Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the ...diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species,
Lotus corniculatus
(Fabaceae) and
Plantago lanceolata
(Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.
We compared the role of grasses and forbs in managed grassland under nutrient‐poor conditions via the experimental removal of one of these two species groups and an evaluation of the removal effects ...over a 5‐year chronosequence (beginning 4 years after removal start), focusing on above‐ground biomass and community composition. There was evidence for the complementarity of grasses and forbs, as shown by better relative performance of both groups in the mixture, measured as the proportional deviation of their above‐ground biomass from that predicted using single‐group plots. Relative performance of forbs was better than that of grasses and did not change significantly throughout the experiment. Relative performance of grasses decreased, reaching a minimum value of 0·03, but then increased to 0·71, in parallel with increasing legume proportion in the above‐ground biomass (from 0·9 to 5·1%). The botanical composition of the grass group did not respond to forb removal. Among the forbs, subordinate species sensitive to light competition became more abundant after removal of grasses; the forb species richness increased on average by 1·6 species per plot. Our results show that the composition and diversity of the forb group is affected by the presence of grasses, and the presence of forbs in a grassland community assures higher temporal stability in above‐ground production. Under increasing depletion of soil nutrients, the grasses derive substantial benefits from the presence of legume species and possibly also from the other forb species. The study supports the need for realistic, long‐term experiments to better understand plant community dynamics.
A scanning tunneling microscopy/atomic force microscopy study is presented of a kinetically driven growth instability, which leads to the formation of ripples during Si homoepitaxy on slightly ...vicinal Si(0
0
1) surfaces miscut in 1
1
0 direction. The instability is identified as step bunching, that occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. We demonstrate, that the growth instability with the same characteristics is observed in two dimensional kinetic Monte Carlo simulation with included Si(0
0
1)-like diffusion anisotropy. The instability is mainly caused by the interplay between diffusion anisotropy and the attachment/detachment kinetics at the different step types on Si(0
0
1) surface. This new instability mechanism does not require any additional step edge barriers to diffusion of adatoms. In addition, the evolution of ripple height and periodicity was analyzed experimentally as a function of layer thickness. A lateral “ripple-zipper” mechanism is proposed for the coarsening of the ripples.
Questions: How is succession on ex-arable land affected by sowing high and low diversity mixtures of grassland species as compared to natural succession? How long do effects persist? Location: ...Experimental plots installed in the Czech Republic, The Netherlands, Spain, Sweden and the United Kingdom. Methods: The experiment was established on ex-arable land, with five blocks, each containing three 10 m × 10 m experimental plots: natural colonization, a low- (four species) and high-diversity (15 species) seed mixture. Species composition and biomass was followed for eight years. Results: The sown plants considerably affected the whole successional pathway and the effects persisted during the whole eight year period. Whilst the proportion of sown species (characterized by their cover) increased during the study period, the number of sown species started to decrease from the third season onwards. Sowing caused suppression of natural colonizing species, and the sown plots had more biomass. These effects were on average larger in the high diversity mixtures. However, the low diversity replicate sown with the mixture that produced the largest biomass or largest suppression of natural colonizers fell within the range recorded at the five replicates of the high diversity plots. The natural colonization plots usually had the highest total species richness and lowest productivity at the end of the observation period. Conclusions: The effect of sowing demonstrated dispersal limitation as a factor controlling the rate of early secondary succession. Diversity was important primarily for its ‘insurance effect’: the high diversity mixtures were always able to compensate for the failure of some species. Abbreviations; ED = Euclidian distance; HD = High diversity; LD = Low diversity; NC = Natural colonization
Ground-living spiders were studied using modified pitfall traps during several years in four characteristic habitats in Giant Mountains (Krkonoše Mts.), the High Sudetes, Czech Republic: alpine ...tundra, subalpine mire, tall-herb stand at the bottom of a glacial corrie, and decaying mountain spruce forest. Ecological and zoogeographical aspects of spider communities were analysed. The spider communities of alpine tundra, subalpine mire, and glacial corrie exhibited long-term stability, whereas the community of decaying mountain forest changed during observations. Small linyphiid spiders, dominating in mature forest, were gradually replaced by larger Iycosid and gnaphosid species. Zoogeographic characterization of mountain habitats was made based on species exhibiting disjunctive area. In contrast to plants, for spiders of boreal origin alpine tundra is the most important habitat for survival, followed by screes, mires, spruce forests, and corries.
