Nitrogen fixation in the High Arctic: a source of ‘new’ nitrogen?

Biological nitrogen (N₂) fixation performed by diazotrophs (N₂ fixing bacteria) is thought to be one of the main sources of plant available N in pristine ecosystems like arctic tundra. However, direct evidence of a transfer of fixed N₂ to non-diazotroph associated plants is lacking to date. Here, we present results from an in situ ¹⁵N–N₂ labelling study in the High Arctic. Three dominant vegetation types (organic crust composed of free-living cyanobacteria, mosses, cotton grass) were subjected to acetylene reduction assays (ARA) performed regularly throughout the growing season, as well as ¹⁵N–N₂ incubations. The ¹⁵N-label was followed into the dominant N₂ fixer associations, soil, soil microbial biomass and non-diazotroph associated plants three days and three weeks after labelling. Mosses contributed most to habitat N₂ fixation throughout the measuring campaigns, and N₂ fixation activity was highest at the beginning of the growing season in all plots. Fixed ¹⁵N–N₂ became quickly (within 3 days) available to non-diazotroph associated plants in all investigated vegetation types, proving that N₂ fixation is an actual source of available N in pristine ecosystems.     

Big game or big loss? High deer densities are threatening woody plant diversity and vegetation dynamics

Land-use change and current game management have favored an increasing population of wild ungulates (especially deer) in many regions of the Northern Hemisphere. Here, we assess the impact of high deer densities (>30 ind km^?2) on the highly diverse woody vegetation of Mediterranean ecosystems, where big game have been favored for the last decades. We examine whether prolonged deer browsing (over 30 years) affected plant composition, diversity and dynamics of the original (non-browsed) vegetation. Deer browsing led to an average decrease of 30.4 % in woody plant diversity (species richness), due to a lack of regeneration for the most preferred plant species. Species belonging to early stages of succession (mostly Labiatae and Cistaceae) were non-preferred by deer. Conversely, the most preferred species belonged mainly to late stages of plant succession. Deer impact on Mediterranean shrublands is causing biotic homogenization of plant communities and is threatening vegetation dynamics by forcing it to return to earlier succession stages. Strict deer population control favouring larger trophies but lower offspring numbers together with an adequate habitat management (increasing grass and acorn availability) would be the most efficient measures to reverse this diversity loss. Restoration work seems only appropriate for the most vulnerable species. We highlight the need of sampling deer-free areas with low or null historical browsing to assess the real impact of deer on woody plant diversity and vegetation dynamics.     

Links between plant species’ spatial and temporal responses to a warming climate

To generate realistic projections of species’ responses to climate change, we need to understand the factors that limit their ability to respond. Although climatic niche conservatism, the maintenance of a species’s climatic niche over time, is a critical assumption in niche-based species distribution models, little is known about how universal it is and how it operates. In particular, few studies have tested the role of climatic niche conservatism via phenological changes in explaining the reported wide variance in the extent of range shifts among species. Using historical records of the phenology and spatial distribution of British plants under a warming climate, we revealed that: (i) perennial species, as well as those with weaker or lagged phenological responses to temperature, experienced a greater increase in temperature during flowering (i.e. failed to maintain climatic niche via phenological changes); (ii) species that failed to maintain climatic niche via phenological changes showed greater northward range shifts; and (iii) there was a complementary relationship between the levels of climatic niche conservatism via phenological changes and range shifts. These results indicate that even species with high climatic niche conservatism might not show range shifts as instead they track warming temperatures during flowering by advancing their phenology.     

Are fire,soil fertility and toxicity,water availability,plant functional diversity,and litter decomposition related in a Neotropical savanna?

