Decomposer Community Research Articles

Response of Microbial Communities to Changing Climate Conditions During Summer Cyanobacterial Blooms in the Baltic Sea.

Frequencies and biomass of Baltic Sea cyanobacterial blooms are expected to be higher in future climate conditions, but also of longer duration as a result of increased sea surface temperature. Concurrently, climate predictions indicate a reduced salinity in the Baltic Sea. These climate-driven changes are expected to alter not solely the phytoplankton community but also the role of microbial communities for nutrient remineralization. Here, we present the response of summer plankton communities (filamentous cyanobacteria, picocyanobacteria, and heterotrophic bacteria) to the interplay of increasing temperature (from 16 to 18°C and 20°C) and reduced salinity (from salinity 6.9 to 5.9) in the Baltic Proper (NW Gotland Sea) using a microcosm approach. Warmer temperatures led to an earlier peak of cyanobacterial biomass, while yields were reduced. These conditions caused a decrease of nitrogen-fixers (Dolichospermum sp.) biomass, while non nitrogen-fixers (Pseudanabaena sp.) increased. Salinity reduction did not affect cyanobacterial growth nor community composition. Among heterotrophic bacteria, Actinobacteria showed preference for high temperature, while Gammaproteobacteria thrived at in situ temperature. Heterotrophic bacteria community changed drastically at lower salinity and resembled communities at high temperature. Picocyanobacteria and heterotrophic bacterial biomass had a pronounced increase associated with the decay of filamentous cyanobacteria. This suggests that shifts in community composition of heterotrophic bacteria are influenced both directly by abiotic factors (temperature and salinity) and potentially indirectly by cyanobacteria. Our findings suggest that at warmer temperature, lower yield of photosynthetic cyanobacteria combined with lower proportion of nitrogen-fixers in the community could result in lower carbon export to the marine food web with consequences for the decomposer community of heterotrophic bacteria.

Microbial decomposers not constrained by climate history along a Mediterranean climate gradient in southern California.

Microbial decomposers mediate the return of CO2 to the atmosphere by producing extracellular enzymes to degrade complex plant polymers, making plant carbon available for metabolism. Determining if and how these decomposer communities are constrained in their ability to degrade plant litter is necessary for predicting how carbon cycling will be affected by future climate change. We analyzed mass loss, litter chemistry, microbial biomass, extracellular enzyme activities, and enzyme temperature sensitivities in grassland litter transplanted along a Mediterranean climate gradient in southern California. Microbial community composition was manipulated by caging litter within bags made of nylon membrane that prevent microbial immigration. To test whether grassland microbes were constrained by climate history, half of the bags were inoculated with local microbial communities native to each gradient site. We determined that temperature and precipitation likely interact to limit microbial decomposition in the extreme sites along our gradient. Despite their unique climate history, grassland microbial communities were not restricted in their ability to decompose litter under different climate conditions across the gradient, although microbial communities across our gradient may be restricted in their ability to degrade different types of litter. We did find some evidence that local microbial communities were optimized based on climate, but local microbial taxa that proliferated after inoculation into litterbags did not enhance litter decomposition. Our results suggest that microbial community composition does not constrain C-cycling rates under climate change in our system, but optimization to particular resource environments may act as more general constraints on microbial communities.

Release of carbon and nitrogen from fodder radish (Raphanus sativus) shoots and roots incubated in soils with different management history

ABSTRACTPlant roots are generally considered to decompose slower than shoots and contribute more to accumulation of soil organic matter, and management history is expected to shape the structure and function of decomposer communities in soil. Here we study the effect of chemical characteristics of shoots and roots from fodder radish (Raphanus sativus oleiformis L.), a widely used cover crop, on the release of their C and N after addition to soil. Shoots and roots were incubated for 180 d at 20°C using four soils with different management histories (organic versus mineral fertiliser, with and without use of cover crops), and the release of CO2 and extractable mineral N was determined. More shoot C than root C was mineralised during the first 10 d of incubation. After 180 d, 58% of the C input was mineralised with no difference between shoots and roots. At the end of incubation, shoots had released more N (42% of shoot N) than roots (28% of root N). Moreover, management history did not affect net mineralisation of added plant C. Residues incubated in soil with a management history involving cover crops showed an enhanced net N mineralisation. Therefore, long-term decomposition of C added in radish shoots and roots is unaffected by differences in chemical characteristics or soil management history. However, the net mineralisation of N in shoots is faster than for N in roots, and net N mineralisation of added materials is higher in soil with than without a history of cover crops.Abbreviations: CC: cover crop; IF: inorganic fertilizer; M: manure

