The relationship between nutrient availability,shoot biomass and species richness in grassland and wetland communities

The relationship was studied between shoot biomass, nutrient concentration in the soil and number of species per unit area. The study was carried out in two different parts of the Netherlands, the Gelderse Vallei (east of Amersfoort) and the Westbroekse Zodden (northwest of Utrecht). Four series of vegetation and soil samples were taken: one series in grassland and wetland communities, one series in grassland communities, one series in fen communities and one series in only one wetland community. The two series in grassland communities show a negative correlation between shoot biomass and species number and a positive correlation between shoot biomass and nutrient concentration in the soil. The opposite was found in the series in the fen communities: there was a positive correlation between species number and shoot biomass and a negative correlation between shoot biomass and nutrient concentrations. The series of samples that had been taken in only one wetland community showed an optimum curve for the relation between shoot biomass and number of species. It is concluded that in the plant communities studied the species richness per unit area increases with increasing productivity at low production levels (< 400–500 g/m²) and decreases with increasing productivity at higher production levels (> 400–500 g/m²).     

Relationship between soil nutrient availability and plant species richness in a tropical semi‐arid environment

Question: What is the relationship between soil fertility and plant species richness in the ‘fertile islands’ occurring beneath two species of legume (Cercidium praecox and Prosopis laevigata)? Location: Tehuacán‐Cuicatlán region, central Mexico. Methods: Plant richness was measured in three micro‐environments (below canopies of C. praecox, below canopies of P. laevigata and in areas without canopies). The concentration of soil nutrients (C, N and P), C and N in the microbiota, and processes of ecosystem functioning (net C mineralization rate and N mineralization) were measured. The relationship between soil variables and plant richness were assessed with ANCOVAs. Results: Soil nutrients and species richness increases markedly under fertility islands. There were higher concentrations of C and N in the soil, faster rates of C mineralization, and higher species richness under P. laevigata canopies. The relationship between soil fertility and species richness was always positive except for total N, ammonium and net C mineralization rate under C. praecox, and for available P under P. laevigata. Conclusions: The sign of the relationship between soil fertility and species richness varies according to the nutrient and the micro‐environment. Positive relationships could result from between species complementarity and facilitation. Negative relationships could be explained by a specific limitation threshold for some soil resources (P and N for plants and C for the soil microbiota) which eliminate the possibilities of between species complementarity and facilitation above that threshold. As in all observational studies, these relationships should be considered only correlational.     

Relationship between species richness and spatial and temporal distance from seed source in semi‐natural grassland

Question: How do traditional management practices of field margins maintain the biodiversity of native grassland species? Location: Semi‐natural grassland on the field margins of traditional and consolidated agricultural fields on Awaji Island, central Japan. Methods: The distance to the nearest traditional field margin to the study sites was determined because the traditional field was considered as a seed source of native vegetation to the semi‐natural grasslands under study. We selected field margins in consolidated fields of different ages and distances from seed sources. Indicator species for both field types were sought. Regression analysis and detrended correspondence analysis (DCA) were used to determine the effect of spatial and temporal distances on the species composition of native vegetation. Results: Species richness differed significantly between the margin of traditional and consolidated fields. We identified significant indicator species of traditional fields, but not of consolidated fields. In consolidated fields, species richness increased significantly with age and decreased significantly with increasing distance to the source. At younger sites, species richness decreased faster with distance to the source because of strong negative correlation, but not at older sites. DCA ordination plots similarly indicated that similarities of vegetation composition in consolidated and traditional fields decreased with distance, and the effect of distance decreased with age. Conclusions: The species composition of the grassland margins of consolidated field was more similar to the margins of traditional fields if the consolidated fields were older, and/or closer to traditional fields. This pattern suggests that dispersal may play a role in the establishment of species on field margins.     

Relationship between plant species richness and biomass in an arid sub-alpine grassland of the central Himalayas,Nepal

The hump-shaped relationship between plant species richness and biomass is commonly observed at fine scale for herbaceous vegetation in temperate climates. This relationship predicts that herbaceous species richness is highest at an intermediate level of biomass that corresponds to moderate competition or disturbance. However, this relationship has not previously been investigated in high arid sub-alpine mountain grasslands. We tested the humped-back prediction in the arid Trans-Himalayan mountain grassland with a seasonal grazing system. The study area is located in the bottom of a U-shaped valley, in the Manang district (3500 m a.s.l.). We sampled two hundred plots (1m × 1m) in two different types of pastures: common pasture and old field, which both have similar grazing practices. There was a significant unimodal relationship between species richness and biomass only in the common pasture, and when the two sites were analyzed together. The species turnover is estimated by DCA in standard deviation unit. The turnover was lower in the old field than in the common pasture. The unimodal relationship between plant species richness and biomass did not disappear after accounting for unknown environmental gradients expressed as DCA (detrended correspondence analysis) axes and spatial variables. The species richness is highest at 120 ± 40 g/m². The results indicate that a hump-shaped relationship is also found in arid Trans-Himalayan grasslands.     

