Reduced Species Richness Research Articles

Nitrogen addition interacted with salinity-alkalinity to modify plant diversity, microbial PLFAs and soil coupled elements: A 5-year experiment

Atmospheric nitrogen (N) deposition has greatly increased in the past 50 years due to fossil fuel combustion and the use of synthetic fertilizers. Because N is the limiting nutrient for plant growth in terrestrial ecosystems, atmospheric deposition of N has the potential to increase biomass production, reduce species richness, inhibit microbial growth, and result in soil acidification. However, few studies have evaluated whether and how N inputs affect plant species diversity and the interactions among soil elements in saline-alkaline grassland ecosystems. The Songnen grassland of China is characterized by heterogeneous patches of saline-alkaline soils. A 5-year nitrogen deposition experiment was conducted in two contrasting saline-alkaline communities. Results showed that increasing N input increased the plant biomass production and reduced plant species richness in the low saline-alkaline stress community, but salinity-alkalinity was able to alleviate the negative effects of nitrogen input on community diversity. Plant communities were more sensitive to N addition than microbial communities. N addition induced a shift from N to P as the limiting factor in temperate grassland ecosystems. In particular, salinity-alkalinity in the high stress community increased the conversion rate from N to P limitation. These results highlight the importance of the integrative study of the plant-soil-microbe system in ecosystems under global N enrichment. Our study emphasizes the need for future research to understand the mechanisms that control biogeochemical cycling and maintain ecosystem stability under the combined conditions of N addition and other stress factors, such as saline-alkalinity.

Repeated fires reduce plant diversity in low‐elevation Wyoming big sagebrush ecosystems (1984–2014)

AbstractSagebrush is one of the most imperiled ecosystems in western North America, having lost about half of its original 62 million hectare extent. Annual grass invasions are known to be increasing wildfire occurrence and burned area, but the lasting effects (greater than five years post‐fire) that the resulting reburns have on these plant communities are unclear. We created a fire history atlas from 31 yr (1984–2014) of Landsat‐derived fire data to sample along a fire frequency gradient (zero to three fires) in an area of northern Nevada that has experienced frequent fire in this time period. Thirty‐two percent of our study area (13,000 km2) burned in large fires (over 404 ha) at least once, 7% burned twice, and 2% burned three or more times. We collected plant abundance data at 28 plots (N = 7 per fire frequency), with an average time since fire of 17 yr. We examined fire's effect on plant diversity using species accumulation curves, alpha diversity (Shannon's dominance, Pielou's evenness, and number of species), and beta diversity (Whittaker, Simpson, and Z indexes). For composition, we used non‐metric multidimensional scaling. We then used PERMANOVA models to examine how disturbance history, temperature, precipitation, and aridity around the time of the fire affected subsequent community composition and diversity. One fire fundamentally changed community composition and reduced species richness, and each subsequent fire reduced richness further. Alpha diversity decreased after one fire. Beta diversity declined after the third fire. Cover of exotics was 10% higher in all burned plots, and native cover was 20% lower than in unburned plots, regardless of frequency. PERMANOVA models showed fire frequency and antecedent precipitation as the strongest predictors of beta diversity, while time since fire and vapor pressure deficit for the year of the fire were the strongest predictors of community composition. Given that a single fire has such a marked effect on species composition, and repeated fires reduce richness and beta diversity, we suggest that in lower elevation big sagebrush systems fire should be minimized as much as possible, perhaps even prescribed fire. Restoration efforts should be focused on timing with wet years on cooler, wetter sites.

Effects of Atypical Antipsychotic Treatment and Resistant Starch Supplementation on Gut Microbiome Composition in a Cohort of Patients with Bipolar Disorder or Schizophrenia.

