Effects of nanoplastic exposure routes on leaf decomposition in streams.

Polystyrene nanoparticles (PS NPs) released from plastic products have been demonstrated to pose a threat to leaf litter decomposition in streams. Given the multitrophic systems of species interactions, the effects of PS NPs through different exposure routes on ecosystem functioning remain unclear. Especially dietary exposure, a frequently overlooked pathway leading to toxicity, deserves more attention. A microcosm experiment was conducted in this study to assess the effects of waterborne and dietary exposure to PS NPs on the litter-based food chain involving leaves, microbial decomposers, and detritivores (river snails). Compared to waterborne contamination, dietary contamination resulted in lower microbial enzyme activities and a significantly higher decrease in the lipid content of leaves. For river snails, their antioxidant activity was significantly increased by 20.21%-69.93%, and their leaf consumption rate was significantly reduced by 16.60% through the dietary route due to the lower lipid content of leaves. Besides, the significantly decreased nutritional quality of river snails would negatively influence their palatability to predators. The findings of this study indicate that dietary exposure to PS NPs significantly impacts microbial and detritivore activities, thus affecting their functions in the detritus food chain as well as nutrient cycling.

Root nitrogen reallocation: what makes it matter?

Root nitrogen (N) reallocation involves remobilization of root N-storage pools to support shoot growth. Representing a critical yet underexplored facet of plant function, we developed innovative frameworks to elucidate its connections with key ecosystem components. First, root N reallocation increases with plant species richness and N-acquisition strategies, driven by competitive stimulation of plant N demand and synergies in N uptake. Second, competitive root traits and mycorrhizal symbioses, which enhance N foraging and uptake, exhibit trade-offs with root N reallocation. Furthermore, root N reallocation is attenuated by N-supply attributes such as increasing litter quality, soil fungi-to-bacteria ratios, and microbial recruitment in the hyphosphere/rhizosphere. These frameworks provide new insights and research avenues for understanding the ecological roles of root N reallocation.

Climate warming accelerates carbon release from foliar litter-A global synthesis.

With over one-third of terrestrial net primary productivity transferring to the litter layer annually, the carbon release from litter serves as a crucial valve in atmospheric carbon dioxide concentrations. However, few quantitative global projections of litter carbon release rate in response to climate change exist. Here, we combined a global foliar litter carbon release dataset (8973 samples) to generate spatially explicitly estimates of the response of their residence time (τ) to climate change. Results show a global mean litter carbon release rate ( k $$ k $$ ) of 0.69 year-1 (ranging from 0.09-5.6 year-1). Under future climate scenarios, global mean τ is projected to decrease by a mean of 2.7% (SSP 1-2.6) and 5.9% (SSP 5-8.5) during 2071-2100 period. Locally, the alleviation of temperature and moisture restrictions corresponded to obvious decreases in τ in cold and arid regions, respectively. In contract, τ in tropical humid broadleaf forests increased by 4.6% under SSP 5-8.5. Our findings highlight the vegetation type as a powerful proxy for explaining global patterns in foliar litter carbon release rates and the role of climate conditions in predicting responses of carbon release to climate change. Our observation-based estimates could refine carbon cycle parameterization, improving projections of carbon cycle-climate feedbacks.

Fast Bacterial Succession Associated with the Decomposition of Larix gmelinii Litter in Wudalianchi Volcano.

In order to understand the role of microorganisms in litter decomposition and the nutrient cycle in volcanic forest ecosystems, the dominant forest species Larix gmelinii in the volcanic lava plateau of the Wudalianchi volcano was considered as the research object. We analyzed the response of bacterial community structure and diversity to litter decomposition for 1 year, with an in situ decomposition experimental design using litter bags and Illumina MiSeq high-throughput sequencing. The results showed that after 365 days, the litter quality residual rate of Larix gmelinii was 77.57%, and the litter N, P, C:N, C:P, and N:P showed significant differences during the decomposition period (p < 0.05). The phyla Cyanobacteria and the genus unclassified_o_Chloroplast were the most dominant groups in early decomposition (January and April). The phyla Proteobacteria, Actinobacteriota, and Acidobacteriota and the genera Massilia, Pseudomonas, and Sphingomona were higher in July and October. The microbial communities showed extremely significant differences during the decomposition period (p < 0.05), with PCoa, RDA, and litter QRR, C:P, and N as the main factors driving litter bacteria succession. Microbial functional prediction analysis showed that Chloroplasts were the major functional group in January and April. Achemoheterotrophy and aerobic chemoheterotrophy showed a significant decrease as litter decomposition progressed.