The nucleation and growth of two-dimensional islands is studied with Monte Carlo simulations of a pair-bond solid-on-solid model of epitaxial growth. The conventional description of this problem in ...terms of a well-defined critical island size fails because no islands are absolutely stable against single atom detachment by thermal bond breaking. When two-bond scission is negligible, we find that the ratio of the dimer dissociation rate to the rate of adatom capture by dimers uniquely indexes both the island size distribution scaling function and the dependence of the island density on the flux and the substrate temperature. Effective pair-bond model parameters are found that yield excellent quantitative agreement with scaling functions measured for
Fe
Fe(001)
.
The seasonal dynamics of a community of endomycorrhizal fungal morphotypes in the roots of three grassland species (Achillea millefolium, Poa angustifolia, Plantago lanceolata) was evaluated, ...together with the effects of experimental treatment (mowing and phosphorus application) and the host plant properties. Strong seasonal variability was found in the fungal community, where clear seasonal patterns can be distinguished for several fungal morphotypes. The sampling date explained 20 to 30% of the total compositional variability for all three host species. The Plantago roots host the highest number of arbuscular mycorrhizal (AM) fungal populations. There are two co-dominant fungal morphotypes in Achillea roots (assigned to the genera Scutellospora and Glomus) and only one strongly dominant morphotype (assigned to Glomus), in the Poa roots. All three host species have a comparable pattern of richness of AM morphotypes with a single peak in the summer, possibly aligned with the flowering time of the host. This study found only a limited effect of mowing (on the abundance of Scutellospora-like morphotypes in the Poa roots) and no effect of fertilization with phosphorus. The effect of developmental age of individual host plants on the composition of the endomycorrhizal community was found in Plantago, but not in Achillea or Poa.
The recently observed kinetic growth instability of homoepitaxial layers on Si(001) was investigated by in-situ scanning tunneling microscopy (STM ) experiments. In the step-flow regime the ...instability consists of straight step bunches, and it vanishes both during two-dimensional (2-D) island growth and at high temperatures. Kinetic Monte Carlo (KMC) simulations were performed to identify the dominating mechanism causing the instability. Strong evidence for the presence of an asymmetric step-edge barrier with the behavior of an
inverse Ehrlich–Schwoebel barrier is found. Comparison between the experiments and the simulations reveal that only double atomic height
D
B steps, which form kinetically in a rather narrow temperature range, develop this type of step-edge barrier.
In this paper, we reflect on a number of aspects of ordination methods: how should absences be treated in ordination and how do model-based methods, including Gaussian ordination and methods using ...generalized linear models, relate to the usual least-squares (eigenvector) methods based on (log–) transformed data. We defend detrended correspondence analysis by theoretical arguments and by reanalyzing data that previously gave bad results. We show by examples that constrained ordination can yield more informative views on effects of interest compared to unconstrained ordination (where such effects can be invisible) and show how constrained axes can be interpreted. Constrained ordination uses an ANOVA/regression approach to enable the user to focus on particular aspects of species community data, in particular the effects of qualitative and quantitative environmental variables. We close with an analysis examining the interaction effects between two factors, and we demonstrate how principal response curves can help in their visualisation. Example data and Canoco 5 projects are provided as Supplementary Material.
Theoretical results for unstable homoepitaxy due to additional barriers to hopping at step edges are reviewed. Using both kinetic Monte Carlo simulations and numerical integration of a continuum ...equation, it was demonstrated that on a singular surface, pyramidal features (mounds) appear whose size and slope increases according to a power law. On a vicinal surface, ripples are created due to an instability of step edges. The ripples then undergo a secondary instability and break-up leading to a surface morphology indistinguishable from the one observed on the singular surface. In addition, deposition noise is shown to be an important factor in mound coarsening during unstable homoepitaxial growth. Computer simulations identify two regimes, high-temperature deterministic coarsening and a low-temperature noisy regime.
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