Effects Of Litter Mixtures Research Articles

Macrophyte litter mixtures mediate decomposition processes in coastal sediments

Understanding litter decomposition processes in coastal macrophyte habitats is critically important for predicting ecosystem functioning. However, decomposition processes of litter mixtures in coastal habitats remain largely unexplored. Here, we evaluated the litter mixture effects on the decomposition of six marine macrophytes (two seagrasses and four macroalgae) through in situ litter-mixing experiments with five levels of litter species richness and 36 different litter compositions. We found that the litter species identity and composition, rather than species richness, were crucial in structuring benthic faunal communities. Macroalgal litter, particularly Sargassum sp., hosted higher numbers of polychaetes and crustaceans than seagrass litter. More macroalgal presence induced faster decomposition rates of seagrass litter in the late stage, but not in the early stage. These findings suggest that changes in macrophyte diversity and composition can alter decomposition processes and, consequently, the sediment organic carbon stock through the transition of litter sources and benthic faunas.

Litter mixture effects on nitrogen dynamics during decomposition predominantly vary among biomes but little with litter identity, diversity and soil fauna

Nitrogen (N) is essential for net primary production, with much of the required N in terrestrial ecosystems derived from recycling via litter decomposition. The diversity and identity of plant species and decomposer organisms affect N cycling during litter decomposition, yet the generality and magnitude of these effects remain uncertain. To fill this gap, a decomposition experiment with four leaf litter species that differed widely in initial litter quality was conducted including single species and all possible multispecies mixtures, with and without microarthropods access across a broad latitudinal gradient covering four major forest biomes of the Northern Hemisphere. The results showed that leaf litter N dynamics (both N loss and N immobilization) in single species treatments depended primarily on litter species identity and the local environmental context. We found strong mixture effects, that overall tended to increase N loss and to reduce 15N transfer. The relative mixture effects on N dynamics differed among forest biomes, but were little affected by the other factors we manipulated. The N loss of individual litter species in mixtures not only depended on litter identity and soil microarthropod access, but also on forest biomes; while 15N transfer depended strongly on litter mixing, independently of litter species richness or composition of the mixtures. Litter N dynamics were mainly driven by a small subset of litter traits, regardless of species richness and microarthropod access. Overall, our results highlight that litter mixture strongly affects N dynamics during decomposition, with the mixture effects predominantly varying among forest biomes but little with litter identity, diversity and microarthropod access. To improve predictions on how changes in tree species composition and diversity may impact nutrient dynamics in forest ecosystems in face of increasing N deposition, interactions between litter and soil but also within litter mixtures need closer attention.

Non-additive effects of Chinese fir leaf litter mixtures of different ages on soil N2O emissions in a monoculture plantation treated with N and P additions

Non-additive effects of Chinese fir leaf litter mixtures of different ages on soil N2O emissions in a monoculture plantation treated with N and P additions

Litter mixture effects on decomposition change with forest succession and are influenced by time and soil fauna in tropical mountain Andes

Abstract In highly transformed regions, such as the tropical Andes, identifying the influence of forest succession and soil fauna on non-additive effects of litter decomposition is crucial for gaining a more realistic understanding of carbon dynamics and nutrient cycles. The objective of this paper was to analyze the changes of litter mixture effects on decomposition between different soil fauna treatments (macrofauna inclusion vs macrofauna exclusion) and successional stages (mature forests vs secondary forests) in upper Andean tropical forests along time by using a reciprocal translocation experiment of 1,344 litterbags that ran for 18 months with six common native Andean species. Thought t-tests, linear regressions, and linear mixed models, I found that litter mixture effects vary among sites and increase with time in secondary forests until the year of decomposition in litterbags with macrofauna exclusion. Mature forests exhibited strong antagonistic effects, while pronounced synergistic effects were observed in secondary forests. Although soil macrofauna did not increase significantly litter decomposition and synergistic effects in the mixtures at any of the stages of decay, it is likely that soil macrofauna may impact litter mixtures through top-down effects within soil food webs, rather than exerting a direct effect in the litter consumption as has been reported in tropical lowland ecosystems. Overall, this study supports the idea that litter mixtures exhibit significant variability across sites, can change with successional stage, and are influenced by soil fauna depending on the stage of decay in tropical Andean montane forests.

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.

