Wet Sites Research Articles

Mosquito diversity and abundance in English wetlands – empirical evidence to guide predictions for wetland suitability for mosquitoes (Diptera: Culicidae)

Abstract The absence of habitat-based guidance for wetland managers on the British mosquito assemblages has in recent years prevented development of the ecological aspect of medical entomology in the UK. This has been particularly relevant in the context of emerging mosquito-borne disease and the creation of wetlands for biodiversity and flood-alleviation goals. This study aimed to provide empirically derived habitat-based predictions in order to assess the suitability of English wetland habitats for mosquitoes. Entomological field data on mosquito density and diversity were collected at 12 English wetlands in 2017 and 2018 using immature and adult mosquito surveys. Wetlands were chosen representing a number of wetland categories that included coastal, urban, wet woodland and established freshwater wetlands to identify key species and functional groups to inform predictions of mosquitoes by aquatic habitat type. Nineteen species were recorded from eight functional groups, totalling 38,577 adult female (19 mosquito species groups) and ~2,000 immature mosquitoes in 13 aquatic habitat types. Approximately 90% of all trapped mosquitoes were attributed to one of five species groups. The most common species were: Aedes (Och.) caspius (Pallas, 1771) (~35% of all mosquitoes), associated with coastal estuarine and flooded grassland sites, Ae. cantans/annulipes (19.7%) in wet woodland field sites, Anopheles claviger (16.2%) and Coquillettidia richiardii (12.6%) with the widest occurrence, found in nearly all field sites, and Ae. detritus (6.9%) in brackish field sites. Across the study, adult mosquito activity increased from week 21 with wet woodland Aedes mosquitoes, until week 40 with open-flood water species, with greatest diversity of species during weeks 23–30. The resulting data inform efforts towards developing predictive tools for non-entomologists to accurately predict the presence and abundance of British mosquitoes in a given habitat, using local knowledge of seasonal aquatic habitats.

Fine Root Density Dynamics and Carbon Stock of Eucalyptus spp.: Interplay of Age, Genotype, and Edaphoclimatic Conditions.

Roots play a fundamental role in forest ecosystems, but obtaining samples from deep layers remains a challenging process due to the methodological and financial efforts required. In our quest to understand the dynamics of Eucalyptus roots, we raise three fundamental questions. First, we inquire about the average extent of the roots of two contrasting Eucalyptus genotypes. Next, we explore the factors that directly influence the growth and depth of these roots, addressing elements such as soil type, climate, and water availability. Lastly, we investigate how the variation in Eucalyptus species may impact root growth patterns, biomass, and carbon stock. In this study, we observed that the maximum root depth increased by an average of 20% when genotypes were grown on sites with higher water availability (wet site). E. urophylla stands had a higher biomass and carbon stock (5.7 Mg C ha-1) of fine roots when cultivated on dry sites (annual rainfall~727 mm) than the wet sites (annual rainfall~1590 mm). In E. grandis × E. camaldulensis stands, no significant differences were observed in the stock of fine root biomass (3.2 Mg C ha-1) between the studied environments. Our results demonstrated that genotypes with greater drought tolerance (E. grandis × E. camaldulensis) tend to maintain higher stocks of fine root biomass (3.2-6.3 Mg ha-1) compared to those classified as plastic (E. urophylla), regardless of the edaphoclimatic conditions of the cultivation site. Finally, our research helps understand how Eucalyptus trees adapt to their environment, aiding sustainable forest management and climate change mitigation. We also provide a practical tool to estimate underground biomass, assisting forest managers and policymakers in ensuring long-term forest sustainability.

Limited intraspecific variation in drought resistance along a pronounced tropical rainfall gradient

Assessing within-species variation in response to drought is crucial for predicting species' responses to climate change and informing restoration and conservation efforts, yet experimental data are lacking for the vast majority of tropical tree species. We assessed intraspecific variation in response to water availability across a strong rainfall gradient for 16 tropical tree species using reciprocal transplant and common garden field experiments, along with measurements of gene flow and key functional traits linked to drought resistance. Although drought resistance varies widely among species in these forests, we found little evidence for within-species variation in drought resistance. For the majority of functional traits measured, we detected no significant intraspecific variation. The few traits that did vary significantly between drier and wetter origins of the same species all showed relationships opposite to expectations based on drought stress. Furthermore, seedlings of the same species originating from drier and wetter sites performed equally well under drought conditions in the common garden experiment and at the driest transplant site. However, contrary to expectation, wetter-origin seedlings survived better than drier-origin seedlings under wetter conditions in both the reciprocal transplant and common garden experiment, potentially due to lower insect herbivory. Our study provides the most comprehensive picture to date of intraspecific variation in tropical tree species' responses to water availability. Our findings suggest that while drought plays an important role in shaping species composition across moist tropical forests, its influence on within-species variation is limited.

