Abiotic Variables Research Articles

Carbon Flow Allocation Patterns of CH4, CO2, and Biomass Production Vary with Sewage and Sediment Microbial and Biochemical Factors in the Anaerobic Sewer Environment.

Understanding the carbon (C) fate in municipal sewers is imperative for optimizing current sewer-C-degradation control and treatment efficiency, aligning with China's C-neutrality strategy in determining the exact C budget of the wastewater system. This study used laboratory batch tests mimicking the anaerobic sewer environment and sewage-sediment stratification to evaluate C flow allocation (CFA) patterns in response to biotic and abiotic variables. We quantified the C equivalent mass (CEM) and used absolute quantitative 16S rRNA gene amplicon sequencing to characterize the microbiome. The substantial methane production (CH4, 17.2%-18.8%) required both activated sediment and exogenous C, while biomass production (BP, 63.1%-74.9%) formed C sink predominated as the main CFA direction under the stratified state. This was supported by the high diversity, interspecific interactions, and metabolic capacity of the sediment microbiome. However, CH4 and BP patterns demonstrated non-synchronicity and opposite dynamic characteristics. Carbon dioxide (CO2, 64.0%-81.3%) production dominated the sewage CFA. The absolute abundance of the sediment microbiome, which was 5.6 times higher than that of the sewage, exhibited a strong increase in magnitude across the phases. It was primarily associated with biomass growth and N metabolism, whereas sewage showed differentiated and competing communities and appeared to act mainly as the exogenous C sources. We constructed a binary quadratic linear model revealing the non-linear relationship between ACK activity, DOC degradation rate, and CEMCH4 rate; the former maintained low CH4 production when the available substrate was insufficient. The influence of N and S factors on the CFA is complex and multi-faceted. These findings highlight the importance of further investigations into the process-based framework of the sewer C budget, focusing on the C source-emission-sink functions and mass balance.

Nitrogen Addition Increased the Greenhouse Gas Emissions of Permafrost Peatland Due to the Abundance of Soil Microbial Functional Genes Increasing in the Great Khingan Mountains, Northeast China

Permafrost peatlands are sensitive to changes in nitrogen levels because they are largely nitrogen-limited ecosystems. However, the microbial mechanisms by which the addition of nitrogen increases the emission of greenhouse gasses from permafrost peatlands remain unclear. This study was conducted to decipher the relationship between greenhouse gas emissions and soil microorganisms under nitrogen addition. Here, we performed a 154-day experimental investigation in order to assess the release of greenhouse gasses such as CO2, CH4, and N2O from the soils. Additionally, we examined the correlation between the rates of these gas emissions and the presence of crucial microbial functional genes in the soil. The results showed that the addition of low (0.01 g kg−1), medium (0.02 g kg−1), and high (0.04 g kg−1) levels of nitrogen increased the cumulative CO2 emissions by 2.35%–90.42%, respectively. The cumulative emissions of CH4 increased by 17.29%, 25.55% and 21.77%, respectively. The cumulative emissions of N2O increased 2.97, 7.49 and 7.72-fold. The addition of nitrogen increased the abundance of functional genes in the bacteria, fungi, methanogens, denitrifying bacteria, and nitrogen-fixing bacteria in soil by modifying abiotic soil variables and providing sufficient substrates for microorganisms. The results indicated that the addition of nitrogen can significantly promote the emission of greenhouse gasses by increasing the abundance of functional microbial genes in the soil of permafrost peatlands. These findings highlight the importance of considering nitrogen deposition and the nitrogen released from thawing permafrost when predicting the future greenhouse gasses emitted from permafrost peatlands.

