Unimodal Pattern Research Articles

A unique cardiac electrocardiographic 3D model. Toward interpretable AI diagnosis.

Mathematical models of cardiac electrical activity are one of the most important tools for elucidating information about heart diagnostics. In this paper, we present an efficient mathematical formulation for this modeling simple enough to be easily parameterized and rich enough to provide realistic signals. It relies on a five dipole representation of the cardiac electric source, each one associated with the well-known waves of the electrocardiogram signal. Beyond the physical basis of the model, the parameters are physiologically interpretable as they characterize the wave shape, similar to what a physician would look for in signals, thus making them very useful in diagnosis. The model accurately reproduces the electrocardiogram signals of any diseased or healthy heart. This new discovery represents a significant advance in electrocardiography research. It is especially useful for diagnosis, patient follow-up or decision-making on new therapies; is also a promising tool for well-performing, transparent and interpretable AI approaches.

Plant species richness on the Tibetan Plateau: patterns and determinants

Whether current hypotheses for geographic patterns of species richness (SR) have a strong explanatory power for the Tibetan Plateau (TP) with extreme climatic conditions remains unclear. In comparison with the classic ‘water–energy dynamics hypothesis', the unique climate factors (e.g. extreme low temperature and low oxygen partial pressure) on the TP likely significantly affect the spatial variation of SR. Here, we investigate geographic patterns and determinants of SR on the TP through a systematic field investigation. We systematically analyzed a total of 2013 plant communities covering 11 different vegetation types on the TP. To compare this SR with that of other sites across the globe, we compiled a global database containing information on 87 forest and 3660 grassland plots. The SR per 400 m2 in the forests and shrubs and that per 1 m2 in alpine grasslands and deserts was 62.76 (± 1.80 SE), 44.53 (± 7.57 SE), 16.84 (± 0.39 SE) and 3.62 (± 0.55 SE), respectively. The SR of forests and shrubs decreased with latitude and altitude, whereas that of alpine grasslands and deserts showed a unimodal pattern along the altitudinal gradient. Unique climate factors, such as extreme low temperature, mean diurnal temperature and oxygen partial pressure, act synergistically with water–energy dynamics and influence the spatial pattern of SR on the TP. Furthermore, the tree SR on the TP was lower than that of global tropical and subtropical broadleaf forests but higher than that of temperate conifer forests. Alpine meadows had a higher SR than other sites; however, the SR in alpine desert grasslands and alpine deserts was lower. Our findings provide novel insights into the mechanisms underlying the spatial variation in plant diversity, especially on plateaus and in high‐latitude regions. Our findings and the SR map with 1 km resolution provide important benchmarks for biodiversity conservation and may help to improve predictions of the effect of climate change on biodiversity.

Salinity Induces Allometric Accumulation of Sulfur in Plants and Decouples Plant Nitrogen‐Sulfur Correlation in Alpine and Arid Wetlands

AbstractSalinization alters the elemental balance of wetlands and induces variations in plant survival strategies. Sulfur (S) plays vital roles in serving regulatory and catalytic functions in stress resistance of plants. Yet, how plant S and its relationships with nitrogen (N) vary across natural environmental gradients are not well documented. We collected 1,366 plant samples and 230 water and sediment samples from 230 wetlands in Tibetan Plateau and adjacent arid regions of western China, to analyze the effects of environmental variables on plant S accumulation and N‐S correlations. We found that plant S correlated with N in unimodal patterns. Salinity, rather than temperature or nutrient supply, promoted disproportionate accumulation of S but limited N uptake, inducing decoupling of N‐S correlation in plants. Toward high salinity, the faster increasing rates of total S than that of glutathione, the most abundant organic‐S compound in plant resistance, provided potential evidences explaining the decoupled plant N‐S correlation. A salinity of 3.9‰ was calculated to be a threshold at which substantial changes in plant N‐S correlation occurred. We designed a conceptual model to illustrate the mechanisms driving variations of N‐S correlation in plants and environments along salinity gradient. Furthermore, high salinity filtered out the salt‐sensitive species and reassembled the communities. In conclusion, increased salinity affected wetland plants by inducing S accumulation in plants and selecting salt‐tolerant species with high S concentrations at community level, providing evidences for plant adaptive mechanisms to salinity in arid regions.

Plant community assembly is jointly shaped by environmental and dispersal filtering along elevation gradients in a semiarid area, China.

