Decomposition Of Litter Mixtures Research Articles

Moss removal facilitates decomposition and net nitrogen loss of monospecific and mixed-species litter in a boreal peatland

AbstractLitter decomposition plays an important role in biogeochemical cycling in boreal peatlands, where mosses, especially Sphagnum species, are a determinant. In recent decades, these peatlands have experienced a decline in moss cover due to abrupt climate warming and atmospheric nitrogen (N) deposition. To reveal the effect of the reduction in moss cover on litter decomposition, we adopted a field living moss removal experiment (with the senesced tissues remaining) in a Sphagnum-dominated boreal peatland, and investigated litter mass loss and net N loss of three deciduous woody species decomposing in monocultures and mixtures over 3 years. Based on the observed and predicted mass loss and net N loss of litter mixtures, we divided litter mixing effects into additive (no significant difference), synergistic (observed value greater than predicted value), and antagonistic (observed value lower than predicted value) effects. Across 3 years of decomposition, moss removal increased litter mass loss and net N loss, irrespective of single- or mixed-species compositions. Moss removal generally changed litter mixing effects on mass loss from antagonistic to additive effects in the initial 2 years, but from synergistic to additive effects after 3 years of decomposition. Regarding net N loss of litter mixtures, moss removal often resulted in a shift from additive to synergistic effects or from antagonistic to additive effects after 2 and 3 years of decomposition. Our observations suggest that the declines in living moss cover can accelerate litter decomposition and nutrient release, and highlight that living moss loss makes litter mixture decomposition predictable by reducing non-additive effects in boreal peatlands. Given the widespread occurrence of reduced moss cover in boreal peatlands, the mechanisms explaining living moss controls on litter decomposition and N cycling should receive significant attention in further studies.

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.

Decomposition of litter mixtures induces non-additive effects on soil priming across a riparian land use gradient

While litter traits have been used for decades to predict decomposition rates through the Leaf Economics Spectrum (LES) acquisitive to conservative trait lens, litter trait and litter mixture effects on soil carbon (C) priming effects (PE) is less known. To assess whether the LES can predict soil C PE during the decomposition of litter mixtures from complex ecosystems, a 99-day incubation experiment was conducted. The experiment involved soil and leaf litter from three Canadian riparian land uses (grasslands, deciduous agroforests, and coniferous agroforests), incubated as single plant species, and as plant species mixtures in their natural proportions. Natural abundance δ13C-isotopic analysis was used to assess the proportion of CO2 derived from leaf litter versus soil C mineralization at initial (0–21 days, stage I) and later (22–99 days, stage II) stages of decomposition. Single species positions on the LES mirrored litter-C mineralization dynamics, yet PE emissions remained harder to predict with LES traits. Nonetheless, higher PE emissions relative to litter-C mineralization were observed with litter from LES species expressing conservative traits compared to LES species expressing acquisitive traits. Leaf litter mixtures from both agroforests, expressing high leaf litter trait functional dissimilarity, resulted in synergistic, non-additive effects on soil PE. These findings contribute to our understanding of the effects of leaf litter functional traits and trait mixing on soil PE, highlighting that mixed-species litter decomposition can lead to non-additive effects on soil C dynamics in forested riparian ecosystems.

Impact of nitrogen addition on single and mixed tree leaf litter decomposition depends on N forms in subtropical China

Increased nitrogen (N) inputs via atmospheric deposition are believed to influence leaf litter decomposition rate in forests. However, whether inorganic and organic N deposition produces a consistent influence on leaf litter decomposition is uncertain in forests, especially leaf litter mixtures. Using a fertilization experiment, we investigated the impact of inorganic (NH4Cl) and organic (urea and glycine) N on decomposition of single leaf litter (Liquidambar formosana, Pinus elliottii, Pinus massoniana, and Schima superba) and mixed broadleaf and coniferous (equal mass ratio) leaf litter using the litterbag method in a subtropical forest in southern China. Both inorganic and organic N addition increased mineral soil β-1,4-glucosidase, cellobiohydrolase, β-1,4-N-acetylglucosaminidase, L-leucine aminopeptidase, and acid phosphatase enzyme activities. During 780-day incubation, single litter decomposition was accelerated by NH4Cl addition but was not affected by either urea or glycine addition. Irrespective of added N forms, N addition shifted litter mixing effects on decomposition from synergistic effects to either additive or antagonistic effects. Accordingly, N addition generally decelerated litter mixture decomposition rates. Compared to coniferous litter, N addition-induced changes in litter mixing effects were often lower for broadleaf litter within the litter mixtures. These findings suggest that the impact of N enrichment on litter decomposition depends upon litter types and N forms, and highlight that N forms should be incorporated into assessing the consequence of atmospheric N deposition on the biogeochemical cycles in subtropical forests.

