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Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

O funcionamento da floresta tropical é de importância global para as respostas às mudanças climáticas e é criticamente determinado pelos padrões de disponibilidade de água. A água subterrânea está intimamente relacionada à água do solo através da profundidade do lençol freático, que tem sido historicamente negligenciado em estudos ecológicos. Florestas com lençol freático raso (< 5 m) estão sub-representadas nas redes de pesquisa florestal e ausentes nas medições de fluxo de gases, embora representem ~ 50% da Amazônia e devam responder de forma diferente às secas relacionadas às mudanças globais. Aqui revisamos os padrões de profundidade do lençol freático e suas consequências para plantas, resultados emergentes, e avançamos em um modelo conceitual que integra o ambiente e as distribuições de características funcionais para prever os efeitos das mudanças climáticas. As florestas com lençol freático raso têm uma composição de espécies distinta, com árvores mais aquisitivas na obtenção de recursos e hidrologicamente vulneráveis, dosséis mais baixos e menor biomassa do que as florestas com lençol freático profundo. Durante os anos climáticos 'normais', as florestas com lençol freático raso têm maior mortalidade e menor produtividade do que as florestas com lençol freático profundo, mas durante secas moderadas, a mortalidade é amortecida e a produtividade aumenta. No entanto, durante secas severas, as florestas com lençol freático raso podem ser mais sensíveis devido às raízes superficiais e características funcionais de intolerância à seca. Nossas evidências apoiam a hipótese de que as florestas com lençol freático raso, historicamente negligenciadas, sejam resilientes à seca moderada, desafiando a visão predominante dos efeitos negativos generalizados da mudança climática nas florestas amazônicas que ignora gradientes de profundidade do lençol freático, mas prevê que elas podem entrar em colapso sob secas muito fortes.

La función de los bosques tropicales es de importancia mundial para las respuestas al cambio climático y está críticamente determinada por los patrones de disponibilidad de agua. El agua subterránea está estrechamente relacionada con el agua del suelo a través de la profundidad del nivel freático (NF), pero históricamente se há negligenciado en los estudios ecológicos. Los bosques con NF poco profundos (NF < 5 m) están subrepresentados en las redes de investigación forestal y ausentes en las mediciones de flujo de gases, aunque representan ~ 50% de la Amazonía y se espera que respondan de manera diferente a las sequías relacionadas con el cambio climático global. Aquí revisamos los patrones de NF y las consecuencias para las plantas, los resultados emergentes y avanzamos en un modelo conceptual que integra distribuciones ambientales y de rasgos funcionales para predecir los efectos del cambio climático. Los bosques con NF poco profundos tienen una composición de especies distinta, con árboles más adquisitivos en la obtención de recursos e hidrológicamente más vulnerables, dosel más bajo y menor biomasa que los bosques de NF profundo. Durante los años climáticos 'normales', los bosques con NF poco profundos tienen una mayor mortalidad y menor productividad que los bosques con NF profundos, pero durante sequías moderadas la mortalidad se amortigua y la productividad aumenta. Sin embargo, durante una sequía severa, los bosques de NF poco profundos pueden ser más sensibles debido a raíces poco profundas y rasgos de intolerancia a la sequía. Nuestra evidencia apoya la hipótesis de que los bosques de NF poco profundos, mayoritariamente desconsiderados, son resistentes a sequías moderadas, desafiando la visión predominante de impactos negativos generalizados del cambio climático en los bosques amazónicos, que ignora los gradientes de NF, pero predice que podrían colapsar bajo sequías muy fuertes.

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Allochthonous resource fluxes mediated by organisms crossing ecosystem boundaries may be essential for supporting the structure and function of resource-limited environments, such as tropical islands and surrounding coral reefs. However, invasive species, such as black rats, thrive on tropical islands and disrupt the natural pathways of nutrient subsidies by reducing seabird colonies. Here, we used stable isotopes of nitrogen and carbon to examine the role of seabirds in subsidizing the terrestrial food webs and adjacent coral reefs in the Abrolhos Archipelago, Southwest Atlantic Ocean. By sampling invasive rats and multiple ecosystem compartments (soil, plants, grasshoppers, tarantulas, and lizards) within and outside seabird colonies, we showed that seabird subsidies led to an overall enrichment in 15 N across the food web on islands. However, contrary to other studies, δ15 N values were consistently lower within the seabird colonies, suggesting that a higher seabird presence might produce a localized depletion in 15 N in small islands influenced by seabirds. In contrast, the nitrogen content (%N) in plants and soils was higher inside the colonies, corresponding to a higher effect of seabirds at the base of the trophic web. Among consumers, lizards and invasive rats seemed to obtain allochthonous resources from subsidized terrestrial organisms outside the colony. Inside the colony, however, they showed a more direct consumption of marine matter, suggesting that subsidies benefit these native and invasive animals both directly and indirectly. Nonetheless, in coral reefs, scleractinian corals assimilated seabird-derived nitrogen only around the two smaller and lower-elevation islands, as demonstrated by the substantially higher δ15 N values in relation to the reference areas. This provides evidence that island morphology may influence the incorporation of seabird nutrients in coral reefs around rat-invaded islands, likely because guano lixiviation toward seawater is facilitated in small and low-elevation terrains. Overall, these results showed that seabirds affected small islands across all trophic levels within and outside colonies and that these effects spread outward to coral reefs, evidencing resiliency of seabird subsidies even within a rat-invaded archipelago. Because rats are consumers of seabird chicks and eggs, however, rat eradication could potentially benefit the terrestrial and nearshore ecosystems through increased subsides carried by seabirds.

