Dominant Decomposers Research Articles

Tree species richness increases spatial variation but not overall wood decomposition

Empirical evidence for the positive relationship between tree species richness and wood decomposition is weak, despite the greater numbers of decomposers in diverse stands. Tree species identity affects decomposition rates strongly by altering soil communities and micro-environments. It is therefore likely that tree species richness influences spatial variation rather than the mean rate of decomposition. We used a neighbourhood approach to test this hypothesis by quantifying decomposition rates and decomposer activities within deadwood, whilst measuring the surrounding micro-environments.Using the BEF-China experimental platform, we placed three fine branches from seven tree species across richness gradients for one and two years. As expected, plot species richness increased the spatial variation of wood decomposition of three species but decreased the mean rate of wood decomposition of two species. Neighbourhood trees altered wood decomposition in two ways. First, increasing amounts of leaf tannins reduced termite activities and the number of fungal fruitbodies. Second, higher species richness increased tree volumes and thus cooled the understory, which reduced the occurrence and feeding intensity of ectothermic termites. Neighbourhood species richness showed positive effects on decomposer activities (i.e. termite occurrence, fruitbody number and mycelium cover) after two years, probably by weakening resource limitation of deadwood biomass and increasing the stages of decay. Neighbourhood metrics had comparable (after 1 year) and even stronger effects (after 2 years) on decomposer activities than wood traits. Our study reveals that tree species richness promotes spatial variation in wood decomposition rates by enhancing environmental heterogeneity. Our results explain how young regenerating species-rich forests, where termites are the dominant decomposers, can maintain deadwood stocks and decomposer activities over relatively longer time spans.

How feedback loops between meso- and macrofauna and organic residues contrasting in chemical quality determine decomposition dynamics in soils

The concept of feedback loops between changes in chemical quality of decomposing organic residues and changes in faunal communities was employed in studying how such feedback loops, representing distinct ecological successional stages, determine decomposition dynamics in soils. A 52-week litterbag decomposition study was superimposed onto an 18-year long term field experiment. Four types of organic residues contrasting in chemical quality (i.e., nitrogen (N), lignin, polyphenols, cellulose) were incorporated into soil annually to assess decomposition and associated meso- and macrofauna communities. In the first 4 weeks after residue incorporation (loop #1), the abundances (densities) of both mesofauna and macrofauna were positively influenced by labile cellulose and N. The mesofauna Collembola and Acari contributed 70–100% and 0–30% to the decomposition, respectively, while the macrofauna beetles and flies contributed 20–90% and 10–66%, respectively. The abundances were highest under groundnut (high N, low lignin) ([1.35 and 0.85 individual number (g dry litter)−1] for mesofauna and macrofauna, respectively). The presence of macrofauna at week 2 led to a mass loss (R2 = 0.67**), indicating that macrofauna preceded mesofauna in degrading residue. In week 8 (transition of loop #2 to #3), only macrofauna (beetles dominated contributing 65%) played an important role in lignin decomposition (R2 = 0.56**), resulting in a mass loss (R2 = 0.52**). In week 52 (loop #4) macrofauna, ants (Formicidae) replaced beetles as the dominant decomposers showing a feedback reaction to availability of protected cellulose. The Formicidans contributed 94% to the decomposition and influenced losses of mass (R2 = 0.36*) and N (R2 = 0.78***). The feedback loop concept provides a more comprehensive “two-sided” view into decomposition, as regulated simultaneously by two factors, than earlier “one-sided” approaches to soil fauna-mediated decomposition.

Tripartite Symbiotic Digestion of Lignocellulose in the Digestive System of a Fungus-Growing Termite.

