Vegetation transition following drainage in a high‐latitude hyper‐oceanic ecosystem

Questions: How does draining affect the composition of vegetation? Are certain functional groups favoured? Can soil parameters explain these differences? Location: Central Faroe Islands, treeless islands in the northern boreal vegetation zone. Since 1987, an area of 21 km² at 100–200 m a.s.l. was drained in order to provide water for hydro‐electric production. Method: Vegetation and soil of a drained area and a control, undrained neighbouring area of approximately the same size were sampled in 2007. Six sites were sampled in each area. The vegetation was classified with cluster analysis. Results: Four plant communities were defined in the area: Calluna vulgaris–Empetrum nigrum–Vaccinium myrtillus heath, Scirpus cespitosus–Eriophorum angustifolium blanket mire, Carex bigelowii–Racomitrium lanuginosum moss‐heath, Narthecium ossifragum–Carex panacea mire. Heath was more extensively distributed within, and was the dominant community of the drained area, whereas moss‐heath was more extensive in the undrained area. Blanket mire and mire had approximately the same distribution in both areas. For the blanket mire, species composition indicated drier conditions in the drained than in the undrained area. The drained area had higher frequencies of woody species and lichens, grasses had finer roots and available soil phosphate was considerably higher, whereas the undrained area had higher frequencies of grasses and sedges. Conclusion: The dominant plant communities were different in the two areas, which indicated that the blanket mire was drying in the drained area. Higher concentration of soil phosphate in the drained area also indicated increased decomposition of organic soils owing to desiccation.     

Factors influencing above‐ground and soil seed bank vegetation diversity at different scales in a quasi‐Mediterranean ecosystem

Questions

Are factors influencing plant diversity in a fire‐prone Mediterranean ecosystem of southeast Australia scale‐dependent?

Location

Heathy woodland, Otways region, Victoria, southeast Australia

Methods

We measured patterns of above‐ground and soil seed bank vegetation diversity and associated them with climatic, biotic, edaphic, topographic, spatial and disturbance factors at multiple scales (macro to micro) using linear mixed effect and generalized dissimilarity modelling.

Results

At the macro‐scale, we found species richness above‐ground best described by climatic factors and in the soil seed bank by disturbance factors. At the micro‐scale we found species richness best described above‐ground and in the soil seed bank by disturbance factors, in particular time‐since‐last‐fire. We found variance in macro‐scale β‐diversity (species turnover) best explained above‐ground by climatic and disturbance factors and in the soil seed bank by climatic and biotic factors.

Conclusions

Regional climatic gradients interact with edaphic factors and fire disturbance history at small spatial scales to influence species richness and turnover in the studied ecosystem. Current fire management regimes need to incorporate key climatic–disturbance–diversity interactions to maintain floristic diversity in the studied system.

     

Incorporating functional dissimilarities into sample‐based rarefaction curves: from taxon resampling to functional resampling

Question: Indices of functional diversity have been seen as the key for integrating information on species richness with measures that focus on those components of community composition related to ecosystem functioning. For comparing species richness among habitats on an equal‐effort basis, so‐called sample‐based rarefaction curves may be used. Given a study area that is sampled for species presence and absence in N plots, sample‐based rarefaction generates the expected number of accumulated species as the number of sampled plots increases from 1 to N. Accordingly, the question for this study is: can we construct a ‘functional rarefaction curve’ that summarizes the expected functional dissimilarity between species when n plots are drawn at random from a larger pool of N plots? Methods: In this paper, we propose a parametric measure of functional diversity that is obtained by combining sample‐based rarefaction techniques that are usually applied to species richness with Rao's quadratic diversity. For a given set of N presence/absence plots, the resulting measure summarizes the expected functional dissimilarity at an increasingly larger cumulative number of plots n (n≤N). Results and Conclusions: Due to its parametric nature, the proposed measure is progressively more sensitive to rare species with increasing plot number, thus rendering this measure adequate for comparing the functional diversity of species assemblages that have been sampled with variable effort.     

