Organic carbon in subsoils amounts to 40–60% of the global soil carbon pool and is generally characterized by apparent turnover times of hundreds to thousands of years and an increasing spatial ...variability with depth. The objective of this study was to analyze the amounts and distribution of SOC and to elucidate the turnover and storage mechanisms throughout deep soil profiles of a sandy Dystric Cambisol on Pleistocene glacial deposits under beech forest in northern Germany. The soil was sampled within a grid design at three replicated profiles, each at 8 sampling depths (10, 35, 60, 85, 110, 135, 160, 185cm) and 8 horizontal sampling points. 192 samples were analyzed for bulk density, texture, pH, SOC, total N, 13C-SOC, oxalate- and dithionite-extractable Fe and Al, root bio- and necromass, and microbial biomass C. For each sampling depth, a multi-effect model analysis was performed to identify the parameters explaining SOC variability. While SOC in the topsoil is only related to pH and dithionite-extractable Al, SOC in the subsoil is always related to root bio- and necromass and to Fe oxides and/or silt content. The comparison of SOC within rooted and root-free subsoil samples showed an up to 10 times higher SOC content in the rooted soil samples in comparison to the root-free samples. While the SOC content in the root-free soil declined with increasing depth the rooted soil samples showed no stratification with depth but were characterized by a higher spatial variability of SOC. At the same time, SOC in rooted soil samples has the same δ13C values as in root-free samples, indicating a similar degree of microbial processing. Microbial biomass C (Cmic) was not different between rooted and root-free samples, resulting in much higher Cmic:SOC ratios in the root-free soil. Since rooted soil samples are characterized by significantly higher silt and oxalate-extractable Fe (Feo) contents, it appears that roots preferentially grow into these chemically and physically slightly more favorable zones. At the same time, these higher inputs were apparently better stabilized through sorption to silt and metal oxyhydroxides, thus leading to the longer-term SOC sequestration in these hot-spots enhancing the spatial variability of SOC in subsoils.
•Spatial variability of SOC increases with increasing depth.•Cmic:SOC-ratios are lower in rooted samples indicating poorer microbial growth substrate than in the root-free samples.•Textural and mineralogical variability in subsoil influences both root distribution and SOC stabilization.
Heavy metal (HM) pollution and the need to preserve the environment have gathered increasing scientific attention. The immobilization of HMs into less-soluble, less mobile, and less toxic forms in ...addition to the improvement of
Medicago sativa
L. growth and HMs accumulation were evaluated after the application of marble waste (MW) and/or beneficial PGP rhizobacteria and mycorrhizae to the mining soil compost. A greenhouse assay was conducted to elucidate the influence of both amendment and beneficial microorganisms. The application of marble waste to the soil-compost resulted in decreasing the bioavailability of metals (Cu, Zn, Pb, and Cd), thus ameliorating the installation of the vegetal cover for 6 months of culture. Cultivation of
M. sativa
under 5% MW-amended soil for 6 months increased the shoot dry weight by almost twofold, while the inoculation with rhizobacteria-mycorrhizae combined with the application of 15% MW resulted in an improvement of 3.5-fold in case of shoot dry weight. In addition, the application of marble waste amendment or their combination with metallo-resistant bacteria resulted in decreasing HM accumulation leading to HM content below the threshold recommended for animal grazing. Thus, the application of amendments and beneficial microorganisms appeared to guarantee the safe cultivation of alfalfa for 6 months of culture. The dual combination amendments and beneficial microorganisms showed the good potential to restore HM polluted soils and could stand as a novel approach for restoration of HM-contaminated soils.
Many raised bogs in Central Europe are in an unfavorable state: drainage causes high emissions of carbon dioxide (CO2) and nitrous oxide (N2O), while rewetting may result in high methane (CH4) ...emissions. Also, the establishment of typical bog species is often hampered during restoration. Measures like topsoil removal (TSR) or introduction of target vegetation are known to improve restoration success in other systems, but experiences on bogs after long‐term agricultural use are scarce and their climate effects including carbon losses from TSR are unknown. In a field trial in north‐western Germany, consisting of seven plots (intensive grassland, IG, and six restoration approaches), we explored the effects of rewetting, TSR and Sphagnum introduction on greenhouse gas (GHG) emissions. We measured GHG fluxes to obtain two‐year GHG budgets and applied a radiative forcing model to assess the time‐dependent climate effects. Existing uncertainty of decomposition processes in the translocated topsoil has been incorporated by different topsoil accounting scenarios. According to our data, rewetting alone reduced CO2 emissions by approximately 75% compared to IG, but substantially increased CH4 emissions. After TSR and rewetting, on‐site CO2 emissions were close to zero or, with Sphagnum introduction, net negative while CH4 emissions remained very low. The climatic warming effect of TSR including C export becomes less climate warming than rewetting nutrient‐rich peatlands after a few decades. For raised bog restoration, we therefore recommend a TSR sufficient to achieve nutrient‐poor and acidic conditions needed for rapid Sphagnum establishment.
