Role In Community Structure Research Articles

Seed dispersal by Martu peoples promotes the distribution of native plants in arid Australia

Commensal relationships between wild plants and their dispersers play a key ecological and evolutionary role in community structure and function. While non-human dispersers are often considered critical to plant recruitment, human dispersers have received much less attention, especially when it comes to non-domesticated plants. Australia, as a continent historically characterized by economies reliant on non-domesticated plants, is thus a key system for exploring the ecological role of people as seed dispersers in the absence of agriculture. Here, we utilize a controlled observation research design, employing ecological surveys and ethnographic observations to examine how seed dispersal and landscape burning by Martu Aboriginal people affects the distribution of three preferred plants and one (edible, but non-preferred) control species. Using an information theoretic approach, we find that the three preferred plants show evidence of human dispersal, with the strongest evidence supporting anthropogenic dispersal for the wild bush tomato, Solanum diversiflorum.

Microbial co-occurrence network demonstrates spatial and climatic trends for global soil diversity

Despite recent research efforts to explore the co-occurrence patterns of diverse microbes within soil microbial communities, a substantial knowledge-gap persists regarding global climate influences on soil microbiota behaviour. Comprehending co-occurrence patterns within distinct geoclimatic groups is pivotal for unravelling the ecological structure of microbial communities, that are crucial for preserving ecosystem functions and services. Our study addresses this gap by examining global climatic patterns of microbial diversity. Using data from the Earth Microbiome Project, we analyse a meta-community co-occurrence network for bacterial communities. This method unveils substantial shifts in topological features, highlighting regional and climatic trends. Arid, Polar, and Tropical zones show lower diversity but maintain denser networks, whereas Temperate and Cold zones display higher diversity alongside more modular networks. Furthermore, it identifies significant co-occurrence patterns across diverse climatic regions. Central taxa associated with different climates are pinpointed, highlighting climate’s pivotal role in community structure. In conclusion, our study identifies significant correlations between microbial interactions in diverse climatic regions, contributing valuable insights into the intricate dynamics of soil microbiota.

Long-term application of nitrogen and phosphorus fertilizers changes the process of community construction by affecting keystone species of crop rhizosphere microorganisms

Keystone species of microbial communities play a very important role in community structure and ecosystem function; however, the effect of long-term nitrogen (N) and phosphorus (P) fertilizers on key taxa and the mechanisms of community construction of rhizosphere microbial communities remain unclear. In this study, the effect of nine fertilization treatments (N0P0, N0P1, N0P2, N1P0, N1P1, N1P2, N2P0, N2P1, and N2P2) on soil microbial community diversity, keystone species, and construction methods in the crop rhizosphere were studied in a loess hilly area after 26 years of fertilization. The results showed that fertilization significantly increased the nutrient contents of the rhizospheric soil and root system and significantly affected microbial community composition (based on the Bray-Curtis distance) and community construction process (β-nearest taxon index: βNTI). The decrease in the abundance of oligotrophic bacteria (from phyla Acidobacteriota and Chloroflexi) in the keystone species of bacterial communities shifted the community construction process from homogenizing dispersal to variable selection process and was significantly regulated by soil factors (total P and carbon-N ratio). However, the decrease in the abundance of keystone species (from phylum Basidiomycota) in the fungal communities did not have a significant effect on community construction, which was mainly affected by root characteristics (root N content and soluble sugar). This study found that long-term N and P fertilization changed the keystone species composition of bacterial communities by affecting the nutrient content of the rhizospheric soil, such as total P, so that the construction mode of communities changed from a stochastic to a deterministic process, and the N2 fertilization, especially the N1P2 treatment was better for increasing network stability (modularity and clustering coefficient).

