Unimodal Pattern Research Articles

Soil depths and developmental stages of biological soil crusts are more important than shrub cover in structuring prokaryotic communities

The influence of microhabitat factors on prokaryotic communities within desert ecosystems, particularly those residing in biological soil crusts (biocrusts), remains poorly understood. This study aimed to elucidate the relative importance of different microhabitats, including soil depths, biocrust developmental stages, and shrub cover, in shaping soil prokaryotic communities. To achieve this, we conducted an in-depth investigation of soil prokaryotic communities using high-throughput amplicon sequencing in the Tengger desert, China. Our results showed that difference of soil properties, prokaryotic alpha, beta diversities and abundances of taxa and functional groups primarily differed between soil depths and among biocrust developmental stages. Furthermore, the impact of shrub cover on the aforementioned parameters was found to be modified by biocrust development. Specifically, we observed higher soil nutrient levels in the upper biocrust layer compared to the subsoil, with a consistent increasing trend during biocrust development in both soil layers. Conversely, soil pH displayed contrasting patterns. Prokaryotic alpha diversity exhibited a V-shaped pattern with biocrust development, initially decreasing and then increasing, and was higher in the subsoil compared to the biocrust layer. Additionally, although prokaryotic alpha diversity showed differences between shrub cover or not, the specific effect depended on biocrust stages. Cyanobacteria, phototrophic and nitrogen-fixing prokaryotes were more abundant in the upper biocrust layer, following a unimodal pattern with biocrust development, initially increasing, and then decreasing; while Actinobacteriota and Acidobacteriota showed higher abundance in the subsoil, with varying trends between the two soil depths during biocrust development. Soil pH and total P emerged as key regulators of prokaryotic communities across different microhabitats. This study contributes to our comprehensive understanding of the complex dynamics governing prokaryotic communities in desert ecosystems.

Seasonal variation in the diurnal activity pattern of Eurasian blackbirds (Turdus merula) in the forest

Camera traps are increasingly used to estimate the density of animals as well as their activity patterns. As camera traps allow monitoring of animals over long periods of time without disturbance, they are especially useful to observe changes in diurnal activity patterns over time. In ornithology, camera trapping is still in its infancy. To our knowledge, no study has yet investigated the activity pattern of a songbird over the full annual cycle. We used camera traps in the Rammert, a small mountainous forest area near Rottenburg in Southwest Germany to monitor the diurnal activity pattern of forest-dwelling Eurasian blackbirds (Turdus merula). As the activity level of animals is known to be affected by day light, we used double-anchoring transformation of day times to account for the variation in sunrise and sunset across the different seasons. By generating activity models, we investigated the pattern of blackbird activity during the four seasons of the year and compared the patterns of male and female birds, respectively. A significant difference between a unimodal activity pattern in spring and a bimodal pattern for the rest of the year was found which might be related to breeding and territorial behaviour in spring. Moreover, we observed that the activity pattern of males and females overlapped greatly but still showed some variation in the number and timing of density peaks.

The effects of grazing and fencing on grassland productivity and diversity in alpine grassland ecosystem in the Tibetan highland

Anthropogenic activities, such as grazing and fencing, have been known to alter the productivity and biodiversity of grassland ecosystems, potentially affecting their functioning. However, the impact of these activities on aboveground biomass (AGB) and plant diversity in alpine grasslands at different altitudes, as well as how they may be affected by soil nutrients and environmental climate, is not well understood. To address this knowledge gap, a study was conducted in the Lhasa Valley of Tibet. In 2013, twelve metal fences were set up at mountainous transects, and field surveys were conducted at twelve paired sites in early August 2021. The results of the study showed that AGB was slightly higher in fenced sites compared to grazed sites at altitudes from 4000 to 5100 m, but decreased with altitude at a slower rate in grazed sites. Plant diversity indices exhibited a unimodal pattern with increasing altitude, with no significant differences between fenced and grazed sites. Soil nutrients and environmental climate were found to be positively correlated with plant diversity indices and AGB at both fenced and grazed sites. Multiple linear regression models revealed that AGB and the Shannon index were largely influenced by soil nutrients (AP and AN) rather than by growing season soil temperature at fenced sites, while AGB and the Shannon index were more impacted by growing season soil temperature than by soil nutrients at grazed sites. These findings provide important insights into the impacts of grazing and fencing on above-ground biomass and plant diversity in mountainous environments.

