Intraspecific plant diversity is a major component of community diversity, yet its role in shaping plant-microbial interactions and soil functioning remains poorly understood. In particular, plant genotypic diversity may modulate ecosystem responses to defoliation, a key driver of ecosystem processes in grazed systems. We subjected genotypic monocultures and mixtures of the grass Anthoxanthum odoratum to defoliation and quantified carbon fluxes, root exudation, and soil enzymatic activity. Using stable isotope labelling, we traced the movement of litter-derived 15N and photosynthetically derived 13C between plants and soil. The composition of soil fungal communities was assessed using ITS metabarcoding. Both defoliation and genotypic diversity increased root exudation, which was positively correlated with soil enzymatic activities and plant uptake of litter-derived 15N. The relative benefit of enhanced N mineralisation under defoliation depended on plant genotypic diversity: incorporation of 15N into leaves relative to 15N incorporation into soil microbial biomass was significantly higher in genotypic mixtures than in monocultures. Higher plant genotypic diversity was associated with lower soil fungal diversity, while defoliation increased saprotroph abundance. Plant genotypic diversity and defoliation jointly regulate plant-microbial interactions, with genotypic diversity enhancing plant performance under defoliation by shifting the partitioning of mineralised N from soil microbial biomass to plants.

A central goal of ecology is understanding how the architecture of food webs, which represent the structural backbone of ecosystems, affects their stability. The analysis of stability in the classical sense of population dynamics (i.e. return to equilibrium) can be successful for a single instance of an empirical food web but ignores the multiplicity of alternative states in which the system could be found as a result of intrinsic variability and fluctuations. Here we propose and test a new methodology to reconstruct, from single empirical observations of a food web, the viable ensemble of alternative realizations respecting the observed resource-consumer linkages and empirical energetics. The reconstruction can be handled analytically within a maximum-entropy framework which predicts how empirical food webs access a multitude of alternative states with comparable stability and reactivity. The (measurable) entropy of the reconstructed ensemble directly quantifies this multiplicity and serves as a novel proxy of system resilience, that is the rate of return to equilibrium in response to an external perturbation. We show that the associated ensemble fluctuations provide explicit predictions for the expected response of food webs to external perturbations, such as anthropogenic or climate-induced stresses. We do that by validating the proposed fluctuation-response relation on empirical soil food webs subjected to experimentally controlled perturbations, confirming that intrinsic fluctuations in the unperturbed state predict responses to subsequent stresses. The perturbed states are associated with higher entropy, indicating less likely spontaneous recovery. ### Competing Interest Statement The authors have declared no competing interest.

Soil food webs contribute significantly to ecosystem energy (carbon) fluxes, but how energy flow through them is affected by both intensification of land management and extreme climatic events, such as drought, is poorly understood. Here, we quantified in situ the energetics and stability of soil food webs under experimental drought across a range grasslands in the United Kingdom with contrasting management intensity. Over the short term of a growing season and a wide range of environmental conditions, drought increased food web energy fluxes and respiration resulting in more unpredictable distribution of fluxes. Intensive grassland management similarly increased energy fluxes and total ecosystem respiration. Our statistical modelling confirmed that the changes observed in soil food web energy fluxes under drought and intensive management trigger an increase in ecosystem respiration mediated by decreased predictability in the distribution of the soil food web energy fluxes. The latter was also linked to reduced population level return time, likely caused by the recovery of metabolically faster components of the food webs such as bacteria. The study thus shed lights on how land use intensification combined with climate change alters pathways of below-ground energy flux and processes that may cause net emissions of C from soil

Plain Language Summary Global change factors like drought and elevated atmospheric CO2 concentrations can impact litter decompositions, an important ecosystem process, via changes to litter properties and the decomposer community. Examining links between litter properties, decomposers and decomposition is therefore critical to understand how both drought and elevated CO2 will affect nutrient release and cycling of belowground environments. ### Competing Interest Statement The authors have declared no competing interest. Data will be submitted to the Natural Environment Research Council (NERC) data repository (Environmental Information Data Center) upon acceptance of the manuscript. Natural Environment Research Council, NE/S002189/1, NE/S015833/1 Research Ireland, 20/FFP-P/8584

Springtails (Collembola) inhabit soils from the Arctic to the Antarctic and comprise an estimated ~32% of all terrestrial arthropods on Earth. Here, we present a global, spatially-explicit database on springtail communities that includes 249,912 occurrences from 44,999 samples and 2,990 sites. These data are mainly raw sample-level records at the species level collected predominantly from private archives of the authors that were quality-controlled and taxonomically-standardised. Despite covering all continents, most of the sample-level data come from the European continent (82.5% of all samples) and represent four habitats: woodlands (57.4%), grasslands (14.0%), agrosystems (13.7%) and scrublands (9.0%). We included sampling by soil layers, and across seasons and years, representing temporal and spatial within-site variation in springtail communities. We also provided data use and sharing guidelines and R code to facilitate the use of the database by other researchers. This data paper describes a static version of the database at the publication date, but the database will be further expanded to include underrepresented regions and linked with trait data.