Environmental filtering (EF) and dispersal filtering (DF) are widely known to shape plant community assembly. Particularly in arid and semi-arid mountainous regions, however, it remains unclear whether EF or DF dominate in the community assembly of different life forms or how they interact along elevational gradients. This research aims to reveal how different ecological processes influence herbaceous and woody community assembly and how they respond to various environmental drivers and elevational gradients. Here we integrated taxonomic diversity (TD), phylogenetic diversity (PD), and ecological drivers across an elevational gradient of 1,420 m in the Helan Mountain Nature Reserve, in typical arid and semi-arid areas of China. This study showed that the TD and PD of herbaceous communities significantly increase linearly with changing elevation gradients, while woody 'TD' showed a unimodal pattern, and there was little relationship between woody 'PD' and elevation. Herbaceous species exhibited significant phylogenetic clustering at low elevations, where they were influenced by climate, aspect, and tree cover. However, woody species exhibited random patterns across elevations. Herbaceous and woody species' taxonomic and phylogenetic beta diversity is governed primarily by spatial turnover rather than nestedness. Spatial turnover is caused primarily by EF and DF's combined influence, but their relative importance differs between herbaceous and woody communities. Therefore, we conclude that the responses of herbaceous and woody plants along elevation gradients in the Helan Mountains are decoupled due to their different adaptation strategies to climate factors in the drylands. These findings are important for understanding the assembly mechanisms driving plant communities in dryland under the context of dramatic increases in drought driven by climate warming.

Functional Diversity and Primary Production Predict Future Patterns of Periphyton Productivity after Species Extinction

Understanding of the trait-based ecology of the periphytic algal community has increased in the last decade. However, the relationship between their functional diversity and ecosystem functions, such as primary production, has been speculated on, but yet not proven. Human impacts promote changes in biotic communities leading to a risk of extinction, with consequences for the functioning of aquatic ecosystems. In this study, we unraveled the associations between the taxonomic and functional components of periphytic algal diversity, stream eutrophication, and productivity patterns. Furthermore, we simulated future patterns of species extinction to predict how productivity may change when facing extinction. Primary production and taxonomic and functional diversity of the periphytic algal communities were estimated in five streams across a trophic gradient in the Ave River basin (northwest Portugal). Our results demonstrated that eutrophication led to a unimodal pattern of taxonomic diversity, while functional diversity tended to increase with increasing eutrophication. We found that only functional diversity had a positive association with primary production. The extinction estimations indicated that almost all species found in our study were at high extinction risk. When we spatially scaled our extinction simulations, we found poor-productive streams after the extirpation of a few species. However, at the regional scale, the ecosystem supports the extinction of at least 40% of species before turning into a poor-productive system. Intermediate levels of disturbance are probably beneficial for the diversity of periphytic algal communities, to a certain extent. Moreover, functionally diverse communities were more productive, and the alleged future extinction of species is likely to lead to poor-productive streams if regionally focused conservation initiatives are not implemented. We recommend that, using simulations of functional extinction, it is possible to infer how the loss of these microorganisms could alter ecosystem functioning, to better predict human impacts on aquatic ecosystems.

Functional space expansion driven by transitions between energetically advantageous traits in the deep sea.

Climate change is shifting community structure and biodiversity on a global scale, in part due to alterations of chemical and thermal energy availability. These changes may impact ecosystem functioning through their influence on functional diversity. We investigate patterns of functional diversity, functional niches, and functional traits in bivalve communities across the energetic gradient of the deep Atlantic Ocean. We use the functional traits feeding type, tiering, and motility level to define the axes of functional space and the unique combinations of these traits as functional niches. We find that increased energy affords new species, added into functional space through niche expansion rather than niche packing. Underlying this pattern are complex dynamics of gains and losses of individual functional niches, with few adapted to the low- and high-energy extremes, and most occurring at intermediate energy. Adaptive qualities of specific traits are evidenced by those functional niches occurring at energetic extremes. Tradeoffs between these traits within the intermediate energy zone underlie an increased coexistence of functional niches, which in turn drives a unimodal pattern of functional niches and expansion of used functional space. This work suggests that energy-limited communities may be especially vulnerable to continued shifts in food availability through the Anthropocene.

