Litter Fragments Research Articles

Enlarging interface reverses the dominance of fungi over bacteria in litter decomposition

Soil microorganisms are primary decomposers driving carbon and nutrient cycling in terrestrial ecosystems. One prevailing view is that fungi, rather than bacteria, play a predominant role in litter decomposition. However, the roles of bacteria and factors that restrict their activity during decomposition remain unclear. We hypothesized that the limiting activity of bacterial decomposers is associated with litter size beyond chemical quality. To address this gap, we conducted a 180-d decomposition microcosm experiment to investigate the effect of fragment size (large, 1–2 mm; middle, 0.18–0.28 mm; small, <0.07 mm) of oak and pine litters on bacterial or fungal decomposition. Bacterial and fungal decomposition were accelerated with fragment size decrease, suggesting that an interface effect existed between microbial decomposers and litter. Generally, the decomposition ability of bacteria was more sensitive to changes in fragment size compared to fungi. Fungi resulted in faster decomposition of large fragments than bacteria. For small oak litter fragments, bacteria showed faster decomposition than fungi, whereas the opposite was true for small pine litter. Therefore, the decomposition dominance of bacteria and fungi was regulated by fragment size and influenced by the chemical quality of litter, especially the lignin:N ratio. The contrasting decomposition dominances of bacteria versus fungi were likely attributed to filamentous fungi penetrating litter interiors and forming mycelial bridges between scattered litters. Bacteria resided on litter surfaces and even formed biofilms. Consistent with the findings of the microcosm experiment, the proportion of small fragments was greater in the fresh litter layer than in the decomposed layer in the field, and greater in the pine forest than in the oak forest, suggesting the fresh, large, and low-quality litter was preferentially fragmented by fungi. Consequently, the dominance of fungi and bacteria during litter decomposition in the conventional view should be revisited considering the litter size.

Deepened snow cover accelerates litter decomposition by stimulating microbial degradation

Changing precipitation patterns and global warming have greatly changed winter snow cover, which can affect litter decomposition process by altering soil microenvironment or microbial biomass and activity. However, it remains unknown how and to what extent snow cover affects litter decomposition during winter and over longer periods of time. Here, we conducted a meta-analysis to synthesize litter decomposition studies under different levels of snow cover. Overall, deepened snow significantly enhanced litter decomposition rate and mass loss by 17% and 3%, respectively. Deepened snow enhanced litter carbon loss by 7% but did not impact the loss of litter nitrogen or phosphorus. Deepened snow increased soil temperature, decreased the frequency of freeze-thaw cycles, and stimulated microbial biomass carbon and bacterial biomass during winter, but had no effect on these parameters in summer. The promoting effect of deepened snow cover on litter decomposition in winter is mainly due to its positive effect on microbial decomposition by increasing soil temperature and reducing freeze-thaw cycles exceeded its negative effect on physical fragmentation of litter by reducing freeze-thaw cycles. Our findings indicate that the changes in winter snow cover under global change scenarios can greatly impact winter litter decomposition and the associated carbon cycling, which should be taken into consideration when assessing the global carbon budget in modeling.

Litter consumption by macrodetritivores depends more on mechanical than on nutritional constraints

Ecosystem functions greatly depend on trophic interactions between consumers and their resources. Resource consumption depends on ingestion, digestion, and allocation processes. Mechanical constraints are expected to influence ingestion, while metabolic and nutritional constraints are expected to influence allocation. Leaf litter are resources presenting a high mechanical and nutritional heterogeneity that depends on plant identity and on physical and microbial processing over the course of decomposition. Litter consumption by detritivores is known to depend on metabolic and nutritional constraints but the importance of mechanical constraints is yet unknown. After accounting for metabolic constraints on consumption rate, we tested the relative importance of mechanical and nutritional constraints in explaining litter consumption rates by detritivores. For this, we exposed 16 leaf treatments (eight leaf species either just leached or leached and microbially conditioned) to four aquatic and five terrestrial detritivore taxa in laboratory no‐choice consumption experiments. We investigated two mechanical constraints: grabbing and fragmenting the resource, by measuring suitable couples of mechanical traits for both litter and detritivores. We also investigated four nutritional constraints related to N, P, K and Ca contents in both detritivores and litter. For each constraint, we also tested if trait matching significantly contribute to explain consumption. Our analysis revealed that both mechanical and nutritional constraints are influencing mass‐independent consumption rate but that mechanical constraints predominate over nutritional constraints. Litter fragmentation, studied through litter toughness and detritivore biting force, was especially important to explain consumption rate. Nutritional constraints were dominated by P constraints. Trait‐matching had very weak importance and was significant only for P constraints. Our findings highlight the importance of mechanical constraints for litter consumption by detritivores.