Constraints on colonization and species richness along a grassland productivity gradient: the role of propagule availability

An important goal in ecology is to discern under what habitat conditions community structure is primarily regulated by local ecological interactions and under what conditions community structure is more regulated by the pool of available colonists. I conducted a seed addition experiment in successional grassland to evaluate the relative significance of neighbourhood biotic interactions and propagule availability in regulating plant colonization and species richness along a natural gradient of grassland productivity. In undisturbed field plots, seed additions of 34 species led to an increase in species richness in locations of low productivity, an effect that declined in magnitude as productivity increased. In disturbed plots, seed additions led to a relatively constant increase in species richness at all levels of productivity. The results support the hypothesis that the role of propagule availability in regulating colonization dynamics and species richness declines in significance relative to local-scale competitive interactions as habitat productivity increases.     

Relationship between global warming and species richness of vascular plants

We analyzed climatological and geographical variables in 90 countries from the Northern Hemisphere to determine the significant variability of plant species richness as it relates to broad-scale levels of global warming. This variability was quantified by the parameters of temperature and precipitation. Of the 27 temperature variables and 13 precipitation variables, 6 variables had negative influences on species richness while 5 variables had positive impacts. When we estimated the effect of higher temperatures, we found that a 1 or 2°C rise in global warming produced an increase in species richness of 1.6 or 3.2%, respectively.     

Nitrate availability and hydrophyte species richness in shallow lakes

1. Submerged plant richness is a key element in determining the ecological quality of freshwater systems; it has often been reduced or completely lost. 2. The submerged and floating‐leaved macrophyte communities of 60 shallow lakes in Poland and the U.K. have been surveyed and species richness related to environmental factors by general linearised models. 3. Nitrogen, and more specifically winter nitrate, concentrations were most important in explaining species richness with which they were inversely correlated. Phosphorus was subsidiary. Such an inverse relationship is consistent with findings in terrestrial communities. Polish lakes, with less intensively farmed catchments, had greater richness than the U.K. lakes. 4. The richest U.K. communities were associated with winter nitrate‐N concentrations of up to about 1–2 mg L^?1 and may correspond with ‘good’ ecological quality under the terms of the European Water Framework Directive. Current concentrations in European lowlands are often much higher.     

Seasonal changes in the relationship between plant species richness and community biomass in early succession

We analysed the relationship between plant species richness and productivity on first-year-old fields at two similar sites in central Europe. At both sites, a wide range of productivity levels was available resulting from different long-term fertilisation. In order to identify underlying mechanisms of the species richness–productivity relationship we included the seasonal dynamics and the number of individuals of each species in our analysis. We sampled 10 and 21 plots, respectively, at the two sites in May, June and July by harvesting all aboveground parts of vascular plants in 0.25 m² subplots. Species richness, number of individuals of each species and community biomass as a surrogate of productivity were recorded in each sample.At one site, the relationship between species richness and biomass was significantly positive in the May and June harvest. This relationship disappeared in the July harvest due to a reduction in species richness at high productivity levels. The relations between species richness and number of individuals and between number of individuals and biomass paralleled the species richness–productivity relation but the individual number–biomass relationship remained positive until the last harvest. Between-species differences in individual number–community biomass relationships and their seasonal dynamics revealed “interspecific competitive exclusion” even though the species richness–biomass relationships were not negative or hump-shaped. At the second site, species richness was not related to productivity or to number of individuals. Our study demonstrated the importance of temporal dynamics and regional processes in understanding species richness–productivity patterns.     

内蒙古草地叶片磷含量与土壤有效磷的关系

植物体内特别是叶片的P含量特征及其与环境的关系一直是植物生理生态学研究的一个热点。已有研究发现, 与全球植物数据相比, 中国植物叶片的P含量相对较低, 导致N/P高于全球平均水平, 并推测这是由于中国土壤全P含量较低引起的。该研究选取内蒙古草地来验证这一假设, 分析了36个样地57种优势植物叶片的P含量与土壤全P和有效P含量的关系。主要结果如下: 内蒙古草地叶片P含量较低而N/P较高, 与之前的研究结论一致; 在种群、样地和物种3个水平上, 叶片P含量、N/P与土壤P含量都没有显著的相关关系, 尽管土壤有效P含量的解释力高于土壤全P; 另一方面, 内蒙古草地土壤的有效P含量与全国土壤普查的结果接近, 高于美国及澳大利亚的平均值, 但低于世界土壤信息库里报道的全球土壤有效P平均值。鉴于内蒙古草地土壤的全P和有效P含量都不能准确反映叶片P含量, 且土壤的有效P含量也并不明显低于世界其他地区, 因此植物叶片P含量低、N/P高是由于土壤P含量低引起的这一假设在内蒙古草地不成立, 而且叶片P含量也与土壤P的可利用性无关。     

