Mass outbreaks of herbivore insects perturb the functional properties of forests, by substantially altering water and nutrient cycling of infested trees. Less clear is how low to moderate herbivory ...affects the vertical flow of nutrients from trees to the soil. We report on the effects of low to moderate infestation levels of the woolly beech aphid (Phyllaphis fagi L.) on the nutrient dynamics and hydrology of European beech (Fagus sylvatica L.). We traced the vertical dynamics of macro and micronutrients via throughfall (TF), stemflow (SF) and Oa litter leachates from potted saplings underneath infested and uninfested control trees. The low infestation levels were insufficient to significantly alter TF and litter leachate composition, although, on average, the release of K and DOC and the immobilization of N (NH₄–N) in TF solution were more pronounced under aphid infestation. SF chemistry was significantly altered by aphid activity exhibiting intensified fluxes of K (+159 %), Mg (+82 %), Mn (+93 %), S (+86 %), SO₄–S (+62 %), DOS (+137 %), DOC (+51 %) and DON (+62 %), compared to control trees. SF is likely enriched by low and mid-level aphid activity due to its increased residence time in the canopy. It has interaction with large areas of aboveground vegetative surface area representing a cumulative flux of solutes and particulates from both foliar and woody surfaces from above-lying portions of the canopy. Accordingly, SF might be a useful indicator to evaluate the impact of sap- and leaf-feeding herbivores on forest ecosystems.
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BFBNIB, DOBA, EMUNI, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The heterogeneous nature of the size and shape of particulate matter (PM) deposited onto forest canopies is acknowledged. However, it is uncertain how PM interacts with the forest canopy and how it ...is transported and cycled via the hydrological processes of throughfall and stemflow. To improve our understanding of particulate cycling in forested watersheds, this study quantifies the geometric configuration of PM in bulk precipitation, throughfall, stemflow, and upper soil (Oa horizon) solution in both leafed and leafless periods in a European beech (Fagus sylvatica L.) forest in Germany. Circular equivalence diameter, circularity, elongation ratio, perimeter-to-area ratio, and fractal dimension were calculated for all 43,278 individual particulates in bulk precipitation, throughfall, stemflow, and Oa solutions. Loss on ignition measurements were also conducted to determine the organic matter content of the particulates. From a physical point of view, the opposite trends for circular equivalence diameter and perimeter-to-area ratio of PM between stemflow or throughfall and bulk precipitation during both leafless and leafed periods were the most striking. For bulk precipitation, the PM's mean circular equivalence diameter was significantly larger in the leafless period than the leafed period, with the reverse observed for throughfall and stemflow. Mean perimeter-to-area ratios (μm−1) of PM of both stemflow and throughfall were significantly larger in the leafless period than the leafed period. The opposite trend was observed for bulk precipitation and Oa solution. The percent organic matter of PM was not statistically significantly different across solutions or canopy state. Our results indicate that the differential routing of PM through the canopy indeed influences the geometry of PM among solution types as compared to the bulk precipitation. The effects of these changes on the chemistry of the PM and its impact of particulate cycling, and the impacts of shifting seasonality with climate change, warrants further investigation.
•Particulate matter (PM) transport through forests may be affected by its geometry.•Quantified PM geometry of bulk precipitation, throughfall, stemflow, Oa solution.•Differential routing of PM through the canopy and phenology influenced PM geometry.•Organic matter varied between 2.2% and 3.7% across PM sources and canopy state.•Examination of effects of differential PM geometry on elemental cycling is needed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The size of stemflow infiltration areas around the boles of trees is currently a topic of interest and debate within the hydrologic community. There is a gap in our knowledge of stemflow infiltration ...areas in many wooded ecosystems and a need for more than the few studies that have examined stemflow infiltration areas directly. Hence, this field study was specifically undertaken to mitigate the existing data gap by providing direct measurements of stemflow infiltration areas from high stemflow‐producing American beech (Fagus grandifolia Ehrh.) trees. Different stemflow rates (290, 72 and 31 L h−1) were simulated using dye‐infused stemflow and the areas of stemflow infiltration around four trees determined by measuring the areal extent of dye on the soil surface. Our results revealed that stemflow infiltration areas ranged from 0.0035 to 0.0951 m2 tree−1. The mean basal area funnelling ratio was 46.5 ± 1.8, whereas the funnelling ratios per unit infiltration areas,
FP,It, were between 32.0 and 258.4. Despite intentionally high stemflow rates, chosen to compensate for the high infiltration capacities of forest soils, these results reinforce the fact that stemflow is an extremely localized input in natural forests. Thus, these results, even if specific to F. grandifolia within a particular forest and soil type, support a growing body of work indicating that stemflow infiltration areas are usually <1 m2, and often much smaller, in natural forests. Moreover, the high values of
FP,It provide further evidence indicating that stemflow inputs are important for the development of hot spots in near‐trunk soils.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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 µm. All PM diameter frequency distributions were skewed significantly to the right. Optimal power transformations of PM diameter distributions were between −1.00 and −1.56. 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.