Previous studies identified shifts in gut microbiota associated with atypical antipsychotic (AAP) treatment that may link AAPs to metabolic burden. Dietary prebiotics such as resistant starch may be beneficial in obesity and glucose regulation, but little is known mechanistically about their ability to modify gut microbiota in AAP-treated individuals. This investigation was undertaken to delineate mechanistically the effects of AAP treatment and resistant starch supplementation on gut microbiota in a psychiatric population. Cross-sectional cohort study. The study was performed in an outpatient setting. A total of 37 adults with a diagnosis of bipolar disorder or schizophrenia who were treated with an AAP (clozapine, olanzapine, risperidone, quetiapine, or ziprasidone [21 patients]) or lithium and/or lamotrigine (16 patients) for at least 6 months. Patients in the AAP group received raw unmodified potato starch (resistant starch) daily for 14 days. Of the 37 patients, the mean ± SD age was 52.2 ± 12.5 years, and 57% were male. The primary outcome was gut microbiome DNA composition. Microbiome DNA obtained from stool samples from all patients was subject to 16S ribosomal RNA (rRNA) gene sequencing before and during resistant starch supplementation. Inter- and intragroup microbial diversity measures were performed by permutational multivariate analysis of variance and the Inverse Simpson Diversity Index, respectively. Differentially abundant organisms were detected by using linear discriminant analysis effect size. Although no significant difference in overall microbiota composition was detected at baseline between AAP users and nonusers, non-AAP users showed increased fractional representation of Alistipes. AAP-treated women exhibited decreased diversity compared with non-AAP-treated women. Although the microbiome of AAP-treated patients varied with resistant starch administration, an increased abundance of the Actinobacteria phylum was observed. These data suggest that AAP treatment is associated with measurable differences in gut microbiota, particularly in female AAP-treated patients in whom reduced species richness was observed. Additionally, variable microbiome responses to resistant starch supplementation were seen, with a significant increase in starch degraders.

Back to the future: conserving functional and phylogenetic diversity in amphibian-climate refuges

Climate refuges have been used by several species over historical climate change. Ectothermic species often display good models for climate change studies because they are highly sensitive to temperature. Analysis of species loss with ecosystem and evolutionary values helps to understand environmental processes and climate change consequences. We determined the functional and phylogenetic diversity of amphibians in the Atlantic Forest hotspot, using multiple models representing present and future conditions. Through a novel approach, we predict species’ threat status by 2080, following the IUCN’s criterion B1. Our results estimate a drastic reduction in species richness, ecosystem functioning and evolutionary history at low latitudes and altitudes. We show that species will tend to disperse to the areas with milder temperatures (i.e., high latitudes/altitudes). Some of these areas are the same climate refuges that have been suggested for the Late Pleistocene. We highlight that 60% of amphibians can become threatened under predicted-future conditions. This work advances the knowledge on climate refuges for amphibian ecology and evolution, supporting complementary tools for conservation strategies.

Reduced skin bacterial diversity correlates with increased pathogen infection intensity in an endangered amphibian host.

The fungal pathogen Batrachochytrium dendrobatidis (Bd) infects the skin of amphibians and has caused severe declines and extinctions of amphibians globally. In this study, we investigate the interaction between Bd and the bacterial skin microbiome of the endangered Sierra Nevada yellow-legged frog, Rana sierrae, using both culture-dependent and culture-independent methods. Samples were collected from two populations of R.sierrae that likely underwent Bd epizootics in the past, but that continue to persist with Bd in an enzootic disease state, and we address the hypothesis that such "persistent" populations are aided by mutualistic skin microbes. Our 16S rRNA metabarcoding data reveal that the skin microbiome of highly infected juvenile frogs is characterized by significantly reduced species richness and evenness, and by strikingly lower variation between individuals, compared to juveniles and adults with lower infection levels. Over 90% of DNA sequences from the skin microbiome of highly infected frogs were derived from bacteria in a single order, Burkholderiales, compared to just 54% in frogs with lower infection levels. In a culture-dependent Bd inhibition assay, the bacterial metabolites we evaluated all inhibited the growth of Bd. Together, these results illustrate the disruptive effects of Bd infection on host skin microbial community structure and dynamics, and suggest possible avenues for the development of anti-Bd probiotic treatments.

The Gastric Microbiome Is Perturbed in Advanced Gastric Adenocarcinoma Identified Through Shotgun Metagenomics.

