Detrital Food Webs Research Articles

The isotopic signature of the \u201carthropod rain\u201d in a temperate forest

Forest canopy is densely populated by phyto-, sapro-, and microbiphages, as well as predators and parasitoids. Eventually, many of crown inhabitants fall down, forming so-called ‘arthropod rain’. Although arthropod rain can be an important food source for litter-dwelling predators and saprophages, its origin and composition remains unexplored. We measured stable isotope composition of the arthropod rain in a temperate mixed forest throughout the growing season. Invertebrates forming arthropod rain were on average depleted in 13C and 15N by 1.6‰ and 2.7‰, respectively, compared to the soil-dwelling animals. This difference can be used to detect the contribution of the arthropod rain to detrital food webs. Low average δ13C and δ15N values of the arthropod rain were primarily driven by the presence of wingless microhytophages, represented mainly by Collembola and Psocoptera, and macrophytophages, mainly aphids, caterpillars, and heteropterans. Winged arthropods were enriched in heavy isotopes relative to wingless specimens, being similar in the isotopic composition to soil-dwelling invertebrates. Moreover, there was no consistent difference in δ13C and δ15N values between saprophages and predators among winged insects, suggesting that winged insects in the arthropod rain represented a random assemblage of specimens originating in different biotopes, and are tightly linked to soil food webs.

Incorporation of marine organic matter by terrestrial detrital food webs: abiotic vs. biotic vectors

Marine organic matter can potentially enter terrestrial ecosystems via abiotic or biotic vectors. The former is facilitated by e.g. waves, tides, winds, etc.; the latter – by the activity of organisms, e.g. seabird migration. However, differences in its assimilation rate in detrital food webs at different distance from water remain generally unexplored. To fill this gap, we compared the consumption of marine organics by terrestrial invertebrates within coastal ecosystems of the Black sea using stable isotope analyses of carbon and nitrogen. We focused on relatively inland (100 m from the coast) forested areas with the recently established overwintering colonies of the great cormorant (Phalacrocorax carbo) and control ecosystems isolated from any marine organic matter input. Guano and cormorant food leftover input led to the significant increase of δ15N values of soil, litter and all trophic groups of soil invertebrates. However, δ13C values changed to a smaller extent. The importance of marine resources (in a form of guano) as a carbon source for soil arthropods was relatively low: approximately 15% of their diet. In contrast, coastal soil invertebrates were significantly enriched with 13C compared to control and cormorant-influenced ecosystems as they were greatly dependent on the seaweed and other marine resources (on average 45% of coastal invertebrate diet). We conclude that marine resources delivered by an abiotic vector may form the basis of the soil food web diets in a 15 m zone from the water edge. Alternatively, the biotic transfer further inland (forest on a cliff 100 m away from the water edge) with e.g. nitrogen-rich seabird guano or food remains may geographically extend proliferation of marine nutrients into terrestrial ecosystems. As far as we know, our results are among the first to demonstrate the spatial zoning of mechanisms securing bottom-up subsidy of biogenic elements to soil ecosystems having originated from the sea.

Mathematical modelling of the interaction of winter wheat (Triticum aestivum) and Fusarium species (Fusarium spp.)

The existing methods of pathogen control in agroecosystems are insufficiently effective against Fusarium species due to the high variability and specific biology of these fungi . The aim of our work was to reconstruct the kinetic mechanisms that determine the biomass of Fusarium species in the agroecosystem, and to find out the optimal ways to manipulate the structure of detrital food webs, which would minimize the risk of Fusarium contamination. The studied system consisted of three components: mycophagous soil nematodes, the soil phase of Fusarium species, and winter wheat seedlings. Two system models were compared: general (based on general postulates of population dynamics) and lab-specific (taking into account the peculiarities of the conditions of the laboratory experiment). Based on the results of parameter estimation and global sensitivity analysis, three model parameters were identified with a strongest impact on the biomass of Fusarium species: (1) the reproduction rate of mycophagous nematodes due to the feeding on Fusarium, (2) the death rate of mycophagous nematodes, and (3) the carrying capacity of Fusarium species. Based on the results of stochastic modelling, the internal variability of the biomass dynamics of Fusarium species exceeded by two orders of magnitude the internal variability of abundance dynamics of mycophagous nematodes. The developed model made it possible to obtain fundamentally new information about the basic mechanisms of interaction of Fusarium species, mycophagous nematodes and winter wheat plants, and highlight the most promising mechanisms which can reduce the biomass of Fusarium species in the soil.