Fungus-growing termites are efficient in degrading and digesting plant substrates, achieved through the engagement of symbiotic gut microbiota and lignocellulolytic Termitomyces fungi cultivated for protein-rich food. Insights into where specific plant biomass components are targeted during the decomposition process are sparse. In this study, we performed several analytical approaches on the fate of plant biomass components and did amplicon sequencing of the 16S rRNA gene to investigate the lignocellulose digestion in the symbiotic system of the fungus-growing termite Odontotermes formosanus (Shiraki) and to compare bacterial communities across the different stages in the degradation process. We observed a gradual reduction of lignocellulose components throughout the process. Our findings support that the digestive tract of young workers initiates the degradation of lignocellulose but leaves most of the lignin, hemicellulose, and cellulose, which enters the fresh fungus comb, where decomposition primarily occurs. We found a high diversity and quantity of monomeric sugars in older parts of the fungus comb, indicating that the decomposition of lignocellulose enriches the old comb with sugars that can be utilized by Termitomyces and termite workers. Amplicon sequencing of the 16S rRNA gene showed clear differences in community composition associated with the different stages of plant biomass decomposition which could work synergistically with Termitomyces to shape the digestion process. IMPORTANCE Fungus-farming termites have a mutualist association with fungi of the genus Termitomyces and gut microbiota to support the nearly complete decomposition of lignocellulose to gain access to nutrients. This elaborate strategy of plant biomass digestion makes them ecologically successful dominant decomposers in (sub)tropical Old World ecosystems. We employed acid detergent fiber analysis, high-performance anion-exchange chromatography (HPAEC), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), and amplicon sequencing of the 16S rRNA gene to examine which lignocellulose components were digested and which bacteria were abundant throughout the decomposition process. Our findings suggest that although the first gut passage initiates lignocellulose digestion, the most prominent decomposition occurs within the fungus comb. Moreover, distinct bacterial communities were associated with different stages of decomposition, potentially contributing to the breakdown of particular plant components.

Comparative study of gut microbiota from decomposer fauna in household composter using metataxonomic approach.

Household composter is one of the fragmented habitats, which still ensures the survival of many animals, especially decomposer fauna. The components of organic matter in the composter are complex, thus providing opportunities for obtaining high diversity of decomposer fauna. The ability of decomposer fauna to break down organic matter may be supported by their gut microbiota. In this study, we compared the diversity, the abundance and distribution of gut prokaryotic microbiota among several decomposer fauna members, namely cockroaches, millipedes, beetle larvae, and snails, as well as the compost from a household composter in Surabaya, Indonesia, using a metataxonomic approach. Microbial community DNA was isolated from the guts of four types of dominant decomposer fauna and the compost. A total of 42 phyla and 497 genera were observed in five samples with the predominant bacteria belonging to the Proteobacteria phylum which appeared in all samples. The highest diversity of gut bacteria was found in cockroach although not higher than the compost as a habitat for the decomposer fauna. A total of 1131 operational taxonomic units derived from 232 genera were found in compost and guts of four decomposer fauna species. Similarities between the microbial community structures found in the gut of the four decomposer fauna to those found in compost indicated that the environment had a strong effect on the overall gut microbiota of the decomposer fauna.

Competition of insect decomposers over large vertebrate carrion: Necrodes beetles (Silphidae) vs. blow flies (Calliphoridae).

Large carrion is inhabited by highly variable and interactive communities of insects. Positive interactions in carrion insect communities have been recently the focus in carrion ecology. In contrast, competition between carrion insects is rather undervalued. Here we provide evidence that blow flies (Calliphoridae) and Necrodes beetles (Silphidae), dominant decomposers of large carcasses in terrestrial habitats, compete over carrion. By reanalyzing the results from 90 pig carcasses, we demonstrated that the contribution of the flies and the beetles to the decay was negatively related. The greater part of the large carrion pool was monopolized by blow flies, whereas Necrodes beetles abundantly colonized carcasses, on which blow flies were less effective as decomposers. In behavioral assays, we found that adult beetles killed 4 times more frequently feeding than postfeeding third instar larvae of the flies, with the large decrease in the killing frequency after the larvae reached the age of early third instar. Therefore, adult Necrodes beetles preferentially killed the larvae that were before or in their peak feeding. The study provides evidence that the interaction between blow flies and Necrodes beetles is a combination of indirect exploitative effects of the flies and direct interference effects of the beetles (the mixed competition).