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Human activities have impacted many environments on earth, and thus several species are facing an increased risk of extinction. The environmental crisis requires rapid tools to assess the ecosystem health accurately. Studies have been conducted with visual indices that quantify habitat integrity by predicting species richness and diversity. However, whether a diverse clade can predict habitat integrity has not been used. The genus Argia (Rambur, 1842) is one of the most locally diverse groups in southeastern Mexico. In this context, we hypothesized that the occurrence, species richness, and diversity of adults Argia spp. could be a better predictor of the Visual-Based Habitat Assessment Score (VBHAS) than the other taxonomic levels or less diverse clades. We found that the richness and diversity of Argia spp. are positively correlated with VBHA scores, as same as taxonomic ratios. Simultaneously, VBHA scores increase to 23.51 times when Argia spp. diversity increases. We discuss the possible use of a diverse Odonata clade, as Argia spp. could surrogate habitat integrity for local long-term biomonitoring programs. This approach requires testing with other indices and verifying a reliable and consistent relationship between diverse clades and environmental assessment scores.

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Amazonian rainforest is undergoing increasing rates of deforestation, driven primarily by cattle pasture expansion. Forest-to-pasture conversion has been associated with increases in soil methane (CH4) emission. To better understand the drivers of this change, we measured soil CH4 flux, environmental conditions, and belowground microbial community structure across primary forests, cattle pastures, and secondary forests in two Amazonian regions. We show that pasture soils emit high levels of CH4 (mean: 3454.6 ± 9482.3 µg CH4 m-2 d-1), consistent with previous reports, while forest soils on average emit CH4 at modest rates (mean: 9.8 ± 120.5 µg CH4 m-2 d-1), but often act as CH4 sinks. We report that secondary forest soils tend to consume CH4 (mean: -10.2 ± 35.7 µg CH4 m-2 d-1), demonstrating that pasture CH4 emissions can be reversed. We apply a novel computational approach to identify microbial community attributes associated with flux independent of soil chemistry. While this revealed taxa known to produce or consume CH4 directly (i.e. methanogens and methanotrophs, respectively), the vast majority of identified taxa are not known to cycle CH4. Each land use type had a unique subset of taxa associated with CH4 flux, suggesting that land use change alters CH4 cycling through shifts in microbial community composition. Taken together, we show that microbial composition is crucial for understanding the observed CH4 dynamics and that microorganisms provide explanatory power that cannot be captured by environmental variables.

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Dramatic coral loss has significantly altered many Caribbean reefs, with potentially important consequences for the ecological functions and ecosystem services provided by reef systems. Many studies examine coral loss and its causes-and often presume a universal decline of ecosystem services with coral loss-rather than evaluating the range of possible outcomes for a diversity of ecosystem functions and services at reefs varying in coral cover. We evaluate 10 key ecosystem metrics, relating to a variety of different reef ecosystem functions and services, on 328 Caribbean reefs varying in coral cover. We focus on the range and variability of these metrics rather than on mean responses. In contrast to a prevailing paradigm, we document high variability for a variety of metrics, and for many the range of outcomes is not related to coral cover. We find numerous "bright spots," where herbivorous fish biomass, density of large fishes, fishery value, and/or fish species richness are high, despite low coral cover. Although it remains critical to protect and restore corals, understanding variability in ecosystem metrics among low-coral reefs can facilitate the maintenance of reefs with sustained functions and services as we work to restore degraded systems. This framework can be applied to other ecosystems in the Anthropocene to better understand variance in ecosystem service outcomes and identify where and why bright spots exist.

