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  • 1
    Language: English
    In: Biogeochemistry, 2011, Vol.106(3), pp.461-473
    Description: Dissolved organic carbon (DOC) is an important component of the C cycle in forest ecosystems, but dynamics and origin of DOC in throughfall and soil solution are yet poorly understood. In a 2-year study, we analyzed the radiocarbon signature of DOC in throughfall and soil solution beneath the Oa horizon and at 90 cm depth in a Norway spruce forest on a Podzol soil. A two-pool mixing model revealed that throughfall DOC comprised mainly biogenic C, i.e. recently fixed C, from canopy leaching and possibly other sources. The contribution of fossil DOC from atmospheric deposition to throughfall DOC was on average 6% with maxima of 8–11% during the dormant season. In soil solution from the Oa horizon, DO 14 C signature was highly dynamic (range from −8‰ to +103‰), but not correlated with DOC concentration. Radiocarbon signatures suggest that DOC beneath the Oa horizon originated mainly from occluded and mineral associated organic matter fractions of the Oa horizon rather than from the Oi or Oe horizon. Relatively old C was released in the rewetting phase following a drought period in the late summer of 2006. In contrast, the DO 14 C signature indicated the release of younger C throughout the humid year 2007. In soil solutions from 90 cm depth, DO 14 C signatures were also highly dynamic (−127‰ to +3‰) despite constantly low DOC concentrations. Similar to the Oa horizon, the lowest DO 14 C signature at 90 cm depth was found after the rewetting phase in the late summer of 2006. Because of the variation in the DO 14 C signatures at this depth, we conclude that DOC was not equilibrated with the surrounding soil, but also originated from overlaying soil horizons. The dynamics of DO 14 C in throughfall and soil solution suggest that the sources of DOC are highly variable in time. Extended drought periods likely have a strong influence on release and translocation of DOC from relatively old and possibly stabilized soil organic matter fractions. Temporal variations as well as the input of fossil DOC needs to be considered when calibrating DOC models based on DO 14 C signatures.
    Keywords: Dissolved organic carbon ; Forest soils ; Norway spruce ; Throughfall ; Radiocarbon ; C
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 2
    Language: English
    In: Forest Ecology and Management, 15 December 2013, Vol.310, pp.110-119
    Description: Climate models predict increasing frequency and intensity of summer drought events for Central Europe. In a field experiment, we investigated the response of young beech ( L.) to extreme and repeated summer drought and the modulation of drought response patterns along the natural gradient of light availability at the study site. In autumn 2008, two-year-old, nursery derived beech – as used for forest conversion practices – was planted under a Norway spruce stand primarily opened through winter storm. Precipitation was manipulated in the growing seasons of 2009 through 2011, inducing a pronounced gradient of water availability. Individual drought-stress doses (DSD) and light doses (LD) were calculated for each beech sapling during the three growing seasons. Plant growth, CO -assimilation rate and stomatal conductance were reduced with increasing drought stress, but facilitated by increasing light availability. Progressive acclimation to water and light limitation during the three years of the experiment led to a decreased drought and shade sensitivity of diameter growth. Water-use efficiency, root/shoot ratio and rooting depth, were increased with decreasing water availability. Mean fine root diameter and specific fine root length correlated positively with both DSD and LD. Proceeding low-light acclimation was indicated by progressively increasing specific leaf area and reduced leaf dark-respiration. Present results suggest that nursery-induced high-light acclimation of the beech saplings, exacerbated light limitation upon transplant and hence productivity decline under co-occurring water limitation.
    Keywords: European Beech ; Drought ; Light ; Restoration ; Acclimation ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 3
    Language: English
    In: Forest Ecology and Management, 15 October 2016, Vol.378, pp.181-192
    Description: Decomposition rates of coarse woody debris (CWD) have been investigated in many studies, however data on fungal biomass and the related enzymatic activities in decomposing CWD are scarce. Here, we investigated the relations between fungal biomass, enzyme activities and CWD properties in sap- and heartwood of decomposing logs of 13 different temperate European tree species, exposed for 6 years on the ground. Fungal biomass was significantly higher in sapwood than in heartwood and higher in deciduous than in coniferous species, and represented 0.3–4.4% of CWD dry mass. In deciduous sapwood, fungal biomass may represent up to 29% of the total N stock in CWD. Fungal biomass correlated positively with the N content of CWD and, in heartwood, negatively with extractives. Enzyme activities were higher in deciduous than in coniferous CWD and for hydrolases higher in sapwood than in heartwood. Correlations between enzyme activities and the ergosterol content were generally weak. Hydrolytic enzymes were frequently found in all decaying tree species, whereas ligninolytic oxidoreductases showed high variability specifically in deciduous wood. Fungal biomass and enzymatic activities confirm the assumption that, in the initial stage, the decomposition of deciduous CWD is faster than of coniferous CWD under comparable conditions.