On The Role of Community Structure in Evolution of Opinion Formation: A New Bounded Confidence Opinion Dynamics

The process of opinion formation and evolution is an important part of the study of opinion dynamics. However, the existing opinion dynamics ignore the relationship between opinion evolution and community structure. To address the limitation, we build a novel bounded confidence opinion dynamics model (called LPA-HK for simplicity). Based on the Hegselmann-Krause (HK) model, the label propagation algorithm (LPA) is introduced in the LPA-HK model to study the relationship between opinion evolution and community partition from the micro-perspective of the evolutionary process. Each agent has an opinion as well as a label indicating the agent’s community. The iterations of agents’ states involve two stages: label and opinion updates. The labels and opinions of agents evolve dynamically until the group reaches a stable state. We perform simulations to examine the effect of the model parameters on opinion evolution and community partitions. We show that group reaches a consensus as the confidence level increases to a critical value and the partitions of high quality are obtained when the confidence level is greater than the critical value. We apply the LPA-HK model to three kinds of real networks to solve the community detection problem. The effectiveness of the LPA-HK model is verified by comparing the results with two existing community detection results based on modularity optimization algorithms.

Examining the gender imbalance in the National Community Health Assistant Programme in Liberia: a qualitative analysis of policy and Programme implementation.

The Revised National Community Health Services Policy (2016-2021) (RNCHSP) and its programme implementation, the Liberian National Community Health Assistant Programme (NCHAP), exhibit a critical gender imbalance among the Community Health Assistants (CHAs) as only 17% are women. This study was designed to assess the gender responsiveness of the RNCHSP and its programme implementation in five counties across Liberia to identify opportunities to improve gender equity in the programme. Using qualitative methods, 16 semi-structured interviews were conducted with policymakers and 32 with CHAs, other members of the community health workforce and community members. The study found that despite the Government of Liberia's intention to prioritize women in the recruitment and selection of CHAs, the planning and implementation of the RNCHSP were not gender responsive. While the role of community structures, such as Community Health Committees, in the nomination and selection of CHAs is central to community ownership of the programme, unfavourable gender norms influenced women's nomination to become CHAs. Cultural, social and religious perceptions and practices of gender created inequitable expectations that negatively influenced the recruitment of women CHAs. In particular, the education requirement for CHAs posed a significant barrier to women's nomination and selection as CHAs, due to disparities in access to education for girls in Liberia. The inequitable gender balance of CHAs has impacted the accessibility, acceptability and affordability of community healthcare services, particularly among women. Strengthening the gender responsiveness within the RNCHSP and its programme implementation is key to fostering gender equity among the health workforce and strengthening a key pillar of the health system. Employing gender responsive policies and programme will likely increase the effectiveness of community healthcare services.

Signals of Potential Species Associations Offer Clues about Community Organisation of Stream Fish across Seasons

Simple SummarySpecies interactions are one of the main factors affecting community assembly, yet the role of such interactions remains mostly unknown. Here, we investigated roles of potential species associations in fish community assembly in the Qiupu River, China. Our results suggested that potential species associations might have been underestimated in stream fish community assembly. The contribution of potential species associations to fish community assembly can be reflected by interaction network structures. Omnivorous species play an important role in maintaining network structure as they may have more associations with other species. This study highlights the importance of capturing species associations in river ecosystems across different geographical and environmental settings.Environmental filtering, spatial factors and species interactions are fundamental ecological mechanisms for community organisation, yet the role of such interactions across different environmental and spatial settings remains mostly unknown. In this study, we investigated fish community organisation scenarios and seasonal species-to-species associations potentially reflecting biotic associations along the Qiupu River (China). Based on a latent variable approach and a tree-based method, we compared the relative contribution of the abiotic environment, spatial covariates and potential species associations for variation in the community structure, and assessed whether different assembly scenarios were modulated by concomitant changes in the interaction network structure of fish communities across seasons. We found that potential species associations might have been underestimated in community-based assessments of stream fish. Omnivore species, since they have more associations with other species, were found to be key components sustaining fish interaction networks across different stream orders. Hence, we suggest that species interactions, such as predation and competition, likely played a key role in community structure. For instance, indices accounting for network structure, such as connectance and nestedness, were strongly correlated with the unexplained residuals from our latent variable approach, thereby re-emphasising that biotic signals, potentially reflecting species interactions, may be of primary importance in determining stream fish communities across seasons. Overall, our findings indicate that interaction network structures are a powerful tool to reflect the contribution of potential species associations to community assembly. From an applied perspective, this study should encourage freshwater ecologists to empirically capture and manage biotic constraints in stream ecosystems across different geographical and environmental settings, especially in the context of the ever-increasing impacts of human-induced local extinction debts and species invasions.