First Record of Fungal Diversity in the Tropical and Warm-Temperate Middle Miocene Climate Optimum Forests of Eurasia

The middle Miocene Climate Optimum (MMCO) was the warmest interval of the last 23 million years and is one of the best analogs for proposed future climate change scenarios. Fungi play a key role in the terrestrial carbon cycle as dominant decomposers of plant debris, and through their interactions with plants and other organisms as symbionts, parasites, and endobionts. Thus, their study in the fossil record, especially during the MMCO, is essential to better understand biodiversity changes and terrestrial carbon cycle dynamics in past analogous environments, as well as to model future ecological and climatic scenarios. The fossil record also offers a unique long-term, large-scale dataset to evaluate fungal assemblage dynamics across long temporal and spatial scales, providing a better understanding of how ecological factors influenced assemblage development through time. In this study, we assessed the fungal diversity and community composition recorded in two geological sections from the middle Miocene from the coal mines of Thailand and Slovakia. We used presence-absence data to quantify the fungal diversity of each locality. Spores and other fungal remains were identified to modern taxa whenever possible; laboratory codes and fossil names were used when this correlation was not possible. This study represents the first of its kind for Thailand, and it expands existing work from Slovakia. Our results indicate a total of 281 morphotaxa. This work will allow us to use modern ecological data to make inferences about ecosystem characteristics and community dynamics for the studied regions. It opens new horizons for the study of past fungal diversity based on modern fungal ecological analyses. It also sheds light on how global variations in fungal species richness and community composition were affected by different climatic conditions and under rapid increases of temperature in the past to make inferences for the near climatic future.

Responses of soil microbial community composition and enzyme activities to long-term organic amendments in a continuous tobacco cropping system

Organic amendment may be an effective management practice for alleviating soil degradation in continuous cropping systems. However, few studies focus on the effects of long-term organic amendments on soil microbial community and microbial nutrient status in continuous tobacco fields. Here, an 11-year field experiment was conducted to investigate the effects of organic amendments on plant and soil physiochemical properties, microbial communities, ecoenzymatic stoichiometry, and glomalin-related soil protein (GRSP) accumulation in a continuous tobacco field. Five treatments were applied: CK (no fertilizer); CF (chemical fertilizer only); CFS (chemical fertilizer plus corn straw); CFO (chemical fertilizer plus oilseed residues); CFM (chemical fertilizer plus composted pig manure). Organic amendments increased soil microbial abundances. Application of organic fertilizers significantly reduced gram-positive to gram-negative bacterial ratios, but significantly increased fungi/bacteria ratios, probably because gram-negative bacteria and fungi are the dominant decomposers of increased available nutrients and recalcitrant materials, respectively. Organic amendments significantly enhanced soil enzyme activities, except for the difference in β-1,4-N-acetylglucosaminidase, Leucine aminopeptidase, and polyphenol oxidase (PPO) activities between the CF and CFO. The lowest soil organic carbon (SOC) content in CFS among organic amendments treatments was probably because the positive priming effects of straw and the highest peroxidase and PPO activities increased stable SOC mineralization rates due to the high C:N:P ratio of nutrients input. Microbial activities were limited by carbon, nitrogen, and phosphorus in CFS, while carbon and phosphorus were the limiting factors in CK, CF, CFO, and CFM. Relative to CF, CFO significantly enhanced microbial carbon and phosphorus limitation, whereas CFM significantly decreased microbial carbon limitation. CFM had the highest GRSP content among treatments. Our results demonstrated that combined application of composted pig manure and chemical fertilizers is a consistently effective measure for alleviating soil degradation in continuous tobacco fields.