    Keywords: Dead Wood Decomposition ; Temperate Forests ; Lignocellulolytic Enzymes ; Nitrogen Content ; Deciduous and Coniferous Trees ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 4
    In: Journal of Geophysical Research: Biogeosciences, September 2012, Vol.117(G3), pp.n/a-n/a
    Description: Although land‐water carbon (C) transport represents a critical link in the global C cycle, rare attempts have been made to compare hydrologic controls over storm pulses of dissolved organic C (DOC) and particulate organic C (POC) in mountainous watersheds. An immersible UV/Vis spectrophotometer was used to comparatively investigate the rapid storm responses of stream water DOC and POC in a small mountainous forested watershed in South Korea. High‐frequency measurements at 5‐min intervals during 42 hydrologic events, including monsoon storms and winter snowmelts, showed consistent patterns: POC concentrations were lower than DOC concentrations during base flow and small storm events but exceeded them during the peak flow periods of intense storm events. Although both the DOC and POC concentrations had hysteretic relationships with discharge, the POC concentrations showed larger increases and variations after crossing a threshold discharge on the rising limb of the storm hydrograph. Stronger responses to intense storms resulted in a disproportionately large export of POC at high flow, whereas a large portion of the total DOC flux was exported under prevailing low‐flow conditions. The results demonstrate the potential of in situ optical measurements for investigating fine‐resolution dynamics of the DOC and POC export during storm events. Stronger storm responses of the POC export compared to the limited response range of the DOC export suggest that erosion‐induced POC export will become more important as a major pathway for the hydrologic soil C loss from mountainous watersheds in response to an increasing occurrence of extreme storm events. In situ optical monitoring captured differential storm responses of DOC and POC POC export was more variable on rising discharge than limited DOC responses Strong storm responses lead to disproportionately large POC export at high flow
    Keywords: Dissolved Organic Carbon ; Extreme Events ; In Situ Sensors ; Mountainous Watersheds ; Particulate Organic Carbon ; Soil Carbon Loss
    ISSN: 0148-0227
    E-ISSN: 2156-2202
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  • 5
    Language: English
    In: Science of the Total Environment, 2007, Vol.377(2), pp.308-318
    Description: The fate and behaviour of total arsenic (As) and of As species in soils is of concern for the quality of drinking water. To estimate the relevance of organic As species and the mobility of different As species, we evaluated the vertical distribution of organic and inorganic As species in two uncontaminated and two contaminated upland soils. Dimethylarsinic acid (up to 6 ng As g ), trimethylarsine oxide (up to 1.5 ng As g ), 4 unidentified organic As species (up to 3 ng As g ) and arsenobetaine (up to 15 ng As g ), were detected in the forest soils. Arsenobetaine was the dominant organic As species in both unpolluted and polluted forest soils. No organic As species were detected in the contaminated grassland soil. The organic As species may account for up to 30% of the mobile fraction in the unpolluted forest floor, but never exceed 9% in the unpolluted mineral soil. Highest concentrations of organic As species were found in the forest floors. The concentrations of extractable arsenite were highest in the surface horizons of all soils and may represent up to 36% of total extractable As. The concentrations of extractable arsenate were also highest in the Oa layers in the forest soils and decreased steeply in the mineral soil. In conclusion, the investigated forest soils contain a number of organic As species. The organic As species in forest soils seem to result from throughfall and litterfall and are retained mostly in the forest floor. The relative high concentrations of extractable arsenite, one of the most toxic As species, and arsenate in the forest floor point to the risk of their transfer to surface water by superficial flow under heavy rain events.