Microbial landscapes in Trinervitermes trinervoides termite colonies are affected by mound compartments and soil properties but not by symbiotic Podaxis fungi

Termites are important ecosystem engineers and play key roles in modulating microbial communities within and outside their mounds. Microbial diversity within termite mounds is generally lower than surrounding soils, due to termite-associated antimicrobial compounds and active sanitary behaviours. Microbial symbionts of termites can also influence the microbial landscape, by inhibiting or out-competing other microbes. Certain members of the arid habitat fungal genus Podaxis (Agaricomycetes; Agaricaceae) are symbiotic with savannah specialist grass-cutting termites, with the potential to influence mound-associated microbiomes. To test this, we characterized fungal (ITS2) and bacterial (16S rRNA) communities within and outside 49 Trinervitermes trinervoides mounds with and without Podaxis fruiting bodies across a 1000 km transect in South Africa. We predicted that Podaxis would be a dominant member of the fungal communities in mounds and negatively impact microbial diversity. Further, we explored how environmental variables shaped microbial communities, including whether soil elemental composition affected Podaxis presence. As expected, we observed less diverse fungal communities, but not bacterial communities, within than outside mounds, while microbial communities differed by sampling regions and mound compartments. Podaxis sequences were present in 48 out of 49 mounds in low relative abundances, and neither fruiting body presence nor sequence abundance were associated with microbial community diversity or composition. There was, however, an overall association between the presence of Podaxis fruiting bodies and elemental composition, with different elements displaying varying associations depending on geographic region. Both environmental variables and soil elements associated with fungal and bacterial taxa, indicating that they are key drivers of microbial community composition. Taken together, our findings suggest that microbial landscapes in termite mounds are not strongly influenced by Podaxis but mainly driven by termite filtering and regional abiotic variables and elemental compositions.

Remotely Sensed Variables Predict Grassland Diversity Better at Scales Below 1,000 km as Opposed to Abiotic Variables That Predict It Better at Larger Scales

AbstractGlobal spatial patterns of vascular plant diversity have been mapped at coarse grain based on climate‐dominated environment–diversity relationships and, where possible, at finer grain using remote sensing. However, for grasslands with their small plant sizes, the limited availability of vegetation plot data has caused large uncertainties in fine‐grained mapping of species diversity. Here we used vegetation survey data from 1,609 field sites (>4,000 plots of 1 m2), remotely sensed data (ecosystem productivity and phenology, habitat heterogeneity, functional traits and spectral diversity), and abiotic data (water‐ and energy‐related, characterizing climate‐dominated environment) together with machine learning and spatial autoregressive models to predict and map grassland species richness per 100 m2 across the Mongolian Plateau at 500 m resolution. Combining all variables yielded a predictive accuracy of 69% compared with 64% using remotely sensed variables or 65% using abiotic variables alone. Among remotely sensed variables, functional traits showed the highest predictive power (55%) in species richness estimation, followed by productivity and phenology (48%), spectral diversity (48%) and habitat heterogeneity (48%). When considering spatial autocorrelation, remotely sensed variables explained 52% and abiotic variables explained 41%. Moreover, Remotely sensed variables provided better prediction at smaller grain size (<∼1,000 km), while water‐ and energy‐dominated macro‐environment variables were the most important drivers and dominated the effects of remotely sensed variables on diversity patterns at macro‐scale (>∼1,000 km). These findings indicate that while remotely sensed vegetation characteristics and climate‐dominated macro‐environment provide similar predictions for mapping grassland plant species richness, they offer complementary explanations across broad spatial scales.

Multitrophic Diversity of the Biotic Community Drives Ecosystem Multifunctionality in Alpine Grasslands.

Biodiversity and ecosystem multifunctionality are currently hot topics in ecological research. However, little is known about the role of multitrophic diversity in regulating various ecosystem functions, which limits our ability to predict the impact of biodiversity loss on human well-being and ecosystem multifunctionality. In this study, multitrophic diversity was divided into three categories: plant, animal, and microbial communities (i.e., plant diversity, rodent diversity, and bacterial and fungal diversity). Also, 15 ecosystem functions were divided into four categories-water conservation, soil fertility, nutrient cycling and transformation, and community production-to evaluate the significance of biotic and abiotic variables in maintaining ecosystem multifunctionality. Results indicated that species diversity at multiple trophic levels had a greater positive impact on ecosystem multifunctionality than species diversity at a single trophic level. Notably, the specific nature of this relationship depended on the niche breadths of plants, indicating that plants played a key role in linking above and belowground trophic levels. Abiotic factors such as altitude and pH directly acted on ecosystem multifunctionality and could explain changes in ecosystem functions. Overall, our study offers valuable insights into the critical role of multitrophic species diversity in preserving ecosystem multifunctionality within alpine grassland communities, as well as strong support for the importance of biodiversity protection.