Nitrogen addition mediates monospecific and mixed litter decomposition in a boreal peatland

Litter decomposition is a key determinant of soil organic matter accumulation in boreal peatlands. Climate warming and atmospheric nitrogen (N) deposition have recently increased N availability in boreal peatlands. However, how increased N availability alters decomposition dynamics of plant litter is uncertain in these ecosystems, especially for litter mixtures. Here, we collected fresh litter of four common species (Betula fruticosa, Ledum palustre, Eriophorum vaginatum, and Sphagnum palustre) in a poor fen of northeast China, and established an N addition (6 g N m−2 year−1) experiment to assess the effect of increased N availability on monospecific and mixed litter decomposition in the hummocks and hollows after one and three years of decomposition. In both hummocks and hollows, N addition increased mass loss of four monospecific litter after one year of decomposition but only accelerated litter decomposition of E. vaginatum and S. palustre with low litter quality after three years of decomposition. Moreover, N addition effects on monospecific litter decomposition were negatively related to monospecific litter decomposition in the absence of N addition. Irrespective of decomposition position, additive effects were more frequent than synergistic effects during decomposition of litter mixtures. In addition, N addition generally changed synergistic effects to additive effects after one and three years of decomposition, and such changing trends were stronger in hummocks than in hollows. These observations suggest that litter quality mediates N addition effects on monospecific litter decomposition, and highlight that increased N availability will alter mixed litter decomposition by reducing synergistic effects in boreal peatlands.

Fauna access outweighs litter mixture effect during leaf litter decomposition

Decomposition rates of litter mixtures reflect the combined effects of litter species diversity, litter quality, decomposers, their interactions with each other and with the environment. The outcomes of those interactions remain ambiguous and past studies have reported conflicting results (e.g., litter mixture richness effects). To date, how litter diversity and soil fauna interactions shape litter mixture decomposition remains poorly understood. Through a sixteen month long common garden litter decomposition experiment, we tested these interaction effects using litterbags of three mesh sizes (micromesh, mesomesh, and macromesh) to disentangle the contributions of different fauna groups categorized by their size at Wuhan botanical garden (subtropical climate). We examined the decomposition of five single commonly available species litters and their full 26 mixtures combination spanning from 2 to 5 species. In total, 2325 litterbags were incubated at the setup of the experiment and partly harvested after 1, 3, 6, 9, and 16 months after exposure to evaluate the mass loss and the combined effects of soil fauna and litter diversity. We predicted that litter mixture effects should increase with increased litter quality dissimilarity, and soil fauna should enhance litter (both single species litter and litter mixtures) decomposition rate. Litter mass loss ranged from 26.9 % to 87.3 %. Soil fauna access to litterbags accelerated mass loss by 29.8 % on average. The contribution of soil mesofauna did not differ from that of soil meso- and macrofauna. Incubation duration and its interactions with litter quality dissimilarities together with soil fauna determined the litter mixture effect. Furthermore, the litter mixture effect weakened as the decomposition progresses. Faunal contribution was broadly additive to the positive mixture effect irrespective of litter species richness or litter dissimilarity. This implies that combining the dissimilarity of mixture species and contributions of different soil fauna provides a more comprehensive understanding of mixed litter decomposition.

Decomposition of diverse litter mixtures affected by drought depends on nitrogen and soil fauna in a bamboo forest