Soil life supports the functioning and biodiversity of terrestrial ecosystems. Springtails (Collembola) are among the most abundant soil arthropods regulating soil fertility and flow of energy through above- and belowground food webs. However, the global distribution of springtail diversity and density, and how these relate to energy fluxes remains unknown. Here, using a global dataset representing 2470 sites, we estimate the total soil springtail biomass at 27.5 megatons carbon, which is threefold higher than wild terrestrial vertebrates, and record peak densities up to 2 million individuals per square meter in the tundra. Despite a 20-fold biomass difference between the tundra and the tropics, springtail energy use (community metabolism) remains similar across the latitudinal gradient, owing to the changes in temperature with latitude. Neither springtail density nor community metabolism is predicted by local species richness, which is high in the tropics, but comparably high in some temperate forests and even tundra. Changes in springtail activity may emerge from latitudinal gradients in temperature, predation and resource limitation in soil communities. Contrasting relationships of biomass, diversity and activity of springtail communities with temperature suggest that climate warming will alter fundamental soil biodiversity metrics in different directions, potentially restructuring terrestrial food webs and affecting soil functioning.

The supply of recent photosynthate from plants to soils is thought to be a critical mechanism regulating the activity and diversity of soil biota. In the Arctic, large-scale vegetation transitions are underway in response to warming, and there is an urgent need to understand how these changes affect soil biodiversity and function. We investigated how abundance and diversity of soil fungi and invertebrates responded to a reduction in fresh below-ground photosynthate supply in treeline birch and willow, achieved using stem girdling. We hypothesised that birch forest would support greater abundance of ectomycorrhizal (ECM) fungal species and fauna than willow shrubs, and that girdling would result in a rapid switch from ECM fungi to saprotrophs as canopy supply of C was cut, with a concomitant decline in soil fauna. Birch forest had greater fungal and faunal abundance with a large contribution of root-associated ascomycetes (ericoid mycorrhizal fungi and root endophytes) compared to willow shrub plots, which had a higher proportion of saprotrophs and, contrary to our expectations, ECM fungi. Broad-scale soil fungal and faunal functional group composition was not significantly changed by girdling, even in the third year of treatment. Within the ECM community, there were some changes, with genera that are believed to be particularly C-demanding declining in girdled plots. However, it was notable how most ECM fungi remained present after 3 years of isolation of the below-ground compartment from contemporary photosynthate supply. Synthesis. In a treeline/tundra ecosystem, distinct soil communities existed in contrasting vegetation patches within the landscape, but the structure of these communities was resistant to canopy disturbance and concomitant reduction of autotrophic C inputs.

Modification of soil food webs by historical land management may alter the response of ecosystem processes to climate extremes, but empirical support for this is limited and the mechanisms involved remain unclear. Here, we quantified how historical grassland management modifies transfers of recent photosynthate and soil nitrogen through plants and soil food web in response to drought, using in situ 13C and 15N pulse-labelling in paired intensively and extensively managed fields. We show that intensive management decreased plant carbon capture, its transfer through key components of food webs and soil respiration compared to extensive management. Drought only affected carbon transfer pathways in intensively managed grasslands, by increasing plant C assimilation but decreasing its transfer to plant roots, bacteria and Collembola. However, drought lowered the reduction of added nitrate to nitrous oxide in extensively managed grassland only. Our findings indicate that intensive management disrupts fluxes of recent photosynthates belowground, which impaired resistance of this process in response to drought. By contrast, extensive grassland management provides a greater potential to buffer impacts to drought by promoting the transfer of recent photosynthate belowground. Our work highlights that capture and rapid transfer of photosynthate through multitrophic networks is a key process for maintaining grassland resilience to drought.

