Community Biomass Production Research Articles

Community‐wide trait means and variations affect biomass in a biodiversity experiment with tree seedlings

The structure of a plant community in terms of functional traits can strongly affect community productivity. Two components may contribute to this, community‐wide trait means (mass‐ratio hypothesis) or community‐wide trait variations (diversity hypothesis) across species and individuals. We compared the explanatory power of the two hypotheses for explaining biomass variation among individuals and communities as measures of productivity. We set up experimental communities of tree seedlings that ranged in species richness from 1 to 8. We measured above‐ and belowground biomass, leaf area, specific leaf area and height of all individuals separately after 16 months of growth and calculated species‐level values by averaging across all individuals of each species grown in monoculture. Using species‐ and individual‐level trait data, we calculated community‐ (CWM) and neighbourhood‐weighted mean (NWM) values to assess the mass‐ratio hypothesis and community functional dissimilarity (FD) and average trait dissimilarity of target individuals to neighbours (ATD), i.e. trait variations, to assess the diversity hypothesis. CWMs explained much more variation in community biomass than did species richness or FD, supporting the mass‐ratio hypothesis. The explanatory power of CWMs increased when calculated with individual‐level data, demonstrating positive effects of trait adjustments of individuals in response to species richness, i.e. plasticity in the broad sense. FD calculated with individual‐level data also increased community biomass, lending some support to the diversity hypothesis. The effects of trait means and variations on community biomass were related to effects of trait means and variations on the biomass of individuals. Overall, our results suggest that trait means rather than trait variations may drive community biomass productivity at the earliest stage of forest development.

Nitrogen-fixer enhances lipid yields in algal polycultures

Current algal biomass research still focuses mainly on identifying and growing monocultures that produce high amounts of lipids or other target compounds. However, monocultures might have a lower efficiency of utilizing resources, due to their limited physiological resource use possibilities, compared to algal polycultures. Recent studies showed that species diversity enhances the lipid production of microalgae. To identify the general patterns of enhanced lipid production in diverse microalgal communities it is essential to investigate links between resource use complementarity and the corresponding lipid production.Cyanobacteria and Chlorophyta are highly differentiated in their light spectrum utilization and nutrient requirements, e.g., some Cyanobacteria species can fix atmospheric nitrogen. To investigate whether these two groups are complementary in terms of optimizing biomass and neutral lipid production, we compared the growth of several species of Cyanobacteria and Chlorophyta in monocultures and polycultures consisting of species from both groups. Results show that lipid production increases with increasing functional diversity and that using just two different functional groups of microalgae provides a positive biodiversity effect. Lipid yields were particularly enhanced by the presence of a nitrogen-fixing cyanobacterium. Additionally, lipid yields were decoupled from higher biomass production in diverse communities. In summary, our results show that the enhancement of lipid production due to biodiversity can be achieved through combining just two physiologically different taxonomic groups and including a nitrogen fixer. This may make achieving the benefits of biodiversity in algal mass cultivation more straightforward.

Both mass ratio effects and community diversity drive biomass production in a grassland experiment

The maintenance of biodiversity is crucial for ecosystem processes such as plant biomass production, as higher species richness is associated with increased biomass production in plant communities. However, the effects of evenness and functional diversity on biomass production are understudied. We manipulated the composition of an experimental grassland by sowing various seed mixtures and examined the effects of diversity and evenness on biomass production after three years. We found that biomass production increased with greater species and functional richness but decreased with greater species and functional evenness. Standing biomass increased but species number and functional richness decreased with increasing proportion of perennial grasses. Our findings emphasise the importance of productive dominant species, as the proportion of perennial grasses had a positive effect on standing biomass, while species and functional evenness had a negative effect on it. Thus, our findings support the theory that, besides diversity, dominance effects and the so-called mass ratio hypothesis may also play a key role in explaining primary biomass production.