Decay stages of wood and associated fungal communities characterise diversity\u2013decomposition relationships

The biodiversity–ecosystem function relationship is a central topic in ecology. Fungi are the dominant decomposers of organic plant material in terrestrial ecosystems and display tremendous species diversity. However, little is known about the fungal diversity–decomposition relationship. We evaluated fungal community assemblies and substrate quality in different stages of wood decay to assess the relationships between fungal species richness and weight loss of wood substrate under laboratory conditions. Wood-inhabiting fungal communities in the early and late stages of pine log decomposition were used as a model. Colonisation with certain species prior to inoculation with other species resulted in four-fold differences in fungal species richness and up to tenfold differences in the rate of wood substrate decomposition in both early- and late-decaying fungal communities. Differences in wood substrate quality had a significant impact on species richness and weight loss of wood and the relationships between the two, which were negative or neutral. Late communities showed significantly negative species richness–decay relationships in wood at all decay stages, whereas negative relationships in early communities were significant only in the intermediate decay stage. Our results suggest that changes in fungal communities and wood quality during wood decomposition affect the fungal diversity–decomposition relationship.

Biochar alters soil microbial communities and potential functions 3–4 years after amendment in a double rice cropping system

The effects of biochar application on soil microbial communities and functional characteristics and their correlations with soil fertility properties were explored in a double rice cropping system three to four years after a single biochar amendment. Three treatments including a control, a low (24 t ha−1), and a high (48 t ha−1) application rate of straw-derived biochar were constructed. Biochar amendment significantly increased the abundance of bacteria and fungi by up to 102 % and 178 %, respectively, which might be probably caused by the increases in soil total organic carbon (TOC), total nitrogen, and rice biomass as compared with the control. However, the abundance of archaea was only slightly elevated after biochar amendments. Bacteria/fungi ratios were significantly decreased by up to 61.4 % in the biochar treatments, probably because fungi were the dominant decomposers of increased recalcitrant carbon from biochar and rice biomass. Biochar stimulated the relative abundance of Acidobacteria, which favours soil organic carbon accumulation. Biochar increased the relative abundances of Mortierella and Westerdykella, which are more beneficial to plant growth and TOC degradation. Furthermore, potential phytopathogens of Athelia and Penicillium were decreased with biochar amendment. The results demonstrate that biochar application should be sustained as an effective measure for improving the microbial characteristics of paddy field by ameliorating its soil properties.

Trait-Based Models of Decomposition with Interspecific and Environmental Interactions

Most saprotrophic fungi are dominant decomposers, and they play a vital role in the carbon cycle and stability of ecosystem. Previous researchers examined that how traits and environments influence the decomposition rate(DR), but few studies last long enough to scale short-term results up to long-term trends. In this paper, we build several trait-based models of decomposition with interspecific and environmental interactions to describe both short- and long-term trends. First, we build the model of decomposition ratio versus time with covariates – hyphal extension ratio and moisture tolerance for each species. Second, we define Interspecific Interference Ratio (IIR) to reflect interactions between fungi species and rank the relative competitiveness based on Grey System Theory with four evaluation indices: hyphal extension rate, moisture niche width, the hyphal density and thermal niche width. Then, we predict the relative advantages and disadvantages for different species by IIR and analyze the impact of biodiversity. Finally, we perform sensitivity and robustness analysis of our models, which exhibits the wide prospects and a deeper understanding of the role of fungi in the ecosystem.

Microbial utilization of rice root residue‐derived carbon explored by DNA stable‐isotope probing

AbstractDespite the vast carbon (C) stock of crop root residues in arable ecosystems, the microbial assimilation mechanism of crop root derived‐C is poorly understood. In this study, a DNA‐based stable isotope probing (DNA‐SIP) approach was used to explore and characterize the diversity of the soil bacterial community assimilating C derived from 13C‐labelled rice root residues during a 90‐day incubation. Overall, 13C‐assimilating bacterial groups with various characteristics were identified with the occurrence of strong priming effects on soil native C. Significant increases of Actinobacteria, Proteobacteria and Bacteroidetes abundances within the 13C‐assimilating bacterial community were observed. Generally, Streptomyces were the predominant utilizers of 13C derived from rice root residues within a 28‐day incubation. The 13C‐labelling of Pseudomonas, which was continuously detected during incubation, indicated stronger effects at the later decomposition stage. The role of genera Kitasatospora, Catenulispora, Nocardioides, Flavisolibacter and Niastella in 13C‐labelled rice root residues assimilation was also observed. Meanwhile, incorporation of rice root residues stimulated the growth of certain bacterial groups that incorporated unlabelled native soil C, including Chloroflexi, Acidobacteria, Planctomycetes, Verrumicrobia and Nitrospirae.Highlights The microbial mechanism of the utilization of crop root residues is largely neglected. We explored the diversity of bacterial communities assimilating rice root residues with DNA‐SIP Actinobacteria, Proteobacteria and Bacteroidetes were dominant decomposers of root residues Streptomyces and Pseudomonas were consistently detected as key assimilators during decomposition

Evolution of Termite Symbiosis Informed by Transcriptome-Based Phylogenies.