Litter quality and climate regulate the effect of invertebrates on litter decomposition in terrestrial and aquatic ecosystems: A global meta-analysis.

Although the exclusion effects of invertebrate decomposers on litter decomposition have been extensively studied in different experimental contexts, a thorough comparison of the exclusion effects of invertebrate decomposers with different body sizes on litter decomposition and its possible regulatory factors in terrestrial and aquatic ecosystems is still lacking. Here, through a meta-analysis of 1207 pairs of observations from 110 studies in terrestrial ecosystems and 473 pairs of observations from 60 studies in aquatic ecosystems, we found that invertebrate exclusion reduced litter decomposition rates by 36 % globally, 30 % in terrestrial ecosystems, and 44 % in aquatic ecosystems. At the global scale, the exclusion effects of macroinvertebrates and mesoinvertebrates on litter decomposition rates (reduced by 38 % and 36 %, respectively) were greater than those of the combination of macroinvertebrates and mesoinvertebrates (reduced by 30 %). In terrestrial and aquatic ecosystems, the effects of invertebrate exclusion on litter decomposition rates were mainly regulated by climate and initial litter quality, but the effects of invertebrate exclusion with different body sizes were regulated differently by climate, initial litter quality, and abiotic environmental variables. These findings will help us better understand the role of invertebrate decomposers in litter decomposition, especially for invertebrate decomposers with different body sizes, and underscore the need to incorporate invertebrate decomposers with different body sizes into dynamic models of litter decomposition to examine the potential effects and regulatory mechanisms of land-water-atmosphere carbon fluxes.

Reading tea leaves worldwide: Decoupled drivers of initial litter decomposition mass-loss rate and stabilization.

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Global contribution of invertebrates to forest litter decomposition.

Forest litter decomposition is an essential component of global carbon and nutrient turnover. Invertebrates play important roles in litter decomposition, but the regional pattern of their effects is poorly understood. We examined 476 case studies across 93 sites and performed a meta-analysis to estimate regional effects of invertebrates on forest litter decomposition. We then assessed how invertebrate diversity, climate and soil pH drive regional variations in invertebrate-mediated decomposition. We found that (1) invertebrate contributions to litter decomposition are 1.4 times higher in tropical and subtropical forests than in forests elsewhere, with an overall contribution of 31% to global forest litter decomposition; and (2) termite diversity, together with warm, humid and acidic environments in the tropics and subtropics are positively associated with forest litter decomposition by invertebrates. Our results demonstrate the significant difference in invertebrate effects on mediating forest litter decomposition among regions. We demonstrate, also, the significance of termites in driving litter mass loss in the tropics and subtropics. These results are particularly pertinent in the tropics and subtropics where climate change and human disturbance threaten invertebrate biodiversity and the ecosystem services it provides.

Biodiversity mitigates drought effects in the decomposer system across biomes.

Multiple facets of global change affect the earth system interactively, with complex consequences for ecosystem functioning and stability. Simultaneous climate and biodiversity change are of particular concern, because biodiversity may contribute to ecosystem resistance and resilience and may mitigate climate change impacts. Yet, the extent and generality of how climate and biodiversity change interact remain insufficiently understood, especially for the decomposition of organic matter, a major determinant of the biosphere-atmosphere carbon feedbacks. With an inter-biome field experiment using large rainfall exclusion facilities, we tested how drought, a common prediction of climate change models for many parts of the world, and biodiversity in the decomposer system drive decomposition in forest ecosystems interactively. Decomposing leaf litter lost less carbon (C) and especially nitrogen (N) in five different forest biomes following partial rainfall exclusion compared to conditions without rainfall exclusion. An increasing complexity of the decomposer community alleviated drought effects, with full compensation when large-bodied invertebrates were present. Leaf litter mixing increased diversity effects, with increasing litter species richness, which contributed to counteracting drought effects on C and N loss, although to a much smaller degree than decomposer community complexity. Our results show at a relevant spatial scale covering distinct climate zones that both, the diversity of decomposer communities and plant litter in forest floors have a strong potential to mitigate drought effects on C and N dynamics during decomposition. Preserving biodiversity at multiple trophic levels contributes to ecosystem resistance and appears critical to maintain ecosystem processes under ongoing climate change.

Detritivores accelerate litter mixture decomposition effect via greater consumption of high quality litter.