Compositional Profiles and Spatial Distribution of Microplastics Across Three Selected Rivers in Rivers State, Nigeria

Microplastics (MP) are ubiquitous and persistent contaminants in waterbodies and a pervasive and preventable threat to the health of marine ecosystems. These particles are defined as &lt;5 mm in size and can be introduced into the environment via primary sources such as the use and disposal of microbeads in cosmetic, cleaning products and sandblasting, as well as secondary sources which include the fragmentation of litter by mechanical or UV light-induced degradation. This study was conducted to investigate the concentrations of microplastic contaminants in Imo River, Ntawogba River and New Calabar River as well as the physicochemical and microbial characteristics of the water bodies. Composite sampling technique was used in this study. The physicochemical analysis of the water samples was carried out both in-situ and ex-situ while the microbiological analysis was performed ex-situ to determine the load using APHA 9215B/9610B and ASTM D 5465-93 (Pour plate) test methods. The total heterotrophic bacteria were more predominant than the other microbial groups in samples obtained from the three rivers. The relatively higher hydrocarbon-utilizing bacteria counts obtained in samples collected from Ntwawogba River is suggestive of benign hydrocarbon contamination of the river. Two techniques (Fourier Transform Infrared Spectroscopy, FTIR and Gas Chromatography-Mass Spectrometry, GC-MS) were used to identify the microplastics and their concentrations. The reference spectra for the FTIR results were in the spectral range stretching from 4000–650cm-1 where the prominent absorption peak at 2920 cm-1 corresponded to aliphatic C-H (Hydrocarbon) stretching, indicating the presence of CH2 (Alkene) and CH3 (Alkane) groups in the microplastic samples, at 1725 cm-1 associated with carbonyl (C=O). The band at 1600 cm-1 is characteristic of aromatic C=C stretching, at 1200-1000 cm-1 range suggesting C-O stretching vibrations. The region between 800 and 700 cm-1 corresponded to out-of-plane bending vibrations commonly seen in aromatic groups while the GC-MS polymer identification library produced results of both qualitative and quantitative assessment of the microplastics. The eight (8) priority MP polymers found in the water samples were polyethylene (PE), polyethylene terephthalate, dioctyl terephthalate, polybrominated diphenyl ether, tetrabromobisphenol A, polypropylene, acrylic fibre, and polystyrene. SEM images of the MPs were acquired at various magnifications to capture their surface features, shapes, and sizes. PE was found to be the most ubiquitous MP (45.74%, 45.84% and 47.76%) across Imo, Ntawogba and New Calabar River, respectively.&#x0D; Results obtained indicate the pervasiveness of MPs in the studied rivers and signify threat to aquatic organisms and man via their biomagnification through the food chain.

Effects of copper and cadmium on stream leaf decomposition: evidence from a microcosm study.

We seek to understand how copper and cadmium act on leaf litter decomposition by their effects on microbial conditioning and litter fragmentation by invertebrates. In this study, we evaluated, in an integrated manner, different biological elements responsible for functioning of streams. Thus, we performed a microcosm assay with different concentrations for the two metals and their combination, evaluating their effects on fungi sporulation rate, consumption rate by shredders, and, consequently, the leaf litter decomposition rates. Sporulation rates were affected by all copper concentrations tested 10 × = 16µg L-1 and 25 × = 40µg L-1) but significantly reduced only at the highest concentration of cadmium (25 × = 22.5µg L-1). Increased copper and cadmium concentrations reduced the consumption of leaf litter by Phylloicus at 60%. The concentrations (10 × and 25 ×) of both metals resulted in a reduction in decomposition rates. When combined, copper and cadmium negatively affected microbial conditioning, consumption by shredders, and leaf litter decomposition. Increases in concentrations of copper and cadmium directly affected organic matter decomposition in aquatic environments. Thus, the presence of a high concentration of heavy metals in aquatic environments alters the functioning of ecosystems. As trace-elements occur in a combined manner in environments, our results show that the combined effects of different metals potentiate the negative effects on ecosystem processes.

