Aquatic hyphomycetes (AH) play central role in decomposition and nutrient cycling in headwater streams, yet the extent and ecological significance of their stoichiometric plasticity remain poorly understood. Here we investigated the plasticity young, intermediate, and old mycelium of four AH species under contrasting nitrogen (N) and phosphorus (P) availabilities and examined whether nutrient storage is advantageous for re-colonising fresh substrates. Our results revealed that P content remained plastic across species, whereas N plasticity was constrained and taxon dependent. Young mycelium exhibited strict homoeostasis, whereas older mycelium was plastic. Finally, no advantage of nutrient storage for poor-medium colonisation was evidenced, suggesting that storage might be more involved in competitive exclusion issues. Stoichiometric plasticity of AH is thus not a fixed, species-level trait but varies dynamically with mycelial metabolic activity, and differentially for N and P. Accounting for intra-mycelial heterogeneity would be necessary for fully understanding fungal roles in freshwater ecosystems.

Plant litter decomposition governs how much carbon soils store and emit, yet the microbial traits that shape ecosystem-scale decay remain unresolved. Metagenomes can quantify genes encoding plant cell-wall-degrading enzymes, but it is unclear whether ecosystem differences in decay reflect distinct enzymatic repertoires, and whether these data improve prediction beyond climate and soil properties. We paired standardized green and rooibos tea-bag decomposition assays across 3–24 months with 295 soil metagenomes from 264 global sites. Using 196 European plots for primary inference, we built a stage-resolved catalogue of 17.6 million carbohydrate-active enzyme (CAZyme) genes. Forest microbiomes decomposed tea faster than grasslands, but this was not explained by greater CAZyme family richness. Instead, ecosystems differed in CAZyme abundance, subfamily and protein-sequence variation, and allocation across biochemical stages of plant cell-wall decay, with evidence of ecosystem-specific selection. CAZyme profiles added explanatory power for 24-month mass loss and improved within-ecosystem prediction but generalized poorly across ecosystems and continents. By showing that ecosystem differences in decomposition arise from the stage-specific distribution of shared enzymatic functions rather than their presence alone, this work shifts microbial trait inference beyond gene inventories and provides a mechanistic genomic framework for carbon-cycle modelling within defined environmental limits.

In temperate European forests, soil fungal communities, dominated by saprotrophic and ectomycorrhizal (ECM) species, represent almost 25% of soil organic carbon (C) in the soil. However, the decomposition dynamics of fungal necromass, the bioavailability of its associated elements and its role in soil C stabilisation remain poorly understood. We investigated how intrinsic chemical properties-particularly melanin content, nitrogen (N) and phosphorus (P) levels-influence the microbial decomposition of fungal necromass in a temperate oak forest. We compared two types of fungal necromass: Laccaria bicolor (low melanin content) and Fomitiporia robusta (high melanin content). We monitored mass loss, stoichiometric ratios and microbial enzymatic activity over a six-month period in soil. Additionally, we analysed bacterial and fungal community structures via DNA metabarcoding, and estimated microbial biomass using qPCR during the decomposition process. The highly melanised necromass showed limited mass loss and reduced enzymatic activity, indicating greater recalcitrance. Contrasting C:P and C:N ratio profiles during the decomposition of the two types of substrate suggest that melanin plays a key role in the decomposition dynamics of the fungal necromass, while P and N do not appear to be determining factors in this process. Copiotrophic bacteria and saprotrophic fungi dominated the early stages of decomposition, while in later stages, oligotrophic bacteria and certain ECM genera became dominant. Our findings confirm that fungal necromass decomposition is strongly influenced by its intrinsic chemical properties, and particularly by its melanin content. This substrate constitutes a unique ecological niche, shaping the succession of specialised microbial guilds (i.e. the fungal necrobiome). Finally, our results highlight the significant abundance of certain fungal guilds, such as ECM fungi, raising questions about the potential role of these symbiotic fungi in the decomposition of fungal necromass or their passive, but massive, colonisation of this soil micro-niche.Read the free for this article on the Journal blog.

