Future Environmental Change Research Articles

Latitudinal gradients and ocean fronts strongly influence protist communities in the southern Pacific Ocean

Abstract Protist communities in the southern Pacific Ocean make a major contribution to global biogeochemical cycling, but remain understudied due to their remote location. We therefore have limited understanding of how large-scale physical gradients (e.g. temperature) and mesoscale oceanographic features (e.g. fronts) influence microeukaryote diversity in this region. We performed a high-resolution examination of protist communities along a latitudinal transect (>3000 km) at 150°W in the central southern Pacific Ocean that encompassed major frontal regions, including the sub-tropical front (STF), the sub-Antarctic front (SAF), and the polar front (PF). We identified distinct microbial communities along the transect that were primarily delineated by the positions of the STF and PF. Some taxa were not constricted by these environmental boundaries and were able to span frontal regions, such as the colonial haptophyte Phaeocystis. Our findings also support the presence of a Latitudinal Diversity Gradient (LDG) of decreasing diversity of the protist community with increasing latitude, although some individual taxa, notably the diatoms, do not adhere to this rule. Our findings show that oceanographic features and large-scale physical gradients have important impacts on marine protist communities in the southern Pacific Ocean that are likely to strongly influence their response to future environmental change.

Short Communication: Numerically simulated time to steady state is not a reliable measure of landscape response time

Abstract. Quantifying the timescales over which landscapes evolve is critical for understanding past and future environmental change. Computational landscape evolution models are one tool among many that have been used in this pursuit. We compare numerically modeled times to reach steady state for a landscape adjusting to an increase in rock uplift rate. We use three different numerical modeling libraries and explore the impact of time step, grid type, numerical method for solving the erosion equation, and metric for quantifying the time to steady state. We find that modeled time to steady state is impacted by all of these variables. Time to steady state varies inconsistently with time step length, both within a single model and among different models. In some cases, drainage rearrangement extends the time to reach steady state, but this is not consistent in all models or grid types. The two sets of experiments operating on Voronoi grids have the most consistent times to steady state when comparing across time step and metrics. On a raster grid, if we force the drainage network to remain stable, time to steady state varies much less with computational time step. In all cases we find that many measures of modeled time to steady state are longer than that predicted by an analytical equation for bedrock river response time. Our results show that the predicted time to steady state from a numerical model is, in many cases, more reflective of drainage rearrangement and numerical artifacts than the time for an uplift wave to propagate through a fixed drainage network.

Immune defense adaptation of Strauchbufo raddei population in heavy metal polluted area: Insights from developmental and environmental perspectives

The adjustment of immune defense mechanisms is a crucial aspect of biological adaptation to stressful environments. Amphibians, with their unique metamorphic process, experience distinct life stages and exhibit diverse immune defense components. While previous studies have focused on specific immune changes during particular life stages under stress, this research addresses a critical gap by exploring the adaptive immune defense strategies of Strauchbufo raddei in heavy metal-polluted environments. We conducted laboratory experiments, exposing offspring from both polluted and unpolluted areas to control and heavy metal treatments, while continuously monitoring changes in immune components during key metamorphic stages. Notably, we examined the role of the skin microbiome, a crucial but often overlooked barrier against pathogens. The results indicated that individuals from polluted areas exhibited some tolerance to heavy metal exposure, though overall immune function remained diminished. During metamorphosis, when immune defenses are most vulnerable, the skin microbiome rapidly enriched beneficial bacteria, preventing pathogenic colonization and playing a pivotal role in maintaining immune defense in contaminated environments. Moreover, our research highlights energy allocation strategies involving corticosterone and body fat content, enabling populations to maintain development despite immune compromise. The immune adaptations observed may be fixed through genetic assimilation, suggesting a rapid evolutionary response to environmental stress. However, this reduces phenotypic plasticity, making populations more vulnerable to future environmental changes. This study provides key insights into the survival strategies of amphibian populations in heavy metal-contaminated areas, laying the foundation for future research on molecular and evolutionary adaptations.

