Aquatic hyphomycete diversity and identity affect leaf litter decomposition in microcosms

We conducted a microcosm experiment with monocultures and all possible combinations of four aquatic hyphomycete species, Articulospora tetracladia, Flagellospora curta, Geniculospora grandis and Heliscus submersus, to examine the potential effects of species richness on three functional aspects: leaf litter decomposition (leaf mass loss), fungal production (ergosterol buildup) and reproductive effort (released spores). Both species richness and identity significantly affected fungal biomass and conidial production (number and biomass of released spores), whereas only species identity had a significant effect on leaf mass loss. In mixed cultures, all measures of fungal functions were greater than expected from the weighted performances of participating species in monoculture. Mixed cultures outperformed the most active monoculture for biomass accumulation but not for leaf mass loss and conidial production. The three examined aspects of aquatic hyphomycete activity tended to increase with species richness, and a complementary effect was unequivocally demonstrated for fungal biomass. Our results also suggest that specific traits of certain species may have a greater influence on ecosystem functioning than species number.     

How plant allometry influences bud phenology and fruit yield in two Vaccinium species

Background and AimsUnderstanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants’ allometric traits, which are predictors of fruit production.MethodsWe measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass.Key ResultsDuring the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log–log scale model.ConclusionsGrowing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.     

Effects of plant species richness on stand structure and productivity

Aims Aboveground biomass production commonly increases with species richness in plant biodiversity experiments. Little is known about the direct mechanisms that cause this result. We tested if by occupying different heights and depths above and below ground, and by optimizing the vertical distribution of leaf nitrogen, species in mixtures can contribute to increased resource uptake and, thus, increased productivity of the community in comparison with monocultures.Methods We grew 24 grassland plant species, grouped into four nonoverlapping species pools, in monoculture and 3- and 6-species mixture in spatially heterogeneous and uniform soil nutrient conditions. Layered harvests of above- and belowground biomass, as well as leaf nitrogen and light measurements, were taken to assess vertical canopy and root space structure.Important findings The distribution of leaf mass was shifted toward greater heights and light absorption was correspondingly enhanced in mixtures. However, only some mixtures had leaf nitrogen concentration profiles predicted to optimize whole-community carbon gain, whereas in other mixtures species seemed to behave more 'selfish'. Nevertheless, even in these communities, biomass production increased with species richness. The distribution of root biomass below ground did not change from monocultures to three- and six-species mixtures and there was also no indication that mixtures were better than monocultures at extracting heterogeneously as compared to homogeneously distributed soil resources. We conclude that positive biodiversity effect on aboveground biomass production cannot easily be explained by a single or few common mechanisms of differential space use. Rather, it seems that mechanisms vary with the particular set of species combined in a community.     

Correlations between salinity and growth of the seagrass Amphibolis antarctica (labill.) Sonder & Aschers., In Shark Bay,Western Australia,using a new method for measuring production rate

A method of estimating above-ground productivity in situ of the seagrass Amphibolis antarctica (Labill.) Sonder & Aschers. has been devised, using tags to determine rates of leaf turnover. This has proved an effective tool in establishing the behavior of the species in relation to the gradient of increasing salinity which is present in Shark Bay. No seagrass was found beyond 64%_o, but measurement of production and biomass within dense patches of seagrass at different salinities revealed that these were at a maximum at a salinity of 42%_o, decreasing as the salinity increased and also at lower oceanic concentrations. Production rates ranged from 2 to 17 g dry weight m^?2 day^?1 with biomass from 600 to 2000 g m^?2, thus Amphibolis antarctica is one of the more productive Australian seagrass species, even in the hypersaline conditions of the Bay. Despite the obvious correlation between above-ground production and salinity, it is pointed out that the results are not taken to imply causality.     

Functional morphology and microclimate of Festuca orthophylla, the dominant tall tussock grass in the Andean Altiplano

