Mesocosm Experiment Research Articles

Rainwater-borne H2O2 accelerates roxarsone degradation and reduces bioavailability of arsenic in paddy rice soils

Contamination of rice by arsenic represents a significant human health risk. Roxarsone -bearing poultry manure is a major pollution source of arsenic to paddy soils. A mesocosm experiment plus a laboratory experiment was conducted to reveal the role of rainwater-borne H2O2 in the degradation of roxarsone in paddy rice soils. While roxarsone could be degraded via chemical oxidation by Fenton reaction-derived hydroxyl radical, microbially mediated decomposition was the major mechanism. The input of H2O2 into the paddy soils created a higher redox potential, which favored certain roxarsone-degrading and As(III)-oxidizing bacterial strains and disfavored certain As(V)-reducing bacterial strains. This was likely to be responsible for the enhanced roxarsone degradation and transformation of As(III) to As(V). Fenton-like reaction also tended to enhance the formation of Fe plaque on the root surface, which acted as a filter to retain As. The dominance of As(V) in porewater, combined with the filtering effect of Fe plaque significantly reduced the uptake of inorganic As by the rice plants and consequently its accumulation in the rice grains. The findings have implications for developing management strategies to minimize the negative impacts from the application of roxarsone-containing manure for fertilization of paddy rice soils.

Resilience to changes in salinity and predator diversity in representative Gulf of Mexico estuarine fish predator-prey interactions

Predators strongly influence ecological communities and subsequent ecosystem function by directly consuming prey individuals and indirectly by inciting alterations in prey behavior, termed non-consumptive effects (NCEs). Gulf of Mexico estuaries support complex food webs structured by numerous species interactions maintained in constant environmental flux from variation in salinity. Environmental variation presents a source of physiological stress for estuarine fish and plays a role in their distributions and subsequent interactions. Here, we present the results of a mesocosm experiment examining if acute changes in salinity disrupt NCEs of different predators on estuarine prey. We exposed Gulf killifish (Fundulus grandis) to visual and/or olfactory cues from a common estuarine predator, red drum (Sciaenops ocellatus), and from a freshwater predator that is a transient species in lower portions of estuaries, largemouth bass (Micropterus salmoides), under either decreasing, constant, or increasing salinity. Killifish decreased shoal size and movement in response to olfactory cues or both visual and olfactory cues compared to when they were exposed to no cues or visual cues, demonstrating variable perceived risk dependent on cue type. Behavioral response did not vary by predator species, implying a generalized response to different fish predators. Prey did not change behavior when exposed to decreasing salinity compared to constant salinity. However, prey movement increased with increasing salinity, indicating that salinity changes may provide cues to search for different habitats instead of a stressor. Our experiment indicates that estuarine predator-prey interactions may be resilient to acute salinity changes given the broad tolerances of euryhaline species.

The metabolic network response and tolerance mechanism of Thalassia hemprichii under high sulfide based on widely targeted metabolome and transcriptome

Costal eutrophication leads to increased sulfide levels in sediments, which has been identified as a major cause of the global decline in seagrass beds. The seagrass Thalassia hemprichii, a dominant tropical species in the Indo-Pacific, is facing a potential threat from sulfide, which can be easily reduced from sulfate in porewater under the influence of global climate change and eutrophication. However, its metabolic response and tolerance mechanisms to high sulfide remain unclear. Thus, the current study investigated the physiological responses and programmed metabolic networks of T. hemprichii through a three-week mesocosm experiment, integrating physiology, stable isotope, widely targeted metabolomics, transcriptomics, and microbial diversity assessments. High sulfide reduced the sediment microbial diversity, while increased sediment sulfate reduced bacterial abundance and δ34S. The exposure to sulfide enhanced root δ34S while decreased leaf δ34S in T. hemprichii. High sulfide was shown to inhibit photosynthesis via damaging PSII, which further reduced ATP production. In response, abundant up-regulated differentially expressed genes in energy metabolism, especially in oxidative phosphorylation, were activated to compensate high energy requirement. High sulfide also promoted autophagy by overexpressing the genes related to phagocytosis and phagolysosome. Meanwhile, metabolomic profiling revealed that the contents of many primary metabolites, such as carbohydrates and amino acids, were reduced in both leaves and roots, likely to provide more energy and synthesize stress-responsive secondary metabolites. Genes related to nitrate reduction and transportation were up-regulated to promote N uptake for sulfide detoxification. High sulfide levels specifically enhanced thiamine in roots, while increased jasmonic acid and flavonoid levels in leaves. The distinct differences in metabolism between roots and leaves might be related to sulfide levels and the growth-defense trade-off. Collectively, our work highlights the specific mechanisms underlying the response and tolerance of T. hemprichii to high sulfide, providing new insights into seagrass strategies for resisting sulfide.