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We assessed the impacts of forest-to-pasture conversion on the dynamic of soil microbial communities, especially those involved in the N-cycle, and their potential functions, using DNA-metagenomic sequencing coupled with the quantification of marker genes for N-cycling. We also evaluated whether the community's dynamic was reestablished with secondary forest growth. In general, the microbial community structure was influenced by changes in soil chemical properties. Aluminum and nitrate significantly correlated to community structure and with 12 out of 21 microbial phyla. The N-related microbial groups and their potential functions were also affected by land-use change, with pasture being clearly different from primary and secondary forest systems. The microbial community analysis demonstrated that forest-to-pasture conversion increased the abundance of different microbial groups related to nitrogen fixation, including Bacteroidetes, Chloroflexi and Firmicutes. In contrast, after pasture abandonment and with the secondary forest regeneration, there was an increase in the abundance of Proteobacteria taxa and denitrification genes. Our multi-analytical approach indicated that the secondary forest presented some signs of resilience, suggesting that the N-related microbial groups and their potential functions can be recovered over time with implications for future ecological restoration programs.

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Nitrous oxide (N2O), a main greenhouse gas that contributes to ozone layer depletion, is released from soils. Even when it has been argued that agriculture is the main cause of its increase in the atmosphere, natural ecosystems are also an important source of N2O. However, the impacts of human activities on N2O emissions through biodiversity loss or primary productivity changes in natural ecosystems have rarely been assessed. Here, we analyzed the effects of vegetation attributes such as plant diversity and production, as drivers of N2O emission rates, in addition to environmental factors. We measured N2O emissions monthly during 1 year in 12 sites covering a large portion of the Rio de la Plata grasslands, Argentina, and related these emissions with climate, soil and vegetation attributes. We performed spatial and temporal models of N2O emissions separately, to evaluate which drivers control N2O in space and over time independently. Our results showed that in the spatial model, N2O emissions decreased with increments in plant species richness, with concomitant reductions in soil [Formula: see text] whereas N2O emissions increased with primary productivity. By contrast, in the temporal model, monthly precipitation and monthly temperature were the main drivers of N2O emissions, with positive correlations, showing important differences with the spatial model. Overall, our results show that biological drivers may exert substantial control of N2O emissions at large spatial scales, together with climate and soil variables. Our results suggest that biodiversity conservation of natural grasslands may reduce regional greenhouse gas emissions, besides maintaining other important ecosystem services.

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Ecosystems are being stressed by climate change, but few studies have tested food web responses to changes in precipitation patterns and the consequences to ecosystem function. Fewer still have considered whether results from one geographic region can be applied to other regions, given the degree of community change over large biogeographic gradients. We assembled, in one field site, three types of macroinvertebrate communities within water-filled bromeliads. Two represented food webs containing both a fast filter feeder-microbial and slow detritivore energy channels found in Costa Rica and Puerto Rico, and one represented the structurally simpler food webs in French Guiana, which only contained the fast filter feeder-microbial channel. We manipulated the amount and distribution of rain entering bromeliads and examined how food web structure mediated ecosystem responses to changes in the quantity and temporal distribution of precipitation. Food web structure affected the survival of functional groups in general and ecosystem functions such as decomposition and the production of fine particulate organic matter. Ecosystem processes were more affected by decreased precipitation than were the abundance of micro-organisms and metazoans. In our experiments, the sensitivity of the ecosystem to precipitation change was primarily revealed in the food web dominated by the single filter feeder-microbial channel because other top-down and bottom-up processes were weak or absent. Our results show stronger effects of food web structure than precipitation change per se on the functioning of bromeliad ecosystems. Consequently, we predict that ecosystem function in bromeliads throughout the Americas will be more sensitive to changes in the distribution of species, rather than to the direct effects caused by changes in precipitation.

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Leaf traits are closely associated with nutrient use by plants and can be utilized as a proxy for nutrient cycling processes. However, open questions remain, in particular regarding the variability of leaf traits within and across seasonally dry tropical forests. To address this, we considered six leaf traits (specific area, thickness, dry matter content, N content, P content and natural abundance (15)N) of four co-occurring tree species (two that are not associated with N2-fixing bacteria and two that are associated with N2-fixing bacteria) and net N mineralization rates and inorganic N concentrations along a precipitation gradient (537-1036 mm per year) in the Yucatan Peninsula, Mexico. Specifically we sought to test the hypothesis that leaf traits of dominant plant species shift along a precipitation gradient, but are affected by soil N cycling. Although variation among different species within each site explains some leaf trait variation, there is also a high level of variability across sites, suggesting that factors other than precipitation regime more strongly influence leaf traits. Principal component analyses indicated that across sites and tree species, covariation in leaf traits is an indicator of soil N availability. Patterns of natural abundance (15)N in foliage and foliage minus soil suggest that variation in precipitation regime drives a shift in plant N acquisition and the openness of the N cycle. Overall, our study shows that both plant species and site are important determinants of leaf traits, and that the leaf trait spectrum is correlated with soil N cycling.