Biogeochemical response of subtropical treatment wetlands to different flow conditions

The biogeochemical response to different flow conditions within two parallel, well-performing flow-ways (FWs) in Everglades Stormwater Treatment Area (STA)-2 was studied. Three flow events in FW1, an emergent aquatic vegetation (EAV) based system and three flow events in FW3, a submerged aquatic vegetation (SAV) dominated system, were carried out between August 2015 and July 2017. These flow events included either low or moderate flow that was preceded and/or followed by no flow. These flow scenarios were designed to simulate different hydraulic and hydrologic conditions that STAs experience during full-scale operations. Hydraulic loading rates (HLRs, flow volume per day/wetland effective treatment area) during the flow events ranged from 0.5 to 10.4 cm d−1 with resulting phosphorus loading rates (PLRs, daily load/wetland effective treatment rate) of 1 to 20 mg P m−2 d−1. The ability of these flow-ways to remove and transform P in the water column under different flow conditions was evaluated using water quality data from autosamplers and weekly grab samples collected at six monitoring stations along each flow-way.Distinct water column concentration gradients of total phosphorus (TP) from inflow to outflow at all phases of the flow events for both flow-ways were observed. The magnitude at which P is removed from the water column increased with fractional distance from the inflow and was greater for the EAV-dominated system (FW1) than the SAV-based system (FW3). This system response translated to higher TP concentration reduction in EAV than SAV. Inflow to outflow TP concentration reductions for EAV were 94, 88, and 86% for moderate (MF), low (LF), and no flow (NF), respectively. For SAV, TP concentration reductions were 73, 71, and 64% for MF, LF, and NF, respectively. A significant increase in TP concentrations [largely dissolved organic P (DOP) and particulate P (PP)] in the SAV-dominated system was observed under no flow condition. The increase was attributed to in-situ production of PP through several mechanisms that likely include phytoplankton growth, periphyton sloughing, litter fragmentation, and resuspension via entrainment or bioturbation. While soluble reactive P (SRP) was the dominant form of inflow TP removed along the EAV FW, PP accounted for most of the reduction in TP concentration along the SAV FW, under both flow and no flow conditions. Particulate P and DOP comprised the residual P pool at the outflow region of each FW with slightly higher concentrations in the SAV than the EAV FW under no flow condition. The removal of P from the water column in the EAV FW was largely attributed to biotic processes (i.e., P uptake by biota) while coupled biotic and abiotic processes regulated P reduction in the SAV FW.