Understanding the effects of livestock grazing on dryland plant communities within the context of abiotic variability

AbstractDrylands, which cover more than 40% of the Earth's terrestrial surface, face rising agricultural demand and the influence of climate change. Understanding how livestock grazing pressure and local climate affect these environments is pivotal for informed land management. We studied big sagebrush plant communities in southwestern Wyoming over grazing gradients created by artificial livestock watering points. To explore the role of abiotic factors in shaping plant community response to grazing, we assessed the response of plant functional groups to grazing while accounting for soil texture variability across a precipitation gradient. Our models estimated that sagebrush cover responded positively to grazing intensity, with a 6% increase in cover with intensity when comparing the heaviest grazing treatment with the lowest grazing intensity. Perennial bunchgrass cover, the primary forage component, had a small negative response, a 3% decrease in cover from the lowest grazing intensity to the highest. Grazing intensity had no effect on bunchgrass density, perennial forbs, or rhizomatous grasses. Compared with abiotic factors, grazing intensity had a small effect on perennial bunchgrass and bare ground. We found that precipitation explained a 13% increase in perennial bunchgrass cover and a 34% decrease in bare ground cover compared with a 6% increase with increasing intensity across our grazing gradients. Sand content also had a larger effect on perennial bunchgrass cover and density than grazing. Increased sand content was associated with increased bunchgrass cover and density, supporting the inverse texture hypothesis. Our results show that while livestock grazing impacts sagebrush plant communities, its effect is small when compared with the effects of climate and soil. Our study contributes to a growing body of research emphasizing the need to contextualize plant community responses to grazing within specific climatic and edaphic conditions, which will promote effective land management in dryland ecosystems.

Deciphering Regulatory Role of Melatonin in Foliar Nastic Movements of Portulaca oleracea: Visual Insights from Histology and Anatomy

AbstractPlant nastic movements exhibit unique behavioural patterns that synchronize with external cues. Given that the foliar nastic motions of Portulaca species are solely circadian, it is intriguing to investigate whether and how melatonin governs these movements. Analysis of histological traits concurrent with anatomical traits such as stomatal behaviour provides visual data on the plant species' gnosophysiology, offering clues and validation of the influence of multiple external stimuli on hydraulic forces that in turn alter turgor pressure. The current study aims to elucidate how exogenous melatonin modulates foliar nastic movements in Portulaca oleracea. Our findings indicate that melatonin functions as an intracellular hydraulic flux controller, influencing idioblast and crystal densities, as well as stomatal behaviour. Timepoint studies at specific Zeitgebers reveal that abiotic variables such as light and temperature can influence the endogenous melatonin concentration of P. oleracea. Therefore, this hormone potentially serves as an additional internal regulator of turgor pressure, influenced by both light and temperature. Thus, melatonin plays a crucial role in shaping the characteristic foliar nastic movements observed in P. oleracea, inherently tied to the circadian rhythm. Further investigation into idioblast and crystal torques, along with their angular momentum, is warranted to calculate the hydraulic forces at work in the leaf lamina. Thus the study underscores the multifaceted role of melatonin in navigating nastic movement processes through turgor pressure alterations brought about by intracellular depositions. The study in future could unravel melatonin's pleiotropic actions and the underlying mechanisms of foliar idiosyncratic nastic motions in other plant species as well. Moreover, both histology and anatomy play vital roles in the present study as it has provided visual evidence of the underlying mechanisms of foliar nastic movements in P. oleracea. Graphical Abstract

Biotic and abiotic properties mediating sediment microbial diversity and function in a river-lake continuum.

