Beech Leaf Research Articles

Rapid transfer of 15N from labeled beech leaf litter to functional soil organic matter fractions in a Rendzic Leptosol

Our main objective was to trace and to quantify the stabilization of nitrogen released from litter decomposition in different functional soil organic matter fractions. To identify the fate of nitrogen in a free-range experiment, 15N-labeled beech litter was deposited on the bare soil surface of three 2 m × 2 m plots on a Rendzic Leptosol under beech (Fagus sylvatica L.) with mull humus form near Tuttlingen (Swabian Jura, Germany). The 15N composition of bulk soil and soil fractions was monitored for three years by sampling the litter layer and the Ah horizon (0–5, 5–10 cm) after 140, 507, and 876 d. A combined density and particle size fractionation procedure allowed the isolation of different functional soil organic matter fractions: free light fraction, occluded organic matter, and organo-mineral associations. The first flush in the 15N enrichment was observed in the bulk soil within 140 d, due to plant debris transferred to the free light fraction by probably bioturbation and soluble compounds being leached from the litter directly to the clay fractions. The observed rates within the first 140 d indicated a quick transfer of 15N-enriched compounds from litter into the free light fraction, with a rate of 0.07 μg kg−1 d−1, and to the clay fractions, with a rate of 0.31 μg kg−1 d−1. In contrast, transfer to the occluded light fractions was delayed, with rates of 0.01 μg kg−1 d−1 (> 20 μm) and 0.001 μg kg−1 d−1 (< 20 μm), respectively. After 876 d, we recovered 9% of the added label in the 0–10 cm soil horizon, of which more than 4% was found in the organo-mineral fraction (0–5 cm), nearly 3% in the light fractions (0–5 cm), and another 2% unspecified in the bulk soil of 5–10 cm depth. We therefore conclude that the clay fractions act as the main sink for the recovered 15N. The rapid incorporation and the high preservation of 15N in the clay fractions revealed the dominant role of organo-mineral associations in the stabilization of nitrogen in the investigated soil.

Effects of stoichiometry and temperature perturbations on beech leaf litter decomposition, enzyme activities and protein expression

Abstract. Microbes are major players in leaf litter decomposition and therefore advances in the understanding of their control on element cycling are of paramount importance. Our aim was to investigate the influence of leaf litter stoichiometry in terms of carbon (C) : nitrogen (N) : phosphorus (P) ratios on the decomposition processes and to track changes in microbial community structures and functions in response to temperature stress treatments. To elucidate how the stoichiometry of beech leaf litter (Fagus sylvatica L.) and stress treatments interactively affect the microbial decomposition processes, a terrestrial microcosm experiment was conducted. Beech litter from different Austrian sites covering C:N ratios from 39 to 61 and C:P ratios from 666 to 1729 were incubated at 15 °C and 60% moisture for six months. Part of the microcosms were then subjected to severe changes in temperature (+30 °C and −15 °C) to monitor the influence of temperature stress. Extracellular enzyme activities were assayed and respiratory activities measured. A semi-quantitative metaproteomics approach (1D-SDS PAGE combined with liquid chromatography and tandem mass spectrometry; unique spectral counting) was employed to investigate the impact of the applied stress treatments in dependency of litter stoichiometry on structure and function of the decomposing community. In litter with narrow C:nutrient (C:N, C:P) ratios, microbial decomposers were most abundant. Cellulase, chitinase, phosphatase and protease activity decreased after heat and freezing treatments. Decomposer communities and specific functions varied with site, i.e. stoichiometry. The applied stress combined with the respective time of sampling evoked changes of enzyme activities and litter pH. Freezing treatments resulted in a decline in residual plant litter material and increased fungal abundance, indicating slightly accelerated decomposition. Overall, a strong effect of litter stoichiometry on microbial community structures and functions was detected, but decomposition was mainly driven by a combination of the investigated factors. Temperature perturbations resulted in short- to medium-term alterations of microbial functions; especially high temperature treatments blocked decomposing enzymes.