Edaphic and epigeic macrofauna responses to land use change in Brazil

The expansion of sugarcane (Saccharum spp.) over extensive pasture areas has been one of the primary land-use change (LUC) scenarios in central-southern Brazil. However, LUC could negatively affect soil fauna along with the multiple functions and services associated with these organisms. Numerous groups of macroinvertebrates inhabiting the soil surface (i.e., epigeic) or the soil profile (i.e., edaphic) are fundamental for litter fragmentation, soil structuring and stabilization, water infiltration, biogeochemical cycling. In this study, both the edaphic and epigeic macrofauna communities were surveyed simultaneously to assess responses induced by the expansion of sugarcane cultivation over extensive pastures and to investigate whether the magnitude of such responses to LUC differs according to the community niche (i.e., soil profile versus surface). We hypothesized that LUC to a semi-perennial crop such as sugarcane would increase the density and diversity of the edaphic macrofauna, while the epigeic community would be negatively affected by LUC due to drastic changes in surface litter. The studied areas were two sites varying in soil texture (i.e., clay versus sandy soils) each including the following land uses: i) native vegetation, ii) extensive pasture, iii) newly planted sugarcane crop (sugarcane); and iv) established sugarcane (sugarcane ratoon). To evaluate edaphic macrofauna the TSBF methodology was adopted, while pitfall traps were installed at the same sampling points to collected epigeic macrofauna. The evaluated community attributes were density, Shannon diversity index, evenness index, richness of soil macrofauna taxa, as well as the chemical and physical attributes of the soil. Linear mixed effects analysis showed that LUC affected the relative abundance of edaphic (Land use p = 0.1191 r2marginal = 0.28, r2conditional = 0.33) and epigeic (Land use p = 0.0176; r2marginal = 0.22, r2conditional = 0.32) macroinvertebrates. Both groups showed the greatest density of organisms under native vegetation. Coleoptera and earthworms were associated with pasture areas, especially in clayey soil. Response ratios of LUC effects on macrofauna showed stronger responses of the epigeic compared to edaphic macrofauna, indicating a greater sensitivity of surface-dwelling organisms and their functions to disturbances such as those caused by LUC. In general, the density and diversity of macrofauna exhibited a positive correlation with soil organic matter, microbial carbon and nitrogen, macroporosity, and total porosity, and a negative correlation with soil density (p < 0.05). Also, the conversion of pasture to sugarcane cultivation (planting) causes significant macrofauna losses, particularly, in the clay soil. The cultivation of ratoon sugarcane led to a reduction of the density, taxonomic richness, diversity, and evenness of macrofauna. Given the importance of epigeic macroinvertebrates for litter fragmentation and decomposition, these results may indicate a rapid loss of key soil functions related to decomposition and carbon and nutrient cycling following LUC.

Ideas and perspectives: Alleviation of functional limitations by soil organisms is key to climate feedbacks from arctic soils

Abstract. Arctic soils play an important role in Earth's climate system, as they store large amounts of carbon that, if released, could strongly increase greenhouse gas levels in our atmosphere. Most research to date has focused on how the turnover of organic matter in these soils is regulated by abiotic factors, and few studies have considered the potential role of biotic regulation. However, arctic soils are currently missing important groups of soil organisms, and here, we highlight recent empirical evidence that soil organisms' presence or absence is key to understanding and predicting future climate feedbacks from arctic soils. We propose that the arrival of soil organisms into arctic soils may introduce “novel functions”, resulting in increased rates of, for example, nitrification, methanogenesis, litter fragmentation, or bioturbation, and thereby alleviate functional limitations of the current community. This alleviation can greatly enhance decomposition rates, in parity with effects predicted due to increasing temperatures. We base this argument on a series of emerging experimental evidence suggesting that the dispersal of until-then absent micro-, meso-, and macroorganisms (i.e. from bacteria to earthworms) into new regions and newly thawed soil layers can drastically affect soil functioning. These new observations make us question the current view that neglects organism-driven “alleviation effects” when predicting future feedbacks between arctic ecosystems and our planet's climate. We therefore advocate for an updated framework in which soil biota and the functions by which they influence ecosystem processes become essential when predicting the fate of soil functions in warming arctic ecosystems.

Chemistry Matters: High Leaf Litter Consumption Does Not Represent a Direct Increase in Shredders' Biomass.

Changes in riparian vegetation can alter the input and quality of leaf litter in aquatic ecosystems, but the effects of these changes on litter fragmentation by invertebrate shredder communities in tropical streams remain poorly studied. The caddisfly genus Phylloicus Müller, 1880 (Trichoptera: Calamoceratidae) is highly abundant in Neotropical streams, representing a great part of shredder biomass, which uses the allochthonous litter as a food resource and for case-building. We investigated leaf consumption by Phylloicus sp. under different leaf conditioning (leached and unleached) and plant species (Eucalyptus grandis, Erythrina falcata, and Inga uruguensis). The effects of leaf conditioning and plant species were measured using microcosm treatments, with one free Phylloicus sp. larva per 2-l microcosm, and a decomposition control to correct for microbial decomposition. Our study suggests that phosphorus and caloric values of leaf litter are more important than leaf hardness and nitrogen in driving leaf consumption by Phylloicus sp. On the one hand, higher consumption was observed in treatment with unleached leaves than in leached leaf treatment due to higher nutrient concentration and caloric values on unleached leaves. On the other hand, Phylloicus sp. larvae preferred leached leaves for case building over unleached leaves, as leached leaves are less prone to the activity of the decomposing community, thus lowering the need for constant case renewal. Finally, high litter consumption is not necessarily converted into biomass by Phylloicus sp. larvae. In this sense, Phylloicus sp. larvae showed selectivity for resources with high caloric content for consumption and low caloric content for case-building.