A river-lake system plays an important role in water management by providing long-term and frequent water diversions. However, hydrological connectivity in the system can have a profound effect on sediment microbial communities through pH, nutrient concentrations, and benthos invertebrates. Consequently, identifying the key environmental factors and their driving mechanisms is vital for microbial adaptation strategies to extreme environments. In this study, we analyzed the significant difference in sediment bacterial and fungal community structures and diversity indices among Dongting Lake and its tributary rivers, which worked as a typical river-connected lake ecosystem. There were significant differences in biotic and abiotic environments in the sediment habitats of Dongting Lake and its tributary rivers. Random forest analysis revealed that pH and Mollusca were found to be the most important abiotic and biotic variables for predicting both bacterial and fungal community structures, respectively. The beta diversity decomposition analyses showed that the bacterial and fungal community compositional dissimilarities among different sections were dominated by species replacement processes, with more than half of the OTUs in each section being unique. Notably, both biotic and abiotic factors affected the number and the relative abundance of these bacterial and fungal unique OTUs, leading to changes in community composition. Mollusca, pH, TP, NO3-N, and NH4-N were negatively related to the relative abundance of Actinobacteria, Acidobacteria, Gemmatimonadetes, Planctomycetes, and Ascomycota, while Annelida and ORP were positively related to the relative abundance of Actinobacteria and Gemmatimonadetes. Additionally, PICRUSt analysis revealed that the functional dissimilarity among lakes and rivers was strengthened in unique species compared to all species in bacterial and fungal communities, and the changes of functional types helped to improve the habitat environment in the main Dongting Lake and promote the process of microbial growth. From our results, the role of macrozoobenthos and physicochemical characteristics in driving the sediment microbial community spatial variations became clear, which contributed to further understanding of the river-lake ecosystem.

Lost in space and time: robust demography and enhanced resilience buffer adverse environmental effects in a highly isolated and sedentary pre-pleistocene landscape vertebrate

BackgroundFew animal populations have been studied under the framework of the OCBIL theory, which addresses the ecology and evolution of biodiversity on old climatically buffered infertile landscapes. Available genetic data challenge the low connectivity and high genetic differentiation predicted for isolated tepui-summit vertebrate communities, suggesting potential dispersal among summits. However, the OCBIL theory posits reduced dispersibility, enhanced resilience to habitat fragmentation and inbreeding due to small populations. We tested these hypotheses by conducting the first analytic evaluation of the spatial ecology and population biology of a tepui-summit vertebrate at multiple spatial scales.ResultsWe used harmonic radar tracking (100 individuals/448 points of contact) and capture-mark-recapture data (596 individuals captured/52 recaptured) to reveal the temporal niche, microhabitat use, population size, and dispersal abilities of the tepui-summit endemic toad Oreophrynella quelchii on Roraima-tepui. Abundance was determined using a closed population model incorporating sources of variation in capture probability. We tested the relative influence of biotic and abiotic variables on distances moved through model selection. Our data indicate that the population size of O. quelchii is remarkably large (ca. 12 million individuals), with strong seasonal demographic fluctuations. Ecology and observed limited spatial movements challenge the likelihood of active dispersal among tepui tops in this species. Our results are counter to those predicted by the available genetic data but support two hypotheses of the OCBIL theory: reduced dispersibility and enhanced resilience. However, they do not support the expectation of a small refugial population size.ConclusionWe postulate that the insular, hostile tepui-summit environment tends to produce robust demographic populations, likely to buffer stochastic adverse environmental effects, rather than diversity, as observed in much younger post-Pleistocene Neotropical landscapes. Our results draw attention to the value of faunal studies using an OCBIL framework to better understand the ecology and evolution of this unique biota worldwide.