Local above‐ground persistence of vascular plants: Life‐history trade‐offs and environmental constraints

Questions: 1. Which plant traits and habitat characteristics best explain local above‐ground persistence of vascular plant species and 2. Is there a trade‐off between local above‐ground persistence and the ability for seed dispersal and below‐ground persistence in the soil seed bank? Locations: 845 long‐term permanent plots in terrestrial habitats across the Netherlands. Methods: We analysed the local above‐ground persistence of vascular plants in permanent plots (monitored once a year for ca. 16 year) with respect to functional traits and habitat preferences using survival statistics (Kaplan‐Meier analysis and Cox’ regression). These methods account for censored data and are rarely used in vegetation ecology. Results: Local above‐ground persistence is determined by both functional traits (especially the ability to form long‐lived clonal connections) and habitat preferences (especially nutrient requirements). Above‐ground persistence is negatively related to the ability for dispersal by wind and to the ability to accumulate a long‐term persistent soil seed bank (‘dispersal through time’) and is positively related to the ability for dispersal by water. Conclusions: Most species have a half‐life expectation over 15 years, which may contribute to time lags after changes in habitat quality or ‐configuration (‘extinction debt’). There is evidence for a trade‐off relationship between local above‐ground persistence and below‐ground seed persistence, while the relationship with dispersal in space is vector specific. The rate of species turnover increases with productivity.     

Community‐wide effects of below‐ground rhizobia on above‐ground arthropods

1. Plants take nutrients for their growth and reproduction from not only soil but also symbiotic microbes in the rhizosphere, and therefore below‐ground microbes may indirectly influence the above‐ground arthropod community through changes in the quality and quantity of plants. 2. Rhizobia are root‐nodulating bacteria that provide NH₄⁺ to legume plants. We examined bottom‐up effects of rhizobia on the community properties of the arthropods on host plants, using a root‐nodulating soybean strain (R+) and a non‐nodulating strain (R?) in a common garden. 3. R+ plants grew larger and produced a greater number of leaves than R? plants. We observed 28 species of herbivores and three taxonomic groups of predators on R+ and R? plants. The herbivorous species were classified into sap feeders (12 species) and chewers (16 species). 4. The species richness of overall herbivores, sap feeders, and chewers on R+ plants was greater than that on R? plants. Rhizobia positively affected the abundance of chewers. 5. The community composition of herbivores was significantly different between R? and R+ plants, although species diversity and evenness did not differ. 6. Rhizobia‐induced bottom‐up effects were transmitted to the third trophic level. The abundance, taxonomic richness, and diversity of the predators on R+ plants were greater but evenness was lower than those on R? plants. The community composition of predators was not affected by rhizobia. 7. These results indicate that the below‐ground microbes initiated bottom‐up effects on above‐ground herbivores and predators through trophic levels.     

博斯腾湖湖滨湿地植物多样性对季节变化的响应

研究生物多样性对季节的响应对于维持生态系统稳定、保护生物多样性、解析群落构建机制具有重要意义。本文以博斯腾湖湖滨湿地为研究对象,探究不同季节植物群落的物种多样性与功能多样性的变化规律。结果显示：(1)物种多样性指数随季节变化没有显著改变;功能多样性指数中,功能丰富度由春季到夏季逐渐减小,功能离散度逐渐增大;不同季节的功能均匀度差异性不显著;(2)植物功能性状在不同季节间差异显著;春季叶绿素含量显著低于夏季;夏季比叶面积和叶干物质含量显著高于秋季;叶片含水量和厚度由春季到秋季呈递增趋势;(3)影响Pielou指数和功能丰富度的主要环境因子分别为土壤铵态氮和速效磷;影响Shannon-Wiener指数、Simpson指数和功能均匀度的主要环境因子为土壤有机质;影响功能离散度的主要环境因子为土壤含水量;(4)影响最大株高的主要环境因子为土壤pH值;影响叶干物质含量的主要环境因子为土壤速效钾;影响叶片厚度和比叶面积的主要环境因子为土壤总磷;而影响叶片含水量的主要环境因子为土壤硝态氮;叶绿素含量与土壤因子无显著相关关系。     

土壤微生物生态过程与微生物功能基因多样性

土壤微生物在陆地生态系统中具有重要的生态功能,包括参与地球化学物质循环、污染物降解、环境剧烈变化的缓冲等.土壤微生物的生态功能与土壤功能联系密切,微生物群落结构与组成变化会直接影响土壤功能的发挥.土壤微生物通过具有生物活性的酶参与一系列的代谢活动,编码酶的功能基因成为微生物功能标记物.近10年中,以功能基因多样性为核心的分子生态学研究迅速发展,为从功能基因角度了解土壤微生物的生态功能提供了一个新的切入点.本文综述了与土壤微生物生态功能相关的功能基因多样性研究进展,并对该领域的发展前景提出展望.     