Fungal community composition shifts along a leaf degradation gradient in a European beech forest

The fungal communities in living and decomposed leaves of European Beech (Fagus sylvatica) were compared to identify the phyllosphere fungi involved in litter decomposition at a site in Bavaria, Germany. New primers were designed to cover a broad range of fungal ribosomal DNA sequence diversity. Following ‘environmental PCR’, clone libraries from each of five samples of living leaves (surface-sterilized and untreated), freshly fallen, initially and highly decomposed leaves, were screened using RFLP fingerprinting. Statistical analysis (ANOSIM) revealed that the fungal communities colonizing living (a) and initially decomposed leaves (c) significantly differed between each other and from freshly fallen (b) and highly decomposed leaves (d). Fungal assemblages of a and d were statistically indistinguishable from each other and from the endophyllous fungal community in living leaves. The results showed that endophyllous fungi play a role throughout the whole decomposition process of beech leaf litter. Therefore, clarification of the life cycle of certain endophytic and/or soil fungi may only be achieved by considering both phyllosphere and soil habitats.

Contribution of 15N-labelled leaf litter to N turnover, nitrous oxide emissions and N sequestration in a beech forest during eleven years

Aims Decomposition of leaf litterfall plays a major role for nitrogen (N) dynamics in soils. However, little is known as to which extent beech leaf litter contributes to N turnover and nitrous oxide (N2O) emissions within one decade after litterfall.

Stoichiometric controls of nitrogen and phosphorus cycling in decomposing beech leaf litter

Resource stoichiometry (C:N:P) is an important determinant of litter decomposition. However, the effect of elemental stoichiometry on the gross rates of microbial N and P cycling processes during litter decomposition is unknown. In a mesocosm experiment, beech (Fagus sylvatica L.) litter with natural differences in elemental stoichiometry (C:N:P) was incubated under constant environmental conditions. After three and six months, we measured various aspects of nitrogen and phosphorus cycling. We found that gross protein depolymerization, N mineralization (ammonification), and nitrification rates were negatively related to litter C:N. Rates of P mineralization were negatively correlated with litter C:P. The negative correlations with litter C:N were stronger for inorganic N cycling processes than for gross protein depolymerization, indicating that the effect of resource stoichiometry on intracellular processes was stronger than on processes catalyzed by extracellular enzymes. Consistent with this, extracellular protein depolymerization was mainly limited by substrate availability and less so by the amount of protease. Strong positive correlations between the interconnected N and P pools and the respective production and consumption processes pointed to feed-forward control of microbial litter N and P cycling. A negative relationship between litter C:N and phosphatase activity (and between litter C:P and protease activity) demonstrated that microbes tended to allocate carbon and nutrients in ample supply into the production of extracellular enzymes to mine for the nutrient that is more limiting. Overall, the study demonstrated a strong effect of litter stoichiometry (C:N:P) on gross processes of microbial N and P cycling in decomposing litter; mineralization of N and P were tightly coupled to assist in maintaining cellular homeostasis of litter microbial communities.

Effects of Resource Chemistry on the Composition and Function of Stream Hyporheic Biofilms

Fluvial ecosystems process large quantities of dissolved organic matter as it moves from the headwater streams to the sea. In particular, hyporheic sediments are centers of high biogeochemical reactivity due to their elevated residence time and high microbial biomass and activity. However, the interaction between organic matter and microbial dynamics in the hyporheic zone remains poorly understood. We evaluated how variance in resource chemistry affected the microbial community and its associated activity in experimentally grown hyporheic biofilms. To do this we fed beech leaf leachates that differed in chemical composition to a series of bioreactors filled with sediment from a sub-alpine stream. Differences in resource chemistry resulted in differences in diversity and phylogenetic origin of microbial proteins, enzyme activity, and microbial biomass stoichiometry. Specifically, increased lignin, phenolics, and manganese in a single leachate resulted in increased phenoloxidase and peroxidase activity, elevated microbial biomass carbon:nitrogen ratio, and a greater proportion of proteins of Betaproteobacteria origin. We used this model system to attempt to link microbial form (community composition and metaproteome) with function (enzyme activity) in order to better understand the mechanisms that link resource heterogeneity to ecosystem function in stream ecosystems.