Exploring microplastic pollution in a Mediterranean river: The role of introduced species as bioindicators

Studies of plastic contamination in freshwater ecosystems and their biota remain scarce, despite the fact that the vast majority of plastic waste initially passes through lotic ecosystems. Biomonitoring provides valuable information regarding plastic pollution and microplastic threats to biota and human health. The aim of this study was to explore the potential use of a non-indigenous fish species as a bioindicator of microplastic pollution in an Eastern Mediterranean River. Our study area is located in a heavily modified and vastly impacted urban river which flows through the largest part of the Metropolitan area of Athens, Greece. We used an introduced chub species (Squalius vardarensis) to assess microplastic ingestion in the river. The results indicated moderate occurrence and abundance of microplastics in the fish gastrointestinal tracts; one-third of specimens (35%) contained microplastics, although the average number of microplastics per specimen was relatively low (1.7 ± 0.2). Overall, the abundance of microplastics in the water confirmed the moderate level of microplastics contamination in our study area. The major polymer types of microplastics identified by FT-IR analysis were: polyethylene (PE), polyvinyl alcohol (PVA) and polypropylene (PP); reflecting the fragmentation of larger litter from industrial packaging and/or household goods. Surface runoff of the urban environment, via motorways and major road networks, could be the contributing factor to the reported microplastics. Our results suggest that generalist's non-indigenous species such as chubs could be used as bioindicators of microplastics in inland waters. Introduced fishes can be a feasible, nondestructive, and cost-effective option for the assessment of microplastics in freshwater ecosystems, while freshwater chubs' high abundance and omnipresence in European rivers further serve this scope. However, it is worth noting that the suitability of any particular species as a bioindicator of microplastics may depend on a variety of factors, including their feeding behavior, habitat, and exposure to microplastics in their environment.

Microplastics in road dust: A practical guide for identification and characterisation

The contamination of the environment by microplastics (MPs) in road dust poses a serious ecological and health concern. MPs have been detected in road dust worldwide and their presence has been mainly attributed to plastic litter fragmentation and vehicle tyre abrasion. Although current technologies such as Raman and Fourier Transform InfraRed spectroscopy as well as Scanning Electron Microscopy are capable of detecting MPs in road dust, the analysis of MPs shape and MPs smaller than 20 μm is limited and often labour demanding. More accurate, cost-effective and rapid techniques have now become necessary to analyse MPs in road dust, particularly since the development of large infrastructure projects that incorporate recycled plastic into road assets and roadside furniture. Nile red (NR) staining is a promising technique to identify MPs in environmental samples; however, it has not yet been applied to road dust. This study investigates the use of NR fluorescence microscopy to detect MPs in road dust and provides information about MP amount, shape and size distribution. The staining duration and temperature, solvent selection and NR concentration were optimised considering 33 different road dust materials, including 13 types of plastic. The NR staining procedure developed in this work is capable of successfully differentiating between MPs down to 1 μm and other non-plastic road dust materials. Future applications include assessing the contribution of plastic-modified roads to MP pollution, comparing the level of MP pollution in urban and rural areas and providing a rapid, simple, inexpensive and reliable monitoring approach for further studies to compare MP using a singular optimised methodology.