Litter chemistry influences decomposition through activity of specific microbial functional guilds

AbstractNiche differentiation among species is a key mechanism by which biodiversity may be linked to ecosystem function. We tested a set of widely invoked hypotheses about the extent of niche differentiation in one of the most diverse communities on Earth, decomposer microorganisms, by measuring their response to changes in three abundant litter resources: lignin, cellulose, and nitrogen (N). To do this, we used the model system Arabidopsis thaliana to manipulate lignin, cellulose, and N availability and then used high‐throughput sequencing to measure the response of microbial communities during decay. Resequencing the decomposer communities after incubation of decomposed litter with pure substrates showed that groups of species had unique substrate use profiles, such that species organized into functional “guilds” of decomposers that were associated with individual litter chemicals. Low concentrations of lignin, cellulose, or N in the litter caused unique shifts in decomposer community composition after 1 yr of decay. Low cellulose plants had low levels of fungi in all decomposer guilds, low lignin plants had high levels of fungi in all decomposer guilds, and low N plants had low levels of fungi in decomposer guilds associated with sucrose and lignin. The relative abundance of decomposer guilds correlated with the total loss of individual litter chemicals during litter decay in the field. In addition, N fertilization shifted decomposer communities during both the early and later stages of decay to those dominated by decomposers in the cellulose guild. Our results contrast the assumption that major carbon (C) and N degradation mechanisms are uniform across whole decomposer communities and instead suggest that decomposition arises from complementarity among groups of metabolically distinct taxa.

Fertilization shapes a well-organized community of bacterial decomposers for accelerated paddy straw degradation

Straw, mainly dry stalks of crops, is an agricultural byproduct. Its incorporation to soils via microbial redistribution is an environment-friendly way to increase fertility. Fertilization influences soil microorganisms and straw degradation. However, our up to date knowledge on the responses of the straw decomposers to fertilization remains elusive. To this end, inoculated with paddy soils with 26-year applications of chemical fertilizers, organic amendments or controls without fertilization, microcosms were anoxically incubated with 13C-labelled rice straw amendment. DNA-based stable isotope probing and molecular ecological network analysis were conducted to unravel how straw degrading bacterial species shift in responses to fertilizations, as well as evaluate what their roles/links in the microbiome are. It was found that only a small percentage of the community ecotypes was participating into straw degradation under both fertilizations. Fertilization, especially with organic amendments decreased the predominance of Firmicutes- and Acidobacteria-like straw decomposers but increased those of the copiotrophs, such as β-Proteobacteria and Bacteroidetes due to increased soil fertility. For the same reason, fertilization shifted the hub species towards those of high degrading potential and created a more stable and efficient microbial consortium. These findings indicate that fertilization shapes a well-organized community of decomposers for accelerated straw degradation.

Species turnover and invasion of dominant freshwater invertebrates alter biodiversity–ecosystem‐function relationship

AbstractFreshwater ecosystems rely on allochthonous resources. Integration of these subsidies depends on diversity of both terrestrial resources and aquatic shredder and decomposer communities, but the diversity effects on leaf litter breakdown and decomposition are less clear in aquatic than terrestrial ecosystems. We need a better understanding of this relationship because aquatic communities are rapidly changing with species invasions and anthropogenic impacts. Here, we experimentally disentangled the effects of leaf and shredder richness on leaf litter breakdown by macroinvertebrates in mesocosm experiments using three species of amphipods, a dominant guild of crustaceans in European freshwater ecosystems. Increased leaf richness led to lower‐than‐predicted leaf consumption by native shredders, with mixed evidence of resource‐switching or prioritization of preferred food items within a leaf mix. Higher shredder species richness never promoted leaf consumption rates compared to predictions from relevant single‐species experiments, and instead sometimes substantially decreased leaf consumption. We then conducted a meta‐analysis of leaf litter consumption rates by seven widely distributed amphipod species (the three used in the experiments and four additional species). As expected based on our own experiments, nonnative amphipod species generally had lower biomass‐adjusted leaf litter consumption rates, although their larger body size led to higher per‐individual leaf consumption rates. Contamination of the water by metals, pesticides, and other chemicals additionally significantly decreased leaf litter consumption by multiple native and nonnative species compared to unpolluted systems. While the meta‐analysis suggested that litter consumption, and thus breakdown, would decline if native shredders are replaced by nonnative heterospecifics, complete species replacement is not the only outcome following immigration in a meta‐community context. Our experiments suggest that breakdown rates could remain reasonably high where native species coexist with nonnative arrivals. Experiments that neglect the ecological realism of species coexistence will necessarily mischaracterize effects on ecosystem functioning.

