Stemflow production is affected by a suite of biotic and abiotic factors. It has proven difficult to determine the importance of individual canopy structure metrics on stemflow production. The disentanglement of the role and importance of individual canopy structure metrics would advance our understanding of the dynamics of stemflow production. This work employed ten isolated (i.e. no overlapping crowns) experimental European beech (Fagus sylvatica L.) saplings to examine the effects of various canopy structural metrics on stemflow production in east‐central Germany. The following canopy structural metrics were utilized in a hierarchical cluster analysis using Ward's method to separate the saplings into groups: primary branch count per unit projected crown area, secondary branch count per unit projected crown area, total branch count per unit projected crown area, mean branch inclination angle, minimum branch inclination angle, maximum branch inclination angle, total dry woody biomass per unit projected crown area, total foliar dry biomass per unit projected crown area and total dry biomass per unit projected crown area. Cluster group means revealed that saplings, which generate the largest stemflow yields, once controlled for sapling size, have straighter boles (but some trunk lean), more steeply inclined branches, a larger number of branches, more woody surface area and fewer numbers of leaves. Our results may prove valuable as a guide to researchers wishing to couple LiDAR and fine‐scale architectural models with the canopy metrics that govern stemflow to provide a better understanding of the canopy on the hydrology and biogeochemistry of forests. Copyright © 2013 John Wiley & Sons, Ltd.

We hypothesized that biodiversity improves ecosystem functioning and services such as nutrient cycling because of increased complementarity. We examined N canopy budgets of 27 Central European forests of varying dominant tree species, stand density, and tree * Corresponding author: M. and shrub species diversity (Shannon index) in three study regions by quantifying bulk and fine particulate dry deposition and dissolved below canopy N fluxes. Average regional canopy N retention ranged from 16% to 51%, because of differences in the N status of the ecosystems. Canopy N budgets of coniferous forests differed from deciduous forest which we attribute to differences in biogeochemical N cycling, tree functional traits and canopy surface area. The canopy budgets of N were related to the Shannon index which explained 14% of the variance of the canopy budgets of N, suggesting complementary aboveground N use of trees and diverse understorey vegetation. The relationship between plant diversity and canopy N retention varied among regional site conditions and forest types. Our results suggest that the traditional view of belowground complementarity of nutrient uptake by roots in diverse plant communities can be transferred to foliar uptake in forest canopies.

Understanding the dynamics of metals and radionuclides in soil environments is necessary for evaluating risks to pristine sites. An iron-rich creek soil of a former uranium-mining district (Ronneburg, Germany) showed high porewater concentrations of heavy metals and radionuclides. Thus, this study aims to (i) evaluate metal dynamics during terminal electron accepting processes (TEAPs) and (ii) characterize active microbial populations in biostimulated soil microcosms using a stable isotope probing (SIP) approach. In biostimulated soil slurries, concentrations of soluble Co, Ni, Zn, As, and unexpectedly U increased during Fe(III)-reduction. This suggests that there was a release of sorbed metals and As during reductive dissolution of Fe(III)-oxides. Subsequent sulfate-reduction was concurrent with a decrease of U, Co, Ni, and Zn concentrations. The relative contribution of U(IV) in the solid phase changed from 18.5 to 88.7% after incubation. The active Fe(III)-reducing population was dominated by delta-Proteobacteria (Geobacter) in (13)C-ethanol amended microcosms. A more diverse community was present in (13)C-lactate amended microcosms including taxa related to Acidobacteria, Firmicutes, delta-Proteobacteria, and beta-Proteobacteria. Our results suggested that biostimulated Fe(III)-reducing communities facilitated the release of metals including U to groundwater which is in contrast to other studies.