Temperature factors are a primary driver of the forest bryophyte diversity and distribution in the southeast Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) is an amplifier of global climate change, where the climate change is happening faster or more dramatically. Bryophytes play an important role in forest communities, and they are sensitive to climate change. In this study, we selected 75 sites in locations in the southeast QTP with well-developed forests and collected bryophytes from soils, stones, trees, and dead wood. By utilizing the large sample set obtained, we investigated the responses of the forest bryophyte diversity and distribution to climate change. We extracted and measured 10 climate factors, including nine macroclimate factors: humidity-, temperature-, solar radiation-related factors, and one microclimate factor, canopy density. We used the ordinary least squares (OLS) to establish simple and multiple regression models between the Shannon diversity index and climate factors and utilized the canonical correspondence analysis (CCA) to investigate the response of the total bryophyte distribution and the differential response of bryophytes growing on soils, stones, trees, and dead wood to climate. We found that most climate factors showed unimodal patterns with the forest bryophyte diversity, and when climate change exceeded the optimal threshold for bryophyte growth, with even small increases, this led to a decrease in the bryophyte diversity. In contrast to previous studies on the response of bryophytes to the climate in other regions, we found temperature factors (i.e., minimal temperature and daily temperature range) were the most influential drivers of the forest bryophyte diversity and distribution, regardless of the growth substrate in the southeast QTP. According to the total explained variance of climate factors to the bryophyte distribution, the bryophytes growing on trees (10.6%) and dead wood (14.3%) were more sensitive to climate than those growing on soils (6.9%) and stones (7.7%). Therefore, with continued global warming, the forest bryophytes of the QTP will face a great threat, as they are most effected by temperature change among all of the climate factors.

Combustion and emissions characteristics of methanol/gasoline CISI engines under different injection modes

Methanol was a promising alternative fuel for spark ignition engines due to its liquid nature, large octane number and high oxygen content. The combined injection technology had the advantages of greater control flexibility, less engine knock tendency, and less engine-out emissions. However, the preferable injection mode of methanol/gasoline dual fuel engine was rarely reported. In this study, the combustion and emission characteristics of methanol/gasoline dual fuel engine with different injection modes, methanol direct injection plus gasoline port injection (MDI + GPI) or gasoline direct injection plus methanol port injection (GDI + MPI), were studied experimentally. The results showed that MDI + GPI mode was preferred for methanol/gasoline dual fuel engines, as this mode yielded higher engine brake effective mean pressure, larger heat release rate, lower cyclic variation, and less particle number emissions. An unimodal nucleation pattern particle size distribution can be observed for the MDI + GPI mode, which was beneficial for the after-treatment of particles in gasoline particle filter.

Size distribution and exposure assessment of polybrominated diphenyl ethers at a formal E-waste recycling plant in China

Waste household appliances are dismantled and formally recycled in authorized plants in China. Based on the air and dust samples collected from two typical workshops, including manual dismantling workshop (DisW) and mechanical crushing workshop (CruW), size distribution of particulate matters (PM) and polybrominated diphenyl ethers (PBDEs) were studied. The results showed that coarse particles (>2.1 μm) constituted the majority of PM in both workshops, and the air concentrations of ∑16PBDE were 55.0 ng/m3 in the DisW and 14.1 ng/m3 in the CruW, respectively. The size distribution of particle-bound PBDEs showed a unimodal distribution pattern, with the peak in the fraction 5.8–9.0 μm in the DisW and 4.7–5.8 μm in the CruW, respectively. The heavy brominated BDEs (octa-to deca-BDE) dominated the congener pattern in different size particles, and the percentage of BDE-209 showed a decreasing trend as the decreasing of particle size. Based on the International Commission on Radiological Protection model, the deposition fluxes of particle-bound ∑16PBDEs in the head airways region, tracheobronchial region, and alveolar region were 129, 4.63, 7.22 ng/h in the DisW, and 29.0, 1.26, 2.60 ng/h in the CruW, respectively, indicating that the majority of PBDEs deposited in the head airways region. The values of estimated daily intake for BDE-47, -99, −153, −209 and ∑16PBDEs in both workshops were in range of 0.052–18.9 ng/(kg·d) via inhalation, and 0.032–229 ng/(kg·d) via dust ingestion, all of which were below the reference doses. These results provided new data for exposure risk assessment related with formal e-waste recycling.

Interannual characteristics and driving mechanism of CO2 fluxes during the growing season in an alpine wetland ecosystem at the southern foot of the Qilian Mountains.