To explore the mixing effect of litter decomposition and the role of detritivores, we conducted a laboratory-based microcosm experiment to study the influence of detritivores on litter mixture decomposition by using two litter species with contrasting quality, i.e., Cinnamomum camphora and Michelia × alba, and a detritivore (isopoda). After 100 days incubation, the decomposition rate of litter mixture was 52.1%, slower than that of M. alba (62.6%) and significantly faster than that of C. camphora (33.6%). The addition of isopods significantly increased litter decomposition rate, with C. camphora, M. alba, and the mixture increased by 14.4%, 20.1% and 22.1%, respectively. There was no significant mixing effect without isopods. Adding isopods significantly promoted the mixing effect of litter decomposition, with a value of the litter mixture decomposition effect of 8.6%. The detritivores increased litter decomposition rate and mixing effect through increasing consumption of litter with better quality.

Fungal traits help to understand the decomposition of simple and complex plant litter.

Litter decomposition is a key ecosystem process, relevant for the release and storage of nutrients and carbon in soil. Soil fungi are one of the dominant drivers of organic matter decomposition, but fungal taxa differ substantially in their functional ability to decompose plant litter. Knowledge is mostly based on observational data and subsequent molecular analyses and in vitro studies have been limited to forest ecosystems. In order to better understand functional traits of saprotrophic soil fungi in grassland ecosystems, we isolated 31 fungi from a natural grassland and performed several in vitro studies testing for i) leaf and wood litter decomposition, ii) the ability to use carbon sources of differing complexity, iii) the enzyme repertoire. Decomposition strongly varied among phyla and isolates, with Ascomycota decomposing the most and Mucoromycota decomposing the least. The phylogeny of the fungi and their ability to use complex carbon were the most important predictors for decomposition. Our findings show that it is crucial to understand the role of individual members and functional groups within the microbial community. This is an important way forward to understand the role of microbial community composition for the prediction of litter decomposition and subsequent potential carbon storage in grassland soils.

Identification of bacteria and fungi responsible for litter decomposition in desert steppes via combined DNA stable isotope probing.

Introduction: Soil microorganisms play crucial roles in determining the fate of litter in desert steppes because their activities constitute a major component of the global carbon (C) cycle. Human activities lead to increased ecosystem nitrogen (N) deposition, which has unpredictable impacts on soil microorganism diversity and functions. Nowadays, it is necessary to further study the succession of these microorganisms in the process of litter decomposition in desert steppe, and explore the effect of N deposition on this process. This issue is particularly important to resolve because it contributes to the broader understanding of nutrient cycling processes in desert steppes. Methods: In this study, DNA stable isotope probing (DNA-SIP) was used to study changes in soil bacterial and fungal community composition and function during 8 weeks of culture of 13C-labeled litter in desert steppes. Results: The results were as follows: (1) Actinomycetota, Pseudomonadota, and Ascomycota are the main microorganisms involved in litter decomposition in desert steppes; (2) N deposition (50 kg ha-1 year-1) significantly increased the relative abundance of some microorganisms involved in the decomposition process; and (3) N deposition likely promotes litter decomposition in desert steppes by increasing the abundances of N cycles bacteria (usually carrying GH family functional genes). Discussion: These findings contribute to a deeper understanding of the C assimilation mechanisms associated with litter residue production, emphasizing the importance of extensive C utilization.

Extension of the soil monitoring network via tea bag initiatives: A 3000 km latitudinal gradient in European Russia.

The increasing popularity and recognition of citizen science approaches to monitor soil health have promoted the idea to assess soil microbial decomposition based on a standard litter sample - tea bags. Although tea bag initiatives are expanding across the world, the global datasets remain biased in regard to investigating regions and biomes. This study aimed to expand the tea bag initiative to European Russia, which remains a "white spot" on the tea bag index map. We also added urban soils into the analysis, which were underestimated previously. We compared the standard and local tea brands to explore possible adaptations of the standard approach to regions with limited access to standard tea brands. The established monitoring network included natural and urban sites in six vegetation zones along a 3000 km latitudinal gradient. There was a very close linear relationship (R2 = 0.94-0.98) in the mass loss of alternative and standard tea litter. The mass loss of green tea in soil along the latitudinal gradient showed an increasing trend from north to south. Variations in the microbial decomposition of green tea were mainly explained by the latitudinal gradient, with low soil temperature identified as key factors hampering decomposition. Mass loss of the more recalcitrant rooibos tea was mainly determined via land use, with decomposition rates on average 1.3 times higher in urban soils. This pattern was in line with higher soil temperatures and pH in urban sites compared to natural counterparts. The findings of our study could prove valuable in extending the tea bag network of soil decomposition assessment into broader territories, including urban areas. Additionally, they could facilitate the involvement of citizen science and complete the database for C cycle modeling depending on climatic conditions.