Floristic Composition and Diversity in Response to Varying Degrees of Disturbance in Tropical Dry Deciduous Forests of Southern Haryana, India

The aim of the current investigation was to study the effects of anthropogenic disturbances on the vegetation structure of the three Tropical Dry Deciduous Forests of Southern Haryana i.e., Mandhana, Ghasola, and Mandhiali in the Bhiwani, Charkhi Dadri, and Mahendergarh districts, respectively. The data were collected from March, 2020 to March, 2021. The floristic composition was quantified by randomly placing 15 quadrats per site (45 in total). A disturbance index was developed for each site and high, medium and low disturbance areas were identified based on prevailing disturbances that were found to be maximum for Mandhiali (21), followed by Ghasola (16) and Mandhana (9). Ecological parameters such as frequency, density, abundance, basal area, IVI, and diversity indices were calculated for each siteduring the study. A total of 50 species of plants representing 44 genera and 25 families were observed consisting of 14 trees, 9 shrubs, and 27 herbs during the investigation of floristic composition. The species richness decreased with an increase in the disturbance level on the three sites viz., Mandhana (40), Ghasola (33), and Mandhiali (29) respectively. The value of Shannon Weiner diversity index (H’) and Pielou Index of evenness (E) declined with an increasing disturbance while Simpson index of dominance (Cd) increased as the disturbance levels increased across the three sites. The results offer significant evidence that anthropogenic disturbances in arid regions of South Haryana play a vital role in community structure and composition. In a forest ecosystem, anthropogenic disturbances cause habitat fragmentation along with soil erosion, loss of soil fertility and biodiversity, etc. The selected forests are in urgent need of management activities to check the intensity of disturbances by controlling anthropogenic pressure on these ecosystems and save them from further degradation. Thus, the present study intensifies the need for phytosociological studies crucial for proper management and conservation purposes.

Effect of multiple agricultural stressors on freshwater ecosystems: The role of community structure, trophic status, and biodiversity-functioning relationships on ecosystem responses

The toxicity and widespread use of agricultural pesticides threaten freshwater biodiversity, but their long-term effects under different nutrient concentrations are poorly understood. We evaluated the single or combined effects of two pesticides (chlorpyrifos and diuron) under different nutrient regimes (mesotrophic and eutrophic) on community structure and ecosystem functions in replicated pond mesocosms. The individual application of nutrients and pesticides affected community composition and species richness. Ecosystem functioning was generally less sensitive to chemical stress than community structure, while eutrophication fostered the dominance of species that are more resilient to pesticides. Stressor interactions were significant at different time points, with late stressor interactions affecting the recovery of community composition. We also found that the correlation between biodiversity and relevant ecosystem functions, such as primary productivity and total ecosystem respiration, can be shifted from positive to negative under particular stress conditions. Our study demonstrates that nutrients enrichment is a key factor influencing the resilience of freshwater ecosystems to multiple stressors and that functional redundancy allows maintaining constant levels of functioning even under high toxic stress pressure.

Niche overlap and species co-occurrence patterns in carabid communities of the northern Chinese steppes.