Temporal and spatial variation in reproductive benefits in a partial migrant.

In partial migrant systems, where residents and migrants coexist within a population, residents are commonly predicted to gain a reproductive advantage over migrants through priority access to high-quality territories and an earlier breeding start. Annual variation in reproductive benefits has been suggested to be important for the coexistence of both strategies in a population, as differences in wintering conditions experienced by the two strategies may result in a periodic reproductive advantage for migrants. However, the importance of spatial environmental variation for reproductive output in partially migrant populations remains largely unexplored. We investigated variation in the reproductive output of migrants and residents in a population of Swiss red kites (Milvus milvus) both temporally, across and within years, and spatially, along an elevational gradient. We gathered 4 years of reproductive data combined with 183 GPS-derived full annual cycles from individuals breeding in the Swiss Alpine foothills. At low, but not high, elevations, residents produced more fledglings than migrants. We also found evidence for annual variation in the reproductive advantage of the two strategies. Furthermore, while reproductive output did decline with a later breeding start, there was no difference in the start of breeding between the two migration strategies. The results of this study suggest that differences in reproductive output between migrants and residents in partial migrant populations can vary both due to the use of spatially distinct overwintering grounds and because the strategies are differently affected by spatial variables in the breeding area, such as elevation. The study emphasizes that spatial and temporal variation in reproductive benefits must be considered when predicting how migratory species will respond to future environmental change.

Natural and anthropogenically driven change of organic carbon burial rate in two alpine lakes from the southeastern margin of the Tibetan Plateau

The rate of organic carbon (OC) burial in lakes depends considerably on natural and anthropogenic factors. Delineating how and to what extent potential drivers shape a lake’s OC burial rate is crucial for anticipating OC sequestration under future environmental change scenarios. Alpine lakes provide valuable opportunities for studying the influence of climate warming and atmospheric nitrogen (N) deposition on OC burial in lakes, owing to the lack of human activities in their catchments; however, this aspect has not been sufficiently documented. Here, the OC burial rate was reconstructed in two alpine lakes (Heihai and Jiren) from the southeastern margin of the Tibetan Plateau over the past ∼ 160 years, and the associated drivers were identified by resolving the temporal trends in organic matter (OM) input from specific sources to lake sediments via paleolimnological methods. The results demonstrated a consistently low OC burial rate (6.21–10.86 g m−2 yr−1) in Lake Heihai. The low hydrogen index (HI), moderate Paq, and high long-chain n-alkane flux revealed that submerged macrophytes and terrestrial plants are major contributors to the sequestrated OC. The notable decrease in the OC burial rate after 1980 was hypothesized to be caused by regional climate warming during this period because a greater export of terrestrial materials under such a climate can inhibit light penetration, diminishing submerged macrophyte productivity and OM input. In contrast, the synchronous input of higher amounts of terrestrial plant OM was largely degraded owing to the increased water temperature and the intensification of water column stratification. In Lake Jiren, a notably high OC burial rate (13.82–46.75g m−2 yr−1) was observed. The high HI, Paq, and short-chain n-alkane flux showed that phytoplankton and submerged macrophytes were the major contributors to the sequestrated OC. The two-phase increase in the OC burial rate in this lake, including a slow increase after 1947 and a rapid increase after 1983, might have resulted from strengthening aquatic primary productivity and OM input, driven by anthropogenic intensification of nutrient emissions, especially reactive N, from highly urbanized areas and the subsequent long-term atmospheric transport and deposition of these materials over the lake basin. A comparative analysis of the results between the two lakes suggested that atmospheric N deposition has a stronger influence on the OC burial than climate warming. These drivers affect the OC burial rate by altering aquatic productivity rather than the terrestrial OM input. This study provides a basic for predicting future OC burial scenarios in warmer climates with more intense anthropogenic N emissions.

