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  • 1
    Language: English
    In: Soil Biology and Biochemistry, February 2011, Vol.43(2), pp.333-338
    Description: Changes in the soil water regime, predicted as a consequence of global climate change, might influence the N cycle in temperate forest soils. We investigated the effect of decreasing soil water potentials on gross ammonification and nitrification in different soil horizons of a Norway spruce forest and tested the hypotheses that i) gross rates are more sensitive to desiccation in the Oa and EA horizon as compared to the uppermost Oi/Oe horizon and ii) that gross nitrification is more sensitive than gross ammonification. Soil samples were adjusted by air drying to water potentials from about field capacity to around −1.0 MPa, a range that is often observed under field conditions at our site. Gross rates were measured using the N pool dilution technique. To ensure that the addition of solute label to dry soils and the local rewetting does not affect the results by re-mineralization or preferential consumption of N, we compared different extraction and incubation times. T times ranging from 10 to 300 min and incubation times of 48 h and 72 h did not influence the rates of gross ammonification and nitrification. Even small changes of water potential decreased gross ammonification and nitrification in the O horizon. In the EA horizon, gross nitrification was below detection limit and the response of the generally low rates of gross ammonification to decreasing water potentials was minor. In the Oi/Oe horizon gross ammonification and nitrification decreased from 37.5 to 18.3 mg N kg  soil d and from 15.4 to 5.6 mg N kg  soil d when the water potential decreased from field capacity to −0.8 MPa. In the Oa horizon gross ammonification decreased from 7.4 to 4.0 mg N kg  soil d when the water potential reached −0.6 MPa. At such water potential nitrification almost ceased, while in the Oi/Oe horizon nitrification continued at a rather high level. Hence, only in the Oa horizon nitrification was more sensitive to desiccation than ammonification. Extended drought periods that might result from climate change will cause a reduction in gross N turnover rates in forest soils even at moderate levels of soil desiccation. ► Even small changes of water potential decreased gross N turnover rates in the O horizon. ► Only in the Oa horizon gross nitrification was more sensitive to desiccation than ammonification. ► A reduction in gross N turnover rates can be expected in forest soils even at moderate desiccation.
    Keywords: 15n Pool Dilution Technique ; Norway Spruce ; Forest Soil ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, July 2017, Vol.110, pp.1-7
    Description: Previous work has shown that the drying/rewetting (D/W) of soils mobilizes phosphorus (P), and that the effect of D/W on P release likely depends on the soil microbial community composition. We tested the hypotheses that (i) P release after D/W from fungi is lower than from bacteria and that (ii) gram-positive bacteria are less susceptible to D/W than gram-negative bacteria. We investigated the release of dissolved organic (DOP) and inorganic phosphorus (DIP) from bacterial and fungal biomass after rewetting of an artificial soil that was desiccated to different degrees. For this purpose, sterilized soil amended with growth medium was inoculated separately with one of two bacterial strains ( gram-negative and gram-positive) or with one fungal strain ( ). The bacterial strains were grown for 7 days, the fungus for 25 days at 50% soil water holding capacity. After the pre-incubation period, microbial biomass P (Pmic) was determined by chloroform fumigation extraction, and soils were desiccated at 20 °C for 5–8 days until pF 6 (−100 MPa) was reached, while the controls were kept permanently at 50% water holding capacity. At different degrees of desiccation, samples were destructively harvested and soils were extracted with water to measure the release of DIP and DOP. The net release of total dissolved P per unit Pmic following D/W was in the order  =  In case of , net release started already after desiccation to pF 4 (−1.0 MPa) and increased with further desiccation. For and , a tendency for net release was only observed after severe desiccation up to pF 6. Our results suggest that the effect of D/W on P release from microbial biomass depends largely on the microbial community composition, with fungi and gram-positive bacteria being less susceptible to D/W than gram-negative bacteria.