Understanding how biodiversity and ecosystem functioning respond to changes in the environment is fundamental to the maintenance of ecosystem function. In realistic scenarios, the biodiversity-ecosystem functioning path may account for only a small share of all factors determining ecosystem function. Here, we investigated the strength to which variations in environmental characteristics in a Neotropical savanna affected functional diversity and decomposition. We sought an integrative approach, testing a number of pairwise hypotheses about how the environment, biodiversity, and functioning were linked. We used structural equation modelling to connect fire frequency, soil fertility, exchangeable Al, water availability, functional diversity of woody plants, tree density, tree height, and litter decomposition rates in a causal chain. We found significant effects of soil nutrients, water availability, and Al on functional diversity and litter decomposition. Fire did not have a significant direct effect on functional diversity or litter decomposition. However, fire was connected to both variables through soil fertility. Functional diversity did not influence rates of litter decomposition. The mediated effects that emerged from pairwise interactions are encouraging not only for predicting the functional consequences of changes in environmental variables and biodiversity, but also to caution against predictions based on only environmental or only biodiversity change.     

Carbon and nitrogen storage of a restored wetland at Illinois’ Emiquon Preserve: potential for carbon sequestration

Recovery of the submersed vegetation is a target for the management of soft-water shallow lakes if they are to meet water quality and biodiversity standards. Knowledge of patterns of macrophyte space occupation and time to recovery is poor and mostly restricted to free floating species or riparian vegetation. Here we use pre- and post-impact monitoring data over 20 years showing the evolution of submersed aquatic vegetation of lake Baciver (Pyrenees), and develop models to infer space occupation and time to recovery. We use pre-impact macrophyte distribution in relation to bathymetry-derived data to fit logistic models to further simulate lake equilibrium scenarios. Depth and slope were found to be the best predictors, and models suggested that an assemblage dominated by Sparganium angustifolium was, at time of this study, over 95% of its potential distribution area. A dense, newly grown monospecific Isoetes lacustris population occupied <10% of its potential area and model projections suggest that it will take decades to recover. An I. lacustris residual population remains below the estimated depth threshold for survival and is bound to disappear. The lake appears to evolve towards a new steady-state where the current lake hypsography promotes the expansion of algae (Nitella sp.) over angiosperms.     

Food,shelter or competitors? Overlapping of life stages and host plant selection in a Neotropical stink bug species

Phytophagous insects may choose host plants based on conditions that enhance offspring performance. However, some insect species may also select plants based on attributes that enhance their own performance regardless of the consequences for offspring survival. An approach evaluating both hypotheses could provide a more comprehensive understanding of the host plant selection by phytophagous insects. In this study, we described the life stages of a Neotropical stink bug, Edessa contermina, co-occurring on Byrsonima verbascifolia plants in a conservation area of the Brazilian Savannah. We also empirically evaluated how food supply, shelter availability and competitors’ density on the host plants affected the densities of nymphs, adults and mating pairs. We identified and described five life stages of E. contermina. The amount of plant resources did not explain the nymph, adult and mating pairs’ density. However, adults and mating pairs chose plants with a low density of nymphs, probably because egg laying on the host plants with a high density of competitors may negatively affect offspring performance.     

Associations between canopy and understory species increase along a rainshadow gradient in the Alps: habitat heterogeneity or facilitation?

