use system s based on their similar ity . The observations were carried out on 18 plots representing six land use systems in Jangkok watershed (Lombok Island) i.e. primary forest (PF), disturbed forest (DF), Mahogany - woodlot (MW), candlenut - agroforestry (CA), multistrata - agroforestry (MA), and simple - agroforestry (SA). The species diversity level was measured using Shannon-Weiner diversity index , while C- stocks according to the method of RaCSA ( Rapid Carbon Stock Appraisal ) . Results showed that forest conversion to agricultural land use s reduced the number and density of the species , average w ood density and tree basal area . The PF represented the highest biodiversity index (3.46), while the other land uses were categorised in medium and low. Largest C-stock was found in PF and in (30 years old) of MW average d of 500 Mg ha - 1 , while the lowest was in S A of 68 Mg ha - 1 , while in other land uses wa s 219 Mg ha - 1 . The quantity of C- stock was not related to species diversity and its density , but closely related (p of tree (R 2 =0.84), basal area of all sizes tree (R 2 =0.86), and with the basal area of big trees ( diameter > 30 cm ) (R 2 =0.71). Based on the number and species density, agroforestry system ( MA and CA ) resembled the characteristics of natural forest ( DF and PF ) . /spanEN-GBspan style=

RESTORATION OF BIODIVERSITY AND ECOSYSTEM

Succession is one of the most studied processes in ecology and succession theory provides strong predictability. However, few attempts have been made to influence the course of succession thereby testing the hypothesis that the passage of one stage is essential to enter a next one. At each stage of succession ecosystem processes may be affected by the diversity of species present, but there is little empirical evidence showing that plant species diversity may affect succession. The main objective in the present study is to test if there is any effect of plant species diversity on the functioning of artificially-created grassland communities. We were mostly interested in how successful is the sowing of meadow species into newly abandoned land and how long do the effect of initial sowing persist, how is affected the set of natural colonizers, which includes both the weed species and also the later successional species arriving naturally into the zone. One of the main questions concerning succession is to which extent the trajectory may be predictable or not. What will be the consequence of the different succession pathways for ecosystem processes, such as productivity and resource utilization, as well as species composition of both above and belowground communities? What will be the subsequent effects of feed back to vegetation development through initial manipulation of vegetation after land abandonment? And, finally, how general may results be when obtained in specific conditions? Our hypothesis is that an increase in the initial plant species diversity at the start of secondary succession enhances the amount of biomass produced and consequently stimulates the soil microbial biomass and the abundance of soil invertebrates. It has been suggested that changes in plant species diversity affect several ecosystem processes, such as primary productivity, nutrient retention and vegetation dynamics. A positive impact of species diversity on plant productivity has been explained by the complementarity of resource use among plant species or their functional groups.

Direct and indirect bottom-up and top-down forces shape the abundance of the orb-web spider Argiope bruennichi

Species abundance in local communities is determined by bottom-up and top-down processes, which can act directly and indirectly on the focal species. Studies examining these effects simultaneously are rare. Here we explore the direct top-down and direct and indirect bottom-up forces regulating the abundance and predation success of an intermediate predator, the web-building spider Argiope bruennichi (Araneae: Araneidae). We manipulated plant diversity (2, 6, 12 or 20 sown species) in 9 wildflower strips in a region of intensive farmland. To identify the major factors regulating the distribution and abundance of A. bruennichi, we quantified three characteristics of vegetation (species diversity, composition and vegetation structure) as well as the spider's prey community and natural enemies. The distribution and abundance of A. bruennichi was regulated by combined bottom-up and top-down processes as well as by direct and indirect interactions between trophic levels. Four main factors were identified: (1) the strong direct effect of vegetation structure, (2) the positive effect of plant species diversity, which affected spider abundance directly and indirectly through increased densities and size of flower-visiting prey species, (3) the positive or negative direct effects of different plant species, and (4) the strongly negative direct effect of predacious hornets. The advantage of taking a global approach to understand the regulation of species abundance is highlighted first by the quantification of the relative importance of factors, with a surprisingly strong effect of hornet predators, and second by the discovery of a direct effect of plant diversity, which raises intriguing questions about habitat selection by this spider.