The carbon process of the alpine ecosystem is complex and sensitive in the face of continuous global warming. However, the long-term dynamics of carbon budget and its driving mechanism of alpine ecosystem remain unclear. Using the eddy covariance (EC) technique-a fast and direct method of measuring carbon dioxide (CO2) fluxes, we analyzed the dynamics of CO2 fluxes and their driving mechanism in an alpine wetland in the northeastern Qinghai-Tibet Plateau (QTP) during the growing season (May-September) from 2004-2016. The results show that the monthly gross primary productivity (GPP) and ecosystem respiration (Re) showed a unimodal pattern, and the monthly net ecosystem CO2 exchange (NEE) showed a V-shaped trend. With the alpine wetland ecosystem being a carbon sink during the growing season, that is, a reservoir that absorbs more atmospheric carbon than it releases, the annual NEE, GPP, and Re reached -67.5 ± 10.2, 473.4 ± 19.1, and 405.9 ± 8.9 gCm-2, respectively. At the monthly scale, the classification and regression tree (CART) analysis revealed air temperature (Ta) to be the main determinant of variations in the monthly NEE and GPP. Soil temperature (Ts) largely determined the changes in the monthly Re. The linear regression analysis confirmed that thermal conditions (Ta, Ts) were crucial determinants of the dynamics of monthly CO2 fluxes during the growing season. At the interannual scale, the variations of CO2 fluxes were affected mainly by precipitation and thermal conditions. The annual GPP and Re were positively correlated with Ta and Ts, and were negatively correlated with precipitation. However, hydrothermal conditions (Ta, Ts, and precipitation) had no significant effect on annual NEE. Our results indicated that climate warming would be beneficial to the improvement of GPP and Re in the alpine wetland, while the increase of precipitation can weaken this effect.

Higher-order interactions on disease transmission can reverse the dilution effect or weaken the amplification effect to unimodal pattern

Determining whether species richness protects host species against infectious diseases transmission (i.e., dilution effect) within established communities is a core concern of disease ecology. Previous modeling studies have focused on pairwise transmission between hosts, largely ignoring the impact of neighboring species on pathogen transmission. Here, we modified the multi-host susceptible-infected-recovered (SIR) model to investigate the effects of higher-order interactions on the dilution effect. We found that compared with direct transmission, higher-order interactions that impede pathogen transmission can disproportionately decrease disease risk at high species richness levels under additive community assembly and thereby enhance a dilution effect or neutralizing an amplification effect into a unimodal species richness-disease relationship. Conversely, higher-order interactions that promote infection among host neighbors can enlarge an amplification effect and diminish a dilution effect or even reverse it. Higher-order interactions did not affect the emergence of the dilution effect for substitutive community assembly. Our results provide a unified framework for understanding the dilution and amplification effects and emphasize the importance of taking higher-order interactions into account for understanding mechanisms underlying the dilution effect.

Distribution and Ecology of Phlebotomine Sand Flies (Diptera: Psychodidae) in Endemic and Nonendemic Area of Leishmaniasis in Northern Morocco.

Northern Morocco is endemic for cutaneous and visceral leishmaniasis. Our entomological investigations aim to evaluate the risk of Leishmania transmission by determining the species composition, the density, and seasonal fluctuation of sand fly populations in endemic and nonendemic areas of leishmaniasis in Tetouan province (North-Western Morocco). Using Sticky-paper traps, 8,370 specimens were collected between May and November 2015 in two localities: peri-urban area of Tetouan city, where leishmaniasis is endemic and that of the Oued Laou village where no cases of leishmaniasis have been recorded. Six sand fly species were identified. The genus Phebotomus was represented by five species: Phlebotomus ariasi, Phlebotomus. longicuspis, Phlebotomus perniciosus, Phlebotomus kazeruni, and Phlebotomus sergenti, while the genus Sergentomyia was represented by only one species Sergentomyia minuta. Phlebotomus perniciosus was dominant in the nonendemic area (47%) while Phlebotomus sergenti was dominant in the endemic area (51%). The spatio-temporal distribution of sand fly populations is discussed according to biotic and abiotic variables. Seasonal fluctuation in sand fly density showed a bimodal pattern for the subgenus Larroussius and a unimodal pattern for the subgenus Paraphlebotomus in Tetouan city. But, in Oued Laou village, a unimodal density distribution for species of the Larroussius subgenus and a bimodal seasonal distribution for species of the subgenus Paraphlebotomus were identified. We affirm the coexistence, in the study area, of vectors of both cutaneous and visceral leishmaniasis, namely P. ariasi, P. longicuspis and P. perniciosus vectors of Leishmania infantum and P. sergenti vector of L. tropica. However, the geographic distribution, the specific abundance, and the activity reveal significant differences between endemic and nonendemic areas in the region.