Inconsistent Responses of Rhizosphere Microbial Community Structure and Extracellular Enzyme Activity to Short-Term Nitrogen and Phosphorus Additions in Chinese Fir (Cunninghamia lanceolata) Plantations

Rhizosphere is a hot zone formed by root–microbial interaction, and microbial activities in this zone differ from those in bulk soil. Nitrogen (N) and phosphorus (P) inputs are able to change forest soil nutrient availability, affecting microbial communities and extracellular enzyme secretion. However, the impact of N and P additions on the structure and functions of rhizosphere microbial community in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations are not yet clear. To reveal the impact of short-term N and P inputs on microbial community structure and functions in rhizosphere soil, soil physicochemical properties, phospholipid fatty acids, and seven hydrolytic enzyme activities were measured in Chinese fir rhizosphere soil after one year of nutrient addition. N addition reduced the rhizosphere’s pH and increased ammonium N, but the rhizosphere’s available N (AN) initially wentdown and then up along the P-addition gradient. The rhizosphere fungi:bacteria ratio showed a decline after N addition, while a concave peak change occurred as rhizosphere AN under P addition. Moreover, rhizosphere extracellular enzyme activities and microbial C limitation climbed markedly with N addition rates, while this also showed an obviously unimodal pattern along the P-addition gradient. P addition did not alleviate rhizosphere microbial P limitation. Our findings suggest inconsistent responses of rhizosphere microorganisms of Chinese fir soil to N and P additions. Rhizosphere N availability can regulate microbial community structure and extracellular enzymes by influencing microbial C limitation. The study provides more knowledge on microbial activities in rhizosphere soil of subtropical forests under global changes.

Effect of Tree Size Heterogeneity on the Overall Growth Trend of Trees in Coniferous Forests of the Tibetan Plateau

Tree growth is under the combined influence of abiotic and biotic factors. Trees with different sizes may respond differently to these factors, implying that tree size heterogeneity may also modulate the overall growth trend. To test this hypothesis, we focused on the radial growth trends of natural subalpine forests on the Tibetan Plateau. We first extended the iterative growth model (IGM) to the tree ring scale (IGMR) to test the applicability of the generalized metabolic growth theory to tree growth. As predicted by the IGMR, the radial growth of trees at the aggregate scale is constrained by a unimodal pattern. Using the IGMR, we reconstructed the historical best growth trajectory (HBGT) of trees within the same community based on the tree with the largest radius and/or longest age in the community. From the average difference between the HBGT and the current radial growth rate of trees with different sizes, we constructed an indicator that can measure the overall variation in tree radial growth. Based on this indicator, we found a negative effect of tree size heterogeneity on the overall variability of tree growth across elevations. Further analysis also revealed that the radial growth rate of trees on the Tibetan Plateau has increased significantly compared to the past, where the growing season average temperature and annual minimum temperature were negatively and positively correlated with tree growth below and above the treeline, respectively. Our study not only confirmed that the overall variability of tree growth depends on tree size heterogeneity but also proposed an indicator that reveals net changes in the tree radial growth rate relative to the past. These theoretical advances are highly beneficial for understanding changes in the extent of subalpine forests.

