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  • Dissolved Organic Carbon
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  • 1
    Language: English
    In: Biogeochemistry, 2003, Vol.66(3), pp.265-286
    Description: Although dissolved organic matter (DOM) released from the forest floor plays a crucial role in transporting carbon and major nutrients through the soil profile, its formation and responses to changing litter inputs are only partially understood. To gain insights into the controlling mechanisms of DOM release from the forest floor, we investigated responses of the concentrations and fluxes of dissolved organic carbon (DOC) and nitrogen (DON) in forest floor leachates to manipulations of throughfall (TF) flow and aboveground litter inputs (litter removal, litter addition, and glucose addition) at a hardwood stand in Bavaria, Germany. Over the two-year study period, litter manipulations resulted in significant changes in C and N stocks of the uppermost organic horizon (Oi). DOC and DON losses via forest floor leaching represented 8 and 11% of annual litterfall C and N inputs at the control, respectively. The exclusion of aboveground litter inputs caused a slight decrease in DOC release from the Oi horizon but no change in the overall leaching losses of DOC and DON in forest floor leachates. In contrast, the addition of litter or glucose increased the release of DOC and DON either from the Oi or from the lower horizons (Oe + Oa). Net releases of DOC from the Oe + Oa horizons over the entire manipulation period were not related to changes in microbial activity (measured as rates of basal and substrate-induced respiration) but to the original forest floor depths prior to manipulation, pointing to the flux control by the size of source pools rather than a straightforward relationship between microbial activity and DOM production. In response to doubled TF fluxes, net increases in DOM fluxes occurred in the lower forest floor, indicating the presence of substantial pools of potentially soluble organic matter in the Oe + Oa horizons. In contrast to the general assumption of DOM as a leaching product from recent litter, our results suggest that DOM in forest floor leachates is derived from both newly added litter and older organic horizons through complex interactions between microbial production and consumption and hydrologic transport.
    Keywords: Dissolved organic carbon ; Dissolved organic matter ; Dissolved organic nitrogen ; Forest floor ; Litter manipulation ; Resource availability ; Water flux
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, 2011, Vol.43(8), pp.1742-1745
    Description: Dissolved organic nitrogen (DON) plays a key role in the N cycle of many ecosystems, as DON availability and biodegradation are important for plant growth, microbial metabolism and N transport in soils. However, biodegradation of DON (defined as the sum of mineralization and microbial immobilization) is only poorly understood. In laboratory incubations, biodegradation of DON and dissolved organic carbon (DOC) from Oi and Oa horizons of spruce, beech and cypress forests ranged from 6 to 72%. Biodegradation of DON and DOC was similar in most samples, and mineralization of DON was more important than microbial immobilization. Nitrate additions (0–10 mg N L ) never influenced either DON immobilization by microorganisms or mineralization. We conclude that soil microorganisms do not necessarily prefer mineral N over DON for meeting their N demand, and that biodegradation of DON seems to be driven by the microbial demand for C rather than N. Quantifying the dynamics of DON in soils should include consideration of both C and N demands by microbes. ► Biodegradation of dissolved organic nitrogen (DON) and carbon (DOC) was similar. ► Mineralization of DON was more important than microbial immobilization. ► Nitrate additions never influenced either DON immobilization or mineralization. ► DOC and DON they should be considered as a single pool of dissolved organic matter.
    Keywords: Dissolved Organic Nitrogen ; Dissolved Organic Carbon ; Nitrate ; Biodegradation ; Mineralization ; Microbial Immobilization ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    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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  • 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
    In: Global Change Biology, April 2009, Vol.15(4), pp.825-836
    Description: Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH, NO, Na, K, Ca, Mg). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K, Ca and Mg in soil solutions, however, the Na concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils.
