Two-species Mixtures Research Articles

Drought and plant neighbourhood interactively determine herbivore consumption and performance

Both plant neighbourhood composition and drought have well-known independent effects on insect herbivore performance, but their interactive effects remain elusive. In this study we performed a laboratory experiment to investigate the independent and combined effects of plant neighbourhood composition and drought on the performance of Gypsy moth larvae (Lymantria dispar) feeding on silver birch (Betula pendula) leaves. For this, we collected leaf samples from birch trees growing in a field experiment where we manipulated both host-tree species diversity (three levels: birch monocultures, two-species mixtures associating birch with the pedunculate oak Quercus robur or maritime pine Pinus pinaster, and three-species mixture with pedunculate oak, the maritime pine and birch) and water availability (two levels: irrigated vs. non-irrigated). In most cases, plant neighbourhood composition and irrigation treatments independently and interactively affected herbivore performance traits, especially those related to growth and food (i.e. birch leaves) processing. By addressing the interactive effects of tree species diversity and drought on insect herbivory from the herbivore’s point of view, our study builds toward a better understanding of the multiple ecological drivers of plant-insect interactions.

Effect of plant diversity on phosphorus removal in hydroponic microcosms simulating floating constructed wetlands

Phosphorus (P) removal is one of the major target services of constructed wetlands (CWs) treating wastewater. Previous studies have shown that plant diversity plays an important role in the functioning of CWs for wastewater treatment such as nitrogen removal, but the effect of plant diversity on P removal remains largely unexplored. In particular, less work has been done with free floating species in CW systems without substrate. In this study, we tested whether and how P removal is dependent on species richness and/or specific species composition in hydroponic microcosm stimulating floating CWs. Four common early-spring species (Rumex japonicas, Oenanthe hookeri, Phalaris arundinacea and Reineckia carnea) were transplanted into the microcosms, ranging from a richness gradient of 1–4 species. A total of 15 community treatments (4 monocultures, 6 two-species mixtures, 4 three-species mixtures and 1 four-species mixture) were set up. Our results showed that: (1) effluent total P concentration decreased with increasing species richness, primarily due to higher biomass production and larger plant P pool at higher species richness; (2) communities including Oenanthe hookeri outperformed other communities in removing P, and the interaction between Oenanthe hookeri and Rumex japonicas gave rise to an “under-depletion effect” on wastewater P; and (3) species composition exerted a stronger effect than species richness on P removal from wastewater. Assembling proper plants species composition in floating CWs might be more important than simply increasing species richness for treating wastewater nutrients.

A quantum degenerate Bose–Fermi mixture of 41K and 6Li

We report a new apparatus for the study of two-species quantum degenerate mixture of 41K and 6Li atoms. We develop and combine several advanced cooling techniques to achieve both a large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of an extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for 41K atoms while the 6Li atoms are sympathetically cooled in an optically plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the 41K and 6Li atoms. The Bose–Einstein condensate of 41K has 1.4 × 105 atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of 6Li has a total atom number of 5.4 × 105 at 0.25 Fermi temperature.

Model-independent particle species disentanglement by X-ray cross-correlation scattering

Mixtures of different particle species are often investigated using the angular averages of the scattered X-ray intensity. The number of species is deduced by singular value decomposition methods. The full disentanglement of the data into per-species contributions requires additional knowledge about the system under investigation. We propose to exploit higher-order angular X-ray intensity correlations with a new computational protocol, which we apply to synchrotron data from two-species mixtures of two-dimensional static test nanoparticles. Without any other information besides the correlations, we demonstrate the assessment of particle species concentrations in the measured data sets, as well as the full ab initio reconstruction of both particle structures. The concept extends straightforwardly to more species and to the three-dimensional case, whereby the practical application will require the measurements to be performed at an X-ray free electron laser.

Can niche plasticity promote biodiversity-productivity relationships through increased complementarity?