Objective: Dysbiosis of gastric microbiota such as Helicobacter pylori plays a significant role in pathogenesis and progression of gastric cancer. Our aim was to evaluate the composition and functional effects of gastric microbiota in superficial gastritis (SG) and advanced gastric adenocarcinoma (GC).Methods: We carried out shotgun metagenomic sequencing on gastric wash samples from 6 patients with GC and 5 patients with SG. The taxonomic composition was profiled using MetaPhlAn2 and functional gene pathway was profiled using HUMAnN2. Differences in microbial composition and pathways between the two patient groups were assessed via LEfSe.Results: The gastric microbiota in GC patients was characterized by reduced species richness, enrichment of 13 bacterial taxa and depletion of 31 taxa (q < 0.05). The most representative taxa which were abundant in GC corresponded to the commensals or opportunistic pathogens that usually colonize the oral cavity, including genera Neisseria, Alloprevotella, and Aggregatibacter, species Streptococcus_mitis_oralis_pneumoniae and strain Porphyromonas_endodontalis.t_GCF_000174815. Each of the three GC-associated genera could separate GC from SG completely. In particular, Sphingobium yanoikuyae, a bacterium capable of degrading carcinogenic compounds, was depleted in GC. Functionally, pathways associated with the biosynthesis of lipopolysaccharide (LPS) and L-arginine were enriched in GC, whereas pathways involved in the fermentation of short chain fatty acids (SCFAs) and branched amino acid metabolism were more abundant in SG.Conclusions: Our results present new alterations in the gastric microbiome in patients with GC from a whole-genome perspective, suggesting that microbiome composition and function can be used for prognosis and diagnosis of GC.

Impact of troublesome expansive weed Rumex alpinus on species diversity of mountain pastures in Tatra National Park, Poland

Alpine dock (Rumex alpinus) is a native plant species in many European mountain ranges. It comes from moist brushwood and open tall herb communities, though it has invaded mountain pastures. This troublesome weed forms permanent monodominant stands characterised by low nature conservation and agricultural values. However, to the best of our knowledge, there are no studies assessing the impact of R. alpinus on invaded communities. Therefore, in this study we examined the potential effect of an R. alpinus on species richness, diversity and the composition of invaded vegetation in Tatra National Park, Poland. Invaded plots dominated by R. alpinus had, compared to uninvaded control plots, significantly reduced species richness, as well as low Shannon and Simpson diversity and Pielou evenness indices’ values; the species richness decline in the pairs of invaded-uninvaded plots was as much as 37.7%. Analysing changes in diversity from an increase in R. alpinus coverage revealed that Shannon, Simpson and Pielou’s diversity indices’ values did not considerably change up to 30% of R. alpinus coverage, but a further increase in R. alpinus coverage led to a steep decline in diversity. There was exception in a number of species per plot, which decreased steadily along with the increase of R. alpinus coverage. Multivariate analysis indicated a significant shift in the composition of invaded plots in relation to uninvaded plots, resulting from the shared increase of more shadow-tolerant and higher soil base-, nutrient- and moist-demanding species.

Do the presence and physiological stage of algal mats affect the meiobenthic community in a tropical estuary?

The effects of compacted algal mats growing attached to sediments on the abundance and community structure of intertidal sediment meiofauna and harpacticoid copepod assemblages were evaluated on a tropical estuarine mudflat. Differences in fauna based on the presence of algae (within vs. outside the algal patches) and the physiological stages of the algae (live vs. decomposing algal patches) were compared. In general, lower densities occurred within algal patches for most meiofaunal groups, except for harpacticoids, which showed an increase in number in the live algal patches (LAP). Non-metric MDS analysis clearly distinguished both meiofauna community and harpacticoid assemblage in relation to the presence of algae and the physiological stage. Organic matter, carbohydrates, proteins and photosynthetic pigments were higher within algal patches and highly correlated with meiofauna variables. One species of harpacticoid (Cletocamptus sp.1) dominated the LAP samples and thus reduced species richness and diversity of harpacticoids in these samples. The species Robertsonia mourei occurred exclusively in decomposing algal patches (DAP) and probably is an opportunistic species within the DAP samples. Strong differences regarding live and decomposing algae samples highlighted the importance of physiological stage in understanding meiofaunal responses to algal mats.