Rehabilitation of tropical urban streams improves their structure and functioning.

Urban streams are affected by a complex combination of stressors, which modify physical habitat structure, flow regime, water quality, biological community composition, and ecosystem processes and services, thereby altering ecosystem structure and functioning. Rehabilitation projects have been undertaken in several countries to rehabilitate urban streams. However, stream rehabilitation is still rarely reported for neotropical regions. In addition, most studies focus on structural aspects, such as water quality, sediment control, and flood events, without considering ecosystem function indicators. Here, we evaluated the structure and functioning of three 15-y old rehabilitated urban stream sites in comparison with three stream sites in the best available ecological condition (reference), three sites with moderate habitat alteration, and three severely degraded sites. Compared to degraded streams, rehabilitated streams had higher habitat diversity, sensitive macroinvertebrate taxa richness, and biotic index scores, and lower biochemical oxygen demand, primary production, sediment deposition, and siltation. However, rehabilitated streams had higher primary production than moderate and reference streams, and lower canopy cover, habitat diversity, sensitive macroinvertebrate taxa richness, and biotic index scores than reference streams. These results indicate that rehabilitated streams have better structural and functional condition than degraded streams, but do not strongly differ from moderately altered streams, nor have they reached reference stream condition. Nonetheless, we conclude that rehabilitation is effective in removing streams from a degraded state by improving ecosystem structure and functioning. Furthermore, the combined use of functional and structural indicators facilitated an integrative assessment of stream ecological condition and distinguished stream conditions beyond those based on water quality indicators.

Mechanical traits as drivers of trophic interaction between macrodetritivores and leaf litter.

In ecosystems, the rates of resource consumption by animals drive the flows of matter and energy. Consumption rates are known to vary according to consumer energy requirements, resource nutrient content and mechanical properties. The aim of our study is to determine how mechanical constraints, compared to energetic and nutritional constraints, explain the variation in leaf litter consumption rates by macrodetritivores. In particular, we focus on the impact of litter toughness. To this end, we propose a non-linear model describing leaf litter consumption rates of detritivore as a function of litter toughness. We also investigate a possible match between bite force and litter toughness, since consumer-resource co-occurrence is thought to be driven by the match between invertebrate mandibular traits and resource toughness. Our study was designed as follows: leaf litter from oak and hornbeam was exposed to field physical and microbial decomposition in aquatic and terrestrial ecosystems for selected time periods before it was offered to eight macrodetritivore taxa (three forest stream taxa and five forest soil taxa) in no-choice laboratory feeding experiments. Our findings show that, compared to energetic and nutritional constraints, mechanical traits have a greater impact on litter consumption rate by detritivores. After subtracting the contribution of the detritivore body mass, we report that litter consumption rates depend primarily on litter toughness. A sigmoid function is best suited to characterize the relationship between mass-independent consumption rate and litter toughness. We note that the parameters of our sigmoid model are taxon-specific, suggesting biomechanical thresholds and biological differences among taxa. Interestingly, we found no correlation with detritivore bite force, suggesting that food processing by detritivores does not only depend on mandibles strength.

Tree phylogeny predicts more than litter chemical components in explaining enzyme activities in forest leaf litter decomposition.

Litter decomposition is an important process in ecosystem and despite recent research elucidating the significant influence of plant phylogeny on plant-associated microbial communities, it remains uncertain whether a parallel correlation exists between plant phylogeny and the community of decomposers residing in forest litter. In this study, we conducted a controlled litterbag experiment using leaf litter from ten distinct tree species in a central subtropical forest ecosystem in a region characterized by subtropical humid monsoon climate in China. The litterbags were placed in situ using a random experimental design and were collected after 12 months of incubation. Then, the litter chemical properties, microbial community composition and activities of enzyme related to the decomposition of organic carbon (C) and nitrogen (N) were assessed. Across all ten tree species, Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria were identified as the predominant bacterial classes, while the primary fungal classes were Dothideomycetes, Sordariomycetes and Eurotiomycetes. Mantel test revealed significant correlations between litter chemical component and microbial communities, as well as enzyme activities linked to N and C metabolism. However, after controlling for plant phylogenetic distance in partial Mantel test, the relationships between litter chemical component and microbial community structure and enzyme activities were not significant. Random forest and structural equation modeling indicated that plant phylogenetic distance exerted a more substantial influence than litter chemical components on microbial communities and enzyme activities associated with the decomposition of leaf litter. In summary, plant phylogenic divergence was found to be a more influential predictor of enzyme activity variations than microbial communities and litter traits, which were commonly considered reliable indicators of litter decomposition and ecosystem function, thereby highlighting the previously underestimated significance of plant phylogeny in shaping litter microbial communities and enzyme activities associated with degradation processes in forest litter.