Key Points
Particulate matter distributions significantly skewed to the rightMedian particulate diameter is near 3.0 microns with large difference in maximaOur model reconstructions can be readily used by others
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Dissolved and particulate organic carbon (DOC, POC) and nitrogen (DN, PN) are important constituents and indicators of the C and N dynamics in forested ecosystems, but little is known about fire ...effects on the fluxes of these elements. Biweekly fluxes at three different soil depths (organic layer O, mineral soil A, mineral soil B) were measured with zero-tension lysimeters before and after (prescribed) low-intensity surface fires in a Scots pine forest in central Germany. Measurements of soil organic C and total N concentrations, cold (soluble) and hot (labile) water-extractable DOC and DN, and soil respiration also were conducted for both pre- and post-burn bulk soils. Linear mixed-effect modelling (LMM) revealed that repeated low-intensity fire reduced DOC (−64%) and DN (−11%) fluxes in the organic layer, but increased soil CO2 fluxes (+7%). A nutrient flush from the charred material into the A horizon, as indicated by an enhanced solution pH (+11%) and electrical conductivity (+68%), may have stimulated microbial activity, leading to enhanced DOC (+47%) and DN (+202%) production and fluxes, respectively. The B horizon was unaffected by the fire treatment and retained DOC and DN. In contrast to DOC and DN fluxes, POC and PN fluxes were less affected by the fire treatment and decoupled from those of dissolved organic matter (DOM). Our findings indicate that low-intensity surface fires can significantly affect generally nutrient-poor soil systems by causing a short-term flush (“hot moment”) of DOM in the mineral A horizon (vertical “hot spot”) and by sorption in the mineral B horizon.
•Low-intensity surface fires impacted DOM in forest soils, but not POM fluxes.•The A horizons formed a vertical “hot spot” for fire-affected DOC and DN fluxes.•Linear mixed-effect modelling revealed short- and medium-term effects.•Cold and hot water-extraction acted as a proxy for fire-affected DOM fluxes.•Low-intensity surface fire caused higher CO2 soil respiration rates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Wildfires change the chemical composition of soil organic matter (SOM). Since the effects of fires on organic matter (OM) in soil solution are largely unknown, we sought to compare the quality of ...dissolved organic matter (DOM) and total organic matter (TOM=DOM+particulate OM) between burned and control sites. The sites were subjected to a low-intensity surface fire in a coniferous forest in Germany dominated by spodic Cambisols derived from Triassic sandstone. Soil solutions from three different soil horizons (O, Ah, Bw), and throughfall (TF) were analyzed using solid-state 13C NMR spectroscopy, allowing us to track the initial fire impact on OM vertically through the soil profile and 70days after the fire. In addition, organic layer samples were analyzed by 13C NMR spectroscopy to compare the OM quality. Under control conditions, properties of SOM influence the chemical composition of DOM and TOM in soil solutions. However, with fire, there is an initial increase in aromatic C in SOM, but not in DOM and TOM. Seventy days after the fire treatment, the aromatic C fraction in soil solutions of O and Ah layers increased, possibly due to accelerated oxidation processes, which would make the aromatic C more water-soluble. Our findings highlight the importance of short-term low-intensity fire-induced changes on forest soils that are useful to those seeking to better understand and model the temporal variability in the response of soil chemistry to fire to improve our knowledge of TOM and DOM dynamics in soils.
•Effects of low-intensity ground fire on OM in soil solution and soil were examined.•After the fire, properties of SOM differ from those of OM in soil solution.•Dissolved and total organic matter fractions were differentially affected by fire.•Fire triggers a lag in the chemical composition of topsoil solutions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The Bodélé Depression (Chad) in the central Sahara/Sahel region of Northern Africa is the most important source of mineral dust to the atmosphere globally. The Bodélé Depression is purportedly the ...largest source of Saharan dust reaching the Amazon Basin by transatlantic transport. Here, we have undertaken a comprehensive study of surface sediments from the Bodélé Depression and dust deposits (Chad, Niger) in order to characterize geochemically and isotopically (Sr, Nd and Pb isotopes) this dust source, and evaluate its importance in present and past African dust records. We similarly analyzed sedimentary deposits from the Amazonian lowlands in order to assess postulated accumulation of African mineral dust in the Amazon Basin, as well as its possible impact in fertilizing the Amazon rainforest.
Our results identify distinct sources of different ages and provenance in the Bodélé Depression versus the Amazon Basin, effectively ruling out an origin for the Amazonian deposits, such as the Belterra Clay Layer, by long-term deposition of Bodélé Depression material. Similarly, no evidence for contributions from other potential source areas is provided by existing isotope data (Sr, Nd) on Saharan dusts. Instead, the composition of these Amazonian deposits is entirely consistent with derivation from in-situ weathering and erosion of the Precambrian Amazonian craton, with little, if any, Andean contribution. In the Amazon Basin, the mass accumulation rate of eolian dust is only around one-third of the vertical erosion rate in shield areas, suggesting that Saharan dust is “consumed” by tropical weathering, contributing nutrients and stimulating plant growth, but never accumulates as such in the Amazon Basin.