Does the invasive horse-chestnut leaf mining moth, Cameraria ohridella, affect the native beech leaf mining weevil, Orchestes fagi, through apparent competition?

Apparent competition, through the action of shared natural enemies, is frequently suggested as a possible mechanism underlying the impact of invasive alien species on native species, but examples are rare, particularly in insects. A previous study showed that the beech leaf mining weevil, Orchestes fagi, was significantly less abundant close to horse-chestnut trees infested by the invasive horse-chestnut leaf mining moth, Cameraria ohridella, compared to control sites. Apparent competition through the sharing of natural enemies was proposed as a potential mechanism underlying this effect. To test the occurrence of apparent competition between the two leaf miner species, three observational studies and one experimental manipulation were carried out in Switzerland during 3 years. The total mortality, parasitism, predation and parasitoid diversity of larvae and pupae of O. fagi were compared between sites with and without horse-chestnut trees severely attacked by C. ohridella. Total mortality and predation rates of O. fagi were not significantly different between sites with and sites without C. ohridella. Despite a large overlap between the parasitoid complexes of the two leaf miners, parasitism of O. fagi was found to be positively influenced by the presence of horse-chestnuts infested by C. ohridella in only one of the four studies and only for 1 year. Similarly, parasitoid diversity was not higher near infested horse-chestnut trees compared to control sites. Thus, little evidence for apparent competition was found. Possible reasons, including possible insufficiencies in the experimental circumstances and design, are discussed.

Effects of temperature and litter type on fungal growth and decomposition of leaf litter

The dependence of fungal decomposition of leaf litter on incubation temperature and litter types used as substrata was assessed under pure culture conditions. Isolates of Xylaria sp., a major ligninolytic fungus in cool temperate forests in Japan, were used as the fungal material. Xylaria sp. is mesophilic; maximum growth and decomposition occurred at 25°C. In the temperature test, the decomposition pattern of beech leaf litter by three isolates of Xylaria sp. changed at a threshold at 25°C. Cellulolytic activity increased with temperature from 5 to 25°C, whereas above 25°C ligninolytic activity increased at the expense of cellulolytic activity, leading to suppressed overall decomposition as a result of the higher temperature. The mass loss of leaf litter caused at 20°C by an isolate of Xylaria sp. was variable among 15 litter types and was correlated negatively with acid-unhydrolyzable residue (AUR) content and positively with total carbohydrate content for the 15 litter types. The effects of temperature and litter type on the growth and decomposition of leaf litter by Xylaria sp. may have implications for changes in fungal decomposition of leaf litter that would be predicted in response to future environmental changes

Effects of temperature and litter type on fungal growth and decomposition of leaf litter

The dependence of fungal decomposition of leaf litter on incubation temperature and litter types used as substrata was assessed under pure culture conditions. Isolates of Xylaria sp., a major ligninolytic fungus in cool temperate forests in Japan, were used as the fungal material. Xylaria sp. is mesophilic; maximum growth and decomposition occurred at 25°C. In the temperature test, the decomposition pattern of beech leaf litter by three isolates of Xylaria sp. changed at a threshold at 25°C. Cellulolytic activity increased with temperature from 5 to 25°C, whereas above 25°C ligninolytic activity increased at the expense of cellulolytic activity, leading to suppressed overall decomposition as a result of the higher temperature. The mass loss of leaf litter caused at 20°C by an isolate of Xylaria sp. was variable among 15 litter types and was correlated negatively with acid-unhydrolyzable residue (AUR) content and positively with total carbohydrate content for the 15 litter types. The effects of temperature and litter type on the growth and decomposition of leaf litter by Xylaria sp. may have implications for changes in fungal decomposition of leaf litter that would be predicted in response to future environmental changes