    Keywords: Drying–Rewetting ; Dissolved Phosphorus ; Soil Microbial Biomass ; Saprotrophic Fungi ; Gram-Positive Bacteria ; Gram-Negative Bacteria ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    In: Global Change Biology, April 2009, Vol.15(4), pp.808-824
    Description: In the next decades, many soils will be subjected to increased drying/wetting cycles or modified water availability considering predicted global changes in precipitation and evapotranspiration. These changes may affect the turnover of C and N in soils, but the direction of changes is still unclear. The aim of the review is the evaluation of involved mechanisms, the intensity, duration and frequency of drying and wetting for the mineralization and fluxes of C and N in terrestrial soils. Controversial study results require a reappraisal of the present understanding that wetting of dry soils induces significant losses of soil C and N. The generally observed pulse in net C and N mineralization following wetting of dry soil (hereafter wetting pulse) is short‐lived and often exceeds the mineralization rate of a respective moist control. Accumulated microbial and plant necromass, lysis of live microbial cells, release of compatible solutes and exposure of previously protected organic matter may explain the additional mineralization during wetting of soils. Frequent drying and wetting diminishes the wetting pulse due to limitation of the accessible organic matter pool. Despite wetting pulses, cumulative C and N mineralization (defined here as total net mineralization during drying and wetting) are mostly smaller compared with soil with optimum moisture, indicating that wetting pulses cannot compensate for small mineralization rates during drought periods. Cumulative mineralization is linked to the intensity and duration of drying, the amount and distribution of precipitation, temperature, hydrophobicity and the accessible pool of organic substrates. Wetting pulses may have a significant impact on C and N mineralization or flux rates in arid and semiarid regions but have less impact in humid and subhumid regions on annual time scales. Organic matter stocks are progressively preserved with increasing duration and intensity of drought periods; however, fires enhance the risk of organic matter losses under dry conditions. Hydrophobicity of organic surfaces is an important mechanism that reduces C and N mineralization in topsoils after precipitation. Hence, mineralization in forest soils with hydrophobic organic horizons is presumably stronger limited than in grassland or farmland soils. Even in humid regions, suboptimal water potentials often restrict microbial activity in topsoils during growing seasons. Increasing summer droughts will likely reduce the mineralization and fluxes of C and N whereas increasing summer precipitation could enhance the losses of C and N from soils.
    Keywords: C Mineralization ; Drying ; Nitrate Leaching ; N Mineralization ; Precipitation ; Soil Moisture ; Soil Organic Carbon ; Soil Respiration ; Wetting
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 4
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2018, Vol.181(2), pp.177-184
    Description: Drying and rewetting (D/W) of soils often resulted in the release of soluble phosphorus (P) and nitrogen (N), thereby changing the availability of both nutrients. Most experiments on D/W have been conducted with disturbed mineral soil samples and with rewetting of the soil samples by abrupt change in the water potential. Here, we studied the effect of D/W on the leaching of P and N from undisturbed forest floors of a European beech and a Norway spruce site under near field conditions of desiccation and rewetting. We hypothesized that even under realistic rewetting of undisturbed forest floors, the leaching of P and N is increased after D/W and that the effects are less pronounced for spruce than for beech because of the larger hydrophobicity of the spruce forest floor. Undisturbed forest floor columns were subjected to desiccation at 20°C until a matrix potential of –100 MPa (pF 6.0) was reached, while controls were kept at moist conditions. Columns were irrigated by 22 mm day from day 1–3 and by 10 mm day from day 4–14 given in automated short pulses. Leachates from the soil columns were analyzed for orthophosphate, total P, NH, NO, and total N. In the spruce forest floor the concentrations of total P in leachates and the leachate fluxes were strongly increased after D/W. The increase of solute P was less for beech than for spruce coinciding with less actual rewetting of the beech forest floor. Leaching of total N from the spruce forest floor was not affected by D/W, however, concentrations and leaching of NH increased, while leaching of NO decreased. For beech the leaching of total N and NH increased after D/W, while NO leaching decreased. The results indicate that also under realistic conditions, D/W of forest floors increases solute P and leads to changes in the ratio of NH/NO in solution, thereby altering the availability of the nutrients.
    Keywords: Beech ; Desiccation ; Leaching ; Organic Layer ; Soil Solution ; Spruce
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 5
    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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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2016, Vol.179(5), pp.670-678
    Description: Drying–rewetting cycles (D/W) occur frequently in topsoils and may mobilize phosphorus (P). We investigated the effect of repeated D/W on the release of dissolved inorganic (DIP) and organic P (DOP) from forest floors and A horizons. Samples were taken from 3 European beech sites and from 3 Norway spruce sites. Soils were desiccated up to pF 6 (–100 MPa) in three D/W cycles in the laboratory, while the controls were kept permanently at 50% water holding capacity. After each drying, P was extracted from the soils in water. D/W caused the release of DIP and DOP especially from O layers. There was no general difference in response to D/W between samples from beech and spruce. The net release of DIP after D/W was largest from the Oe horizons (average 50–60 mg P kg) for both beech and spruce forest soils. The net release of DIP from Oi layers was on average 7.8 mg P kg and from spruce Oa layers 21.1 mg P kg. In the A horizons, net DIP release was similar in beech and spruce soils with 0.4 mg P kg. The release of DOP was less than the release of DIP except for the A horizons. Repeated cycles did not increase the release of DIP and DOP. The release of DIP and DOP was positively correlated with the microbial biomass in Oe and Oa layers but not in Oi layers. Our results suggest that D/W may significantly influence the short term availability of dissolved P in both beech and spruce forest soils.