Addressing the factors underlying community patterns is a crucial endeavor as it contributes to a better understanding of the relationship between biodiversity and ecosystem functioning, as well as the associated ecosystem services. For example, detritivore communities play a major role in decomposition processes and related matter and energy fluxes in ecosystems. However, compared to living plant resources, leaf litter resources are nutritionally poor, with low macroelement concentrations. Although detritivore communities are known to depend on the local leaf litter resources, it remains unclear whether the chemical composition of detritivores depends on the locally available leaf litter. The macroelement composition of detritivores is rarely studied and is seldom compared directly to leaf litter chemical quality. Furthermore, leaf litter elements other than carbon (C), nitrogen (N), and phosphorus (P) are not systematically investigated even though large differences in elements such as calcium (Ca), potassium (K), or magnesium (Mg) can occur among both detritivore taxa and leaf litter types.To investigate whether the chemical composition of macrodetritivore communities depends on leaf litter chemistry, we sampled 24 paired French forests sites that differed in their leaf litter chemical composition. At each site, we quantitatively sampled leaf litter transformers (Diplopoda and Isopoda) to estimate their abundance. For each morphospecies, we measured mean individual body mass and analyzed body concentrations of C, N, P, K, Ca, and Mg (hereafter called chemical traits). We also analyzed the same macroelements in the dominant leaf litter at each site. We examined the detritivore taxonomic diversity, chemical community diversity, biomass, and abundance in communities, and tested whether these parameters were influenced by leaf litter chemistry.Results at the morphospecies level were consistent with the homeostasis hypothesis, indicating no specific physiological adaptation to the chemical composition of their trophic resources. Chemical community diversity (i.e., the FDis index based on all six chemical elements) of detritivores was higher at sites with high-quality leaf litter than at the corresponding low-quality leaf litter sites. Furthermore, community-level concentrations of P and Mg in detritivores were positively influenced by litter P and Mg concentrations, respectively.Although effect sizes were limited, our results suggest that leaf litter chemical composition can influence detritivore chemical composition through shifts in the relative abundance of taxa. Ultimately, this may lead to a closer match between the chemical composition of detritivore communities and that of their resources.

Chemical contamination threatens marine biodiversity, but detecting chronic sublethal effects on early-life development remains challenging. In this study, we developed a chronic larval bioassay based on repeated monitoring of development in the shrimp species Palaemon serratus, which is representative of European coastal environments. The larvae were exposed to the insect growth regulator fenoxycarb (0-64 µg.L-1), and the following endpoints were quantified: survival, stage progression, metamorphosis, juvenile growth and energy reserves at metamorphosis. Our objectives were to: (i) define larval life-history and fitness traits that are informative for chronic testing; (ii) propose a statistical workflow suited to heterogeneous endpoint types (binary, continuous and censored) and non-monotonic dose-response relationships; (iii) and investigate the importance of inter-female variability in response. Fenoxycarb altered developmental dynamics, with stage-timing endpoints frequently exhibiting non-monotonic (U-shaped) patterns; development was accelerated at low doses and slowed at higher doses. In contrast, metamorphosis success decreased monotonically with increasing concentration. Juvenile mass declined by ∼20% at intermediate doses, with partial recovery observed at higher doses. Meanwhile, daily weight gain decreased progressively across the gradient. Energy stores at metamorphosis also shifted with exposure, suggesting effects on condition beyond simple delays in development. Several endpoints displayed significant variability between females, indicating that maternal effects can substantially modulate apparent sensitivity. Overall, the experimental design and analysis pipeline capture sublethal and non-monotonic chronic effects, providing a practical framework for incorporating maternal variability into marine chemical risk assessment.

