Transformation of organic rhizodepositions by rhizosphere bacteria and its influence on the availability of tertiary calcium phosphate

This study assesses the influence of saccharides in the rhizodeposition on the phosphate solubilizing ability of rhizosphere bacteria. Water‐soluble rhizodeposits were analyzed of ¹⁴C‐labeled pea plants (Pisum sativum, cv. ‘Grapis’) which were grown at two different levels of P‐nutrition. The sugars produced were fed in vitro either as single compounds or as synthetic mixtures to three bacterial strains and the ability of the bacteria to mobilize Ca₃(PO₄)₂ was measured. The relative glucose proportion of pea exudates decreased under P deficiency while the content of galactose, ribose, xylose and fucose increased. In vitro feeding of single sugars and sugar mixtures showed that the ability of Pseudomonas fluorescens (PsIA12) to dissolve tertiary calcium phosphate was lower with pentoses and the mixed sugars of the P‐deficient plants than with glucose. On the other hand, the shifted sugar pattern observed under P deficiency increased the phosphate mobilization ability of Pantoea agglomerans (D5/23) and Azospirillum sp. (CC 322) considerably. This observation can only partly be explained by the acidification of the nutrient medium. Bacteria also produced different carboxylic anions depending on sugar supply. In addition to low‐molecular mono‐, di‐, and tricarboxylic acids which are known as P‐solubilizing substances, sugar acids also played an important role in cultures D 5/23 and CC 322.     

Phosphorus dynamics in a long‐term P fertilization trial on Luvic Phaeozem at Halle

The soil of the long‐term experiment laid out 1949 in Halle has the potential to supply much P. The P taken up by plants where no P (P0) or 15 kg ha⁻¹ yr⁻¹ (P1) was applied was much greater than the P applied as fertilizer (P1). A decrease in yield was measured only after the first 25 years on P0 soils but the P1 treatment has, so far, shown no decrease. Lactate extractions of the soil did not reflect P‐uptake suitably. The release of P from insoluble into water soluble forms was at a minimum after 30 years in P0 soils. P1 soils have now also declined to this minimum value and it remains to be seen whether yields decrease in this treatment in the future. Parallel to this trend, the P sorption increased in P0 soils. The subsoil also seems to be an important source for P supply, possibly influenced by root exudates. Further work is needed to gain a better understanding of soil P dynamics in connection with root exudates and microbes and to identify parameters which will provide more reliable means of calculating fertilizer P requirements.     

Growth performance,nutrient digestibility and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.     

Spatial distribution of soil heavy metal concentrations as indicator of pollution sources at Mount Križna (Great Fatra,central Slovakia)

The objective of this study was to test the suitability of a simple approach to identify the direction from where airborne heavy metals reach the study area as indication of their sources. We examined the distribution of heavy metals in soil profiles and along differently exposed transects. Samples were taken from 10 soils derived from the same parent material along N-, S-, and SE-exposed transects at 0—10, 10—20, and 20—40 cm depth and analyzed for total Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations. The heavy metal concentrations at 0—10 cm were larger than background concentrations in German arable soils except for Cr (Cd: 0.6—1.8 mg kg^—1; Cr: 39—67; Cu: 40—77; Ni: 87—156; Pb: 48—94; Zn: 71—129; Fe: 26—34 g kg^—1; Mn: 1.1—2.4). Decreasing Cd, Cu, Mn, and Pb concentrations with increasing soil depth pointed at atmospheric inputs. Aluminum and Ni concentrations increased with soil depth. Those of Fe, Cr, and Zn did not change with depth indicating that inputs at most equalled leaching losses. The Pb accumulation in the surface layer (i.e. the ratio between the Pb concentrations at 0—10 to those at 20—40 cm depth) was most pronounced at N-exposed sites; Pb obviously reached Mount Križna mainly by long-range transport from N where several industrial agglomerations are located. Substantial Cd, Cu, and Mn accumulations at the S- and SE-exposed sites indicated local sources such as mining near to the study area which probably are also the reason for slight Cr and Zn accumulations in the SE-exposed soils. Based on a principal component analysis of the total concentrations in the topsoils four metal groups may be distinguished: 1. Cr, Ni, Zn; 2. Mn, Cd; 3. Pb (positive loading), Cu (negative loading); 4. Al, Fe, indicating common sources and distribution patterns. The results demonstrate that the spatial distribution of soil heavy metal concentrations can be used as indication of the location of pollution sources.     