Spatialassociations among overstory and understory species tend to increase ongradients from wet to dry climates. This shift in the strength of spatialassociations has usually been attributed to shared abiotic requirements betweencanopy species and understory assemblages within communities and/or to anincrease in habitat heterogeneity in dry climates and therefore higher betadiversity. On another hand, more important positive effects of tree canopies onunderstory species in drier climates may also explain stronger associations andhigher beta diversity. We examined these three hypotheses along a strongrainshadow gradient that occurs from the wet external Alps to the dry innerAlpsby analyzing with correspondence analysis and canonical correspondence analysisthe species composition of 290 relevés of forests dominated to differentdegrees by Abies alba and Piceaabies.We found important differences in climatic requirements forAbies and Picea, withAbies occurring in warmer and drier habitats thanPicea. The understory species associated with these twospecies showed similar correlations with temperature but not with moisture,withunderstory species of Picea-communities having strongerxeric affinities than understory species ofAbies-communities. We found no significant associationsbetween canopy species and understory composition in the external Alps despitethe fact that Abies and Piceaoccurredin substantially different environments. In contrast,Abiesand Picea occurred in more similar environments in theinner Alps, but the understory assemblages associated with eitherAbies or Picea were significantlydifferent. This increase in canopy-understory associations was in partdetermined by strong differences in moisture between southern and northernaspects in the inner Alps, which affected both canopy and understory speciesdistributions. However, differences between the canopy effects ofPicea and Abies also appeared tocontribute to stronger associations between canopy and understory species, andconsequently to increase beta diversity. This pattern only occurred on southernaspects of the inner Alps but was highly significant. Our results suggest thatspecies distributions may be continuous on the wet ends of moisture gradientsbut discrete on dry ends. Relatively discrete communities at stressful ends ofgradients appear to develop as a result of both habitat differentiation and thepositive effects of overstory species.     

Conservation,propagation, and redistribution (CPR) of Hill’s thistle: paradigm for plant species at risk

Cryopreservation is a valuable tool that could potentially create an alternate plant preservation strategy for species at risk such as Hill’s thistle. The present study is focused on a successful paradigm involving conservation, propagation and redistribution (CPR), emaphasizing the usefulness of cryopreservation techniques for plant conservation using Hill’s thistle (Cirsium hillii. (Canby) Fernald). A cryopreservation protocol was established using the droplet-vitrification method for 5-week-old shoot tips of in vitro grown cultures. More than 90% of shoot tips showed regrowth and nearly all regenerated plants were able to survive in the greenhouse. The survival, growth, and development of plants from cryopreserved shoot buds and their performance in field conditions were all comparable or better than the plants from non-cryopreserved buds. Reintroduced plants flowered following overwintering and the magnitude of flowering was site dependent with ca. 80% flowering observed in one site. The site dependent flowering patterns were assessed using phytohormone profiling and compared to herbivory, a common biotic stressor of these plants. Lower tryptophan concentrations led to higher flowering except in alvars, where the limestone resisted root penetration resulting in poor flowering. The presence of tryptamine in the greenhouse acclimatized or alvar field leaves suggested the preparedness of the plants for herbivory/grazing. Serotonin and melatonin concentrations were lower in flowering plants and in sites where the biotic/abiotic stress was minimal. This study provides evidence of the effectiveness of the CPR model in species recovery programs for endangered species. Physiological characterization of plants developed from cryopreserved tissues can be useful for fundamental and applied research in stress adaptation and reproductive biology of plants.

     

What causes changes in plant litter quality and quantity as consequence of grazing in the Patagonian Monte: Plant cover reduction or changes in species composition?

In Patagonian Monte, as in other arid ecosystems, grazing has triggered changes in vegetation and soil such as plant cover reduction, changes in species composition and soil nutrient losses. Several mechanisms were proposed interconnecting these changes, but evidence supporting them is very scarce. On the basis of published data concerning plant cover by species along grazing gradients and leaf litter production of dominant species, we estimated the effects of grazing on a – quality (N, soluble phenolics and lignin concentrations) and b – quantity (leaf litterfall (LLF) and inputs of nitrogen, soluble phenolics and lignin to the soil) of leaf litter in the Patagonian Monte, discriminating the effect of plant cover reduction from that of species composition. We also evaluated the relationship between senesced leaves traits and the response of species to grazing (i.e. their relative change in plant cover). Grazing causes a reduction in LLF and in the inputs of nitrogen, soluble phenolics and lignin to the soil. In the case of LLF, this reduction was not only a result of the decrease in plant cover but also due to changes in species composition. In contrast, our results showed that the reduction in nitrogen, soluble phenolics and lignin inputs to the soil by LLF is only a consequence of plant cover reduction. Additionally, litter quality was affected through increasing concentration of N and secondary compounds (soluble phenolics and lignin). N and soluble phenolics concentration on senesced leaves were positively related to the response of species to grazing, suggesting that other factors instead of N are relevant to sheep foraging decisions.     