Selection of scale can reverse the importance of stochastic controls on community assembly

ABSTRACTReconciling the long-standing debate on the importance of niche-related and neutral factors on community assembly, recent research suggests that both deterministic and stochastic processes operate simultaneously along a continuum in many biogeographical systems. In particular, stochastic processes seem to lose importance under stressful conditions, which results in the increasing influence of deterministic counterparts. In this paper, I show that, at local scales, this stochasticity–stress relationship can be reversed along the environmental stress gradients within a salt marsh: stochasticity manifested under harshness. Here, low-lying, more stressful sites contained all of the plant species of the local pool (i.e. a greater chance of ecological drift), whereas high-elevation, less stressful sites exhibited reduced species richness due to competitive exclusion (i.e. a lower chance of ecological drift). I conclude that determining whether the importance of stochasticity in shaping community structure is greater under benign or harsh conditions depends on the scale of interest.

Responses of plant 15N natural abundance and isotopic fractionation to N addition reflect the N status of a temperate steppe in China

Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of ¹⁵N (δ¹⁵N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ¹⁵N of major ecosystem N pools and several key species, plant ¹⁵N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia. We carried out a N addition experiment during 2011–14 on a Stipa krylovii steppe in Inner Mongolia, Northern China. We investigated the response of several key N transformation processes, vegetation and soil properties to N addition. Aboveground biomass and belowground biomass (BGB) δ¹⁵N, root and foliar δ¹⁵N of three dominant species (Artemisia frigida, S. krylovii and Leymus chinensis), δ¹⁵N of soil total N and soil KCl-extractable NO₃⁻-N were determined. The responses of isotope fractionation during plant N uptake and reallocation to N addition were also determined. Our results suggest that the N addition rate of 5g N m⁻² yr⁻¹ could be regarded as threshold of early N saturation in this S. krylovii steppe as indicated by an increase in plant fractionation and a decrease in plant δ¹⁵N. When N input rate is >10 g N m–² yr–¹, increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO₃⁻ in extractable soil pools <30-cm soil profile. With N addition, S. krylovii and A. frigida undergo earlier N status shift from N limitation toward N excess compared with L. chinensis, contributing to L. chinensis out-competing other species. Overall, this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.

Community composition, structure and productivity in response to nitrogen and phosphorus additions in a temperate meadow

Global nitrogen (N) enrichment likely alters plant community composition and increases productivity, consequently affecting ecosystem stability. Meanwhile, the effects of N addition on plant community composition and productivity are often influenced by phosphorus (P) nutrition, as the effects of N and P addition and interactions between N and P on plant community structure and productivity are still not well understood. An in situ experiment with N and P addition was conducted in a temperate meadow in northeastern China from 2013 to 2016. The responses of plant community composition, structure, functional group cover, richness and productivity to N and P additions were examined. N addition significantly reduced species richness and diversity but increased aboveground net primary productivity (ANPP) during the four-study-year period. P addition exerted no significant impact on species richness, diversity or ANPP but reduced cover of grasses and increased legume cover. Under N plus P addition, P addition alleviated the negative effects of N addition on community structure by increasing species richness and covers of legume and forbs. N and P additions significantly altered plant community structure and productivity in the functional groups. N addition significantly increased the cover of gramineous and reduced the cover of legume, P addition significantly increased legume cover. Our observations revealed that soil nutrient availability regulates plant community structure and ANPP in response to nutrient enrichment caused by anthropogenic activities in the temperate meadow. Our results highlight that the negative influence of N deposition on plant community composition might be alleviated by P input in the future.