Safedrive dreamer: Navigating safety–critical scenarios in autonomous driving with world models

Achieving stable and reliable autonomous driving in complex traffic environments while ensuring safety under unpredictable conditions is a critical challenge in autonomous driving technology. To address this issue, this study proposes the Safedrive Dreamer navigation framework, which aims to reduce the reliance on trial-and-error learning in real-world scenarios, thereby mitigating the risks associated with dynamic driving conditions and enhancing vehicle foresight. This framework integrates the predictive capabilities of world models with the constrained Markov decision process (CMDP) and safety reinforcement learning to accurately anticipate future environmental changes. This ensures the reliability of autonomous driving routes, thereby improving both safety and efficiency. Furthermore, to reduce trial-and-error costs in real-world applications, this study employs PAC-Bayesian methods to derive generalization error bounds between simulations and reality, enabling a more effective transfer of knowledge and experience from simulations to real-world scenarios. Validation experiments in simulated and real environments showed that Safedrive Dreamer significantly outperformed existing autonomous driving solutions by 3.8% in key safety metrics, excelling in collision avoidance and risk reduction. This study provides new insights into the integration of world models into decision-making processes to enhance decision-making capabilities in safety–critical applications, thereby contributing significantly to the improvement of autonomous driving safety and reliability.

Vegetation, temperature, and Indian Summer Monsoon evolution over the past 4400 years revealed by a pollen record from Drigo Co on the southern Qinghai-Tibet Plateau

Understanding the changes in temperature and precipitation on the southern Qinghai-Tibet Plateau (QTP), which is influenced by the Indian Summer Monsoon (ISM), is crucial for predicting possible future changes in the regional ecological environment under ongoing climate change. However, due to the lack of well-dated, high-resolution paleoclimate records, the trends of temperature and ISM precipitation on the southern QTP since the mid-Holocene are poorly understood. We present a high-resolution pollen record from Dirgo Co, on the southern QTP, spanning the past 4400 years. The decrease in the pollen ratio of Artemisia to Cyperaceae (A/Cy) indicates a downward shift of altitudinal vegetation belts in the Drigo Co area over the past 4400 years, suggesting falling temperatures; and decreases in tree pollen percentages indicate the gradual weakening of the ISM. Our pollen record also indicates five cold phases with the near-simultaneous weakening of the monsoon, during: 4300–4100 cal yr BP, 3600–3400 cal yr BP, 2800–2600 cal yr BP, 1600–1400 cal yr BP, and 700–100 cal yr BP, and these climate anomalies were also recorded elsewhere on the QTP. We suggest that the changes in temperature and ISM intensity on the southern QTP over the past 4400 years were modulated by changes in summer insolation and solar activity. These changes affected the sea surface temperature (SST) over the tropical Pacific and Indian Ocean regions, and they were linked to a positive phase of the El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), which weakened the ISM intensity in the Drigo Co area. Additionally, due to increased evaporation related to high temperatures, combined with intensified grazing activities over the past ∼200 years, the lake level has fallen, and the vegetation cover has decreased. As global temperatures continue to rise, the alpine steppe in the Drigo Co area may increase and the vegetation density may gradually decrease, and at the same time the regional ecological environment may gradually deteriorate.

Temperature and Flow Control Organic Carbon Metabolism in Boreal Headwater Streams