From current to potential distribution: the case of Taxus baccata(Taxaceae, Pinales) on the island of Sardinia (Italy)

Taxus baccata is a relic-declining species, especially at the southern edge of its natural distribution. On the Island of Sardinia, we found 237 locations where yews grow, being indifferent to substrates, preferring moist sites with northern aspects and with an elevation range of 695–1,225 m a.s.l. We applied the Maximum Entropy algorithm (MaxEnt), using 202 field-based sites and 19 bioclimatic variables, to model the present potential distribution. Our model showed high levels of predictive performances with significant values of AUC (training, 0.962; test, 0.963). Annual precipitation, mean temperature of the warmest month and isothermality were the key drivers for the distribution of yew in Sardinia. The response curves showed that T. baccata prefers annual mean temperatures ranging from 8.65 to 12.55 °C and annual mean precipitation from 770 to 1,085 mm. Most potential suitable conditions were found in northern and central Sardinia. We also modelled future habitat suitability for T. baccata under two different scenarios (ssp245 and ssp585), highlighting a predicted drastic reduction, up to >95% in the worst scenario, of the habitat suitability for yews by the end of this century. This is related to climate change and poses increasing concerns about the future of yews in Sardinia.

Atmospheric wet and dry phosphorus deposition in Lake Erhai, China

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai.

Identifying drivers of non-stationary climate-growth relationships of European beech

The future performance of the widely abundant European beech (Fagus sylvatica L.) across its ecological amplitude is uncertain. Although beech is considered drought-sensitive and thus negatively affected by drought events, scientific evidence indicating increasing drought vulnerability under climate change on a cross-regional scale remains elusive. While evaluating changes in climate sensitivity of secondary growth offers a promising avenue, studies from productive, closed-canopy forests suffer from knowledge gaps, especially regarding the natural variability of climate sensitivity and how it relates to radial growth as an indicator of tree vitality. Since beech is sensitive to drought, we in this study use a drought index as a climate variable to account for the combined effects of temperature and water availability and explore how the drought sensitivity of secondary growth varies temporally in dependence on growth variability, growth trends, and climatic water availability across the species' ecological amplitude.Our results show that drought sensitivity is highly variable and non-stationary, though consistently higher at dry sites compared to moist sites. Increasing drought sensitivity can largely be explained by increasing climatic aridity, especially as it is exacerbated by climate change and trees' rank progression within forest communities, as (co-)dominant trees are more sensitive to extra-canopy climatic conditions than trees embedded in understories. However, during the driest periods of the 20th century, growth showed clear signs of being decoupled from climate. This may indicate fundamental changes in system behavior and be early-warning signals of decreasing drought tolerance. The multiple significant interaction terms in our model elucidate the complexity of European beech's drought sensitivity, which needs to be taken into consideration when assessing this species' response to climate change.

The interplay between climate and bedrock type determines litter decomposition in temperate forest ecosystems