It is widely accepted that the measurement of organic and inorganic forms of carbon (C) and nitrogen (N) in soils should be performed on fresh extracts taken from fresh soil samples. However, this is often not possible, and it is common practice to store samples (soils and/or extracts), despite a lack of guidance on best practice. We utilised a case study on a temperate grassland soil taken from different depths to demonstrate how differences in soil and/or soil extract storage temperature (4 or −20 ∘C) and duration can influence sample integrity for the quantification of soil-dissolved organic C and N (DOC and DON), extractable inorganic nitrogen (NH4+ and NO3-) and microbial biomass C and N (MBC and MBN). The appropriateness of different storage treatments varied between topsoils and subsoils, highlighting the need to consider appropriate storage methods based on soil depth and soil properties. In general, we found that storing soils and extracts by freezing at −20 ∘C was least effective at maintaining measured values of fresh material, whilst refrigerating (4 ∘C) soils for less than a week for DOC and DON and up to a year for MBC and MBN and refrigerating soil extracts for less than a week for NH4+ and NO3- did not jeopardise sample integrity. We discuss and provide the appropriate tools to ensure researchers consider best storage practice methods when designing and organising ecological research involving assessments of soil properties related to C and N cycling. We encourage researchers to use standardised methods where possible and to report their storage treatment (i.e. temperature, duration) when publishing findings on aspects of soil and ecosystem functioning. In the absence of published storage recommendations for a given soil type, we encourage researchers to conduct a pilot study and publish their findings.

Soil organisms play a major role on litter decomposition process and nutrient cycling in forest ecosystems. These organisms are extremely sensitive to environmental conditions such as soil temperature and moisture conditions which control their demographic parameters and activity. The ongoing climate change can therefore directly affect soil biota communities and the processes they drive. Besides, climate change can also indirectly affect soil biota by altering tree functional traits (e.g., N, Ca, Mg, water holding capacity) with cascading effects on the litter quality. The aim of this study was to determine the relative effects of increased drought and litter type on microbial biomass (bacteria and fungi) and mesofauna abundance (Collembola and Acari) in three experimental sites representative of the three main forests encountered in the northern part of the Mediterranean Basin (dominated by either Quercus pubescens, Quercus ilex or Pinus halepensis) where rainfall exclusion experiments were taking place. At each site, and in each precipitation treatment (natural and amplified drought plots), we collected and transplanted foliage litters (i.e., species x drought level). After two years, we reported a litter species effect: Q. pubescens litter presented consistently the higher abundance of all soil biota groups compared to Q. ilex and P. halepensis litters in each forest. Surprisingly, despite that the amplified drought treatment induced a modification of the litter quality, we did not reported an indirect reduced precipitation effect on soil biota parameters. While Oribatid Acari abundance decreased with amplified drought in all three forest types, the direct effects on the other soil biota groups were forest-dependent. In P. halepensis forest, amplified drought resulted in higher bacterial and fungal biomasses but lower Collembola abundance. In Q. ilex forest both Collembola and predatory Acari abundances decreased with amplified drought. In addition, the positive relationships between Collembola and Oribatida abundances and litter mass loss disappeared under amplified drought conditions in both Q. ilex and P. halepensis forests. These results suggest a key role played by Ca, Mg, specific leaf area (SLA) and water holding capacity (WHC) as drivers of soil biota parameters. Finally, the study highlights that within the same Mediterranean region, climate change could differently alter the soil organisms inhabiting the litter layer and their contributions to the decomposition process depending on the tree species and soil biota group considered.

Grasslands are under severe threat from ongoing degradation, undermining their capacity to support biodiversity, ecosystem services and human well-being. Yet, grasslands are largely ignored in sustainable development agendas. In this Perspective, we examine the current state of global grasslands and explore the extent and dominant drivers of their degradation. Socio-ecological solutions are needed to combat degradation and promote restoration. Important strategies include: increasing recognition of grasslands in global policy; developing standardized indicators of degradation; using scientific innovation for effective restoration at regional and landscape scales; and enhancing knowledge transfer and data sharing on restoration experiences. Stakeholder needs can be balanced through standardized assessment and shared understanding of the potential ecosystem service trade-offs in degraded and restored grasslands. The integration of these actions into sustainability policy will aid in halting degradation and enhancing restoration success, and protect the socio-economic, cultural and ecological benefits that grasslands provide. Grasslands provide key ecosystem services, but their protection is often ignored in sustainable policy. This Perspective describes grassland degradation and sets out the steps needed to protect these systems and promote their restoration.