Effects of climatic and edaphic conditions on structuring patterns of soil nematode communities in Japanese cedar (Cryptomeria japonica) plantations

Strong associations exist between organism and soil functions in forest ecosystems at large spatial scales; however, it is unclear the community patterns of soil nematodes. Artificial monoculture forests with poor understory vegetation would provide an ideal model system to characterize the relationship between nematode community structures and local habitat conditions. This study aimed to understand how climate and soil properties influence the community structure of soil nematodes in artificial Japanese cedar (Cryptomeria japonica) plantations. The richness, abundance, and community structure of the nematodes were assessed using soils (20 cm in depth) collected from eight 1 ha C. japonica plantations (40–60 years), which were distributed between 24°N and 42°N, with cool temperate, temperate, and subtropical zones in summer. The soil nematode aggregates were identified using a high throughput sequencing of the MiSeq system. The richness of amplicon sequence variances of nematodes revealed a significant unimodal pattern with latitude, with the greatest richness observed at 33°N. In contrast, nematode abundance showed a significant U-shaped pattern with latitude and was lower at mid-latitudes. Nematode community structures in subtropical zones clearly differed from those in the temperate and cool temperate zones. Among the environmental factors measured, mean annual temperature, soil pH, and C content accounted for the greatest variations in nematode communities. These results indicate that nematode richness and abundance displayed opposite patterns along latitudinal gradients. Moreover, the interrelationship between climate and soil conditions was identified as the best predictor of the community structure of soil nematodes in the monocultural C. japonica forest ecosystems. This study provided a useful view of belowground biodiversity for evaluating forest health in Asian coniferous plantations.

Elevational pattern of soil organic carbon release in a Tibetan alpine grassland: Consequence of quality but not quantity of initial soil organic carbon

Soil organic carbon (SOC) dynamics along elevational gradients are highly uncertain due to our limited knowledge of the underlying mechanisms that determine SOC release. By combining field investigation and laboratory aerobic incubation with multiple soil analytical approaches, we explored the determinants of SOC release along an elevational gradient (3200–4200 m) in the Tibetan alpine grassland. We illustrated that the SOC quantity (i.e., the initial standing SOC stock) and SOC quality (i.e., chemical recalcitrance, physico-chemical protection and biological recalcitrant fraction) increased gradually with elevation, reaching a maximum value at the middle altitude (∼3600 m), while an opposite unimodal distribution pattern was observed in CO2–C release. Our results also showed that SOC quality explained more variance in CO2–C release than did SOC quantity and soil properties. The proportion of stable SOC fractions in larger initial SOC stocks is higher, especially the recalcitrant SOC pool and mineral-associated OC fractions, which could be the potential mechanism behind high initial SOC stocks leading to lower soil CO2–C release. Collectively, our results provide compelling evidence that SOC quality plays a primary role in the elevational pattern of CO2–C release in Tibetan alpine grassland. Our findings highlight the importance of SOC quality in predicting SOC dynamics in the Tibetan alpine grassland under climate change scenarios.

Molecular insights into impacts of EDTMPA on membrane fouling caused by transparent exopolymer particles (TEP)

While ethylenediamine tetramethylenephosphonic acid (EDTMPA) has been emerged as a stronger chelating agent than ethylene diamine tetraacetic acid (EDTA) for fouling mitigation, and transparent exopolymer particles (TEP) is a major foulant in membrane-based water treatment process, effects of EDTMPA on TEP fouling and the underlying mechanism have been not yet studied. In this study, Flory-Huggins lattice theory was combined with density functional theory (DFT) technology to explore this subject at molecular level. Filtration experiments showed a unimodal pattern of specific filtration resistance (SFR) of TEP sample with Ca2+ concentration in range of 0–3 mM. For the TEP sample with the peak SFR value at 1.5 mM Ca2+, continuous addition of EDTMPA (from 0 to 100 mg·L−1) resulted in a sustained decrease in SFR. Energy dispersive spectroscopy (EDS) mapping characterization showed the continuing decline of calcium content in the TEP layer with increase of EDTMPA addition, indicating that EDTMPA successfully captured Ca2+ from alginate‑calcium ligation (TEP), and then disintegrated the TEP structure. DFT simulation showed that Ca2+ preferentially coordinated with the terminal carboxyl groups of alginate chains to form a coordination configuration that is conducive to stretch the three-dimensional polymer network. Such a network corresponded to an extremely high SFR according to Flory-Huggins theory. EDTMPA addition caused disintegration of the coordination configuration of Ca2+ binding to terminal carboxyl groups, which further resulted in collapse and flocculation of TEP gel network structure, thus leading to a continuous SFR decrease. This work provided deep thermodynamic insights into effects of EDTMPA on TEP-associated fouling at molecular level, facilitating to better understanding and mitigation of membrane fouling.