At regional scale, it is dominantly considered in the European literature that litter decomposition is higher in soils from calcareous than siliceous bedrocks because of higher pH in the former forest ecosystems. We tested the alternative hypothesis that this should rather be due to differences in physical characteristics of the bedrock, with likely higher decomposition on calcareous than siliceous bedrocks in wet climates because of more favourable texture in the former and nutrient leaching in the latter, and the opposite in dry climates because of higher drought stress in calcareous soils. We assessed, four consecutive years with contrasting climates, the litter decomposition of a unified litter of Abies alba needles with the litterbag method in 70 forest sites located on both bedrocks and in wet oceanic and dry continental climates of the European Alps and the Pyrenees. Average and annual climate data were analysed with principal component analyses and the effects of bedrock type, average and annual climate drought stresses on litter decomposition were analysed, separately in the Alps and the Pyrenees, with analyses of variance. We found, in both mountain ranges, a highly significant bedrock type by average climate drought stress interaction on litter decomposition, due to a strong decrease in litter decomposition from wet oceanic to dry continental sites on calcareous bedrocks only. Although litter decomposition did not change over all years in siliceous sites with increasing climate drought stress, it increased during wet years in the dry continental sites only, in particular in the Pyrenees where interannual climate variability was higher. Together our results strongly support the physical hypothesis and not the chemical hypothesis. We argue that the chemical hypothesis was proposed based on studies only conducted in low elevation wet temperate sites comparing mull humus types from deciduous forests on calcareous soils to mor and moder humus types from evergreen forests on highly sandy siliceous bedrocks. Our study conducted on a wider range of climate and bedrock conditions bring strong evidence that litter decomposition is rather dependent on the physical characteristics of the bedrocks.

Restoration thinning accelerates small tree growth but may slow large tree growth in a multi‐age flood‐dependent forest

Abstract Large tree decline is occurring globally with critical implications for biodiversity and carbon sequestration. Restoration thinning is a potential management action to accelerate tree growth and promote large tree development in forests, yet trials have been limited and results have been mixed. We conducted a large‐scale trial to determine whether restoration thinning could accelerate the development of large trees in river red gum forests in Australia that had experienced widespread woody thickening and a decline of large trees due to long‐term commercial timber harvesting and river regulation. Thinning was conducted on 44 9‐ha plots by removing trees <40 cm diameter from around retained trees at a range of spacings. Initial tree densities ranged from ~260 to ~1860 trees per ha and 8%–86% of trees were removed by thinning. We monitored 1980 trees prior to thinning, and annually for 5 years post‐thinning. We tested the effects of thinning intensity on diameter growth of different sized trees and explored whether long‐ and short‐term water availability affected outcomes. Thinning promoted the growth of small trees <56 cm diameter, especially in drier sites during wet years. Higher thinning intensities reduced the growth rates of large trees (no smaller than 79.5 cm diameter) in wetter sites. For medium‐ and large‐sized trees, long‐ and short‐term water availability were stronger drivers of tree growth than competition due to tree density. Synthesis and applications. Restoration thinning may accelerate tree growth in young river red gum forests where all trees are small. But restoration thinning may be ineffective or detrimental in multi‐aged forests where the goal is to promote the growth rates of trees that are already medium to large in size.

Registration of ‘Independence’ switchgrass

AbstractSwitchgrass (Panicum virgatum L.), a valuable forage and bioenergy crop, is established more easily than other native perennial warm‐season grasses, but its establishment is still slower than that of annual crops. Vigorous switchgrass establishment is crucial for achieving its full potential yield and for effectively competing with weeds for water and nutrient availability. To satisfy this demand, ‘Independence’ (Reg. no. CV‐295, PI 704577) switchgrass was developed at the University of Illinois at Urbana‐Champaign. Independence was selected for establishment vigor, winter survivorship, and high biomass yield for two cycles from ‘Kanlow’. It is characterized by rapid establishment, robust seedling growth, and the capacity to achieve peak production by the second year. Independence is well adapted to USDA hardiness zones 5b–7b. In field experiments conducted from 2016 to 2017, averaged over seven locations and all years, Independence annually yielded 13 Mg ha−1 of biomass, outperforming ‘Cave‐in‐Rock’ by 31%, ‘Liberty’ by 15%, ‘Shawnee’ by 42%, ‘Summer’ by 81%, and ‘Sunburst’ by 129%. In wet marginal sites in Illinois from 2020 to 2023, Independence exhibited an average biomass yield of 12 Mg ha−1, outperforming Shawnee by 31%, Liberty by 27%, and Kanlow by 19%, indicating its potential use on less productive land for annual crops. Independence was publicly released by the University of Illinois at Urbana‐Champaign in October 2021.