AbstractMetabolism in stream ecosystems alters the fate of organic carbon (OC) received from surrounding landscapes, but our understanding of in‐stream metabolic processes in boreal ecosystems remains limited. Determining the factors that regulate OC metabolism will help predict how the C balance of boreal streams may respond to future environmental change. In this study, we addressed the question: what controls OC metabolism in boreal headwater streams draining catchments with discontinuous permafrost? We hypothesized that metabolism is collectively regulated by OC reactivity, phosphorus availability, and temperature, with discharge modulating each of these conditions. We tested these hypotheses using a combination of laboratory experiments and whole‐stream ecosystem metabolism measurements throughout the Caribou‐Poker Creeks Research Watershed (CPCRW) in Interior Alaska, USA. In the laboratory experiments, respiration and dissolved OC (DOC) removal were both co‐limited by the supply of reactive C and phosphorus, but temperature and residence time acted as stronger controls of DOC removal. Ecosystem respiration (ER) was largely predicted by discharge and site, with some variance explained by gross primary production (GPP) and temperature. Both ER and GPP varied inversely with watershed permafrost extent, with an inverse relationship between temperature and permafrost extent providing one plausible explanation. Our results provide some of the first evidence of a functional response to permafrost thaw in stream ecosystems and suggest the role of metabolism in landscape C cycling may increase as climate change progresses.

Patterns and controls of leaf litter nitrogen and phosphorus of broad-leaved tree species across and within the tropics and the extra-tropics

Leaf litter nitrogen (N) and phosphorus (P), as the final products reflecting the foliar nutrient status after resorption, strongly influence forest production and nutrient cycling. However, our nuanced understanding of their general patterns and controls is still lacking, and whether differential regulatory mechanisms exist between climatic zones remains largely incomplete, which introduces substantial uncertainty in the comprehension of net ecosystem productivity and nutrient cycling. Here, we aimed to evaluate patterns of leaf litter N and P concentrations of broad-leaved tree species, and further quantify their controls from climatic, soil physical, soil chemical, and green foliar nutrient factors across and within the tropics and extra-tropics by updating a global dataset comprising 1171 records from 159 studies. We found that tropical tree species exhibited higher leaf litter N concentrations but lower leaf litter P concentrations than extra-tropical tree species. In contrast to previous findings, the effects of climatic and edaphic variables on leaf litter N and P concentrations are more pronounced in the tropics than in the extra-tropics. Different from past bivariate analyses of climate-nutrient relationships for leaf litter, climate exerted more indirect effects on leaf litter N and P concentrations through soil texture, hydrology, nutrient availability, and green foliar nutrients. We also observed direct effects of green foliar N and P concentrations on leaf litter N and P concentrations enhanced from tropical to extra-tropical zones. Overall, this study refines our understanding of differential controls over leaf litter N and P concentrations across climatic zones and highlights the crucial yet often overlooked role of soil physical and chemical properties. These insights further underscore the urgent need to integrate multiple climatic, edaphic, and green foliar nutrient variables into geographically explicit biogeochemical models to improve our understanding of leaf litter-driven forest nutrient cycling in response to future environmental changes for different climatic zones.

Grass leaf structural and stomatal trait responses to climate gradients assessed over the 20th century and across the Great Plains, USA.

Abstract. Using herbarium specimens spanning 133 years and field-collected measurements, we assessed intraspecific trait (leaf structural and stomatal) variability from grass species in the Great Plains of North America. We focused on two widespread, closely related grasses from the tribe Paniceae: Dichanthelium oligosanthes subsp. scribnerianum (C3) and Panicum virgatum (C4). Thirty-one specimens per taxon were sampled from local herbaria from the years 1887 to 2013 to assess trait responses across time to changes in atmospheric [CO2] and growing season precipitation and temperature. In 2021 and 2022, the species were measured from eight grasslands sites to explore how traits vary spatially across natural continental precipitation and temperature gradients. Δ13C increased with atmospheric [CO2] for D. oligosanthes but decreased for P. virgatum, likely linked to increases in precipitation in the study region over the past century. Notably, this is the first record of decreasing Δ13C over time for a C4 species illustrating 13C linkages to climate. As atmospheric [CO2] increased, C:N increased and δ15N decreased for both species and %N decreased for D. oligosanthes. Across a large precipitation gradient, D. oligosanthes leaf traits were more responsive to changes in precipitation than those of P. virgatum. In contrast, only two traits of P. virgatum responded to increases in temperature across a gradient: specific leaf area (increase) and leaf dry matter content (decrease). The only shared significant trend between species was increased C:N with precipitation. Our work demonstrates that these closely related grass species with different photosynthetic pathways exhibited various trait responses across temporal and spatial scales, illustrating the key role of scale of inquiry for forecasting leaf trait responses to future environmental change.