Previous studies have found that C turnover is bound to hotspots of microbial activity. The objective of this study was to analyze the effects of pure energy substrate (glucose), nutrient (mineral N ...or P) and combined substrate and nutrient (glucose + N, glucose + P, sterile DOC, artificial root exudate extract) additions to enzyme activity inside and outside hotspots as a proxy for microbial C turnover in a subsoil. By means of different substrate and nutrient additions, we tested how the limitations of our site were distributed on a small scale and depth-dependently to contribute to an increase in knowledge of subsoil mechanistics. The study site is a sandy Dystric Cambisol under an over 100-year-old beech forest stand in Lower Saxony, Germany. Forty-eight undisturbed soil samples from two depth increments (15–27 cm and 80–92 cm) of three profiles were sprayed homogeneously with easily available C, N and P sources to investigate the impacts of substrates and nutrients on three enzyme activities (acid phosphatase, β-glucosidase and N-acetylglucosaminidase) by using the soil zymography approach. Comparisons of upper and lower subsoils showed significantly fewer and smaller hotspots in the lower subsoil but with a high degree of spatial variation in comparison to the upper subsoil. Different patterns of enzyme distribution between upper and lower subsoil suggest microbial communities with a lower diversity are found in deeper soil regions of the site. Both substrate and nutrient additions stimulated enzyme activities significantly more outside the initial hotspots than within. Because of this, we conclude that microorganisms in the initial hotspots are less limited than in the surrounding bulk soil. Changes in enzyme activities owing to both substrate and nutrient addition were stronger in the lower subsoil than in the upper subsoil, showing differences in limitations and possible changes in microbial community structure with increasing depth. The results of our study emphasize the need to consider spatial factors in microbial turnover processes, especially in lower subsoil regions where stronger substrate and nutrient limitations occur.
The present work deals with the phytotoxicity and the genotoxicity of three heavy metals, namely copper, lead, and zinc on Medicago sativa seeds germination. Indeed, the role of metallo-resistant ...bacteria in lessening heavy metal toxicity was investigated. For this purpose, solutions of Cu, Pb, and Zn were used at the rate of 0.5, 1, 1.5, 2, and 2.5 mM for 4 d, along with untreated control using distilled water. The obtained findings displayed the stronger inhibitory effect of heavy metals on the germination and rhizogenesis process as well as a significant mito-depressive effect in the meristematic cells. For instance, Cu at the rate of 2.5 mM inhibited seed germination by 95 %, root elongation fell from 2.25 (in the control) to 0.14, while the mitotic index was reduced by 155%. Moreover, inoculation with metallo-resistant bacteria attenuated heavy metal toxicity, increased germination, rhizogenesis, mitotic index, and thus plant early growth. Metallo-resistant rhizobacteria inoculation improved the germination percentage by 40 % in the case of Cu and by 24 % in the case of Zn. The overall results suggest the cytotoxicity and the genotoxicity potential of Cu, Pb, and Zn on plants even at low concentrations. Furthermore, metallo-resistant bacteria application lessened heavy metal toxicity. This study confirms the suitability of M. sativa as a plant for the phytoremediation processes.
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•Heavy metals had a phytotoxic–genotoxic effect on the M. sativa germination process.•Germination and root elongation regression suggest different levels of sensitivity.•High metal content had significant inhibition on seeds germination and root elongation.•High metal content had a significant mito-depressive effect in the meristematic cells.•Inoculation with rhizobacteria attenuate heavy metals phytotoxicity and genotoxicity.
Biocrusts are crucial for the biogeochemical cycles of semiarid ecosystems and strongly influenced by environmental factors. We examined topcrusts (0–2 mm) and the underlying subcrust (2–35 mm depth) ...at two sites of the Negev with contrasting rainfall. The results show that sampling sites differing in moisture regime and sampling depth had a significant effect on soil properties. The microbial biomass, the concentrations of water‐soluble carbon and nitrogen fractions, and the activities of eight enzymes of the carbon and nitrogen cycles decreased with decreasing available moisture and with increasing soil depth. The biomass‐specific enzyme activity of topcrusts shows an increase in enzyme activity with increasing biomass in the same proportion. Biomass‐specific enzyme activity revealed a strong nutrient demand and a high relative enzyme activity in subcrusts of the drier study area. Moreover, phosphatase activity was much higher in the biocrust of the drier study site. The ratios of carbon to nitrogen to phosphorous show a strong limitation of the latter two for the subcrusts in the Negev, while the ratio of water‐extractable organic nitrogen to water‐extractable organic carbon underlines the high importance of leaching for subcrusts in semiarid areas. We conclude that Negev topcrusts are highly effective zones of nutrient turnover, adopting to higher amounts of moisture with an increase in biomass and enzyme activity. The subcrusts are an important section of turnover and need to be included into studies on C, N, and P storage in crust covered ecosystems to reveal the processes in deeper soil.