Geographic variation in the acoustic signals of lesser treefrogs Dendropsophus minutus (Anura, Hylidae)

Biological sound archives are a major source to investigate geographic variation in animal acoustic signals and their evolutionary drivers. The acoustic signals of anuran species with wide distribution ranges often vary geographically as a result of isolation by distance and climate amongst other factors. We examined whether the acoustic structure of call notes would vary geographically in lesser treefrogs Dendropsophus minutus using recordings from bioacoustics repositories. We also tested whether climate (mean annual temperature and annual precipitation) drive geographic variation in those signals. The acoustic distance was unrelated to geographic distance, suggesting that isolation by distance solely cannot explain geographic variation in call structure. Overall, lesser treefrogs uttered call notes with lower frequencies and bandwidths in the west of their range. In addition, frogs produced shorter call notes in hotter, wetter sites and narrow-bandwidth notes in hotter environments. We suggest that frogs produce more calls (not measured here) of shorter durations to maximize transmission and minimize the metabolic costs of calling at high air temperatures. We also suggest that hotter environments favor the propagation of lower-bandwidth calls. This study reinforces the feasibility and power of citizen science and acoustic data repositories for understanding the evolution of anuran acoustic signals.

Inferred drought-induced plant allocation shifts and their impact on drought legacy at a tropical forest site.

While droughts predominantly induce immediate reductions in plant carbon uptake, they can also exert long-lasting effects on carbon fluxes through associated changes in leaf area, soil carbon, etc. Among other mechanisms, shifts in carbon allocation due to water stress can contribute to the legacy effects of drought on carbon fluxes. However, the magnitude and impact of these allocation shifts on carbon fluxes and pools remain poorly understood. Using data from a wet tropical flux tower site in French Guiana, we demonstrate that drought-induced carbon allocation shifts can be reliably inferred by assimilating Net Biosphere Exchange (NBE) and other observations within the CARbon DAta MOdel fraMework. This model-data fusion system allows inference of optimized carbon and water cycle parameters and states from multiple observational data streams. We then examined how these inferred shifts affected the duration and magnitude of drought's impact on NBE during and after the extreme event. Compared to a static allocation scheme analogous to those typically implemented in land surface models, dynamic allocation reduced average carbon uptake during drought recovery by a factor of 2.8. Additionally, the dynamic model extended the average recovery time by 5 months. The inferred allocation shifts influenced the post-drought period by altering foliage and fine root pools, which in turn modulated gross primary productivity and heterotrophic respiration for up to a decade. These changes can create a bust-boom cycle where carbon uptake is enhanced some years after a drought, compared to what would have occurred under drought-free conditions. Overall, allocation shifts accounted for 65% [45%-75%] of drought legacy effects in modeled NBE. In summary, drought-induced carbon allocation shifts can play a substantial role in the enduring influence of drought on cumulative land-atmosphere CO2 exchanges and should be accounted for in ecosystem models.

Challenges of Including Wet Grasslands with Variable Groundwater Tables in Large-Area Crop Production Simulations

Large-scale assessments of agricultural productivity necessitate integrated simulations of cropland and grassland ecosystems within their spatiotemporal context. However, simultaneous simulations face limitations due to assumptions of uniform species distribution. Grasslands, particularly those with shallow groundwater tables, are highly sensitive to water availability, undergoing rapid species composition changes. We hypothesised that predicting above-ground biomass (AGB) remains challenging due to these dynamic responses. Ten years of data from four lysimeters at a German wet grassland site, with varying water table treatments, was utilised to test this hypothesis. Correlation analysis revealed a strong positive indirect effect of the water regime on AGB, with a one-year time lag (r = 0.97). The MONICA model initially exhibited fair agreement (d = 0.69) in simulating Leaf-Area-Index (LAI) but performed poorly in replicating AGB (d = 0.3). After removing the species composition change effect from the LAI and AGB datasets, the simulation notably improved, with the overall relative root mean square error (rRMSE) of AGB decreasing from 1.55 to 0.90 between the first and second simulations. This demonstrates MONICA’s ability to predict grass growth patterns amidst changing water supply levels for constant species composition. However, it needs a competition model to capture biomass growth changes with varying water supply.