Are Nature-based Solutions for Built Heritage Conservation Resilient to Climate Change? The Response of Grass-based Soft Caps in Britain and Ireland to Future Climate Scenarios

ABSTRACT Nature-based solutions (NbS) offer an exciting opportunity to work with nature to conserve heritage sites and objects. Soft capping is a novel form of NbS used commonly in Britain and Ireland to help conserve ruined and free-standing walls; soil and vegetation is placed on the wall head to help reduce deterioration by buffering thermal fluctuations and regulating moisture. While this conservation practice has proved cheaper and more effective at reducing deterioration than traditional hard capping, soft caps need to be resilient to future environmental changes. Previous research has shown that the sedum species commonly used in soft caps are vulnerable to climate change. Thus, following feedback from an interactive webinar with practicing heritage professionals, here we assess the climate resilience of four grass species commonly found in western Europe as possible soft-capping species: Festuca rubra (red fescue), Poa pratensis (smooth meadow-grass), Catapodium rigidum (fern-grass) and Poa annua (annual meadow-grass). We use species distribution modelling (Maxent) to assess the likelihood of species survival by mid and end century based on presence probabilities derived using three climate models (HadGEM3-GC31-LL, IPSL-CM6A-LR, and MIROC6). Results show that all four species are resilient under mid-century projections, and P. annua proved resilient under all scenarios. Therefore, using turf-based soft caps incorporating one or more of these grass species could enhance the future resilience of this conservation technique. Given the growing interest in the use of nature-based approaches to heritage conservation, our study represents an important attempt to account for and adapt to a changing climate.

Global invasion risk assessment of Lantana camara, a highly invasive weed, under future environmental change

Invasion risk assessments are essential for making informed decisions, allocating resources, and implementing targeted strategies to prevent or minimize the harmful effects of invasive species on native biodiversity, agricultural productivity, and natural ecosystems. In this study, the random forest algorithm was used to assess the spatial invasion risk of Lantana camara, one of the world’s top 100 worst invasive weeds, across all continents under current and future environmental conditions. The current invasion risk was relatively high on four continents (i.e., Africa, Australia, Oceania, and South America) within approximately 35°N and 35°S latitude, estimated to cover at least 68.98 % of the total land surface. Furthermore, projections for future environmental changes suggested a substantial increase in invasion risk across all continents, with the most significant changes (251.52 %) observed in Europe compared with current invasion levels. Additionally, invasion risk was predicted to extend beyond 35°N latitude. Categorizing 200 countries and territories into distinct risk levels, 27 countries had current invasion potential, and introduction and establishment was predicted in 114 countries. Moreover, at least 45 countries, including Canada, India, Italy, and United States, were projected to transition from no or low invasion risk to high invasion risk and 28 countries had a risk increase of over 50 %. Current study provides valuable insights into the global invasion risk posed by L. camara. These results are expected to be of great utility for invasive weed management, facilitating the development of control and sustainable management strategies for this notorious weed at both global and local scales.

The accuracy of predicting maladaptation to new environments with genomic data.

Rapid environmental change poses unprecedented challenges to species persistence. To understand the extent that continued change could have, genomic offset methods have been used to forecast maladaptation of natural populations to future environmental change. However, while their use has become increasingly common, little is known regarding their predictive performance across a wide array of realistic and challenging scenarios. Here, we evaluate the performance of currently available offset methods (gradientForest, the Risk-Of-Non-Adaptedness, redundancy analysis with and without structure correction and LFMM2) using an extensive set of simulated data sets that vary demography, adaptive architecture and the number and spatial patterns of adaptive environments. For each data set, we train models using either all, adaptive or neutral marker sets and evaluate performance using in silico common gardens by correlating known fitness with projected offset. Using over 4,849,600 of such evaluations, we find that (1) method performance is largely due to the degree of local adaptation across the metapopulation (LA), (2) adaptive marker sets provide minimal performance advantages, (3) performance within the species range is variable across gardens and declines when offset models are trained using additional non-adaptive environments and (4) despite (1) performance declines more rapidly in globally novel climates (i.e. a climate without an analogue within the species range) for metapopulations with greater LA than lesser LA. We discuss the implications of these results for management, assisted gene flow and assisted migration.