Evenness and plant species identity affect earthworm diversity and community structure in grassland soils

Diversity of plant species and the species composition (identity) are known to influence below-ground diversity. In this paper we examine the effects of plant species diversity (richness and evenness), rates of nitrogen application and planting density, on earthworm community structure in grassland. The study was carried out at three sites in Ireland using a Simplex experimental design to define the compositions of the experimental plant communities used.A negative relationship was detected between diversity (evenness) of plant species and diversity of earthworms in the soils. However, plant species identity also affected the structure of the earthworm assemblage. In particular, the legume, Trifolium repens had a strong effect but this was conditional on the rate of nitrogen application. No earthworm species favoured communities dominated by slow growing grasses (Phleum pratense and Dactylis glomerata) (P = 0.02).Higher N inputs reduced earthworm abundance and biomass under T. repens. Earthworm richness, was negatively influenced by elevated amounts of N inputs. No effect of planting density was detected but this factor also did not affect plant biomass production.

Effects of plant species diversity on soil conservation and stability in the secondary succession phases of a semihumid evergreen broadleaf forest in China

One of the most studied aspects of ecosystems in recent years has been the relationship between plant species diversity and ecosystem functions; however, the relationship with one such ecosystem function, soil conservation, has been less well studied. We established forest plots in the secondary succession phases of a semihumid evergreen broadleaf forest in China. The plots differed in plant species richness but had otherwise similar soil-erosion factors, observed surface runoff, sediment, and total phosphorus (P) loss. We analyzed the relationship between plant diversity and soil conservation and stability. Results indicated that the frequency and volume of surface runoff, sediment, and total P loss in the test plots, as well as their CV (coefficients of variation), present significant negative correlations with increasing species richness. The plot with the lowest richness in Yunnan pine, African boxwood, and running mountaingrass (Ass. Pinus yunnanensis, Myrsine africana, and Oplismenus compositus [APMO]) yielded the highest runoff rates, with runoff occurring a total of 77 times: 23, 32, and 22 times in 2001, 2002, and 2003, respectively. The average values for surface runoff, sediment, and total P loss over the three-year study period were, respectively, 960.20 m3 ha−1 y−1 (13.72 thousand ft3 ac−1 yr−1), 11.40 t ha−1 y−1 (4.54 tn ac−1 yr−1), and 127.69 kg ha−1 y−1 (113.82 lb ac−1 yr−1). The CV values for the three parameters were, respectively, 287.6, 534.21, and 315.47. However, in the plot with the highest richness in a native oak species, Evelyn keteleeria, and a species of viola (Ass. Cyclobalanopsis glaucoides, Keteleeria evelyniana, and Viola duelouxii [ACKV]), surface runoff only occurred 9 times: 2, 4, and 3 times, respectively in the three years. The average values for surface runoff, sediment, and total P loss were 75.55 m3 ha−1 y−1 (1.08 thousand ft3 ac−1 yr−1), 0.28 t ha−1 y−1 (0.11 tn ac−1 yr−1), and 4.71 kg ha−1 y−1 (4.20 lb ac−1 yr−1). The CV values for the three parameters were, respectively, 57.93, 187.94, and 59.2. Plant density increased linearly in herb, shrub, and tree layers with increasing plant species richness, whereas plant cover increased logarithmically. Plant species diversity can enhance soil conservation, but this effect was comparatively weak relative to the contributions of plant cover and density to soil conservation. Plant species diversity increases plant density and cover in the local community, indirectly regulating and enhancing soil conservation. Competition and niche theories can explain, to some extent, the increases in plant density and cover. Our results challenge the view of a negative relationship between plant species diversity and productivity.

Unique arthropod communities on different host-plant genotypes results in greater arthropod diversity

Studies on the effect of plant-species diversity on various ecological processes has led to the study of the effects of plant-genetic diversity in the context of community genetics. Arthropod diversity can increase with plant-species or plant-genetic diversity (Wimp et al. in Ecol Lett 7:776–780, 2004). Plant diversity effects can be difficult to separate from other ecological processes, for example, complementarity. We asked three basic questions: (1) Are arthropod communities unique on different host-plant genotypes? (2) Is arthropod diversity greater when associated with greater plant-genetic diversity? (3) Are arthropod communities more closely associated with host-plant genetics than the plant neighborhood? We studied canopy arthropods on Populus fremontii trees randomly planted in a common garden. All trees were planted in a homogeneous matrix, which helped to reduce P. fremontii neighborhood effects. One sample was comprised of few P. fremontii genotypes with many clones. A second sample was comprised of many P. fremontii genotypes with few clones. A second data set was used to examine the relationships between the arthropod community with P. fremontii genetic composition and the neighborhood composition of the focal host plant. Unique arthropod communities were associated with different P. fremontii genotypes, and arthropod community diversity was greater in the sample with greater P. fremontii genotypic diversity. Arthropod community similarity was negatively correlated with P. fremontii genetic distance, but arthropod community similarity was not related to the neighborhood of the P. fremontii host plant.

