Unravelling the impact of environmental variability on mangrove sediment carbon dynamics.

Mangrove ecosystems represent low-cost climate-regulating systems through carbon storage in their sediments. However, considering the complex shifts in shallow coastal ecosystems, it is clear from just a few sets of environmental impacts on their carbon storage that there is a deficit in the information required for preserving this service. Here, we investigated the spatial and temporal variability of hydrographic factors (water temperature, pH, salinity, dissolved oxygen (DO), flow velocity, turbidity) and sediment characteristics (sedimentation rate and sediment grain size) on the intricate carbon dynamics of mangroves by examining which key variable(s) control mangrove sediment organic matter (OM). We used in-situ monitoring to assess the hydrographic dynamics, sedimentation rate, sediment organic content, and granulometry. Laboratory loss-on-ignition and granulometric methods were employed to quantify OM in trapped and bottom sediments and sediment grain size, respectively. Based on the findings, water pH, salinity, and DO were the key regulators of OM in sediments. Despite conventional expectations, the study observed positive effects of DO on OM, highlighting the possible role of aquatic plant photosynthesis and freshwater inflow. Sedimentation rates, usually considered crucial for OM accumulation, showed no significant relationship, emphasizing the importance of sediment content over quantity. Noteworthy findings include the role of sediment grain size in OM storage within mangrove sediments. Even though the grain size class of 63 µm diameter had the highest mean weight across the studied sites, there were significant positive correlations between Trap and Bottom OM with 500 and 2000 µm grain size classes, emphasizing the need to consider sediment characteristics in carbon dynamics assessments. Overall, this research provides valuable insights into the intricate environmental dynamics of mangrove ecosystems that are crucial to understanding and managing these vital coastal habitats.

Coevolutionary hotspots favour dispersal and fuel biodiversity in mutualistic landscapes under environmental changes.

Mutualistic interactions are key to sustaining Earth's biodiversity. Yet, we are only beginning to understand how coevolution in mutualistic assemblages can shape the distribution and persistence of species across landscapes. Here, we combine the geographic mosaic theory of coevolution with metacommunity dynamics to understand how geographically structured selection can shape patterns of richness, dispersal, extinction and persistence of mutualistic species. In this model, species may experience strong or weak reciprocal selection imposed by mutualisms within each patch (i.e. hotspots and coldspots, respectively). Using numerical simulations, we show that mutualistic coevolution leads to a concentration of species richness at hotspots. Such an effect occurs because hotspots sustain higher rates of colonization and lower rates of extinction than coldspots, whether the environment changes or not. Importantly, under environmental changes, coldspots fail to sustain a positive colonization-to-extinction balance. Rather, species persistence within coldspots relies on hotspots acting as biodiversity sources and enhancing population dispersal across the landscape. In fact, even a few hotspots in the landscape can fuel the spatial network of dispersal of populations in the metacommunity. Our study highlights that coevolutionary hotspots can act as biodiversity sources, favouring colonization and allowing species to expand their distribution across landscapes even in changing environments. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Effects of sublethal methylmercury and food stress on songbird energetic performance: metabolic rates, molt and feather quality.

Organisms regularly adjust their physiology and energy balance in response to predictable seasonal environmental changes. Stressors and contaminants have the potential to disrupt these critical seasonal transitions. No studies have investigated how simultaneous exposure to the ubiquitous toxin methylmercury (MeHg) and food stress affects birds' physiological performance across seasons. We quantified several aspects of energetic performance in song sparrows, Melospiza melodia, exposed or not to unpredictable food stress and MeHg in a 2×2 experimental design, over 3 months during the breeding season, followed by 3 months post-exposure. Birds exposed to food stress had reduced basal metabolic rate and non-significant higher factorial metabolic scope during the exposure period, and had a greater increase in lean mass throughout most of the experimental period. Birds exposed to MeHg had increased molt duration, and increased mass:length ratio of some of their primary feathers. Birds exposed to the combined food stress and MeHg treatment often had responses similar to the stress-only or MeHg-only exposure groups, suggesting these treatments affected physiological performance through different mechanisms and resulted in compensatory or independent effects. Because the MeHg and stress variables were selected in candidate models with a ΔAICc lower than 2 but the 95% confidence interval of these variables overlapped zero, we found weak support for MeHg effects on all measures except basal metabolic rate, and for food stress effects on maximum metabolic rate, factorial metabolic scope and feather mass:length ratio. This suggests that MeHg and food stress effects on these measures are statistically identified but not simple and/or were too weak to be detected via linear regression. Overall, combined exposure to ecologically relevant MeHg and unpredictable food stress during the breeding season does not appear to induce extra energetic costs for songbirds in the post-exposure period. However, MeHg effects on molt duration could carry over across multiple annual cycle stages.