Beneath the Leaf-Litter: Can Salamander Personality Influence Forest-Floor Dynamics?

Ecological research demonstrates how intraspecific phenotypic variation can have consequences for community dynamics. However, the effects of animal personalities (i.e., intraspecific behavioral variation) on ecological processes remains relatively understudied. Using Red-backed Salamanders (Plethodon cinereus) and the detrital food web as a model system, we conducted a laboratory mesocosm experiment to explore whether or not the personality type of a top-level predator could affect the community structure within a complex, terrestrial food web. We used behavioral assays to investigate the repeatability of salamander behaviors, and classified individuals as either active or inactive. We then subjected laboratory mesocosms to one of four treatments for 3 mo: one active salamander, one inactive salamander, control (no salamander), and a pre-experimental reference. Our results indicate that the effect of P. cinereus on the detrital food web might be behaviorally mediated, with only the most active salamanders affecting community structure. Specifically, mesocosms housing active salamanders contained less diverse invertebrate communities than all other treatments. This difference was primarily driven by springtails, which were more abundant within mesocosms housing active salamanders. We also found that salamander personality was associated with cover board use inside mesocosms, with inactive salamanders exhibiting a more philopatric use of cover objects than active individuals. Leaf-litter degradation did not differ between treatments, indicating that the ecological effects of salamanders were too weak to influence basal resources within the detrital food web. Our study prompts further questions regarding the potential for animal personalities to influence ecological processes within terrestrial communities.

Flow regime change alters shredder identity but not leaf litter decomposition in headwater streams affected by severe, permanent drying

Abstract Climate change is altering hydrologic regimes globally. In the Mediterranean climate region of south‐western Australia (SWA), climate drying has caused many perennial streams to switch to intermittent flow regimes. Shifts in flow regime are expected to alter physical and biological processes in streams, including litter decomposition, which is the basis of detrital food webs. Decomposition of jarrah (Eucalyptus marginata) leaves and associated macroinvertebrates, were measured over 320 days in 2018–19 using leaf bags in four headwater streams in SWA. Two streams retained perennial reaches and two were formerly perennial streams that are now intermittent. Pre‐planned comparisons that formed a partial multiple before–after, control–impact design were used to compare the results to an experiment conducted in 1982–83 in some of the same streams when all were perennially flowing. Both experiments used coarse and fine‐mesh bags containing 10 g of dry leaves. In one perennial stream, coarse bags lost more weight than fine bags at the last sampling time only, when shredding caddisflies arrived on the leaf bags. In the other perennial stream, leaf‐mining chironomids entered fine‐mesh bags and accelerated decomposition so that they lost more weight than the coarse‐mesh bags. There was no difference in weight loss between fine and coarse‐mesh leaf bags in the two intermittent streams. In 2018–19, decomposition was slower in dry reaches of intermittent streams than in perennial reaches. Leaf weight loss increased with the resumption of flow in intermittent streams, so that by the end of the experiment, similar amounts of leaf weight had been lost in intermittent and perennial reaches. Thus, although the temporal pattern of decomposition differed between intermittent and perennial reaches, after 320 days, they had reached a similar endpoint. Over similar experimental duration, mean leaf weight remaining in perennial reaches at the end of the experiment did not differ between the 1982–83 study and 2018–19, showing that leaf decomposition had not changed in reaches that retained perennial flow. As mean leaf weight remaining also did not differ between intermittent and perennial streams in 2018–19, leaf decomposition was robust to flow regime change. However, since 1982–83, these streams have lost populations of shredding caddisflies and stoneflies, which were replaced by other shredders (e.g. leaf mining chironomids Stenochironomus sp.), showing that there was some redundancy amongst shredder species. As climate change progresses, drying flow regimes will become commonplace in Mediterranean (and other) climate regions globally. This study indicates that litter decomposition may be maintained as streams transition to intermittency although shredder species may change. However, the impact of shredding species on leaf decomposition varies amongst studies, so effects of the loss of shredder species sensitive to drying may also vary, and in some cases their loss may substantially alter ecosystem processes.