    Keywords: Drying–Rewetting ; Dissolved Inorganic Phosphorus Dip ; Dissolved Organic Phosphorus Dop ; Microbial Biomass ; Forest Soils
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 7
    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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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2000, Vol.163(5), pp.517-521
    Description: The forest floor represents the major source of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils. The release mechanisms of DOC and DON from forest floors and their environmental controls as well as the dynamics of concentrations and fluxes are still poorly understood. We investigated the effect of drying and rewetting on the release of DOC and DON from a Norway spruce forest floor. Undisturbed soil columns of 17 cm diameter and 15—20 cm height were taken with 7 replicates from the forest floor of a mature Norway spruce ( [L.] Karst.) site and established at 10°C in the laboratory. Columns were exposed to different periods of drying (3, 5, 10, 20 days). Each drying period was followed by a rewetting for 5 days at an irrigation rate of 10 mm d with a natural throughfall solution. The percolates from the forest floor were collected daily and analyzed for DOC, total N, NH, NO, pH, electrical conductivity and major ions. Drying for 10 and 20 days decreased the water content of the Oi horizon from 280% dry weight to about 30%. The water content of the Oe and the Oa horizon only changed from about 300% to 200%. The fluxes of DOC from the forest floor were moderately effected by drying and rewetting with an increase after 3 and 5 days of drying, but a decrease after 10 and 20 days. On the contrary, the drying for 10 and 20 days resulted in a drastic increase of the DON fluxes and a subsequent decrease of the DOC/DON ratios in the forest floor percolates from about 50 to 3.3. These results suggest that the mechanisms for DOC release in forest floors differ from those for DON and that drying and rewetting cause temporal variations in the DOC/DON ratios in forest floor percolates. Unterschiedliche Auswirkung von Austrocknung auf die Flüsse gelöster organischer Kohlenstoff‐ und Stickstoffverbindungen aus der Humusauflage eines Fichtenbestandes Die Freisetzung gelöster organischer Kohlenstoff‐ (DOC) und Stickstoffverbindungen (DON) findet in Waldökosystemen im wesentlichen in der organischen Auflage statt. Über die Mechanismen der DOC‐ und DON‐Freisetzung aus der organischen Auflage und deren Steuerung durch Umweltfaktoren ist bisher wenig bekannt. Die vorliegende Arbeit untersuchte den Einfluss von Austrocknung und Wiederbefeuchtung auf die Freisetzung von DOC und DON aus der organischen Auflage eines Fichtenwaldökosystems ( [L.] Karst.). Ungestörte Bodensäulen des Auflagehumus mit 17 cm Durchmesser und 15—20 cm Höhe wurden in 7 Parallelen entnommen und bei 10°C im Labor über unterschiedlich lange Perioden ausgetrocknet (3, 5, 10, 20 Tage). Nach jeder Austrocknungsperiode folgte eine 5‐tägige Beregnung (10 mm/Tag) mit natürlichem Bestandesniederschlag. Die Perkolate aus der organischen Auflage wurden täglich gewonnen und auf DOC, gesamt‐N, NH, NO, pH, elektrische Leitfähigkeit und Kationen analysiert. Nach 10 und 20 Tagen Austrocknung nahm der gravimetrische Wassergehalt der Ol‐Lage von 280% auf etwa 30% der Trockenmasse ab. Die Wassergehalte der Of‐ und Oh‐Lage sanken hingegen nur von 300% auf etwa 200%. Die Freisetzung von DOC aus der organischen Auflage wurde nur wenig durch Austrocknung und Wiederbefeuchtung beeinflusst. Nach 3 und 5 Tagen Austrocknung nahmen die DOC‐Flüsse im Perkolat leicht zu, nach 10 und 20 Tagen Austrocknung aber ab. Im Gegensatz dazu bewirkte die Austrocknung über 10 und 20 Tage einen drastischen Anstieg der DON‐Flüsse und infolgedessen eine Abnahme der DOC/DON‐Verhältnisse in den Perkolaten von etwa 50 auf 3.3. Die Ergebnisse zeigen, dass die Mechanismen der Freisetzung aus der organischen Auflage für DOC und DON unterschiedlich sind und dass Austrocknung und Wiederbefeuchtung eine zeitliche Variabilität der DOC/DON‐Verhältnisse in der Bodenlösung verursachen.
    Keywords: Dissolved Organic Carbon ; Dissolved Organic Nitrogen ; Drying ; Forest Floor ; Rewetting ; Soil Solution
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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