Elevated CO2 and Nitrogen Supply Boost N Use Efficiency and Wheat (T. aestivum cv. Yunmai) Growth and Differentiate Soil Microbial Communities Related to Ammonia Oxidization.

Elevated CO2 levels (eCO2) pose challenges to wheat (Triticum aestivum L.) growth, potentially leading to a decline in quality and productivity. This study addresses the effects of two ambient CO2 concentrations (aCO2, daytime/nighttime = 410/450 ± 30 ppm and eCO2, 550/600 ± 30 ppm) and two nitrogen (N) supplements (without N supply-N0 and with 100 mg N supply as urea per kg soil-N100) on wheat (T. aestivum cv. Yunmai) growth, N accumulation, and soil microbial communities related to ammonia oxidization. The data showed that the N supply effectively mitigated the negative impacts of eCO2 on wheat growth by reducing intercellular CO2 concentrations while enhancing photosynthesis parameters. Notably, the N supply significantly increased N concentrations in wheat tissues and biomass production, thereby boosting N accumulation in seeds, shoots, and roots. eCO2 increased the agronomic efficiency of applied N (AEN) and the physiological efficiency of applied N (PEN) under N supply. Plant tissue N concentrations and accumulations are positively related to plant biomass production and soil NO3--N. Additionally, the N supply increased the richness and evenness of the soil microbial community, particularly Nitrososphaeraceae, Nitrosospira, and Nitrosomonas, which responded differently to N availability under both aCO2 and eCO2. These results underscore the importance and complexity of optimizing N supply and eCO2 for enhancing crop tissue N accumulation and yield production as well as activating nitrification-related microbial activities for soil inorganic N availability under future global environment change scenarios.

Interventions for resilient nature‐based solutions: An ecological perspective

Abstract Nature‐based solutions (NbS) have emerged at the science, policy and practitioner interface to address environmental challenges facing society. NbS involve people working with nature to protect, restore or manage ecosystems. Yet NbS vary to the extent they support biological diversity which has implications for ecological resilience. We reviewed how ecological resilience has been conceptualised in the NbS literature. The literature included reference to both resilience to specific disturbances and general resilience to future environmental change. We found reporting of resilience mechanisms was limited except for afforestation efforts where there is increasing recognition of the role of species diversity in contributing to resilience. Reporting was limited for resilience mechanisms that operate within species and populations (e.g. genetic diversity) and at the landscape scale (e.g. connectivity). Resistance was overlooked despite the prevalence of NbS intended to address climate change. From the broader ecological literature, we distilled resilience mechanisms that have been identified for native and experimental ecosystems and suggested interventions for the emergence of resilience mechanisms in NbS. Synthesis. Interventions to conserve biodiversity such as retaining and restoring ecosystems, are critical given that biodiversity, within and across scales of biological organisation, underpins several ecological resilience mechanisms in NbS.

Differences in Metabolic Characteristics of Rhizosphere Fungal Community of Typical Arboreal, Shrubby and Herbaceous Species in Oasis of Arid Region.