No evidence of top‐down effects by ants on litter decomposition in a temperate grassland

AbstractAnts play multiple roles in ecosystems, but their ability to affect decomposition processes in temperate grasslands is relatively unknown. We investigated whether the suppression of ant populations influenced litter decomposition in grasslands via predation of some decomposers (e.g., mites and springtails) and/or microbial activity and composition. We performed two successful ant suppression treatments (seven weeks, 37% suppression, year 1, 10 weeks, 70% suppression, year 2) over the course of a 59‐week experiment. We then assayed the effects of ant suppression using coarse‐ and fine‐mesh litterbags and evaluated litter chemistry, microbial and arthropod communities, and microbial enzyme activity. Ant suppression efforts reduced ant abundance and altered ant, arthropod decomposer, and non‐ant predator community composition. However, ant suppression did not affect decomposer arthropod abundance, litter mass loss, microbial composition, or enzyme activity in litterbags. Litterbag mesh size did not alter microbial composition, perhaps due to a failure to exclude decomposers, as mites and springtails were more or equally abundant in fine‐mesh bags. Nevertheless, mesh size did change litter chemistry, suggesting that mesh size‐mediated microenvironments affect decomposition environment regardless of invertebrate exclusion. Coarse‐mesh litterbags had higher concentrations of microbial sugars, lignin, and N and lower concentrations of litter C and crystalline cellulose than fine‐mesh litterbags. Litterbag mesh size may alter decomposition processes irrespective of invertebrate abundance. We found no evidence that ant predation was an important driver of decomposer populations or decomposition in these systems, and we suspect redundancy at the top of the detrital food web dilutes the role of ants.

Brown meets green: light and nutrients alter detritivore assimilation of microbial nutrients from leaf litter.

In aquatic detrital-based food webs, research suggests that autotroph-heterotroph microbial interactions exert bottom-up controls on energy and nutrient transfer. To address this emerging topic, we investigated microbial responses to nutrient and light treatments during Liriodendron tulipifera litter decomposition and fed litter to the caddisfly larvae Pycnopsyche sp. We measured litter-associated algal, fungal, and bacterial biomass and production. Microbes were also labeled with 14 C and 33 P to trace distinct microbial carbon (C) and phosphorus (P) supporting Pycnopsyche assimilation and incorporation (growth). Litter-associated algal and fungal production rates additively increased with higher nutrient and light availability. Incorporation of microbial P did not differ across diets, except for higher incorporation efficiency of slower-turnover P on low-nutrient, shaded litter. On average, Pycnopsyche assimilated fungal C more efficiently than bacterial or algal C, and Pycnopsyche incorporated bacterial C more efficiently than algal or fungal C. Due to high litter fungal biomass, fungi supported 89.6-93.1% of Pycnopsyche C growth, compared to 0.2% to 3.6% supported by bacteria or algae. Overall, Pycnopsyche incorporated the most C in high nutrient and shaded litter. Our findings affirm others' regarding autotroph-heterotroph microbial interactions and extend into the trophic transfer of microbial energy and nutrients through detrital food webs.