Temporal Variability of Precipitation and Biomass of Alpine Grasslands on the Northern Tibetan Plateau

The timing regimes of precipitation can exert profound impacts on grassland ecosystems. However, it is still unclear how the peak aboveground biomass (AGBpeak) of alpine grasslands responds to the temporal variability of growing season precipitation (GSP) on the northern Tibetan Plateau. Here, the temporal variability of precipitation was defined as the number and intensity of precipitation events as well as the time interval between consecutive precipitation events. We conducted annual field measurements of AGBpeak between 2009 and 2016 at four sites that were representative of alpine meadow, meadow-steppe, alpine steppe, and desert-steppe. Thus, an empirical model was established with the time series of the field-measured AGBpeak and the corresponding enhanced vegetation index (EVI) (R2 = 0.78), which was used to estimate grassland AGBpeak at the regional scale. The relative importance of the three indices of the temporal variability of precipitation, events, intensity, and time interval on grassland AGBpeak was quantified by principal component regression and shown in a red–green–blue (RGB) composition map. The standardized importance values were used to calculate the vegetation sensitivity index to the temporal variability of precipitation (VSIP). Our results showed that the standardized VSIP was larger than 60 for only 15% of alpine grassland pixels and that AGBpeak did not change significantly for more than 60% of alpine grassland pixels over the past decades, which was likely due to the nonsignificant changes in the temporal variability of precipitation in most pixels. However, a U-shaped relationship was found between VSIP and GSP across the four representative grassland types, indicating that the sensitivity of grassland AGBpeak to precipitation was dependent on the types of grassland communities. Moreover, we found that the temporal variability of precipitation explained more of the field-measured AGBpeak variance than did the total amount of precipitation alone at the site scale, which implies that the mechanisms underlying how the temporal variability of precipitation controls the AGBpeak of alpine grasslands should be better understood at the local scale. We hypothesize that alpine grassland plants promptly respond to the temporal variability of precipitation to keep community biomass production more stable over time, but this conclusion should be further tested. Finally, we call for a long-term experimental study that includes multiple natural and anthropogenic factors together, such as warming, nitrogen deposition, and grazing and fencing, to better understand the mechanisms of alpine grassland stability on the Tibetan Plateau.

Impact of ski piste management on mountain grassland ecosystems in the Southern Alps

In the Southern Alps, climate warming induced the use of artificial snow since two decades. In this area, two different ski piste management practices prevail: (1) large and medium ski resorts (M), which guarantee a ski season of four to five months using artificial snow, whereas (2) in the small, local ski resorts (S) it usually lasts two or three months. Our research addresses two main questions: 1) what is the impact of the ski pistes on the physico-chemical properties of the snow, on the soil and on the vegetation of mountain grassland ecosystems and 2) does the impact on the mountain grassland ecosystems change between medium and small ski resorts? Our experimental approach follows a pairwise design of plots on mountain grasslands of the ski pistes and control plots on mountain grasslands outside the pistes, where we examined the snow and soil properties and the vegetation composition. Under the long ski-season management (M) we found a significantly lower soil temperature below the snow cover of the ski pistes than the one below the natural snowpack, but this difference was limited to the period of natural snow cover. Only in M, pistes showed a lower biomass production and species richness in the mountain grassland plant communities compared to the controls, while there was no effect in S. The proportions of plant functional groups' cover changed in both ski resort types between piste and control. The most important factors affecting the observed differences in vegetation between pistes and controls were snow duration, snow and soil chemical properties, with more marked differences in the soil properties in M respect to S. The study concludes that reducing the ski season's length, therefore limiting the artificial snow's input, as in S, is more adequate to minimize the environmental impact in a changing climate.