Most experimental biodiversity-ecosystem functioning research to date has addressed herbaceous plant communities. Comparably little is known about how forest communities will respond to species losses, despite their importance for global biogeochemical cycling. We studied tree species interactions in experimental subtropical tree communities with 33 distinct tree species mixtures and one, two, or four species. Plots were either exposed to natural light levels or shaded. Trees grew rapidly and were intensely competing above ground after 1.5 growing seasons when plots were thinned and the vertical distribution of leaves and wood determined by separating the biomass of harvested trees into 50cm height increments. Our aim was to analyze effects of species richness in relation to the vertical allocation of leaf biomass and wood, with an emphasis on bipartite competitive interactions among species. Aboveground productivity increased with species richness. The community-level vertical leaf and wood distribution depended on the species composition of communities. Mean height and breadth of species-level vertical leaf and wood distributions did not change with species richness. However, the extra biomass produced by mixtures compared to monocultures of the component species increased when vertical leaf distributions of monocultures were more different. Decomposition of biodiversity effects with the additive partitioning scheme indicated positive complementarity effects that were higher in light than in shade. Selection effects did not deviate from zero, irrespective of light levels. Vertical leaf distributions shifted apart in mixed stands as consequence of competition-driven phenotypic plasticity, promoting realized complementarity. Structural equation models showed that this effect was larger for species that differed more in growth strategies that were characterized by functional traits. In 13 of the 18 investigated two-species mixtures, both species benefitted relative to intraspecific competition in monoculture. In the remaining five pairwise mixtures, the relative yield gain of one species exceeded the relative yield loss of the other species, resulting in a relative yield total (RYT) exceeding 1. Overall, our analysis indicates that richness-productivity relationships are promoted by interspecific niche complementarity at early stages of stand development, and that this effect is enhanced by architectural plasticity.

Amino acid profile and sensory characteristics of dry fermented pork loins produced with a mixture of probiotic starter cultures.

Proteolysis is a biochemical process in dry-aged meat products where proteins are metabolized and broken down to polypeptides, peptides, and free amino acids. In the literature it is reported that an appropriate choice of probiotic starter culture limits proteolytic changes in dry-fermented meat products. In this study the combined effect of a mixture of probiotic starter cultures on the free amino acid profile, total count of lactic acid bacteria, and the sensory quality of dry-aged pork loins after fermentation and after storing the vacuum-packed samples was evaluated. LOCK900 and BB12 probiotic strains were the technologically best two-species mixture of starter cultures for the production of probiotic dry-aged pork loins. They allowed us to obtain products with high and stable bacterial count and acceptable sensory quality, both after 21 days of fermentation and after 2 months of cold storage. Changes in the free amino acid profile and increased intensity of the selected sensory attributes result from a significant share of probiotics in meat proteolysis occurring during fermentation and storage. The results suggest the relevance of using probiotic bacteria as a two-species starter culture for the production of dry-aged products. © 2016 Society of Chemical Industry.

Combined use of network inference tools identifies ecologically meaningful bacterial associations in a paddy soil

High-throughput sequencing technologies have recently made it possible to interrogate the phylogenetic diversity of soils at considerable depth. This ability has led to the development of many computational tools to infer interaction networks from environmental samples. Although such tools have widely been used, they have more often served as a visual means to compare microbial communities across environmental gradients than as a means to appreciate microbial interactions associated with certain ecological processes. Previous studies have often regarded a subnetwork (module) as a functional unit but its functionality in ecological context has never been evidenced. To make better use of these tools in appreciating microbial interactions, we propose the combinational use of different inference tools. This ensemble approach permits the use of more independent predictors and the removal of tool-specific predictions in order to increase prediction accuracy. The purpose of the present study is to identify ecologically meaningful bacterial associations using multi-tool approach. Soil samples were collected in time series from experimental paddy rice plots. Bacterial communities were characterized by high-throughput tag sequencing of 16S rRNA gene fragments. We used three tools, Co-occurrence Network inference (CoNet), Molecular Ecological Network Analysis (MENA) and extended Local Similarity Analysis (eLSA), to infer networks from abundance profiles, partitioned the networks into modules, screened for the modules with ≥50% of genus-/species-level nodes, captured the modules that were derived from different tools and shared ≥ 50% of order-level nodes (tool-agreed modules) and tested their robustness against the changes in the tool parameters. By these procedures, two three-tool-agreed modules were found. One represented a guild that is phenotypically associated with aerobic respiration and fermentation and the other represented a guild phenotypically associated with metal/sulphur cycles, all of which are essential processes of water-submerged paddy soils that are mediated by bacteria. These data suggested that the linked members in a module were functionally associated taxa that work together to achieve a distinct function or an ecological process, and thus were ecologically meaningful to the environment. We selected three linked species from a three-tool-agreed module and validated their interactions using co-culture methods. Results showed that the interaction type between Janthinobacterium lividum and Leuconostoc lactis in the two-species mixture was validated to be ambivalent, positive for one partner and negative for the other. However, this type of interaction was not retained when a third party Lactococcus piscium was introduced, signifying the complexity of multi-species interactions. Validation results suggested that the selected species were interacting partners in laboratory but the validated interaction types were different from those inferred. By multi-tool approach, we also found that highly linked nodes, which are often referred to as “keystone species” and are frequently interpreted as the species playing important roles in soils, are tool dependent. Among top ten highly linked nodes, only four are conserved across three tools. These results suggest more research is required on the ecological significance of degree-based identification of keystone species. Overall, the present study highlights the potential utility of combined use of inference tools to identify ecologically meaningful bacterial associations in soils and other environmental samples. It is interesting to see what type of ecologically meaningful bacterial associations can be found in other soils.