Overlooked drivers of the greenhouse effect: The nutrient-methane nexus mediated by submerged macrophytes

Submerged macrophytes remediation is a commonly used technique for improving water quality and restoring habitat in aquatic ecosystems. However, the drivers of success in the submerged macrophytes assembly process and their specific impacts on methane emissions are poorly understood. Thus, we conducted a mesocosm experiment to test the growth plasticity and carbon fixation of widespread submerged macrophytes (Vallisneria natans) under different nutrient conditions. A refined dynamic chamber method was utilized to concurrently collect and quantify methane emission fluxes arising from ebullition and diffusion processes. Significant correlations were found between methane flux and variations in the physiological activities of V. nantas by the fluorescence imaging system. Our results show that exceeding tolerance thresholds of ammonia in the water significantly interfered with the photosynthetic systems in submerged leaves and the radial oxygen loss in adventitious roots. The recovery process of V. natans accelerated the consumption of dissolved oxygen, leading to increase in the populations of methanogen (153.3 % increase of mcrA genes) and subsequently elevating CH4 emission fluxes (23.7 %) under high nutrient concentrations. Conversely, V. natans increased the available organic carbon under low nutrient conditions by radial oxygen loss, further increasing CH4 emission fluxes (94.7 %). Quantitative genetic and modeling analyses revealed that plant restoration processes drive ecological niche differentiation of methanogenic and methane oxidation microorganisms, affecting methane release fluxes within the restored area. The speciation process of V. natans is incapable of simultaneously meeting improved water purification and reduced methane emissions goals.

Cumulative effects of fish disturbance and vegetative propagules reduce the growth advantage of Vallisneria natans

Benthivorous fish disturbance and density-dependent competition from adjacent macrophytes are two important biotic factors that significantly impact the growth of submerged macrophyte pioneer species, which is crucial for the success of eutrophication lake restoration. We conducted an outdoor mesocosm experiment to explore the individual and combined effects of these two factors on water quality and the growth of Vallisneria natans. The experiment involved two levels of fish (Misgurnus anguillicaudatus) disturbance crossed with two levels of Hydrilla verticillata vegetative propagule (shoot) intensity. The results showed that fish disturbance significantly increased the water column total nitrogen (TN), ammonia nitrogen (N-NH4), total phosphorus (TP), and phosphate‑phosphorus (P-PO4). V. natans exhibited restricted plant height elongation and decreased soluble carbohydrate (SC) and starch concentration in fish treatments. Fish disturbance inhibited the growth advantage of V. natans by increasing the extinction coefficient of the water column. There was no statistical significance in total biomass between the two macrophytes in increased vegetative propagule and fish treatments. H. verticillata exhibited a higher relative growth rate (RGR) and summed dominance ratio (SDR3) than V. natans in four treatments and the treatment with three shoots of H. verticillata and one M anguillicaudatus, respectively. Fish disturbance and vegetative propagules showed cumulative effects that negatively affected the RGR_V.H (V. natans relative to H. verticillata). Our findings indicated that benthivorous fish disturbance and vegetative propagules could individually and cumulatively reduce the growth advantage of the pioneer species, V. natans. Our study sheds light on the accumulated effects of multiple disturbances that simultaneously occur in lakes, which holds theoretical and practical importance for lake restoration efforts.