Variation in home‐field advantage and ability in leaf litter decomposition across successional gradients

Abstract It is increasingly recognized that interactions between plants and soil (a)biotic conditions can influence local decomposition processes. For example, decomposer communities may become specialized in breaking down litter of plant species that they are associated with, resulting in accelerated decomposition, known as “home‐field advantage” (HFA). Also, soils can vary inherently in their capacity to degrade organic compounds, known as “ability.” However, we have a poor understanding how environmental conditions drive the occurrence of HFA and ability. Here, we studied how HFA and ability change across three types of successional gradients: coastal sand dunes (primary succession), inland drift sands (primary succession) and ex‐arable fields (secondary succession). Across these gradients, litter quality (i.e. nutrient, carbon and lignin contents) increases with successional time for coastal dunes and decreases for the other two gradients. We performed a 12‐months reciprocal litter transplant experiment under greenhouse conditions using soils and litters collected from early‐, mid‐ and late‐successional stages of each gradient. We found that HFA and ability did not consistently shift with successional stage for all gradients, but were instead specific for each type of successional gradient. In coastal dunes, HFA was positive for early‐successional litter, in drift, sands it was negative for mid‐successional litter, and for ex‐arable fields, HFA increased with successional time. Ability of decomposer communities was highest in mid‐successional stages for coastal dunes and drift sands, but for ex‐arable fields, ability decreased throughout with successional time. High HFA was related to high litter C content and soil and organic matter content in soils and to low litter and soil nutrient concentrations. Ability did not consistently occur in successional stages with high or low litter quality. Synthesis. Our findings show that specific environmental conditions, such as changes in litter or soil quality, along environmental gradients can shape the influence of HFA and ability on decomposition. In sites with strong HFA or ability, interactions between plants, litter and decomposer communities will be important drivers of nutrient cycling and hence have the potential to feedback to plant growth. A plain language summary is available for this article.

Phenotypic responses to microbial volatiles render a mold fungus more susceptible to insect damage.

In decomposer systems, fungi show diverse phenotypic responses to volatile organic compounds of microbial origin (volatiles). The mechanisms underlying such responses and their consequences for the performance and ecological success of fungi in a multitrophic community context have rarely been tested explicitly. We used a laboratory‐based approach in which we investigated a tripartite yeast–mold–insect model decomposer system to understand the possible influence of yeast‐borne volatiles on the ability of a chemically defended mold fungus to resist insect damage. The volatile‐exposed mold phenotype (1) did not exhibit protein kinase A‐dependent morphological differentiation, (2) was more susceptible to insect foraging activity, and (3) had reduced insecticidal properties. Additionally, the volatile‐exposed phenotype was strongly impaired in secondary metabolite formation and unable to activate “chemical defense” genes upon insect damage. These results suggest that volatiles can be ecologically important factors that affect the chemical‐based combative abilities of fungi against insect antagonists and, consequently, the structure and dynamics of decomposer communities.

Micro-decomposer communities and decomposition processes in tropical lowlands as affected by land use and litter type.

We investigated how the land-use change from rainforest into jungle rubber, intensive rubber and oil palm plantations affects decomposers and litter decomposition in Sumatra, Indonesia. Litterbags containing three litter types were placed into four land-use systems and harvested after 6 and 12months. Litter mass loss and litter element concentrations were measured, and different microbial groups including bacteria, fungi and testate amoebae were studied. After 12months 81, 65, 63 and 53% of litter exposed in rainforest, jungle rubber in oil palm and rubber plantations was decomposed. In addition to land use, litter decomposition varied strongly with litter type and short-term effects differed markedly from long-term effects. After 6months, oil palm and rubber litter decomposed faster than rainforest litter, but after 12months, decomposition of rainforest litter exceeded that of oil palm and rubber litter, reflecting adaptation of bacteria and fungi to decompose structural compounds in rainforest litter but not (or less) in rubber and oil palm litter. Bacterial and fungal community composition and testate amoeba species number and density varied strongly with litter type, but little with land use. However, community composition of testate amoebae was mainly affected by land use. Generally, changes in bacteria, fungi and testate amoebae were linked to changes in litter element concentrations, suggesting that element ratios of litter material as basal resource for the decomposer food web shape the structure of decomposer communities and decomposition processes via bottom-up forces. Overall, changing rainforest to monoculture plantations shifts the decomposer community structure and negatively affects litter decomposition.