Understanding how species sort themselves into communities is essential to explain the mechanisms that maintain biodiversity. Important insights into potential mechanisms of coexistence may be obtained from observation of non-random patterns in community assembly. The spatial niche overlap (Pianka index) and co-occurrence (c-score) patterns in carabid species in three types of steppes (desert steppe, typical steppe, and meadow steppe) in China was investigated. Non randomness was tested using null models. Niche overlap values were significantly higher than expected by chance in the desert steppe, where vegetation cover is less abundant and less uniformly distributed, which possibly forces species to concentrate in certain places. In the typical and meadow steppes, results were influenced by the scale of the analysis. At a broad scale, niche separation was found as a result of species segregation among different sectors (habitats) within these steppes, but when the analysis was conducted at a finer scale, species appeared to be no more segregated than expected by chance. The high co-occurrence averages found in the meadow and typical steppes indicate that the distributions of the species found in a site may be negatively affected by the presence of other species, which suggests that some species tend to exclude (or reduce the abundance of) others. The very low c-score average observed in the desert steppe suggests that competition is not involved there. Thus, in more homogeneous landscapes (such as the typical and meadow steppes), competition might play some role in community structure, whereas spatial variation in the abundances of species is more driven by the uneven spatial distribution of vegetation in the landscape where productivity is lower and less uniformly distributed.

Resource partitioning among stranded aquatic mammals from Amazon and Northeastern coast of Brazil revealed through Carbon and Nitrogen Stable Isotopes

Aquatic mammals play an important role in community structure. The present study applied stable isotope analysis (SIA) to evidence trophic relationships and resource partitioning among aquatic mammals inhabiting different environments in the Amazon estuarine complex and adjacent coastal zone (AE) and Northeastern coast (NC) of Brazil. In addition, isotopic niche partitioning among Sotalia guianensis, Inia spp. and Trichechus inunguis within the AE was also evaluated, and ecological S. guianensis stocks were characterized. Among marine delphinids, the carbon isotopic composition in offshore species mirrored that of nearshore species, contradicting the pattern of decreasing δ13C values characteristic of many areas around the world including areas in Southeastern and Southern Brazil. Isotopic niches were highly distinct, with no overlap among the assessed species inhabiting the AE. Inia spp. and T. inunguis occupied significantly larger isotopic niche spaces, suggesting high habitat plasticity. S. guianensis inhabited two coastal regions indicating an ecological distinction. Nitrogen values were similar between S. guianensis from the NC and AE, indicating comparable trophic positions. However, NC specimens presented more variable δ13C values compared to those from AE. SIA results also allowed for insights concerning habitat use and the trophic ecology of dolphin species inhabiting different oceanographic regions off Northern/Northeast Brazil. These findings provide novel data on the stable isotope composition for cetaceans and sirenians from this region, and aid in furthering knowledge on the trophic ecology and habitat use of the investigated species.

Salinity changes root occupancy by arbuscular mycorrhizal fungal species

Understanding the diversity and community composition of arbuscular mycorrhizal (AM) fungi in stressful conditions is fundamental to predicting the occurrence and function of indigenous AM fungal associations in a changing soil environment. Here, using whole-soil inoculum, we investigated the effects of salinity on community structure and colonization rate of AM fungi in roots, and assessed their influence on maize (Zea mays L.) performance. Three different salinity treatments (0, 75, and 150 mM NaCl) were applied to mycorrhizal inoculated and non-inoculated plants. Results showed that salinity levels significantly influenced AM fungal composition and diversity as well as vesicular and hyphal colonization in roots. The AM fungal community composition and diversity index differed slightly under the 0 and 75 mM NaCl treatments, but changed significantly under the 150 mM NaCl treatment. Increased vesicular and declined hyphal colonization were observed under 75 and 150 mM NaCl treatments relative to the control. Further analyses uncovered that plants under the 0 and 75 mM NaCl treatments, where Glomeraceae predominated as root symbionts, had a higher mycorrhizal growth response than plants under the 150 mM NaCl treatment, where Claroideoglomeraceae abundance increased significantly. This study provides evidence that saline stress plays a vital role in community structure and root colonization by AM fungal communities. Additionally, our data suggested that community composition may be more important for mycorrhizal symbiotic function than the rate of root colonization. Finally, while the relative abundance of Claroideoglomeraceae was found to increase with stress in saline soil, their role needs to be further clarified in future studies.