Connecting experimental biodiversity research to real-world grasslands

During the last decades, a number of biodiversity experiments have been established to study the effects of plant diversity on ecosystem functioning. This research has been accompanied by a controversial discussion how “diversity effects” in experimental communities are related to the role of biodiversity in “real-world” ecosystems. To explore potential relationships, we compared plant community characteristics of 12 semi-natural managed reference grasslands to selected 10-year old communities of a large grassland biodiversity experiment (Jena Experiment): two communities initially sown with 60 species (JE60), and two communities assembled naturally during succession from bare soil (JESuc). Compared to semi-natural grasslands (17.6 ± 5.6), JE60 had higher species richness (27.5 ± 0.8), while species richness in JESuc (15.2 ± 0.5) was not different on subplots of 0.64 m2 size. Evenness and spatial heterogeneity were similar among grassland types, but biomass proportions of legumes and forbs were higher in JE60, while JESuc and semi-natural grasslands were dominated by grasses. Structural equation modelling applied to identify the drivers of biomass production in mixtures of the Jena Experiment with similar species richness (sown with 8, 16, and 60 species) and reference grasslands, showed no direct relationships between observed species richness and biomass production. In contrast, functional characteristics related to nitrogen acquisition and use were the most important variables explaining community biomass production. These functional characteristics were either driven by management intensity (fertilisation) in the “real world” reference grasslands or established by sowing in the experimental grasslands. Our results imply that species functional characteristics are key for a better understanding of the mechanisms underlying community assembly and ecosystem functioning and that the drivers of ecosystem functioning are not fundamentally different between experimental and “real-world” grasslands. Thus, experimental studies with designed extinction scenarios may help to predict the consequences of species loss for ecosystem functioning in “real-world” ecosystems.

Genotype identity has a more important influence than genotype diversity on shoot biomass productivity in willow short‐rotation coppices

AbstractWillow (Salixspp.) short‐rotation coppice is commercially grown to produce lignocellulosic biomass to meet renewable bioenergy demands. Most commercial willow coppices are grown in stands of a single genotype, but biomass productivity may be greater in mixed communities, and the productivity in mixed communities may depend on the specific genotypes involved. We assessed the biomass production of four differentSalixgenotypes (“Björn,” “Jorr,” “Loden,” “Tora”) grown without additional nutrient fertilization during one cutting cycle at three locations in Europe (Uppsala in Sweden, Rostock and Freiburg in Germany) in plots of pure and mixed communities. We evaluated (i) the effect of genotype diversity on shoot biomass productivity, including the evidence for complementarity and selection effects; (ii) the influence of individual genotypes on mixed community productivity; and (iii) the productivity of individual genotypes in response to pure vs. mixed culture. Mean shoot biomass production after the first cutting cycle decreased in the order Rostock (8.7 Mg ha−1) > Freiburg (6.9 Mg ha−1) > Uppsala (5.7 Mg ha−1), with values similar to those for other nonfertilized willow stands after the first growth cycle. Consistently across all three locations, increasing genotype diversity did not significantly affect shoot biomass production. Using Bayesian statistics, the addition of the genotypes “Jorr” and “Loden” was predicted to enhance shoot biomass production, while “Tora” and “Björn” are more likely to reduce shoot biomass production in mixed communities. In addition, we found evidence for a negative selection effect due to the genotype “Tora” performing better in mixed than in pure communities in two of the sites (Freiburg, Uppsala). In conclusion, our results imply that increasing genetic richness has no negative effect on productivity and that there is a potential to design site‐specific genotype mixtures of short‐rotation coppice promoting both high genetic diversity and high biomass production.

Origin context of trait data matters for predictions of community performance in a grassland biodiversity experiment.

Plant functional traits may explain the positive relationship between species richness and ecosystem functioning, but species-level trait variation in response to growth conditions is often ignored in trait-based predictions of community performance. In a large grassland biodiversity experiment (Jena Experiment), we measured traits on plants grown as solitary individuals, in monocultures or in mixtures. We calculated two measures of community-level trait composition, i.e., community-weighted mean traits (CWM) and trait diversity (Rao's quadratic entropy; FD) based on different contexts in which traits were measured (trait origins). CWM and FD values of the different measurement origins were then compared regarding their power to predict community biomass production and biodiversity effects quantified with the additive partitioning method. Irrespective of trait origin, models combining CWM and FD values as predictors best explained community biomass and biodiversity effects. CWM values based on monoculture, mixture-mean or community-specific trait data were similarly powerful predictors, but predictions became worse when trait values originated from solitary-grown individuals. FD values based on monoculture traits were the best predictors of community biomass and net biodiversity effects, while FD values based on community-specific traits were the best predictors for complementarity and selection effects. Traits chosen as best CWM predictors were not strongly affected by trait origin but traits chosen as best FD predictors varied strongly dependent on trait origin and altered the predictability of community performance. We conclude that by adjusting their functional traits to species richness and even specific community compositions, plants can change community-level trait compositions, thereby also changing community biomass production and biodiversity effects. Incorporation of these plastic trait adjustments of plants in trait-based ecology can improve its predictive power in explaining biodiversity-ecosystem functioning relationships.