Mussels with luggage: the influence of artificially attached “backpack” devices on mussel movement behavior

BackgroundFreshwater mussels are important keystone and indicator species of aquatic ecosystems. Recent advances in sensor technology facilitate applications to individually track mussels and to record and monitor their behavior and physiology. These approaches require the attachment of sensor devices as “backpacks” to the outer shell surface. The interpretation of such data makes it necessary to understand the influence of these attachments on the horizontal and vertical movement behaviors of freshwater mussels. Over a series of mesocosm experiments, this study systematically investigated the effects of three size- and wiring-specific variants of artificially attached backpacks on the horizontal and vertical movement behavior of Anodonta anatina.ResultsAcross all experiments, equipping mussels with backpacks did not result in a significant influence on horizontal movement for any of the backpack variants. In contrast to this finding, the big backpacks with a high ratio between backpack volume and mussel length resulted in a significantly negative effect on vertical movement, indicating a potential for adverse effects of such devices on mussels, especially in natural settings.ConclusionsThe findings of this study show that assessing the effects of attached devices on mussels requires a species-specific evaluation of potential impacts on the endpoints of interest. Especially for vertical movement patterns, selection of the smallest available devices appears mandatory.

Specific root length regulated the rhizosphere effect on denitrification across distinct macrophytes

Macrophytes influence nitrogen (N) removal from wetlands. However, the specific plant traits responsible for this effect and the related microbial mechanisms remain largely unknown, especially root traits. In a mesocosm experiment, we determined the rhizosphere effect (RE) on microbial N removal processes by incubating rhizosphere and bulk soils collected from 11 macrophyte species. In addition, we examined root traits (involved in chemistry and morphology), along with examining the diversity, compositions, and abundance of bacterial communities involved in denitrification (nirS and nirK) and anammox (hzsB). Across the 11 macrophyte species, the positive RE on denitrification ranged from 66% to 412%, with an average of 194.72%. RE on denitrification was significantly and positively correlated with the recruitment of nir-type denitrifiers in the rhizosphere. We found that higher specific root length (SRL) root promoted the stronger RE, by increasing the abundance of nir-type denitrifiers and further enhancing N removal. Net N removal from water in the wetlands increased with a higher positive RE on nir-type denitrifiers. In addition, SRL significantly influenced the compositions of denitrifiers in the rhizosphere soil. We further found that the enrichment of Azospira, Bradyrhizobium, Sinorhizobium, Rhodopseudomonas, Alcaligenaceae, Bradyrhizobiaceae, and Pleomorphomonas improved the denitrification rate. These findings highlight the potential of root morphology in regulating plant–microbe interactions, thereby improving water purification.

Increasing microplastic exposure had minimal effects on fatty acid composition in zooplankton and yellow perch in a large, in-lake mesocosm experiment

Using 10 m diameter mesocosms in a Canadian boreal lake, we investigated the effects of microplastic (MP) exposure on the body weight and diet of yellow perch ( Perca flavescens) and the fatty acid composition of yellow perch and zooplankton. We exposed the aquatic ecosystem within seven mesocosms for 10 weeks to a mixture of polyethylene, polystyrene, and polyethylene terephthalate fragments, ranging in nominal addition concentrations from 6 to 29 240 particles L−1 (although realized water column concentrations were lower), as well as two negative controls. Increasing MP exposure did not affect yellow perch body weight (growth) or diet, or the overall fatty acid composition of yellow perch muscle or zooplankton. Results were highly variable across mesocosms. Despite high levels of MP ingestion by yellow perch, we did not find evidence of MPs leading to food dilution or any other effect where we could anticipate impacts on food web structure.

Cascading sulfur cycling in simulated oil sands pit lake water cap mesocosms transitioning from oxic to euxinic conditions