Populus euphratica, Tamarix ramosissima, and Sophora alopecuroides are, respectively, typical arboreal, shrubby, and herbaceous species in oases of arid regions. It is important to study the difference in metabolic characteristics of the rhizosphere fungal community of these plant species and their relationships with soil factors for the preservation of delicate arid oasis ecosystems with future environmental changes. In this study, we, respectively, collected 18 rhizosphere soil samples of P. euphratica, T. ramosissima, and S. alopecuroides to explore the difference in rhizosphere fungal metabolic characteristics of different plant life forms and their underlying driving factors. The results showed that (1) soil physicochemical properties (including soil water content, pH, etc.) were significantly different among different plant species (p < 0.05). (2) Rhizosphere fungal metabolic characteristics were significantly different between S. alopecuroides and T. ramosissima (ANOSIM, p < 0.05), which was mainly caused by the different utilization of carboxylic carbon. (3) The RDA showed that the main driving factors of the variations in rhizosphere fungal metabolic characteristics were different among different plant species. The main explanatory variables of the variations in the metabolic characteristics of the rhizosphere fungal community were carbon to nitrogen ratio (23%) and available potassium (17.4%) for P. euphratica, while soil organic carbon (23.1%), pH (8.6%), and total nitrogen (8.2%) for T. ramosissima, and soil clay content (36.6%) and soil organic carbon (12.6%) for S. alopecuroides. In conclusion, the variations in rhizosphere fungal metabolic characteristics in arid oases are dominantly affected by soil factors rather than plant life forms.

Net primary productivity and litter decomposition rates in two distinct Amazonian peatlands.

Measurements of net primary productivity (NPP) and litter decomposition from tropical peatlands are severely lacking, limiting our ability to parameterise and validate models of tropical peatland development and thereby make robust predictions of how these systems will respond to future environmental and climatic change. Here, we present total NPP (i.e., above- and below-ground) and decomposition data from two floristically and structurally distinct forested peatland sites within the Pastaza Marañón Foreland Basin, northern Peru, the largest tropical peatland area in Amazonia: (1) a palm (largely Mauritia flexuosa) dominated swamp forest and (2) a hardwood dominated swamp forest (known as 'pole forest', due to the abundance of thin-stemmed trees). Total NPP in the palm forest and hardwood-dominated forest (9.83 ± 1.43 and 7.34 ± 0.84 Mg C ha-1 year-1, respectively) was low compared with values reported for terra firme forest in the region (14.21-15.01 Mg C ha-1 year-1) and for tropical peatlands elsewhere (11.06 and 13.20 Mg C ha-1 year-1). Despite the similar total NPP of the two forest types, there were considerable differences in the distribution of NPP. Fine root NPP was seven times higher in the palm forest (4.56 ± 1.05 Mg C ha-1 year-1) than in the hardwood forest (0.61 ± 0.22 Mg C ha-1 year-1). Above-ground palm NPP, a frequently overlooked component, made large contributions to total NPP in the palm-dominated forest, accounting for 41% (14% in the hardwood-dominated forest). Conversely, Mauritia flexuosa litter decomposition rates were the same in both plots: highest for leaf material, followed by root and then stem material (21%, 77% and 86% of mass remaining after 1 year respectively for both plots). Our results suggest potential differences in these two peatland types' responses to climate and other environmental changes and will assist in future modelling studies of these systems.

Proxies of hypoxia and submarine groundwater discharge in the coastal ocean: Foraminiferal shell chemical perspectives

Coastal marine settings are important in terms of geochemical cycles and biological productivity. Climate change is predicted to affect coastal environment via hypoxia and Submarine Groundwater Discharge (SGD). Appropriate proxies could help to better understand oxygenation history and the role of SGD in regulating hypoxia. This would also benefit prediction of potential outcomes of future environmental changes. The sensitivity of benthic foraminiferal shell chemistry to environmental conditions opens the possibility to use them as proxies of coastal hypoxia and SGD. We report here that the average Mn/Ca ratios in tests of living benthic foraminiferal shells in the Changjiang River Estuary (CJE) is 2.3 times higher during hypoxia periods than under well-mixed conditions. In addition, Ba/Ca ratios in living benthic foraminiferal shells co-varied well with radon-inferred SGD signals. Fluctuations of Mn/Ca and Ba/Ca ratios in tests of a single foraminiferal shell along successive chambers corresponds well with seasonal-scale variations of hypoxia and SGD. We suggest that Mn/Ca and Ba/Ca ratios within intra-tests of benthic foraminifer can provide a reliable proxy for past hypoxia and SGD trends.