    Keywords: Arsenic Speciation ; Forest Soil ; Forest Floor ; Grassland Soil ; Mobility ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 6
    Language: English
    In: Biogeochemistry, 2011, Vol.103(1), pp.59-70
    Description: The input of heavy metals by atmospheric deposition to forested watersheds substantially decreased during the last decades in many areas. The goal of our study was to identify the present sinks and sources of metals and factors influencing metal mobility at the catchment and soil profile scale. We determined concentrations and fluxes of Cd, Zn, Cu, Cr and Ni in precipitation, litterfall, soil solutions (Oi, Oe, Oa horizon percolates, 20 and 90 cm soil depth) and runoff in a forest ecosystem in NE-Bavaria, Germany for 1 year. The metal concentrations in solutions were mostly 〈10 μg l −1 beside Zn (〈1200 μg l −1 ). The present total deposition was estimated at 1.0, 560, 30, 1.2 and 10.4 g ha −1  year −1 for Cd, Zn, Cu, Cr and Ni, respectively. The mass balance (total deposition minus runoff) at the catchment scale indicated actual retention of Zn, Cu and Ni, but an almost balanced budget for Cr and Cd. Considering the soil profile scale, the Oi horizon still acted as a sink, whereas the Oe and Oa horizons were presently sources for all metals. The solid–solution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. In the mineral soil horizons, K d values derived from field measurements were substantially larger than those predicted with empirical regression equations from Sauvé et al. (Environ Sci Technol 34:1125–1131, 2000; Environ Sci Technol 37:5191–5196, 2003). The mineral soil acted as a sink for all metals beside Cd. Dissolved organic C and pH influenced the metal mobility, as indicated by significant correlations to metal concentrations in Oa percolates and runoff. The solid–solution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. Overall, the decreased deposition rates have obviously induced a source function of the Oe and Oa horizon for metals. Consequently, mobilization of metals from forest floor during heavy rain events and near surface flow conditions may lead to elevated concentrations in runoff.
    Keywords: Heavy metals ; Biogeochemistry ; Forest soils ; Catchment ; Sink and source function
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 7
    Language: English
    In: Forest Ecology and Management, 01 May 2017, Vol.391, pp.86-95
    Description: Deadwood decay is an important ecosystem process in forest ecosystems, but the relative contribution of specific wood properties of tree species, activities of wood-degrading enzymes, and decomposer communities such as fungi and insects is unclear. We ask whether wood properties, in particular differences between angiosperms and gymnosperms, and organismic diversity of colonizers contribute to wood decomposition. To test this, we exposed deadwood logs of 13 tree species, covering four gymnosperms and nine angiosperm species, in 30 plots under different forest management in three regions in Germany. After a decomposition time of 6.5 years and showed the highest decay rates. We found a positive correlation of decay rate with enzyme activities, chemical wood properties (S, K concentration) and organismic diversity, while, heartwood character, lignin content, extractive concentration and phenol content were negatively correlated with decay rate across all 13 tree species. By applying a multi-model inference approach we found that the activity of the wood-degrading enzymes laccase and endocellulase, beetle diversity, heartwood presence, wood ray height and fungal diversity were the most important predictor variables for wood decay. Although we were not able to identify direct cause and effect relations by our approach, we conclude that enzyme activity and organismic diversity are the main drivers of wood decay rate, which greatly differed among tree species. Maintaining high tree species diversity will therefore result in high structural deadwood diversity in terms of decay rate and decay stage.
    Keywords: Wood Decomposition ; Ecosystem Function ; Saproxylic Beetles ; Biodiversity Exploratories ; Deadwood Experiment ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 8
    Language: English
    In: Science of the Total Environment, 2004, Vol.332(1), pp.231-241
    Description: Organotin compounds (OTC) are highly toxic pollutants that have been shown to affect many aquatic ecosystems. Little is known about the input and fate of OTC in terrestrial ecosystems. Here, soil pools, concentrations and fluxes in bulk precipitation, throughfall, fog, litterfall and runoff of OTC and Sn sub(total) were investigated in a forested ecosystem (Picea abies, Karst.) in NE Bavaria, Germany. The concentrations of OTC and Sn sub(total) were generally in the order fog〉throughfall〉bulk precipitation. Average concentrations of OTC sub(total) ranged from 57 ng Sn l super(-1) in fog to 5.8 ng Sn l super(-1) in bulk precipitation. Concentrations of Sn sub(total) were in the same order but between 490 ng Sn l super(-1) in fog and 140 ng Sn l super(-1) in bulk precipitation, on average. Average OTC sub(total) concentrations in litterfall were 12.9 ng Sn g super(- 1) and those of Sn sub(total) in litterfall 38 ng Sn g super(-1). All OTC concentrations in runoff were lower than in bulk precipitation, while those of Sn sub(total) were similar to the concentrations in bulk precipitation. Monobutyltin was the dominating OTC in bulk precipitation, throughfall, fog and litterfall, but was seldom detected in the runoff. The annual total deposition of OTC sub(total) (calculated as throughfall+litterfall) was 172 mg Sn ha super(-1) year super(-1), with 45 mg Sn ha super(-1) year super(-1) represented by litterfall. The annual runoff from the catchment of OTC sub(total) amounted to 25 mg Sn ha super(-1) year super(-1). The total deposition of Sn sub(total) was 4.9 g Sn ha super(-1) year super(- 1), of which 0.2 g Sn ha super(-1) year super(-1) was litterfall. The annual runoff of Sn sub(total) was 2.4 g Sn ha super(-1) year super(-1). The mass balance showed a high retention of OTC and Sn sub(total) in the catchment. The forest soils act as a strong sink for OTC and Sn sub(total). Only small amounts of deposited OTC are released to runoff. The ratio of soil pools to annual accumulation for total OTC (46 years) indicates that OTC inputs have been occurring already for many decades or have been substantially higher in the past than today.