Soil microorganisms require a range of essential elements for their optimal functioning and store several elements in the microbial biomass (MB), such as carbon (C), nitrogen (N), phosphorus (P) and ...sulphur (S), as well as other secondary and trace elements. The C, N and P content of the microbial biomass has been quantified in many studies for many years, whereas S has been the focus only in a few studies, despite the availability of methods and the relevance of MBS for the S turnover in soils. To illustrate the relevance of MBS, this review aims at summarizing the current state of knowledge on the quantities of MBS in different soils, influencing environmental and agricultural management factors, methodological shortcomings, and prospects for soil microbial biomass research. Median MBS contents were 6.0 µg g−1 soil in arable, 7.6 µg g−1 soil in grassland, and 5.7 µg g−1 soil in forest soils. All extractants used led to similar MBS contents in soils with similar soil organic (SO) C contents. MBC and soil pH positively explained MBS, using multiple linear regression analysis. Median MB-C/S ratios increased in the order arable (55), grassland (85), and forest (135) soils. As the overall quantity of MBS data is still small, future studies are required to verify these observations. Moreover, future research needs to more strongly consider stoichiometric relationships of elements in the soil and the soil microbial ionome. The role of S and its complex relationship with the availability of other elements in soils for the soil microbial biomass and its functions remains to be elucidated.
The Red List of threatened habitat types in Germany was first published in 1994 and it is updated approximately every ten years. In 2017 the third version was published by the German Federal Agency ...for Nature Conservation. In the course of the revision, the criteria system was also extended. In doing so, an attempt was made to find a compromise between the consideration of international developments that had taken place and existing national requirements. In particular, short-term developments should become visible through the German Red List status. In addition to ‘National long-term Threat’, the valuation now also includes ‘Current Trend’ and ‘Rarity’. Following the IUCN’s approach, the collapse risk is now represented on the basis of several criteria. However, in contrast to the IUCN procedure, where the worst evaluated criterion is determinative for Red List status, in our procedure all criteria are included in the evaluation. To counteract misleading signal-effects for management decisions, all significant criteria have an influence on the resulting German Red List status (RLG). They are combined in an assessment scheme. In order to map the overall risk of loss, both the long-term threat as a historical reference value and furthermore the current trend must have an influence on RLG. As a result, 65% of habitat types have differing risk of loss.
The main objective of the second Darmstadt trial was to investigate the effects of vegetal fertilizers on soil properties and crop yield in comparison with farmyard manure. The experiment consisted ...of seven treatments: (i) inorganic fertilizers, (ii) vegetal organic fertilizers, (iii) vegetal organic fertilizers equivalent to biodynamic preparations, (iv) cattle farmyard manure, (v) cattle farmyard manure with addition of biodynamic preparations, (vi) high level of cattle farmyard manure, and (vii) high level of cattle farmyard manure with biodynamic preparations. The soil properties analyzed were pH, soil organic C, N, P, and S, soil microbial biomass C, N, and P, basal respiration and fungal ergosterol. The application of vegetal fertilizers had slightly negative effects on soil organic C, no effects on crop yield (potato, winter rye) and microbial biomass, but positive effects on ergosterol in comparison with farmyard manure. The increase in ergosterol was caused by straw return in the vegetal, but also in the inorganic fertilizer treatments. The biodynamic preparations did not affect the contents of soil organic C and total N. The low effectiveness of vegetal fertiliser in maintaining soil organic C levels is of particular importance for organic cropping systems and should be examined further under different site conditions.
Concerns about smoking displacement from public places to private amenities aroused following smoking ban implementation in Bavaria in 2008. We analysed children's exposure to second-hand smoke (SHS) ...before and after the ban, its effect on children's health and prevalence of active smoking in adults.
Six cross-sectional surveys (n = 32,443) on pre-school children in Bavaria were analysed, two surveys before the smoking ban in years 2004 and 2005 (S1 and S2) and four after the ban in 2008, 2012, 2014 and 2016 (S4, S6, S7 and S8). Using multivariable logistic regression, we analysed change in children's intra- and extrauterine SHS exposure and its adverse health effects (Asthma, wheezing, bronchitis and neurodermatitis) as well as change in parental active smoking.
The response rates were 78% for S1, 73% for S2, 61% for S4, 62% for S6, 56% for S7 and 54% for S8. Odds of parents never smoked at home in presence of children increased significantly from before to after the ban with odds ratios (OR) 1.17 (CI
1.01-1.35), 1.65 (CI
1.39-1.95), 2.85 (CI
2.32-3.51), 2.24 (CI
1.84-2.72) and 3.66 (CI
2.89-4.63) for S2, S4, S6, S7 and S8, respectively with S1 as reference. Compared to S4, odds of parents who were not actively smoking is significantly higher in S7 (OR = 1.13 (CI
1.03-1.24)) and S8 (OR = 1.24 (CI
1.13-1.36)). The odds of mothers who never smoked during pregnancy increased over time with OR = 1.22 (CI
1.06-1.40) for S2 and 1.57 (CI
1.33-1.86) for S8 compared to S1. Adverse health effects related to children's exposure to SHS are significantly less in S8 compared to S1.
After 11 years of smoking ban in Bavaria, smoking displacement to homes was disproved. Exposure of children to SHS intrauterine and at home is decreasing. Number of parents who are not actively smoking is increasing over time. Prevalence of health problems in children related to exposure to SHS is decreasing.
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