Effects of resource size on invertebrate assemblages in water-filled treeholes

Water-filled treeholes are important habitat patches for aquatic invertebrates in forest ecosystems. A detailed understanding of the interspecies relationships that occur within them will help in understanding how invertebrate diversity is maintained in forests, particularly with respect to resource utilization. The sequential use of the same food resource among several different species is called a processing chain. In this study, we focused on the aspects of leaf litter in the treeholes as a food and habitat resource, and tested the following hypotheses using artificial containers as treeholes with three different leaf litter samples categorized as “untreated”, “fragmented”, and “pulverized”: (1) inorganic ions would leach out as leaf fragmentation progresses, resulting in water acidification, which consequently affects invertebrates. (2) filter-feeder species that consume microorganisms and fine particle organic matter increase as leaf fragmentation progresses. (3) differences in the size of leaf litter fragments affect the inhabitant species and cause differences in the assemblage structure of invertebrates. We observed an increase in pH and dissolved oxygen (DO) with increasing the fragmentation of leaf litter; however, the results were marginally non-significant. The assemblage composition of aquatic invertebrates did not show clear patterns in relation to the leaf litter treatments. Invertebrate assemblages from treeholes with pulverized leaf litter appeared to be associated with increasing DO. We found that the filter-feeder Tripteroides bambusa (Diptera: Culicidae) was dominant under conditions where treeholes contained fine particles of leaf litter, while the benthic inhabitant Ceratopogonidae sp. (Diptera) dominated under conditions with coarse leaf litter fragments. Our results suggest that fragmentation of leaf litter may have different effects on the different dominant species. We conclude that resource processing does not necessarily have positive effects on the species.

Leaf-associated macroinvertebrate assemblage and leaf litter breakdown in headwater streams depend on local riparian vegetation

Headwater streams harbor diverse macroinvertebrate communities and are hotspots for leaf litter breakdown. The process of leaf litter breakdown mediated by macroinvertebrates forms an important link between terrestrial and aquatic ecosystems. Yet, how the vegetation type in the local riparian zone influences leaf-associated macroinvertebrate assemblages and leaf litter breakdown rates is still not resolved. We investigated how leaf-associated macroinvertebrate assemblages and leaf litter fragmentation rates differ between forested and non-forested sites using experimental leaf litter bags in sixteen sites paired across eight headwater streams in Switzerland. Our results show that sensitive taxa of the invertebrate orders Ephemeroptera, Plecoptera and Trichoptera (EPT) and the functional group of shredders were strongly associated with forested sites with overall higher values of abundance, diversity, and biomass of EPTs in forested compared to non-forested sites. However, the importance of riparian vegetation differed between study regions, especially for shredders. Fragmentation rates, which are primarily the result of macroinvertebrate shredding, were on average three times higher in forested compared to non-forested sites. Our results demonstrate that not only the composition of the aquatic fauna but also the functioning of an essential ecosystem process depend on the vegetation type in the local riparian zone.

The Role of Nyctelia dorsata Fairmaire, 1905 (Coleoptera: Tenebrionidae) on Litter Fragmentation Processes and Soil Biogeochemical Cycles in Arid Patagonia

Decomposition of organic matter and soil nitrogen (N) cycling is a key process in soil fertility. In arid ecosystems, plant litter remains intact for long periods and is gradually consumed by macrodetritivore arthropods. It is suggested that tenebrionid beetles are responsible for most of nutrient cycling from accumulated litter in warm and dry seasons in arid ecosystems. The objective of this work was to extent the role on soil fertility and N cycling to Nyctelia dorsata Fairmaire (Coleoptera: Tenebrionidae) throughout litter fragmentation and consumption in a manipulative pot experiment. Our results showed that litter presence alone is not enough to incorporate N to the soil. N. dorsata consumed a significant fraction of litter and this activity was associated to an increase in soil N contents in the experimental pots. These confirmed that several tenebrionid species positively affects soil fertility in Northeastern Patagonia throughout litter fragmentation/consumption; and that these effects may vary with body size. Consequently, these beetles might be very important into the food/energy web from plants to higher trophic levels in this region.