Factors shaping pelagic-benthic coupling in the process of settlement in an Arctic fjord

Benthic organisms typically possess a planktonic propagule stage in the form of larvae or spores, which enables them to spread over large distances before settlement, and promotes tight pelago-benthic coupling. However, factors driving dispersal and epibenthos recruitment in shallow hard-bottom Arctic communities are poorly known. We therefore conducted a year-round in situ colonization experiment in Isfjorden (Svalbard), and found out that variation in early-stage epibenthic assemblages was explained by the combination of: abiotic (45.9%) and biotic variables (23.9%), and their interactions (30.2%). The upward-facing experimental plates were dominated by coralline algae, and this is the first study showing that at high latitudes coralline algae Lithothamnion sp. settle in high numbers on available substrates during the polar night in winter. The downward-facing plates, which had much less exposure to light, contained more diverse organisms, with a predominance of polychaetas and bryozoans. However, in summer, the barnacle Semibalanus balanoides outcompeted all the other recruits, as a result of massive occurrence of meroplanktonic Cirripedia larvae, triggered by the phytoplankton bloom. In conclusion, the rate and success of epibenthic settlements were dependent mostly on light availability and temperature, suggesting that larval settlement will be impacted by global warming with some taxa benefitting, while others losing.

Shifting spawning phenology in Hudson River American Shad

AbstractObjectiveThe objectives of this study were to investigate potential shift in the phenology of spawning for the Hudson River American Shad Alosa sapidissima and to identify factors contributing to the decline of the Hudson River shad population.MethodsThis study utilized American Shad eggs collected from the Long River Ichthyoplankton Survey. Logistic models were employed to estimate spawning phenology metrics, including the onset, peak, cessation, and duration of the spawning season. Additionally, we investigated the effects of biotic and abiotic variables on spawning timing.ResultThis study suggests that temporal changes in the spawning onset exhibited high variation and were not significant. However, a significantly delayed spawning peak and cessation, along with an extended spawning season, were observed. Additionally, the findings of this study revealed a correlation between the timing of spawning onset and water temperature, indicating that a 1°C increase in water temperature was associated with a 3.66‐day earlier initiation of spawning. Smaller female spawner size was associated with delayed peak and cessation of the spawning season. With a 1‐cm decrease in the average female spawner size, the peak of the spawning season was delayed by 1.79 days and the cessation of the spawning season was delayed by 2.87 days.ConclusionThe findings indicate that water temperature may be a crucial trigger for initiating spawning in Hudson River American Shad, with higher water temperatures associated with earlier spawning onset. Moreover, the findings indicate that the timing of spawning peaks and cessations has been progressively delayed over time, and this is linked to the size of female spawners.

Variation in Community Structure and Abundance of Fish in Simple Structured Shallow Sandy Habitats

ABSTRACTSandy beaches and their surf zones characterise many of the world's open coastlines. They are important breeding, nursery and feeding areas for many species of fish. Despite the commonness and importance of sandy beach surf zones, the dynamics, space occupancy and diversity patterns of residing fish is in many places poorly understood. The aim of this study was to (1) characterise the fish community structure in 11 simple structured sandy surf zones of the northern Baltic Sea and (2) relate variation in fish abundance and community structure to a set of chosen abiotic variables. Using beach seine, weekly or biweekly sampling was conducted at fixed sites at 10 occasions throughout a summer season. A total of 60,006 fish individuals belonging to 20 species were recorded. Changes in abundance and community structure were mainly driven by the variation of only five species reflecting species‐specific recruitment patterns and different spatial responses to abiotic variables. Dominating groups were Gasterosteidae, Ammodytidae and Gobiidae that together formed 86% of the total adult fish catches. Larval numbers were completely dominated by Gobiidae. Multivariate analyses indicated species‐specific responses to measured environmental variables, most important being a combination of wave exposure, beach slope, bottom roughness, and temperature. The present study shows that changes in fish abundance on simple structured sandy sublittoral beaches in the northern Baltic Sea are large over the course of a breeding season. It also reveals that variation in adult and juvenile fish are driven by a set of abiotic factors that influence on the fish assemblage structure through mainly species‐specific, rather than through generic responses. Unravelling the degree to which the sandy shore fish community vary in the northern Baltic Sea will help in managing coastal environments that are increasingly being threatened by many anthropogenic stressors.