Soils of two Antarctic Dry Valleys exhibit unique microbial community structures in response to similar environmental disturbances

BackgroundIsolating the effects of deterministic variables (e.g., physicochemical conditions) on soil microbial communities from those of neutral processes (e.g., dispersal) remains a major challenge in microbial ecology. In this study, we disturbed soil microbial communities of two McMurdo Dry Valleys of Antarctica exhibiting distinct microbial biogeographic patterns, both devoid of aboveground biota and different in macro- and micro-physicochemical conditions. We modified the availability of water, nitrogen, carbon, copper ions, and sodium chloride salts in a laboratory-based experiment and monitored the microbial communities for up to two months. Our aim was to mimic a likely scenario in the near future, in which similar selective pressures will be applied to both valleys. We hypothesized that, given their unique microbial communities, the two valleys would select for different microbial populations when subjected to the same disturbances.ResultsThe two soil microbial communities, subjected to the same disturbances, did not respond similarly as reflected in both 16S rRNA genes and transcripts. Turnover of the two microbial communities showed a contrasting response to the same environmental disturbances and revealed different potentials for adaptation to change. These results suggest that the heterogeneity between these microbial communities, reflected in their strong biogeographic patterns, was maintained even when subjected to the same selective pressure and that the ‘rare biosphere’, at least in these samples, were deeply divergent and did not act as a reservoir for microbiota that enabled convergent responses to change in environmental conditions.ConclusionsOur findings strongly support the occurrence of endemic microbial communities that show a structural resilience to environmental disturbances, spanning a wide range of physicochemical conditions. In the highly arid and nutrient-limited environment of the Dry Valleys, these results provide direct evidence of microbial biogeographic patterns that can shape the communities’ response in the face of future environmental changes.

Functional responses of understory plants to natural disturbance-based management in eastern and western Canada.

Natural disturbance-based management (NDBM) is hypothesized to maintain managed forest ecosystem integrity by reducing differences between natural and managed forests. The effectiveness of this approach often entails local comparisons of species composition or diversity for a variety of biota from managed and unmanaged forests. Understory vegetation is regularly the focus of such comparison because of its importance in nutrient cycling, forest regeneration, and for wildlife. However, larger scale comparisons between regions with distinct species assemblages may require a trait-based approach to better understand understory responses to disturbance. We compared the long-term effects of retention harvesting on understory vegetation in two large experimental study sites located in eastern and western regions of the Canadian boreal forest. These sites included the Sylviculture en Aménagement Forestier Ecosystémique (SAFE) experiment and the Ecosystem Management Emulating Natural Disturbance (EMEND) experiment, located in the eastern and western regions of Canada, respectively. EMEND and SAFE share common boreal understory species but have distinct tree communities, soils, and climate. Both experiments were designed to evaluate how increasing tree retention after harvest affects biodiversity. Here, we examined taxonomic richness, functional diversity, and functional composition (using community trait mean values) of understory plant communities, and also examine intraspecific trait variability (ITV) for five species common and abundant in both experiments. We observed the limited impacts of retention level on richness, functional diversity, and functional composition of understory plants 20 years postharvest. However, ITV of leaf morphological traits varied between retention levels within each experiment, depending on the species identity. Common species had different functional responses to retention level, showing species-specific reactions to environmental variation. Our result suggests that understory plant communities in the boreal forest achieve resilience to disturbance both in terms of interspecific and intraspecific functional trait diversity. Such diversity may be key to maintaining understory biodiversity in the face of future disturbances and environmental change. Our results reveal the significance of ITV in plant communities for understanding responses to forest harvesting and the importance of choosing appropriate traits when studying species responses to the environment.