Growing evidence has shown that, apart from local environmental factors, changes in landscape-level factors by accelerated land-use change can also shape soil pathogenic fungal diversity. However, the global representativeness of such patterns remains unclear. Here, we assess how pathogenic fungal diversity in 511 soil samples worldwide responds to landscape factors, including landscape complexity index based on eight landscape metrics and quantity of different land cover types across six spatial scales (i.e., surrounding landscape, 250 m to 10,000 m radii from the sampling coordinate). We find that while soil variables explain over half of the variance, pathogenic fungal alpha diversity increases with landscape complexity and crop cover proportion, but decreases with grass and tree cover proportion, together explaining 23.4% of the total variance. Landscape factors have weaker impacts on beta diversity, explaining 13.0% of the variance. Across spatial scales, grassland ecosystems exhibit increasingly stronger responses to landscape variables compared to forest ecosystems. Landscape factors have a higher relative contribution to root-associated fungi than leaf/fruit/seed-associated fungi. Our results emphasize the importance of local factors and the complementary role of landscape patterns in shaping global soil pathogenic fungal distributions, highlighting scale-dependent effects across ecosystems and fungal functional groups.

Basal resources generally mirror environmental nutrient concentrations in the elemental composition of their tissue, meaning that nutrient alterations can directly reach consumer level. An increased nutrient content (e.g. phosphorus) in primary and detrital resources under nutrient enriched conditions should favour taxa with a high demand for this nutrient. With the nutrient demand of a taxon being correlated to the elemental composition of its body tissue (e.g. phosphorus content), such above described species shifts likely alter the overall community stoichiometry. However, studies addressing stoichiometry at community level are rare and most often restricted to lacustrine planktonic systems, single streams or limited experimental setups. Relying on a stoichiometric database for >200 taxa and >1300 standardized sampling events of macroinvertebrate assemblages from the French national monitoring programme, we investigated the effect of water phosphorus and nitrogen load on stream macroinvertebrate community stoichiometry. Community stoichiometry was significantly affected by water phosphorus concentration and the effect was strongest at low levels of nitrogen. While we could not confirm our hypothesis of increasing community %P (and decreasing C:P, N:P) with increasing water phosphorus concentrations for the overall community, it clearly followed this pattern for both Insecta and Malacostraca. General differences in the elemental composition among major taxonomic groups and a shift among these groups over the nutrient gradient probably explain the response of community stoichiometry. Our results show that assumptions from Ecological Stoichiometry Theory also hold at the community level, at least for two dominant taxa, and on a large spatial scale, with likely consequences for nutrient cycling and ecosystem function.

In streams, phototrophic biofilms are considered to be a good-quality resource for consumers and are essential to support secondary production. However, with the increasing occurrence of flow intermittency as a consequence of global climate change, limited information exists regarding the impact of drying and rewetting events on biofilm nutritional quality indicators and their consequences for consumers. This study aims at understanding how river intermittency affects the nutritional quality of phototrophic biofilms. Specifically, we examine the effects of drying and rewetting events on their capacity to support secondary production.Our hypothesis was that the capacity of biofilms to support secondary production relies on their nutritional quality: biofilms characterised by higher contents of long-chain fatty acids, nitrogen and phosphorus are expected to provide a better-quality resource for consumers. We also hypothesised that the nutritional quality of biofilms undergoes changes over time during drying events, and that these changes are influenced by their initial algal composition. This is because the algal composition within biofilms may shift in response to drying events, subsequently impacting the nutritional quality of the biofilms.We grew four phototrophic biofilms in flowing water, each with a different nutritional quality, and then exposed them to a short (3 days) or a long dry period (14 days). Biofilms were sampled 3 days and 18 days after rewetting (post-disturbance and post-recovery) to assess alterations in nutritional indicators relative to their pre-disturbance state through pigment, fatty acid and stoichiometric analyses. We fed these biofilms to Gammarids (Gammarus fossarum) for 29 days and measured individual growth, feeding rate and locomotor activity. We also calculated a secondary production index to assess the biofilms' capacity to support higher trophic levels.Our findings revealed that the nutritional quality of biofilms was significantly reduced during the post-disturbance phase. The duration of the dry period had minimal effect on this decline. Subsequently, during the recovery phase, nutritional quality indicators improved for biofilms initially dominated by cyanobacteria, while they either remained unchanged or decreased for biofilms initially dominated by diatoms, in comparison to the pre-disturbance state. As a result, biofilms that initially exhibited a high nutritional quality were disrupted by the dry period, depending on the duration. However, the overall effects of dry period on gammarid's response and on secondary production were less pronounced, which is likely to have resulted from changes in the quantity of available resources.Our study demonstrates that a disturbance can modify the expected and effective qualities of biofilms. It highlights that biochemical parameters cannot reliably predict biofilm capacity to support secondary production. Biofilm history of disturbance, among other parameters, must be taken into account.