Overyielding of fine root biomass as increasing plant species richness in subtropical forests in central southern China

Aims The objectives were to compare the fine root biomass,necromass and their distributions in the soil profile and examine the effects of plant species diversity on the morphological properties of live ?ne roots at different soil depths among four forests along a gradient of increasing plant species richness in subtropical southern China.Methods The fine root samples were collected in March 2010 in four forests:coniferous monoculture(Cun-ninghamia lanceolata),coniferous pioneer species(Pinus massoniana-Lithocarpus glaber),deciduous(Choero-spondias axillaris) and evergreen broadleaved(Cyclobalanopsis glauca-Lithocarpus glaber).In each forest,three soil cores containing fine roots were taken at each of three soil depth(0-10,10-20 and 20-30 cm) at each of up-per,middle and lower slope positions.Living and dead roots were manually separated and then oven dried at 75 °C to constant mass to determine weight.Living roots were scanned with a Win-RHIZO 2005C to measure mor-phological parameters,including total root length,total root volume,number of root tips and forks.Important findings Fine root biomass tended to increase along the gradient from the plantation to evergreen broadleaved forest.Total fine root biomass within the 0-30 cm soil depth differed significantly among the forests,but there were no significant differences in living root biomass.Fine root biomass density decreased exponentially with soil depth at similar rates among the forests.With exception of the plantation,fine root biomass showed clear differences in their distribution in the soil layers,indicating significant belowground spatial niche segregation of the vertical root distribution patterns in the more species-rich stands.Differences in root biomass did not lead to significant differences in fine root morphology on a stand area basis.

Impact of litter species diversity on decomposition processes and communities of soil organisms

The effect of plant species diversity and the C/N ratio of litter on soil processes were analysed in mesocosms in a three year field experiment. Plots 0.5 × 0.5 m with a depth of 15 cm containing sand mixed with loam were used to compare five natural and one artificial litter type (polypropylene string). Natural litters were either monospecific (I: Dactylis glomerata; II: Festuca rubra and III: Trifolium pratense) or were species mixtures (IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants). Differences among treatments in the litter decomposition rate, humic acid content and nematode density depended on the litter quality (C:N ratio) in most cases. By contrast, most of the differences among treatments found in the substratum below the litter cover resulted from litter diversity. The largest increase of carbon and nitrogen amount during growing season was found under litter mixtures (IV, V) and the highest fulvic acid content under the most diverse litter (V). Similarly, the production of algae in the substratum also significantly increased with litter diversity. Higher taxonomic diversity of Nematoda and Collembola and the most mature community of nematodes were observed under the most complex litter. Epigeic macrofauna, both dwelling in and penetrating the litter, did not differ significantly between experimental treatments. However, the highest share of predators was found in the treatment with the richest plant species diversity. In general, the results suggest that the decomposition of diverse plant litter enhances humus acid accumulation in soils. It is likely that algae participate in the process of humus formation.

Weak effects of plant diversity on leaf-litter breakdown in a tropical stream

The relationship between biodiversity and ecosystem functioning is incompletely understood, particularly the relative influence of species richness and composition on functioning. We investigated the effects of plant species diversity on litter breakdown rate (a measure of functioning) and the associated detritivorous macroinvertebrates in a tropical stream in Hong Kong by using single-species and three- and four-species mixtures of leaves with contrasting breakdown rates. We hypothesised that the scarcity of shredding detritivores in Hong Kong streams would limit the scope for diversity effects attributable to differences in leaf composition. Nonetheless, breakdown rates were affected by differences in composition (constituent species within a mixture) rather than richness (number of species in a mixture). Ficus fistulosa (Moraceae) was a key species in mixtures, producing non-additive effects through acceleration of breakdown of other constituent species. There were no other positive (or any negative) non-additive effects of mixing. Leaf diversity did not affect macroinvertebrate functional organisation or taxonomic composition. Assemblages on all litter types were dominated by collector-gatherers (mainly chironomids, >70% of total abundance), and shredders were scarce (<5%). Although diversity had no obvious bottom-up influence on detritivores, non-additive effects of mixing may arise from the influence of litter quality on microbially mediated breakdown in this tropical stream.