Toxic metals can be immobilized on surface sorption sites of soil Fe(III) minerals or can be included in the mineral structure (4, 29). Fe(III)-reducing bacteria (FeRB) can facilitate the release of these metals by reductive dissolution of Fe(III) oxides (9, 17) and bioreduction of Fe(III) oxide-bound trace metals (42). This release might enhance metal stress, suggesting that metal tolerance should be an important attribute for FeRB. Acidophilic FeRB can tolerate millimolar concentrations of Cd, Cu, Ni, and Zn (12), which might be a prerequisite to survival in habitats where low pH facilitates high metal solubility. In contrast, neutrophilic FeRB like Shewanella spp. tolerate only M concentrations (34, 36). Geobacter spp. have not been tested to the best of our knowledge, but metal tolerance proteins are expressed during growth in uranium-contaminated sediments, which might be connected to metal resistance (19).Near Ronneburg (Thuringia, Germany), uranium mining caused severe environmental contamination with metals and radionuclides (20). In creek bank alluvial soils of the Gessenbach, a main drainage system of upstream mining sites (41), high heavy metal concentrations occur both in solid phase and in the pore water of a ground-and surface water-influenced, oxidized, iron-rich Btlc horizon of a Luvic Gleysol. We demonstrated the solubilization of Co, Ni, Zn, As, and U in Btlc soil microcosms during biostimulated microbial Fe(III) reduction that was associated with the activity of microorganisms related to Delta-and Betaproteobacteria, Acidobacteria, and Firmicutes (7). The aims of this study were to (i) determine the heavy metal fraction of the solid phase, which could be released during reductive dissolution of Fe(III) oxides, (ii) estimate the effect of heavy metals on the activity of FeRB in the Gessenbach creek bank soil, and (iii) identify metal-tolerant FeRB, because the permanent exposure to contaminants during the last 50 years should have promoted metal tolerance.Soil geochemistry. Putative binding forms of heavy metals in the Btlc soil solid phase were determined by sequential extraction (8, 43) in samples collected in August 2006. Metal concentrations were analyzed with either ICP-MS (inductively coupled plasma-mass spectrometry) or ICP-OES (optical emission spectrometry) (8). Most metals (20 to 40%) and even 80% of As in Btlc soil were detected in fraction 5, which is representative for amorphous Fe(III) oxides (Fig. 1). A considerable amount of uranium (30%) was recovered in the specifically adsorbed fraction, whereas only Zn and Ni were primarily recovered in the mobile fraction. Zn and Ni also dominated the heavy metal pore water concentration of the creek bank soil, which was sampled monthly from June to November 2007 (7). Pore water heavy metal and As concentrations always peaked in the Btlc horizon (see Fig. S1 in the supplemental material) and reached maximum concentrations of 38.6, 16.4, 3.9, 1.5, 0.6, and 0.3 M for Zn, Ni, Al, Cu, Co, and Cd, respectively. Pore water Fe(II) concentrations, ...

Published by Copernicus Publications on behalf of the European Geosciences Union.L. Thieme et al.: Dissolved organic matter characteristics of deciduous and coniferous forests uous and coniferous forests. Forest management intensity, mainly determined by biomass extraction, contribution of species, which are not site-adapted, and deadwood mass, did not influence DOC concentrations, DOM composition and properties significantly.

[1] Particulate matter (PM) plays an important role in biogeosciences, affecting biosphere-atmosphere interactions and ecosystem health. This is the first known study to quantify and model PM diameter distributions of bulk precipitation, throughfall, stemflow, and organic layer (Oa) solution. Solutions were collected from a European beech (Fagus sylvatica L.) forest during leafed and leafless periods. Following scanning electron microscopy and image analysis, PM distributions were quantified and then modeled with the Box-Cox transformation. Based on an analysis of 43,278 individual particulates, median PM diameter of all solutions was around 3.0 mm. All PM diameter frequency distributions were skewed significantly to the right. Optimal power transformations of PM diameter distributions were between À1.00 and À1.56. The utility of this model reconstruction would be that large samples having a similar probability density function can be developed for similar forests. Further work on the shape and chemical composition of particulates is warranted.

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Abstract. We present the first investigation of the composition of dissolved organic matter (DOM) compared to total organic matter (TOM, consisting of DOM, < 0.45 µm and particulate organic matter 0.45 µm < POM < 500 µm) in throughfall, stemflow and forest floor leachate of common beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.) forests using solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. We hypothesized that the composition and properties of organic matter (OM) in forest ecosystem water samples differ between DOM and TOM and between the two tree species.The 13 C NMR results, derived from 21 samples, point to pronounced differences in the composition of DOM and TOM in throughfall solution at the beech sites, with TOM exhibiting higher relative intensities for the alkyl C region, which represents aliphatic C from less decomposed organic material compared to DOM. Furthermore, TOM shows lower intensities for lignin-derived and aromatic C of the aryl C region resulting in lower aromaticity indices and a diminished degree of humification. Across the ecosystem compartments, differences in the structural composition of DOM and TOM under beech lessened in the following order: throughfall > stemflow ≈ forest floor leachate.In contrast to the broadleaved sites, differences between DOM and TOM in throughfall solution under spruce were less pronounced and spectra were, overall, dominated by the alkyl C region, representing aliphatic C. Explanations of the reported results might be substantiated in differences in tree species-specific structural effects, leaching characteristics or differences in the microbial community of the tree species' phyllosphere and cortisphere. However, the fact that throughfall DOM under beech showed the highest intensities of recalcitrant aromatic and phenolic C among all samples analysed likely points to a high allelopathic potential of beech trees negatively affecting other organisms and hence ecosystem processes and functions.