Microhabitat humidity rather than food availability drives thermo‐hydroregulation responses to drought in a lizard

The regulation of energy, water and thermal balance involves integrated processes that should drive ecological responses of ectotherms to climate change. Functional tradeoffs between thermoregulation and hydroregulation are exacerbated during hot or dry spells, but how microhabitat hydric properties and trophic resource availability influence these tradeoffs remains unknown. Here, we investigated the effects of microhabitat humidity and food availability on thermo‐hydroregulation strategies in the ground‐dwelling common lizard Zootoca vivipara during a simulated hot and dry spell event. We exposed lizards to a five‐day long acute water restriction in hot conditions in the laboratory and manipulated hydric quality of the retreat site (wet or dry shelter) as well as food availability (ad libitum food or food deprivation). Water restriction and food deprivation caused physiological responses such as muscle catabolism and mobilization of caudal energy reserves. Lizards also developed behavioural strategies to conserve water or energy via decreased thermoregulation effort, higher shelter use and increased eye closure behaviours through time. These physiological and behavioural changes were importantly buffered by the presence of a wet shelter but not by food availability. A wet retreat site reduced the behavioural conflicts between thermoregulation and hydroregulation, allowed lizards to maintain a better condition and reduced physiological dehydration. Instead, food intake did not play a major role in the regulation of hydration state and increased behavioural conflicts between thermoregulation and hydroregulation. A better consideration of thermo‐hydroregulation behaviours and microhabitat hydric quality is required to address ectotherm responses to future climate change.

Nontarget effects of pre‐emergent herbicides and a bioherbicide on soil resources, processes, and communities

Community‐type conversions, such as replacement of perennials by exotic annual grasses in semiarid desert communities, are occurring due to plant invasions that often create positive plant–soil feedbacks, which favor invaders and make restoration of native perennials difficult. Exotic annual grass control measures, such as pre‐emergent herbicides, can also alter soil ecosystems directly or indirectly (i.e. via the plant community), yet there are few studies on the topic in natural, non‐cropped landscapes. We asked how spray treatments applied to soil post‐fire with the intention of inhibiting invasive annual grasses (such as Bromus tectorum L.) and releasing existing native perennial grasses affected soil resources, a microbial process, and invertebrates in three climatically varied sagebrush steppe sites. Spray treatments included chemical herbicides (imazapic and rimsulfuron) that strongly affected plant communities and a bioherbicide (Pseudomonas fluorescens strain D7) that did not. Chemical herbicides increased soil mineral nitrogen in proportion to their negative effects on plant cover for 2 years after treatments in all sites and increased soil water and net N mineralization (measured at one site) but did not affect total carbon, nitrogen, or organic matter. Invertebrate responses to herbicides varied by site, and invertebrates increased with chemical herbicides at the highest, wettest site. We show that herbicide treatments can exacerbate pulses of mineral nutrients, which previous studies have shown can weaken ecosystem resistance to invasion. Thus, restoration strategies that increase the likelihood that desired plants can capture mineralized nutrients after herbicide application will likely be more successful.

Hydrological regimes and evaporative flux partitioning at the climatic ends of high mountain Asia

Abstract High elevation headwater catchments are complex hydrological systems that seasonally buffer water and release it in the form of snow and ice melt, modulating downstream runoff regimes and water availability. In High Mountain Asia (HMA), where a wide range of climates from semi-arid to monsoonal exist, the importance of the cryospheric contributions to the water budget varies with the amount and seasonal distribution of precipitation. Losses due to evapotranspiration and sublimation are to date largely unquantified components of the water budget in such catchments, although they can be comparable in magnitude to glacier melt contributions to streamflow. Here, we simulate the hydrology of three high elevation headwater catchments in distinct climates in HMA over 10 years using an ecohydrological model geared towards high-mountain areas including snow and glaciers, forced with reanalysis data. Our results show that evapotranspiration and sublimation together are most important at the semi-arid site, Kyzylsu, on the northernmost slopes of the Pamir mountain range. Here, the evaporative loss amounts to 28% of the water throughput, which we define as the total water added to, or removed from the water balance within a year. In comparison, evaporative losses are 19% at the Central Himalayan site Langtang and 13% at the wettest site, 24 K, on the Southeastern Tibetan Plateau. At the three sites, respectively, sublimation removes 15%, 13% and 6% of snowfall, while evapotranspiration removes the equivalent of 76%, 28% and 19% of rainfall. In absolute terms, and across a comparable elevation range, the highest ET flux is 413 mm yr−1 at 24 K, while the highest sublimation flux is 91 mm yr−1 at Kyzylsu. During warm and dry years, glacier melt was found to only partially compensate for the annual supply deficit.