    Keywords: 14 C ; Dissolved Organic Carbon ; Do 14 C ; Frost ; Leaching ; N Mineralization ; Soil Solution ; Soil ; Thawing
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 6
    Language: English
    In: Plant and Soil, 1 November 2007, Vol.300(1/2), pp.21-34
    Description: Forest soils are frequently subjected to dry-wet cycles, but little is known about the effects of repeated drying and wetting and wetting intensity on fluxes of $\mathrm{N}{\mathrm{H}}_{4}^{+}$, $\mathrm{N}{\mathrm{O}}_{3}^{-}$ and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil (O+M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently wetted by applying different amounts of water (8, 20 and 50 mm day-1) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day-1 during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m-2 (O columns) and 11.4 g N m-2 (O+M columns) over 225 days. Repeated drying and wetting reduced cumulative $\mathrm{N}{\mathrm{H}}_{4}^{+}$ and $\mathrm{N}{\mathrm{O}}_{3}^{-}$ fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing $\mathrm{N}{\mathrm{H}}_{4}^{+}$ (0.6–1.1 g N m-2) and decreasing $\mathrm{N}{\mathrm{O}}_{3}^{-}$ fluxes (7.6–9.6 g N m-2) indicate a reduction in net nitrification in the O+M columns. The negative effect of dry–wet cycles was attributed to reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months. Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean DOC concentrations increased by the treatment from 45 mg 1-1 to 61–77 mg 1-1 in the O tlsbba columns and from 12 mg 1-1 to 21–25 mg 1-1 in the O+M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons to the mineral soil owing to drying and wetting.
    Keywords: Applied sciences -- Materials science -- Surface science ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Applied sciences -- Materials science -- Materials processing ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Biology -- Microbiology ; Biological sciences -- Agriculture -- Agricultural sciences
    ISSN: 0032079X
    E-ISSN: 15735036
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  • 7
    Language: English
    In: Biogeochemistry, 2010, Vol.101(1), pp.243-256
    Description: Fluxes of dissolved organic carbon (DOC) and nitrogen (DON) may play an important role for losses of C and N from the soils of forest ecosystems, especially under conditions of high precipitation. We studied DOC and DON fluxes and concentrations in relation to precipitation intensity in a subtropical montane Chamaecyparis obtusa var. formosana forest in Taiwan. Our objective was, to quantify DOC and DON fluxes and to understand the role of high precipitation for DOC and DON export in this ecosystem. From 2005 to 2008 we sampled bulk precipitation, throughfall, forest floor percolates and seepage (60 cm) and analyzed DOC, DON and mineral N concentrations. Average DOC fluxes in the soil were extremely high (962 and 478 kg C ha −1  year −1 in forest floor percolates and seepage, respectively) while DON fluxes were similar to other (sub)tropical ecosystems (16 and 8 kg N ha −1 year −1 , respectively). Total N fluxes in the soil were dominated by DON. Dissolved organic C and N concentrations in forest floor percolates were independent of the water flux. No dilution effect was visible. Instead, the pool size of potentially soluble DOC and DON was variable as indicated by different DOC and DON concentrations in forest floor percolates at similar precipitation amounts. Therefore, we hypothesized, that these pools are not likely to be depleted in the long term. The relationship between water fluxes in bulk precipitation and DOC and DON fluxes in forest floor percolates was positive (DOC r  = 0.908, DON r  = 0.842, respectively, Spearman rank correlation). We concluded, that precipitation is an important driver for DOC and DON losses from this subtropical montane forest and that these DOC losses play an important role in the soil C cycle of this ecosystem. Moreover, we found that the linear relationship between bulk precipitation and DOC and DON fluxes in forest floor percolates of temperate ecosystems does not hold when incorporating additional data on these fluxes from (subtropical) ecosystems.
    Keywords: Dissolved organic nitrogen ; Dissolved organic carbon ; Precipitation ; Fluxes ; Forest floor ; Subtropical montane forest
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 8
    Language: English
    In: Plant and Soil, 2007, Vol.300(1), pp.21-34
    Description: Forest soils are frequently subjected to dry–wet cycles, but little is known about the effects of repeated drying and wetting and wetting intensity on fluxes of $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ , $${\text{NO}}^{ - }_{3} $$ and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil (O + M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently wetted by applying different amounts of water (8, 20 and 50 mm day −1 ) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day −1 during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m −2 (O columns) and 11.4 g N m −2 (O + M columns) over 225 days. Repeated drying and wetting reduced cumulative $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ and $${\text{NO}}^{ - }_{3} $$ fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ (0.6–1.1 g N m −2 ) and decreasing $${\text{NO}}^{ - }_{3} $$ fluxes (7.6–9.6 g N m −2 ) indicate a reduction in net nitrification in the O + M columns. The negative effect of dry–wet cycles was attributed to reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months. Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean DOC concentrations increased by the treatment from 45 mg l −1 to 61–77 mg l −1 in the O tlsbba columns and from 12 mg l −1 to 21–25 mg l −1 in the O + M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons to the mineral soil owing to drying and wetting.