Effects of temperature and grazing on soil organic carbon storage in grasslands along the Eurasian steppe eastern transect.

Soil represents the largest terrestrial organic carbon pool. To address global climate change, it is essential to explore the soil organic carbon storage patterns and their controlling factors. We investigated the soil organic carbon density (SOCD) in 48 grassland sites along the Eurasian steppe eastern transect (ESET) region, which covers the Inner Mongolia grassland subregion and Mongolia grasslands subregion. Specifically, we analyzed the SOCD in the top 30 cm soil layer and its relationships with climatic variables, soil texture, grazing intensity and community biomass productivity. The results showed that the average SOCD of the ESET was 4.74 kg/m2, and the SOCD of the Inner Mongolia grassland subregion (4.11 kg/m2) was significantly lower than that of the Mongolia grassland subregion (5.79 kg/m2). Significant negative relationships were found between the SOCD and the mean annual temperature (MAT), mean annual precipitation (MAP) and grazing intensity in the ESET region. The MAT and grazing intensity were identified as the major factors influencing the SOCD in the ESET region; the MAP and MAT were the major factors influencing the SOCD in the Inner Mongolia grassland subregion; and the MAT and soil pH were the major factors influencing the SOCD in the Mongolia grassland subregion.

Biodiversity effects in the wild are common and as strong as key drivers of productivity.

More than 500 controlled experiments have collectively suggested that biodiversity loss reduces ecosystem productivity and stability. Yet the importance of biodiversity in sustaining the world's ecosystems remains controversial, largely because of the lack of validation in nature, where strong abiotic forcing and complex interactions are assumed to swamp biodiversity effects. Here we test this assumption by analysing 133 estimates reported in 67 field studies that statistically separated the effects of biodiversity on biomass production from those of abiotic forcing. Contrary to the prevailing opinion of the previous two decades that biodiversity would have rare or weak effects in nature, we show that biomass production increases with species richness in a wide range of wild taxa and ecosystems. In fact, after controlling for environmental covariates, increases in biomass with biodiversity are stronger in nature than has previously been documented in experiments and comparable to or stronger than the effects of other well-known drivers of productivity, including climate and nutrient availability. These results are consistent with the collective experimental evidence that species richness increases community biomass production, and suggest that the role of biodiversity in maintaining productive ecosystems should figure prominently in global change science and policy.

Climate warming reduces the temporal stability of plant community biomass production

Anthropogenic climate change has emerged as a critical environmental problem, prompting frequent investigations into its consequences for various ecological systems. Few studies, however, have explored the effect of climate change on ecological stability and the underlying mechanisms. We conduct a field experiment to assess the influence of warming and altered precipitation on the temporal stability of plant community biomass in an alpine grassland located on the Tibetan Plateau. We find that whereas precipitation alteration does not influence biomass temporal stability, warming lowers stability through reducing the degree of species asynchrony. Importantly, biomass temporal stability is not influenced by plant species diversity, but is largely determined by the temporal stability of dominant species and asynchronous population dynamics among the coexisting species. Our findings suggest that ongoing and future climate change may alter stability properties of ecological communities, potentially hindering their ability to provide ecosystem services for humanity.

Grassland species respond differently to altered precipitation amount and pattern

An increase in precipitation amount with prolonged inter-rainfall intervals is predicted to occur in the Inner Mongolia grassland in the future. However, how the native species respond to such alterations remains poorly understood. We collected the seeds of eight species from a natural community and raised their seedlings by pot culture. The responses of these species to manipulated precipitation amount and inter-rainfall intervals were examined by rainout shelters. The biomass production in seven out of eight species was enhanced by increased precipitation amount. However, the impacts of prolonged inter-rainfall interval differed substantially among species, with one being promoted, two suppressed and five not affected. For most species, biomass allocations among vegetative organs were neither affect by precipitation amount nor by inter-rainfall intervals. In contrast, the impacts on species’ reproductive allocation were highly species-dependent. Soil moisture, soil temperature and soil inorganic nitrogen played important roles in affecting species’ biomass production but the pathways, directions (positive or negative) and magnitudes were species-dependent. Given that these eight species jointly represent about 80% of community biomass production, the impact of altered precipitation pattern on grassland ecosystems may be more difficult to predict than that of altered amount.