Litter decomposition is a fundamental ecosystem service that can be affected by the nonadditive effect of litter mixing. We hypothesize that drought will slow the decomposition of litter mixtures due to a decline in complementary resource use. The presence of soil fauna could favor litter decomposition and mitigate the drought effect, but this depends on soil nitrogen (N) availability to soil fauna. To test these hypotheses, we compared the decomposition of single and all possible litter mixtures (11) of four leaf litter types in litterbags with three mesh sizes (i.e., 0.05-mm, 1-mm, and 5-mm) in control and treatment plots (drought, N addition or both) in an N-enriched bamboo forest ecosystem. Increasing the litter species richness moderately accelerated litter carbon (C) and N loss. The positive effect of litter diversity on decomposition was due to more complementary resource use. Both drought and N addition slowed the C and N loss from diverse litter mixtures, and N addition exacerbated the negative drought effect in this N-enriched forest. These negative effects of abiotic manipulation on litter decomposition were partly attributed to less complementary resource use. Specifically, the complementarity effects of litter mixing on C loss declined significantly, by 50%, with drought, and was even more pronounced in the drought and N addition treantment. The three-way interactions among drought, N addition, and decomposer communities demonstrated that the presence of soil fauna supports complementary resource use and alleviates thedrought constraint, but not the restriction in decomposition caused by N addition in this N-enriched forest. These findings have implications for projected decomposition rates under future global change scenarios, since they suggest that environmental changes affect decomposition through direct effects on soil biota and indirect impacts on within- and among-trophic interactions in forest ecosystems.

Dominant species and evenness level co-regulate litter mixture decomposition in a boreal peatland

Dominant species and evenness level co-regulate litter mixture decomposition in a boreal peatland

Soil fauna accelerate litter mixture decomposition globally, especially in dry environments

Abstract More than half of the net primary production in terrestrial ecosystems returns to the soil through leaf litter fall and decomposition. In terrestrial ecosystems, litter constitutes a mixture of mainly senescent foliage from multiple species. Yet, the effect of litter mixing on litter decomposition rate remains ambiguous. Quantification of the soil fauna contribution and inclusion of their interaction with litter could remove the prevailing ambiguity, as soil fauna might influence the direction and magnitude of litter mixture effects on decomposition. We carried out a global meta‐analysis to elucidate how soil fauna influenced litter mixture decomposition rate based on 55 published studies with 873 fauna inclusion/exclusion observations in field litterbag experiments. We hypothesized that soil fauna inclusion in litter mixture experiments would cause a positive change in the magnitude of mixed litter decomposition. That is, the presence of soil fauna would lead to synergistic litter mixture effects while the absence of soil fauna would lead to antagonistic litter mixture effects. Furthermore, we hypothesized that soil fauna would have a greater positive impact on the litter mixture effect in environments with low precipitation. While litter mixture had a neutral effect on decomposition on average across studies, non‐additive mixture effects were common, with a key role for soil fauna, which generally enhanced decomposition rate compared to the component single‐species litters. In contrast, fauna exclusion resulted in diminished decomposition rate overall. The overall synergistic soil fauna effect on litter mixture decomposition increased under low precipitation. Under high precipitation, the litter mixture effect was positive in the absence of soil fauna but non‐significant in the presence of fauna. Climate imposes a great effect on litter mixture, with synergistic effects increasing towards the equator. Synthesis. These results highlight the importance of soil fauna in mixed litter decomposition, most strongly in dry environments. In this era of global climate change, where some regions are projected to become drier, soil fauna might compensate the expected slower decomposition of litter by increasingly enhancing litter mixture decomposition.

Effects of understory removal and litter addition on leaf and twig decomposition in a subtropical Chinese fir plantation

AbstractSubtropical plantations have been undergoing understory removal and increased plant litter inputs due to global change and anthropogenic activities. However, how understory removal and increased litter inputs affect litter decomposition is still unclear in these plantations. Using a field manipulation experiment, we assessed the effects of understory removal and litter addition on decomposition rates of leaf litter, twig litter, and mixed leaf and twig litter over 16 months of incubation in a subtropical Chinese fir (Cunninghamia lanceolata) plantation in southern China. We also examined the changes in soil chemical properties and fungal and bacterial phospholipid fatty acids (PLFAs) after understory removal and litter addition. Litter decomposition rates were inhibited by understory removal due to the decreased fungal PLFAs and the associated declines in the ratio of fungal to bacterial biomass. Litter addition also retarded litter decomposition rates, despite the increases in soil NH4+‐N concentration and fungal PLFAs. However, both litter decomposition rates and soil microbial PLFAs remained unchanged in the presence of both understory removal and litter addition. In all treatments, mixed leaf and twig litter produced additive effects on litter decomposition rates. These results suggest that understory removal and litter addition interact to affect litter decomposition dynamics and highlight that litter mixture decomposition rates could be easily predicted from component litter in subtropical Chinese fir plantations of southern China.

What drives leaf litter decomposition and the decomposer community in subtropical forests – The richness of the above-ground tree community or that of the leaf litter?