Upscaling field-measured seasonal ground vegetation patterns with Sentinel-2 images in boreal ecosystems

ABSTRACT Aboveground biomass (AGB) and leaf area index (LAI) are key variables of ecosystem processes and functioning. Knowledge is lacking on how well the seasonal patterns of ground vegetation AGB and LAI can be detected by satellite images in boreal ecosystems. We conducted field measurements between May and September during one growing season to investigate the seasonal development of ground vegetation AGB and LAI of seven plant functional types (PFTs) across seven vegetation types (VTs) within three peatland and forest study areas in northern Finland. We upscaled field-measured AGB and LAI with Sentinel-2 (S2) imagery by applying random forest (RF) regressions. Field-measured AGB peaked around the first week of August and, in most cases, one to two weeks later than LAI. Regarding PFTs, deciduous vascular plants had clear unimodal seasonal patterns, while the AGB and LAI of evergreen vegetation and mosses remained steady over the season. Remote sensing regression models explained 24.2–50.2% of the AGB (RMSE: 78.8–198.7 g m−2) and 48.5–56.1% of the LAI (RMSE: 0.207–0.497 m2 m−2) across sites. Peatland-dominant sites and VTs had a higher prediction accuracy. S2-predicted peak dates of AGB and LAI were one to three weeks earlier than the field-based ones. Our findings suggest that boreal ground vegetation seasonality varies among PFTs and VTs and that S2 time series data can be applied to monitor its spatiotemporal patterns, especially in treeless regions.

Soil bacteria and fungi communities are shaped by elevation influences in Colombian forest and páramo natural ecosystems.

The influence of elevation on natural terrestrial ecosystems determines the arrangements of microbial communities in soils to be associated with biotic and abiotic factors. To evaluate changes of fungi and bacteria at the community level along an elevational gradient (between 1000 and 3800 m.a.s.l.), physicochemical measurements of soils, taxonomic identifications of plants, and metabarcoding sequences of the 16S rRNA gene for bacteria and the ITS1 region for fungi were obtained. The bacterial taxonomic composition showed that Acidobacteriota increased in abundance with elevation, while Actinobacteriota and Verrucomicrobiota decreased. Furthermore, Firmicutes and Proteobacteria maintained maximum levels of abundance at intermediate elevations (1200 and 2400 m.a.s.l.). In fungi, Ascomycota was more abundant at higher elevations, Basidiomycota tended to dominate at lower elevations, and Mortierellomycota had a greater presence at intermediate sites. These results correlated with the edaphic parameters of decreasing pH and increasing organic carbon and available nitrogen with elevation. In addition, the Shannon index found a greater diversity in bacteria than fungi, but both showed a unimodal pattern with maximum values in the Andean Forest at 2400 m.a.s.l. Through the microbial characterization of the ecosystems, the elevational gradient, soil properties, and vegetation were found to exert significant effects on microbial communities and alpha diversity indices. We conclude that the most abundant soil microorganisms at the sampling points differed in abundance and diversity according to the variations in factors influencing ecological communities.

Investigation of the Vertical Distribution Characteristics and Microphysical Properties of Summer Mineral Dust Masses over the Taklimakan Desert Using an Unmanned Aerial Vehicle

Investigating the vertical distribution of mineral dust masses and their microphysical properties is crucial for accurately assessing the climate effects of dust. However, there are limited studies related to relevant in situ observations over dust source areas. In this study, the near-surface vertical characteristics (within 500 m a.g.l) of dust mass concentrations in five size fractions (PMs: TSP, PM10, PM4, PM2.5, and PM1) were investigated using an unmanned aerial vehicle (UAV) in Tazhong (TZ) in the Taklimakan Desert (TD) in July 2021. To the best of our knowledge, the vertical profiles of particle number concentration (PNC), effective radius (Reff), and volume concentration (Cv) were obtained for the first time by UAV over the TD. Four scenarios of clear sky, floating dust, blowing sand, and dust storm were selected based on the classification criteria for PMs. The PMs, PNC, Reff, and Cv decreased with height for all scenarios. From clear-sky to dust-storm scenarios PMs, PNC, Reff, and Cv in the column gradually increased. Reff (Cv) increased from 1.15 μm (0.08 μm3/μm2) to 4.53 μm (0.74 μm3/μm2). The diurnal variations of PMs, PNC, and Reff (Cv) revealed a unimodal pattern, with the peak occurring between 13:00 and 16:00, due to the evolution of wind speed and the atmospheric boundary layer in TZ. Unexpectedly, among the three postprecipitation scenarios (P1, P2, and P3), the PNC of P2 was smaller than those of P1 and P3. The Reff (Cv) for P2 was similar to or greater than that for dust storms, which may be associated with moist dust particles on the ground surface being carried into the air by wind. These investigations add to our understanding of the mineral dust vertical characteristics over the source area, and provide a meaningful reference for colocated lidar inversion and dust simulations.