Soil fertility increases with plant species diversity in a long-term biodiversity experiment

Most explanations for the positive effect of plant species diversity on productivity have focused on the efficiency of resource use, implicitly assuming that resource supply is constant. To test this assumption, we grew seedlings of Echinacea purpurea in soil collected beneath 10-year-old, experimental plant communities containing one, two, four, eight, or 16 native grassland species. The results of this greenhouse bioassay challenge the assumption of constant resource supply; we found that bioassay seedlings grown in soil collected from experimental communities containing 16 plant species produced 70% more biomass than seedlings grown in soil collected beneath monocultures. This increase was likely attributable to greater soil N availability, which had increased in higher diversity communities over the 10-year-duration of the experiment. In a distinction akin to the selection/complementarity partition commonly made in studies of diversity and productivity, we further determined whether the additive effects of functional groups or the interactive effects of functional groups explained the increase in fertility with diversity. The increase in bioassay seedling biomass with diversity was largely explained by a concomitant increase in N-fixer, C4 grass, forb, and C3 grass biomass with diversity, suggesting that the additive effects of these four functional groups at higher diversity contributed to enhance N availability and retention. Nevertheless, diversity still explained a significant amount of the residual variation in bioassay seedling biomass after functional group biomass was included in a multiple regression, suggesting that interactions also increased fertility in diverse communities. Our results suggest a mechanism, the fertility effect, by which increased plant species diversity may increase community productivity over time by increasing the supply of nutrients via both greater inputs and greater retention.

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

Current and expected changes in biodiversity have motivated major experiments, which reported a positive relationship between plant species diversity and primary production. As a first step in addressing this relationship, these manipulative experiments controlled as many potential confounding covariables as possible and assembled artificial ecosystems for the purpose of the experiments. As a new step in this endeavor, we asked how plant species richness relates to productivity in a natural ecosystem. Here, we report on an experiment conducted in a natural ecosystem in the Patagonian steppe, in which we assessed the biodiversity effect on primary production. Using a plant species diversity gradient generated by removing species while maintaining constant biomass, we found that aboveground net primary production increased with the number of plant species. We also found that the biodiversity effect was larger in natural than in artificial ecosystems. This result supports previous findings and also suggests that the effect of biodiversity in natural ecosystems may be much larger than currently thought.

Interaction of Plant Species Diversity on Grazing Behavior and Performance of Livestock Grazing Temperate Region Pastures

ABSTRACTThe importance of plant species diversity on performance of livestock grazing temperate region pastures is summarized in this review. As livestock producers seek less capital‐intensive production systems, emphasis is redirected toward low‐input pasture systems that rely on complex species mixtures to produce forage. Increased plant species diversity has been linked to improvements in ecosystem function. While it is recognized that grazing management can have a profound impact on sward composition, which in turn can affect grazing behavior and animal performance, the effects of increased plant species diversity on animal productivity (and vice versa) have not been well explored. This review addresses mechanisms by which grazing livestock alter cool‐season plant species diversity, mechanisms of diet choice, effects of plant species diversity on animal performance, and implications to sustainable domestic livestock grazing systems. We review evidence for these effects at one trophic level, that of grazing livestock in agroecosystems. While grazing behavior research conducted during the last several decades has led to advances in the understanding of plant–animal interactions, improved knowledge of these interactions is crucial for predicting animal performance. Also important is the evaluation of the impact of grazing livestock on mixed sward dynamics. This knowledge will lead to new opportunities to develop environmentally and economically sustainable grazing systems.

Plant Genotypic Diversity Predicts Community Structure and Governs an Ecosystem Process

Theory predicts, and recent empirical studies have shown, that the diversity of plant species determines the diversity of associated herbivores and mediates ecosystem processes, such as aboveground net primary productivity (ANPP). However, an often-overlooked component of plant diversity, namely population genotypic diversity, may also have wide-ranging effects on community structure and ecosystem processes. We showed experimentally that increasing population genotypic diversity in a dominant old-field plant species, Solidago altissima, determined arthropod diversity and community structure and increased ANPP. The effects of genotypic diversity on arthropod diversity and ANPP were comparable to the effects of plant species diversity measured in other studies.

