Functional Group Level Research Articles

Recent strategies to develop polysaccharide-based nanomaterials for biomedical applications.

Polysaccharides are abundant in nature, renewable, nontoxic, and intrinsically biodegradable. They possess a high level of functional groups including hydroxyl, amino, and carboxylic acid groups. These functional groups can be utilized for further modification of polysaccharides with small molecules, polymers, and crosslinkers; the modified polysaccharides have been used as effective building blocks in fabricating novel biomaterials for various biomedical applications such as drug delivery carriers, cell-encapsulating biomaterials, and tissue engineering scaffolds. This review describes recent strategies to modify polysaccharides for the development of polysaccharide-based biomaterials; typically self-assembled micelles, crosslinked microgels/nanogels, three-dimensional hydrogels, and fibrous meshes. In addition, the outlook is briefly discussed on the important aspects for the current and future development of polysaccharide-based biomaterials, particularly tumor-targeting intracellular drug delivery nanocarriers.

Microhabitat variations and seed bank-vegetation relationships in a desert wadi ecosystem

Due to extreme variability in patterns of rainfall, plant seed banks are an important component of desert habitats. Here I report on effects of standing vegetation and three different microhabitats (channel, bank and terrace) on the soil seed bank of a desert wadi ecosystem in the Eastern Desert of Egypt. A total of 450 soil samples at 45 stands were collected to represent the different wadi microhabitats. The germinable seed bank was estimated by controlled counts of seedling emergence. The floristic composition, functional properties and diversity of the soil seed bank, as well as its similarity with the standing vegetation varied among wadi microhabitats. Such variation could be attributed to differences in disturbance intensity among microhabitats (terrace<bank<channel) and variation of soil factors along the microtopographic gradient. Channel showed the highest species richness and size of soil seed bank, followed by bank and then terrace. Moreover the Shannon index of diversity of the seed bank and its similarity with standing vegetation were significantly greater in both channel and bank microhabitats than in terrace. At the level of plant functional groups, number of seeds of annuals was higher in both channel and bank than in terrace. Shrubs were more abundant in seed banks of channel compared to terrace. The size and species richness of seed bank were increased with the total plant cover, annual/perennial ratio and species richness of the standing vegetation.

Effects of experimentally-enhanced precipitation and nitrogen on resistance, recovery and resilience of a semi-arid grassland after drought.

Resistance, recovery and resilience are three important properties of ecological stability, but they have rarely been studied in semi-arid grasslands under global change. We analyzed data from a field experiment conducted in a native grassland in northern China to explore the effects of experimentally enhanced precipitation and N deposition on both absolute and relative measures of community resistance, recovery and resilience--calculated in terms of community cover--after a natural drought. For both absolute and relative measures, communities with precipitation enhancement showed higher resistance and lower recovery, but no change in resilience compared to communities with ambient precipitation in the semi-arid grassland. The manipulated increase in N deposition had little effect on these community stability metrics except for decreased community resistance. The response patterns of these stability metrics to alterations in precipitation and N are generally consistent at community, functional group and species levels. Contrary to our expectations, structural equation modeling revealed that water-driven community resistance and recovery result mainly from changes in community species asynchrony rather than species diversity in the semi-arid grassland. These findings suggest that changes in precipitation regimes may have significant impacts on the response of water-limited ecosystems to drought stress under global change scenarios.

Comparison of EMC and durability of heat treated wood from high versus low water vapour pressure reactor systems

A large number of different heating technologies has been put into use for industrial scale thermal modification of wood. A useful classification of these processes is by the level of water vapour pressure, which ranges from vacuum to high saturated steam pressures. Only high water vapour pressure systems can maintain a finite moisture content during the heat treatment, but little is known about the water vapour pressure dependence of the thermal modification chemistry and the resulting modified wood properties. It is concluded from our analysis that the thermal wood reaction chemistry at the molecular functional group level is quite independent of the process and wood species. Wood properties that are strongly determined by wood chemical composition, such as the fungal durability and the equilibrium moisture content (EMC), can hence be equally achieved by all processes and for all wood species. This finding cannot be transferred to every other thermally modified wood property.