A comparison of decomposition rates and biological colonization of leaf litter from tropical and temperate origins

Litter decomposition is an ecosystem process that allows energy and nutrients transfer from dead plant matter into detrital food webs. Several studies revealed that leaf litter decomposition rates differ across biomes, but the reasons for these differences are not yet clear. Here, we test the role of several leaf litter physical and chemical characteristics as predictors of decomposition rates and whether life forms (evergreen vs. deciduous) differ in decomposition rates. Leaves from dominant riparian trees were collected in four ecoregions (temperate deciduous forest, subtropical seasonal semideciduous forest, tropical Cerrado and subtropical dense ombrophylous forest) and their physical and chemical characteristics were measured. We then determined leaf litter decomposition, colonization by aquatic hyphomycetes and macroinvertebrates in a same stream (i.e., under the same environmental conditions), and consumption rates by shredders under laboratory conditions. Deciduous and evergreen tree species did not differ in the measured litter characteristics, but deciduous leaves decompose faster than evergreens. Leaf litter from tree species from the four ecoregions differed in their physical and chemical characteristics. Litter from temperate deciduous species decomposed faster than litter from the other three ecoregions, generally supported higher aquatic hyphomycete species richness and sporulation rates and higher consumption rates by shredders. There were significant negative correlations between litter decomposition and associated biotic variables and litter initial lignin concentration and lignin:N ratio. We conclude that lignin concentration and lignin:N ratio are important predictors of litter decomposition, although other unmeasured parameters such as micronutrients may also play important roles in this key ecosystem process.

Covariation between plant biodiversity and soil systems in a European beech forest and a black pine plantation: the case of Mount Faito, (Campania, Southern Italy)

Both climate and land-use changes, including the introduction and spread of allochthonous species, are forecast to affect forest ecosystems. Accordingly, forests will be affected in terms of species composition as well as their soil chemical and biological characteristics. The possible changes in both tree cover and soil system might impact the amount of carbon that is stored in living plants and dead biomass and within the soil itself. Additionally, such alterations can have a strong impact on the detrital food web that is linked to litter decomposition. Although there are studies on the influence of plant diversity on soil physical and chemical characteristics, the effects on soil biological activity and carbon storage processes remain largely unknown. The aim of this study was to investigate and compare chemical and biological variables in covariation with plant communities in an autochthonous beech forest (Fagus sylvatica L.) and a black pine plantation (Pinus nigra J.F. Arnold subsp. nigra). Our results confirmed that the two communities were considerably different, with the old-growth beech community having a lower number of plant species and the pine community was in development as a consequence of anthropogenic activities. These aspects of the two communities were also reflected in the soil, with the beech soil having higher nitrogen levels and a more specialized microbial community compared to the pine soil, with most extracellular enzymes (such as peroxidase and chitinase) showing lower activity in the pine soil.

Effects of social organization on the feeding of the striped parrotfish, Scarus iseri

Parrotfishes contribute to important reef processes through their feeding. Individuals may join groups with distinctive social behavior, with unknown implications for their feeding ecology and, ultimately, their functional roles in reef systems. Using Scarus iseri populations in Isla Colon, Panama, we investigated whether individuals belonging to the two main social groups formed by this species (‘Territorial’ and ‘Stationary’ groups) differed in their feeding preferences. Territorial groups had access to a diversity of potential food sources, yet showed selectivity for feeding on sandy substrate. Stationary groups showed high selectivity for filamentous algae, despite this resource being less available for this group than for territorial individuals. Initial phase fish had higher bite rates on plants than terminal phase individuals, while the latter had higher bite rates on soft substrata and sponges, both indicating detritus consumption. Parrotfish sociobiology may therefore influence their relative ecosystem impact, with territorial and terminal individuals in both social groups more involved in the detrital food web and stationary groups contributing to a greater extent on algal removal.