Selectively Logging Old Growth Rain Forest Twice Changes Canopy Ant Species Composition, While Conversion to Oil Palm Changes Composition and Reduces Species Richness and Diversity

Tropical forests around the world, and particularly in Southeast Asia, are being affected by anthropogenic habitat conversion and degradation. Ants, an ecologically important group in the rainforest canopy, have previously been demonstrated to be robust to a single round of selective logging, but are strongly affected by conversion to oil palm. However, the impacts of multiple rounds of selective logging on canopy ants remain unexplored. We studied the ant assemblages across a habitat gradient comprising old growth forest, twice-logged forest and oil palm plantation in Sabah, Malaysian Borneo. Canopy ants were collected using insecticide fogging across 36 sampling sites. Old growth forest and twice-logged forest had similar species richness and Shannon species diversity. These two forest habitats were significantly higher in species richness and Shannon diversity than oil palm plantation. Abundance of canopy ants was similar across all three habitats. There was a significant difference in species composition between all pairs of habitats. Leaf litter depth on the ground was positively related to ant species richness, while canopy cover was positively related to ant abundance. Hence, multiple rounds of logging cause shifts in ant species composition, while forest conversion to oil palm additionally causes reductions in ant diversity. This is of concern, since forests in Sabah and elsewhere are becoming increasingly degraded. Our results indicate that both old growth and twice-logged rain forests can be useful for conservation of canopy ants.

Productivity and diversity of annually harvested reconstructed prairie communities

AbstractBiofuel production from cellulosic feedstocks may increase during the next century. To be sustainable, this production should protect environmental quality and biodiversity. Fertilized mixed‐species prairie can deliver substantial quantities of cellulosic ethanol per unit land area with minimal losses of NO3‐N in drainage water, but the long‐term maintenance of biodiversity in such systems has been uncertain.We report how nitrogen, phosphorus, and potassium fertilizer application, precipitation, and time affected the species composition and productivity of reconstructed prairie communities harvested annually as biofuel feedstocks over a 9‐year period.Results indicated that both precipitation and fertilizer application drove above‐ground biomass production, with the greatest response to fertilizer occurring in wetter than average years. Fertilization reduced species richness, but increased species evenness. Consequently, Simpson's diversity index did not differ between the fertilized and unfertilized communities, though it declined in both communities over time.A total of 59 plant species was recorded, with eight of them explaining most of the differences in vegetation cover between the fertilized and unfertilized treatments. After 9 years, the high fertility community was dominated by the C4 grassAndropogon gerardii,the C3 grassElymus canadensis, and the non‐leguminous forbsHeliopsis helianthoides,Helianthus maximiliani, andMonarda fistulosa, whereas the low fertility community was dominated by the C4 grassesA. gerardiiandSorghastrum nutans, the C3 grassE. canadensis, and the non‐leguminous forbM. fistulosa. Fertilization increased the abundance of flowering forbs available to pollinators in the early, middle and late portions of the growing season.Synthesis and applications. Results of our study suggest that maintenance of reasonably high levels of productivity and biodiversity are possible in fertilized prairie communities harvested annually for bioenergy, with plant cover more evenly distributed among different functional groups. In the future, if policy and markets favour biofuels and better delivery of ecosystem services from harvested land, prairie‐based feedstocks could become part of a renewable energy portfolio that fosters biodiversity and contributes to the provision of floral resources for pollinators.

Comparative effects of urban and agricultural land transformation on Odonata assemblages in a biodiversity hotspot

Rivers of the Cape Floristic Region (CFR) biodiversity hotspot are threatened by land transformation. This region is a centre of endemism for many taxa, including Odonata. These insects are highly sensitive to changes in physical habitat structure, which makes them good bioindicators, and this led to the development of the Dragonfly Biotic Index (DBI). We investigated the effects of local agricultural and urban land transformations on Odonata species richness, assemblage composition and DBI scores in three CFR rivers. A total of 48 sites were selected and categorized as natural, agricultural or urban land use. Adult male Odonata and four environmental variables were recorded over two seasons. Land transformation significantly influenced Odonata assemblage composition but did not always significantly reduce species richness. Average vegetation height also affected Odonata assemblage composition and decreased species richness. Agricultural and urban sites had Odonata assemblages differing from those in the natural areas. Agricultural and urban local land use types reduced opportunities for some endemic species but provided for the persistence and establishment of widespread, generalist species, as indicated by great changes in DBI scores. Mitigating the adverse influences of land transformation through establishment of protected areas is essential for the conservation of rare taxa, particularly in an area with a high number of endemic species.