A novel approach to the determination of the pyruvate and acetate distribution in xanthan

The present work demonstrates a quantitative relation between the physical properties of the order disorder transition in xanthan, such as transition temperature and modulus, and the acetate and pyruvate content. Models have been constructed which reflect simple linear dependence of transition temperature and the logarithm of the modulus on acetate, pyruvate, xanthan and salt concentration. Biphasic transitions in xanthan detected using Differential Scanning Calorimetry (DSC) are proposed to reflect phases containing different acetate and pyruvate levels in each phase. The respective acetate and pyruvate contents in these phases have been estimated. 13C Cross Polarisation Magic Angle Spinning (CPMAS) Nuclear Magnetic Resonance measurements further suggest that the distribution of functional groups measured in solution is reflected in a distribution of environments in solid powders. This could take the form of heterogeneity along an individual chain (intra-chain heterogeneity) or uniform but different levels of functional groups in individual chains (inter-chain heterogeneity). Support for the intra-chain proposal or “blocky” distribution is provided by samples which have been reported to exhibit different transition temperatures despite having apparently the same overall acetate and pyruvate content. This is ascribed to the values of transition temperature being different along an individual chain.

Climate change and climatic events: community-, functional- and species-level responses of bryophytes and lichens to constant, stepwise, and pulse experimental warming in an alpine tundra

We experimentally imposed three different kinds of warming scenarios over 3 years on an alpine meadow community to identify the differential effects of climate warming and extreme climatic events on the abundance and biomass of bryophytes and lichens. Treatments consisted of (a) a constant level of warming with open top chambers (an average temperature increase of 1.87 °C), (b) a yearly stepwise increase of warming (average temperature increases of 1.0; 1.87 and 3.54 °C, consecutively), and (c) a pulse warming, i.e., a single first year pulse event of warming (average temperature increase of 3.54 °C only during the first year). To our knowledge, this is the first climate change study that attempts to distinguish between the effects of constant, stepwise and pulse warming on bryophyte and lichen communities. We hypothesised that pulse warming would have a significant short-term effect compared to the other warming treatments, and that stepwise warming would have a significant mid-term effect compared to the other warming treatments. Acrocarpous bryophytes as a group increased in abundance and biomass to the short-term effect of pulse warming. We found no significant effects of mid-term (third-year) stepwise warming. However, one pleurocarpous bryophyte species, Tomentypnum nitens, generally increased in abundance during the warm year 1997 but decreased in control plots and in response to the stepwise warming treatment. Three years of experimental warming (all treatments as a group) did have a significant impact at the community level, yet changes in abundance did not translate into significant changes in the dominance hierarchies at the functional level (for acrocarpous bryophytes, pleurocarpous bryophytes, Sphagnum or lichens), or in significant changes in other bryophyte or lichen species. The results suggest that bryophytes and lichens, both at the functional group and species level, to a large extent are resistant to the different climate change warming simulations that were applied.

Structure-dependent interactions of polyphenols with a biomimetic membrane system

Polyphenols are naturally-occurring compounds, reported to be biologically active, and through their interactions with cell membranes. Although association of the polyphenols with the bilayer has been reported, the detailed mechanism of interaction is not yet well elucidated. We report on spatio-temporal real-time membrane dynamics observed in the presence of polyphenols. Two distinct membrane dynamics, corresponding to the two classes of polyphenols used, were observed. Flavonoids (epi-gallocatechin-3-gallate, gallocatechin, theaflavin and theaflavin-3-gallate) caused lipid membrane aggregation and rigidification. As simple structural modification through opening of the aromatic C-ring into an olefin bond, present in trans-stilbenes (resveratrol and picead), completely changed the membrane properties, increasing fluidity and inducing fluctuation. There were differences in the membrane transformations within the same class of polyphenols. Structure-dependent classification of membrane dynamics may contribute to a better understanding of the physicochemical mechanism involved in the bioactivity of polyphenols. In general, an increase in the number of hydrophilic side chains (galloyl, hydroxyl, glucoside, gallate) increased the reactivity of the polyphenols. Most notable was the difference observed through a simple addition of the gallate group. Unraveling the importance of these polyphenols, at a functional group level further opens the key to tailored design of bioactive compounds as potential drug candidates.

The impact of livestock grazing on plant diversity: an analysis across dryland ecosystems and scales in southern Africa.