Base Mine Lake (BML), the first full-scale demonstration of oil sands tailings pit lake reclamation technology, is experiencing expansive, episodic hypolimnetic euxinia resulting in greater sulfur biogeochemical cycling within the water cap. Here, Fluid Fine Tailings (FFT)-water mesocosm experiments simulating the in situ BML summer hypolimnetic oxic-euxinic transition determined sulfur biogeochemical processes and their controlling factors. While mesocosm water caps without FFT amendments experienced limited geochemical and microbial changes during the experimental period, FFT-amended mesocosm water caps evidenced three successive stages of S speciation in ∼30 days: (S1) rising expansion of water cap euxinia from FFT to water surface; enabling (S2) rapid sulfate (SO42−) reduction and sulfide production directly within the water column; fostering (S3) generation and subsequent consumption of sulfur oxidation intermediate compounds (SOI). Identified key SOI, elemental S and thiosulfate, support subsequent SOI oxidation, reduction, and/or disproportionation processes in the system. Dominant water cap microbes shifted from methanotrophs and denitrifying/iron-reducing bacteria to functionally versatile sulfur-reducing bacteria (SRB) comprising sulfate-reducing bacteria (Desulfovibrionales) and SOI-reducing/disproportionating bacteria (Campylobacterales and Desulfobulbales). The observed microbial shift is driven by decreasing [SO42−] and organic aromaticity, with putative hydrocarbon-degrading bacteria providing electron donors for SRB. Comparison between unsterile and sterile water treatments further underscores the biogeochemical readiness of the in situ water cap to enhance oxidant depletion, euxinia expansion and establishment of water cap SRB communities aided by FFT migration of anaerobes. Results here identify the collective influence of FFT and water cap microbial communities on water cap euxinia expansion associated with sequential S reactions that are controlled by concentrations of oxidants, labile organic substrates and S species. This emphasizes the necessity of understanding this complex S cycling in assessing BML water cap O2 persistence.

Fauna – Microplastics interactions: Empirical insights from benthos community exposure to marine plastic waste

Microplastic deposition in soft marine sediments raises concerns on their role in sediment habitats and unknown effects on resident macrobenthic communities. To assess the reciprocal influence that MPs and macrobenthos might have on each other, we performed a mesocosm experiment with ambient concentrations of environmental Polyethylene (PE) and a non-manipulated, natural macrobenthic community from the Belgian part of the North Sea (BPNS). Our results show that PE fragments increase mortality of abundant bivalves (specifically Abra alba) after 30 days of exposure but not for the most abundant polychaete Owenia fusiformis, possibly due to its predominant suspension feeding behavior. Fast burial of surface MPs exposes deep-dwelling burrowers to the pollutant, however reducing the amount of MPs interacting with (sub) surface living fauna. We conclude that macrobenthos promotes the sequestration of deposited MPs, counteracting resuspension, and can have cascading effects on biodiversity due to their effect on abundant and functionally important species.

Multi-decadal warming alters predator's effect on prey community composition.

Predator responses to warming can occur via phenotypic plasticity, evolutionary adaptation or a combination of both, changing their top-down effects on prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators may influence natural food webs. Here, we ask whether wild fish subject to warming across multiple generations differ in their impacts on prey communities compared with their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch (Perca fluviatilis), originating from a heated or reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. Overall, in the presence of fish of heated origin, zooplankton abundance was higher and did not change with experimental warming, whereas in the presence of fish of unheated origin, it declined with experimental temperature. Responses in zooplankton taxonomic and size composition suggest that larvae of heated origin consume more large-sized taxa as the temperature increases. Our findings show that differences between fish populations, potentially representing adaptation to their long-term thermal environments, can affect the abundance, biomass, size and species composition of their prey communities. This suggests that rapid microevolution in predators to ongoing climate warming might have indirect cross-generational ecological consequences propagating through food webs.

Attenuation Effect of Azolla spp. on Lambda-Cyhalothrin Toxicity to Aquatic Organisms.

Wetlands play a crucial role in providing valuable ecosystem services, including the removal of various pollutants. In agricultural basins, wetlands are exposed to agrochemical loads. This study aims to assess the attenuation effect of the ubiquitous macrophyte Azolla spp. on the toxicity of lambda-cyhalothrin to sensitive aquatic organisms. An indoor mesocosm experiment was conducted to compare the concentration of lambda-cyhalothrin at different time points after pesticide application in vegetated and unvegetated treatments, including a control without pesticide addition. Toxicity tests were performed throughout the experiment on three organisms: a fish (Cnesterodon decemmaculatus), a macroinvertebrate (Hyalella curvispina), and an amphibian (Boana pulchella). The results demonstrated that lambda-cyhalothrin concentration and toxicity in water were significantly lower in the Azolla spp. treatment. Furthermore, the half-life of lambda-cyhalothrin decreased from 1.2days in the unvegetated treatment to 0.4days in the vegetated treatment. The vegetated treatment also resulted in a significantly lower mortality rate for both H. curvispina and C. decemmaculatus. However, no mortality was observed in B. pulchella for any of the treatments. Sublethal effects were observed in this organism, such as lateral bending of the tail and impairment of the ability to swim, which were attenuated in the vegetated treatment. We conclude that Azolla spp. can effectively reduce the concentration and toxicity of lambda-cyhalothrin, suggesting its potential use in farm-scale best management practices to mitigate the effects of pesticide loads from adjacent crops.