It is well known that soil physico-chemical conditions and the nature of organic matter have important effects on soil micro-arthropod communities, including collembolans. However, mechanisms by which the physical or chemical quality of litter influence collembolan communities remain unclear. Plant secondary metabolites are partially released in soils through leaf and litter leaching and decomposition, and can have a strong influence on soil communities and their activity. In order to disentangle effects of the water-soluble compounds contained in the litter versus its physical effect, a microcosm experiment was set up exposing the collembola species Folsomia candida to either litter or litter leachates mixed to the substratum. Litter from three species with different chemical properties and one mixture (hybrid poplar, white spruce, grass and a mixture of poplar – spruce litter) and two concentrations of litter leachates (at 5% and 10% concentration) were used in microcosm experiments. After 30 days of incubation, reproduction and mortality rates of F. candida were assessed. Results showed that the tree litter leachates had a stronger impact on collembolan fitness compared to the litter itself, with a net reduction of survival and reproduction rates. Between 78 and 100% of mortality was observed in microcosms that received tree leachates, indicating a strong influence of the soluble compounds contained in tree leaves on collembolan. In contrast, collembolan reproduction was positively affected by the grass litter or 10% grass litter leachates compared to control (water). Our findings help to understand how chemical properties and leaf leaching may have important impacts on micro-arthropods communities and litter decomposition processes.

Process‐based models describing biogeochemical cycling are crucial tools to understanding long‐term nutrient dynamics, especially in the context of perturbations, such as climate and land‐use change. Such models must effectively synthesize ecological processes and properties. For example, in terrestrial ecosystems, plants are the primary source of bioavailable carbon, but turnover rates of essential nutrients are contingent on interactions between plants and soil biota. Yet, biogeochemical models have traditionally considered plant and soil communities in broad terms. The next generation of models must consider how shifts in their diversity and composition affect ecosystem processes. One promising approach to synthesize plant and soil biodiversity and their interactions into models is to consider their diversity from a functional trait perspective. Plant traits, which include heritable chemical, physical, morphological and phenological characteristics, are increasingly being used to predict ecosystem processes at a range of scales, and to interpret biodiversity–ecosystem functional relationships. There is also emerging evidence that the traits of soil microbial and faunal communities can be correlated with ecosystem functions such as decomposition, nutrient cycling, and greenhouse gas production. Here, we draw on recent advances in measuring and using traits of different biota to predict ecosystem processes, and provide a new perspective as to how biotic traits can be integrated into biogeochemical models. We first describe an explicit trait‐based model framework that operates at small scales and uses direct measurements of ecosystem properties; second, an integrated approach that operates at medium scales and includes interactions between biogeochemical cycling and soil food webs; and third, an implicit trait‐based model framework that associates soil microbial and faunal functional groups with plant functional groups, and operates at the Earth‐system level. In each of these models, we identify opportunities for inclusion of traits from all three groups to reduce model uncertainty and improve understanding of biogeochemical cycles. These model frameworks will generate improved predictive capacity of how changes in biodiversity regulate biogeochemical cycles in terrestrial ecosystems. Further, they will assist in developing a new generation of process‐based models that include plant, microbial, and faunal traits and facilitate dialogue between empirical researchers and modellers.

Theory suggests that more complex food webs promote stability and can buffer the effects of perturbations, such as drought, on soil organisms and ecosystem functions. Here, we tested experimentally how soil food web trophic complexity modulates the response to drought of soil functions related to carbon cycling and the capture and transfer below-ground of recent photosynthate by plants. We constructed experimental systems comprising soil communities with one, two or three trophic levels (microorganisms, detritivores and predators) and subjected them to drought. We investigated how food web trophic complexity in interaction with drought influenced litter decomposition, soil CO2 efflux, mycorrhizal colonization, fungal production, microbial communities and soil fauna biomass. Plants were pulse-labelled after the drought with 13 C-CO2 to quantify the capture of recent photosynthate and its transfer below-ground. Overall, our results show that drought and soil food web trophic complexity do not interact to affect soil functions and microbial community composition, but act independently, with an overall stronger effect of drought. After drought, the net uptake of 13 C by plants was reduced and its retention in plant biomass was greater, leading to a strong decrease in carbon transfer below-ground. Although food web trophic complexity influenced the biomass of Collembola and fungal hyphal length, 13 C enrichment and the net transfer of carbon from plant shoots to microbes and soil CO2 efflux were not affected significantly by varying the number of trophic groups. Our results indicate that drought has a strong effect on above-ground-below-ground linkages by reducing the flow of recent photosynthate. Our results emphasize the sensitivity of the critical pathway of recent photosynthate transfer from plants to soil organisms to a drought perturbation, and show that these effects may not be mitigated by the trophic complexity of soil communities, at least at the level manipulated in this experiment.