There is increasing concern regarding how plant diversity affects litter decomposition. However, few experiments have simultaneously investigated the independent effects of litter species composition and the richness of above-ground tree communities on litter decomposition. To elucidate the two facets of diversity effects on leaf litter decomposition, a field experiment with litterbags containing monospecific or mixed litter of Schima superba, Cyclobalanopsis glauca, and Castanopsis eyrie was conducted for 30 consecutive months in a subtropical forest. In addition, the fungal community composition of the decomposing litter was assessed in the later decomposition stage. Our results revealed that leaf litter species composition but not litter species richness per se affected decomposition rates, in which the decomposition rates were faster in the presence of S. superba litter but slower in the presence of C. eyrei litter. Soil properties showed stronger impacts on litter mass loss in the earlier stages, while the litter species composition became more important in the later stage. Moreover, above-ground tree species richness had a significant effect on leaf litter decomposition. As expected, the effects of above-ground tree species richness and litter species composition became much stronger with time, probably owing to the indirect effects of concomitant changes in the composition of the litter fungal community, which in turn depended on the changes of microenvironment or on accumulated recalcitrant substances in the late stage of decomposition. Overall, our findings demonstrate that not only litter species composition but also above-ground tree species communities play critical roles in regulating litter decomposition, particularly in the late stage. An investigation into the interactions between plant and decomposer communities is required to gain a full understanding of the mechanisms underlying litter mixture decomposition.

Latitude dictates plant diversity effects on instream decomposition.

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.

Environmental conditions and litter nutrients are key determinants of soluble C, N, and P release during litter mixture decomposition

Plant litter-derived dissolved compounds leaching is an important process for soil carbon (C) sequestration and nutrient cycling. However, knowledge of the biotic and abiotic drivers of dissolved compound release from litter mixture remains limited. Here, we evaluated the loss of soluble C, N, and P during litter mixtures decomposition across an alpine treeline ecotone, and we sought to assess the relative importance of environmental conditions, litter diversity (functional dissimilarity (Rao) and community-weighted mean (CWM) traits), litter chemistry (C quality, nutrients, and stoichiometry) and microbe drive dissolved compound release during the decomposition process. The results showed that dissolved compound release from litter mixtures deviated from predictions based on litter monoculture, with predominantly synergistic effects, and the hierarchical drivers suggested: temperature strongly regulated the release of dissolved compounds and its non-additivity. In particular, freeze-thaw cycles and seasonal snow accelerated the synergistic effects on dissolved compound loss. Litter CWM and Rao traits only accelerated soluble C release and the synergistic effects of soluble P at the last stage of dissolved compound loss, respectively. Litter nutrients directly drove the release of soluble C and P at different stages. Litter C quality and microbes regulated the release of soluble C and P via direct effects, and stoichiometry had an indirect impact, which mainly before 40 % of initial mass loss. Yet, litter chemistry showed a minimal effect on soluble N release, so controls established for the release of soluble C and P might not be valid for soluble N during decomposition. Collectively, our findings advocate the decomposition environment and litter nutrients are key factors for controlling the dissolved compounds leaching, then followed by the interactions of litter C quality, stoichiometry, litter functional diversity, and microbe, which is important for understanding soil organic matter pool and soil fertility in alpine ecosystems.

Functional identity and functional diversity co-regulate litter mixture decomposition and nitrogen release in boreal riparian forest ponds

The relationship between biodiversity and litter decomposition has received considerable attention, but the complex biodiversity effects on decomposition and the underlying mechanisms are still unclear, especially in boreal riparian forest ponds. Here, we collected leaf litter from an N2-fixing species (Alnus sibirica) and two non-N2-fixing species (Betula platyphylla and Betula fruticosa) in a boreal riparian forest, northeast China. Then, we mixed leaf litter with varying composition and evenness to create a large gradient of litter functional identity and functional diversity, and used the litterbag method to examine the effect of altering plant composition on litter mass loss and nitrogen (N) release during 2 years of decomposition in forest ponds. Over 2 years of decomposition, the presence of A. sibirica in litter assemblages accelerated mass loss and N release by improving functional identity and increasing functional diversity of litter mixtures. Irrespective of the dominant species, litter mass loss generally increased with rising evenness, whereas the effect of species evenness on N release was dependent on the dominant species. When all litter mixtures were pooled, litter mixing effects on mass loss and N release correlated positively with litter functional diversity. Moreover, the decomposition dynamics of litter mixtures were regulated by litter functional diversity and the resulting mixing effects, as well as the community-weighted mean traits such as N and lignin concentrations. These findings confirm the importance of litter functional identity and functional diversity in driving decomposition processes of litter mixtures, and also indicate that increased abundance of N2-fixing species will accelerate litter decomposition and enhance N release in boreal riparian forest ponds.