Heatwave-induced functional shifts in zooplankton communities result in weaker top-down control on phytoplankton.

Freshwater ecosystems are increasingly affected by rising annual mean temperatures and heatwaves. While heatwaves are expected to have more immediate effects than mean temperature increases on local communities, comparative experimental studies are largely lacking. We conducted a 1-month mesocosm experiment to test the effect of different warming treatments, constantly raised temperatures (+3°C) and recurring heatwaves (+6°C), on plankton communities. We specifically tested how shifts in zooplankton trait composition and functional groups are reflected in ecosystem function (top-down control on primary producers). We found that heatwaves had a stronger and more immediate effect on zooplankton trait composition (specifically on body length and body mass) and functional groups. Heatwaves led to the decrease of small-bodied grazers (i.e., Rotifera) and the dominance of larger omnivorous Copepoda, and these shifts resulted in weaker top-down control, leading to elevated phytoplankton biomass. Altogether, our results highlight the importance of the indirect effects of heatwaves via inducing shifts in zooplankton functional groups and trait composition, which may lead to algal blooms.

Climate change impacts on a sedimentary coast—a regional synthesis from genes to ecosystems

Climate change effects on coastal ecosystems vary on large spatial scales, but can also be highly site dependent at the regional level. The Wadden Sea in the south-eastern North Sea is warming faster than many other temperate coastal areas, with surface seawater temperature increasing by almost 2 °C over the last 60 years, nearly double the global ocean mean increase. Climate warming is accompanied by rising sea levels, which have increased by approximately 2 mm yr−1 over the last 120 years. For this sedimentary coast, the predicted acceleration of sea-level rise will have profound effects on tidal dynamics and bathymetry in the area. This paper synthesises studies of the effects of ocean warming and sea level rise in the northern Wadden Sea, largely based on research conducted at the Wadden Sea Station Sylt of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research. An increasing rate of sea level rise above a critical threshold will lead to coastal erosion and changes in sediment composition, and may cause the transition from a tidal to lagoon-like environment as tidal flats submerge. This involves changes to coastal morphology, and the decline of important habitats such as muddy tidal flats, salt marshes and seagrass meadows, as well as their ecological services (e.g. carbon sequestration). Ocean warming affects plankton dynamics and phenology, as well as benthic community structure by hampering cold-adapted but facilitating warm-adapted species. The latter consist mostly of introduced non-native species originating from warmer coasts, with some epibenthic species acting as ecosystem engineers that create novel habitats on the tidal flats. Warming also changes interactions between species by decoupling existing predator–prey dynamics, as well as forming new interactions in which mass mortalities caused by parasites and pathogens can play an understudied but essential role. However, Wadden Sea organisms can adapt to changing abiotic and biotic parameters via genetic adaptation and phenotypic plasticity, which can also be inherited across generations (transgenerational plasticity), enabling faster plastic responses to future conditions. Important research advances have been made using next-generation molecular tools (-omics), mesocosm experiments simulating future climate scenarios, modelling approaches (ecological network analysis), and internet-based technologies for data collection and archiving. By synthesising these climate change impacts on multiple levels of physical and biological organisation in the northern Wadden Sea, we reveal knowledge gaps that need to be addressed by future investigations and comparative studies in other regions in order to implement management, mitigation and restoration strategies to preserve the uniqueness of this ecosystem of global importance.