    Keywords: Organotin ; Biogeochemistry ; Forested Catchment ; Bulk Precipitation ; Throughfall ; Fog ; Runoff ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 9
    Language: English
    In: Biology and Fertility of Soils, 2018, Vol.54(6), pp.761-768
    Description: Drying and rewetting (D/W) of soils often leads to a pulse of total dissolved phosphorus (TDP) by lysis of sensitive microorganisms. The relevance of D/W on the P cycle in ecosystems depends on the duration of the TDP release. In forest soils, the forest floor represents a hotspot of microbial activity and is often prone to D/W. Here, we investigated the dynamics of TDP, the microbial P pool (Pmic), and the composition of microbial communities after D/W. Samples were taken from Oi and Oe layers of a European beech and a Norway spruce site and desiccated up to − 100 MPa (pF 6) at 20 °C, while controls were kept moist. TDP and Pmic were measured 0, 1, 3, 7, and 14 days after rewetting and the composition of microbial communities was analyzed by automated ribosomal intergenic spacer analysis after 14 days. After D/W, the largest TDP net release (D/W-control) was from Oe layers with 40–50 mg P kg −1 and inorganic P as the dominant fraction. The TDP concentrations decreased strongly in Oi layers within 1 (beech) to 4 (spruce) days, while remaining stable in Oe layers. The TDP dynamics were linked to the decrease and recovery of Pmic after D/W. Pmic dynamics differed between layers and stand types, suggesting the influence of microbial communities with different D/W sensitivities. The composition of microbial communities varied strongly among sites and layers, while D/W only affected the composition of bacterial and fungal communities in the spruce Oe layer. D/W of forest floors increases the plant available P and affects the P cycle in forest ecosystems.
    Keywords: Drying–rewetting ; Inorganic dissolved phosphorus ; Soil microbial biomass ; Soil microbial communities ; Total dissolved phosphorus
    ISSN: 0178-2762
    E-ISSN: 1432-0789
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  • 10
    Language: English
    In: Biogeosciences, Sept 29, 2016, Vol.13(18), p.5421
    Description: Heavy storm events may increase the amount of organic matter in runoff from forested watersheds as well as the relation of dissolved to particulate organic matter. This study evaluated the effects of monsoon storm events on the runoff fluxes and on the composition of dissolved (#xE2;#x80;#xAF;POC and NO.sub.3 -N#xE2;#x80;#xAF;〉#xE2;#x80;#xAF;DON#xE2;#x80;#xAF;〉#xE2;#x80;#xAF;PON. The integrated DOC fluxes in runoff during the study period were much larger at the deciduous watershed (16#xE2;#x80;#xAF;kg#xE2;#x80;#xAF;C#xE2;#x80;#xAF;ha.sup.-1) than at the mixed watershed (7#xE2;#x80;#xAF;kg#xE2;#x80;#xAF;C#xE2;#x80;#xAF;ha.sup.-1 ), while the integrated NO.sub.3 -N fluxes were higher at the mixed watershed (5.2#xE2;#x80;#xAF;kg#xE2;#x80;#xAF;N#xE2;#x80;#xAF;ha.sup.-1) than at the deciduous watershed (2.9#xE2;#x80;#xAF;kg#xE2;#x80;#xAF;N#xE2;#x80;#xAF;ha.sup.-1). The latter suggests a larger N uptake by deciduous trees. Integrated fluxes of POC and PON were similar at both watersheds. The composition of organic matter in soils and runoff indicates that the contribution of near-surface flow to runoff was larger at the deciduous than at the mixed watershed. Our results demonstrate different responses of particulate and dissolved C and N in runoff to storm events as a combined effect of tree species composition and watershed specific flow paths.
    Keywords: Runoff
    ISSN: 1726-4170
    ISSN: 17264189
    E-ISSN: 17264189
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