Plant growth is driven by the rate of photosynthetic uptake of carbon, the loss of carbon and by allocation of photoassimilates to certain plant compartments, which leads to particular morphologies. Performance, vitality and persistence of a plant are affected by this partitioning process and vice versa. Under harsh climatic conditions such as cold temperature and seasonal drought, perennial plants often invest more in below-ground than above-ground structures. Festuca orthophylla in the subtropical Bolivian Altiplano does not match this ‘rule’. This species produces tall, evergreen tussocks, persisting decades and dominating the semi-arid, Andean landscape over thousands of square kilometers at elevation between 3600 and 4600 m a.s.l. The shallow rooting system represents only 21% of total biomass. The tussock base (root-stocks composed of the network of branching below-ground shoots and tiller meristems) comprises 28% of the total biomass. Although located partly below the soil surface, much of this biomass compartment is functionally above-ground (the basis of shoots). With their below-ground position, tiller meristems are protected against grazing and trampling by camelids as well as, to some degree, against fire and freezing. Fifty one percent of the biomass is above-ground (live leaves and inflorescences). In terms of phytomass (including attached necromass), 75% is above-ground. On average, a tussock consists of 3200 tightly packed total tillers (56% are live). Tillers emerge regularly intravaginally (i.e. within the leaf sheath of an existing mother tiller), resulting in dense canopies with strong self-shading: eighty percent of green foliage experience less than 50% of the incident light. The most important Altiplano plant species thus has morphological traits in favour of protection and survival rather than productivity.     

More plant biomass results in more offspring production in annuals,or does it?

Competitive ability in plants has been previously measured almost exclusively in terms of traits related to growth (biomass) or plant size. In this study, however, we used a multi‐species competition experiment with six annuals to measure relative competitive ability in terms of reproductive output, i.e. the number of offspring produced for the next generation. Under greenhouse conditions, plants of each species were started in pots from germinating seeds and were grown singly (free of competition) and at high density in both monocultures and in mixtures with all study species. Several traits traditionally regarded as determinants of competitive ability in plants were recorded for each species grown singly, including: seed mass, germination time, early growth rate and potential plant size (biomass and height). Under competition, several traits were recorded as indicators of relative performance in both monocultures and mixtures, including: biomass of survivors, total number of survivors, number of reproductive survivors, and reproductive output (total seed production) of the survivors. As expected, species that grew to a larger biomass in isolation had higher seed production in isolation. However, none of the traditional plant growth/size‐related traits, measured either in isolation or under competition, could predict between species variation in reproductive output under competition in either monocultures or mixtures. In mixtures, 97% of this variation in reproductive output could be explained by between‐species variation in the number of reproductive survivors. The results indicate that traits measured on plants grown singly may be poor predictors of reproductive output under competition, and that species’ rank order of competitive ability in terms of the biomass of survivors may bear no relationship to their rank order in terms of the number of offspring produced by these survivors. This has important implications for the interpretation of mechanisms of species coexistence and community assembly within vegetation.     

NET PRIMARY PRODUCTION AND PHENOLOGY ON A SOUTHERN APPALACHIAN WATERSHED

Net primary production (NPP) is an important function of plant communities which has not often been examined seasonally in a forested ecosystem. The major objective of the study was to measure above-ground NPP seasonally and relate it to phenological activity on a hardwood forest watershed at Coweeta Hydrologic Laboratory, North Carolina. NPP was estimated as the increase in biomass, estimated from regression equations on diameter. Diameter increases were measured by vernier tree bands. Phenological observations were made on bud break, leaf emergence, flowering, mature fruit, leaf senescence, and leaf fall. The species studied intensively were Acer rubrum, Quercus prinus, Carya glabra, Cornus florida, and Liriodendron tulipifera. Liriodendron was found to be the most productive species per individual, but Quercus prinus was the most productive per unit ground area. The total watershed estimate of aboveground NPP was 8,754 kg ha^-1 yr^-1 and included 47.9% leaves, 33.2% wood, 7.8% bark, 4.8% reproductive tissues, 4.2% loss to consumers, and 2.1% twigs. Increases in leaf biomass were most rapid in the spring, but woody tissue production peaked in June and continued through August. Since leaf production peaked in the spring, the plants' photosynthetic machinery was activated early in the growing season to support woody tissue production, which followed the period of rapid leaf growth, and reproductive activity. Flowering occurred during the leaf expansion period except for Acer rubrum, which flowered before leaf emergence. Fruit maturation occurred during late summer to early fall, when there were no additional biomass increases. Acer rubrum was an exception as its fruit matured during the period of leaf expansion.     