Critical Component Analysis in Cascading Failures for Power Grids Using Community Structures in Interaction Graphs

Cascading phenomena have been studied extensively in various networks. Particularly, it has been shown that the community structures in networks impact their cascade processes. However, the role of community structures in cascading failures in power grids have not been studied heretofore. In this paper, cascading failures in power grids are studied using interaction graphs. Key evidence has been provided that the community structures in interaction graphs bear critical information about the cascade process and the role of system components in cascading failures in power grids. Furthermore, a centrality measure based on the community structures is proposed to identify critical components of the system, which their protection can help in containing failures within a community and prevent the propagation of failures to large sections of the power grid. Various criticality evaluation techniques, including data driven, epidemic simulation based, power system simulation based, and graph based, have been used to verify the importance of the identified critical components in the cascade process and compare them with those identified by traditional centrality measures. Moreover, it has been shown that the loading level of the power grid impacts the interaction graph and consequently, the community structure and criticality of the components in the cascade process.

Ecological niche overlap between co-occurring native and exotic ungulates: insights for a conservation conflict

Exploitative competition implies an indirect interaction in which a resource exploited by one species is not available for another; e.g., when species share diet or habitat. It plays a key role in community structure and dynamics. Here we evaluated the niche overlap between the exotic aoudad (Ammotragus lervia) and the native Iberian ibex (Capra pyrenaica) where the species coexist in the Iberian Peninsula, along two main dimensions, the trophic niche and the environmental niche. Then we assessed the spatial segregation of the species. We expected that if a niche overlap was high, competition could drive spatial segregation to allow co-existence. We analyzed their trophic niche overlap by using the content of stable isotopes δ15N and δ13C in the hair of both species. To establish environmental niche competition, we compared the similarity in their habitat, estimated by environmental niche models based on the fine-scale presence records of each species obtained from field surveys. To test if spatial segregation occurred, we analyzed both species’ co-occurrence. Our results indicated that both species shared a similar trophic niche measured by stable isotopes, both species showed a similar distribution of suitable areas, and that both species’ environmental niches were more similar than expected. Finally, a negative spatial association was found between the aoudad and Iberian ibex. These results reveal that both species are ecologically similar and suggest that fine-scale spatial segregation might have favoured their co-existence in semiarid Mediterranean mountains. Our results show that integrating information on trophic and environmental niche overlap with fine scale spatial distribution might improve the study of competitive interactions among wild ungulates.

Microbial community structure and function in acid mine drainage from Mengzi, Yunnan Province

In order to explore the microbial communities and functions in distinct environments of acid mine drainage (AMD) ecosystem and fully comprehend the patterns of AMD formation and development, high-throughput sequencing technology was used to study the prokaryotic community composition in AMD puddles and surrounding rills in a mining area in Mengzi, Yunnan Province, China. By combining with physicochemical properties of the samples, we distinguished the key factors affecting the community structure and analyzed the environmental functions of the microflora. We discovered that the main phyla in AMD puddles were Euryarchaeota, Proteobacteria (including the class α-, γ- and δ-Proteobacteria), Nitrospirae, Firmicutes, Actinobacteria, and Acidobacteria. Community structure of the AMD puddles apparently differed from that of the surrounding rills. Microbial diversity was significantly positively correlated with pH, whereas the relative abundance of Thermoplasmata was negatively correlated with pH and this class might play a predominant role in community structure. There was high relative abundance of the genus Ferroplasma (6.60%-86.34%) in different samples of AMD puddles. Acidithiobacillus spp. were the major iron- and/or sulfur-oxidizing bacteria in AMD solutions and sediments, whereas relative abundance of the obligate iron-oxidizer Leptospirillum spp. was lower, and Ferrovum spp. were almost only present in the AMD solutions. In addition, acidophilic or acid-tolerant heterotrophic bacteria were widely distributed in the AMD solutions and sediments, which might promote the growth of iron- and/or sulfur-oxidizers and catalyze the oxidative/reductive dissolution of metal ores. Our results suggested that pH significantly impacted the microbial community structure of AMD environment by affecting the microbial diversity and microflora distribution.