Termitidae comprises ∼80% of all termite species [1] that play dominant decomposer roles in tropical ecosystems [2, 3]. Two major events during termite evolution were the loss of cellulolytic gut protozoans in the ancestor of Termitidae and the subsequent gain in the termitid subfamily Macrotermitinae of fungal symbionts cultivated externally in "combs" constructed within the nest [4, 5]. How these symbiotic transitions occurred remains unresolved. Phylogenetic analyses of mitochondrial data previously suggested that Macrotermitinae is the earliest branching termitid lineage, followed soon after by Sphaerotermitinae [6], which cultivates bacterial symbionts on combs inside its nests [7]. This has led to the hypothesis that comb building was an important evolutionary step in the loss of gut protozoa in ancestral termitids [8]. Wesequenced genomes and transcriptomes of 55termite species and reconstructed phylogenetic trees from up to 4,065 orthologous genes of 68 species. We found strong support for a novel sister-group relationship between the bacterial comb-building Sphaerotermitinae and fungus comb-building Macrotermitinae. This key finding indicates that comb building is a derived trait within Termitidae and that the creation of a comb-like "external rumen" involving bacteria or fungi may not have driven theloss of protozoa from ancestral termitids, as previously hypothesized. Instead, associations with gut prokaryotic symbionts, combined with dietary shifts from wood to other plant-based substrates, may have played a more important role in this symbiotic transition. Our phylogenetic tree provides a platform for future studies of comparative termite evolution and the evolution of symbiosis in this taxon.

Symbiotic Plant Biomass Decomposition in Fungus-Growing Termites.

Termites are among the most successful animal groups, accomplishing nutrient acquisition through long-term associations and enzyme provisioning from microbial symbionts. Fungus farming has evolved only once in a single termite sub-family: Macrotermitinae. This sub-family has become a dominant decomposer in the Old World; through enzymatic contributions from insects, fungi, and bacteria, managed in an intricate decomposition pathway, the termites obtain near-complete utilisation of essentially any plant substrate. Here we review recent insights into our understanding of the process of plant biomass decomposition in fungus-growing termites. To this end, we outline research avenues that we believe can help shed light on how evolution has shaped the optimisation of plant-biomass decomposition in this complex multipartite symbiosis.

Woody encroachment slows decomposition and termite activity in an African savanna.

Woody encroachment can lead to a complete switch from open habitats to dense thickets, and has the potential to greatly alter the biodiversity and ecological functioning of grassy ecosystems across the globe. Plant litter decomposition is a critical ecosystem process fundamental to nutrient cycling and global carbon dynamics, yet little is known about how woody encroachment might alter this process. We compared grass decay rates of heavily encroached areas with adjacent nonencroached open areas in a semi-arid South African savanna using litterbags that allowed or excluded invertebrates. We also assessed the effect of woody encroachment on the activity of termites- dominant decomposer organisms in savanna systems. We found a significant reduction in decomposition rates within encroached areas, with litter taking twice as long to decay compared with open savanna areas. Moreover, invertebrates were more influential on grass decomposition in open areas and termite activity was substantially lower in encroached areas, particularly during the dry season when activity levels were reduced to almost zero. Our results suggest that woody encroachment created an unfavourable environment for invertebrates, and termites in particular, leading to decreased decomposition rates in these areas. We provide the first quantification of woody encroachment altering the functioning of African savanna ecosystems through the slowing of aboveground plant decomposition. Woody encroachment is intensifying across the globe, and our results suggest that substantial changes to the carbon balance and biodiversity of grassy biomes could occur.