Dynamic feedbacks among tree functional traits, termite populations and deadwood turnover

Abstract Changes in the composition of plant functional traits may affect ecosystem processes through influencing trophic interactions. Bottom‐up control by plant species through food availability to animals may vary with time. However, such dynamics and their consequences for deadwood turnover are poorly known for detrital food webs. We introduce a dynamic conceptual model of the feedback of tree functional traits, (deadwood‐feeding) termite populations and deadwood decomposition. We hypothesized that tree functional diversity (in terms of a wood resource economic spectrum [WES]) supports the sustenance of termite populations via complementary food supplied through time, as deadwood varies in traits both initially across species and because of different decomposition rates. Simultaneously, driven by this temporal dynamics of food quality, the consumption of deadwood by termites should hypothetically sustain deadwood turnover in a functionally diverse forest over time. We tested our hypothesis through an 18‐month termite‐exclusion decomposition experiment by incubating coarse (i.e. 5 cm diameter) deadwood of 34 woody species in two subtropical forests in East China. One site still sustained a healthy population of pangolins as the keystone termite predator, whereas another had lost its pangolins due to hunting and illegal wildlife trade. The results supported our hypothesis: in the first 12 months, termites amplified the positive linear relationship between % wood mass loss and initial wood quality (WES). In contrast, between 12 and 18 months, termite‐mediated consumption, and associated wood mass loss, showed a humpback relation with the initial WES. This shift in termite preference of deadwood species along the WES reflects complementary food availability to termites through time. Synthesis. Our findings imply that tree functional composition, with variation in deadwood quality through decomposition time, can help to sustain termite populations and thereby forest carbon turnover. Future studies need to test whether and how our conceptual model may apply to other detrital systems and food webs. In general, food web research would benefit from a stronger focus on temporal patterns for better understanding the interactions of basal resource functional traits and consumers on ecosystem functions.

Combined carbon flows through detritus, microbes, and animals in reference and experimentally enriched stream ecosystems.

Tracking carbon (C) flow through ecosystems requires quantification of myriad biophysical processes, including C routing through microbial and metazoan food webs. Yet detailed organic matter budgets are rarely combined with simultaneous measurement of C flows supporting microbial and animal production. Here, we synthesize concurrent data sets on organic matter, microbes, and macroinvertebrates from two detritus-based stream ecosystems, one of which was subject to experimental nitrogen (N) and phosphorus (P) enrichment. Our synthesis provides new insights into C flow through forest stream ecosystems. Over 3 yr, the reference stream showed a striking balance of inputs and outputs, with a mean surplus of only 7g C·m-2 ·yr-1 (~1% of annual inputs), presumably stored in sediments as fine particulate organic matter (FPOM). In contrast, N and P enrichment over 2 yr resulted in severe deficits of C (-576g C·m-2 ·yr-1 or~170% of annual inputs), a shortfall presumably met by stored C. Our data set provides an ecosystem-based estimate of the fate of forest litter C at ambient nutrient concentrations: 6.2% was leached as dissolved organic C, 40.6% and 8.5% flowed to litter-associated fungi and bacteria, respectively, 7.5% was consumed by macroinvertebrates, 1.8% was exported as coarse particles, and the remainder (35.4%) was presumably fragmented by biophysical processes. Our calculations also allowed an estimate of inputs into the heterogeneous FPOM pool, which is otherwise difficult to obtain. At naturally low nutrient concentrations, 50.7% was derived from fragmented litter, 39.1% from microbial biomass (mostly fungal), and 10.2% from macroinvertebrate egesta. Nutrient addition drove large changes in C fluxes in the experimental stream, especially in flows of leaf litter to fungi (×1.7 pretreatment) and macroinvertebrates (×2.7), and of FPOM to hydrologic export (×2.6). Our results underscore the key roles of both microbes and metazoans in controlling C flow through detritus-based ecosystems, as well as how release from persistent nutrient limitation may perturb steady-state conditions of C inputs vs. outputs. Our analysis also suggests areas for future research, including assessing the relative importance of stored vs. recycled C in fueling detrital food webs subject to altered nutrient regimes and other global-change drivers.