How do additions of submerged macrophytes, large-bodied cladocerans and nutrients impact tropical plankton communities? A mesocosm experiment

AbstractWe investigated the individual and combined impacts of manipulation of submerged macrophytes, large-bodied cladocerans, and nutrients on plankton communities in a tropical hypereutrophic shallow reservoir. We tested how the addition of the macrophyte Ceratophyllum demersum, the cladoceran Sarsilatona serricauda, and nutrients affected phytoplankton and zooplankton diversity, composition, and structure using mesocosms and a factorial design (3 × 3) with eight treatments. During the experiment, the reservoir experienced an intense bloom of algae (207 mg l−1 of biomass), mainly composed of cyanobacteria (> 98%). The submerged macrophytes were found to significantly reduce the biomass of cyanobacteria (by 85%), diatoms (80%), and green algae (78%), while the addition of zooplankton and nutrients led to a 96% reduction for diatoms. While both submerged macrophytes and the added cladocerans impacted the native zooplankton community, the macrophytes exerted stronger effects on phytoplankton and zooplankton diversity, composition, and structure. Intriguingly, nutrient addition did not alter the main effects of macrophytes and large cladocerans. Our findings reveal the positive potential of introducing submerged macrophytes in tropical shallow lakes, even at a low to moderate percentage of the volume inhabited, to control toxic cyanobacterial blooms. Under our experimental conditions, the method was effective even without extra zooplankton grazing and at increased nutrient input.

Single-/Co-Driving of Tetracycline, Triclocarban and Zinc on Microbial Community, Resistome and Function in the Cyanobacteria-Blooming Freshwater Ecosystem.

Environmental concentrations of antimicrobials can inhibit Cyanobacteria, but little is known about their effects on Cyanobacteria-blooming freshwater ecosystem. Here, a 21 days' outdoor freshwater mesocosm experiment was established to study effects of single and combined tetracycline, triclocarban and zinc at environmental concentrations on microbial community, microbial function and antimicrobial resistance using amplicon- and metagenomic-based methods. Results showed that three chemicals reshaped the microbial community with magnified effects by chemical combinations. Relative abundance of Cyanobacteria was decreased in all chemical groups, especially from 74.5 to 0.9% in combination of three chemicals. Microbial community networks were more simplified after exposure. Proteobacteria and Bacteroidetes predominated in Cyanobacteria-degraded ecosystems, and their relative abundances were significantly correlated with antibiotic resistome, suggesting that they might host antibiotic resistance genes. Notably, relative abundance (copy per 16S rRNA gene) of total antibiotic resistome reached five to nine folds higher than the initial abundance in chemical-combined groups. The affected antibiotic resistance genes referred to a wide range of antibiotic classes. However, weak effects were detected on biocide/metal resistance and microbial virulence. Three chemicals posed complicated effects on microbial function, some of which had consistent variations across the groups, while some varied greatly in chemical groups. The findings highlight sensitivity of Cyanobacteria-blooming ecosystem to antimicrobials.

Evolution and distribution of antibiotic resistance genes in submerged macrophytes and biofilm systems: From seasonal monitoring to mesocosm experiments

The aquatic ecosystem has been extensively investigated as a hotspot for the spread of antibiotic resistance genes (ARGs); yet, the evolution and distribution of ARGs profiles in submerged macrophytes biofilms and surrounding water remained unclear. In this study, the dynamic distribution and seasonal variations of microbial communities and ARGs profiles were investigated, alongside their assembly processes and mutual interactions. Bacitracin and multidrug resistance genes were predominant, constituting more than 60% of the total ARGs abundance. The deterministic processes (<65%), influenced by the physicochemical properties of the river environment, governed the assembly and composition of ARGs profiles, exhibiting significant seasonal variation. The peak diversity (21 types) and abundance (0.316 copy ratios) of ARGs were detected during the summer. Proteobacteria and Actinobacteria were the dominant bacterial phyla, accounting for 38.41–85.50% and 4.03–27.09% of the microbial community, respectively. Furthermore, Proteobacteria, especially genera such as Acinetobacter, Burkholderia, and Pseudomonas, with various resistance sequences, were the primary carriers of multiple ARGs. Notably, the genetic exchanges between biofilms and surrounding water facilitated the further propagation of high-risk ARGs, posing greater ecological risks. Redundancy analysis indicated that the total nitrogen and temperature in water determined the fate of pathogenic-resistant species. These findings provided theoretical support for the mitigation of ARGs contamination in aquatic environments.