A general understanding of grazing effects on plant diversity in drylands is still missing, despite an extensive theoretical background. Cross-biome syntheses are hindered by the fact that the outcomes of disturbance studies are strongly affected by the choice of diversity measures, and the spatial and temporal scales of measurements. The aim of this study is to overcome these weaknesses by applying a wide range of diversity measures to a data set derived from identical sampling in three distinct ecosystems. We analyzed three fence-line contrasts (heavier vs. lighter grazing intensity), representing different degrees of aridity (from arid to semiarid) and precipitation regimes (summer rain vs. winter rain) in southern Africa. We tested the impact of grazing intensity on multiple aspects of plant diversity (species and functional group level, richness and evenness components, alpha and beta diversity, and composition) at two spatial scales, and for both 5-yr means and interannual variability. Heavier grazing reduced total plant cover and substantially altered the species and functional composition at all sites. However, a significant decrease in species alpha diversity was detected at only one of the three sites. By contrast, alpha diversity of plant functional groups responded consistently across ecosystems and scales, with a significant decrease at heavier grazing intensity. The cover-based measures of functional group diversity responded more sensitively and more consistently than functional group richness. Beta diversity of species and functional types increased under heavier grazing, showing that at larger scales, the heterogeneity of the community composition and the functional structure were increased. Heavier grazing mostly increased interannual variability of alpha diversity, while effects on beta diversity and cover were inconsistent. Our results suggest that species diversity alone may not adequately reflect the shifts in vegetation structure that occur in response to increased grazing intensity in the dryland biomes of southern Africa. Compositional and structural changes of the vegetation are better reflected by trait-based diversity measures. In particular, measures of plant functional diversity that include evenness represent a promising tool to detect and quantify disturbance effects on ecosystems.

The Relationships Between MBO System Strength and Goal‐Climate Quality and Strength

We adopted Bowen and Ostroff's () HRM system strength concept so as to test it within the context of a management by objectives (MBO) system, which was utilized by six independent firms owned by a large, diversified family business group in Turkey. For this purpose, we surveyed the middle managers to measure 10 context‐specific metafeatures of the MBO system. By using aggregated scores at the functional group level (N = 47), we captured the distinctiveness, consistency, and consensus dimensions of this HRM practice. We tested and compared three alternative theoretical models of HRM strength where the three dimensions have compensatory, additive, and distinctiveness mediated effects on climate quality and strength. Results support the compensatory model and indicate that the strength of the MBO system (as a reflective latent variable representing the shared variance of the system's distinctiveness, consistency, and consensus) is positively related to business units’ quality and strength of goal climate. In addition, distinctiveness—but not consistency and consensus—of the MBO system appears to be particularly critical for the emergence of a strong and high‐quality goal climate. Lastly, implications and limitations of the study as well as possible future research directions are discussed. © 2014 Wiley Periodicals, Inc.

Short‐term spatial stability in trophic interactions

Summary The concept of stability in ecological theory has been a subject of debate for more than 40 years. Its value lies in being the explanatory principle underlying equilibrium in nature. Until now, the possibility of spatial stability in trophic interactions, defined as resilience of trophic activity (e.g. herbivore/algae or predator/prey) within patches after a disturbance, has not been explored. This concept requires the demonstration of two properties: (i) the return after a strong disturbance to a reference level of intensity of the trophic interaction (intensity criterion), and (ii) positive spatial correlation between pre‐ and post‐disturbance intensity of the trophic interaction (spatial determinism criterion). The first criterion can be assessed by checking the consistency of intensities of grazing effects between years and the second criterion by correlating the intensities of grazing between years on the same set of patches. We used a spatially explicit test, repeated after experimental disturbance of the same plots in two consecutive years, to test for the existence of spatial stability in the effects of grazing on rocky shore algal assemblages. The detection of spatial stability depended on the level of resolution at which the prey assemblages were examined (species, functional group and trophic level) and allowed us to demonstrate stability in grazing effects, which shape the mosaic of patches on the high rocky shore at scales of 10s of meters. The community analysed was highly resilient due to its domination by species that can quickly re‐colonize and recover to pre‐disturbance levels and showed spatial determinism because of the tendency of both grazers and algae to colonize particularly favourable areas. Synthesis. The most important findings are as follows: (i) spatial stability was confirmed for a trophic interaction, and (ii) spatial determinism in these systems was detectable. We suggest that patches exhibiting predictability in trophic interaction strength can function as initiators of recovery after disturbance and at the same time represent the deterministic initial condition that might shape long‐term spatial configurations within the landscape.