Detrital subsidy alters the soil invertebrate community and reduces infection of winter wheat seedlings by Fusarium wilt

Biological control of pathogenic Fusarium species through the promotion of detrital food webs is a promising option for agricultural production and could be of high value in organic farming. To obtain quantitative information on the impact of detrital subsidy on the development of Fusarium infection in winter wheat seedlings, we established a 60-day laboratory experiment in which the soil was amended with either a N-poor or a N-rich mixture of straw and compost containing the same amount of organic carbon (200 g C m−2).Compared with the control treatment (no subsidy), shoot biomass decreased by 27% in the N-poor mulch treatment and increased by 24% in the N-rich mulch treatment. For both of the added mulch treatments, the population of mycophagous and predatory mites increased fivefold compared to the control. The abundance of Enchytraeidae also increased in both N-poor (by 68%) and N-rich (by 46%) mulch treatments.Unexpectedly, the abundance of gene copies of total soil fungi and of genus Fusarium in particular, as well as the abundance of Fusarium-specific polysaccharide protein conjugate (FPPC), were not affected by either mulch addition. Nevertheless, wheat seedlings were not infected by Fusarium wilt in either mulch treatment, whereas in the control treatment, the infection incidence was about 9%.The quantitative information obtained here may be important for the development of an ecological control method for cereal diseases caused by pathogenic Fusarium species.

Sulfur deposition changed the community structure of soil nematodes by affecting omnivores-predators

Nematodes generally occupy multiple trophic levels in detrital food webs, which play a vital role in energy flow, material conversion and nematodes community structure stability in the underground ecosystem. Sulfur (S) is one of the important soil nutrients, and it plays an important role in the nutrient cycle of grassland ecosystem. However, the impacts of S on soil fauna and subsurface detrital food webs in grassland ecosystems were rarely studied. Accordingly, to investigate the effects of sulfur deposition on soil nematodes and detrital food webs, we conducted a S addition experiment with distinct intensities from 0 to 50 g S m−2 yr−1 (S 0, S 1, S 2, S 5, S 10, S 15, S 20, and S 50) to simulated sulfur deposition in a meadow steppe of northern China. We documented a significant effect of S addition on the diversity and richness of nematodes, and the species richness of soil nematodes was high in the study site. But S addition had no significant effect on the total abundance and dominant species of nematodes (Cervidellus and Aphelenchus). Results of correlation analysis and structural equation modeling consistently indicated that omnivores-predators were significantly affected by sulfur addition. A significant increase in the Structural Index (which indicates food web structure) suggested increased top-down forces and changed community structure, although bacterivores, fungivores, plant parasites did not significantly. The present results suggest that sulfur deposition would change the composition of nematode community, affect the stability of nematode community structure, and increase the disturbance to the underground ecosystem. The study provides that the detailed information of the response of nematode to S deposition can be used to analyze the process of global change affecting the underground ecosystem.

Can photocatalytic and magnetic nanoparticles be a threat to aquatic detrital food webs?

Freshwaters are likely to serve as reservoirs for engineered nanomaterials (ENMs) due to their accelerated unintentional release, increasing the relevance of assessing their impacts on aquatic biota and the ecosystem processes they drive. Stream-dwelling microbes, particularly fungi, and invertebrate shredders play an essential role in the decomposition of organic matter and transfer of energy to higher trophic levels. We assessed the impacts of two photocatalytic (nano-TiO2 and erbium doped nano-TiO2) and one magnetic (nano-CoFe2O4) ENMs on detrital-based food webs in freshwaters by exposing chestnut leaves, colonized by stream-dwelling microbes, to a series of concentrations (0.25–150 mg L−1) of these ENMs. Microbial decomposition and biomass of fungal communities, associated with leaves, were not affected by the ENMs. However, the activities of antioxidant enzymes of microbial decomposers were significantly (P < 0.05) stimulated by ENMs in a concentration-dependent way, suggesting oxidative stress in stream microbial communities. The stronger responses of these stress biomarkers against nano-TiO2 (increase upto 837.5% for catalase, 1546.8% for glutathione peroxidase and 1154.6% for glutathione S-transferase) suggest a higher toxicity of this ENM comparing to the others. To determine whether the effects could be transferred across trophic levels, the invertebrate shredder Sericostoma sp. was exposed to ENMs (1 and 50 mg L−1) for 5 days either via contaminated water or contaminated food (leaf litter). Leaf consumption rate by shredders decreased significantly (P < 0.05) with increasing concentrations of ENMs via food or water; the effects were more pronounced when exposure occurred via contaminated food (up to 99.3%, 90.7% and 90.3% inhibition by nano-Er:TiO2, nano-CoFe2O4 and nano-TiO2, respectively). Overall, the tested photocatalytic and magnetic ENMs can be harmful to microbial decomposers and invertebrate shredders further compromising detrital-based food webs in streams.