High food quality increases infection of Gammarus pulex (Crustacea: Amphipoda) by the acanthocephalan parasite Pomphorhynchus laevis

Parasitism is an important process in ecosystems, but has been largely neglected in ecosystem research. However, parasites are involved in most trophic links in food webs with, in turn, a major role in community structure and ecosystem processes. Several studies have shown that higher nutrient availability in ecosystems tends to increase the prevalence of parasites. Yet, most of these studies focused on resource availability, whereas studies investigating resource quality remain scarce. In this study, we tested the impact of the quality of host food resources on infection by parasites, as well as on the consequences for the host. Three resources were used to individually feed Gammarus pulex (Crustacea: Amphipoda) experimentally infected or not infected with the acanthocephalan species Pomphorhynchus laevis: microbially conditioned leaf litter without phosphorus input (standard resource); microbially conditioned leaf litter enriched in phosphorus; and microbially conditioned leaf litter without phosphorus input but complemented with additional inputs of benthic diatoms rich in both phosphorus and eicosapentaenoic acid. During the 110 day experiment, infection rate, parasite load, host survival, and parasite-mediated behavioral traits implicated in trophic transmission were measured (refuge use, geotaxis and locomotor activity). The resources of higher quality, regardless of the infection status, reduced gammarid mortality and increased gammarid growth. In addition, higher quality resources increased the proportion of infected gammarids, and led to more cases of multi-infections. While slightly modifying the geotaxis behavior of uninfected gammarids, resource quality did not modulate the impact of parasites on host behavior. Finally, for most parameters, consumption of algal resources had a greater impact than did phosphorus-enriched leaf litter. Therefore, manipulation of resource quality significantly affected host–parasite relationships, which stressed the need for future research to investigate in natura the relationships between resource availability, resource quality and parasite prevalence.

Interaction engineering: Non-trophic effects modify interactions in an insect galler community.

Theory suggests that non-trophic interactions can be a major mechanism behind community stability and persistence, but community-level empirical data are scarce, particularly for effects on species interactions mediated through changes in the physical environment. Here, we explored how ecosystem engineering effects can feed back to the engineer, not only modulating the engineer's population density (node modulation) but also affecting its interactions with other species (link modulation). Gall induction can be viewed as ecosystem engineering since galls serve as habitat for other species. In a community-level field experiment, we generated treatments with reduced or elevated ecosystem engineering by removing or adding post-emergence galls to different plots of their host plant in the Brazilian Cerrado. We tested the effect of post-emergence galls on the galler, as well as on the galler-parasitoid and galler-aphid interactions. The manipulation of post-emergence galls had little effect on the galler-abundance and survivorship were not affected, and gall volume changed only slightly-but modified interactions involving the galler, parasitoid wasps and inquiline aphids. Aphid inquilines negatively affected density-dependent parasitism rates (interaction modification) likely by killing parasitised galling larvae. Post-emergence galls interfered with aphid inquilinism-likely by the provision of alternative habitat for aphids-and thus interfered with the negative effect of aphids on parasitism (modification of an interaction modification). This work is one of the few studies to demonstrate experimentally the role played by environment-mediated interaction modification at a community level in the field. Moreover, by manipulating a species' ecosystem engineering effect (post-emergence galls) instead of the species itself, we demonstrate the novel result that populations can be regulated by non-trophic effects initiated by their own activities that alter their interaction with other species. This reveals that indirect interactions mediated via the environment offer new pathways of feedback loops for population regulation. Our results indicate that interaction modification has the potential to be a key regulatory mechanism underlying interaction variation in nature, and play a major role in community structure, dynamics and stability.

The role of community structure on the nature of explosive synchronization.

In this paper, we analyze explosive synchronization in networks with a community structure. The results of our study indicate that the mesoscopic structure of the networks could affect the synchronization of coupled oscillators. With the variation of three parameters, the degree probability distribution exponent, the community size probability distribution exponent, and the mixing parameter, we could have a fast or slow phase transition. Besides, in some cases, we could have communities which are synchronized inside but not with other communities and vice versa. We also show that there is a limit in these mesoscopic structures which suppresses the transition from the second-order phase transition and results in explosive synchronization. This could be considered as a tuning parameter changing the transition of the system from the second order to the first order.