Read the free Plain Language Summary for this article on the Journal blog.

More than half of the world's rivers dry up periodically, but our understanding of the biological communities in dry riverbeds remains limited. Specifically, the roles of dispersal, environmental filtering and biotic interactions in driving biodiversity in dry rivers are poorly understood. Here, we conduct a large-scale coordinated survey of patterns and drivers of biodiversity in dry riverbeds. We focus on eight major taxa, including microorganisms, invertebrates and plants: Algae, Archaea, Bacteria, Fungi, Protozoa, Arthropods, Nematodes and Streptophyta. We use environmental DNA metabarcoding to assess biodiversity in dry sediments collected over a 1-year period from 84 non-perennial rivers across 19 countries on four continents. Both direct factors, such as nutrient and carbon availability, and indirect factors such as climate influence the local biodiversity of most taxa. Limited resource availability and prolonged dry phases favor oligotrophic microbial taxa. Co-variation among taxa, particularly Bacteria, Fungi, Algae and Protozoa, explain more spatial variation in community composition than dispersal or environmental gradients. This finding suggests that biotic interactions or unmeasured ecological and evolutionary factors may strongly influence communities during dry phases, altering biodiversity responses to global changes.

In the common prawn, Palaemon serratus (Pennant, 1777), the females release larvae twice a year (winter and summer layings). We investigated seasonal differences in larval phenotypes and their consequences on larval performance. We measured the biomass and carbon (C) and nitrogen (N) content (proxy of lipid and protein reserves) at hatching of larvae laid by 6 winter and 6 summer females collected on the coast of Seine-Maritime (France). We incubated these larvae at 3 temperatures (12, 16, and 20 degrees C) and quantified the effects of temperature and season on survival, development time, biomass, and C and N content and ratio at metamorphosis. At hatching, winter larvae were larger than summer larvae, but their C/N was similar. Development time increased with decreasing temperature, with no seasonal difference. Within the same clutch, the longer the development time, the greater the weight of the larvae, without affecting their C/N ratio. Seasonal differences in maternal per offspring investment were not as pronounced as expected. Surprisingly, the summer larvae survived and grew better than the winter ones, at least at 16 and 20 degrees C.

COVID-19 outbreak led to a massive dissemination of protective polypropylene (PP) face masks in the environment, posing a new environmental risk amplified by mask photodegradation and fragmentation. Masks are made up of a several kilometres long-network of fibres with diameter from a few microns to around 20 µm. After photodegradation, these fibres disintegrate, producing water dispersible debris. Electrokinetics and particle stability observations support that photodegradation increases/decreases the charge/hydrophobicity of released colloidal fragments. This change in hydrophobicity is related to the production of UV-induced carbonyl and hydroxyl reactive groups detectable after a few days of exposure. Helical content, surface roughness and specific surface area of mask fibres are not significantly impacted by photodegradation. Fragmentation of fibres makes apparent, at the newly formed surfaces, otherwise-buried additives like TiO2 nanoparticles and various organic components. Mortality of gammarids is found to increase significantly over time when fed with 3 days-UV aged masks that carry biofilms grown in river, which is due to a decreased abundance of microphytes therein. In contrast, bacteria abundance and microbial community composition remain unchanged regardless of mask degradation. Overall, this work reports physicochemical properties of pristine and photodegraded masks, and ecosystemic functions and ecotoxicity of freshwater biofilms they can carry.