Spatially distributed cytokinins: Metabolism, signaling, and transport.

Cytokinins are mobile phytohormones that regulate plant growth, development, and environmental adaptability. The major cytokinin species include isopentenyl adenine (iP), trans-zeatin (tZ), cis-zeatin (cZ), and dihydrozeatin (DZ). The spatial distributions of different cytokinin species in different organelles, cells, tissues, and organs are primarily shaped by biosynthesis via isopentenyltransferases (IPT), cytochrome P450 monooxygenase, and 5'-ribonucleotide phosphohydrolase and by conjugation or catabolism via glycosyltransferase or cytokinin oxidase/dehydrogenase. Cytokinins bind to histidine receptor kinases in the endoplasmic reticulum or plasma membrane and relay signals to response regulators in the nucleus via shuttle proteins known as histidine phosphotransfer proteins. The movements of cytokinins from sites of biosynthesis to sites of signal perception usually require long-distance, intercellular, and intracellular transport. In the past decade, ATP-binding cassette (ABC) transporters, purine permeases (PUP), AZA-GUANINE RESISTANT (AZG) transporters, equilibrative nucleoside transporters (ENT), and Sugars Will Eventually Be Exported transporters (SWEET) have been characterized as involved in cytokinin transport processes. This review begins by introducing the spatial distributions of various cytokinins and the subcellular localizations of the proteins involved in their metabolism and signaling. Highlights focus on an inventory of the characterized transporters involved in cytokinin compartmentalization, including long-distance, intercellular, and intracellular transport, and the regulation of the spatial distributions of cytokinins by environmental cues. Future directions for cytokinin research are also discussed.

Schools as Hubs of Health: A Comprehensive Supplemental Nutrition Assistance Program-Education Model for Promoting Wellness in Low-Income Communities.

Research indicates that health interventions are most effective when they address multiple social determinants of health to support positive behavior. Schools as Hubs of Health, a comprehensive model of nutrition and physical activity education, was developed to support wellness within school communities defined as low-income by the national Supplemental Nutrition Assistance Program Education (SNAP-Ed). Components of the model include the following: classroom education; garden education; youth engagement; staff training; parent and community engagement; and policies, systems, and environments. Findings over the last decade indicate positive outcomes in nutrition and physical activity behaviors, youth leadership and engagement, and systems and environmental changes that support health and wellness.

Pleiotropic Role of Rainbow Trout CXCRs in Response to Disease and Environment: Insights from Transcriptional Signatures and Structure Analysis.

Chemokines are cytokines with chemoattractant capacities that exert their physiological functions through the binding of chemokine receptors. Thus, chemokine and receptor complexes exert important roles in regulating development and homeostasis during routine immune surveillance and inflammation. Compared to mammals, the physiology and structure of chemokine receptors in fish have not been systematically studied. Furthermore, the salmonid-specific whole genome duplication has significantly increased the number of functional paralogs of chemokine receptors. In this context, in the current study, trout exhibited 17 cxcr genes, including 12 newly identified and 5 previously identified receptors. Interestingly, gene expression of brain cxcr1 and cxcr4, kidney cxcr3 and cxcr4, and spleen cxcr3, cxcr4, and cxcr5 subtypes were altered by bacterial infection, whereas brain cxcr1, kidney cxcr1 and cxcr7, and liver cxcr2, cxcr3, and cxcr4 subtypes were changed in response to environmental changes. Based on protein structures predicted by ColabFold, the conserved amino acids in binding pockets between trout CXCR4.1 subtypes and human CXCR4 were also analyzed. Our study is valuable from a comparative point of view, providing new insights into the identification and physiology of salmonid chemokine receptors.

Unveiling the evolution of phytoplankton communities: Decades-long insights into the southern Yellow Sea, China (1959-2023).