Structural and functional characteristics of high alpine soil macro-invertebrate communities

Soil macro-invertebrates play an important role in the formation and functioning of soils, which makes them indispensable for all terrestrial ecosystems, including high alpine soils. However, in the latter, knowledge on species identity, diversity, and functionality of macro-invertebrate soil communities is scarce. Here, we address this knowledge gap by investigating the structural and functional composition of soil macro-invertebrate communities in high alpine sites of the European Alps that differ in sheep grazing intensity (low, medium, and high). Abundance data were combined with the analysis of natural variations in stable isotope ratios (13C/12C, 15N/14N) of food sources and soil animals, allowing insight into the trophic structure of the decomposer community. The presence of sheep significantly increased the abundance of Nematocera, but reduced the abundance of most other taxa. Diplopoda were found exclusively at the low elevation site with almost no sheep grazing, while Diptera larvae increased in numbers at higher elevation sites. Lumbricidae species were abundant at all sites except the highest site, which was intensively grazed by sheep and also used as a resting place. In contrast, trophic relations were not affected by sheep grazing intensity, four trophic groups were clearly distinguished, pointing to a relatively simple food web structure: (1) primary decomposers, (2) secondary decomposers and dung feeders, (3) root and fungal feeders, and (4) predators. We suggest that the shallow soils with high organic matter do not allow the formation of more complex food webs.

Inducible phenotypic plasticity in plants regulates aquatic ecosystem functioning.

Differences among individuals within species affect community and ecosystem processes in many systems, and may rival the importance of differences between species. Intraspecific variation consists of both plastic and genetic components that are regulated by different processes and operate on different time scales. Therefore, probing which mechanisms can affect traits sufficiently strongly to affect ecosystem processes is fundamental to understanding the consequences of individual variation. We find that a dominant deciduous tree of Pacific Northwest riparian ecosystems, red alder, exhibits strong and synergistic responses to nutrient resources and herbivory stress. These induced responses, which include shifting nutrient and plant secondary metabolite composition, have cascading effects on aquatic ecosystem function. Defense responses suppress leaf litter decomposition in small streams, thus altering the rate of energy capture for one of the most abundant terrestrial carbon sources entering aquatic systems. We find that alder responses to herbivory stress largely depend on availability of soil nutrients, with modification of the highly cytotoxic diarylheptanoid group of secondary metabolites being favored in nutrient-poor environments and modification of the typically dose-dependent ellagitannins being favored in nutrient-rich environments. Importantly, these findings identify traits for herbivore resistance in alder trees and demonstrate that plastic responses occurring within a species and over short time scales substantially alter a key function of an adjacent ecosystem. Furthermore, demonstrating plasticity among alder secondary metabolites lends insight into this system, in which decomposer communities are known to adjust to the secondary chemistry of local alder trees to facilitate rapid decomposition of locally derived leaf litter.

Negative effects of litter richness on root decomposition in the presence of detritivores

Abstract Decomposition is a vital process underlying many ecosystem functions. Although a growing number of studies have tested how litter richness affects the decomposition of above‐ground plant organs, knowledge remains limited about the decomposition of root mixtures. Here, we used a field experiment in a subtropical forest to investigate how species richness in root litter mixtures (air‐dried fresh fine roots) affects the decomposition of root litter material. On the basis of the concept of resource complementarity, we hypothesized that root litter would decompose faster as the richness of the root litter mixture increased. In addition, we expected the presence of detritivores would modify the effect of root richness on mass loss, because detritivores might experience bottom‐up effects from specific plant species and might affect microbial decomposer communities. We found that the richness level of root litter mixtures did not affect mass loss in the absence of detritivores. In the presence of detritivores, all root litter types decomposed faster. Notably, the positive effect of detritivores was stronger at low root litter richness than at high root litter richness, particularly during the early stages of decomposition (the first two sampling points) when litter mass loss was roughly double at low root litter richness compared to that at high root litter richness. The composition of the root fungal community measured at the last sampling point did not differ significantly across root richness levels, and was not affected by the presence of detritivores. Synthesis. Our findings demonstrate that detritivores modify the relationship between root litter diversity and root litter decomposition in subtropical forest ecosystems. This highlights an importance of cascade effects between different trophic organisms on ecosystem functioning. A plain language summary is available for this article.