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Invasive transformer species change the character, condition, form, or nature of ecosystems and deserve considerable attention from conservation scientists. We applied the transformer species concept to the plague bacterium Yersinia pestis in western North America, where the pathogen was introduced around 1900. Y. pestis transforms grassland ecosystems by severely depleting the abundance of prairie dogs (Cynomys spp.) and thereby causing declines in native species abundance and diversity, including threatened and endangered species; altering food web connections; altering the import and export of nutrients; causing a loss of ecosystem resilience to encroaching invasive plants; and modifying prairie dog burrows. Y. pestis poses an important challenge to conservation biologists because it causes trophic-level perturbations that affect the stability of ecosystems. Unfortunately, understanding of the effects of Y. pestis on ecosystems is rudimentary, highlighting an acute need for continued research.

La Bacteria de la Peste como una Especie Transformadora en los Perritos de las Praderas y los Pastizales del Oeste de Norteamérica Resumen Las especies invasoras transformadoras cambian el carácter, la condición, la forma o la naturaleza de los ecosistemas y merecen atención considerable por parte de los científicos de la conservación. Aplicamos el concepto de especie transformadora a la bacteria de la peste Yersinia pestis en el oeste de Norteamérica, en donde el patógeno fue introducido alrededor de 1900. Y. pestis transforma los ecosistemas de pastizal al disminuir severamente la abundancia de los perritos de las praderas (Cynomys spp.) y por lo tanto causa declinaciones en la abundancia y diversidad de las especies nativas, incluidas las especies amenazadas y en peligro; altera las conexiones de las redes alimenticias; altera la importación y exportación de nutrientes; causa la pérdida de resiliencia del ecosistema ante las plantas invasoras; y modifica las madrigueras de los perritos. Y. pestis es un reto importante para los biólogos de la conservación ya que causa perturbaciones de nivel trófico que afectan la estabilidad de los ecosistemas. Desafortunadamente, el entendimiento de los efectos de Y. pestis sobre los ecosistemas es rudimentario, lo que resalta una necesidad aguda de investigación continua.

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Estuaries and coastal seas provide valuable ecosystem services but are particularly vulnerable to the co-occurring threats of climate change and oxygen-depleted dead zones. We analyzed the severity of climate change predicted for existing dead zones, and found that 94% of dead zones are in regions that will experience at least a 2 °C temperature increase by the end of the century. We then reviewed how climate change will exacerbate hypoxic conditions through oceanographic, ecological, and physiological processes. We found evidence that suggests numerous climate variables including temperature, ocean acidification, sea-level rise, precipitation, wind, and storm patterns will affect dead zones, and that each of those factors has the potential to act through multiple pathways on both oxygen availability and ecological responses to hypoxia. Given the variety and strength of the mechanisms by which climate change exacerbates hypoxia, and the rates at which climate is changing, we posit that climate change variables are contributing to the dead zone epidemic by acting synergistically with one another and with recognized anthropogenic triggers of hypoxia including eutrophication. This suggests that a multidisciplinary, integrated approach that considers the full range of climate variables is needed to track and potentially reverse the spread of dead zones.

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Climate change is affecting the amount and complexity of plant inputs to tropical forest soils. This is likely to influence the carbon (C) balance of these ecosystems by altering decomposition processes e.g., "positive priming effects" that accelerate soil organic matter mineralization. However, the mechanisms determining the magnitude of priming effects are poorly understood. We investigated potential mechanisms by adding (13)C labeled substrates, as surrogates of plant inputs, to soils from an elevation gradient of tropical lowland and montane forests. We hypothesized that priming effects would increase with elevation due to increasing microbial nitrogen limitation, and that microbial community composition would strongly influence the magnitude of priming effects. Quantifying the sources of respired C (substrate or soil organic matter) in response to substrate addition revealed no consistent patterns in priming effects with elevation. Instead we found that substrate quality (complexity and nitrogen content) was the dominant factor controlling priming effects. For example a nitrogenous substrate induced a large increase in soil organic matter mineralization whilst a complex C substrate caused negligible change. Differences in the functional capacity of specific microbial groups, rather than microbial community composition per se, were responsible for these substrate-driven differences in priming effects. Our findings suggest that the microbial pathways by which plant inputs and soil organic matter are mineralized are determined primarily by the quality of plant inputs and the functional capacity of microbial taxa, rather than the abiotic properties of the soil. Changes in the complexity and stoichiometry of plant inputs to soil in response to climate change may therefore be important in regulating soil C dynamics in tropical forest soils.