The earthworm species Eisenia fetida accelerates the decomposition rate of cigarette butts on the soil surface

Cigarette butts (CBs) represent the most common, though poorly biodegradable, type of waste on Earth. Thrown on the soil surface, they can remain unchanged for years, poisoning surrounding ecosystems with toxins accumulated during the smoking process. However, there is practically no data on the effect of smoked CBs on soil biota or soil animals in particular, nor on the potential of edaphic fauna to facilitate their decomposition. One of the most promising agents among soil animals are earthworms, which are known to be beneficial in the processes of recalcitrant organic matter degradation and stimulation of microbial activity in detrital food webs. In a microcosm experiment with the sod podzolic soil, we aimed at testing the effect of the commonly cultured epigeic earthworm Eisenia fetida (Savigny 1826) on the biodegradation rate of CBs and the possible adverse effects of this waste on the species. The experiment had a full-factorial design with three categorical predictors: CB number (0, 1 and 3 per microcosm); smoking condition (smoked and unsmoked CBs) and two levels of earthworm amendment (0 and 4 per microcosm). During 70 days of the experiment, we did not observe any smoked CB-induced mortality of earthworms. The addition of E. fetida significantly increased the CB mass loss across all treatment combinations. Specifically, earthworms improved the decomposition rate from 30 to 36% (p < 0.05), on average. However, this improvement was mainly associated with CB paper wrapping consumption. The inhibition of CO2 emission in microcosms with CBs and earthworms suggested the direct consumption of this waste by E. fetida, rather than modulation of the degradation potential of a microbial community. E. fetida appears to thus be a moderately promising agent for CB biodegradation with the simultaneous reduction in carbon loss from soil through the microbial channel in the studied soil type. These results open perspectives for the further evaluation of the role of soil macroinvertebrates in recalcitrant organic waste management in general and CBs in particular. SummaryWe demonstrated that earthworms can efficiently decompose smoked and unsmoked cigarette butts regardless of their toxic potential and simultaneously reduce associated microbial activity.

Detrital food web contributes to aquatic ecosystem productivity and rapid salmon growth in a managed floodplain.

Similar to many large river valleys globally, the Sacramento River Valley has been extensively drained and leveed, hydrologically divorcing river channels from most floodplains. Today, the former floodplain is extensively managed for agriculture. Lack of access to inundated floodplains is recognized as a significant contributing factor in the decline of native Chinook Salmon (Oncorhynchus tshawytscha). We observed differences in salmon growth rate, invertebrate density, and carbon source in food webs from three aquatic habitat types—leveed river channels, perennial drainage canals in the floodplain, and agricultural floodplain wetlands. Over 23 days (17 February to 11 March, 2016) food web structure and juvenile Chinook Salmon growth rates were studied within the three aquatic habitat types. Zooplankton densities on the floodplain wetland were 53x more abundant, on average, than in the river. Juvenile Chinook Salmon raised on the floodplain wetland grew at 0.92 mm/day, 5x faster than fish raised in the adjacent river habitat (0.18 mm/day). Two aquatic-ecosystem modeling methods were used to partition the sources of carbon (detrital or photosynthetic) within the different habitats. Both modeling approaches found that carbon in the floodplain wetland food web was sourced primarily from detrital sources through heterotrophic pathways, while carbon in the river was primarily photosynthetic and sourced from in situ autotrophic production. Hydrologic conditions typifying the ephemerally inundated floodplain—shallower depths, warmer water, longer water residence times and predominantly detrital carbon sources compared to deeper, colder, swifter water and a predominantly algal-based carbon source in the adjacent river channel—appear to facilitate the dramatically higher rates of food web production observed in the floodplain. These results suggest that hydrologic patterns associated with seasonal flooding facilitate river food webs to access floodplain carbon sources that contribute to highly productive heterotrophic energy pathways important to the production of fisheries resources.