Diversity and distribution of Pteridophytes in Biligiri Rangaswamy Temple (BRT) Tiger Reserve, Karnataka

An updated list of the pteridophytes known to occur in the Biligiri Rangaswamy Temple (BRT) Tiger Reserve has been presented. It comprises two classes, 24 families, 49 genera, and 102 species, including 11 subspecies. Four families were identified as monotypic. Among the 102 species collected, six were endemic to south India, 10 were confined to south India and Sri Lanka, and eight were in the threatened category. We make available baseline biodiversity information on the pteridophytes of the study area and provide details on taxonomic diversity and distribution along the elevation gradient. The relationship between elevation and species richness in the study area showed a unimodal pattern. Color photographs of species from each family are also provided. The presence of many threatened and endemic species in the area implies that a high priority should be given to protecting and conserving these species of pteridophytes in the BRT Tiger Reserve.

Comparative Effect of Physiological Salts upon Micellization of T1304 and T1307.

We present a comprehensive investigation on the interaction of tetronics (T1304 and T1307) with some important physiological salts (NaH2PO4, KH2PO4, Na2CO3, NaCl, and KI). Thermodynamic and microstructural aspects of these interactions were studied as a function of the solution temperature, pH and salt concentration. Characterizations were performed using turbidimetric, calorimetric, and scattering techniques. We show that, at ambient temperature, T1304 molecules aggregated to form spherical core-shell aggregates displaying a unimodal distribution pattern. On the other hand, unimers and large clusters dominated in the case of highly hydrophilic T1307. Its micellization was promoted in the presence of salts as per the following trend: NaCl < KH2PO4 < NaH2PO4 ≪ Na2CO3. Aggregation was found to be endothermic, and hydrophobic interactions (TΔSmic > ΔHmic) prevailed. The enthalpy-entropy compensation plot was found to be linear for both copolymers. Demicellization occurred in the presence of KI as it facilitated the buildup of water structures around the copolymer chains. This could be verified from the increase in the cloud point, critical micelle concentration, and free energy. Overall, the temperature and salts inflicted a stronger hydrophobic effect upon T1304 in comparison to T1307.

Diversity and composition of plants species along elevational gradient: research trends

Studies on species richness patterns along elevation gradients are fascinating and gaining attention. We compiled data from 118 studies of elevational gradients in a broad range of organisms of plant species throughout the world between 2001 and 2021 to estimate the patterns of species richness and their determinants. The present study showed that more than half (57%) of studies had found unimodal hump-shaped richness patterns (maximum diversity at the middle and lower edges), followed by a monotonic decline (26%), in different taxa of the plant. Nearly one-fifth of studies (17.5%) followed either monotonic incline, reverse hump-shaped, or non-distinct patterns. A more uniform model as a unimodal hump shape was present in extensive studies in mountainous regions. Despite the latitudinal and elevational variation, both hemispheres showed similar patterns of species richness for all plant taxa. Some taxa showed bimodality, and some others showed multi-model patterns of elevation-species richness patterns with peak diversity due to topographical and climatic factors. Upper and lower elevational ranges may provide temperature and rainfall extremes, reducing species diversity. The mid-domain effect may explain this species richness pattern. However, the current study confirmed the presence of a hump-shaped species richness pattern as a result of the size of the midpoint elevation or elevation range considered for an individual species. The higher the midpoint value, the longer the elevation range that favors a unimodal pattern. Due to inclusion of limited number of species, universal pattern of species richness along elevational gradient and their determinants could not be anticipated. We need more succinct and regional researches focusing specific taxa and delimiting factors.