Biodiversity as a creator of productivity and interspecific competitiveness of winter cereal species in mixed cropping

The study evaluated the productivity of three species of winter cereals – wheat, rye, and triticale – in sole cropping and in mixtures of two and three species. Asymmetrical interspecific competition was noted during generative growth stages. The greatest competitive strength was observed for triticale in the mixture with wheat during the heading stage. In the two-species mixtures with equal proportions (50:50), triticale produced greater biomass. In the three-species mixture, the productivity of rye and triticale depended mainly on their initial high share in the crop (50%). Wheat, despite having a high share in the mixture, did not display high productivity, because the yield per spike and harvest index decreased. Rye in the mixed cropping with wheat produced significantly higher spike weight and culm weight in comparison with sole cropping. Triticale, despite being strongly competitive in the canopy during the generative growth phase, attained high grain yield per spike. The low competition coefficients for triticale relative to rye suggest that these two species have a similar competitive pressure during the period of harvests.

Overyielding of temperate mixed forests occurs in evergreen–deciduous but not in deciduous–deciduous species mixtures over time in the Netherlands

Recent studies show that mixed species forests sometimes have higher stand productivity than monospecific forests, which we refer to as overyielding. Yet, results for temperate forests are ambiguous, possibly because forests differ in local site conditions, thinning history and forest age. In line with the niche complementarity hypothesis, we expect stronger overyielding for forests with species differing in both leaf phenology (evergreen or deciduous) and shade tolerance. We also hypothesize that overyielding will decrease with stand development because of decreasing resource availability. We compared 4 two-species mixtures with their corresponding monospecific stands from long-term field measurements in the Netherlands. The mixtures were Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)–common beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.)–common oak (Quercus robur L.), common oak–common beech, and common oak–silver birch (Betula pendula Roth). Overyielding was observed in 2 of the 4 mixtures: Douglas-fir–common beech mixtures had 35.9% and 36.7% higher volume growth relative to Douglas-fir and common beech monocultures, respectively; Scots pine–common oak mixtures had 20.3% and 31.2% higher volume growth relative to Scots pine and common oak monocultures, respectively, on average over time. Furthermore, overyielding was relatively constant for the two mixtures through stand development. This result was robust after accounting for possible effects of site quality and thinning history, where site quality contributed independently to stand productivity and thinning history had no effect. No significant overyielding effects were observed for the two deciduous mixed stands, i.e. common oak–common beech and common oak–silver birch. Mixing tree species in temperate forests resulted in overyielding for evergreen–deciduous species mixtures, but not for deciduous–deciduous species mixtures. This indicates that leaf phenology contributes to overyielding effects. Overyielding was higher in the Douglas-fir–common beech mixtures than the Scots pine–common oak mixtures, which coincides with a stronger contrast in shade tolerance between Douglas-fir and common beech and thus stronger complementarity. Our results support the complementarity hypothesis and imply that such mechanisms are maintained with stand development. It therefore appears that mixing evergreen with deciduous species with contrasting shade tolerance is a valid management strategy for increasing diversity and productivity of temperate forests in the Netherlands.