Decomposition of leaf litter mixtures across biomes: The role of litter identity, diversity and soil fauna

Abstract At broad spatial scales, the factors regulating litter decomposition remain ambiguous, with the understanding of these factors largely based on studies investigating site‐specific single litter species, whereas studies using multi litter species mixtures across sites are rare. We exposed in microcosms containing single species and all possible mixtures of four leaf litter species differing widely in initial chemical and physical characteristics from a temperate forest to the climatic conditions of four different forests across the Northern Hemisphere for 1 year. Calcium, magnesium and condensed tannins predicted litter mass loss of single litter species and mixtures across forest types and biomes, regardless of species richness and microarthropod presence. However, relative mixture effects differed among forest types and varied with the access to the litter by microarthropods. Access to the microcosms by microarthropods modified the decomposition of individual litter species within mixtures, which differed among forest types independent of litter species richness and composition of litter mixtures. However, soil microarthropods generally only little affected litter decomposition. Synthesis. We conclude that litter identity is the dominant driver of decomposition across different forest types and the non‐additive litter mixture effects vary among biomes despite identical leaf litter chemistry. These results suggest that across large spatial scales the environmental context of decomposing litter mixtures, including microarthropod communities, determine the decomposition of litter mixtures besides strong litter trait‐based effects.

Mistletoe litter accelerates the decomposition of recalcitrant host litter in a semi‐arid savanna, south‐west Zimbabwe

AbstractLitter mixing plays an important role in enhancing carbon and nutrient cycling, but little is known about the effects of nutrient‐rich mistletoe litter on the decomposition of slow‐decaying litter in nutrient‐poor environments. We investigated the effects of mistletoe litter on the decomposition and nutrient release of host Vachellia karroo litter in semi‐arid savanna, south‐west Zimbabwe. Mass loss and nutrient release was quantified in litter of each single species, two‐species, three‐species and four‐species mixtures of mistletoe, Erianthemum ngamicum, Plicosepalus kalachariensis and Viscum verrucosum, and the host V. karroo in 30 × 30 cm nylon‐mesh litterbags under field conditions at 2‐month intervals for one year. Repeated‐measures analysis of variance was used to test the effects of litter type, incubation time and their interaction on mass loss and nutrient release. The effects of initial litter quality, incubation time and litter mixture on decomposition rate were also tested. Litter mixtures of mistletoes and V. karroo decomposed three times faster than V. karroo decomposing alone, and decomposition of litter mixtures was influenced by initial litter quality and incubation time. Further, non‐additive effects are reported, with synergistic interactions being greater after 12 months and common regarding mass loss, phosphorus and carbon, whereas antagonistic interactions were common in nitrogen release. These effects varied both in magnitude and direction between litter‐mixing treatments and with incubation time (P < 0.05). Our findings show that mistletoe litter enhance the decomposition of recalcitrant host litter consistent with findings in other ecosystems that contain hemiparasites, suggesting that hemiparasite litter plays an important role in carbon and nutrient flux in this system. Further, by enhancing the decomposition and nutrient release rate of recalcitrant host litter, mistletoes increase nutrient availability to other organisms within the ecosystem lending support to the premise that parasitic plants function as keystone species in environments where they occur.

Non‐negligible contribution of subordinates in community‐level litter decomposition: Deciduous trees in an evergreen world

Abstract Subordinate species have relatively low abundance compared to dominant species; however, they may contribute significantly to functional diversity and ecosystem functionality, particularly if they differ strongly from the dominants in key traits. Here we investigated whether this phenomenon might be applied to litter decomposition as a key carbon and nutrient cycling process. We hypothesized that species litter mass‐weighted predictions of community‐level litter decomposition based on dominant rates only, would deviate strongly from observed community‐level rates, and that predictions would improve as subordinates with strongly contrasting traits were combined with those of their dominant counterparts. We tested this hypothesis through a 1‐year field decomposition experiment across a chronological sequence in a subtropical evergreen broadleaved forest. The experiment included the single‐species litter of evergreen dominants, evergreen subordinates and deciduous subordinates, respectively, as well as community‐level litter mixtures. The expected community‐weighted mean decomposition rates based on the evergreen dominants alone, with or without the addition of evergreen subordinates, deviated strongly from those of observed community litter mixtures at the middle and late succession stages, but not at the early stage. When adding deciduous subordinates to this expectation, there was no longer any difference to the observed community litter decomposition rate across succession stages. Deciduous subordinates alone explained 7%, 21% and 15% of the total variation in community litter mixture decomposition rate for early, middle and late successional stages, respectively, which is more than would be expected from their litter mass fraction. Synthesis. Deciduous subordinates with strongly contrasting nutritional and water‐storage traits compared to the dominant evergreens significantly impacted litter decomposition at the community‐level in spite of their low abundance. This study highlights the importance of ‘being different’ for subordinates to be influential in ecosystem carbon cycling.