Are vascular epiphytes nitrogen or phosphorus limited? A study of plant (15) N fractionation and foliar N : P stoichiometry with the tank bromeliad Vriesea sanguinolenta

Although there is unambiguous evidence for vascular epiphytic plants to be limited by insufficient water and nutrient supply under natural conditions, it is an open debate whether they are primarily phosphorus (P) or nitrogen (N) limited. Plant (15) N fractionation and foliar N : P stoichiometry of a tank epiphyte (Vriesea sanguinolenta), and its response to combined N-P fertilization, were studied under semi-natural conditions over 334 d to clarify the type of nutrient limitation. Plants collected in the field and experimental plants with limited nutrient supply showed significant plant (15) N fractionation (mean 5‰) and plant N : P ratios of c. 13.5. Higher relative growth rates and declines in plant (15) N fractionation (0.5‰) and in foliar N : P ratios to 8.5 in the high N-P treatment indicated that these epiphytes were P limited in situ. The critical foliar N : P ratio was 10.4, as derived from the breakpoint in the relationship between plant (15) N fractionation and foliar N : P. We interpret the widespread (15) N depletion of vascular epiphytes relative to their host trees as deriving from (15) N fractionation of epiphytes as a result of P limitation. High foliar N : P ratios (> 12) corroborate widespread P limitation (or co-limitation by N and P) of epiphytic bromeliads and, possibly, other epiphyte species.     

Accounting for the capacity of common and rare species to contribute to diversity spatial patterns: Is it a sampling issue or a biological effect?

The contribution of common species to overall species richness in many cases is greater than that of rare species. However, the explanation of this phenomenon remains vague. One hypothesis is that this is a sampling issue and not a biological one. Therefore standardization methods like the information index and empirical variance have been proposed. But, these standardizations do not explicitly compare the significance of the dataset size of the common and rare sub-assemblage. Here, we investigate the role of dataset size in accounting for the capacity of common and rare species to contribute to diversity spatial patterns. We used a dataset of 5148 vascular plant species recorded in 16,439 sample plots in the Greek Natura 2000 network. Species were ranked according to the number of sample plots they occupied in ascending (rare to common), descending (common to rare) and random order. We analyzed the correlation between the richness of each sub-assemblage and total species richness. When comparing among sub-assemblages with equal number of species, common species are clearly the better predictors of total species richness. But, when comparing among sub-assemblages with equal number of occurrence records, the patterns changed. Common and rare species contribution to the overall richness pattern was comparable, with rare species contributing slightly less than widespread species in some cases and the opposite in other cases. However in all cases, sub-assemblages of random species remarkably outperformed the equal sized sub-assemblages of common or rare species. Our results suggest that common and rare species are biased samples of the community and that equal sized random samples are more representative; thus the greater contribution of common species than rare species to biodiversity patterns might be more a sampling issue than a biological effect of commonness or rarity.     

Testing Allsop and West’s size at sex change invariant within a fish species: a spurious ratio or a useful group descriptor?

Recently, it has been suggested that sequential hermaphrodites, from a variety of taxa and a wide range of sizes, change sex at the same relative size. It is said that there exists an invariant (a constant ratio) for such a life trait. However, recent criticisms point out that these results could be a statistical artefact. It has been argued that the wider the range of x-axis values (from 2 mm to 1.5 m in the case of sex change), the higher the probability of identifying an invariant by chance. Here, the invariance of the size at sex change ratio is analysed within a single fish species for which the size of sex change varies within a range of only 6.5 cm. Our results support the invariant rule that fishes change sex when reaching 79% of their maximum size.     