The interaction between arbuscular mycorrhizal fungi and soil phosphorus availability influences plant community productivity and ecosystem stability

Summary Arbuscular mycorrhizal fungi (AMF) can influence plant community composition and diversity. Previous research has shown that the addition of nutrients reduces the effectiveness of AMF. However, the ways in which soil nutrient availability and AMF interact and affect plant community productivity and ecosystem stability are still poorly understood. We examined the impact of AMF suppression and phosphorus (P) addition on plant diversity, community productivity and temporal stability (TS) in a field experiment. AMF root colonization and the concentration of an AMF‐specific phospholipid fatty acid were significantly reduced after application of the fungicide benomyl as a soil drench. The TS of the plant community was higher in communities without benomyl application compared with communities with benomyl application indicating that AMF contribute to the TS of plant communities. AMF suppression increased productivity at the plant species, functional group and community levels under high P addition rates. At the zero P addition rate, AMF did not affect plant community productivity, as the dominant species Artemisia frigida was more abundant in control plots with AMF, while the subdominant species Stipa krylovii was more abundant in the benomyl‐treated plots with reduced AMF abundance. Compensatory effects between C3 grasses and non‐N2‐fixing forbs were observed in the control plots with AMF along the gradient of P addition rates, but these effects were not detected among plant species in the benomyl‐treated plots under AMF suppression above an addition rate of 4.76 P2O5 m−2 year−1. Although AMF suppression did not influence the diversity of the plant communities, it did decrease the diversity of N2‐fixing forbs at the zero P addition rate and above an addition rate of 18.90 g P2O5 m−2 year−1, indicating that AMF play key roles in the maintenance of N2‐fixing forbs at these P addition rates. P addition led to biodiversity losses at application rates below 2.36 g P2O5 m−2 year−1 at the community level. Synthesis. Arbuscular mycorrhizal fungi and soil P availability interact to influence the productivity and TS of a plant community by mediating compensatory effects among plant species and functional groups.

Recent changes in macroalgae distribution patterns in the Orbetello lagoon (Italy)

1 - This study related recent distribution changes in seven macroalgae taxa (Acetabularia acetabulum, Chaetomorpha linum, Cladophora sp., Gracilariopsis longissima, Spyridia sp., Ulva laetevirens, Valonia aegagrophyla) to spatial (basin) and temporal (time) trophic differences in a meso-eutrophic Mediterranean coastal lagoon (Orbetello, Italy). 2 - In July 2003 and July 2009, the coverage percentage (CP) of each considered taxon was measured in 38 stations equally distributed in the Western and Eastern lagoon basins. All data were analysed using SURFER v8.0 software along with ANOVA, ANOSIM and multivariate analyses to produce geostatistical spatial distribution maps and to estimate statistical probabilities for “basin” and “time” factors. 3 - Data from this study were integrated with data on phanerogams reported by Giovani et al. (2010) to evaluate changes occurring at a functional group level from 2003-2009 using the Ecological Evaluation Index (EEI). 4 - Observed macroalgae changes may have been due to lagoon management activities performed during the study period. The removal of direct nitrate inputs seems to have forced specie-specific shifts that were highly significant only in the Western basin. 5 - Statistically significant differences at the taxon level have been indicated for Spyridia sp. (basin and time) and Cladophora sp. (time) taxa. Other non-significant changes included a rarefaction of Chaetomorpha linumin the Western basin and Spyridia sp. in the Eastern basin, and an increase of Gracilariopsis longissima, C. linum and Valonia aegagrophyla in the Eastern basin. 6 - EEI application indicated a general improvement in water quality due to management measures applied in Western basin, whereas the Eastern basin evidences stability/slight degradation from 2003-2009

Spatio temporal and environmental factors influencing macroalgal β diversity in the Red Sea, Egypt

Abstract β Diversity is an ecological concept used to describe the turnover of species across a wide range of spatial and temporal scales, but such knowledge is lacking for macroalgal assemblages of the Red Sea. β Diversity patterns for Red Sea macroalgae were evaluated from different sites (Hurghada, Safaga, and Al-Quseir) and seasons across different environmental disturbances. β Diversity was studied by partitioning the total number of species (γ diversity) into additive components. Geographical heterogeneity was more important than seasonal heterogeneity in structuring macroalgae both at species and functional group levels. Species replacement as a component of β diversity produced dissimilarity in species composition and taxonomic structure. Replacement of species between sites was responsible for the presence of new functional groups of macroalgae. High β diversity and taxonomic similarity values were characteristic of the macroalgae of the Red Sea. The occurrence of small macroalgal thalli that have short life cycles induced high species replacement and subsequently high β diversity, with spatial heterogeneity and environmental gradient as drivers of β diversity. Anthropogenic disturbance at the Safaga site was suggested to induce variation of macroalgal assemblages and functional groups. Excluding rare species from the data set did not change the high values of b diversity.