Summary A broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms. We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning. Synthesis . Gaining a greater understanding of plant–soil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio‐temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning.

Abandoned lands are increasingly used to establish fast-growing tree plantations, and are often rapidly colonized by a high density of herbaceous undergrowth. These weeds are generally removed since they compete with trees for resources, in particular soil nutrients. However, mixing herbaceous litter with the litter of planted trees could also stimulate the activity of decomposers and associated nutrient release due to an increase of litter quality (lower C:N ratio), plant diversity (more diverse litter traits) and water holding capacity. The objective was to determine the impact of herbaceous litter on the litter decomposition process of white spruce and hybrid poplar litters alone or in mixtures.Litter mass loss rate, nutrient release and decomposer communities were monitored on single and mixed-species litters using litterbags during two years in three plantations types (hybrid poplar, white spruce and mixed plantations). Litters within mixtures were separated by species to identify species-specific responses of leaf mass loss.N release of all litter types increased with the presence of herbaceous litter. This finding could be linked to the greater abundance of decomposers and fungal biomass brought about by the herbaceous litter. Addition of herbaceous litter had no effect on spruce litter mass loss but had positive effects on poplar and mixed spruce/poplar litter mass loss. Abundance of fungi and mites was more affected by litter quality, whereas the abundance of collembola was more affected by the diversity of resources than by litter quality.In these 10-year plantations with poplar, increased litter mass loss for poplar and mixed litters and N release associated to the presence of herbaceous litter showed that weeds may change soil C sequestration and N cycling.

Tree species influence the litter decomposition process by influencing litter quality and soil microclimate. Furthermore, over the long term, trees could promote soil communities that are particularly capable of degrading the litter they encounter most often. Thus, plant litter could decompose faster when placed in the habitat from which it was derived than in a foreign habitat, which has been termed home field advantage (HFA) of litter decomposition. In mixed-plant species environments however, it is not known whether a specific decomposer community under one tree species is affected by the presence of another tree species in the vicinity. To address this question, we tested if spruce and poplar litters showed HFA in mono-specific and in mixed species plantations under each tree species by reciprocally transplanting litter in the two plantation types. Decomposition rates, as well as the composition and ability of decomposer communities to degrade the different types of litter, were monitored during two years. Only spruce litter exhibited a faster decomposition rate at home. This HFA could be explained by higher abundance of decomposers. Furthermore, cellulose and poplar litter decomposed less or similarly in spruce plantations, suggesting that soil communities of that environment were capable of specifically degrading spruce litter. In mixed plantations, HFA was in the same direction as in mono-specific plantations, but was not as strong, indicating that HFA is sensitive to the surrounding plant community. Furthermore, this “mixed environment” had synergistic effects on decomposition rates under poplar trees. These ‘tree environment-specific’ results highlighted the possible importance of spatial distribution of each litter on decomposition rates in mixed stands. Thus, the influence of litter dispersal should be taken into account in future studies.