Closely related protist strains have different grazing impacts on natural bacterial communities

Heterotrophic protists are abundant in most environments and exert a strong top-down control on bacterial communities. However, little is known about how selective most protists are with respect to their bacterial prey. We conducted feeding trials using cercomonad and glissomonad Cercozoa by assaying them on a standardized, diverse bacterial community washed from beech leaf litter. For each of the nine protist strains assayed here, we measured several phenotypic traits (cell volume, speed, plasticity and protist cell density) that we anticipated would be important for their feeding ecology. We also estimated the genetic relatedness of the strains based on the 18S rRNA gene. We found that the nine protist strains had significantly different impacts on both the abundance and the composition of the bacterial communities. Both the phylogenetic distance between protist strains and differences in protist strain traits were important in explaining variation in the bacterial communities. Of the morphological traits that we investigated, protist cell volume and morphological plasticity (the extent to which cells showed amoeboid cell shape flexibility) were most important in determining bacterial community composition. The results demonstrate that closely related and morphologically similar protist species can have different impacts on their prey base.

Meteorologischer und phänologischer Jahresrückblick 2009 | Meteorological and phenological annual review for 2009

In 2009, average temperatures above the norm, and in particular the extremely warm months of April, May and August, significantly influenced the development of vegetation in Switzerland. In contrast, the drought that prevailed temporarily did not influence this development. The growing season began in normal time or slightly delayed with hazel flowering in March. Few weeks later, at the time of the last spring phenological phases, vegetation was early, in particular the beech leaf unfolding. A warm April and unusually high temperatures in May are responsible for this turnaround. The early arrival of phenological summer was truly exceptional, with some new record dates. Thus, in summer 2009, due to the heat in May and August, an advance of vegetation development of two to three weeks compared to the standard was temporarily observed. Unlike most previous years, the fall of 2009 showed a clear trend to the late occurrence of autumnal phenological phases that are leaf colouring and leaf fall.

Proteome analysis of fungal and bacterial involvement in leaf litter decomposition

Fungi and bacteria are key players in the decomposition of leaf litter, but their individual contributions to the process and their interactions are still poorly known. We combined semi-quantitative proteome analyses (1-D PAGE-LC-MS/MS) with qualitative and quantitative analyses of extracellular degradative enzyme activities to unravel the respective roles of a fungus and a bacterium during litter decomposition. Two model organisms, a mesophilic Gram-negative bacterium (Pectobacterium carotovorum) and an ascomycete (Aspergillus nidulans), were grown in both, pure culture and co-culture on minimal medium containing either glucose or beech leaf litter as sole carbon source. P. carotovorum grew best in co-culture with the fungus, whereas growth of A. nidulans was significantly reduced when the bacterium was present. This observation suggests that P. carotovorum has only limited capabilities to degrade leaf litter and profits from the degradation products of A. nidulans at the expense of fungal growth. In accordance with this interpretation, our proteome analysis revealed that most of the extracellular biodegradative enzymes (i.e. proteases, pectinases, and cellulases) in the cultures with beech litter were expressed by the fungus, the bacterium producing only low levels of pectinases.

Species richness analysis and ITS rDNA phylogeny revealed the majority of cultivable foliar endophytes from beech (Fagus sylvatica)

Endophytic fungi are hard to detect due to their non-pathogenic nature. We combined species and abundance data with that obtained in an earlier study to re-evaluate current knowledge about diversity of cultivable endophytes in Fagus sylvatica foliage. Fungal ITS sequences were used for identification and phylogenetic analysis, for the evaluation of morphotype concepts, and for validation of morphological identification. Morphological and molecular delimitation of isolates corresponded well and did not significantly change values for species richness estimators. The present analyses largely increased the known species richness of beech endophytes from 64 to 83 observed and about 100 estimated taxa. According to the ITS phylogeny, beech leaf endophytes belong to the main non-parasitic and non-lichenised orders of Pezizomycotina and have close affinities to plant and insect pathogens.