Daily and Seasonal Activity Patterns of Plateau Pikas (Ochotona curzoniae) on the Qinghai-Tibet Plateau, China, and Their Relationship with Weather Condition.

Exploring the activity patterns of small mammals is important for understanding the survival strategies of these animals, such as foraging and mating. The purpose of the present study was to determine the activity of free-living plateau pikas (Ochotona curzoniae) in different months and seasons (cold and warm seasons), with a particular emphasis on the effects of weather condition. Based on a camera-trapping survey conducted from October 2017 to September 2018, we evaluated the activity patterns and activity levels of plateau pikas inhabiting the eastern Qinghai-Tibet Plateau in China. The effects of environmental factors on the activity of plateau pikas were examined using the generalized additive mixed model (GAMM). The results showed that: (1) The plateau pikas exhibited unimodal patterns of activity during the cold season (October-April). During the warm season (May-September), the activity patterns of the plateau pikas were bimodal. Their activity levels were highest in June. (2) During the cold season, their activity levels rose gradually over the course of the day to a peak near noon, and they were not significantly higher after sunrise than they were before sunset. During the warm season, their activity peaks were in the morning and afternoon, and their activity levels were substantially lower after sunrise than they were before sunset. (3) The plateau pikas were more active under conditions with lower ambient temperatures and precipitation during the cold and warm seasons. While relative air humidity was positively correlated with the activity of the plateau pikas during the warm season, wind speed was negatively correlated with the pikas' activity during the cold season. Overall, these results collectively indicate that plateau pikas occupy habitats with cool and less windy microclimates during the cold season, and with cool and moist microclimates during the warm season. Information on the time allocation of pikas' activity levels during different seasons should provide a baseline for understanding their potential for adaptation to climate change.

Within leaf nitrogen allocation regulates the photosynthetic behavior of xerophytes in response to increased soil rock fragment content

There is limited information on how plant functional traits vary with soil rock fragment content (RFC), especially for xerophytes growing in stony soils. We examined leaf functional traits of three xerophytes (Sophora davidii; Cotinus szechuanensi; and Artemisia vestita) grown under an RFC gradient in a heavy loamy soil. Our results show that photosynthetic capacity increased linearly with RFC in S. davidii, whereas unimodal patterns were observed for the other two species. The RFC that maximized photosynthetic capacity (Asat) and photosynthetic N use efficiency (PNUE) were achieved by allocating more N to photosynthetic apparatus at the expense of cell walls. For C. szechuanensis, the increased fraction of photosynthetic N allocated to carboxylation (PC) bioenergetics (PB), and thylakoid light-harvesting components (PL) together contributed to the higher Asat and PNUE values. As for S. davidii, both PC and PB mainly contributed to higher Asat and PNUE, whereas for A. vestita only PB was the main contributor. Our results suggest that increased non-capillary porosity of high RFC soil conditions through promoting the root growth of S. davidii and C. szechuanensis ensures sufficient water and N supply for photosynthetic capacity. In shallow-rooted species A. vestita, low RFC soil maintained higher nitrate N in the topsoil, enhancing leaf photosynthetic capacity. We conclude that rock fragments promoted leaf photosynthetic capacity in the studied loamy soil system, but the promoting effect was species-specific. The results highlight the relevance of consideration of soil rock fraction in evaluation of photosynthetic behavior of xerophytes in heterogeneous rocky soils.