Does an earthworm species acclimatize and/or adapt to soil calcium conditions? The consequences of soil nitrogen mineralization in forest soil

Calcium (Ca)-rich food can increase feeding of Lumbricidae. Earthworms can be genetically differentiated at a small spatial scale and acclimatize to the local environment during growth. Soil feeding and subsequent cast production by earthworms affects soil N mineralization. Here, we hypothesized that soil feeding and subsequent cast production by Lumbricidae species increases with high soil Ca content and that this increase is stronger in worms from high-Ca soil. We also hypothesized that changes in the soil feeding of Lumbricidae species along with the Ca content affects the soil N mineralization via changes in the cast production. Using a geophageous earthworm species (Eisenia japonica) originated from two different Ca environments (calcareous soil and sedimentary soil), we investigated cast production and soil N mineralization in three soils (sedimentary soil, sedimentary soil with Ca addition, and calcareous soil). The soil feeding of E. japonica from both origins did not always increase despite the high soil Ca content. We suggest that both the Ca content and other soil conditions (e.g., soil C:N) might be major factors in increasing soil feeding by E. japonica. Furthermore, the influence of Ca addition on cast production varied according to the earthworm origin. As expected, these differences in cast production are linked to soil N mineralization (especially nitrification). In summary, our study suggests that the acclimatization and/or adaptation of Lumbricidae species to local environmental factors not only soil Ca content explains spatially heterogeneous soil N mineralization in forest soil.     

Disentangling the relative effects of ambient energy,water availability,and energy–water balance on pteridophyte species richness at a landscape scale in China

Understanding what factors generate geographic variation in species richness is a fundamental goal of ecology and biogeography. Water and energy are considered as the major environmental factors influencing large-scale patterns of species richness, but their roles vary among taxa and regions. Pteridophytes are an ideal group of organisms for examining the relationship between species richness and their environment because the distribution of pteridophytes is usually in equilibrium with contemporary climate to a greater degree than those of seed plants and most terrestrial vertebrates partly due to the lightness of their spores, which is highly capable of long-distance dispersal by wind, and partly due to their single-spore reproduction strategy. Using correlation and regression analyses and structural equation modeling technique, we examine the relationship of pteridophyte species richness in 151 localities from across China with environmental factors representing energy, water, and energy–water balance. We found that pteridophyte species richness is correlated to water availability more strongly than to ambient energy. Furthermore, we found that of all environmental variables considered, energy–water balance has played the most important role in regulating pteridophyte species richness gradients in China.     

Regeneration processes of biological soil crusts,macro-cryptogams and vascular plant species after fine-scale disturbance in a temperate region: Recolonization or successional replacement?

Open base-rich sandy habitats are often characterised by an extensive cover of biological soil crusts (BSCs). We studied the impact of mechanical disturbances on cyanobacteria/algae-dominated BSCs, macro-cryptogams (bryophytes, lichens), phanerogams and their regeneration processes in a 3-year field experiment in a temperate region. We compared controls with two fine-scale disturbance regimes, each based on 50 plots (20 cm×20 cm): 1. BSCs were raked (weak disturbance), 2. BSCs were completely removed (strong disturbance). We used a Sileno conicae-Cerastion semidecandri habitat as a model area for the field study and ask if the crusts are able to regenerate or will be replaced by macro-cryptogams and/or phanerogams.     

Mass-culling of a threatened island flying fox species failed to increase fruit growers’ profits and revealed gaps to be addressed for effective conservation