A Latitudinal Cline in the Taxonomic Structure of Eelgrass Epifaunal Communities is Associated With Plant Genetic Diversity

ABSTRACTAimBiogenic structural complexity increases mobile animal richness and abundance at local, regional and global scales, yet animal taxa vary in their response to complexity. When these taxa also vary functionally, habitat structures favouring certain taxa may have consequences for ecosystem function. We characterised global patterns of epifaunal invertebrates in eelgrass (Zostera marina) beds that varied in structural and genetic composition.LocationNorth America, Europe and Asia.Time Period2014.Major Taxa StudiedPeracarid crustaceans and gastropod molluscs.MethodsWe sampled epifaunal invertebrate communities in 49 eelgrass beds across 37° latitude in two ocean basins concurrently with measurements of eelgrass genetic diversity, structural complexity and other abiotic and biotic environmental variables. We examined how species richness, abundance and community composition varied with latitude and environmental predictors using a random forest approach. We also examined how functional trait composition varied along with community structure.ResultsTotal species richness decreased with latitude, but this was accompanied by a taxonomic shift in dominance from peracarid crustaceans to gastropods, which exhibited different sets of functional traits. Greater eelgrass genetic diversity was strongly correlated with both richness and abundance of peracarids, but less so for gastropods.Main ConclusionsOur results add to a growing body of literature that suggests genetic variation in plant traits influences their associated faunal assemblages via habitat structure. Because peracarids and gastropods exhibited distinct functional traits, our results suggest a tentative indirect link between broad‐scale variation in plant genetic diversity and ecosystem function.

The assembly and dynamics of ecological communities in an ever‐changing world

AbstractAlternative perspectives on the maintenance of biodiversity and the assembly of ecological communities suggest that both processes cannot be investigated simultaneously. In this concept and synthesis, we challenge this view by presenting major theoretical advances in structural stability and permanence theory. These advances, which provide complementary views, allow studying the short‐ and long‐term dynamics of ecological communities as changes in species richness, composition, and abundance. Here, the global attractor, technically named informational structure (IS), is the central element to construct from information of species' intrinsic growth rates and their strength and sign of interactions. The global attractor has four main properties: (1) It contains all the limits of what is feasible and unfeasible of the dynamical behavior of an ecological system, therefore, (2) it provides a thorough characterization of all combinations of species' richness and composition in which species can coexist (i.e., feasible and stable equilibrium), (3) as well as all connections (paths) of assembly between coexisting communities. Importantly, (4) such topology of coexisting communities and their connections changes when environmental (abiotic and biotic) variation affects the ability of species to grow and interact with others. Overall, these four properties allow switching from a traditional evaluation of species coexistence at equilibrium to a much more realistic nonequilibrium perspective where changes in the structure of the global attractor underlie the transient ecological dynamics. Several fields in ecology can benefit from the study of an IS. For instance, it can serve to evaluate community responses after the end of a perturbation, to design restoration trajectories, to study the consequences of biological invasions on the persistence of native species within communities, or to assess ecosystem health status. We illustrate this latter possibility with empirical observations of 7 years in Mediterranean annual grasslands. We document that extremely wet or dry years generate ISs supporting few coexisting communities and few assembly paths. The remaining communities distinguish winners from losers of ongoing climate change and indicate the limits to future community assembly opportunities. A fully tractable operational framework is readily available to understand and predict the assembly and dynamics of ecological communities in an ever‐changing world.

Biotic homogenization in multisystem cascade reservoirs: insights from sedimentary photopigment analysis.