Carbon Storage Potential and Saturation Behavior of Soils As Influenced by Level of C Input and Soil Types in Indian Sub-Continent

ABSTRACT Agricultural soils have the potential to store C (carbon), thereby improving soil health, and contributing to climate change mitigation. However, the capacity of a soil to hoard C may be limited. We tested the C saturation behavior of agricultural soils belonging to predominant soil orders (Inceptisols, Entisols, Alfisols, Aridisols and Vertisols) in Indian Subcontinent. A mesocosm experiment in open environmental conditions was conducted with six rate of farmyard manure (FYM) addition (0, 2.5, 5.0, 10.0, 20.0 and 40 Mg ha−1) for three and half years and total carbon (TC) was analyzed. Addition of more than 10 Mg FYM ha−1 enhanced TC content of soil with the period of experimentation irrespective of soil orders. Application of C input of the agriculturally recommended addition of FYM in India at 5.0 Mg ha−1 maintained the soil TC content. Without addition of any C input, sometimes there was depletion in native carbon. With higher levels of C additions, all the soils did not show any evidence of C saturation, thereby suggesting their higher potential to additional C storage. Indian agricultural soils could contribute significantly toward achieving the target of “4 per 1000” initiative of the United Nations. Higher organic carbon in soils would make agroecosystems more resilient toward extreme climate events and sustain crops productivity thereby could help to meet the food demand of the ever-increasing population of the country in the years to come.

Eurasian watermilfoil (Myriophyllum spicatum) alters its root topology but conserves its root branching in response to freshwater cultural eutrophication

Cultural eutrophication is the main cause of the decline of submerged plants in freshwater ecosystems. While many studies have focused on the nutrient uptake by the roots of these plants, less attention has been given to the effects of eutrophication on root structure. We designed a mesocosm experiment with Eurasian watermilfoil (Myriophyllum spicatum), a submerged plant indigenous to the Eurasian continent. The responses of plant functional traits, including growth traits, morphological traits and root topological indices, to different nitrogen (N) and phosphorus (P) concentrations were elucidated. We found that high P concentrations suppressed all the morphological traits and reduced the root topological traits, whereas N concentrations had a comparatively minor effect. Although the root branching of M. spicatum did not change, its root topology became more dichotomous with fewer exterior root links being formed in nutrient-rich habitats, and the root form changed from deep and thin to shallow and dense with increasing P concentrations. The root nutrient absorption ability of M. spicatum may decrease with cultural eutrophication, and this change most likely reduces its anchoring ability and increases its sensitivity to dislodge from the sediment if disturbed by hydraulic forces.

Dung beetles drive direct and indirect changes in ecosystem multifunctionality

Abstract Measuring ecosystem multifunctionality (EMF) could be a valuable method for assessing whether nature‐based solutions, such as introducing non‐native species to benefit ecosystem functioning, yield net positive outcomes. While EMF metrics may provide a coarse overview of the functioning of a system, such metrics can obscure the interactions among multiple simultaneously occurring ecosystem functions. This could limit the predictive value and overall efficacy of EMF metrics for the management of environmental change impacts on ecosystem functioning. We carried out a mesocosm experiment with dung beetle temporal species richness (diversity) treatments in a pasture ecosystem in Aotearoa New Zealand and quantified cascading biotic and abiotic effects of introduced dung beetles (Onthophagus binodis and Onitis alexis) on multiple ecosystem functions. We measured nine individual ecosystem functions affected by dung beetles, including dung removal, total soil carbon, nitrogen, phosphorus, soil microbial respiration, nitrate N, ammonium N, anaerobically mineralisable N and pasture biomass production. We first tested the effects of temporal dung beetle diversity on the nine individual ecosystem functions. We then tested how introduced dung beetle temporal diversity affects ecosystem multifunctionality by calculating EMF metrics using the averaging, threshold and the Hill numbers approaches. Finally, to investigate the underlying interactions among individual functions, we tested the direct and indirect effects of introduced dung beetles on the nine ecosystem functions using structural equation modelling (SEM). Only one out of the nine individual ecosystem functions was significantly affected by dung beetle introductions, whereas five of the six calculated EMF metrics increased significantly with temporal diversity of introduced dung beetles. However, when modelled within an SEM framework, dung beetle temporal diversity was found to directly affect dung removal, but with cascading effects on total N and anaerobically mineralisable N. Our results suggest that introducing and increasing dung beetle temporal diversity enhances the provisioning of multiple ecosystem functions, but that our ability to detect and explain changes in ecosystem multifunctionality is critically dependent on how EMF is quantified. Read the free Plain Language Summary for this article on the Journal blog.