The role of Nyctelia circumundata (Coleoptera: Tenebrionidae) on litter fragmentation processes and soil fertility in northeastern arid patagonia

Decomposition of organic matter and soil properties linked to carbon (C) and nitrogen (N) cycling are considered key processes in soil fertility. In arid ecosystems, most plant litter remains intact for long periods and is gradually consumed by macrodetritivore arthropods. Tenebrionid beetles (Coleoptera: Tenebrionidae) are the most abundant macrodetritivores in many arid environments worldwide, and it is widely suggested that these beetles are responsible for most of the nutrient cycling from accumulated litter in warm and dry seasons in these ecosystems. In this study, the role of Nyctelia circumundata Lesne (Coleoptera: Tenebrionidae) on soil fertility and litter fragmentation during the warm-dry season was experimentally evaluated in northeastern Patagonia, using microcosm experiments in the laboratory.Our results showed that the presence of litter alone is not enough to incorporate organic matter (OM), as well as nitrogen (N) or carbon (C) into the soil. Adult individuals of N. circumundata consumed a significant fraction of the litter offered in the experimental pots (∼10 %) and this activity was also associated to increased soil N, C, and OM contents, and the C/N ratio. These facts highlighted that litter fragmentation, consumption, and its subsequent conversion into feces by N. circumundata positively affects soil fertility in northeastern Patagonia. Considering that tenebrionid beetles are a major group of primary consumers in deserts, these beetles play an important role in aboveground food web and a key energy conduit from plants (as litter) to higher trophic levels in this region. Finally, taking into account the ecological relevance of tenebrionid beetles for soil nutrient cycling (both at local and ecosytem scales) demonstrated in this work, we recommend incorporating these beetle assemblages into future conservation strategies for arid Patagonia.

Edaphic fauna and physico-chemical atributes of soil in different phytophysionomies of Cerrado

ABSTRACT The edaphic community comprises several organisms that perform ecological functions in the environment, such as litter fragmentation, nutrient cycling, and modifications of soil structure, in addition to acting as food chain regulators. Thus, the objective of this study was to evaluate the composition of the edaphic fauna and the physical and chemical attributes of soil in different physiognomies of Cerrado in the Parque Estadual do Mirador (PEM). The study was carried out in two Cerrado formations (Sparse Cerrado and Typical Cerrado) in PEM, where 100 pitfall traps were installed. The edaphic organisms were screened and identified in terms of orders, suborders, subfamilies, families, abundance, richness, Shannon diversity, and Pielou’s equitability. A total of 4,149 individuals were collected from two experimental plots. The plot in the Typical Cerrado showed greater taxonomic richness (25 groups) and greater Shannon diversity (H’ = 1.65), while the plot in Sparse Cerrado presented 19 edaphic groups and Shannon diversity equal to H’ = 1.51. The factorial exploration explained 84.43% of the original data from the Sparse Cerrado and 90.84% from the Typical Cerrado. It is concluded that the plot in the Typical Cerrado showed greater differences in terms of richness and abundance due to the more favorable conditions for soil fauna, such as a high content of organic material and greater vegetation cover.

Nanoplastic toxicity towards freshwater organisms

The fragmentation of plastic litter into smaller fragments, known as microplastics and nanoplastics, as well as their toxicity and environmental distribution have become issues of high concern. Furthermore, the popularization of bioplastics as a greener substitute of conventional plastics represents a challenge for the scientific community in view of the limited information concerning their potential environmental impact. Here, we systematically review the recent knowledge on the environmental fate and toxicity of nanoplastics in freshwater environments, discuss the results obtained thus far, and identify several knowledge gaps. The sources and environmental behaviors of nanoplastics are presented considering in vitro, in vivo, and in silico studies with a focus on real exposure scenarios. Their effects on organisms are classified based on their impact on primary producers, primary consumers, and secondary consumers. This review covers the main results published in the last four years, including all relevant experimental details and highlighting the most sensitive toxicity endpoints assessed in every study. We also include more recent results on the potential environmental impact of biodegradable plastics, a type of material belonging to the category of bioplastics for which there are still scarce data. This review identifies a need to perform studies using secondary nanoplastics rather than synthetic commercial materials as well as to include other polymers apart from polystyrene. There is also an urgent need to assess the possible risk of nanoplastics at environmentally realistic concentrations using sublethal endpoints and long-term assays.