Diversity and distribution character of wood-rotting fungi in the secondary forest ecosystem of Liaodong areas, Northeast China

During July to September of 2013, field investigations and specimen collections on wood-rotting fungi were carried from three sites in the secondary forests (Qingyuan forest farm, Laotudingzi National Nature Reserve and Baishilaizi Nature Reserve) of eastern Liaoning Province. A total of 1062 specimens were collected and recorded, and 92 species were identified, belonging to48 genera. Among the three studying sites, Baishilaizi Nature Reserve had the most abundant polypore species and the Shannon diversity index was 4.04. The species biogeography of eastern Liaoning could be divided into 4 groups at genus level. The main elements were North temperate element and cosmopolitan element, and floristic analysis showed a distinct north temperate character. White rot species were the dominant decomposers here. Most species distributed in the fallen wood with decay stages 2 and 3. The wood dominant hosts of wood-rotting fungi were the Acer genus in the secondary forests of eastern Liaoning Province, and 243 specimens were collected from maples, occupying 23.2% of the total.

Changes of soil bacterial activities and functions after different N additions in a temperate forest.

It has been shown that different nitrogen (N) addition led to various influences on soil microbial activities in forest ecosystems; however, the changes of bacteria were still unclear. In this work, inorganic N (NH4NO3) and organic N (urea and glycine) were fertilized with different ratios (5:0, 1:4, 3:2, 2:3, and 1:4) on temperate forest soils, while fungicide (cycloheximide) was simultaneously added on half of each treatment to inhibit fungal activities (leaving only bacteria). After a 3-year field experiment, soil samples were harvested, then microbial enzymatic activities involved in carbon (C), and N and phosphorus (P) cycles were determined. Under laboratory conditions, four purified bacteria which were isolated from sample site had been inoculated in sterilized soils under different N types and enzymatic activities were assayed after 90-day incubation. The results showed that cellulase and polyphenol oxidase activities of non-fungicide-added treatments increased after N addition and greater organic N accelerated the increases. However, these enzymatic activities of fungicide-added treatments were not significantly influenced by N addition and N types. It may be due to the insufficient ability of bacteria to synthesize enough enzymes to decompose complex organic C (such as cellulose and lignin) into available compound, although N-limitation was alleviated. Alkaline phosphatase activities increased after N addition in both non-fungicide-added and fungicide-added treatments, and the acceleration on bacterial alkaline phosphatase activities was even greater. Furthermore, organic N showed at least 2.5 times promotion on bacteria alkaline phosphatase than those of inorganic N, which indicated greater alleviation of bacterial P-limitation after the addition of organic N. All the results indicated that soil bacteria may be seriously limited by soil available C but become the dominant decomposer of the complex P compounds after N addition, particularly greater organic N.

Linking microbial community composition to C loss rates during wood decomposition

Although decaying wood plays an important role in global carbon (C) cycling, how changes in microbial community are related to wood C quality and then affect wood organic C loss during wood decomposition remains unclear. In this study, a chronosequence method was used to examine the relationships between wood C loss rates and microbial community compositions during Chinese fir (Cunninghamia lanceolata) stump decomposition. Our results showed that microbial community shifted from fungi-dominated at early stages (0–15 years) to relatively more bacteria-dominated at later stages (15–35 years) of wood decomposition. Fungal phospholipid fatty acid (PLFA) content primarily explained wood C loss rates at early stages of wood decomposition. Fungal biomass was positively correlated with proportions of relatively high-quality C (e.g., O-alkyl C), but bacterial biomass was positively correlated with low-quality C. In addition, fungi appeared to be the dominated community under low wood moisture (<20%) at early stages, but fungal biomass tended to decrease and bacterial biomass increased with increasing wood moisture at later stages. Our findings suggest that the fungal community is the dominant decomposer of wood at early stages and may be positively influenced by relatively high-quality wood C and low wood moisture. Bacterial community may benefited from low-quality wood C and high wood moisture at later stages. Enhanced understanding of microbial responses to wood quality and environment is important to improve predictions in wood decomposition models.