Impact of flooding on potential and realised grassland species richness

In order to reduce flood risk, river management policies advise floodplain restoration and the recreation of water retention areas. These measures may also offer opportunities for the restoration of species-rich floodplain habitats through rewetting and the restoration of flood dynamics. The potential to enhance biodiversity in such flood restoration areas is, however, still subject to debate. In this paper we investigate whether flooding along a small altered lowland river can contribute to the potential and realised species richness of semi-natural meadows. We compare the seed bank and vegetation composition of flooded and non-flooded semi-natural meadows and test the hypothesis that flooding contributes to an input of diaspores into the meadow seed banks, thereby promoting seed density and potential species richness. Furthermore we hypothesise that, where habitat conditions are suitable, flooding leads to a higher realised species richness. Results showed that seed densities in flooded meadows were significantly higher than in non-flooded meadows. The seed banks of flooded meadows also contained a higher proportion of exclusively hydrochorous species. However, the seed bank species richness, as well as the species richness realised in the vegetation did not differ significantly between flooded and non-flooded meadows. Finally, the seed bank and standing vegetation of flooded sites showed larger differences in species composition and Ellenberg nitrogen distribution than non-flooded sites. From these results we conclude that, although flooding does contribute to the density and composition of the seed bank, most imported seeds belong to only a few species. Therefore, it is unlikely that flooding substantially enhances the potential species richness. Furthermore, even if new species are imported as seeds into the seed bank, it seems unlikely that they would be able to establish in the standing vegetation. However, it is unclear which factors impede the establishment of imported species in the vegetation. The implications of our findings for flood meadow restoration are discussed.     

Effects of light and nutrient availability on dry matter and N allocation in six successional grassland species

Summary Recent discussions on determinants of competitive success during succession require the study of the combined effect of light and nutrient availability on growth and allocation. These effects can be used to predict the outcome of competition at changing resource availabilities. This work is part of a study on the successional sequence in permanent grassland starting after fertilizer application is stopped, but with continued mowing, in order to restore former species-rich communities. This yields a successional sequence which proceeds from grasslands with a high nutrient availability and a closed canopy, to grasslands with a low nutrient availability and an open canopy. If allocation is related to competitive ability, species from the productive stages would be expected to allocate more biomass and nitrogen to leaves, which could make them better competitors for light, while species from the unproductive stages would allocate more biomass to roots, which could make them better nutrient competitors. This study reports on growth, specific leaf area (SLA), vertical display of leaves, and allocation of biomass and nitrogen of six grassland species from this successional sequence at 16 combinations of light and nutrient supply. Species from the poorer successional stages reached a lower final dry weight than species from the richer stages, over all treatment combinations. The experimental design made it possible to test for unique effects of the resource ratio effect of light and nutrients on allocation characteristics. This resource-ratio effect was defined as the ratio light intensity/(light intensity + nutrient supply rate), using standardized levels for the treatments. The within-species variation (plasticity) in both allocation of dry matter and nitrogen was linearly related to this resource-ratio effect. Some interspecific differences in this relationship were found which could be related to the position of the species along the successional gradient. However, the range of plasticity in allocation pattern expressed within each species was much larger than the differences between species. It was concluded that allocation differences between these grassland species are relatively unimportant, given the large amount of plasticity in these traits. Interspecific differences in SLA and vertical stature seemed to be more important in explaining the position of species along the successional gradient.     

The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia

In this study, we examined to what extent the internal site factors (light and soil conditions) are responsible for herb layer diversity in oak-dominated forest stands growing on different substrates in central Bohemia (Czech Republic). We collected data on herb layer diversity, light and nutrient availability at nine oak stands, representing the range of environmental variability for these types of forests in the region. We found that species richness increased with light availability, but only if the site occupied predominantly by fast-colonizing species was excluded from the analysis (P < 0.05). Species richness correlated positively with soil pH and negatively with nitrogen (N) concentration in humus (P < 0.05). The highest species richness was found at sites with not only low N soil concentration, but also simultaneously with high phosphorus (P) soil concentration. Despite this finding, however, herb layer diversity is evidently threatened much more in P-rich soils than in P-poor soils. It seems that the enhancement of N in an ecosystem due to litter accumulation and N deposition generally leads to only a minor increase in N availability at P-poor sites, but a considerable increase at P-rich sites. Therefore, species richness can be exceptionally high at P-rich sites, but only under conditions of strong N limitation.     