Unconventional Bose-Einstein condensation in a system with two species of bosons in thep-orbital bands in an optical lattice

In the context of Gross-Pitaevskii theory, we investigate the unconventional Bose-Einstein condensations in the two-species mixture with $p$-wave symmetry in the second band of a bipartite optical lattice. A new imaginary-time propagation method is developed to numerically determine the $p$-orbital condensation. Different from the single-species case, the two-species boson mixture exhibits two non-equivalent complex condensates in the intraspecies-interaction-dominating regime, exhibiting the vortex-antivortex lattice configuration in the charge and spin channels, respectively. When the interspecies interaction is tuned across the SU(2) invariant point, the system undergoes a quantum phase transition toward a checkerboard-like spin density wave state with a real-valued condensate wavefunction. The influence of lattice asymmetry on the quantum phase transition is addressed. Finally, we present a phase-sensitive measurement scheme for experimentally detecting the UBEC in our model.

Exotic Haldane superfluid phase of soft-core bosons in optical lattices

We propose to realize an exotic Haldane superfluid (HSF) phase in an extended Bose-Hubbard model on the two-leg ladder (i.e., a two-species mixture of interacting bosons). The proposal is confirmed by means of large-scale quantum Monte Carlo simulations, with a significant part of the ground-state phase diagram being revealed. Most remarkably, the newly discovered HSF phase features both superfluidity and the non-local topological Haldane order. The effects induced by varying the number of legs are furthermore explored. Our results shed light on how topological superfluid emerges in bosonic systems.

Salinity and disturbance mediate direct and indirect plant-plant interactions in an assembled marsh community.

Direct and indirect plant-plant interactions play important roles in structuring plant communities, but the relative importance of physical stress and biological disturbance in mediating competitive outcomes remains debated. We conducted two common garden experiments to examine the influence of salinity and disturbance (sediment accretion and clipping) on competitive interactions among three native sedges (Scirpus mariqueter, Scirpus triqueter, and Carex scabrifolia) in the Yangtze estuary. In both experiments, the relative competitive abilities of these plants shifted among different treatments. Competition importance rather than intensity significantly decreased with increasing stress. At the community level, competition importance showed reduced variation along the stress gradient in the disturbance experiment. Notably, the performance of these sedges in three-species mixtures could not be predicted by their competitive relationships in two-species mixtures, which was an indication of indirect interactions. Salinity, disturbance and indirect interactions all affected the competitive dynamics of these sedges, which could explain their different performances and natural distributions in the Yangtze estuary. Our findings of the complex effects of physical factors and multi-species interactions, as well as the different patterns of competition importance along stress gradients at the species level and the community level can improve our understanding of plant community organization in salt marshes and other ecosystems with sharp environmental gradients.

Presence of Trifolium repens Promotes Complementarity of Water Use and N Facilitation in Diverse Grass Mixtures.

Legume species promote productivity and increase the digestibility of herbage in grasslands. Considerable experimental data also indicate that communities with legumes produce more above-ground biomass than is expected from monocultures. While it has been attributed to N facilitation, evidence to identify the mechanisms involved is still lacking and the role of complementarity in soil water acquisition by vertical root differentiation remains unclear. We used a 20-months mesocosm experiment to investigate the effects of species richness (single species, two- and five-species mixtures) and functional diversity (presence of the legume Trifolium repens) on a set of traits related to light, N and water use and measured at community level. We found a positive effect of Trifolium presence and abundance on biomass production and complementarity effects in the two-species mixtures from the second year. In addition the community traits related to water and N acquisition and use (leaf area, N, water-use efficiency, and deep root growth) were higher in the presence of Trifolium. With a multiple regression approach, we showed that the traits related to water acquisition and use were with N the main determinants of biomass production and complementarity effects in diverse mixtures. At shallow soil layers, lower root mass of Trifolium and higher soil moisture should increase soil water availability for the associated grass species. Conversely at deep soil layer, higher root growth and lower soil moisture mirror soil resource use increase of mixtures. Altogether, these results highlight N facilitation but almost soil vertical differentiation and thus complementarity for water acquisition and use in mixtures with Trifolium. Contrary to grass-Trifolium mixtures, no significant over-yielding was measured for grass mixtures even those having complementary traits (short and shallow vs. tall and deep). Thus, vertical complementarity for soil resources uptake in mixtures was not only dependant on the inherent root system architecture but also on root plasticity. We also observed a time-dependence for positive complementarity effects due to the slow development of Trifolium in mixtures, possibly induced by competition with grasses. Overall, our data underlined that soil water resource was an important driver of over-yielding and complementarity effects in Trifolium-grass mixtures.