From individuals to communities: How singleton invasive pine saplings lead to biodiversity change in the Brazilian Cerrado hotspot

AbstractQuestionsHow do newly established species interact with existing assemblage members to alter local biodiversity? This question is especially topical given growing concerns about increased temporal turnover levels relative to background rates. Pine (Pinus spp.), a major invasive taxon in the Southern Hemisphere, is progressively dominating remaining fragments of the Brazilian savanna (Cerrado), a biodiversity hotspot. Because the Cerrado's diversity is linked to habitat heterogeneity we argue that the impact of these invasive singleton pines will be mediated by differences in local habitat structure. Here we use isolated invasive pines (Pinus elliottii) in the Cerrado as a study system to test the prediction that changes in the diversity of native communities, in the presence of newly established exotic individuals, will be greatest in the dominant vegetation layer of a habitat.LocationItirapina Ecological Station, southeast of Brazil.MethodsWe used a stratified random survey in 5 m × 5 m pairs of plots invaded by a single pine individual, each matched by control uninvaded plots; both shrub and grass vegetation layers were sampled in both habitats. In total, 300 plots were sampled, 114 in the shrub‐dominated campo sujo and 186 in the grass‐dominated campo úmido.ResultsOver 400 plant species were recorded. In both habitats, we detect marked shifts in species richness of the dominant vegetation layer. In line with our prediction, the nature of these changes is mediated by local habitat structure. We find significantly reduced species richness in the shrub layer of the shrub‐dominated habitat, but elevated species richness in the grass layer of the grass‐dominated habitat in invaded sites (vs. control). In the grass layer of campo úmido, pine initially decreases dominance thus allowing more species to colonize the plots.ConclusionsThe shape of the diversity vs. establishment time relationship is layer‐dependent, with a significant relationship between dominance/evenness and pine size in the grass layer but no relationship in the shrub layer. Our results show that, although complex, the consequences for local biodiversity of non‐native species establishment are not haphazard and thus contribute to the understanding of species co‐existence.

Grass management intensity affects butterfly and orthopteran diversity on rice field banks

Agricultural intensification through landscape homogenization has been identified as one of the main drivers of the recent biodiversity decline in European farmlands. In particular, the loss of non-cropped habitats has often deprived farmland species of feeding and nesting sites, refuge areas, and dispersal corridors. In this framework, well-managed field margins may play a key role for wildlife conservation in agroecosystems, providing additional suitable habitat patches for many species, which also include several natural agents of pests’ biological control. In rice crops, paddy banks are usually heavily managed by farmers, which remove vegetation through chemical or mechanical procedures, with a consequent limitation of the potential role of levees in maintaining a functional agroecosystem. The aim of this study was to investigate the response of butterfly and orthopteran diversity to different grass management practices on rice field banks, namely herbicide spraying, mowing, and no management. Between April and September 2016, we sampled butterflies and orthopterans on 30 and 22 paddy levees respectively, located in three sites within the intensive rice crop district of northern Italy. Herbicides spraying proved to be the most detrimental practice for these insects, producing a considerable reduction in species richness and abundance in comparison with unmanaged and mown banks. The impacts of mowing were less pronounced than those of chemical treatments; however, frequent cutting caused a significant reduction in butterfly and orthopteran diversity on levees. Our results highlight the importance of unmanaged banks in preserving insect diversity in rice crops, while herbicide spraying should be avoided. Low frequency and rotational mowing could represent sustainable management solutions to meet biodiversity and husbandry requirements in this agroecosystem.