Thermal acclimation of leaf dark respiration of beech seedlings experiencing summer drought in high and low light environments

Little is known about how environmental factors shape the short- and long-term responses of leaf respiration to temperature under field conditions despite the importance of respiration for plant and stand carbon balances. Impacts of water availability and canopy cover on leaf dark respiration (R) and temperature sensitivity were assessed in beech (Fagus sylvatica L.) seedlings in a sub-Mediterranean population. We studied seedlings established within canopy gaps (39% global site factor; GSF) that were subject to either no watering (unwatered plants; UW) or regular watering (2-10% higher volumetric topsoil water content as summer progressed; W plants) and seedlings established beneath the adjacent understorey (12% GSF). Leaf R rose exponentially with diurnal increases in temperature; the same temperature sensitivity (Q(10): 2.2) was found for understorey and gap plants, irrespective of watering treatment. Respiration estimated at 25 degrees C (R(25)) was lower in the understorey than the gaps and was significantly lower in the unwatered than in the watered gap plants by the end of summer (0.65 versus 0.80 micromol m(-2) s(-1)). R(25) declined with increasing summer temperature in all plants; however, respiration estimated at the prevailing ambient temperature did not change through the summer. There were parallel declines in R(25) and concentrations of starch and soluble sugars with increasing summer temperature for gap plants. We conclude that seasonal shifts in temperature-response curves of beech leaf R occur in both low- and high-light environments; since leaf R decreased with increasing plant water deficit, such shifts are likely to be greater whenever plants experience summer drought compared to scenarios where plants experience high rainfall in summer.

Significant seasonal variation in the hydrogen isotopic composition of leaf-wax lipids for two deciduous tree ecosystems (Fagus sylvativa and Acerpseudoplatanus)

Compound specific hydrogen isotope ratios (δD) of long chain sedimentary n-alkanes, which mostly originate from the leaf waxes of higher terrestrial plants, are increasingly employed as paleoclimate proxies. While soil water is the ultimate hydrogen source for these lipids and the isotopic fractionation during biosynthesis of lipids is thought to remain constant, environmental parameters and plant physiological processes can alter the apparent hydrogen isotopic fractionation between leaf-wax lipids and a plant’s source water. However, the magnitude and timing of these effects and their influence on the isotopic composition of lipids from higher terrestrial plants are still not well understood. Therefore we investigated the seasonal variability of leaf-wax n-alkane δD values for two different temperate deciduous forest ecosystems that are dominated by two different tree species, Beech (Fagus sylvatica) and Maple (Acerpseudoplatanus).We found significant seasonal variations for both tree species in n-alkane δD values of up to 40‰ on timescales as short as one week. Also, the isotopic difference between different n-alkanes from the same plant species did vary significantly and reached up to 50‰ at the same time when overall n-alkane concentrations were lowest.Since δD values of soil water at 5 and 10cm depth, which we assume represent the δD value of the major water source for the investigated beech trees, were enriched in autumn compared to the spring by 30‰, whereas n-alkane δD values increased only by 10‰, we observed variations in the apparent fractionation between beech leaf derived n-alkanes and soil water of up to 20‰ on a seasonal scale. This observed change in the apparent fractionation was likely caused by differences in leaf water isotopic enrichment. Based on mechanistic leaf water models we conclude that changes in the isotopic difference between water vapor and soil water were the most likely reason for the observed changes in the apparent fractionation between n-alkanes and soil water.The large variability of n-alkane concentrations and δD values over time implies a continuous de novo synthesis of these compounds over the growing season with turnover times possibly as short as weeks. The signal to reach the soil therefore represents an integrated record of the last weeks before leaf senescence. This holds true also for the sedimentary record of small catchment lakes in humid, temperate climates, where wind transport of leaf-wax lipids is negligible compared to transfer through soil and the massive input of leaves directly into the lake in autumn.