Impenetrable mass-imbalanced particles in one-dimensional harmonic traps

Strongly interacting particles in one dimension subject to external confinement have become a topic of considerable interest due to recent experimental advances and the development of new theoretical methods to attack such systems. In the case of equal mass fermions or bosons with two or more internal degrees of freedom, one can map the problem onto the well-known Heisenberg spin models. However, many interesting physical systems contain mixtures of particles with different masses. Therefore, a generalization of the recent strong-coupling techniques would be highly desirable. This is particularly important since such problems are generally considered non-integrable and thus the hugely successful Bethe ansatz approach cannot be applied. Here we discuss some initial steps towards this goal by investigating small ensembles of one-dimensional harmonically trapped particles where pairwise interactions are either vanishing or infinitely strong with focus on the mass-imbalanced case. We discuss a (semi)-analytical approach to describe systems using hyperspherical coordinates where the interaction is effectively decoupled from the trapping potential. As an illustrative example we analyze mass-imbalanced four-particle two-species mixtures with strong interactions between the two species. For such systems we calculate the energies, densities and pair-correlation functions.

Use of near-infrared reflectance spectroscopy to quantify diet mixing in a generalist marine herbivore

The diet of individual animals in the field is governed by behavioural preference as well as factors intrinsic and extrinsic to the organism that may constrain their ability to obtain preferred foods. Accurate measurements of individual diets are essential to understanding how consumers can impact communities, but can be difficult to obtain. We aim to determine whether near-infrared reflectance spectroscopy (NIRS) can be used to quantify the degree of diet mixing in the diet of a generalist herbivore, the marine gastropod Lunella torquatus. NIRS successfully classified five algal diets and could quantify the proportions of these species in two-species combinations. We then assessed whether NIRS could predict dietary composition post-digestion by contrasting faecal material from single-species and mixed diets. Partial least squares methods were used to develop prediction models that effectively discriminated among species and, for most species, effectively predicted the proportion of a given species in all possible two-species mixtures. NIRS thus has the potential to provide a non-invasive method for assessing the realised diets of free-living herbivores.

Driving mechanisms of overstorey–understorey diversity relationships in European forests

Forest ecosystem multifunctionality and the provision of ecosystem services benefit from high biodiversity, including from the understorey. Hence, it is crucial to get insight into the mechanisms that influence the composition and diversity in this forest layer. Understorey species have specific environmental requirements which are influenced by the overstorey in a species-specific way. Mixing tree species may create a heterogeneous pattern of environmental conditions similar to the component species’ monocultures, or induce new environmental conditions. We quantified overstorey–understorey taxonomic and functional diversity relationships at different spatial scales in an innovative large-scaled European diversity-oriented research platform that allows the separation of tree species identity and diversity effects. We considered our results in relation to the divergent patterns expected, depending on whether environmental heterogeneity or novel environment creation is the mechanism driving overstorey–understorey diversity relationships.We examined the understorey in mature forests in six European regions. Per region, three to five tree species were selected and 28–43 plots of 30m×30m were established (209 in total), covering a tree species richness gradient from monocultures to three- to five-species mixed plots. Within each plot, we performed vegetation surveys in three vegetation quadrats. We examined the understorey compositional variation among and within regions and the influence of overstorey taxonomic and functional diversity on understorey diversity at different spatial scales.The understorey composition showed clear interregional differences. We found lower compositional differentiation among quadrats with a higher tree species richness level (Finland, Germany and Italy). These quadrats share more tree species and probably have more similar environmental conditions. Neither overstorey taxonomic nor functional diversity affected the stand-level understorey species richness. At the forest-level, adding two-species mixtures to component monocultures clearly increased the understorey species richness, while adding mixtures with a higher tree species richness level to component monocultures had a negligible or negative impact.Overstorey–understorey diversity relationships depend on the spatial scale. At the stand-level, our results lacked support for the environmental heterogeneity hypothesis and revealed the possibility of novel environment creation in tree-by-tree mixed stands. At the forest-level, favouring the mixture of two-species mixed stands and their component monoculture stands offers the best prospects for a higher understorey species richness.