Fewer S‐alleles are maintained in plant populations with sporophytic as opposed to gametophytic self‐incompatibility

Plants use self‐incompatibility to reject pollen bearing alleles in common at the S‐locus. These systems are classified as gametophytic (GSI) if recognition involves haploid pollen or sporophytic (SSI) if recognition involves diploid paternal genotypes. Dominance in SSI systems reduces the number of S‐alleles, but it has not been clear which system should maintain greater diversity when all else is equal. We simulated finite populations to compare the equilibrium number of S‐alleles in populations with either GSI or a co‐dominant SSI system. When population size was constant, SSI systems maintained more S‐alleles than GSI systems. When populations fluctuated in response to an S‐Allee effect, fewer S‐alleles were observed in SSI systems when S‐allele diversity was low, and SSI populations were vulnerable to extinction over a broader range of parameters. Turnover rates at the S‐locus were also faster in SSI populations experiencing strong S‐Allee effects. Given the variable expectations concerning S‐allele diversity in these systems, we reviewed published estimates of S‐allele diversity. GSI populations have significantly more S‐alleles on average than SSI populations (GSI = 25.70 and SSI = 16.80). Dominance likely contributes to this pattern, although the demographic consequences of the S‐Allee effect may be important in populations with fewer than 10 S‐alleles.     

Effects of different components of diversity on productivity in artificial plant communities

In an experiment on artificial plant communities, the effects of three components of plant diversity—plant species diversity, plant functional group diversity and plant functional diversity—on community productivity and soil water content were compared. We found that simple regression analysis showed a positive diversity effect on ecosystem processes (productivity and soil water content). However, when three components of diversity were included in the multiple regression analyses, the results showed that functional group diversity and functional diversity had more important effects on productivity and resource use efficiency. These results suggested that, compared with species number, functional differences among species and the range of functional traits carried by plants are the basis of biodiversity effects on ecosystem functioning. These diversity effects of increasing functional group diversity or functional diversity were likely because species differing greatly in size, life form, phenology and capacity to capture and use resources efficiently in diverse communities realize complementary resource use in temporal, spatial, and biological ways.     

Plant‐mediated interactions among above‐ground and below‐ground life stages of a root‐feeding weevil

1. Interactions among herbivores mediated by plant responses to herbivore injury may have large impacts on herbivore population densities. Responses may persist for weeks after injury and may affect not only the initial (inducing) herbivore, but also herbivores that are spatially or temporally separated from the initial attacker. 2. In many plant–insect interactions, multiple life stages of the insect may be associated with the same plant, and these various stages may interact indirectly with one another via induced responses. The rice water weevil (RWW), Lissorhoptrus oryzophilus, a serious global pest of rice, is one such insect. A series of experiments were performed with root‐feeding larvae and leaf‐feeding adults of the RWW using three conventional rice varieties. 3. The first objective of this study was to test whether RWW adult feeding on rice leaves resulted in altered oviposition by subsequent adults. The hypothesis for the first objective was that RWW adult feeding would decrease plant suitability, resulting in reduced oviposition by subsequent adults. 4. The second objective was to test whether injury by RWW larvae to rice roots resulted in altered oviposition by subsequent adults. The hypothesis for the second objective was that below‐ground RWW larval feeding would decrease plant suitability of rice to above‐ground RWW adults, resulting in decreased oviposition. 5. Results provided inconsistent support for the first hypothesis, indicating that responses differed among combinations of variety and injury level. Conversely, consistent support for the second hypothesis was found, indicating that larval feeding on roots decreased suitability of rice plants for oviposition.     

Mass‐ratio and complementarity effects simultaneously drive aboveground biomass in temperate Quercus forests through stand structure

Forests play a key role in regulating the global carbon cycle, a substantial portion of which is stored in aboveground biomass (AGB). It is well understood that biodiversity can increase the biomass through complementarity and mass‐ratio effects, and the contribution of environmental factors and stand structure attributes to AGB was also observed. However, the relative influence of these factors in determining the AGB of Quercus forests remains poorly understood. Using a large dataset retrieved from 523 permanent forest inventory plots across Northeast China, we examined the effects of integrated multiple tree species diversity components (i.e., species richness, functional, and phylogenetic diversity), functional traits composition, environmental factors (climate and soil), stand age, and structure attributes (stand density, tree size diversity) on AGB based on structural equation models. We found that species richness and phylogenetic diversity both were not correlated with AGB. However, functional diversity positively affected AGB via an indirect effect in line with the complementarity effect. Moreover, the community‐weighted mean of specific leaf area and height increased AGB directly and indirectly, respectively; demonstrating the mass‐ratio effect. Furthermore, stand age, density, and tree size diversity were more important modulators of AGB than biodiversity. Our study highlights that biodiversity–AGB interaction is dependent on the regulation of stand structure that can be even more important for maintaining high biomass than biodiversity in temperate Quercus forests.