Grazing and spring snow counteract the effects of warming on an alpine plant community in Tibet through effects on the dominant species

Although studies have investigated the independent effects of warming, snow, and grazing on alpine plant community properties – including plant species richness, evenness, and diversity - the interactive effects of these climate and grazing factors have not been addressed experimentally in cold systems. We investigate the effects of these climate change and grazing factors using 5 years of data collected from a relatively long-term (2009–2015), fully-factorial field experiment in an alpine meadow ecosystem on the central Tibetan Plateau. Specifically, we investigate: 1) how experimental warming, spring snow addition, and yak grazing independently and interactively affect plant community properties, including diversity metrics and relative contributions of different plant life forms to the total plant cover, and 2) how the changes in plant community properties are associated with the proportional cover of the dominant plant species, Kobresia pygmaea within the total vegetation cover. We found that warming reduced species richness and increased species evenness and the proportional cover of shrubs within the total vegetation cover. Snow addition also increased species evenness. Grazing increased the proportional cover of K. pygmaea within the total vegetation cover, while decreasing that of grasses. Grazing also counteracted warming-induced increases in shrubs. Treatment-induced changes in K. pygmaea cover were strongly correlated with the indices of plant community properties and were generally in the opposite direction of changes in species evenness and diversity. We conclude that the projected increases in spring snowstorms and maintaining moderate levels of grazing can counteract some warming effects on the plant community. Moreover, the performance of the dominant species can regulate plant community responses to climate change and livestock grazing on the central Tibetan Plateau.

Reversal of nitrogen-induced species diversity declines mediated by change in dominant grass and litter.

Atmospheric nitrogen (N) deposition reduces plant diversity. However, it often remains unclear how dominant species and litter accumulation feedbacks mediate N-induced plant diversity declines. We tested mechanisms of N-induced diversity change through dominant grasses and litter in a 7-year field experiment. Nitrogen addition reduced species richness, Shannon-Wiener diversity (H') and evenness from the second to the fourth year, however, surprisingly, increased them in the sixth and seventh year. The reversal in the response of diversity to N addition was explained by changes in grass dominance and standing litter accumulation. The diversity recovery during later years in fertilized plots was attributed to a decrease in the dominant grass and an increase in standing litter: standing litter reduced bud numbers of the dominant grass by decreasing light availability. The decreased light availability by standing litter reduced completion from the dominant species, which resulted in diversity increase. The negative feedback between dominant grasses and standing litter led to transient N-induced diversity loss in the short-term, but recovery of plant diversity in the long-term. Grassland management that affects litter accumulation, such as firing, grazing and mowing, can therefore, have substantial effects on the long-term response of plant diversity to N deposition.

Rainfall-dependent influence of snowfall on species loss

The response of plant diversity to increased snowfall, i.e., precipitation that falls in a solid state rather than a liquid state, is unclear. We investigated the potential effects of 12 year snowfall augmentation on species richness using coordinated distributed experiments, including ten sites across a rainfall gradient of 211–354 mm and spanning 440 km in length in the temperate steppe. Snowfall augmentation decreased species richness rather than enhancing it. Abiotic factor driven by soil pH was the dominant determinant affecting the variation in species richness under changing precipitation regimes, overriding biotic factor. The strongest reduction in species richness induced by snowfall augmentation occurred in the low-rainfall sites. Our study provides insights into the relationship between precipitation and biodiversity in arid and semiarid regions.

Testing the Enemy Release Hypothesis on tall-statured grasses in South Africa, using Arundo donax, Phragmites australis, and Phragmites mauritianus as models

The Enemy Release Hypothesis (ERH) predicts that introduced plant species can escape herbivory and therefore have a competitive advantage over native plants, which are exposed to both generalist and specialist natural enemies. In this study, the ERH was explored using the invasive alien species, Arundo donax and two native tall-statured grasses, the cosmopolitan Phragmites australis and African endemic Phragmites mauritianus in South Africa. It was predicted that A. donax would have reduced species richness of herbivores compared with the native Phragmites spp., that it would be devoid of specialist herbivores and would thus be experiencing enemy escape in the adventive range. The herbivore assemblages were determined from both field surveys and a literature review. The assumptions of the ERH were for the most part not met; 13 herbivores were found on A. donax compared with 17 on P. australis and 20 on P. mauritianus. Arundo donax had two specialist herbivores from its native range, and shared native herbivores with Phragmites spp. Although A. donax had reduced species richness and diversity compared with that found in the native distribution, it has partially re-acquired a herbivore assemblage which is similar to that found on analogous native species. This suggests that enemy release may not fully explain the invasive success of A. donax in South Africa.