Melanization of mycorrhizal fungal necromass structures microbial decomposer communities

Abstract Mycorrhizal fungal necromass is increasingly recognized as an important contributor to soil organic carbon pools, particularly in forest ecosystems. While its decomposition rate is primarily determined by biochemical composition, how traits such as melanin content affect the structure of necromass decomposer communities remains poorly understood. To assess the role of biochemical traits on microbial decomposer community composition and functioning, we incubated melanized and non‐melanized necromass of the mycorrhizal fungus Meliniomyces bicolor in Pinus‐ and Quercus‐dominated forests in Minnesota, USA and then assessed the associated fungal and bacterial decomposer communities after 1, 2 and 3 months using high‐throughput sequencing. Melanized necromass decomposed significantly slower than non‐melanized necromass in both forests. The structure of the microbial decomposer communities depended significantly on necromass melanin content, although the effect was stronger for fungi than bacteria. On non‐melanized necromass, fungal communities were dominated by r‐selected ascomycete and mucoromycete microfungi early and then replaced by basidiomycete ectomycorrhizal fungi, while on melanized necromass these groups were co‐dominant throughout the incubation. Bacterial communities were dominated by both specialist mycophageous and generalist taxa. Synthesis. Our results indicate that necromass biochemistry not only strongly affects rates of decomposition but also the structure of the associated decomposer communities. Furthermore, the observed colonization patterns suggest that fungi, and particularly ectomycorrhizal fungi, may play a more important role in necromass decomposition than previously recognized.

Decomposition of coarse woody debris in a long‐term litter manipulation experiment: A focus on nutrient availability

Abstract The majority of above‐ground carbon in tropical forests is stored in wood, which is returned to the atmosphere during decomposition of coarse woody debris. However, the factors controlling wood decomposition have not been experimentally manipulated over time scales comparable to the length of this process. We hypothesized that wood decomposition is limited by nutrient availability and tested this hypothesis in a long‐term litter addition and removal experiment in a lowland tropical forest in Panama. Specifically, we quantified decomposition using a 15‐year chronosequence of decaying boles, and measured respiration rates and nutrient limitation of wood decomposer communities. The long‐term probability that a dead tree completely decomposed was decreased in plots where litter was removed, but did not differ between litter addition and control treatments. Similarly, respiration rates of wood decomposer communities were greater in control treatments relative to litter removal plots; litter addition treatments did not differ from either of the other treatments. Respiration rates increased in response to nutrient addition (nitrogen, phosphorus, and potassium) in the litter removal and addition treatments, but not in the controls. Established decreases in concentrations of soil nutrients in litter removal plots and increased respiration rates in response to nutrient addition suggest that reduced rates of wood decomposition after litter removal were caused by decreased nutrient availability. The effects of litter manipulations differed directionally from a previous short‐term decomposition study in the same plots, and reduced rates of bole decomposition in litter removal plots did not emerge until after more than 6 years of decomposition. These differences suggest that litter‐mediated effects on nutrient dynamics have complex interactions with decomposition over time. A plain language summary is available for this article.

Drought in spring increases microbial carbon loss through respiration in a Mediterranean pine forest

We investigated the effect of drought in spring (earlier onset of summer drought) on litter decomposition in a Mediterranean pine forest, in Greece. We exposed litterbags filled with decomposed or fresh pine litter in the forest floor from January to November and simulated drought from April to May (season with usually high activity in soil). The drought treatment resulted in a significant increase of microbial respiration and litter weight loss and a decrease of microbial C. Both litter types were similarly affected by drought, but differed in parameters related to decomposer community succession (Collembola and Acari abundances, organic C and N, microbial N). Our results indicate that drought during the highly biologically active season might have significant implications for soil Carbon sequestration/storage.