Small rainfall pulses affected leaf photosynthesis rather than biomass production of dominant species in semiarid grassland community on Loess Plateau of China.

In the semiarid region Loess Plateau of China, rainfall events, typically characterised as pulses, affect photosynthesis and plant community characteristics. The response of dominant species and grassland community to rainfall pulses was evaluated through a simulation experiment with five pulse sizes (0, 5, 10, 20 and 30mm) in the semiarid Loess Plateau of China in June and August of 2013. The study was conducted in a natural grassland community dominated by Bothrichloa ischaemum (L.)Keng and Lespedeza davurica (Lax.) Schindl. In June, the leaf photosynthetic rate (Pn), transpiration rate, stomatal conductance, intercellular CO2 concentration of both species and soil water content increased rapidly after rainfall pulses. B. ischaemum was more sensitive to the pulses and responded significantly to 5mm rainfall, whereas L. davurica responded significantly only to rainfall events greater than 5mm. The magnitude and duration of the photosynthetic responses of the two species to rainfall pulse gradually increased with rainfall sizes. The maximum Pn of B. ischaemum appeared on the third day under 30mm rainfall, whereas for L. davurica it appeared on the second day under 20mm rainfall. Soil water storage (0-50cm) was significantly affected under 10, 20 and 30mm rainfall. Only large pulses (20, 30mm) increased community biomass production by 21.3 and 27.6% respectively. In August, the effect of rainfall on the maximum Pn and community characteristics was generally not significant. Rainfall pulses affected leaf photosynthesis because of a complex interplay between rainfall size, species and season, but might not induce a positive community-level feedback under changing rainfall patterns.

Convergent high diversity in naturally colonized experimental grasslands is not related to increased productivity

Initial plant diversity might control subsequent community assembly processes and plant productivity. To study these effects, we used a biodiversity experiment (Jena Experiment) with subplots of different sown diversity that were never weeded and spontaneously colonized control plots of different size (3.5×3.5m, 20×20m) with and without mowing in an 8-year study. On non-sown bare plots without mowing, colonizer accumulation depended on plot size resulting in a loss of diversity in large, undisturbed (unmown) control plots after initial colonization. On sown plots that were mown, species richness converged to high levels due to the accumulation of internal colonists (species belonging to the experimental pool of sown species), while initially high species richness of external colonists (species not belonging to the experimental pool) and residents (species sown on the plot) declined over time. The convergence of total species richness at higher levels was paralleled by increased taxonomic (Simpson index, QSimp), phylogenetic (QPhylo) and trait (FDQ) diversity, whereby FDQ was greatest on plots with low resident species richness after several years. Rates of change in terms of species colonization and extinction decelerated over time irrespective of resident species richness, mowing or plot size. While the contribution of residents declined and that of colonists increased, community biomass production did not change over time. The biomasses of residents and colonists were greatest at higher levels of species richness, partial QPhylo and FDQ of the respective species group, but community biomass was consistently weakly related to total species richness and diversity indices. Our study shows that in contrast to the period of succession, “mature” plant communities resulting from natural assembly processes, favouring the coexistence of multiple species and thus high biodiversity, do no longer show significant relationships between species richness and variables related to ecosystem functioning such as primary productivity.

Complementarity among four highly productive grassland species depends on resource availability.