Effects of litter mixtures on aerobic decomposition rate and its temperature sensitivity in a boreal peatland

Litter mixing effects during decomposition remain inconclusive for boreal peatlands, and such effects may vary with climate warming and associated shifts in vegetation composition. Here, litters were collected from four common species (deciduous shrub Betula fruticosa, evergreen shrub Ledum palustre, graminoid Eriophorum vaginatum, and moss Sphagnum divinum) in a boreal peatland of northeast China, resulting in 15 species combinations with species richness ranging from one to four. We determined litter mixing effects on carbon (C) mineralization rate and mass loss under aerobic conditions at 10 °C and 20 °C in a 315-d incubation experiment, and assessed the differences in litter mass loss for the individual species within monocultures and mixtures. Non-additive effects on C mineralization and mass loss were prevalent during decomposition of litter mixtures. Moreover, the sensitivity of C mineralization and mass loss to rising incubation temperature (Q10) was found to be non-additive in five and three out of 11 mixtures, respectively. Notably, mass loss of other litters in the mixtures was generally promoted by B. fruticosa, but inhibited by S. divinum in two- and three-species litter mixtures. Furthermore, B. fruticosa increased and S. divinum decreased Q10 values for mass loss of other litters in four out of seven cases. These findings suggest that the shifts in plant community composition will not only influence community-level litter decomposition through altered litter mixing effects during decomposition, but also modulate the response of litter decomposition to rising temperature in boreal peatlands.

Microbial activity, microarthropods and the phenomenon of positive, non-additive decomposition of mixed litter

Litter decomposition is a fundamental ecosystem process that is essential to nutrient cycling, to the flow of energy through the decomposer food web, and to soil carbon sequestration. For a given climate, litter quality is a major controller of decomposition via its impacts on the activities of decomposer communities, including those of microarthropods and microorganisms. In nature, litter quality can be strongly affected by the composition of mixtures of litter from different plant species or litter of varying age. In contrast with the decomposition of single litter types, the decomposition of litter mixtures may be non-additive, making its prediction difficult. Positive, non-additive decomposition may occur, for example, when microarthropod density is increased in one litter type due to the presence of a second litter type, or when microbial activity in one litter type is stimulated by the presence of a second litter type. We tested the involvement of microarthropod and microbial communities in positive, non-additive decomposition using a model clover litter - oat straw mixture. We found that positive, non-additive decomposition was not associated with changes in microarthropod density, but was associated with significant increases in microbial activity.

Functional identity rather than functional diversity or species richness controls litter mixture decomposition in a subtropical forest

While growing evidence has shown consistently positive plant diversity effects on primary productivity, diversity effects on litter decomposition remain inconclusive. Our aim was to evaluate the relative importance of functional identity (FI), functional diversity (FD) and species richness (SR) for litter mixture decomposition and litter mixing effects. 32 mixtures of leaf litter from seven tree species were constructed by creating two independent gradients of FD and SR. Decomposition of these mixtures was measured using laboratory microcosms. Moreover, component litter was separated from mixtures to assess species-specific responses to mixing. FI but not FD or SR significantly influenced litter mixture decomposition. Six and nine litter mixtures separately exhibited synergistic and antagonistic non-additive effects with litter mixing effects ranging from −8.97% to 16.82%, which did not significantly relate to FD or SR. Mass loss of two fast-decomposing species was inhibited and that of two out of five slow-decomposing species was accelerated by the presence of other species. Chemical traits of a given component species and trait differences between this species and its neighbors significantly influenced its response to litter mixing. These results suggest that relationship between FD and litter mixing effect is far from generalizable and highlight that analyzing species-specific responses to mixing is useful in exploring mechanisms underlying interactions among component litter.