Wildfire impacts on seedbank and vegetation dynamics in Calluna heath

Moorlands dominated by Calluna vulgaris (hereafter Calluna) are globally rare and under increasing threat of wildfires due to climate change. The soil seedbank is important for community resilience, but research on its contribution to regenerating vegetation after moorland fires has, to date, focused on prescribed fire or on the short‐term (≤ 2 year) impacts of wildfire. To address the role of the seedbank in long‐term vegetation regeneration, we studied a chronosequence of six wildfire sites within a Scottish moorland catchment, ranging from 2 to 64 years since burning. We recorded vegetation composition and sampled the seedbank. Calluna and Erica spp. comprised 66 and 27% of germinated seeds, respectively, and the majority of vegetation species were not represented in the seedbank. Canonical correspondence analysis (CCA) revealed that time since fire was a strong predictor of vegetation species composition, but it had no effect on seedbank composition, suggesting that the same species dominate the seedbank regardless of burning. Whilst total seed density was not affected by time since wildfire, the effect on the non‐Calluna seedbank was more notable. The proportion of non‐Calluna species decreased with time in both vegetation and seedbank as Calluna cover was re‐established and the seedbank of other species became gradually depleted. Whilst relative non‐Calluna cover in the vegetation was at a maximum in recently burnt areas and declined with time since fire, the species richness and proportion of non‐Calluna in the seedbank followed a unimodal pattern after fire and reached a peak after approximately 35 years. Our results contribute to the knowledge of how moorland ecosystems regenerate after severe disturbances, which are likely to become more common as the climate changes.

Size distributions of molecular markers for biogenic secondary organic aerosol in urban Beijing

To understand the source, formation, and seasonality of biogenic secondary organic aerosol (BSOA), a nine-stage cascade impactor was utilized to collect size-segregated particulate samples from April 2017 to January 2018 in Beijing, China. BSOA tracers derived from isoprene, monoterpene, and sesquiterpene were measured with gas chromatography-mass spectrometry. Isoprene and monoterpene SOA tracers exhibited significant seasonal variations, with a summer maximum and a winter minimum. Dominance of 2-methyltetrols (isoprene SOA tracers) with a good correlation with levoglucosan (a biomass burning tracer), which was combined with the detection of methyltartaric acids (possible indicators for aged isoprene) in summer, implies possible biomass burning and long-range transport. In contrast, sesquiterpene SOA tracer (β-caryophyllinic acid) was dominant in winter and was probably associated with the local burning of biomass. Bimodal size distributions were observed for most isoprene SOA tracers, consistent with previous laboratory experiments and field studies showing that they can be formed not only in the aerosol phase but also in the gas phase. Monoterpene SOA tracers cis-pinonic acid and pinic acid showed a coarse-mode peak (5.8–9.0 μm) in four seasons due to their volatile nature. Sesquiterpene SOA tracer β-caryophyllinic acid showed a unimodal pattern with a major fine-mode peak (1.1–2.1 μm), which is linked to local biomass burning. The tracer-yield method was used to quantify the contributions of isoprene, monoterpene, and sesquiterpene to secondary organic carbon (SOC) and SOA. The highest isoprene SOC and SOA concentrations occurred in summer (2.00 μgC m−3 and 4.93 μg m−3, respectively), contributing to 1.61% of OC and 5.22% of PM2.5, respectively. These results suggest that BSOA tracers are promising tracers for understanding the source, formation, and seasonality of BSOA.

Rarity of microalgae in macro, meso, and microhabitats

ABSTRACT Climate change and human-induced habitat degradations result in loss of species diversity in natural ecosystems. While the extinction of macroscopic organisms has been well documented in the scientific literature and public media, we have only limited knowledge on the loss of microscopic elements of the ecosystems. Because rarity coincides with the increased risk of extinction, we investigated the commonness and rarity of microalgae in the Pannonian ecoregion. We reviewed the published literature of microalgal research in Hungary over the last 140 years and created a species-by-site matrix containing 2489 algae species and 1145 localities. Analysing this dataset, we found that although the core-satellite hypothesis suggests a bimodal site occupancy distribution, microalgae displayed a unimodal pattern with a high number of rarely occurring species. We also demonstrated that the well-known negative relationship between body size of organisms and number of occupied habitats holds for microalgae. Rarity values of taxa have a phylogenetic signal indicating that in terms of rarity, closely related species (desmids, dinoflagellates, euglenophytes) show considerable similarities. The various habitat types showed differences in the number of rare taxa. Small- and medium-sized habitats (bog lakes, streams, oxbows) hosted the majority of rare species. These results highlight the conservation importance of small habitats in preserving microbial diversity.