Positive species richness-productivity relationships are common in biodiversity experiments, but how resource availability modifies biodiversity effects in grass-legume mixtures composed of highly productive species is yet to be explicitly tested. We addressed this question by choosing two grasses (Arrhenatherum elatius and Dactylis glomerata) and two legumes (Medicago × varia and Onobrychis viciifolia) which are highly productive in monocultures and dominant in mixtures (the Jena Experiment). We established monocultures, all possible two- and three-species mixtures, and the four-species mixture under three different resource supply conditions (control, fertilization, and shading). Compared to the control, community biomass production decreased under shading (-56%) and increased under fertilization (+12%). Net diversity effects (i.e., mixture minus mean monoculture biomass) were positive in the control and under shading (on average +15 and +72%, respectively) and negative under fertilization (-10%). Positive complementarity effects in the control suggested resource partitioning and facilitation of growth through symbiotic N2 fixation by legumes. Positive complementarity effects under shading indicated that resource partitioning is also possible when growth is carbon-limited. Negative complementarity effects under fertilization suggested that external nutrient supply depressed facilitative grass-legume interactions due to increased competition for light. Selection effects, which quantify the dominance of species with particularly high monoculture biomasses in the mixture, were generally small compared to complementarity effects, and indicated that these species had comparable competitive strengths in the mixture. Our study shows that resource availability has a strong impact on the occurrence of positive diversity effects among tall and highly productive grass and legume species.

Nutrient uptake and lipid yield in diverse microalgal communities grown in wastewater

Microalgae show great potential as feedstock for biofuel production. Some of the advantages they offer over terrestrial energy crops are a high productivity and the possibility to use waste streams (e.g., wastewater for inorganic nutrients and flue gas for CO2 input). Most of the published literature on microalgal cultivation has focused on monocultures of a single strain. An alternative approach would be to cultivate multispecies communities, which can increase production if the different species in the culture have different requirements and complement each other. To study the effect of multispecies communities, we cultivated 12 different species in monocultures and randomly selected communities of three, five and seven species. This was performed using municipal wastewater, with no further nutrient addition. Growth rate, biomass production, nutrient depletion and lipid production were measured. In general, it was observed that the mean growth and nutrient depletion increased with increasing number of species in the community. The variability (e.g., nutrient removal, resource use efficiency) between communities decreased with an increasing number of species. Biomass production in communities with the strongest growth was similar to, but not higher than the production in monocultures with the strongest growth (i.e., non-transgressive overyielding). However, the highest lipid content was obtained from some of the multispecies communities, which indicates transgressive overyielding in terms of lipid production. Combining communities randomly is probably not the best approach to increase algal biomass production, carefully selecting species, based on prior knowledge of physiology and ecology, might be a more effective approach to increase productivity.

Shrub–ephemeral plants interactions in semiarid north-central Chile: Is the nurse plant syndrome manifested at the community level?

Models of plant–plant interactions suggest that nurse plants are critical for the maintenance of biodiversity and ecosystem functions in arid and semiarid lands. At the community scale, however, empirical support of this idea is limited and context-dependent. Following on a preliminary work which suggested that a dominant shrub in north-central Chile (Porlieria chilensis) had nurse plant effects, we tested the effects of this and two other shrubs (Adesmia bedwellii and Proustia cuneifolia) on community biomass production, species density, and species composition of ephemeral plants in the semiarid scrub of the Bosque Fray Jorge National Park (Chile) over four consecutive years. We tested for main and interactive effects of shrubs and precipitation on total biomass production and species density of ephemeral plant communities using Generalized Linear Mixed Models (GLMM). To analyze the effects of shrubs and precipitation on species composition we used Canonical Correspondence Analysis (CCA) and t-value biplot analysis. Total biomass production increased significantly with precipitation and was consistently lower beneath shrub canopies, particularly under A. bedwellii and P. chilensis. Although ephemeral plant species density generally was higher in open areas, differences between open and shrub canopy samples diminished with increasing precipitation. Finally, despite significant differences in ephemeral plant species composition between open areas and shrub canopies, we found no evidence of shrub species-specific effects. In conclusion, our results do not support a classical nurse plant syndrome in the semiarid scrub of the Bosque Fray Jorge National Park although shrubs can increase local diversity by favoring some ephemeral plant species that are absent in open areas.

Plant Functional Diversity Can Be Independent of Species Diversity: Observations Based on the Impact of 4-Yrs of Nitrogen and Phosphorus Additions in an Alpine Meadow.