Forest plantation diversification with Leguminosae tree species: Consequences on litter decomposition and nutrient recycling

AbstractMixed tree plantations provide greater ecosystem services than monocultures. Leguminosae tree species can be appropriate complements to achieve a sustainable soil management target. A key aspect of species trait complementarity is the litter mixture effects in the litter decomposition process. We evaluated how the mixture of poplar litter (Populus deltoides Marsh.) with Leguminosae tree species modulated the litter decomposition process and C, N and P recycling, through changes driven by the Leguminosae litter chemical traits. Under field conditions, we compared poplar litter alone (monoculture) with its 50:50 mixture with Enterolobuim contortisiliquum (Vell.) Morong., or Peltophorum dubium (Spreng.). Compared to poplar litter, its mixture with E. contortisiliquum had a 25% lower C:N ratio and a similar N:P ratio, whereas mixture with P. dubium had a 9% lower C:N and a 29% lower N:P ratios. The mixture with E. contortisiliquum showed a 64% faster decomposition rate, and 55% and 203% faster C and N release rates, respectively, compared to poplar. In contrast, in the mixture with P. dubium, there was no difference in the litter, C and N decay rates with poplar litter alone. The mixture with P. dubium had a 37% lower P retention compared to poplar, whereas P was released rather than retained in the mixture with E. contortisiliquum. The mixture with E. contortisiliquum showed a net antagonistic effect in the litter decomposition rate. However, in the mixture, poplar litter decomposed 33% faster and the E. contotrtisiliquum litter decomposed 35% slower than species alone. The C:N and N:P ratios in the litter mixture were relevant traits shaping the magnitude and direction of litter decomposition and nutrient recycling processes. The incorporation of both Leguminosae to monospecific poplar plantations could contribute to counteract P limitation in this system and to improve soil fertility and functioning.

The effects of N-addition on litter mixture effects depend on decomposition time: A case from mixed-litter decomposition in the Gurbantunggut Desert.

Changes in nitrogen (N) deposition and litter mixtures have been shown to influence ecosystem processes such as litter decomposition. However, the interactive effects of litter mixing and N-deposition on decomposition process in desert regions remain poorly identified. We assessed the simultaneous effects of both N addition and litter mixture on mass loss in a litterbag decomposition experiment using six native plants in single-species samples with diverse quality and 14-species combinations in the Gurbantunggut Desert under two N addition treatments (control and N addition). The N addition had no significant effect on decomposition rate of single-species litter (expect Haloxylon ammodendron), whereas litter mass loss and decomposition rate differed significantly among species, with variations positively correlated with initial phosphorus concentration and negatively correlated with initial lignin concentration. After 18 months, the average mass loss across litter mixtures did not overall differ from those predicted from single species either in control or N addition treatments, that is, mixing of different species had no non-additive effects on decomposition. The N addition, however, did modify the direction of mixture effects and interacted with incubation time. Added N transformed synergistic effects of litter mixtures to antagonistic effects on mass loss after 1 month of decomposition, while transforming neutral effects of litter mixture to synergistic effects after 6 months of decomposition. Our results demonstrated that initial chemical properties played an important role in litter decomposition, while no effects of litter mixture on decomposition process in this desert region. The N addition altered the litter mixture effects on mass loss with incubation time, implying that increased N deposition in the future may have profound effects on carbon turnover to a greater extent than previously thought in desert ecosystems.

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.

Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient

Abstract Litter decomposition is controlled by climate, litter quality and decomposer communities. Because the decomposition of specific litter types is also influenced by the properties of adjacent types, mixing litter types may result in non‐additive effects on overall decomposition rates. The strength of these effects seems to depend on the litter functional diversity. However, it is unclear which functional traits or combination of traits explain litter mixture effects and whether these depend on the range of trait values and the ecosystems involved. These uncertainties hamper our ability to predict decomposition in plant communities. We aimed at understanding whether and how functional diversity (measured as functional dispersion, FDis) influences litter decomposition, and how this influence varies among different climates and across decomposition stages. We calculated FDis based on litter traits related to nutrient concentrations or to litter recalcitrance, and tested whether these diversity measures and climatic parameters (soil moisture and temperature) explained litter mixture effects on decomposition. Additive mixture effects (i.e. decomposition of mixtures equalling the mean decomposition of the single litter types) were common in most of the evaluated climates. Non‐additive, negative effects were mainly restricted to the driest and warmest sites, and decreased with time. Non‐additive effects increased in magnitude with the mixtures' FDis, with positive effects being related to FDis in nutrient traits and negative effects being related to FDis in recalcitrance traits. Synthesis. Litter mixing did not have strong effects on decomposition rates across the studied climatic gradient overall, and the direction and intensity of the mixture effects were context dependent. The effects were stronger and more negative in the dryer ecosystems. Where effects were found, functional diversity calculated from selected groups of traits (related to nutrients or litter recalcitrance) predicted mixture effects, especially where trait ranges were broad, though much of the variation remains unexplained. We propose that functional diversity metrics based on litter traits that are mechanistically relevant, applied to diverse site‐specific litter mixtures in different climates, can help to better understand under which conditions and in which direction litter diversity affects decomposition.