Reproductive phenologies of phyllostomid bat populations and ensembles from lowland Amazonia.

Natural selection should favor individuals that synchronize energy-demanding aspects of reproductive activity with periods of high resource abundance and predictability, leading to seasonal patterns of reproduction at the population level. Nonetheless, few studies-especially those on bats in the Neotropics-have used rigorous quantitative criteria to distinguish among phenological patterns for different populations from the same habitat or for the same species in different habitats. To explore such issues, we quantified annual patterns of reproduction in male and in female bats from lowland Amazonia (environs of Iquitos, Peru), and did so at the level of populations and ensembles. Five species exhibited unimodal patterns including Artibeus obscurus, A. planirostris, Carollia benkeithi, Phyllostomus hastatus, and Rhinophylla pumilio. Two species (A. lituratus and Glossophaga soricina) evinced bimodal patterns with reproductive peaks separated by patterns of inactivity, whereas four species (C. brevicauda, C. perspicillata, Sturnira lilium, and S. tildae) evinced a bimodal pattern in which peaks in activity occur in tandem, with the first peak generally markedly higher than the second peak. Frugivore, gleaning animalivore, and nectarivore ensembles exhibited bimodal, unimodal, and bimodal reproductive phenologies, respectively. Nonetheless, interannual variation in phenology (i.e., the monthly timing of peaks within a season rather than the number of peaks per year) characterized four (A. obscurus, C. brevicauda, C. perspicillata, and S. lilium) of the eight species and each of the three ensembles (frugivores, gleaning animalivores, and nectarivores) with adequate sampling. Regardless of interspecific variation in strategies, the phenology of reproduction enhances the likelihood that parturition and recruitment of young into the population occurs during the wet season, the period of likely highest resource abundance. Based on a comparison of our results with those from other well-studied bat populations, four species did not exhibit geographic variation in reproductive phenologies (A. obscurus, G. soricina, C. brevicauda, and R. pumilio), whereas three species evinced such geographic variation (A. lituratus, A. planirostris, and C. perspicillata). Climate change will likely alter the seasons and extents of propitious times for reproductive activities, as well as the reliability of proximate cues for initiating reproduction, compromising current reproductive strategies and leading to altered phenological patterns of reproduction or reproductive success, possibly resulting in local extinction of some species.

H3K27me3-H3K4me1 transition at bivalent promoters instructs lineage specification in development

BackgroundBivalent genes, of which promoters are marked by both H3K4me3 (trimethylation of histone H3 on lysine 4) and H3K27me3 (trimethylation of histone H3 on lysine 27), play critical roles in development and tumorigenesis. Monomethylation on lysine 4 of histone H3 (H3K4me1) is commonly associated with enhancers, but H3K4me1 is also present at promoter regions as an active bimodal or a repressed unimodal pattern. Whether the co-occurrence of H3K4me1 and bivalent marks at promoters plays regulatory role in development is largely unknown.ResultsWe report that in the process of lineage differentiation, bivalent promoters undergo H3K27me3-H3K4me1 transition, the loss of H3K27me3 accompanies by bimodal pattern loss or unimodal pattern enrichment of H3K4me1. More importantly, this transition regulates tissue-specific gene expression to orchestrate the development. Furthermore, knockout of Eed (Embryonic Ectoderm Development) or Suz12 (Suppressor of Zeste 12) in mESCs (mouse embryonic stem cells), the core components of Polycomb repressive complex 2 (PRC2) which catalyzes H3K27 trimethylation, generates an artificial H3K27me3-H3K4me1 transition at partial bivalent promoters, which leads to up-regulation of meso-endoderm related genes and down-regulation of ectoderm related genes, thus could explain the observed neural ectoderm differentiation failure upon retinoic acid (RA) induction. Finally, we find that lysine-specific demethylase 1 (LSD1) interacts with PRC2 and contributes to the H3K27me3-H3K4me1 transition in mESCs.ConclusionsThese findings suggest that H3K27me3-H3K4me1 transition plays a key role in lineage differentiation by regulating the expression of tissue specific genes, and H3K4me1 pattern in bivalent promoters could be modulated by LSD1 via interacting with PRC2.