Past studies have widely documented the decrease in species diversity in response to addition of nutrients, however functional diversity is often independent from species diversity. In this study, we conducted a field experiment to examine the effect of nitrogen and phosphorus fertilization ((NH4)2 HPO4) at 0, 15, 30 and 60 g m-2 yr-1 (F0, F15, F30 and F60) after 4 years of continuous fertilization on functional diversity and species diversity, and its relationship with productivity in an alpine meadow community on the Tibetan Plateau. To this purpose, three community-weighted mean trait values (specific leaf area, SLA; mature plant height, MPH; and seed size, SS) for 30 common species in each fertilization level were determined; three components of functional diversity (functional richness, FRic; functional evenness, FEve; and Rao’s index of quadratic entropy, FRao) were quantified. Our results showed that: (i) species diversity sharply decreased, but functional diversity remained stable with fertilization; (ii) community-weighted mean traits (SLA and MPH) had a significant increase along the fertilization level; (iii) aboveground biomass was not correlated with functional diversity, but it was significantly correlated with species diversity and MPH. Our results suggest that decreases in species diversity due to fertilization do not result in corresponding changes in functional diversity. Functional identity of species may be more important than functional diversity in influencing aboveground productivity in this alpine meadow community, and our results also support the mass ratio hypothesis; that is, the traits of the dominant species influenced the community biomass production.

Dominance by an obligate annual affects the morphological characteristics and biomass production of a planted wetland macrophyte community

Aims biodiversity–ecosystem function experiments can test for causal relationships between planting diversity and community productivity. Planting diversity is routinely introduced as a design element in created wetlands, yet substantive support for the finding that early diversity positively affects ecosystem functioning is lacking for wetlands. We conducted a 2-year diversity–productivity experiment using freshwater wetland mesocosms to investigate community biomass production as affected by planted macrophyte functional richness. Methods a richness gradient of macrophytes in four emergent wetland plant functional groups was established in freshwater mesocosms for two consecutive years. species-specific aboveground morphological traits of plant size were measured at peak growth in both years; rooting depth was measured for each species in the second year. aboveground biomass (agb) and belowground biomass (bgb) were harvested after peak growth in the second year; first year agb was estimated from morphological traits in constructed regression equations. Net richness effects (i.e. both complementarity effects and selection effects) were calculated using an additive partitioning method. Important Findings species richness had a positive effect on community agb relative to monocultures in the first year. in the second year, mean agb was significantly reduced by competition in the most species-rich mixtures and all mixtures underyielded relative to the average monoculture. Competition for soil resources was weaker belowground, whereby root distribution at depths >20 cm was reduced at the highest richness levels but overall bgb production was not affected. Changes in species biomass were strongly reflected by variation in species morphological traits, and species above and belowground performances were highly correlated. The obligate annual (Eleocharis obtusa), a dominant competitor, significantly contributed to the depression of perennial species’ growth in the second growing season. To foster primary productivity with macrophyte richness in early successional communities of created wetlands where ruderal strategies are favored and competition may be stronger than species complementarity, unsystematic planting designs such as clustering the same or similar species could provide protection for some individuals. additionally, engineering design elements fostering spatial or temporal environmental variability (e.g. microtopography) in newly created wetlands helps diversify the responses of wetland macrophyte species to their environment and could allow for greater complementarity in biomass production.

Experimental evidence for strong stabilizing forces at high functional diversity of aquatic microbial communities.

Unveiling the mechanisms that promote coexistence in biological communities is a fundamental problem in ecology. Stable coexistence of many species is commonly observed in natural communities. Most of these natural communities, however, are composed of species from multiple trophic and functional groups, while theory and experiments on coexistence have been focusing on functionally similar species. Here, we investigated how functional diversity affects the stability of species coexistence and productivity in multispecies communities by characterizing experimentally all pairwise species interactions in a pool of 11 species of eukaryotes (10 protists and one rotifer) belonging to three different functional groups. Species within the same functional group showed stronger competitive interactions compared to among-functional group interactions. This often led to competitive exclusion between species that had higher functional relatedness, but only at low levels of species richness. Communities with higher functional diversity resulted in increased species coexistence and community biomass production. Our experimental findings and the results of a stochastic model tailored to the experimental interaction matrix suggest the emergence of strong stabilizing forces when species from different functional groups interact in a homogeneous environment. By combining theoretical analysis with experiments we could also disentangle the relationship between species richness and functional diversity, showing that functional diversity per se is a crucial driver of productivity and stability in multispecies community.