Litter Mixing Alters Microbial Decomposer Community to Accelerate Tomato Root Litter Decomposition.

ABSTRACTMixing plant litters of multiple species can alter litter decomposition, a key driver of carbon and nutrient cycling in terrestrial ecosystems. Changes in microbial decomposer communities is proposed as one of the mechanisms explaining this litter-mixture effect, but the underlying mechanism is unclear. In a microcosm litterbag experiment, we found that, at the early stage of decomposition, litter mixing promoted tomato root litter decomposition, thus generating a synergistic nonadditive litter-mixture effect. The transplanting decomposer community experiment showed that changes in microbial decomposer communities contributed to the nonadditive litter-mixture effect on tomato root litter decomposition. Moreover, litter mixing altered the abundance and diversity of bacterial and fungal communities on tomato root litter. Litter mixing also stimulated several putative keystone operational taxonomic units (OTUs) in the microbial correlation network, such as Fusarium sp. fOTU761 and Microbacterium sp. bOTU6632. Then, we isolated and cultured representative isolates of these two taxa, named Fusarium sp. F13 and Microbacterium sp. B26. Subsequent in vitro tests found that F13, but not B26, had strong decomposing ability; moreover, these two isolates developed synergistic interaction, thus promoted litter decomposition in coculture. Addition of F13 or B26 both promoted the decomposing activity of the resident decomposer community on tomato root litter, confirming their importance for litter decomposition. Overall, litter mixing promoted tomato root litter decomposition through altering microbial decomposers, especially through stimulating certain putative keystone taxa.IMPORTANCE Microbial decomposer community plays a key role in litter decomposition, which is an important regulator of soil carbon and nutrient cycling. Though changes in decomposer communities has been proposed as one of the potential underlying mechanisms driving the litter-mixture effects, direct evidence is still lacking. Here, we demonstrated that litter mixing stimulated litter decomposition through altering microbial decomposers at the early stage of decomposition. Moreover, certain putative keystone taxa stimulated by litter mixing contributed to the nonadditive litter-mixture effect. In vitro culturing validated the role of these taxa in litter decomposition. This study also highlights the possibility of regulating litter decomposition through manipulating certain microbial taxa.

Functional and phylogenetic diversity promote litter decomposition across terrestrial ecosystems

AbstractAimLitter decomposition is a vital process of carbon and nutrient cycling in terrestrial ecosystems. Despite rapid declines in plant diversity worldwide, the effects of plant diversity on litter decomposition, along with the factors driving their directions and magnitudes, remain uncertain.LocationGlobal.Time period1985–2018.Major taxa studiedPlants.MethodsBy synthesizing 492 paired observations of leaf litter mixtures and monocultures from 110 studies, we conducted a global meta‐analysis of the effects of litter mixtures on litter decomposition rates, which were calculated askcoefficients frommt/m0 = e−kt, wheremtwas the remaining mass of leaf litter at yeartandm0was the initial litter mass at the beginning of experiments.ResultsLitter mixtures on average increased litter decomposition rates by 5.6% (95% confidence intervals, 3.0–8.1%), and the effects of litter mixtures increased with litter species richness, the functional diversity of chemical traits (leaf C, N, P contents and C : N ratio) and phylogenetic diversity consistently across terrestrial ecosystems. The decomposer abundance and function, including soil fauna abundance, microbial biomass, and extracellular enzyme activities, were positively associated with litter mixture effects on decomposition rates. The structural equation models accounted for 48.6% of the global variation in litter decomposition rates and revealed that the positive effects of litter functional diversity on decomposer abundance and function led to increased litter decomposition rates, while litter phylogenetic diversity had a positive direct effect on litter decomposition rates.Main conclusionsAs indicators for complementarity effects, functional diversity of the chemical traits and phylogenetic diversity lead to more positive litter mixture effects on decomposition. The positive litter diversity effects on decomposition rates are mechanistically linked with soil fauna abundance, microbial biomass, and extracellular enzyme activities. Our results suggest that plant diversity, especially functional and phylogenetic diversity, increases decomposer abundance and function, and thus plays a key role in carbon and nutrient cycling across terrestrial ecosystems.