Sediments and flow have mainly independent effects on multitrophic stream communities and ecosystem functions.

Stream ecosystems are affected by multiple abiotic stressors, and species responses to simultaneous stressors may differ from those predicted based on single-stressor responses. Using 12 semi-natural stream channels, we examined the individual and interactive effects of flow level (low or high flow) and addition of fine sediments (grain size <2mm) on key ecosystem processes (leaf breakdown, algal biomass accrual) and benthic macroinvertebrate and fungal communities. Both stressors had mostly independent effects on biological responses, with sand addition being the more influential of the two. Sand addition decreased algal biomass and microbe-mediated leaf breakdown significantly, whereas invertebrate shredder-mediated breakdown only responded to flow level. Macroinvertebrate community composition responded significantly to both stressors. Fungal biomass decreased and shredder abundance increased when sand was added; thus, organisms at different trophic levels can exhibit highly variable responses to the same stressor. Terrestrial endophytic fungi were abundant in low-flow flumes where leaf mass loss was also highest, indicating that terrestrial endophytes may contribute importantly to leaf decomposition in the aquatic environment. Leaf breakdown rates depended on the identity and abundance of the dominant decomposer species, suggesting that the effects of anthropogenic activities on ecosystem processes may be driven by changes in the abundance of a few key species. The few observed interactive effects were all antagonistic (i.e., less than the sum of the individual effects); for example, increased flow stimulated algal biomass accumulation but this effect was largely cancelled by sand. While our finding that sand and stream flow did not have strong synergistic effects can be considered reassuring for management, future experiments should manipulate these and other human stressors in experiments that run for much longer periods, thus focusing on the long-term impacts of multiple simultaneously operating stressors.

Differences in fungal and bacterial physiology alter soil carbon and nitrogen cycling: insights from meta‐analysis and theoretical models

Since fungi and bacteria are the dominant decomposers in soil, their distinct physiologies are likely to differentially influence rates of ecosystem carbon (C) and nitrogen (N) cycling. We used meta-analysis and an enzyme-driven biogeochemical model to explore the drivers and biogeochemical consequences of changes in the fungal-to-bacterial ratio (F : B). In our meta-analysis data set, F : B increased with soil C : N ratio (R(2) = 0.224, P < 0.001), a relationship predicted by our model. We found that differences in biomass turnover rates influenced F : B under conditions of C limitation, while differences in biomass stoichiometry set the upper bounds on F : B once a nutrient limitation threshold was reached. Ecological interactions between the two groups shifted along a gradient of resource stoichiometry. At intermediate substrate C : N, fungal N mineralisation fuelled bacterial growth, increasing total microbial biomass and decreasing net N mineralisation. Therefore, we conclude that differences in bacterial and fungal physiology may have large consequences for ecosystem-scale C and N cycling.

Bottom-up determination of soil collembola diversity and population dynamics in response to interactive climatic factors

Soil invertebrate contributions to decomposition are climate dependent. Understanding the influence of abiotic factors on soil invertebrate population dynamics will strengthen predictions regarding ecosystem functioning under climate change. As well as being important secondary decomposers, mycophagous collembola exert a strong influence on the growth and activity of primary decomposers, particularly fungi. Species-specific grazing preferences for different fungi enable fungal community composition to influence the direct impacts of climate change on collembola populations. We investigate the interactive roles of altered abiotic conditions (warming, wetting and drying) and the identity of the dominant decomposer fungus in determining collembola community dynamics in woodland soil mesocosms. The bottom-up influence of the dominant component of the fungal resource base was an important mediator of the direct climatic impacts on collembola populations. The positive influences of warming and wetting, and the negative influence of drying, on collembola abundance and diversity were much less pronounced in fungal-inoculation treatments, in which populations were reduced compared with uninoculated mesocosms. We conclude that the thick, sclerotised cords of the competitively dominant decomposer fungi reduced the biomass of smaller, more palatable soil fungi, limiting the size of collembola populations and their ability to respond to altered abiotic conditions.