The existing literature provides limited insights into the dynamics of phytoplankton communities and the spatial heterogeneity of physicochemical parameters in multisystem cascade reservoirs (interconnected reservoirs derived from different rivers). The existing studies are concentrated on cascade reservoirs (interconnected reservoirs derived from the same river). To address this knowledge gap, the aims of the present study were as follows: (1) investigate the spatial heterogeneity, within and between reservoirs, of geochemical parameters associated with the eutrophication process, considering total phosphorus, chlorophyll-a, pheophytin, and metals (chromium, copper, nickel, lead, zinc, iron, and manganese); (2) evaluate sediment quality at the designated locations; (3) assess differences in the richness and concentration of sedimentary photopigments between the reservoirs. Application of principal component analysis revealed discernible gradients for the abiotic variables, although the differences were not statistically significant (one-way PERMANOVA test, p > 0.05). The observations suggested a tendency towards spatial homogeneity within and between the reservoirs. The metal concentrations were consistent with regional reference values, while phosphorus levels in the sediment approached the threshold for classification as pollution (~ 2000mg/kg). Analysis of pigments indicated low dissimilarity among the reservoirs, which could be mainly attributed to the eutrophication process and high connectivity of the sampled areas. To counteract ongoing biotic homogenization, it is essential to reduce nutrient inputs and invest in ecological protection and restoration programs. The analysis of sedimentary photopigments provides an efficient and cost-effective alternative way to assess phytoplankton communities.

Measuring insect osmoregulation in vitro: A reference guide

Osmoregulation is influenced by a wide variety of biotic and abiotic variables, and maintenance of systemic osmoregulatory homeostasis is critical to insect fitness. Because insects are so small, accurately quantifying renal organ function is technically challenging, and often requires specialized equipment. On top of this, nearly a century of toiling in the laboratory has led to a wide and still growing variety of methods that can be difficult for novice researchers to disentangle. Here, we provide a reference guide for the most used in vitro approaches in the study of insect osmoregulation, including the Ramsay assay, Ussing chamber, epithelial potential measurement, scanning ion-selective electrode technique, and hindgut assays. Along the way, we highlight the history of each methodological innovation.

Mapping an Indicator Species of Sea-Level Rise along the Forest–Marsh Ecotone

Atlantic White Cedar (Chamaecyparis thyoides) (AWC) anchors a globally threatened ecosystem that is being impacted by climate change, as these trees are vulnerable to hurricane events, sea-level rises, and increasing salinity at the forest–marsh ecotone. In this study, we determined the current amount and distribution of AWC in an area that is experiencing sea-level rises that are higher than the global average rate. We used a combination of a field investigation and aerial photo interpretation to identify known locations of AWC, then integrated Sentinel-1 and 2A satellite data with abiotic variables into a species distribution model. We developed a spectral signature of AWC to aid in our understanding of phenology differences from nearby species groups. The selected model had an out-of-bag error of 7.2%, and 8 of the 11 variables retained in the final model were derived from remotely sensed data, highlighting the importance of including temporal data to exploit divergent phenology. Model predictions were strong in live AWC stands and, accurately, did not predict live AWC in stands that experienced high levels of mortality after Hurricane Sandy. The model presented in this study provides high utility for AWC management and tracking mortality dynamics within stands after disturbances such as hurricanes.

Increasing plant species diversity benefits soil protein accumulation in a subtropical forest

Abstract Protein, derived from plant and microbial residues, constitutes a significant portion of soil nitrogen or organic carbon pool and plays a crucial role in determining soil nitrogen and carbon sequestration. Though diversifying plant species has been regarded as a promising strategy for promoting soil nitrogen or organic carbon accumulation during vegetation restoration or afforestation, how increasing plant species diversity (PSD) would influence soil protein pool remains unknown. We selected 45 plots covering a natural gradient of PSD, which was reflected by the Shannon index and varied from 0.15 to 3.57, in a subtropical karst forest. The major objective was to investigate the impact of increasing PSD on soil protein abundance, with soil protein depolymerization rate and multiple biotic and abiotic variables being measured to explore the underlying mechanism. The relative abundance of soil protein, that is proportion in soil organic matter varied between 24.1 and 34.0% with an average of 29.2 ± 2.3% across the 45 plots. Soil protein abundance increased on average by 1.56% with each unit of PSD increase. Nevertheless, soil protease activity, protein depolymerization rate and microbial amino acid uptake rate all significantly (p < 0.05) decreased as PSD increased. The mechanism underlying the increase of soil protein abundance in response to higher PSD included three aspects, that is stimulating microbial biomass and subsequent microbial residue input to the soil, promoting mineral protection of soil protein via elevating levels of soil exchangeable calcium and magnesium, and decreasing soil protease activity and protein depolymerization due to aggravated soil microbial phosphorus limitation. Synthesis and application: Our study suggests that increasing PSD is an efficient way to promote soil protein accumulation. Given that protein is a major component of soil nitrogen or organic carbon pool, diversifying plant species during vegetation restoration or afforestation would hence benefit soil nitrogen and organic carbon sequestration.