Habitat heterogeneity increases leaf litter retention and fragmentation in a Cerrado savanna stream

Leaf litter fragmentation is one of the main determinants of the availability of food resources for aquatic biota, and this process is strongly influenced by the retention capacity of streams. Retention capacity depends on habitat heterogeneity, as well as on other factors such as leaf litter characteristics and microhabitat diversity. However, the effects of these factors have not yet been clearly understood. In this study, our hypotheses were as follows: (i) habitat heterogeneity increases leaf litter retention, particularly of larger leaves, and (ii) water flow enhances leaf litter fragmentation by promoting physical abrasion of leaf litter, particularly of softer leaves. We tested these hypotheses using (i) the proportion of leaves in transport and the variation of retentive structures such as rock, pebbles, trunks, and roots for habitat heterogeneity in three reaches and (ii) litterbags of two mesh sizes (fine and coarse) incubated in riffle and pool habitats in three reaches of a headwater stream of the Cerrado biome. Our results demonstrated that habitat heterogeneity and leaf litter size increased leaf litter retention rates, and that water flow is an important factor for leaf litter fragmentation in tropical streams. Large leaves interacted with local conditions of streambed heterogeneity (trunks and roots) to reduce transport distances, and hydrology (water flow) accelerated the fragmentation of soft leaves. Our findings suggest that management strategies promoting the accumulation of woody leaf litter ​in the streambed (trunks and roots) can be valuable to increase the retention capacity of streams, on the other hand the water flow increases the processing of allochthonous organic matter.

Synergistic interactions between detritivores disappear under reduced rainfall.

Understanding the consequences of altered rainfall patterns on litter decomposition is critical to predicting the feedback effect of climate change on atmospheric CO2 concentrations. Although their effect on microbial decomposition has received considerable attention, their effect on litter fragmentation by detritivores, the other dominant decomposition pathway, remains largely unexplored. Particularly, it remains unclear how different detritivore species and their interactions respond to changes in rainfall quantity and frequency. To fill this knowledge gap, we determined the contribution to litter decomposition of two detritivore species (millipede and isopod), separately and in combination, under contrasting rainfall quantity and frequency in a temperate forest. Although halving rainfall quantity and frequency decreased topsoil moisture by 7.8 and 13.1%, respectively, neither millipede- nor isopod-driven decomposition were affected by these changes. In contrast, decomposition driven by both detritivore species in combination was 65.5% higher than expected based on monospecific treatments under high rainfall quantity, but unchanged or even lower under low rainfall quantity. This indicates that although detritivore activity is relatively insensitive to changes in rainfall patterns, large synergistic interactions between detritivore species may disappear under future rainfall patterns. Incorporating interspecific interactions between decomposers thus seems critical to evaluate the sensitivity of decomposition to altered rainfall patterns.

Mechanical fragmentation of leaf litter by fine root growth contributes greatly to the early decomposition of leaf litter

Understory plant root proliferation into the litter layer occurs in many forest ecosystems and dramatically accelerates litter decomposition and nutrient release in the early stages. Mechanical fragmentation of leaf litter by fine roots could be one main reason, but its mechanism is poorly understood. To quantitatively assess the influence of fine roots on the mechanical fragmentation of leaf litter in the early decomposition process, we examined the effects of fine root mass of Lolium multiflorum on morphological and physical characteristics of decomposing litters of Symplocos setchuensis, a dominant species in a mid-subtropical evergreen broad-leaved forest of China, via a litter bag simulation experiment. The results showed that there were various fine root growth forms in/on decomposing litters, including the penetration and tearing of leaf epidermis, and the “walking or inserting” between the mesophyll tissue and the leaf veins. Fine root mass had a significant positive effect on the mass loss during litter decomposition (F = 8.543, P < 0.01). In a duration of 170-day leaf litter incubation, the mass remaining ration was significantly higher in no roots treatments and fewer roots treatments than that in more roots treatments. In the case of more roots, the physical tensile strength of leaf litter fragments was 0.156 N/mm, which was significantly lower than that under the treatments with fewer roots and no roots (P < 0.05). More fine roots penetrating the litter layer could significantly promote the intensity of mechanical fragmentation by changing the morphology, structure, and physical properties of the leaf litter. The fine root biomass in the litter layer was positively correlated with the decomposition rate, and the specific root length and specific root tip density were two important indicators related to decomposition. In conclusion, fine roots growing into litter promoted the intensity of mechanical fragmentation by increasing root length and producing new root tips and by actively regulating litter traits, so as to improve the utilization efficiency of nutrient release in the early decomposition process.