Exotic tree seedlings are much more competitive than natives but show underyielding when growing together

Aims Invasive species continue to be a worldwide threat to ecosystems mainly as a cause for biodiversity loss. Forest ecosystems, for example, are subject to a change in species composition due to the invasion of exotic species. Specifying the attributes that cause the strong competitiveness of several exotic species may improve the ability to understand and effectively manage plant invasions in the future. In this study the following hypotheses were tested: (1) biomass production of below- and aboveground plant components of the exotic tree species is higher than that of the natives, resulting in a higher competitiveness of the exotics; (2) the exclusion of root competition has a positive effect on the biomass production of the inferior native species; and (3) mixtures of native and exotic species yield a higher biomass production than the respective monocultures.Methods A pot experiment, containing about 2000 tree seedlings, was established. We investigated the biomass productivity and growth reactions of two native (Quercus robur L., Carpinus betulus L.) and two exotic tree species (Prunus serotina Ehrh., Robinia pseudoacacia L.) in different intra- and interspecific, competitive situations with and without the influence of root competition.Important findings The biomass production of both exotic species was significantly higher and led to a strong competitive advantage, resulting in a biomass decrease of the less competitive native species. The high belowground biomass of both exotic species had a negative effect on the biomass production. The competitive pressure of exotic tree seedlings on the native ones was largely driven by root competition. Furthermore, mixtures of native and exotic tree species had a higher productivity than their growth in monocultures would have predicted. Competition was lower for exotic species in mixtures with the less productive native species compared to the competition in monocultures or in mixture with the other highly productive exotic species. Accordingly, both highly competitive exotic species produced less biomass in mixture with each other compared to monocultures. Despite the significantly higher biomass of P. serotina in all mixtures and in monoculture, R. pseudoacacia seemed to be the dominating species. Due to its strong root competition, R. pseudoacacia significantly reduced the biomass production of P. serotina .     

Linking multiple-level tree traits with biomass accumulation in native tree species used for reforestation in Panama

To improve establishment yield and carbon accumulation during reforestation, analyses of species adaptations to local environments are needed. Here we measured, at the individual scale, links between biomass accumulation and multiple-level tree traits: biomass partitioning, crown morphology and leaf physiology. The study was carried out on one- and three-year-old individuals of five tropical tree species assigned to pioneer (P) or non-pioneer (NP) functional groups. Among the species, Cedrela odorata, Luehea seemannii and Hura crepitans showed the greatest biomass accumulation. On our seasonally dry site, species performance during the first year was dependent on a greater investment in above-ground foraging, while performance after three years was mainly related to water relations. However, large biomass accumulations were not simply associated with an efficient water use but also with contrasting water uses, based on inter-specific relationships. Generally, greater carbon isotope discrimination (Δ_leaf) was related to greater allocation to roots. Species with high Δ_leaf generally showed high leaf potential nitrogen use efficiency (PNUE), suggesting that lower water use efficiency (WUE) increases the efficiency of photosynthetically active N. Also, PNUE was negatively correlated to leaf mass per area (LMA), implying that photosynthetically active N is diluted as total leaf mass increases. Finally, no distinction in measured traits, including biomass accumulation, was observed between the two functional groups.     

<Emphasis Type="Italic">Phragmites</Emphasis><Emphasis Type="Italic">australis</Emphasis>: How do genotypes of different phylogeographic origins differ from their invasive genotypes in growth,nitrogen allocation and gas exchange?

It has been suggested that in plant invasions, species may develop intrinsically higher gas exchange and growth rates, and greater nitrogen uptake and allocation to shoots, in their invasive range than in their native habitat under excess nutrients. In this study, native populations of two old world Phragmites australis phylogeographic groups (EU and MED) were compared with their invasive populations in North America [NAint (M) and NAint (Delta)] under unlimited nutrient availability and identical environmental conditions in a common garden. We expected that both introduced groups would have higher growth, nitrogen uptake and allocation, and gas exchange rates than their native groups, but that these enhanced traits would have evolved in different ways in the two introduced ranges, because of different evolutionary histories. Biomass, leaf area, leaf nitrogen concentrations (NH₄ ⁺ and NO₃ ^?) and transpiration rates increased in introduced versus native groups, whereas differences in SLA, leaf pigment concentrations and assimilation rates were due to phylogeographic origins. Despite intrinsic differences in the allocation of C and N in leaves, shoots and rhizome due to phylogeographic origin, the introduced groups invested more biomass in above-ground tissues than roots and rhizomes. Our results support the concept that invasive populations develop enhanced morphological, physiological and biomass traits in their new ranges that may assist their competiveness under nutrient-enriched conditions, however the ecophysiological processes leading to these changes can be different and depend on the evolutionary history of the genotypes.     