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.

Diversity-decomposition relationships in forests worldwide.

Plant species diversity affects carbon and nutrient cycling during litter decomposition, yet the generality of the direction of this effect and its magnitude remains uncertain. With a meta-analysis including 65 field studies across the Earth's major forest ecosystems, we show here that decomposition was faster when litter was composed of more than one species. These positive biodiversity effects were mostly driven by temperate forests but were more variable in other forests. Litter mixture effects emerged most strongly in early decomposition stages and were related to divergence in litter quality. Litter diversity also accelerated nitrogen, but not phosphorus release, potentially indicating a decoupling of nitrogen and phosphorus cycling and perhaps a shift in ecosystem nutrient limitation with changing biodiversity. Our findings demonstrate the importance of litter diversity effects for carbon and nutrient dynamics during decomposition, and show how these effects vary with litter traits, decomposer complexity and forest characteristics.

Average leaf litter quality drives the decomposition of single-species, mixed-species and transplanted leaf litters for two contrasting tropical forest types in the Congo Basin (DRC)

Under similar site conditions, leaf litter decomposition beneath Central African rainforests was largely driven by average leaf litter quality. Although significant, the additional variability related to litter mixing and to the decomposition environment was limited. Under given site conditions, litter decomposition is expected to mainly depend on its average quality. However, the additional impacts of litter diversity as well as of the local decomposition environment remain rather inconclusive. This study investigates the litter mixture effects on decomposition and home-field advantage for two emblematic old growth forest types of the Congo Basin: the Scorodophloeus zenkeri Harms mixed forests and the evergreen Gilbertiodendron dewevrei (De Wild.) J. Leonard monodominant forests. Based on a litterbag experiment, variations in leaf litter mass loss were measured from the eight most important tree species under mixed and monodominant forests and for all possible two-species combinations. Remaining mass was largely explained (90%) by a multivariate measure of initial litter quality including 11 functional traits, which performed better than any single leaf litter trait. For the litter mixtures, the average deviation from expectation based on simple additive effects ranged from slightly synergistic (+ 2.56%) to slightly antagonistic (− 0.86%) after 1 and 6 months, respectively. Mixture identity and chemical dissimilarity contributed to explaining the mixing effects, yet the effect of chemical dissimilarity at the whole mixture level was only detected through an interaction with incubation time. In addition, the initial decomposition rates of S. zenkeri and G. dewevrei were accelerated under their own forest type. In agreement with the “home-field advantage” theory, our results highlighted that the functional composition of the host forest did have an indirect impact on decomposition. In addition, leaf litter decomposition was mainly controlled by average litter quality, which in turn was closely related to a multivariate measure of green leaf quality. This suggests that increased knowledge of tree species leaf traits in tropical forests would greatly help in better understanding the litter decomposition dynamics.

Is litter decomposition enhanced in species mixtures? A meta-analysis

Litter decomposition is a key process in the carbon balance of soils. Commonly, plant litters occur in mixtures where the species differ in quality traits such as the nutrient concentration and organic carbon quality. Many studies explored if mixing litters retards or speeds up litter decomposition compared to species decomposing alone, with varying results. To identify consistent trends with an overarching quantitative synthesis, we test in a meta-analysis whether on average across studies, the mass loss of mixed litters of two plant species is faster than the average mass loss of single litters. We hypothesise that larger trait divergence of the litter quality of the species in a mixture results in a faster mass loss of the mixture than expected based on the single species. Furthermore we hypothesise that part of the variation in litter mixture mass loss can be explained by experimental design and environmental factors. Explanatory variables used were chemical litter trait dissimilarity in the C, N, P, lignin, cellulose, phenolics concentration as well as soil properties, ecosystem, climate, the duration of litter decomposition and the experimental design. Interactions were studied if supported by mechanistic hypotheses. In the majority of studies and on average, we found that the mass loss of mixed litters is equal to the weighted average of the mass loss of the constituent single litters. None of the hypothesised explanatory variables was consistently associated with litter mixture effects on the mass loss and explained variation in mass loss of significant models was invariably only a few percent of all variation. While further data exploration might elucidate further, interactive, patterns, many of these could not be explored due to lacking data. This meta-analysis therefore refutes the notion that mixing litters in general enhances rates of decomposition. We conclude that the effects of litter mixing are in many cases predictable from the decomposition rates of the individual species. According to our results, any interactive effects (positive or negative) between litter species are contextual, and cannot be generalized and predicted beyond the context in which the results were obtained.