Solar park promoted microbial nitrogen and phosphorus cycle potentials but reduced soil prokaryotic diversity and network stability in alpine desert ecosystem.

Solar park (SP) is rapidly growing throughout the planet due to the increasing demand for low-carbon energy, which represents a remarkable global land-use change with implications for the hosting ecosystems. Despite dozens of studies estimating the environmental impacts of SP based on local microclimate and vegetation, responses of soil microbial interactions and nutrient cycle potentials remain poorly understood. To bridge this gap, we investigated the diversity, community structure, complexity, and stability of co-occurrence network and soil enzyme activities of soil prokaryotes and fungi in habitats of ambient, the first, and sixth year since solar park establishment. Results revealed different response patterns of prokaryotes and fungi. SP led to significant differences in both prokaryotic and fungal community structures but only reduced prokaryotic alpha diversity significantly. Co-occurrence network analysis revealed a unimodal pattern of prokaryotic network features and more resistance of fungal networks to environmental variations. Microbial nitrogen and phosphorus cycle potentials were higher in SP and their variances were more explained by network features than by diversity and environmental characteristics. Our findings revealed for the first time the significant impacts of SP on soil prokaryotic and fungal stability and functional potentials, which provides a microbial insight for impact evaluation and evidence for the optimization of solar park management to maximize the delivery of ecosystem services from this growing land use.

Comparisons of carbon and nitrogen dynamics of litterfall components in adjacent Pinus densiflora and Quercus variabilis stands

This study aimed to determine the effects of the stand and month on the carbon (C) and nitrogen (N) concentrations and the inputs of the litterfall components in adjacent Pinus densiflora and Quercus variabilis stands. The monthly C concentrations of the litterfall components were significantly higher in the P. densiflora stand than in the Q. variabilis stand, whereas the monthly N concentrations of the leaf and miscellaneous litter were higher in the Q. variabilis stand than in the P. densiflora stand. The coefficient variations of the N concentrations were higher than those of C concentrations of the litterfall components. The monthly C and N inputs of the leaf litter showed a unimodal pattern in the Q. variabilis stand, whereas multimodal patterns in the P. densiflora stand could be seen. The annual total C inputs were not significantly different between the P. densiflora [2 691 kg(C)·ha<sup>–1</sup>·yr<sup>–1</sup>] and Q. variabilis [2 439 kg(C)·ha<sup>–1</sup>·yr<sup>–1</sup>] stands. However, the annual total N inputs were significantly higher in the Q. variabilis [44.5 kg(N)·ha<sup>–1</sup>·yr<sup>–1</sup>] stand than in the P. densiflora [38.6 kg(N)·ha<sup>–1</sup>·yr<sup>–1</sup>] stand. These results indicate that the C and N dynamics in the litterfall components were affected by the species and sampling months in adjacent P. densiflora and Q. variabilis stands.

Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process

In this study, mechanisms of membrane fouling caused by polysaccharides with different molecular structures in polyaluminum chloride (PACl) coagulation-ultrafiltration (C-UF) process were explored. Carrageenan and xanthan gum were chosen for model foulants of straight chain and branched chain polysaccharides, respectively. Filtration experiments showed that, with PACl dosage of 0–5 mM, specific filtration resistance (SFR) of carrageenan and xanthan solution showed a unimodal pattern and a continuous decrease pattern, respectively. A series of experimental characterizations indicated that the different SFR pattern was closely related to structure of foulants layer. Density functional theory (DFT) calculation suggested that Al3+ preferentially coordinating with the terminal sulfonyl groups of carrageenan chains to promote gel layer formation at low PACl concentration (0.15 mM). There existed a chemical potential gap between bound water in gel layer and free water in the permeate, so that, filtration through gel layer corresponded to rather high SFR for overcoming this gap. In contrast, Al3+ coordinating with the non-terminal sulfonyl groups of carrageenan at high PACl concentration caused transition from gel layer to cake layer, leading to SFR decrease. However, xanthan gum itself can form a dense gel layer with a complex polymer network by virtue of the interlacing of main chains and branches. Al3+ coordinating with the carboxyl groups on branched chains of xanthan gum resulted in clusters of polymer chains and flocculation, corresponding to the reduced SFR. This proposed molecular-level mechanism well explained membrane fouling behaviors of polysaccharides with different molecular structure, and also facilitated to optimize C-UF process for water treatment.

Using an acoustic complexity index to help monitor climate change effects on avian diversity

Passive recording technologies have become a valuable tool for ecologists to accumulate large data sets on vocalizing species assemblages and to study the response of biodiversity to regional and global environmental change. However, the process of interpreting these recordings and identifying species can be time-consuming. To automate this process, and to derive diversity metrics directly from the audio files, soundscape ecologists developed and published many bioacoustics indices, which are calculated using computer algorithms that mathematically summarize the acoustic energy in a recording. Of these indices, the acoustic complexity index (ACI) is perhaps the most widely proposed surrogate of bird species richness. Although several studies have shown the ACI to have positive correlations with species richness, it remains unknown how well the ACI will perform over large, habitat-diverse, regions. Our aim, here, was to examine whether site-level bird species richness (alpha diversity) correlated with the ACI across a large heterogenous mountain region. Further, we explored whether the elevational trends for alpha diversity and the ACI exhibited similar unimodal patterns with corresponding maximums and whether any shifts in the elevation of these maximums could be tracked over time in response to climate change. We deployed recording devices along two extensive transects on the Pacific Crest Trail in California, USA; these included a 689-km trail section in northern California and a 531-km section in southern California. Point counts for birds from the field were combined with the interpretation of the recordings to estimate alpha diversity using a Bayesian multispecies occupancy model. We found that alpha diversity exhibited a positive linear relationship with the ACI on both trail sections. However, these relationships were not strong (low R2 values). Similar mid-elevation maximums for alpha diversity and the ACI were observed along the northern trail section. Power analysis revealed that with repeated annual surveys using our protocols, we could detect an average shift in the elevation of either maximum species richness or ACI of approximately 100 m over 20 years (i.e., 5 m/yr), which could be improved in precision to 50 m (i.e., 2.5 m/yr) with a 5-fold increase in survey effort. Although there was considerable unexplained variation in our diversity- and ACI-elevation trends, which we suspect was due to microhabitat and microclimate effects, we concluded that the ACI was a useful, albeit coarse, surrogate of alpha diversity across large regions. The ACI warrants consideration by ecologists and land managers for application in large-scale monitoring programs.

Microbial Carbon Use Efficiency in Coastal Soils Along a Salinity Gradient Revealed by Ecoenzymatic Stoichiometry

AbstractSoil salinity affects the microbial carbon use efficiency (CUE) that in turn regulates soil‐atmosphere gas exchange and soil C sequestration. So far, little is known about CUE in salt‐affected soils. Hereby, CUE across coastal soils with electric conductivity (EC) ranging from 0.14 dS m−1 to 13.65 dS m−1 was investigated using stoichiometric modeling. Contrary to the belief that CUE decreases with salinity increase, this present study showed that CUE follows a unimodal pattern along the saline gradient with the highest CUE observed at EC = 2 dS m−1. When EC > 2 dS m−1, both CUE and soil microbial growth rate significantly decrease with salinity indicating that microorganisms sacrifice growth for survival/adaptation to high salt stress. When EC < 2 dS m−1, CUE shows a significant positive correlation with EC, but microbial community growth rates remain stable. We also observed that microbial growth becomes limited by carbon scarcity and that the degree of carbon constraint is significantly aggravated with EC. This implies that elevating CUE can be the preferred mechanism for microorganisms to stabilize elemental stoichiometry and maintain growth rate. Our results revealed that along the saline gradient, the dominant factor of CUE shifted from the ecological stoichiometry to salinity, which provides an insight into the microbial‐driven carbon cycling in salt‐affected soils.