Shoot-level biomass allocation is affected by shoot type in Fagus sylvatica

Aims The present study aims (i) to examine if recently reported interspecific shoot-level biomass allocational trade-offs, i.e. isometric trade-offs between leaf mass (LM) and stem mass (SM) and between leaf size and leaf number, hold intraspecifically and (ii) to explore whether those scaling relationships are independent of shoot type (i.e. long vs. short shoots).Methods In order to address our questions, we used Fagus sylvatica saplings growing under a broad light range that were sampled in the Western Carpathians Mountains (Slovakia).Important findings We found that: (i) intraspecific shoot-level biomass allocational trade-offs differ from those reported interspecifically and that (ii) long and short shoots differ in biomass allocation scaling coefficients. Allometric relationships with slopes statistically smaller than 1.0 or higher than^-1.0, were found between SM and LM and between mean leafing intensity and individual leaf mass, respectively, in long shoots. In contrast, isometric scaling was found in short shoots. This suggests that leaf mass in short shoots is unaffected by shoot stem mass, in contrast to long shoots. Short shoots also had a larger fraction of biomass allocated to leaves. Beech shoots, as has been observed in other shoot dimorphic species, are specialized, with short shoots specializing in carbon gain and long shoots in space acquisition. A greater shift in LM than in SM among species during speciation shifting from allometric intraspecific relationships to an isometric interspecific scaling relationship between those traits could explain the discrepancies between the outputs of the present intraspecific study and others similar studies. This study draws attention to the importance of considering shoot types in future studies dealing with allocation rules in species with dimorphic shoots.     

A functional trait-based approach to understand community assembly and diversity–productivity relationships over 7 years in experimental grasslands

Several multi-year biodiversity experiments have shown positive species richness–productivity relationships which strengthen over time, but the mechanisms which control productivity are not well understood. We used experimental grasslands (Jena Experiment) with mixtures containing different numbers of species (4, 8, 16 and 60) and plant functional groups (1–4; grasses, legumes, small herbs, tall herbs) to explore patterns of variation in functional trait composition as well as climatic variables as predictors for community biomass production across several years (from 2003 to 2009). Over this time span, high community mean trait values shifted from the dominance of trait values associated with fast growth to trait values suggesting a conservation of growth-related resources and successful reproduction. Increasing between-community convergence in means of several productivity-related traits indicated that environmental filtering and exclusion of competitively weaker species played a role during community assembly. A general trend for increasing functional trait diversity within and convergence among communities suggested niche differentiation through limiting similarity in the longer term and that similar mechanisms operated in communities sown with different diversity. Community biomass production was primarily explained by a few key mean traits (tall growth, large seed mass and leaf nitrogen concentration) and to a smaller extent by functional diversity in nitrogen acquisition strategies, functional richness in multiple traits and functional evenness in light-acquisition traits. Increasing species richness, presence of an exceptionally productive legume species (Onobrychis viciifolia) and climatic variables explained an additional proportion of variation in community biomass. In general, community biomass production decreased through time, but communities with higher functional richness in multiple traits had high productivities over several years. Our results suggest that assembly processes within communities with an artificially maintained species composition maximize functional diversity through niche differentiation and exclusion of weaker competitors, thereby maintaining their potential for high productivity.     

Competition between two grass species with and without grazing over a productivity gradient

Soil nutrient-level and herbivory are predicted to have opposing effects on the allocation pattern of the competitive dominant plant species. Lower stem and higher leaf allocation are favoured when plants are grazed, whereas a higher stem allocation is favoured at high nutrient levels. Grazing by hares and geese can prevent invasion of the tall Elymus athericus, into short vegetation of Festuca rubra, at unproductive stages of salt-marsh succession but not at more productive stages. We hypothesise that the negative effect of herbivory on Elymus decreases due to increasing soil nitrogen levels and shifts the competitive balance towards this species. We tested how simulated grazing and nitrogen availability affected the competitive balance between adult plants of both grass species in a greenhouse experiment. Elymus had a higher above-ground biomass production, invested relatively more in stem and root tissue and had a larger shoot length than Festuca. The above-ground relative yield of Elymus in mixtures of both species increased with increasing nitrogen levels. This indicates that Elymus was the superior competitor at high soil fertility. Although clipping removed relatively more biomass from Elymus than from Festuca and exceeded the observed biomass removal in field conditions, it did not change the competitive balance between both species. Decreasing effects of herbivory due to increasing nitrogen levels are not a likely explanation for the invasion of Elymus in productive marshes. The results suggest that once Elymus has established it can easily invade vegetation dominated by Festuca irrespective of grazing by herbivores such as hares and geese. Herbivory by small herbivores may mainly retard the invasion of this plant by influencing establishment itself.     