The role of environmental filtering in the functional structure of fish communities in tropical wetlands

AbstractUnderstanding the mechanisms that structure communities has been a major challenge in ecological theory. In wetlands with a clear seasonal hydroperiod (wet and dry seasons), such as Sian Ka'an Biosphere Reserve (SKBR), Mexico, fish communities experience successive habitat contraction/expansion, with a high mortality rate during the dry season. In this study, we tested the role of environmental filtering in structuring fish communities along an environmental gradient in permanent pools, during three consecutive stages of the dry season. We analysed fish communities using a functional dispersion index weighted by the relative abundance compared against a null model. While the concentration of dissolved oxygen remained low throughout the season, depth and temperature showed a gradient as the season progressed. Independently of their starting composition, at the end of the dry season the communities were dominated by a combination of the same three species. For the key function of locomotion, the functional dispersion was significantly lower at the end of the season in three of the five pools. For food acquisition, no significant differences were found. When the overall functional variation was considered, at the beginning of the dry season no single community differed significantly compared to the random models. However, as the season progressed, significant differences were recorded in four of the five pools. Our study supports the hypothesis that environmental filters have a major role in community structure in severe environmental conditions. Furthermore, our results show that the role of environmental filters gain importance as the dry season progresses.

Contrasting grass nitrogen strategies reflect interspecific trade-offs between nitrogen acquisition and use in a semi-arid temperate grassland

Nitrogen (N) niche differentiations play an important role in community structure and biogeochemical cycling in terrestrial ecosystems. However, very few studies have examined how plant N strategies specialize via trade-offs between N acquisition and use abilities under natural field conditions. A field experiment was conducted to investigate N strategies by coexisting grass species using the in-situ stable isotope labeling technique. We injected 15N–labeled nitrate, 15N–labeled ammonium, and 13C-15N-labeled glycine solutions in early and late vegetative growing seasons. Shoot δ15N and N concentration were measured to determine the N uptake and use abilities of 4 common species. All plant species preferred to take up nitrate (the dominant N form) over ammonium and glycine, and N-acquisition capacity varied with temporal variation of soil N. However, the dominant species was more N-conservative than less-dominant species and had lower overall N uptake rates (shoot 15N excess 48 hours after injection) and higher N use efficiencies (aboveground biomass : N ratio). The different N strategies may reflect mixed effects of environmental filtering and interspecific competition and have significant implications for species coexistence as well as for ecosystem functions such as nutrient cycling.

De Novo Sequencing and Comparative Analysis of Schima superba Seedlings to Explore the Response to Drought Stress.

Schima superba is an important dominant species in subtropical evergreen broadleaved forests of China, and plays a vital role in community structure and dynamics. However, the survival rate of its seedlings in the field is low, and water shortage could be a factor that limits its regeneration. In order to better understand the response of its seedlings to drought stress on a functional genomics scale, RNA-seq technology was utilized in this study to perform a large-scale transcriptome sequencing of the S. superba seedlings under drought stress. More than 320 million clean reads were generated and 72218 unique transcripts were obtained through de novo assembly. These unigenes were further annotated by blasting with different public databases and a total of 53300 unique transcripts were annotated. A total of 31586 simple sequence repeat (SSR) loci were presented. Through gene expression profiling analysis between drought treatment and control, 11038 genes were found to be significantly enriched in drought-stressed seedlings. Based on these differentially expressed genes (DEGs), Gene Ontology (GO) terms enrichment and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) enrichment analysis indicated that drought stress caused a number of changes in the types of sugars, enzymes, secondary mechanisms, and light responses, and induced some potential physical protection mechanisms. In addition, the expression patterns of 18 transcripts induced by drought, as determined by quantitative real-time PCR, were consistent with their transcript abundance changes, as identified by RNA-seq. This transcriptome study provides a rapid method for understanding the response of S. superba seedlings to drought stress and provides a number of gene sequences available for further functional genomics studies.