The large‐scale restoration of fire and water regimes in Everglades National Park reveal little change in plant diversity along an elevational gradient

Quantifying the response of plant diversity to large‐scale restoration is essential for measuring management success. One of the world's largest restoration efforts began in 2000 in the Everglades ecosystem in Florida, United States, through the Comprehensive Everglades Restoration Plan. In coordination with ongoing fire management, this restoration effort aims to restore natural hydrologic and fire regimes in this dynamic ecosystem. Restored water and fire regimes in the Everglades interact along an elevational gradient between seasonally inundated marl prairie and frequently burned pine rockland on Long Pine Key in Everglades National Park. To determine the impact of management on plant community richness and composition, we resampled transects spanning the elevational gradient between marl prairie and pine rockland initially sampled prior to the implementation of current restoration efforts (circa 1997–1999). We measured percent plant cover and developed generalized linear mixed models to determine the effects of fire frequency, average water depth, and elevation on plant species richness and composition across the two time periods. Additionally, we used species‐level random effects to examine how individual species respond to each environmental variable. We failed to detect any systematic shifts in plant composition in response to fire and water management. However, we found that complex interactions between fire and water structure plant composition and maximize species richness along gradients of water depth and elevation, with low, moderate, and high burn frequencies increasing richness in wet, moderately wet, and dry sites, respectively.

Natural regeneration or tree planting in a tropical forest‐to‐pasture damaged area: which is more efficacious for soil ecosystem recovery?

This study assessed whether a natural regeneration or active tree‐planting reforestation strategy better restored the C and N‐cycle processes and associated microbiota within soils after 18 years in a Premontane Wet Life zone site in Monteverde, Costa Rica, compared to adjacent old secondary forest and pasture soils (both >60 years). Our findings apply to small‐scale restoration sites (<0.5 ha plots) commonly used in Monteverde. Both restoration strategies showed recovering soil C and N‐cycle processes with similar levels of TN, NH4+, NO3−, Biomass‐C, and efficiency of organic C use. Both strategies appeared to positively influence the recovery of the levels and community compositional stability of the Actinobacterial, Acidobacterial, N‐fixing (N‐Fixer) bacterial, ammonium‐oxidizing bacterial, and complex organic C‐degrading fungal communities. The main differences between the two strategies were that the tree‐planted and pasture soils had similar compositions of the Actinobacterial, N‐Fixer, and Fungal complex organic C degrader, while the natural regeneration and pasture soils had similar compositions of these groups and the Acidobacteria. However, the community compositions of all five microbial groups were different between restored forest and the old secondary forest soils. These results suggest that while the soil ecosystems from both reforestation strategies are recovering, after 18 years, there is still more recovery to occur. Lastly, possible indicators of post‐restoration soil ecosystem enhancement included increasing constancy of critical microbial group composition, efficiency of organic C conversion to biomass, Biomass‐C, NH4+, NO3−, and levels of Acidothermus, Acidobacteria subgroups 2, 3, and 5, Archaeorhizomyces, Anaeromyxobacter, Bradyrhizobium, Nitrosomonas, Flavobacterium, and Nitrospira.

Brine formation in cold desert, shallow groundwater systems: Antarctic Ca-Cl brine chemistry controlled by cation exchange, microclimate, and organic matter

Groundwater in the McMurdo Dry Valleys of Antarctica is commonly enriched in calcium and chloride, in contrast to surface and groundwater in temperate regions, where calcium chemistry is largely controlled by the dissolution of carbonates and sulfates. These Antarctic Ca-Cl brines have extremely low freezing points, which leads to moist soil conditions that persist unfrozen and resist evaporation, even in cold, arid conditions. Several hypotheses exist to explain these unusual excess-calcium solutions, including salt deliquescence and differential salt mobility and cation exchange. Although the cation exchange mechanism was shown to explain the chemistry of pore waters in permafrost cores from several meters depth, it has not been evaluated for near-surface groundwater and wetland features (water tracks) in which excess-calcium pore-water solutions are common. Here, we use soluble salt and exchangeable cation concentrations to determine whether excess calcium is present in water-track brines and if cation exchange could be responsible for calcium enrichment in these cold desert groundwaters. We show that calcium enrichment by cation exchange is not occurring universally across the McMurdo Dry Valleys. Instead, evidence of the present-day formation of Ca-Cl−rich brines by cation exchange is focused in a geographically specific location in Taylor Valley, with hydrological position, microclimate, soil depth, and organic matter influencing the spatial extent of cation exchange reactions. Up-valley sites may be too cold and dry for widespread exchange, and warm and wet coastal sites are interpreted to host sediments whose exchange reactions have already gone to completion. We argue that exchangeable cation ratios can be used as a signature of past freeze-concentration of brines and exchange reactions, and thus could be considered a geochemical proxy for past groundwater presence in planetary permafrost settings. Correlations between water-track organic matter, fine sediment concentration, and cation exchange capacity suggest that water tracks may be sites of enhanced biogeochemical cycling in cold desert soils and serve as a model for predicting how active layers in the Antarctic will participate in biogeochemical cycling during periods of future thaw.