Effect of spacing and nitrogen fertilization on the establishment and biomass production of short rotation poplar in Finland

Short rotation trials cuttings poplar (Populus x rasumowskyana) in Southern Finland investigated establishment of poplar plantations and the effects of spacing and application of nitrogen fertilizer on biomass production over a period of 6 years. Thicker cuttings grew better whilst those of less than 1 cm diameter grew only moderately. Nitrogen fertilization improved height and diameter growth and above-ground dry mass yield. Woody biomass production was 4·2 dry tons/ha per year, at 300 kg/ha nitrogen. A spacing of 15 000 stems/ha gave the best yield after 4 years, but 5000 stems/ha was a more productive spacing in the next 2 years.     

Adaptive characteristics of grassland community structure and leaf traits along an altitudinal gradient on a subtropical mountain in Chongqing,China

Community structure and leaf traits are important elements of terrestrial ecosystems. Changes of community structure and leaf traits are of particular use in the study of the influence of climate change on terrestrial ecosystems. Patterns of community structure (including species richness, above- and below-ground biomass) and leaf traits (including leaf mass per area (LMA), nitrogen content both on mass and area bases (N _mass and N _area), and foliar δ¹³C) from 19 grassland plots along an altitudinal transect at Hongchiba in Chongqing, China, were analyzed. Species richness along the altitudinal transect had a hump-shaped pattern. Above-ground biomass had a quadratic decrease along the altitudinal gradient whereas below-ground biomass had the opposite pattern. Change of above-ground biomass of various taxonomic groups with altitude was also studied. Poaceae showed strong negative relationships and Asteraceae showed a hump-shaped relationship with increase of altitude. Five common species of the grassland, Trifolium pratense, Geranium wilfordii, Aster tataricus, Leontopodium leontopodioides, and Spiraea prunifolia, were particularly studied for variation of leaf traits along the altitudinal gradient. Averaged for all species, LMA, N _area and foliar δ¹³C had positive correlations with altitude. N _mass did not change significantly as altitude increased. LMA and N _area showed significant positive relationships with foliar δ¹³C. The adaptive features of leaf traits among different species were not consistent. The study highlights specific adaptation patterns in relation to altitude for different plant species, provides further insights into adaptive trends of community structure and leaf traits in a specific ecological region filling a gap in the definition of global patterns, and adds to the understanding of how adaptive patterns of plants may respond to global climate change.     

Interspecific trait variability and local soil conditions modulate grassland model community responses to climate

Medium‐to‐high elevation grasslands provide critical services in agriculture and ecosystem stabilization, through high biodiversity and providing food for wildlife. However, these ecosystems face elevated risks of disruption due to predicted soil and climate changes. Separating the effects of soil and climate, however, is difficult in situ, with previous experiments focusing largely on monocultures instead of natural grassland communities. We experimentally exposed model grassland communities, comprised of three species grown on either local or reference soil, to varied climatic environments along an elevational gradient in the European Alps, measuring the effects on species and community traits. Although species‐specific biomass varied across soil and climate, species'' proportional contributions to community‐level biomass production remained consistent. Where species experienced low survivorship, species‐level biomass production was maintained through increased productivity of surviving individuals; however, maximum species‐level biomass was obtained under high survivorship. Species responded directionally to climatic variation, spatially separating differentially by plant traits (including height, reproduction, biomass, survival, leaf dry weight, and leaf area) consistently across all climates. Local soil variation drove stochastic trait responses across all species, with high levels of interactions occurring between site and species. This soil variability obscured climate‐driven responses: we recorded no directional trait responses for soil‐corrected traits like observed for climate‐corrected traits. Our species‐based approach contributes to our understanding of grassland community stabilization and suggests that these communities show some stability under climatic variation.     