We obtained historical and observational data on phytoplankton communities from 1959 to 2023 to explore the responses of the phytoplankton community structure to long-term environmental changes in the southern Yellow Sea (SYS), China. The results revealed a decrease in the proportions of diatom cell abundance within the phytoplankton community by 8 %, accompanied by a corresponding increase in that of dinoflagellates. Dominant phytoplankton species were mainly chain-forming diatoms before 2000, and large dinoflagellate species from the genera Tripos and Noctiluca increased their dominance after 2000. Warm-water phytoplankton species have increased in dominance over the study period. Correlation analysis revealed that the ocean warming and alterations in nutrient structure (N/P and Si/N ratios) were mostly responsible for the long-term evolution trend, and these changes may result in an increase in dinoflagellate harmful algal blooms, reduced efficiency of the biological carbon pump, and heightened hypoxia in the future, which should draw our attention.

Toxic effects of triclosan in aquatic organisms: A review focusing on single and combined exposure of environmental conditions and pollutants.

Triclosan (TCS) is an antibacterial agent commonly used in personal care products. Due to its widespread use and improper disposal, it is also a pervasive contaminant, particularly in aquatic environments. When released into water bodies, TCS can induce deleterious effects on developmental and physiological aspects of aquatic organisms and also interact with environmental stressors such as weather, metals, pharmaceuticals, and microplastics. Multiple studies have described the adverse effects of TCS on aquatic organisms, but few have reported on the interactions between TCS and other environmental conditions and pollutants. Because aquatic environments include a mix of contaminants and natural factors can correlate with contaminants, it is important to understand the toxicological outcomes of combinations of substances. Due to its lipophilic characteristics, TCS can interact with a wide range of substances and environmental stressors in aquatic environments. Here, we identify a need for caution when using TCS by describing not only the effects of exposure to TCS alone on aquatic organisms but also how toxicity changes when it acts in combination with multiple environmental stressors.

Sand fly-borne diseases in Europe: epidemiological overview and potential triggers for their emergence and re-emergence.

Phlebotomine sand flies (Diptera: Phlebotominae) are vectors of human and animal pathogens, including Leishmania species protozoan parasites and viruses of the genus Phlebovirus. In Europe, visceral zoonotic leishmaniasis caused by Leishmania infantum, a deadly disease when left untreated, is endemic in southern countries, and dogs are the main reservoir hosts for human infection. Most phleboviruses cause asymptomatic infections or flu-like syndromes in humans, but Toscana phlebovirus can cause meningitis and encephalitis. These diseases are likely to re-emerge, posing a growing threat to public and animal health. Potential triggers include the movement of humans and dogs, increasing numbers of immunosuppressive conditions, climate change and other human-mediated environmental changes. An overview of the main epidemiological characteristics of the pathogens transmitted by sand flies in Europe and the potential triggers involved in their emergence and re-emergence are reviewed here. There is a need to implement mandatory notification of human and canine leishmaniases and human phleboviruses and coordinated epidemiological surveillance programmes at a European level, and to raise awareness among healthcare professionals and citizens about sand fly-borne diseases, following a One Health approach.

"We Used to Have Four Seasons, but Now There Is Only One": Perceptions Concerning the Changing Climate and Environment in a Diverse Sample of Israeli Older Persons.

Solastalgia is the pain caused by the loss of solace and isolation from one's environment. Solastalgia is contrasted with nostalgia, which is defined as melancholy characterized by homesickness or the distance from one's home. The present study examines the two concepts of solastalgia and nostalgia in the context of climate change among diverse populations of older Israelis. In total, 50 older persons from four different population groups (e.g., veteran Israeli Jews, Israeli Arabs, immigrants from the former Soviet Union, and Ethiopian immigrants) were interviewed. All interviews were transcribed and analyzed thematically. Members of all four groups expressed emotional distress and grief associated with the changing climate, increased environmental pollution, and the disappearance of nature. Perceptions around the undesirability of these changes were quite unanimous, thus leading us to conclude that the outcomes associated with solastalgia and nostalgia are quite similar despite different etiological explanations.

Harvesting Bertholletia excelsa Bonpl. in a western Amazon rural community: local ecological knowledge and meaning to "nut-crackers".