Modelling optimal ligninolytic activity during plant litter decomposition.

A large fraction of plant litter comprises recalcitrant aromatic compounds (lignin and other phenolics). Quantifying the fate of aromatic compounds is difficult, because oxidative degradation of aromatic carbon (C) is a costly but necessary endeavor for microorganisms, and we do not know when gains from the decomposition of aromatic C outweigh energetic costs. To evaluate these tradeoffs, we developed a litter decomposition model in which the aromatic C decomposition rate is optimized dynamically to maximize microbial growth for the given costs of maintaining ligninolytic activity. We tested model performance against > 200 litter decomposition datasets collected from published literature and assessed the effects of climate and litter chemistry on litter decomposition. The model predicted a time-varying ligninolytic oxidation rate, which was used to calculate the lag time before the decomposition of aromatic C is initiated. Warmer conditions increased decomposition rates, shortened the lag time of aromatic C oxidation, and improved microbial C-use efficiency by decreasing the costs of oxidation. Moreover, a higher initial content of aromatic C promoted an earlier start of aromatic C decomposition under any climate. With this contribution, we highlight the application of eco-evolutionary approaches based on optimized microbial life strategies as an alternative parametrization scheme for litter decomposition models.

Polyethylene microplastic-induced microbial shifts affected greenhouse gas emissions during litter decomposition in coastal wetland sediments.

Microplastic contamination has become increasingly aggravated in coastal environments, further affecting biogeochemical processes involved with microbial community shifts. As a key biogeochemical process mainly driven by microbiota in coastal wetland sediments, litter decomposition contributes greatly to the global greenhouse gas (GHG) budget. However, under microplastic pollution, the relationship between microbial alterations and GHG emissions during litter decomposition in coastal wetlands remains largely unknown. Here, we explored the microbial mechanism by which polyethylene microplastic (PE-MP) influenced greenhouse gas (i.e., CH4, CO2 and N2O) emissions during litter decomposition in coastal sediments through a 75-day microcosm experiment. During litter decomposition, PE-MP exposure significantly decreased cumulative CH4 and CO2 emissions by 41.07% and 25.79%, respectively. However, there was no significant change in cumulative N2O emissions under PE-MP exposure. The bacterial, archaeal, and fungal communities in sediments exhibited varied responses to PE-MP exposure over time, as reflected by the altered structure and changed functional groups of the microbiota. The altered microbial functional groups ascribed to PE-MP exposure and sediment property changes might contribute to suppressing CH4 and CO2 emissions during litter decomposition. This study yielded valuable information regarding the effects of PE-MP on GHG emissions during litter decomposition in coastal wetland sediments.

Large herbivore grazing accelerates litter decomposition in terrestrial ecosystems.

Plant litter decomposition is critical for carbon and nutrient cycling globally. However, the effect of large herbivore grazing on litter decomposition and its mechanisms remain less explored. Here, 1203 paired observations and 381 independent experiments were analyzed to determine how litter decomposition and nutrient cycling respond to changes in grazing intensity. Grazing significantly increased litter decomposition rate by 14.08 % and litter carbon release by 5.03 %, and this effect was observed in grasslands and croplands but not in forests. The positive grazing effect was also found under sheep and cattle/yak grazing. Moderate grazing advanced the home-field advantage effect but inhibited under heavy grazing for grazed litters. The grazing effect was larger for high quality litter than for low quality litter. Litter decomposition slowed under >10 years heavy grazing but accelerated under moderate grazing. The effects of large herbivore grazing on litter decomposition were jointly influenced by grazing intensity, livestock type, climate condition, decomposition duration, litter quality, and soil properties. Our results demonstrated that large herbivore grazing accelerates litter decomposition globally and emphasized the significance and importance of grazing intensity on litter decomposition, which should be integrated into terrestrial ecosystem models.