Human-wildlife conflicts (HWC) pose a growing threat to biodiversity worldwide and solutions can be as sound as the understanding of the HWC itself. Conservation biologists therefore must carefully examine their local situations to inform on which approach and strategies may be best. In this context, Mauritius implemented what may be the first mass-culls of an already threatened native species when it culled the flying fox (Pteropus niger) in 2015 and 2016 to try increase fruit producers’ profits. Although the Red List category of the species consequently worsened to ‘Endangered’ and fruit production dropped substantially, a third mass-cull was decided in 2018. A critical analysis is important to draw lessons that may help to prevent recurrences particularly that HWC involving Pteropus spp. are common and set to worsen. We synthesized the best literature available locally and also elsewhere in relevant situations, to critically appraise the setting, nature, timeline of events and outcome of both completed mass-culling campaigns to explore why and how they happened so as to help towards devising better approaches to such conflicts. The idea to cull P. niger originated around 2002 and a small cull was done in 2006. The first mass-cull started immediately after Mauritius’ biodiversity protection law was weakened in 2015 primarily to legalize culls of threatened native species, but still breached the law in place then. The 2016 mass-cull was recommended in line with the law, but was not evidence-based and consequently did not result in improved profits of fruit producers. Appeals supported by best scientific evidence from local and international organizations and conservationists to the effect that culls will not increase fruit production, but instead further endanger the species, were ignored. To forestall recurrences here and elsewhere, it matters to recognize their precursor signs and the conditions that favoured them including why the mass-culls were not stopped. The events provide a rare opportunity to explore the strategy that was used by conservationists and open the way to propose impactful alternatives or additional actions instead. The situation also exemplifies an eroding commitment towards biodiversity conservation, eased by withdrawal from evidence-based policy that suit short term goals of election cycles at the expense of longer term environmental interests.     

Relationships between species diversity or community structure and productivity of woody-plants in a broad-leaved Korean pine forest in Jiaohe,Jilin, China北大核心CSCD

Aims: Based on the dataset of a broad-leaved Korean pine forest in Jiaohe, Jilin Province, this research compared the influences of species diversity and community structure on productivity. We aim to explain the relationship between diversity and productivity for better forest management. Methods: We used the data of 10 973 woody-plants in a 11.76 hm2 large sample plot and analyzed the correlations between 7 different indices of species diversity or community structure and productivity. Structural equation model was used to compare the effects of species diversity and community structure on productivity. Important findings: The results showed that: (1) Both species diversity and community structure had significant effects on productivity when they were considered separately in linear regression analysis, i.e. species evenness was negatively correlated with productivity, the Shannon index of community structure was positively correlated with productivity and the Gini index was negatively correlated with productivity. (2) In the structural equation model, when simultaneously considered, community structure had stronger influence on productivity than species diversity. Our research suggests that, the effects of community structure on productivity are greater than species diversity and it is important to increase community structure complexity to improve forest productivity during forest management.     

Etiology and genetic factors in clefts of lip and/or palate reported at children’s hospital,Lahore, Pakistan

The etiology of cleft lip (CL) and/or cleft palate (CP) has been extensively studied in industrialized countries and is suggested to be heterogeneous with increasing evidence that both genetic and environmental factors are operating. To evaluate this assertion in a developing country like Pakistan, a case finding cross-sectional study was completed from 1^st July 2010 to 31^st May 2011 for 100 cases of CL and/or CP referred to the Genetic Clinic of the Children’s Hospital, Lahore, Pakistan. A clinical examination followed by necessary diagnostic work-up was completed for each case. The cause of CL and/or CP was clear in 18% of the children (n = 18). Environmental causes were found in 6 children (four mothers developed hyperthermia during the 2^nd month of gestation, one mother was diabetic, and one mother was a known case of epilepsy and took sodium valproate throughout her pregnancy). Six children were suffering from known genetic malformation syndromes (each with Jarcho-Levin syndrome, Oral-Facial-Digital syndrome type XI, Oral-Duplication syndrome, Kabuki syndrome, Fronto-nasal dysplasia and Nager syndrome). Novel chromosomal aberrations were identified in 2 children. In 82% of the children (n = 82) the cause of oro-facial clefts remained unknown. Impact of gender and consanguinity on the development of CL and/or CP was also studied. Prevalence of CP was significantly more among female children as compared to that in males (P < 0.05). Associated anomalies were present in 18% of the cases, anomalies of the craniofacial region being the most common. These findings were compared with regional and international studies.