INTRODUCTION: The collection of Bertholletia excelsa Bonpl. (castanha-da-Amazônia; Brazil nuts) seeds make up part of the everyday activities of the traditional populations that have inhabited all of the Amazon basin since remote times. Nonetheless, knowledge about these harvesting activities in native forest areas has not been well documented. The present study was designed to better understand the significance of this harvesting activity as well as the traditional ecological knowledge of the harvesters. METHODS: Utilizamos entrevistas semiestruturadas para a coleta de dados com extrativistas de castanha, moradores de Caroebe, Roraima (n = 18) durante o período de março de 2021 a março de 2022. The data analysis was based on the frequency of responses to socio-economic questions and their knowledge about that plant species as well as why those interviewees chose that line of work. We also adopted the Spearman and Mann-Whitney non-parametric tests to correlate variables identified in the study, and selected sections of their depositions to highlight the traditional knowledge of the interviewees and their experiences as harvesters. RESULTS: Constatamos que as razões para a escolha do trabalho com o extrativismo para todos os entrevistados é a necessidade de renda complementar, tradição familiar (55%), the sense of well-being provided by contact with the natural environment (25%), and a favorable disposition toward that type of work (11%). Harvesting involves collective work, and many of the interviewees had engaged in those efforts to help their families since their childhood or adolescence. The older harvesters cited more animal species that consumed the Brazil nuts (ρ = 0.60; p = 0.009) and perceived more and greater changes in the environment that were prejudicial to the Brazil nut trees (U = 9.50; p = 0.022). The interviewees who reported lower incomes cited more significant cultural changes and more suggestions concerning conservation activities. According to their statements, deforestation, and the burning and illegal cutting of native trees, including Brazil nut trees, have contributed to environmental change in the region and raised significant concerns about the future of harvesting activities. CONCLUSION: The activities of the "nut-crackers" represent to them more than just a simple source of income, as harvesting provides them with a connection to nature that promotes their well-being and cultural heritage. The nut harvesters have gained specific knowledge concerning both environmental and cultural changes. Those changes have mainly come about through the expansion of agricultural activities and the felling of native forests-which are the main threats to the future of Brazil nut extraction. Attributing value to the folk knowledge of those harvesters would strengthen the local economy, promote forest conservation, and help to better understand the impacts of anthropic activities on the forest and the harvesting of natural products.

Geologically calibrated mammalian tree and its correlation with global events, including the emergence of humans.

A robust timetree for Mammalia was constructed using the time calibration function of BEAST v1.10.4 and MEGA 11. The analysis involved the application of times of the most recent common ancestors, including a total of 19 mammalian fossil calibration ages following Benton et al. (Palaeontologia Electronica, 2015, 1-106) for their minimum ages. Additionally, fossil calibration ages for Gorilla, Pan, and a geologic event calibration age for otters were incorporated. Using these calibration ages, I constructed a geologically calibrated tree that estimates the age of the Homo and Pan splitting to be 5.69 Ma. The tree carries several significant implications. First, after the initial rifting at 120 Ma, the Atlantic Ocean expanded by over 500 km around Chron 34 (84 Ma), and vicariant speciation between Afrotheria (Africa) and Xenarthra (South America) appears to have commenced around 70 Ma. Additionally, ordinal level differentiations began immediately following the K-Pg boundary (66.0 Ma), supporting previous hypothesis that mammalian radiation rapidly filled ecological niches left vacant by non-avian dinosaurs. I constructed a diagram depicting the relationship between base substitution rate and age using an additional function in BEAST v1.10.4. The diagram reveals an exponential increase in the base substitution rate approaching recent times. This increased base substitution rate during the Neogene period may have contributed to the expansion of biodiversity, including the extensive adaptive radiation that led to the evolution of Homo sapiens. One significant driving factor behind this radiation could be attributed to the emergence and proliferation of C4 grasses since 20 Ma. These grasses have played a role in increasing carbon fixation, reducing atmospheric CO2 concentration, inducing global cooling, and initiating Quaternary glacial-interglacial cycles, thereby causing significant climatic changes.

Impact of kelp forest on seawater chemistry - A review.

Kelp forests, globally distributed in cool temperate and polar waters, are renowned for their pivotal role in supporting species diversity and fostering macroalgae productivity. These high-canopy algal ecosystems dynamically influence their surroundings, particularly by altering the physicochemical properties of seawater. This review article aims to underscore the significance of kelp forests in modifying water masses. By serving as effective carbon sinks through the absorption of bicarbonate (HCO3-) and carbon dioxide (CO2) for photosynthesis, kelp forests mitigate nearby acidity levels while enhancing dissolved oxygen concentrations, essential for sustaining diverse marine communities. Additionally, kelp beds have exhibited the need to use inorganic ions (NO3-, NO2-, PO43-) from seawater in order to grow, albeit with associated increases in NH4+ concentrations. Specific examples and findings from relevant studies will be presented to illustrate the profound impact of kelp forests on seawater chemistry, emphasizing their vital role in marine ecosystems.