Response of oxidative stress enzymes in charophyte &lt;i&gt;Nitellopsis obtusa&lt;/i&gt; exposed to allochthonous leaf extracts from beech &lt;i&gt;Fagus sylvatica&lt;/i&gt;

* Corresponding author. E-mail: reda_grigutyte@yahoo.com Leaf litter is one of the allochthonous sources of dissolved organic carbon (DOC) in freshwater ecosystems. Th roughout the degradation of leaves, a lot of chemical compounds are set free into water, which may promote oxidative stress via generation of reactive oxygen species and / or by disturbance of the intracellular oxidative balance in aquatic organisms. We investigated concentrationand time-dependent relationships for the activities of oxidative stress enzymes in macrophytic algae cells of Nitellopsis obtusa, induced by beech Fagus sylvatica leaf extracts, respectively, 0.11–55.0 mg L–1 DOC (aft er 24 h) and 1.1 mg L–1 DOC aft er (15 min – 24 h). Th e oxidative stress enzymes included catalase (CAT – E. C. 1.11.1.6), glutathione reductase (GR – E. C. 1.6.4.2), cytosolic and microsomal glutathione S-transferase (GST – E. C. 2.5.1.18). A signifi cant increase in sGST and mGST activities aft er a 24-h exposure to 1.1–11.0 mg L–1 and to 5.5 mg L–1 DOC of beech leaf extracts was detected. sGST activity signifi cantly increased in the whole period of exposure, while mGST activity decreased below control levels when exposed for 1–4 h. Glutathione reductase activity increased signifi cantly at all DOC concentrations of beech leaf extracts aft er 24 h of exposure. Th e highest elevation of GR activity was observed in extracts containing 5.5 mg L–1 DOC and the lowest activity increment at 0.11 mg L–1 DOC. A statistically signifi cant increase in GR activity started aft er 1 h (at 1.1 mg L–1 DOC) and was evident until the end of the 24-h exposure. Th e activity of catalase increased signifi cantly only at the lowest (1.1 mg L–1) DOC concentration aft er 24 h of exposure. Beech leaf extracts induced a statistically signifi cant time-dependent elevation of CAT activity during the whole period of exposure. In general, an increase of antioxidative enzyme activities in charophyte Nitellopsis obtusa indicated that the defence mechanisms against oxidative stress were induced when cells had been exposed to beech leaf extracts.

Tree species mediated effects on leaf litter dynamics in pure and mixed stands of oak and beech

This study aimed to evaluate the relative importance of the factors whereby tree species composition can influence leaf litter dynamics. Leaf litter production and chemical composition were measured in pure and mixed stands of oak ( Quercus petraea Liebl.) and beech ( Fagus sylvatica L.). Pure and mixed leaf litter of both species were incubated in each stand type to assess separately the environmental, litter quality, and litter mixture effects on decomposition. To better understand the environmental effects, ground climate was measured in the different stands and the effects of soil water content on decomposition were evaluated using roofs to simulate drought conditions. Although total leaf litter amounts were not affected by stand composition, leaf decomposition varied with litter quality and with the environmental conditions. In the same environment, oak leaf litter disappeared on average 1.7 times faster than beech leaf litter. Decomposition of oak leaves increased significantly in the mixed-species litterbags. In contrast, the overall mass loss of the mixed litter tallied with the mass loss estimated by examining the decomposition of the component litter separately (additive-effect hypothesis). The effects of stand type appeared in the third year of incubation: leaf mass loss of both species was greater in the beech stand. In addition, soil water content affected leaf decomposition: the oak and beach leaf mass losses dropped by 24% and 17%, respectively, in the dry modality.