Nutrient limitation or home field advantage: Does microbial community adaptation overcome nutrient limitation of litter decomposition in a tropical peatland?

Abstract Litter decomposition is an important control on carbon accumulation in tropical peatlands. Stoichiometric theory suggests that decomposition is regulated by elemental ratios in litter while the home field advantage (HFA) hypothesis predicts that decomposer communities are adapted to local conditions. To date, the relative importance of these contrasting theories for litter decomposition and therefore the carbon balance of tropical peatlands remain poorly understood. We conducted two in situ litter decomposition experiments in a lowland tropical peatland. The first experiment tested the importance of the stoichiometric theory using a factorial nutrient addition experiment at two sites with contrasting vegetation (Raphia taedigera and Campnosperma panamensis) to assess how nutrient addition affected microbial enzyme activity and litter mass loss at the peat surface and at 50 cm depth. The second experiment tested the importance of HFA by reciprocal translocation of leaf litter from R. taedigera and C. panamensis forests, which differed in both litter chemistry and soil nutrient availability, to separate the influence of litter chemistry and soil/site properties on litter mass loss. The activities of hydrolytic enzymes involved in the decomposition of large plant polymers were stimulated by nitrogen addition only where nitrogen availability was low relative to phosphorus, and were stimulated by phosphorus addition where phosphorus availability was low. The addition of nitrogen, but not phosphorus, increased leaf litter decomposition under waterlogged conditions at 50 cm depth, but not at the peat surface. Decomposition was greatest for autochthonous litter irrespective of site nutrient status, indicating that adaptation of the microbial community to low nutrients can partly overcome nutrient limitation, and suggesting that HFA can influence litter decomposition rates. Synthesis. Our study shows that leaf litter decomposition and the activity of microbial enzymes in tropical peatlands are constrained in part by nutrient availability. However, such nutrient limitation of litter decomposition can be overcome by adaptation of the microbial community.

Effects of local forest continuity on the diversity of fungi on standing dead pines

Abstract Human-induced fragmentation affects forest continuity, i.e. availability of a suitable habitat for the target species over a time period. The dependence of wood-inhabiting fungi on landscape level continuity has been well demonstrated, but the importance of local continuity has remained controversial. In this study, we explored the effects of local forest continuity (microhabitat and stand level) on the diversity of wood-inhabiting fungi on standing dead trunks of Scots pine (Pinus sylvestris L.). We studied species richness and community composition of decomposers and Micarea lichens on 70 trunks in 14 forests in central Finland that differed in their state of continuity. We used dendrochronological methods to assess the detailed history of each study trunk, i.e. the microhabitat continuity. The stand continuity was estimated as dead wood diversity and past management intensity (number of stumps). We recorded 107 species (91 decomposers, 16 Micarea lichens), with a total of 510 occurrences. Using generalized linear mixed models, we found that none of the variables explained decomposer species richness, but that Micarea species richness was positively dependent on the time since tree death. Dead wood diversity was the most important variable determining the composition of decomposer communities. For Micarea lichens, the community composition was best explained by the combined effect of years from death, site and dead wood diversity. However, these effects were rather tentative. The results are in line with those of previous studies suggesting the restricted significance of local forest continuity for wood-inhabiting fungi. However, standing dead pines that have been available continuously over long periods seem to be important for species-rich communities of Micarea lichens. Rare specialists (e.g. on veteran trees) may be more sensitive to local continuity, and should be at the center of future research.

Drivers of decomposition and the detrital invertebrate community differ across a hummock-hollow microtopology in Boreal peatlands

ABSTRACTIn boreal peatlands, low decomposition rate is the underlying cause of carbon sequestration. Decomposition of litter can be affected by factors relating to soil moisture and temperature, the quality of the litter, and by the biotic decomposer community, among others. Exploring how these drivers interact will provide better understanding of carbon dynamics in boreal peatlands. We measured the decomposition of three common peatland plant functional types (moss, sedge, shrub), and associated microarthropod communities using litterbags placed in hollows (wet depressions) and hummocks (dry, raised areas) of a boreal peatland in Ontario, Canada. Decomposition was significantly different between all plant litter types, and greatest in sedge, but was not significantly different between hummock and hollow microhabitats. The decomposer community displayed an opposite pattern, significantly affected by microhabitat where richness and abundance of microarthropods was greater in hollows than hummocks. Oribatid mites were the dominant microarthropod with respect to both richness and abundance. Plant litter type did not affect community structure in hollows, but was a determinant of oribatid dominance in hummocks. These results suggest that abiotic environmental conditions are the main drivers of community structure for decomposers, while plant litter quality is a more important determinant of decomposition dynamics in boreal peatlands.

Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream

Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of β-glucosidase, cellobiohydrolase and phosphatase were gradually reduced with increasing emersion time, while β-xylosidase reduction was similar when emersion last for 7 or more days, and the phenol oxidase reduction was similar at 14 and 21days of leaf emersion. Microbial biomass and fungal sporulation were reduced after 21days of emersion. The structure of microbial assemblages was affected by the duration of the emersion period. The shifts in fungal assemblages were correlated with a decreased microbial capacity to degrade lignin and hemicellulose in leaf litter exposed to emersion. Additionally, some resilience was observed in leaf litter mass loss, bacterial biomass, some enzyme activities and structure of fungal assemblages. Our study shows that drought can strongly alter structural and functional aspects of microbial decomposers. Therefore, the exposure of leaf litter to increasing emersion periods in temperate streams is expected to affect decomposer communities and overall decomposition of plant material by decelerating carbon cycling in streams.

Leaf litter decomposition and diversity of arthropod decomposers in tropical Muyong forest in Banaue, Philippines

The Muyong forest, an indigenous secondary forest in Banaue, Ifugao, Philippines, plays a crucial role in the Muyong–Payoh system, a continuum of secondary forest and rice terrace, of the Banaue rice terraces by providing water and nutrients to the rice plants in the Payoh terraces. In recent decades, the planting of introduced tree species in the Muyong forest has threatened the sustainable provision of ecosystem services such as water balance and nutrient cycling. To further understand nutrient cycling in the Muyong–Payoh systems, this study was conducted in Poitan, Banaue, Ifugao to gather preliminary baseline data on floral diversity, leaf litterfall rate, leaf litter decomposition rate, and diversity and succession of arthropods in decomposing leaf litter in a Muyong forest. Vegetation analysis was done by identifying and describing the trees growing inside the five 10 m × 10 m quadrat sampling plots. Monthly leaf litter fall was collected in 1 m × 1 m litter traps, and the dry weight was determined after oven-drying at 65 °C for 48 h. Leaf litter decomposition experiment was established by laying out 12 nylon mesh bags containing fresh leaf litter in each of the four sites on the forest floor and one bag was retrieved every month to determine the change in dry weight of the leaf litter. Six bulk soil samples were collected from the Muyong forest floor and analyzed for organic matter, pH, available P and exchangeable K. Fresh leaf litter samples were analyzed for total N, P and K contents. Arthropods in the collected decomposing leaf litter were extracted using Berlese funnel and later identified up to families level using arthropod taxonomic key. The diversity of plants in the Muyong forest includes thirty-eight tree species belonging to 19 families dominated by indigenous tree species. Results showed that the monthly leaf litter fall was higher during the dry months of March to May and lower during the wet months. The estimated total leaf litter fall in Muyong forest was comparable to published litter fall from tropical secondary forests. The N, P and K contents of fresh leaf litter range from 1.0 to 1.2, 0.11 and 0.40%, respectively. The first month of decomposition has the fastest rate while the decomposition rate during the next 4 months ranged from 0.125 to 0.251. Complete decomposition or mass lost in the leaf litter in the Muyong forest took place within 5 months. The soil arthropods identified in the decomposing leaf litter were composed of 13 orders and 28 families. Majority of the collected arthropods were insects while other species including mites, spiders, millipedes and sowbugs were also present. Detrivore and fungivore Families were found to be dominant in the decomposing leaf litter. Moreover, the composition and succession of arthropod decomposer community varied in the three sampling methods and with the changing quality of the litter material as decomposition progressed. The wide diversity and succession of leaf litter decomposers consisting of detritivores, predators, fungivore and herbivore coupled with abundant rainfall and warm temperature are the two main factors that contribute to the fast rate of leaf litter decomposition and nutrient turn over in the Muyong forest. Thus, the Muyong forest can sustain the productivity of rice planted in the adjoining downstream Payoh terraces. Hence, the conservation and management of the Muyong forest is critical in maintaining the ecological functions of the Muyong–Payoh continuum.