Headwater streams are characterised by predominantly heterotrophic functioning resulting from leaf litter input, but autochthonous primary production can also contribute to energy fluxes and the supply of nutrients. While much work has focused on the role of polyunsaturated fatty acids as essential nutrients, less attention has been paid to the significance of sterols in stream food webs. Yet these molecules are essential to arthropods that can only synthesise cholesterol from a limited range of dietary sterols. In a headwater stream, we tracked the transfer of dominant sterols from allochthonous and autochthonous resources to 5 benthic macroinvertebrates. Despite their formal functional feeding group, all the taxa tended to be opportunistic omnivores that relied on all available resources. These behaviours could be attributed to nutritional constraints in the stream food web, but these constraints were not related to the sterol supply from the different basal sources. Dominant sterols from detrital sources (leaf litter, fine benthic organic matter [FBOM]) and primary producers (epilithic biofilms, bryophytes) were all & UDelta;5-sterols (& beta;-sitosterol, campesterol, stigmasterol, epibrassicasterol). The levels of cholesterol detected in macroinvertebrates, as well as the presence of desmosterol, indicate efficient dealkylation activity of these & UDelta;5-sterols. Leaf litter has consistently shown high & beta;-sitosterol/stigmasterol ratios, giving it greater nutritional value than usually accepted. But bryophytes, and especially epilithic biofilms, contained cholesterol, providing a direct supply to invertebrates, thereby promoting their growth. Detrital particles (FBOM) colonised by microalgae could be the best-balanced diet to avoid sterol deficiencies due to their cholesterol content and high & beta;-sitosterol/stigmasterol ratios.

In decapod crustaceans, the conditions experienced during embryonic development trigger phenotypic plasticity of the larvae at hatching. The objective of this study was to test the effects of temperature during embryonic development of Palaemon serratus on the phenotypic plasticity of hatching larvae. We incubated egg-bearing females from eggs laying to hatching at four temperatures (10, 15, 18 and 20 degrees C). Weight, carbon and nitrogen contents were measured on newly laid eggs and on freshly hatched larvae. The duration of embryonic development was negatively correlated with incubation temperature. At 20 degrees C, all females abandoned their eggs during development. Incubation temperature had no effect on the weight and the percentage of N of the larvae at hatching, while it did affect their percentage of C and their C/N ratio. Embryos incubated at 10 degrees C seemed to produce larvae with fewer lipid reserves than those incubated at 15 and 18 degrees C. They probably overconsumed their lipid reserves to compensate for the metabolic losses due to the low temperature. These results provide information on the link between maternal investment per egg and larval development in P. serratus.

In forested headwater streams, inconspicuous food resources such as epilithic microalgae can play a major role owing to their content of long chain polyunsaturated fatty acids (PUFAs) that are essential for macroinvertebrate development. Yet, the use of these resources and their consequences for consumers and life-history traits remain scarcely studied, especially for non-herbivorous taxa. Using instream mesocosms, we aimed to understand how two macroinvertebrate species, a shredder detritivore (Gammarus pulex) and a scraper (Rhithrogena semicolorata), use available organic resources under light versus shaded conditions (high and low amounts of phototrophic biofilm, respectively). We specifically focused on the origin of carbon (C) and essential lipids (PUFAs, sterols) assimilated by the two species and the effects of these compounds on their survival and growth. When autotrophic biofilms were available (mesocosms exposed to light), both species experienced significantly higher growth than in mesocosms placed in the dark. In Rhithrogena nymphs, the survival and imago emergence rates were positively affected by access to autotrophic biofilms. Using stable isotope analysis (delta C-13 and delta N-15), we demonstrated that under dark conditions both macroinvertebrates assimilated C of detrital origin. Under light conditions, most of the C assimilated by R. semicolorata was derived from autotrophic biofilms and around 11% from fine detrital particles (FPOM). Gammarus pulex derived part of its C from detrital sources (mainly FPOM) and from autotrophic biofilms. The results of isotopic analyses (delta C-13) on fatty acids (FAs) and sterols showed that the scraper Rhithrogena was entirely dependent on autotrophic biofilms to meet its dietary FAs and sterol requirements. In contrast, detrital sources were quantitatively important for G. pulex both in terms of C and sterol supply, irrespective of the conditions tested. For these consumers, microalgae seemed to be a complementary food source, but yet essential to cover a large part of their requirements in long-chain PUFAs. This study clearly confirmed the ecological importance of autotrophic biofilms for two functional feeding groups of macroinvertebrates in headwater streams providing new insights on the trophic origin of sterols and long-chain PUFAs in their diet.