Depuis quelques annees, la sylviculture intensive prend de l’ampleur au Canada afin de rapprocher la source de fibres des usines, d’accroitre la productivite des plantations, et de diminuer la pression de coupe sur les forets naturelles. Toutefois, un debat sur le type d’amenagement optimal des plantations oppose l’amenagement mono- et plurispecifique. Malgre des effets antagonistes possibles sur la productivite des arbres, il semblerait que les plantations mixtes procureraient des avantages au niveau des proprietes du sol, de la stabilite environnementale, mais aussi du maintien de la biodiversite et de la valeur esthetique. Les especes vegetales et leur melange sont susceptibles d’influencer le processus de decomposition selon deux mecanismes qui operent a differentes echelles : l’effet ressource par la production de litiere possedant des caracteristiques physiques et chimiques propres qui constituent la ressource nutritive pour les decomposeurs, et l’effet habitat qui correspond a l’effet a plus long terme de l’arbre sur son environnement en influencant les microconditions climatiques et edaphiques, et donc les communautes d’organismes presents dans le sol. Le melange de diverses especes engendrerait a la fois une plus grande diversite d’habitats et de ressources favorisant une plus grande diversite et abondance des organismes decomposeurs, ce qui accelererait le processus de decomposition et la remise a disposition des nutriments dans le sol. Il est important de mieux comprendre le fonctionnement de ces ecosystemes pour en effectuer une bonne gestion et pour optimiser les services ecosystemiques que ces plantations fournissent. Ainsi cette these visait a mieux comprendre l’influence de la mixite de deux essences forestieres, a savoir l’epinette blanche et le peuplier hybride, en comparaison a des plantations pures sur le processus de decomposition des litieres en separant l’effet ressource de l’effet habitat. Cette etude a ete menee sur des plantations intensivement amenagees qui etaient largement colonisees par des herbacees. Ainsi une autre partie de cette these consistait a determiner si la presence d’herbacees etait benefique au processus de decomposition des litieres et a la liberation des elements nutritifs dans les differentes plantations mono- ou pluri-specifiques. Finalement, dans l’optique de relier ces donnees avec le fonctionnement global de l’ecosysteme, le stockage de carbone de la phytomasse aerienne et dans le sol (excepte les racines) a ete etudie dans les deux types de plantations. La qualite des ressources et l’effet du melange des arbres et des litieres sur les decomposeurs ont ete etudies dans une experimentation de decomposition in-situ avec des litter bags de chaque type de litiere (peuplier, epinette, herbacees, ainsi que leur melange) dans chaque type de plantations. Cette etude a ete appuyee par une experimentation ex-situ utilisant une espece cible d’organisme du sol, Folsomia candida (collembola). Un interet particulier a ete porte sur le role et l’impact des metabolites secondaires contenus dans les especes vegetales concernees sur le processus de decomposition mais aussi sur leurs interactions avec les organismes decomposeurs. xx Concernant l’effet habitat, la plantation monospecifique de peuplier semblait etre defavorable a la colonisation de la litiere par la mesofaune, probablement du a l’effet negatif des lixiviats de feuilles de peuplier mais egalement a la faible accumulation des litieres. A l’inverse, la plantation pure d’epinette favorisait la decomposition de sa propre litiere par la selection d’organismes plus specialises. Les resultats de cette etude ne montraient pas d’amelioration du processus de decomposition avec le melange du peuplier et de l’epinette (effet habitat) ou de leurs litieres (effet ressource). En revanche, le melange de ces deux especes en plantation a tamponne les effets contrastes du peuplier et de l’epinette sur les organismes et le taux de decomposition observes dans les plantations monospecifiques. Le stockage de carbone et la productivite du peuplier etaient superieurs dans les plantations mixtes par rapport aux plantations monospecifiques. Finalement, la litiere d’herbacees semblait etre benefique pour l’abondance d’organismes decomposeurs et favorisait la liberation d’azote des litieres d’arbres. Cet aspect pourrait contrebalancer l’effet negatif de la presence d’herbacees qui entrent en competition avec les arbres pour les ressources. Ces resultats nous indiquent qu’apres 10 ans, les plantations mixtes optimiseraient la productivite et le stockage de carbone, double avantage generalement recherche dans les systemes sylvicoles.

Summary Over a century of agricultural abandonment across the Mediterranean region has favoured the installation of the pioneer expansionist species Aleppo pine ( Pinus halepensis Miller). This species synthesizes a wide range of secondary metabolites that are partially released during needle decomposition, and which can thus affect the ‘brown food chain’. Litter decomposition is a key process connecting ecosystem structure and function, and involving microbial and faunal components. The goal of this study was to determine the effect of chemical compounds from Aleppo pine needles on the litter decomposition process along a gradient of Mediterranean forest secondary succession. Using in situ litterbags, we compared the dynamics of decomposers, particularly the relative contributions of fungal and mesofauna biomass to litter mass loss (calculations based on the measured decomposer biomass, published fungal growth efficiency and mesofauna feeding rate), against the dynamics of secondary metabolites associated with decomposed needles in three successional stages (early, middle and late, i.e. pinewoods that were aged 10, 30 and over 60 years old). Our first key finding was that fungi accounted for the largest portion of overall litter mass loss (60–79%) and detritivorous mesofauna contributed to 8–12%. In the early stage of succession, fungal biomass after 6 months of decomposition was lower than in middle and late stages, and may be responsible for the delay in litter colonization by mesofauna. We linked this result to a clearly longer residence time for phenolic compounds in young pine forest, leading to an overall slowdown in the decomposition process. Synthesis . Litter phenolic content emerged as a key functional trait for predicting litter decomposition, delaying the colonization of litter by decomposers in Mediterranean forest ecosystems. Another key finding is that the relative contributions of fungi and detritivores to needle mass loss were different between the successional stages. From the food‐web perspective, the organic matter available for higher trophic levels thus remains unchanged beyond 30 years after pine colonization.