Linking different resources to recognize vascular epiphyte richness and distribution in a mountain system in southeastern Mexico

Mesoamerican mountains are important centers of endemism and diversity of epiphytes. The Sierra Madre of Chiapas in southeastern Mexico is a mountainous region of great ecological interest due to its high biological richness. We present the first checklist of epiphytes for this region based on a compilation of various information sources. In addition, we determined the conservation status for each species based on the Mexican Official Standard (NOM-059-SEMARNAT-2010), endemism based on geopolitical boundaries, spatial completeness with inventory completeness index, richness distribution with range maps, and the relationship between climatic variables (temperature and rainfall) with species richness using generalized additive models. Our dataset includes 9,799 records collected between 1896 and 2017. Our checklist includes 708 epiphytes within 160 genera and 26 families; the most species-rich family was Orchidaceae (355 species), followed by Bromeliaceae (82) and Polypodiaceae (79). There were 74 species within a category of risk and 59 species considered endemic. Completeness of epiphyte richness suggests that sampling is still largely incomplete, particularly in the lower parts of the mountain system. Species and family range maps show the highest richness at high elevations, while geographically richness increases towards the southeast. Epiphyte richness increases with increased rainfall, although a unimodal pattern was observed along the temperature gradient with a species richness peak between 16 and 20 C°. The Sierra Madre of Chiapas forms a refuge to more than 40% of all epiphytes reported for Mexico and its existing network of protected areas overlaps with the greatest epiphyte richness.

Influence of Thermal Maturity on the Time-Resolved Emission Spectrum (TRES) Fluorescence Lifetime Characteristics of Crude Oils: A Preliminary Study Based on a Thermal Simulation Experiment of Crude Oils

The time-resolved emission spectrum (TRES) fluorescence lifetime characteristics of crude oil have great application potential to classify the oil type and reveal its origin in a multisource petroleum system. However, the influence of thermal maturity on the TRES fluorescence lifetime characteristics of crude oil is still unclear. This study collected typical crude oil samples from deep reservoirs in the Tabei area of the Tarim Basin and obtained a group of pyrolyzed oils with different maturities by a thermal simulation experiment. The TRES average fluorescence lifetime value (τA) and profile pattern (λ–τ) of both pyrolyzed and crude oil samples were investigated. The results indicate that, with increasing maturity, the τA values of pyrolyzed oil slightly increase when EasyRo < 0.90% but decrease when EasyRo > 0.90%. Meanwhile, the λ–τ pattern shows no obvious changes when EasyRo < 1.53% but changes significantly when EasyRo > 1.53%. Based on the TRES fluorescence lifetime characteristics, the deep crude oils in various blocks of the Tabei area are divided into TB-I and TB-II types, which correspond well with their physical properties, diagnostic biomarkers, and carbon isotopic values. The TB-I crude oils are widely distributed in the Shunbei, Hadexun, Repu, and Halahatang blocks. This type of crude oil has a short τA value and exhibits an obvious platform pattern in its λ–τ profile. The TB-II crude oils are distributed only in the Yuke block. This type of crude oil has a long τA value and shows a unimodal pattern in its λ–τ profile. The TRES fluorescence lifetime parameters can effectively classify crude oils with different sources and can further identify the thermal maturity of crude oils with the same sources by combining them with the physical and geochemical parameters of crude oils, which exhibits great application potential to crude oils and individual petroleum inclusions in deep multisource petroleum systems.