Our understanding of ecosystem functioning is strongly linked to the study of predator–prey relationships and food web structures. However, trophic ecology has often focused on identifying taxonomic relationships and quantifying the biomass or energy ingested by consumers, but has often failed to integrate the importance of the nutritional quality of resources in ecological dynamics. Underlying this gap is the multi‐dimensional nature of resource quality which has hampered any consensus on the definition of resource nutritional quality. In this special issue, we aimed at gathering a subset of articles exemplifying the diversity of variables by which resources quality is quantified, the diversity of research topics that can be tackled in ecology – from physiological or evolutionary aspects to ecosystem processes – and propose some perspectives on the integration of nutritional quality within broader ecological concepts. Using a semi‐automated literature analysis, we map the current landscape of the ‘resources nutritional quality' research of the last 30 years. We depict how it has been quantified through physical, biological or chemical indicators, the use of these parameters being largely dependent on the type of ecosystem studied and on the investigated ecological process. We then position the articles published in this special issue of Oikos within this landscape, showing they cover a small but relatively well representative subset of the domains of resources quality‐related issues. Articles in this special issue browse a range of individual and population‐level approaches (embracing evolutionary questions) to community related questions, include methodological issues and ecosystem‐wide approaches using trophic quality indicators as tracers of resources origin. Based on these studies and on the literature review, we identify a non‐exhaustive list of challenges and perspectives of research that we consider of highest priority in the large topic of trophic ecology.

Motivation Ecological stoichiometry investigates the equilibrium and the fluxes of chemical elements and energy between organisms and their environment. Several studies have pointed out the value of integrating stoichiometric traits for a better understanding of the mechanisms behind community and ecosystem processes. Especially in the light of globally changing nutrient levels in freshwater systems, the link between stoichiometric traits and nutrient cycling or trophic interactions can improve our investigations of a species' or community's response to these changes. Benthic macroinvertebrate assemblages are widely used for biomonitoring in freshwaters, providing a large number of datasets gathering information about their taxonomic diversity at many different spatial and temporal scales. Likewise, an increasing number of large databases gives ready access to information on a variety of macroinvertebrate biological traits. The addition of stoichiometric traits to this pool of available information could thus expand the application of trait approaches and facilitate the study of the links between nutrient cycling and ecosystem functioning. Main types of variables contained The database contains information on the elemental contents of 188 taxa, in terms of the major nutrients %C, %N and %P and the corresponding molar ratios C:N, C:P and N:P. We provide calculated taxon mean values as well as the underlying raw data at the individual level that were obtained from field sampling, supplemented by a literature search ( n = 1,555; 174 taxa). Major taxa and level of measurements The database contains information on 188 macroinvertebrate taxa, available at species ( n = 33), genus (96), tribe (9), subfamily (6), family (42), order (1) or class (1) levels. Software format .csv file.

All living organisms theoretically have an optimal stoichiometric nitrogen: phosphorus (N: P) ratio, below and beyond which their growth is affected, but data remain scarce for microbial decomposers. Here, we evaluated optimal N: P ratios of microbial communities involved in cellulose decomposition and assessed their stability when exposed to copper Cu(II). We hypothesized that (1) cellulose decomposition is maximized for an optimal N: P ratio; (2) copper exposure reduces cellulose decomposition and (3) increases microbial optimal N: P ratio; and (4) N: P ratio and copper modify the structure of microbial decomposer communities. We measured cellulose disc decomposition by a natural inoculum in microcosms exposed to a gradient of N: P ratios at three copper concentrations (0, 1 and 15 mu M). Bacteria were most probably the main decomposers. Without copper, cellulose decomposition was maximized at an N: P molar ratio of 4.7. Contrary to expectations, at high copper concentration, the optimal N: P ratio (2.8) and the range of N: P ratios allowing decomposition were significantly reduced and accompanied by a reduction of bacterial diversity. Copper contamination led to the development of tolerant taxa probably less efficient in decomposing cellulose. Our results shed new light on the understanding of multiple stressor effects on microbial decomposition in an increasingly stoichiometrically imbalanced world. Copper contamination reduces the optimal N: P ratio and the range of N: P ratios for cellulose decomposition by bacterial decomposers.