Circadian Variation of Peripheral Blood Cells in Horses Maintained in Different Environmental and Management Conditions.

The aim of our study was to analyze circadian rhythm of the hematological profile of horses housed in a loose box and paddock during the different seasons (spring, summer, autumn, and winter). Blood samples were performed every 4 h for 48 consecutive hours. Red blood cells (RBCs), hemoglobin (HGB), hematocrit (HCT), white blood cells (WBCs), platelets (PLTs), and leukocyte subpopulations (neutrophils, basophils, eosinophils, lymphocytes, and monocytes) were analyzed, and, at the same time, environmental conditions were recorded. A statistically significant effect of housing conditions (p < 0.0001) was observed on all hematological values except for WBC during winter and for neutrophils (p < 0.0001) during spring and autumn. A statistically significant effect of season (p < 0.0001) was found for RBC, HCT, and PLT and for all leukocyte cells (p < 0.0001) except for basophils. The single Cosinor method revealed a daily rhythm of hematological parameters during spring in both groups, and a daily rhythm for lymphocytes and neutrophils was observed during spring and summer in horses kept in a loose box and during winter in horses housed in a paddock. Our results revealed that the response of the immune system is regulated by circadian physiology. Knowledge of the periodic temporal structure of mammals should be considered when evaluating animals' adaptation to temporizations imposed by the environment.

Watershed-Mediated Ecomorphological Variation: A Case Study with the Twin-Striped Clubtail Dragonfly (Hylogomphus geminatus).

Anthropogenic land-cover change is modifying ecosystems at an accelerating rate. Changes to ecomorphologically variable taxa within those ecosystems serve as early-warning signs that resources on which humans and other animals depend are being altered. One known ecomorphologically variable taxon is Hylogomphus geminatus, a species of dragonfly in the southeastern United States that shows pronounced variation in total body length across its limited geographic range. We measured total length of live as well as preserved museum specimens of H. geminatus and the sympatric species Progomphus obscurus (as a means for comparison). Both species showed significant size differences linked to HUC-8 watersheds in which they occur. H. geminatus showed additional significant differences on either side of the Apalachicola River, Florida, for all comparisons by sex. In overlapping watersheds, the species tended to show the same trends in length relative to their respective averages. Smaller body length was associated with more urban and agricultural land cover. These findings indicate that ecomorphological variation is tied to the watershed scale and point to significant variations on either side of the Apalachicola River. More thorough future analyses would be needed to verify trends in body length and identify the drivers behind them.

Anthropogenic Influence on Moth Populations: A Comparative Study in Southern Sweden.

As moths are vital components of ecosystems and serve as important bioindicators, understanding the dynamics of their communities and the factors influencing these dynamics, such as anthropogenic impacts, is crucial to understand the ecological processes. Our study focuses on two provinces in southern Sweden, Västergötland and Småland, where we used province records from 1974 to 2019 in combination with light traps (in 2020) to record the presence and abundance of moth species, subsequently assessing species traits to determine potential associations with their presence in anthropogenically modified landscapes. This study design provides a unique opportunity to assess temporal changes in moth communities and their responses to shifts in environmental conditions, including anthropogenic impacts. Across the Västergötland and Småland provinces in Sweden, we recorded 776 moth taxa belonging to fourteen different taxonomic families of mainly Macroheterocera. We captured 44% and 28% of the total moth species known from these provinces in our traps in Borås (Västergötland) and Kalmar (Småland), respectively. In 2020, the species richness and abundance were higher in Borås than in Kalmar, while the Shannon and Simpson diversity indices revealed a higher species diversity in Kalmar. Between 1974 and 2019, the colonisation rates of the provinces increased faster in Småland. Ninety-three species were found to have colonised these provinces since 1974, showing that species richness increased over the study period. We reveal significant associations between the probability of a species being present in the traps and distinct traits compared to a provincial species pool. Traits over-represented in the traps included species with a high variation in colour patterns, generalist habitat preferences, extended flight periods, lower host plant specificity, and overwintering primarily as eggs. Our findings underscore the ongoing ecological filtering that favours certain species-specific traits. This study sheds light on the roles of climate change and anthropogenic impacts in shaping moth biodiversity, offers key insights into the ecological processes involved, and can guide future conservation efforts.