Responses of fen plant species to groundwater level and light intensity

Characteristic species of sedge-moss fen communities occur in constantly wet, nutrient-poor sites with a high penetration of light through the vegetation canopy. We studied the effects of water table depth and differences in light intensity on the performance of fen species. Three fen species (Carex curta, Viola palustris, Hydrocotyle vulgaris) and one species with a wide range of occurrence (Poa trivialis) were grown for 10 weeks in a sedge-moss peat substrate at 4 different water levels and 3 light intensities. In all species differences in light availability had a larger effect on biomass production than differences in water level. Under a light availability reduced to only 10% the root weight ratio of all the species decreased while leaf weight ratio increased. The biomass allocation ratios were hardly affected by differences in water level. For Viol a and Hydrocotyle an interaction between the two factors was observed. Poa did not show particular differences compared to the other species. We discuss the results in the context of the establishment of fen species in riparian vegetation. It is suggested that the occurrence of fen species in the landscape is directly related to the availability of light, whereas the relationship between fen species occurrence and hydrological conditions seems to be an indirect one.     

Seasonality in fruit availability affects frugivorous primate biomass and species richness

We examine the effect of total annual food abundance and seasonal availability on the biomass and species richness for frugivorous primates on three continents (n=16 sites) by data on fruit fall. We reveal that the best‐fit models for predicting primate biomass include total annual fruit fall (positive), seasonality (negative) and biogeography (Old World>New World and mainland>island) and that these factors explain 56–67% of the variation. For the number of species, the best‐fit models include seasonality (negative) and biogeography (Old World>New World and mainland>island) but not total annual fruit fall. Annual temperature has additional effects on primate biomass when the effects of fruits and biogeography are controlled, but there is no such effect on species richness. The present results indicate that, measured on local scales, primate biomass and number of species is affected by the seasonal variation in food availability.     

Diaspore and gap availability are limiting species richness in wet meadows

Species pool theory claims that diaspore and microsite availability limit species richness in plant communities. Wet meadows (Calthion) and litter meadows (Molinion, Caricion davallianae) belonging to the most species-rich meadows in the foothills of the Alps have suffered from a strong decrease since the 1970s. Restoration efforts including nutrient impoverishment and rewetting management after drainage and fertilization did not result in the re-establishment of the former species richness although the abiotic filter would have been appropriate for the re-colonization of many locally extinct species. In our experiment at four sites in the largest fen of Southwest-Germany we tested if the restoration success was seed- and gap-limited. We applied sowing and hay spreading (hay seed) as treatments to make seeds available and harrowing to increase gap availability. Sowing seeds or hay seed of species of the former meadow types increased species richness immediately. The proportion of re-established species was higher when additional harrowing was applied. Species richness could be increased not only in vascular plants but also in bryophytes when hay spreading was applied. The strongest re-development towards the target communities (defined through the abiotic filter and the species richness before drainage and fertilization) took place on those sites where hay spreading and harrowing were applied. Sowing seeds and hay seed were traditional techniques to establish e.g. litter meadows, both techniques have been applied for centuries. Even harrowing was described as early as the 19th century to increase the chance of establishing certain species. Therefore, the “application of the knowledge coming from the species pool theory” (although not named during this time) has been common practice since at least the 19th century.     

Relationship between plant species richness and biomass in a coastal Maine Quercus-Pinus forest

Abstract. Several researchers have hypothesized that plant species richness has a unimodal relationship with biomass, while others have argued for a linear relationship. Data from various types of herbaceous communities show some support for the unimodal hypothesis, but this has not been tested extensively for forests and questions remain concerning its generality. We used linear and quadratic regression models to examine the relationship between overstory biomass and richness in a coastal Maine Quercus-Pinus forest across and within cover types using data from two plot sizes (2500-m² quadrats and 625-m² sub-quadrats). Understory data from 1-m² plots were also analysed. Richness was quadratically related to biomass at both plot sizes for all cover types combined, but the amount of variation explained by the models was very low (R²s < 0.09). Richness and biomass were not significantly related at either plot size for the mixed mesic cover type, the most common type in the forest. The best fit (R²= 0.43) was obtained with a quadratic model for the conifer cover type at the sub-quadrat level, with the quadratic model for the 1-m² data having the second highest R² (0.24). Across all six data sets, the quadratic model was the only one with a significant fit in two cases, and had considerably higher R²s (1.3–1.9 ×) in two others. The remaining two data sets could not be fit with a significant model of either type. For this forest, these results suggest little support for a linear relationship between plant species richness and biomass and variable, often weak, support for a unimodal relationship. Density, a potentially confounding variable in this type of analysis, was only weakly correlated with richness and was not found to alter the relationship between biomass and richness.     

Functional composition rather than species richness determines root characteristics of experimental grasslands grown at different light and nutrient availability

Plant and Soil - Results from many biodiversity experiments have established evidence for positive effects of diversity on aboveground plant productivity. However, less is known about the...