Evolution of Goldstone mode in binary condensate mixtures

We show that the third Goldstone mode in the two-species condensate mixtures, which emerges at phase-separation, gets hardened when the confining potentials have separated trap centers. The {\em sandwich} type condensate density profiles, in this case, acquire a {\em side-by-side} density profile configuration. We use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution and density profiles for these phase transitions at $T=0$.

Quantum spin dimers from chiral dissipation in cold-atom chains.

We consider the nonequilibrium dynamics of a driven dissipative spin chain with chiral coupling to a one-dimensional (1D) bosonic bath, and its atomic implementation with a two-species mixture of cold quantum gases. The reservoir is represented by a spin-orbit coupled 1D quasicondensate of atoms in a magnetized phase, while the spins are identified with motional states of a separate species of atoms in an optical lattice. The chirality of reservoir excitations allows the spins to couple differently to left- and right-moving modes, which in our atomic setup can be tuned from bidirectional to purely unidirectional. Remarkably, this leads to a pure steady state in which pairs of neighboring spins form dimers that decouple from the remainder of the chain. Our results also apply to current experiments with two-level emitters coupled to photonic waveguides.

Interactive Effects of Nitrogen and Water Addition on Competitive Hierarchies Between Early- and Late- Successional Plant Species

Increased nitrogen (N) and water availability, resulting from global changes or ecosystem management, were predicted to promote plant productivity and change community composition through shifts in competition hierarchies. So far, however, it still remains unclear how competitive interactions respond to N and water additions, which will be important to understand how plant community composition changes. To test plant competition ability in different successional stages under N and water addition treatments, a pot experiment under field conditions was performed. Six dominant plant species, three early-successional species, Artemisia lavandulaefolia, Artemisia capillaris, and Pennisetum centrasiaticum versus three late-successional species, Stipa krylovii, Leymus chinensis, and Artemisia frigida, were grown in monocultures and in twospecies mixtures under factorial combinations of N and water addition treatments. We found that (1) there were interactive effects of N addition, water addition and interspecific competition on plant biomass; (2) For a given species, competitive abilities were correlated with biomass difference of neighboring species; (3) N and water additions interactively increased competition intensity and shifted species competitive hierarchies; (4) Late-successional species had stronger competitive abilities in the N addition treatment, whereas early-successional species had stronger competitive abilities after water addition or N water addition. Our results show that N and water additions increased the intensity and impact of interspecific competition on plant growth, which has great implications for community structures. Since interspecific differences in competitive abilities were not well explained by species biomass, species identity, such as plant functional traits, should be included to predict the impact of increased N and water availability on plant communities and ecosystem functions.

Leaf litter mixtures and neighbour effects: Low-nitrogen and high-lignin species increase decomposition rate of high-nitrogen and low-lignin neighbours

In natural ecosystems plant litter is typically a mixture of more than one species and the rate of decomposition can be faster (synergistic) or slower (antagonistic) than the average of its component species (non-additive effects). We analysed the decomposition rates of two-species mixtures to determine if there were consistent non-additive effects of litter mixing on decomposition and how do they compare with the effects of species identity on mixture decomposition. Then we tested if non-additive effects were consistently associated with the presence of particular species in the mixture, to the combination of Fast- or Slow-decomposing species, or to initial litter quality of mixtures. We found: (a) that species identity was the primary determinant of the decomposition rate of mixtures, and (b) we detected significant, but weak, non-additive effects which were consistently synergistic in the most chemically heterogeneous mixtures. However, slower decomposing species appeared to increase the decomposition rate of faster decomposing species (30 times out of 41 after 2 months of incubation, and 17 times out of 24 after 9 months of incubation). During the initial stages of decomposition, low-lignin mixtures showed mostly synergistic effects, whereas high-lignin mixtures showed antagonistic effects. At more advanced stages of decomposition, mixtures containing species with highest difference in initial N content had more synergistic effects, whereas those with similar initial N content showed both synergistic and antagonistic effects. Our results confirm previous findings about the importance of chemical heterogeneity of mixtures as a driver of decomposition rates of litter mixtures. We propose that mechanisms related to carbon priming may be related to synergistic effects in most heterogeneous mixtures, while nitrogen interaction with carbon may be resulting in antagonistic effects in homogeneous and Slow-decomposing species mixtures.