The chemical and isotope compositions found in the Bodélé Depression are varied at the local scale, and have contrasting signatures in the “silica-rich” dry lake-bed sediments and in the “calcium-rich” mixed diatomites and surrounding sand material. This unexpected finding implies that the Bodélé Depression material is not “pre-mixed” at the source to provide a homogeneous source of dust. Rather, different isotope signatures can be emitted depending on subtle vagaries of dust-producing events. Our characterization of the Bodélé Depression components indicate that the Bodélé “calcium-rich” component, identified here, is most likely released via eolian processes of sand grain saltation and abrasion and may be significant in the overall global budget of dusts carried out by the Harmattan low-level jet during the winter.
•No evidence of Bodélé and/or Saharan dust signature in Amazon Basin deposits.•Predominance of weathering products from local Amazonian sources.•Geochemical and isotopic heterogeneity of Bodélé Depression source.•Identification of a Bodélé “Ca-rich” source of Harmattan dust.•Role of sand dunes in atmospheric dust distribution and global dust cycle.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Even if mires have proven to be relatively reliable archives over the temporal trends in atmospheric mercury deposition, there are large discrepancies between sites regarding the magnitude of the ...anthropogenic contribution to the global mercury cycle. A number of studies have also revealed significant differences in mercury accumulation within the same mire area. This raises the question of which factors, other than mercury deposition, affect the sequestration of this element in peat. One such factor could be vegetation type, which has the potential to affect both interception and retention of mercury. In order to assess how small-scale differences in vegetation type can affect mercury sequestration we sampled peat and living plants along three transects on a northern Swedish mire. The mire has two distinctly different vegetation types, the central part consists of an open area dominated by
Sphagnum whereas the surrounding fen, in addition to
Sphagnum mosses, has an understory of ericaceous shrubs and a sparse pine cover. A few main patterns can be observed in our data; (1) Both peat and
Sphagnum-mosses have higher mercury content (both concentration and inventory) in the pine-covered fen compared to the open
Sphagnum area (100% and 71% higher for peat and plants, respectively). These differences clearly exceed the 33% difference observed for lead-210, which is considered as a good analogue for atmospheric mercury deposition. (2) The differences in mercury concentration between peat profiles within a single vegetation type can largely be attributed to differences in peat decomposition. (3) When growing side by side in the open
Sphagnum area, the moss species
Sphagnum subsecundum has significantly higher mercury concentrations compared to
S. centrale (24
±
3 and 18
±
2
ng
Hg
g
−1, respectively). Based on these observations we suggest that species composition, vegetation type and decomposition can affect the mercury sequestration in a peat record, and that any changes in these properties over time, or space, have the potential to modify the mercury deposition signal recorded in the peat.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Soil organic matter (SOM) and its water-soluble components play an important role in terrestrial carbon cycling and associated ecosystem functions. Chemically, they are complex mixtures of organic ...compounds derived from decomposing plant material, microbial residues, as well as root exudates, and soil biota. To test the effect of the ecosystem type (forest and grassland) and fires events on the chemistry of dissolved organic matter (DOM), we applied a combination of laser-desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) and 2D (1H and 13C) nuclear magnetic resonance (NMR) spectroscopy to water-extractable organic matter (WEOM) from a range of top soil samples. The aim was to assess the suitability of LDI-TOF-MS for the rapid characterization of WEOM. Therefore, we evaluated the effects of sample (pH and dilution) conditions and use of positive or negative reflector mode to identify the conditions under which LDI-TOF-MS best distinguished between WEOM from different sources. Thirty-six samples were measured with both analytical techniques and their chemical patterns were statistically evaluated to distinguish firstly the effect of the type of ecosystem (forest versus grassland) on WEOM characteristics, and secondly the impact of fire on the chemical composition of WEOM. The nonmetric multidimensional scaling (NMDS) analysis of the most suitable experimental LDI-TOF-MS conditions showed a clear separation between the type of vegetation and fire-induced changes, mostly reflecting the presence of poly(ethylene glycol) in grassland soils. Discrimination among WEOM from different vegetation types was preserved in the fire treated samples. The calculation of the relative abundance of certain functional structures in the WEOM samples revealed a common composition of forest and grassland WEOM, with polysaccharides and proteins making up to 60%. The compositional impact of forest fire on WEOM was more pronounced compared to the one of grassland, leading to a decline in the main components, and an increase in amino-sugars, fatty acids, and sterols. The recorded 1H NMR and heteronuclear single quantum coherence (HSQC) spectra showed a decrease of the carbohydrate signal in WEOM from fire-treated samples, which was more pronounced in forest than in grassland soils.
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•A combination of LDI-TOF-MS and 2D NMR spectroscopy was applied to WEOM.•Assessment of well LDI-TOF-MS performance for the rapid characterize of WEOM.•Evaluation of best experimental LDI-TOF-MS conditions differentiating WEOM.•LDI-TOF-MS data showed an increase of fatty acids as result of earlier burnings.•NMR data showed a decrease of carbohydrates in WEOM from fire treated samples.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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