Analysis of O F-layer humus mass variation in a mixed stand of European beech and Norway spruce: An application of structural equation modelling

A number of different research approaches have been used to investigate the influence of tree species on the particular ecological parameters in mixed forest stands. While it is widely recognized that trees have species-specific effects on particular resources like radiation, water and nutrients more interacting effects of mixtures are assumed to exist. In this paper we examine the spatial variation of humus mass in a mixed stand and discuss the influence of specific spatial factors on humus mass variation. Our study site is located in the Solling area, an intermediate mountain range in the south of Lower Saxony in Germany. It is located in a 130–140-year-old European beech ( Fagus sylvatica L.) and Norway spruce ( Picea abies (L). Karst.) mixed stand. To better understand processes which determine amount of humus mass variation within mixed stands of European beech and Norway spruce we measured humus mass of the O F and ecological factors at sample points (litter fall of beech and spruce, radiation, and precipitation beneath the forest canopy). We used a structural equation model (SEM) to analyse data for the effect of species-specific litter input, radiation and throughfall on humus mass variation. Additional to classical regression approaches SEM enables us to consider latent, non-observed, factors or variables. In this paper we present a special SEM, a so-called linear structural relationship (LISREL) model, showing how self-formulated latent variables like “decomposition environment” and “decomposition inhibition” affect the humus mass of the O F layer. Latent structures are of great importance in order to understand and analyse processes determining humus mass variation. In our model, “latent variables” are identified, which explain the contribution of measured variables to improvement or deterioration of humus decomposition, and hence more or less accumulation of organic material in the surface humus layers, in our case the O F layer. Spruce needle input impedes humus dynamics, while beech leaf litter input and higher throughfall amounts show supporting effects. These model results are in agreement with formerly reported findings, but yield further an interval-scaled combined measure which is better founded and more comprehensive than earlier descriptive approaches to the single ecological factors involved. Besides of the ecological interpretation of the results we succeed in determining a valid structural equation model taking into account all relevant ecological factors of humus decomposition.

Comparaison des effets de la compétition par les graminées (Graminoïdes) et le genêt (Cytisus scoparius) sur la croissance et les traits fonctionnels de plants de hêtre (Fagus sylvatica)

• The effect of two weeds (grasses and broom, Cytisus scoparius) competition on the growth and functional traits of European beech saplings (Fagus sylvatica) was investigated in an experimental plantation in the French Massif central. • We hypothesized that grasses would have a much more harmful effect than broom on beech growth through strong competition for soil water and nitrogen. • A randomized block design was used with three separate blocks, each possessing three types of vegetation; grasses (mainly Agrostis capillaris, Holcus mollis and H. lanatus), broom, and bare soil as a control. • Two years after plantation beech sapling growth was significantly greater in bare soil than with competition from grasses, and was intermediate on broom. Growth was positively correlated with beech leaf nitrogen content (Nm) and xylem water potential (Ψx). N and Ψx were dependent, with nitrogen uptake probably decreasing with increasing drought. There was no clear correlation between growth and light transmitted 10 cm below the apex of the saplings. • Beech leaf mass on an area basis (LMA) was correlated with the three resource variables (water, nitrogen and light) and with growth, confirming that LMA is a sensitive functional trait integrating the degree of stress experienced by the saplings. • The results suggest that broom is less competitive than grasses and, if properly managed on a sufficiently well-watered site, can generate satisfactory conditions for beech establishment and growth.

Beech leaf degradation in laboratory experiments: Effects of eight detritivorous invertebrate species

This work addresses the impact of eight detritivorous species of soil macro-invertebrates (three millipedes, two woodlice and three earthworms) on short-term carbon mineralization and mechanical breakdown of beech leaves. The production rate, size class distribution and OM content of invertebrate faeces were also measured. Hierarchical clustering (HC) and multivariate analysis were performed to find relevant functional groups among the species studied. Our results identified three groups of macro-invertebrates on the basis of their impacts on beach leaf degradation (hierarchical clustering): (1) invertebrates that produce fresh faeces with high N contents compared with other species (i.e. polydesmidae and a single species of lumbricidae); (2) other lumbricidae that fragment litter into fine particles in their faeces and actively stimulate CO 2 release; (3) other arthropods that fragment litter into coarse particles and have weak impacts on OM mineralization. These groups over-ride taxonomy, and are proposed as a tentative functional classification of litter dwelling invertebrates. On the other hand, an idiosyncratic impact of species was observed in each group, highlighting how much empirical data are still needed to propose a robust functional classification of litter invertebrates.