Effects of plant species diversity, atmospheric [CO2], and N addition on gross rates of inorganic N release from soil organic matter

AbstractA significant challenge in predicting terrestrial ecosystem response to global changes comes from the relatively poor understanding of the processes that control pools and fluxes of plant nutrients in soil. In addition, individual global changes are often studied in isolation, despite the potential for interactive effects among them on ecosystem processes. We studied the response of gross N mineralization and microbial respiration after 6 years of application of three global change factors in a grassland field experiment in central Minnesota (the BioCON experiment). BioCON is a factorial manipulation of plant species diversity (1, 4, 9 and 16 prairie species), atmospheric [CO2] (ambient and elevated: 560 μmol mol−1), and N inputs (ambient and ambient +4 g N m−2 yr−1). We hypothesized that gross N mineralization would increase with increasing levels of all factors because of stimulated plant productivity and thus greater organic inputs to soils. However, we also hypothesized that N addition would enhance, while elevated [CO2] and greater diversity would temper, gross N mineralization responses because of increased and reduced plant tissue N concentrations, respectively. In partial support of our hypothesis, gross N mineralization increased with greater diversity and N addition, but not with elevated [CO2]. The ratio of gross N mineralization to microbial respiration (i.e. the ‘yield’ of inorganic N mineralized per unit C respired) declined with greater diversity and [CO2] suggesting increasing limitation of microbial processes by N relative to C in these treatments. Based on these results, we conclude that the plant supply of organic matter primarily controls gross N mineralization and microbial respiration, but that the concentration of N in organic matter input secondarily influences these processes. Thus, in systems where N limits plant productivity these global change factors could cause different long‐term ecosystem trajectories because of divergent effects on soil N and C cycling.

Rapid effects of plant species diversity and identity on soil microbial communities in experimental grassland ecosystems

Changes in plant community structure, including the loss of plant diversity may affect soil microbial communities. To test this hypothesis, plant diversity and composition were experimentally varied in grassland plots cultivated with monocultures or mixtures of 2, 3 or 4 species. We tested the effects of monocultures versus mixtures and of plant species composition on culturable soil bacterial activity, number of substrates used and catabolic diversity, microbial biomass N, microbial respiration, and root biomass. These properties were all measured 10 months after seeding the experiment. Soil bacterial activity, number of substrates used and catabolic diversity were measured in the different plant communities using BIOLOG GN and GP microplates, which are redox-based tests measuring capacity of soil culturable bacteria to use a variety of organic substrates. Microbial biomass N, microbial respiration, and root biomass were insensitive to plant diversity. Culturable soil microbial activity, substrates used and diversity declined with declining plant diversity. Their activity, number of substrates used and diversity were significantly higher in plots with 3 and 4 plant species than in monocultures and in plots with 2 species. There was also an effect of plant species composition. Culturable soil microbial activity and diversity was higher in the four-species plant community than in any of the plant monocultures suggesting that the effect of plant diversity could not be explained by the presence of a particular plant species. Our results showed that changes in plant diversity and composition in grassland ecosystems lead to a rapid response of bacterial activity and diversity.

Effects of Plant Species Diversity and Composition on Nitrogen Cycling and the Trace Gas Balance of Soils

Experiments addressing the role of plant species diversity for ecosystem functioning have recently proliferated. Most studies have focused on plant biomass responses. However, microbial processes involved in the production of N2O and the oxidation of atmospheric CH4 could potentially be affected via effects on N cycling, on soil diffusive properties (due to changes in water relations and root architecture) and by more direct interactions of plants with soil microbes. We studied ecosystem-level CH4 and N2O fluxes in experimental communities assembled from two pasture soils and from combinations of 1, 3, 6, 8 or 9 species typical for these pastures. The soils contrasted with respect to texture and fertility. N2O emissions decreased with diversity and increased in the presence of legumes. Soils were sinks for CH4 at all times; legume monocultures were a smaller sink for atmospheric CH4 than non-legume monocultures, but no effect of species richness per se was detected. However, both the exchange of CH4 and N2O strongly depended on plant community composition, and on the interaction of composition with soil type, indicating that the functional role of species and their interactions differed between soils. N2O fluxes were mainly driven by effects on soil nitrate and on nitrification while soil moisture had less of an effect. Soil microbial C and N and N mineralisation rates were not altered. The driver of the interactive soil type×plant community composition-effects was less clear. Because soil methanotrophs may take longer to respond to alterations of N cycling than the 1/2 year treatment in this study, we also tested species richness-effects in two separate 5-year field studies, but results were ambiguous, indicating complex interactions with soil disturbance. In conclusion, our study demonstrates that plant community composition can affect the soil trace gas balance, whereas plant species richness per se was less important; it also indicates a potential link between the botanical composition of plant communities and global warming.