Climate, host ontogeny and pathogen structural specificity determine forest disease distribution at a regional scale

Predicting forest health at a regional level is challenging as forests are simultaneously attacked by multiple pathogens. Usually, the impacts of each pathogen are studied separately, however, interactions between them can affect disease dynamics. Pathogens can interact directly by competing for the same niche, but also facilitate or suppress each other via indirect effects through the host. We studied 66 native Mediterranean Pinus nigra stands located in the Pyrenees which were affected by two pathogens with different structural specificity: Dothistroma pini causing Dothistroma needle blight and Diplodia sapinea causing Diplodia shoot blight. We explored the ecology of both pathogens and whether the diseases they caused had an impact on trees and recruits. No signs of competition were found on adult trees. Diplodia shoot blight was restricted to the warmest and driest areas, while no climatic restrictions were identified for Dothistroma needle blight. Both diseases caused additive effects on crown defoliation and defoliated trees showed stagnated growth. In the regeneration layer, signs of disease suppression were found. In the warmest and driest areas, seedling mortality was mainly associated with Diplodia shoot blight, even though both pathogens were detected. Clear signs of D. pini spillover from canopy trees to recruits were found. However, seedling mortality caused by Dothistroma needle blight was only restricted to the coldest and wettest sites where D. sapinea could not survive. Large crowns in adult trees probably allow both pathogens to co‐exist and cause additive impacts. The smaller size of recruits and a higher susceptibility to environmental stress compared to adult trees probably facilitates the effects of Diplodia shoot blight which masked those caused by Dothistroma needle blight. By considering climatic constraints, host ontogeny and structural specificity, we could dissect the disease impacts of two different pathogens and successfully explain forest health at a regional scale.

Site-specific additionality in aboveground carbon sequestration in set-aside forests in Flanders (northern Belgium)

IntroductionIn situ carbon sequestration in forests is important in the context of climate change mitigation, and setting aside managed forests has been proposed as an option for increased carbon sequestration. Comparing set-aside and managed forests may provide insights and rules of thumb on the potential for additional in situ carbon sequestration in set-aside forest.MethodsIn an observational study, we compared re-inventory data from the network of set-aside forest reserves in Flanders, which have been unmanaged for 17–66 years (2 surveys with a 10 years interval), with re-inventory data from the regional forest inventory, representing the overall forest area in Flanders (2 surveys with a 15 years interval).ResultsThe aboveground carbon pools and sequestration rates were higher in the set-aside forests compared to the average forest in Flanders. In the average Flemish forest, the aboveground carbon pool increased from 64.7 to 85.1 tC ha−1, over a period of 15 years. In the set-aside forests, the mean pool was higher at the first measurement and further increased from 84.8 to 102.4 tC ha−1, over a period of 10 years. The mean aboveground annual carbon sequestration rate was 1.3 tC ha−1 year−1 in the average forest in Flanders and 1.8 tC ha−1 year−1 in the set-aside forests. The stocks and fluxes depended on the soil conditions and were higher in set-aside forests on silt and sandy silt sites compared to wet and sand sites. The set-aside forests on dry sites showed additionality in in situ aboveground carbon sequestration. We saw no indication of approaching a culmination point in the first decades following set-aside: plots with high carbon pools did not show lower carbon sequestration. In conclusion, set-aside forests can combine high carbon pools with high sequestration rates on suitable sites. Under the current management policy, we expect Flemish forests—regular and set-aside—to further increase their carbon pools in the coming decades.