Exploring the potential effects of climate change on the Western Scotian Shelf ecosystem, Canada

Climate change is expected to cause profound changes in marine ecosystems that will vary in magnitude and effect among regions. We explore the potential effects of climate change on the western Scotian Shelf ecosystem in eastern Canada using an ecosystem model and two scenarios of climatic changes. The model includes the effects of temperature, pH, oxygen, decreased primary productivity and change in zooplankton size structure. These factors had differential, and sometimes opposing additive effects on the functional groups and species. The results also illustrate how the effects of climate change can be further enhanced or ameliorated by predator–prey interactions. At the individual species or functional group level, some effects were negligible, but at the ecosystem level, the combined predicted effect of climate change on the western Scotian Shelf led to a reduction in biomass of 19% to 29% with an associated decrease in catches of 20% and 22%. Dramatic declines in biomass due to climate drivers could be alleviated in part by a 50% decrease in exploitation rate.

Quantitative Evaluation of Interaction Force between Functional Groups in Protein and Polymer Brush Surfaces

To understand interactions between polymer surfaces and different functional groups in proteins, interaction forces were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Various polymer brush surfaces were systematically prepared by surface-initiated atom transfer radical polymerization as well-defined model surfaces to understand protein adsorption behavior. The polymer brush layers consisted of phosphorylcholine groups (zwitterionic/hydrophilic), trimethylammonium groups (cationic/hydrophilic), sulfonate groups (anionic/hydrophilic), hydroxyl groups (nonionic/hydrophilic), and n-butyl groups (nonionic/hydrophobic) in their side chains. The interaction forces between these polymer brush surfaces and different functional groups (carboxyl groups, amino groups, and methyl groups, which are typical functional groups existing in proteins) were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Furthermore, the amount of adsorbed protein on the polymer brush surfaces was quantified by surface plasmon resonance using albumin with a negative net charge and lysozyme with a positive net charge under physiological conditions. The amount of proteins adsorbed on the polymer brush surfaces corresponded to the interaction forces generated between the functional groups on the cantilever and the polymer brush surfaces. The weakest interaction force and least amount of protein adsorbed were observed in the case of the polymer brush surface with phosphorylcholine groups in the side chain. On the other hand, positive and negative surfaces generated strong forces against the oppositely charged functional groups. In addition, they showed significant adsorption with albumin and lysozyme, respectively. These results indicated that the interaction force at the functional group level might be a suitable parameter for understanding protein adsorption.

Reproductive responses of alpine plants to grassland degradation and artificial restoration in the Qinghai–Tibetan Plateau

AbstractArtificial grassland establishment has been implemented in the alpine region of Qinghai–Tibetan Plateau in China as a mitigation tool against grassland degradation, one of the major environmental problems in this region. We hypothesized that both grassland degradation and artificial restoration may alter the reproductive modes of the alpine vegetation at the levels of individual species as well as plant functional groups. By investigating a long‐term field study of grassland degradation and artificial restoration experiments, we found that alpine plants can maintain a highly plastic relationship between sexual and asexual reproduction, that is, the alpine plants in degraded grasslands increased their efforts towards sexual reproduction while those in artificially restored grasslands promoted their efforts in vegetative reproduction with in the year after restoration. The high reproductive plasticity of the alpine plants can be regulated through a number of mechanisms, which include changing proportion of clonal species in the plant composition, altering number ratio of sexual and vegetative propagules, shifting biomass allocation for sexual and vegetative reproduction at both individual species and functional group levels. These conclusions demonstrate how crucial it is to consider manipulation of reproductive modes needed to restore the structure and stability of degraded alpine grasslands.

Benchmarking successional progress in a quantitative food web.

Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of ecological theory to form a complete picture of successional progress within a pelagic food web. This comprehensive synthesis may be used as a benchmark for quantifying successional progress in other ecosystems.

Environmental determinism and neutrality in vegetation at millennial time scales

AbstractQuestionsAt millennial scales, is the historic evolution of tropical plant communities the result of ‘random walk’? Are presence and abundance of taxa independent of environmental variability?LocationLake Petén‐Itzá, Guatemala, Central American lowlands.MethodsWe use an 86 000‐yr‐long pollen record to study the relative contribution of neutral mechanisms and environmental determinism in configuring vegetation in the Central American lowlands. By using variance ratios, we evaluated the role of neutral drift at community and functional group levels. Additionally, regression analyses were applied to explain persistence and abundance of individual taxa as a function of regional moisture availability and fire frequency.ResultsEnvironmental fluctuations drove vegetation dynamics in the Central American lowlands during the late Pleistocene. When the data set was stratified according to moisture availability and fire frequency, variance ratios further supported our findings. Regression analyses revealed that whereas species’ presence was independent of both moisture availability and fire frequency, their abundance was closely associated with both.ConclusionsNeutrality, probably expressed in the face of stressors, through factors such as the existence of microrefugia, survival of relictual individuals and phenotypic and phenologic plasticity, was probably crucial in preventing biodiversity losses. Climate, however, was the main driver of vegetation dynamics in the Yucatan Peninsula during the late Pleistocene.

Effects of Stocking Rate on the Variability of Peak Standing Crop in a Desert Steppe of Eurasia Grassland

Proper grazing management practices can generate corresponding compensatory effects on plant community production, which may reduce inter-annual variability of productivity in some grassland ecosystems. However, it remains unclear how grazing influences plant community attributes and the variability of standing crop. We examined the effects of sheep grazing at four stocking rate treatments [control, 0 sheep ha(-1) month(-1); light (LG), 0.15 sheep ha(-1 )month(-1); moderate (MG), 0.30 sheep ha(-1) month(-1); and heavy (HG), 0.45 sheep ha(-1) month(-1)] on standing crop at the community level and partitioned by species and functional groups, in the desert steppe of Inner Mongolia, China. The treatments were arranged in a completely randomized block design over a 9-year period. Standing crop was measured every August from 2004 to 2012. Peak standing crop decreased (P < 0.05) with increasing stocking rate; peak standing crop in the HG treatment decreased 40 % compared to the control. May-July precipitation explained at least 76 % of the variation in peak standing crop. MG and HG treatments resulted in a decrease (P < 0.05) in shrubs, semi-shrubs, and perennials forbs, and an increase (P < 0.05) in perennial bunchgrasses compared to the control. The coefficients of variation at plant functional group and species level in the LG and MG treatments were lower (P < 0.05) than in the control and HG treatments. Peak standing crop variability of the control and HG community were greatest, which suggested that LG and MG have greater ecosystem stability.

Dominant Functional Group Effects on the Invasion Resistance at Different Resource Levels

BackgroundFunctional group composition may affect invasion in two ways the effect of abundance, i.e. dominance of functional group; and the effect of traits, i.e. identity of functional groups. However, few studies have focused on the role of abundance of functional group on invasion resistance. Moreover, how resource availability influences the role of the dominant functional group in invasion resistance is even less understood.Methodology/Principal FindingsIn this experiment, we established experimental pots using four different functional groups (annual grass, perennial grass, deciduous shrub or arbor and evergreen shrub or arbor), and the dominant functional group was manipulated. These experimental pots were respectively constructed at different soil nitrogen levels (control and fertilized). After one year of growth, we added seeds of 20 different species (five species per functional group) to the experimental pots. Fertilization significantly increased the overall invasion success, while dominant functional group had little effect on overall invasion success. When invaders were grouped into functional groups, invaders generally had lower success in pots dominated by the same functional group in the control pots. However, individual invaders of the same functional group exhibited different invasion patterns. Fertilization generally increased success of invaders in pots dominated by the same than by another functional group. However, fertilization led to great differences for individual invaders.Conclusions/SignificanceThe results showed that the dominant functional group, independent of functional group identity, had a significant effect on the composition of invaders. We suggest that the limiting similarity hypothesis may be applicable at the functional group level, and limiting similarity may have a limited role for individual invaders as shown by the inconsistent effects of dominant functional group and fertilization.