Kelp forests

Vergés and Campbell introduce the kelp forest ecosystem.

Exploring trophic effects of spotted knapweed (Centaurea stoebe L.) on arthropod diversity using DNA metabarcoding

Biological invasions are of particular concern in grasslands, as these systems are highly susceptible to changes in ecosystem energy flows following invasions by exotic plants. Spotted knapweed (Centaurea stoebe L.), a Eurasian, perennial forb, is considered one of the most ecologically harmful invasive plants in North American grasslands and may lead to changes in trophic dynamics, particularly within arthropod communities, which depend on plants for food and habitat. Using DNA metabarcoding to assess community dynamics of arthropods collected from pitfall traps and sweep nets, we explored the effects of C. stoebe density on the alpha, beta and functional diversity of arthropods in a semi-arid grassland in British Columbia, Canada. We used trait-based approaches to investigate the functional responses of terrestrial arthropod communities to better understand the effects of C. stoebe on trophic dynamics. Our study found seasonal differences in the beta-diversity of arthropods, but no differences in arthropod alpha-diversity in knapweed populations. However, our study found a significant reduction in detritivore relative abundance coupled with increases in predator relative abundance, indicating that knapweed density altered the detrital food web. Conversely, herbivores were unaffected by knapweed density, suggesting evidence for greater stability of the grazing food web. Further, predator:prey ratios were highest under high knapweed density. These ratios suggest that top-down effects are likely stronger than the bottom-up effects of C. stoebe invasion. DNA metabarcoding provides the tools to develop detailed surveys of species diversity across a range of environments and trophic levels, which could be a useful guide for planning restoration.

Effects of novel, non-native detritus on decomposition and invertebrate community assemblage

When non-native primary producers become successful, the structure and function of native detrital food webs can be fundamentally altered. Salt marsh estuaries of the southeastern USA are in part detritus-based ecosystems and rely on the annual production of detritus from a single native species, the smooth cordgrass Spartina alterniflora. Over the last several decades, the success of a novel primary producer, the red macroalga Agarophyton vermiculophyllum (formerly Gracilaria vermiculophylla), in a system historically devoid of macroalgae provides the opportunity to measure the effect of non-native basal resources on native detrital pathways. We conducted 2 in situ experiments to compare (1) decomposition rates of A. vermiculophyllum and S. alterniflora and (2) invertebrate colonization rates onto dead A. vermiculophyllum and S. alterniflora. Relative to S. alterniflora, we found that A. vermiculophyllum decomposes more rapidly, losing 80% or more of its biomass within 3 wk, while S. alterniflora lost ~50%. Experimental litterbags with decomposed A. vermiculophyllum and S. alterniflora harbored similar highly abundant invertebrate communities that differed greatly from denuded areas. Our results demonstrate that A. vermiculophyllum provides a complementary source of labile organic matter relative to S. alterniflora, boosting the amount of food and available habitat for small invertebrates of intertidal salt marshes and mudflats. Thus, non-native macrophytes may differentially affect community and ecosystem properties just as much when dead as alive, especially when they are biologically distinct from native species.