Investigating the Biotic and Abiotic Drivers of Body Size Disparity in Communities of Non‐Volant Terrestrial Mammals

ABSTRACTAimThe species that compose local communities possess unique sets of functional and ecological traits that can be used as indicators of biotic and abiotic variation across space and time. Body size is a particularly relevant trait because species with different body sizes typically have different life history strategies and occupy distinct niches. Here we used the body sizes of non‐volant (i.e., non‐flying) terrestrial mammals to quantify and compare the body size disparity of mammal communities across the globe.LocationGlobal.Time PeriodPresent.Major Taxa StudiedNon‐volant terrestrial mammals.MethodsWe used IUCN range maps of 3982 terrestrial mammals to identify 1876 communities. We then combined diet data with data on climate, elevation and anthropogenic pressures to evaluate these variables' relative importance on the observed body size dispersion of these communities and its deviation from a null model.ResultsDispersion for these communities is significantly greater than expected in 54% of communities and significantly less than expected in 30% of communities. The number of very large species, continent, range sizes, diet disparity and annual temperature collectively explain > 50% of the variation in observed dispersion, whereas continent, the number of very large species, and precipitation collectively explain > 30% of the deviation from the null model.Main ConclusionsClimate and elevation have minimal predictive power, suggesting that biotic factors may be more important for explaining community body size distributions. However, continent is consistently a strong predictor of dispersion, likely due to it capturing the combined effects of climate, size‐selective human‐induced extinctions and more. Overall, our results are consistent with several plausible explanations, including, but not limited to, competitive exclusion, unequal distribution of resources, within‐community environmental heterogeneity, habitat filtering and ecosystem engineering. Further work focusing on other confounding variables, at finer spatial scales and/or within more causal frameworks is required to better understand the driver(s) of these patterns.

Insect seedling herbivory is influenced by multiple factors, but the plant apparency theory is more supported than other hypotheses – A case study in a subtropical forest

Insect herbivory is ubiquitous in various ecosystems, and directly influences the growth and survival of individual plants, especially during their vulnerable early life stages like the seedling phase. This, in turn, exerts a significant influence on forest community diversity and structure, as well as ecosystem function and stability. Notable variation in herbivory has been detected both among and within plant species. For decades, many hypotheses have been proposed to explain such variations, including both biotic and abiotic variables. However, most studies have considered only one or several of these hypotheses by focusing on a few potential variables, and their results were usually inconsistent; thus, the factors driving herbivory remain unclear. In this study, we examined leaf herbivory by insects of woody species seedlings in a subtropical forest in southwestern China over two seasons. In total, 24 potential variables that represented abiotic resource availability, characters of individual seedlings, conspecific and heterospecific species, and the whole seedling community were selected to test several commonly discussed alternative herbivory hypotheses. Overall, our findings showed that the plant apparency hypothesis was more supported than the other hypotheses in explaining insect seedling herbivory. Our results further indicated that the mechanisms and causes of insect herbivory are complex, multifactorial, species-specific and vary with seasons, indicating that there may be no uniform rules in explaining herbivory for all seedlings. Consequently, such complexity may play an important role in promoting species coexistence and biodiversity maintenance in seedling communities, which may further translate into the following generation of saplings or even adult communities. Changes in the community of insect herbivores and/or variables influencing insect herbivory, may disrupt stability of the original seedling community, thus affecting the regeneration and development of the entire forest community. Therefore, we suggest that issues related to insect herbivory should be considered when developing forest management and conservation.