Overyielding in grassland communities: testing the sampling effect hypothesis with replicated biodiversity experiments

We derive and test some assumptions and predictions of the Sampling Effect Hypothesis (SEH) by examining the relationship between the traits of species in monoculture and their relative abundance in mixture, and by comparing polyculture performance with single-species plots. Although we found a positive relationship between production in monoculture and dominance in mixtures as predicted by the SEH, the relationship had low explanatory power. Counter to predictions, the species with the highest monoculture biomass were not able to strongly dominate all mixtures; instead the dominance of these species decreased with increasing species richness. On average, polycultures did not achieve greater biomass than (transgressively overyield) the species in each mixture, or at each site, that was most productive in monoculture. However, mixture yields did transgressively overyield both the monoculture biomass of the dominant species in the mixtures, and the weighted average of all monocultures (non-transgressive overyielding), both of which were positively related to increasing species richness. The varying responses of different overyielding tests resulted because resource partitioning and positive interactions were often counter-balanced by selection for species with lower biomass than the highest-yielding monocultures. Judging whether or not mixtures overyield therefore depends in part upon which species is the basis for comparison. We present a new general framework for overyielding analysis where every monoculture provides a potential comparison and from which the most relevant tests can be selected.     

Legume species differ in the responses of their functional traits to plant diversity

Plants can respond to environmental impacts by variation in functional traits, thereby increasing their performance relative to neighbors. We hypothesized that trait adjustment should also occur in response to influences of the biotic environment, in particular different plant diversity of the community. We used 12 legume species as a model and assessed their variation in morphological, physiological, life-history and performance traits in experimental grasslands of different plant species (1, 2, 4, 8, 16 and 60) and functional group (1–4) numbers. Mean trait values and their variation in response to plant diversity varied among legume species and from trait to trait. The tall-growing Onobrychis viciifolia showed little trait variation in response to increasing plant diversity, whereas the species with shorter statures responded in apparently adaptive ways. The formation of longer shoots with elongated internodes, increased biomass allocation to supporting tissue at the cost of leaf mass, reduced branching, higher specific leaf areas and lower foliar δ¹³C values indicated increasing efforts for light acquisition in more diverse communities. Although leaf nitrogen concentrations and shoot biomass:nitrogen ratios were not affected by increasing plant diversity, foliar δ¹⁵N values of most legumes decreased and the application of the ¹⁵N natural abundance method suggested that they became more reliant on symbiotic N₂ fixation. Some species formed fewer inflorescences and delayed flowering with increasing community diversity. The observed variation in functional traits generally indicated strategies of legumes to optimize light and nutrient capturing, but they were largely species-dependent and only partly attributable to increasing canopy height and community biomass with increasing plant diversity. Thus, the analysis of individual plant species and their adjustment to growth conditions in communities of increasing plant diversity is essential to get a deeper insight into the mechanisms behind biodiversity–ecosystem functioning relationships.     

Why are many anthropogenic agroecosystems particularly species-rich?

Species-rich meadow and pasture habitats are recognised by the European Union Habitats Directive as targets for biodiversity conservation. High species richness is hypothesised to be associated with diversity in plant functional traits and life-history strategies, which are potentially restricted in situations of extremely high and low biomass production. However, variability in functional traits has yet to be investigated across a broad biomass range in nature. We measured variability in a range of functional traits and Grime's competitor, stress-tolerator, ruderal (CSR) strategies for species comprising lowland meadows, subalpine pastures, abandoned grassland and field margins at sites in northern Italy, alongside peak above-ground biomass. The factor most highly and positively correlated with species richness was strategy richness (the number of CSR strategies; Pearson's r = 0.864, P < 0.0001, n = 39), followed by variance in traits involved in leaf resource economics and the timing of flowering. Species richness, trait variance and strategy richness were greatest at intermediate biomass. Thus whilst extremes of biomass production were associated with relatively few taxa exhibiting similar trait values and specialised strategies, greater species richness was apparent in meadows and pastures in which species exhibited divergence in resource economics trait values, reproductive timing and strategy richness.     

Sediment addition enhances transpiration and growth of Spartina alterniflora in deteriorating Louisiana Gulf Coast salt marshes

Transpiration, leaf conductance, net photosynthesis, leaf growth, above-ground biomass and regeneration of new culms were studied in a rapidly subsiding Spartina alterniflora Lois. salt marsh following the addition at 47 and 94 Kg m^–2 of new sediment. Plant growth was enhanced in response to sediment addition as was evident by a significant increase in leaf area, above-ground biomass production and regeneration of new culms (p 0.05). Leaf conductance and transpiration rates were significantly greater in sediment treated plants than in control plants (p 0.05). Enhanced production of culms per unit area of marsh resulted in increased leaf area which allowed a greater capacity for net photosynthesis and contributed to increases in above-ground biomass of sediment treated plots.