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The key importance of coarse woody debris (CWD) for biodiversity is well acknowledged. However, its role in terrestrial nutrient and carbon cycles is less studied, in particular in central Europe. We analysed the decay process of spruce Picea abies (L.) Karst., the most common tree species in Switzerland. The aims were: (i) to examine the usefulness of ultrasonic wave measurements for characterising of decay processes; (ii) to assess changes in physical and chemical variables of CWD during the decay process in relation to site-specific humus forms. We analysed 25 logs, five per decomposition class within a five-class system, for their density, moisture, C, N and P contents, lignin and cellulose. We also applied ultrasonic measurements to the radial axis of decaying logs using the Sylvatest-Duo 1 tool. In addition, we described eight soil profiles below the sampled logs and analysed the soil samples for total C, N and P and water pH. All the soils sampled were classified as humiferous Brunisol (eutric Cambisol) with various humus types.The propagation speed of ultrasonic waves was found to be directly proportional to the average tree density and inversely proportional to C content. These preliminary results point out the potential usefulness of this technique for further studies of wood decay. Wood density was found to decrease during wood decay (434-308 mg g À1 ), whereas moisture increased (94-258%). Carbon and lignin concentrations remained stable, while N and P contents both increased between classes 3 and 5 (N: 0.41-1.26 mg g À1 and P: 0.01-0.06 mg g À1). These general decay patterns are in accordance with previous studies of other tree species and of P. abies in other geographic regions. However, we did find some site-specific patterns, e.g. N and P were lower and wood density declined less than in other studies. Climatic factors at the study site slow down biological activity and they also seem to explain the morphology of the humus forms and their variations. We found no concordance between the humus morphology and the wood-decay state. We recommend performing long-term experiments in Central European forests to investigate the different factors that may influence CWD decomposition, such as edaphic and climatic conditions, in a controlled way.

which should be cited to refer to this work. richness decreased, with the exception of gastropods, and soil fauna abundance increased with urban warming. Our data also show that plant species richness positively affected litter decomposition by increasing soil fauna species richness and microbial activity. A multivariate analysis of organic compounds in litter residues confirmed the importance of soil fauna species richness and garden management on litter decomposition processes. Overall, we showed, that also in intensively managed urban green spaces, such as gardens, biodiversity of plants and soil fauna drives key ecosystem processes. Urban planning strategies that integrate soil protecting management practices may help to maintain important ecosystem services in this heavily used urban environment.

Keywords: Shrinkage analysis (ShC) Soil porosity Earthworms Arbuscular mycorrhizal fungi (AMF) Plant root Soil structure s u m m a r y Soil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots (Allium porrum), AMF (Glomus intraradices) and earthworms (Allolobophora chlorotica). The study was performed on homogenised soil microcosms and the experiments lasted 35 weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydrostructural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23 g cm À3 despite an initial bulk density of 1.15 g cm À3 . This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soilplant-microbe complex previously described.

Earthworms, arbuscular mycorrhiza fungi (AMF) and roots are important components of the belowground part of terrestrial ecosystem. However, their interacting effects on soil properties and plant growth are still poorly understood. A compartmental experimental design was used in a climate chamber in order to investigate, without phosphorus (P) addition, the single and combined effects of earthworms (Allolobophora chlorotica), AMF (Glomus intraradices) and roots (Allium porrum) on soil structure, nutrient concentration and plant growth. In our experimental conditions, plant roots improved soil structure stability (at the level of macroaggregates) whereas earthworms decreased it. AMF had no effect on soil structure stability but increased P transfer from the soil to the plant and significantly increased plant biomass. Earthworms had no direct influence on P uptake or plant biomass, and the N/P ratio measured in the shoots indicated that P was limiting. Interactions between AMF and earthworms were also observed on total C and N content in the soil and on total root biomass. Their effects varied temporally and between the different soil compartments (bulk soil, rhizosphere and drilosphere). After comparison with other similar studies, we suggest that effects of earthworms and AMF on plant production may depend on the limiting factors in the soil, mainly N or P. Our experiment highlights the importance of measuring physical and chemical soil parameters when studying soil organism interactions and their influence on plant performance.

International audienc

No abstract

Abstract1. Subterranean detritivores such as earthworms can increase soil nutrient availability through their burrowing and casting activities. A number of recent studies have explored whether these changes caused by earthworms may in turn affect plant performance and resistance to herbivores, but no formal synthesis of this literature has been conducted to date.2. We tested for the effects of earthworms on plant growth, resistance and chemical defences against insect herbivores by performing a meta-analysis of the existing literature up to 2016. We also explored ecological factors that might explain among-studies variation in the magnitude of the earthworm effects on plant growth and resistance.3. We found that earthworm presence increases plant growth (by 20%) and nitrogen content (by 11%). Overall, earthworms did not affect plant resistance against chew-