Transformation of Brazil's biomes: The dynamics and fate of agriculture and pasture expansion into native vegetation.

Land use and cover change (LUCC) in Brazil encompass a complex interplay of diverse factors across different biomes. Understanding these dynamics is crucial for informed decision-making and sustainable land management. In this study, we comprehensively analyzed LUCC patterns and drivers using 30 m resolution MapBiomas Collection 6.0 data (1985-2020). By mapping deforestation of primary and secondary natural vegetation, natural vegetation regeneration, and transitions between pasture, soybean, agriculture, and irrigation, we shed light on the intricate nature of LUCC in Brazil. Our findings highlight significant and increasing trends of deforestation in primary vegetation in the country. Simultaneously, the Atlantic Forest, Caatinga, Pampa, and other regions of the Cerrado have experienced intensification processes. Notably, the pasture area in Brazil reached its peak in 2006 and has since witnessed a gradual replacement by soybean and other crops. While pasture-driven deforestation persists in most biomes, the net pasture area has only increased in the Amazon and Pantanal, decreasing in other biomes due to the conversion of pasturelands to intensive cropping in other regions. Our analysis further reveals that primary and secondary vegetation deforestation accounts for a substantial portion of overall forest loss, with 72 % and 17 %, respectively. Of the cleared areas, 48 % were in pasture, 9 % in soybean cultivation, and 16 % in other agricultural uses in 2020. Additionally, we observed a lower rate of deforestation in the Atlantic Forest, a biome that has been significantly influenced by anthropogenic activities since 1986. This holistic quantification of LUCC dynamics provides a solid foundation for understanding the impacts of these changes on local to continental-scale land-atmosphere interactions. By unraveling the complex nature of LUCC in Brazil, this study aims to contribute to the development of effective strategies for sustainable land management and decision-making processes.

Response of protists to nitrogen addition, arbuscular mycorrhizal fungi manipulation, and mesofauna reduction in a tropical montane rainforest in southern Ecuador.

The tropical Andes are a species-rich and nitrogen-limited system, susceptible to increased nitrogen (N) inputs from the atmosphere. However, our understanding of the impacts of increased N input on belowground systems, in particular on protists and their role in nutrient cycling, remains limited. We explored how increased N affects protists in tropical montane rainforests in Ecuador using high-throughput sequencing (HTS) of environmental DNA from two litter layers. In addition, we manipulated the amount of arbuscular mycorrhizal fungi (AMF) and mesofauna, both playing a significant role in N cycling and interacting in complex ways with protist communities. We found that N strongly affected protist community composition in both layers, while mesofauna reduction had a stronger effect on the lower layer. Changes in concentration of the AMF marker lipid had little effect on protists. In both layers, the addition of N increased phagotrophs and animal parasites and decreased plant parasites, while mixotrophs decreased in the upper layer but increased in the lower layer. In the upper layer with higher AMF concentration, mixotrophs decreased, while in the lower layer, photoautotrophs increased and plant parasites decreased. With reduced mesofauna, phagotrophs increased and animal parasites decreased in both layers, while plant parasites increased only in the upper layer. The findings indicate that to understand the intricate response of protist communities to environmental changes, it is critical to thoroughly analyze these communities across litter and soil layers, and to include HTS.

Updating the dual C and O isotope-Gas-exchange model: A concept to understand plant responses to the environment and its implications for tree rings.

The combined study of carbon (C) and oxygen (O) isotopes in plant organic matter has emerged as a powerful tool for understanding plant functional responses to environmental change. The approach relies on established relationships between leaf gas exchange and isotopic fractionation to derive a series of model scenarios that can be used to infer changes in photosynthetic assimilation and stomatal conductance driven by changes in environmental parameters (CO2 , water availability, air humidity, temperature, nutrients). We review the mechanistic basis for a conceptual model, in light of recently published research, and discuss where isotopic observations do not match our current understanding of plant physiological response to the environment. We demonstrate that (1) the model was applied successfully in many, but not all studies; (2) although originally conceived for leaf isotopes, the model has been applied extensively to tree-ring isotopes in the context of tree physiology and dendrochronology. Where isotopic observations deviate from physiologically plausible conclusions, this mismatch between gas exchange and isotope response provides valuable insights into underlying physiological processes. Overall, we found that isotope responses can be grouped into situations of increasing resource limitation versus higher resource availability. The dual-isotope model helps to interpret plant responses to a multitude of environmental factors.