    Keywords: Dissolved organic carbon ; DOC properties ; Dry–wet cycles ; Forest soil ; Inorganic nitrogen ; Soil solution
    ISSN: 0032-079X
    E-ISSN: 1573-5036
    Source: Springer Science & Business Media B.V.
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  • 9
    Language: English
    In: Soil Biology and Biochemistry, June 2002, Vol.34(6), pp.813-822
    Description: The forest floor in temperate forests has become recognized for its importance in the retention of elevated inputs of dissolved inorganic nitrogen (DIN) and as a source of dissolved organic matter (DOM). A laboratory leaching experiment was conducted over the period of 98 d to examine the origin of dissolved organic carbon (DOC) and nitrogen (DON) in a deciduous forest floor, and the effect of resource availability and microbial activity on the production mechanisms involved. The experiment was composed of different types of treatments: exclusion of specific forest floor layers (no Oi, no Oe) and addition of carbon sources (glucose, cellulose, leaf, wood) and NH sub(4)NO sub(3) (nitrogen). The cumulative amount of CO sub(2) evolution was positively related to the availability of C sources at each treatment: glucose 〉 leaf = wood = cellulose 〉 control = no Oe = nitrogen 〉 no Oi. DOC release was related to the amount of C sources but showed no clear correlation with CO sub(2) evolution. An increase in C availability generally led to a reduction in the release of DON as well as DIN. In contrast, the amendment of NH sub(4)NO sub(3) reduced the cumulative DOC release but enhanced the release of both DON and DIN. Fresh leaf litter was a more important DOC source than labile substrates (glucose and cellulose) as well as more stable substrates (forest floor materials and wood). Among forest floor layers, more humified horizons (Oe and Oa) were the primary source of DIN and made a similar contribution to DOM release as the Oi layer. The changes in DOM composition detected by a humification index of the leachates, in combination with a shift in the final microbial biomass C, suggested that DOM released from the soluble pools of added litter or the Oi layer contained a substantial amount of microbially processed organic matter. Our study demonstrated the importance of C availability in regulating microbial activity and immobilization of dissolved N in an N-enriched forest floor. However, the discrepancy between substrate lability and DOC production, in combination with a rapid microbial processing of DOC released from labile C pools, illustrated the complicated nature of microbial production and consumption of DOC in the forest floor.
    Keywords: Dissolved Organic Matter ; Dissolved Organic Carbon ; Dissolved Organic Nitrogen ; Dissolved Inorganic Nitrogen ; Forest Floor ; C and N Availability ; Soil Microbial Activity ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 10
    Language: English
    In: Forest Ecology and Management, 2007, Vol.242(2), pp.133-141
    Description: Forest ecosystems in Taiwan are frequently influenced by typhoons that cause large amounts of litter input to the soil. The rapid decomposition of such litter under the high precipitation and temperature conditions may trigger nutrient losses via seepage. Our goal was to investigate the effects of exceptionally high inputs of var. leaves to the soil on the solute fluxes and concentrations of mineral elements, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in a Lithic Leptosol. We simulated the effect of a typhoon by adding the annual aboveground litterfall (4600 kg ha ) and about 3 times the annual litterfall (13,900 kg ha ) as fresh leaves in a single event to small manipulation plots. All plots were also subjected to the natural litterfall. Soil solution was collected 4 months before and 15 months following the litter manipulation in 14 days intervals underneath the forest floor with free draining lysimeters and by ceramic suction cups at 60 cm depth. The 3-fold litter addition caused increased fluxes of K, Mg, Ca, and NH in forest floor percolates as compared to the 1-fold litter treatment. DOC and DON fluxes also increased, but this was only statistically significant for DON. DON was the dominant form of N both in forest floor percolates and in seepage. The 3-fold litter manipulation increased the seepage fluxes of K, DON, and DOC relative to the 1-fold treatment with largest differences recorded for K, reaching 12.4 kg ha 15 month . The fluxes of DOC with forest floor percolates and with seepage in both treatments exceeded published values by far. Our results suggest that the decomposition of large amounts of fresh leaf litter may trigger K losses from the ecosystem via seepage, whereas the probability for additional N and DOC losses is moderate. For Ca and Mg, additional losses seem to be rather unlikely.
    Keywords: Chamaecyparis Obtusa Var. Formosana ; Dissolved Organic Matter ; Fluxes ; Mineral Elements ; Soil Solution ; Taiwan ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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