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.

Leaf Nutrients and Macroinvertebrates Control Litter Mixing Effects on Decomposition in Temperate Streams

Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, TraitCWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.

Effects of management on plant litter traits and consequences for litter mass loss and Collembola functional diversity in a Mediterranean agro-forest system

Plant litter decomposition depends on the nutrient content and the amount of recalcitrant materials such as lignin and phenolic compounds. These traits are inherent to the plant species providing the litter. In agro-ecosystems, the type of land management may also shape litter traits and then influence the litter decomposition process. However, the effects of management practice/intensity on litter traits have not been addressed in previous studies, particularly in Mediterranean systems. Our aim was to test the effect of management practices on litter traits associated to nutritional quality and recalcitrance and the resulting effects on fungal biomass, Collembola communities and decomposition parameters in cork-oak agro-forest systems. A litterbag experiment was conducted using litter of dominant plant species, Quercus suber L. and Agrostis pouretii L., collected in an organic agro-forest system and in its neighbor conventional farm. We also tested the effects of litter mixtures using these two contrasting litter types, and the subsequent effects on Collembola communities and decomposition parameters. Land management influenced initial litter traits, mostly in terms of phenolics concentration, higher on the conventional site, and P concentrations, that were higher on the organic farm. After the decomposition experiment, fungal biomass was significantly higher on Quercus litters from the conventional management, while %P and %phenolics were significantly higher in litters from organic compared to conventional management. Collembola richness was significantly higher in Quercus treatments and in litter mixtures compared to single Agrostis litters. These recorded more epigeous species and collembolans with bigger body size, which apparently found more suitable habitat or resource availability in mixtures than in single Agrostis litters. Mixed litters also favored higher fungal biomass, and P and phenolics concentrations, in relation to single litters. Yet, land management and litter mixtures did not explain litter mass loss. Decay rates were higher in Agrostis than in Quercus litter, due to the differences in the initial litter traits (lignin, phenolics and P contents). Particularly, litter mass loss was positively related to P concentration and negatively associated to the concentration of phenolics.

Plant diversity loss reduces soil respiration across terrestrial ecosystems.

The rapid global biodiversity loss has led to the decline in ecosystem function. Despite the critical importance of soil respiration (Rs) in the global carbon and nutrient cycles, how plant diversity loss affects Rs remains uncertain. Here we present a meta-analysis using 446 paired observations from 95 published studies to evaluate the effects of plant and litter mixtures on Rs and its components. We found that total Rs and heterotrophic respiration (Rh) were, on average, greater in plant mixtures than expected from those of monocultures. These mixture effects increased with increasing species richness (SR) in both plant and litter mixtures. While the positive effects of species mixtures remained similar over time for total Rs, they increased over time for Rh in plant mixtures but decreased in litter mixtures. Despite the wide range of variations in mean annual temperature, annual aridity index, and ecosystem types, the plant mixture effects on total Rs and Rh did not change geographically, except for a more pronounced increase of total Rs in species mixtures with reduced water availability. Our structural equation models suggested that the positive effects of SR and stand age on total and Rh were driven by increased plant inputs and soil microbial biomass. Our results suggest that plant diversity loss has ubiquitous negative impacts on Rs, one of the fundamental carbon-cycle processes sustaining terrestrial element cycling and ecosystem function.

Litter species richness and composition effects on fungal richness and community structure in decomposing foliar and root litter

Litter species richness influences fungal diversity because of resource heterogeneity. Litter species composition effects on decomposition have been studied mostly in aboveground litter. However, little is known about the effects of litter diversity of roots and litter type effect on fungal diversity in general. We addressed litter species composition and richness effects on diversity of ectomycorrhizal (EcM), saprotrophic and pathogenic fungi in decomposing foliar and root litter in the Satakunta forest diversity experiment by varying litter species richness from one to four species in 560 litter bags incubated under tree canopies. After one year of decomposition, there were no significant non-additive effects of litter mixtures on mass loss. Litter species composition was the strongest predictor for saprotroph and plant pathogen community structure in foliar litter, but its effect on root litter fungal composition was much weaker. Litter diversity strongly enhanced fungal richness in foliar but not in root substrate. We found no evidence for host litter preferences in host-specific EcM fungi. Our study suggests that litter species richness and especially certain litter species may influence decomposition through modifying fungal community composition both in foliar and root litter.