Shooting range contamination: mobility and transport of lead (Pb), copper (Cu) and antimony (Sb) in contaminated peatland

Purpose

Small arm shooting ranges located in peatland areas are gathering increased attention due to severe metal and antimony (Sb) contamination and challenging conditions for remediation. The goal of the present study was to gain further understanding of the distribution, binding and transport of lead (Pb), copper (Cu) and Sb in peatland contaminated by small arm shooting range activities.

Materials and methods

A field experiment was carried out at a recently closed shooting range facility in Norway, including (i) peat soil sampling for various selective extractions (water, chemical extractions, extractions by diffusive gradients in thin films, DGT), (ii) establishing groundwater wells for groundwater sampling and monitoring of groundwater level and (iii) sampling of water and sediments in surface water. The results from groundwater monitoring were used to carry out hydrogeological numerical simulations using Seep/W and CTran/W. These models were used to evaluate the residence time of the contaminants in the peatland.

Results and discussion

Increased metal concentrations were observed in the top layer of the peatland, indicating low vertical transport. Groundwater revealed high concentrations of Pb (22 ± 5 μg/L), Cu (16 ± 6 μg/L) and Sb (11 ± 2 μg/L), the dominating contaminant source to the downstream surface water. Hydrogeological modelling indicated that transport mainly happened in the upper peat layer, as a result of a higher hydraulic conductivity close to the surface and a high groundwater table. Pb (6.9 ± 0.1 μg/L), Cu (24.0 ± 0.0 μg/L) and Sb (7.4 ± 0.1 μg/L) concentrations in the stream samples confirmed the spreading of contaminants at levels toxic to aquatic organisms. Pb and Cu were most likely associated with dissolved organic carbon (DOC), whereas Sb showed no correlation with DOC.

Conclusions

The elements contaminating the peatland may leak to the nearby water course over a long-term period. Copper showed the highest concentration in the stream water despite considerably higher levels of Pb in the peat soil. Strong complexation of Cu to dissolved organic matter might explain this observation. Only a little fraction of the contaminants is transported in a particulate form, and therefore are increased sedimentation measures not considered as viable remediation option.

     

Effects of light and short-term temperature elevation on the 48-h hatching success of cold-stored Acartia tonsa Dana eggs

The effects of light and short-term temperature elevation on the 48-h egg hatching success (HS) of cold-stored (2 °C) Acartia tonsa Dana (Copepoda: Calanoida) eggs were examined in the present study. The eggs can be stored for up to 7.5 months and maintain their high hatching rate under optimal conditions. Intensively produced eggs from the copepod A. tonsa may be hatched and used as an inoculum for producing copepod nauplii as live feed for fish larvae. The HS for eggs that were directly exposed to LED light declined rapidly after 1 month of storage (from 91 to 25 %), and these eggs did not hatch at all after 3 months of storage. The highest HS found was for eggs stored in complete darkness. The HS for eggs stored in normoxic (≥7 mg DO L^?1) and anoxic (≤0.03 mg DO L^?1) seawater was not affected by short-term temperature transitions from 2 °C up to 9 or 17 °C for a period of 12 or 24 h, when hatched 1 week post-exposure. The global mean HS for eggs stored in normoxic seawater was 85.9 % and significantly lower compared to eggs stored under anoxic conditions after 3 weeks of storage (91.8 %) (P = 0.001; SNK).     

Leaching of carbon and nitrogen from a sandy soil substrate: A comparison between suction plates and ion exchange resins

To determine boundary effects on leaching, we investigated (1) how filter materials affect the concentrations of dissolved organic carbon (DOC) and nitrate (NO₃‐N) in soil percolates and (2) whether ion exchange resins and suction plates are equally suited to capture NO₃‐N. DOC leaching was higher with PE suction plates and plate material did not affect NO₃‐N leachate concentrations. Cumulative NO₃‐N leaching was similar for glass suction plates and ion exchange resins.     

Repeated monitoring of organic carbon stocks after eight years reveals carbon losses from intensively managed agricultural soils in Western Germany

Past land‐use changes, intensive cropping with large proportions of root crops, and preferred use of mineral fertilizer have been made responsible for proceeding losses of soil organic C (SOC) in the plough layer. We hypothesized that in intensive agriculturally managed regions changes in SOC stocks would be detectable within a decade. To test this hypothesis, we tracked the temporal development of the concentrations and stocks of SOC in 268 arable sites, sampled by horizon down to 60 cm in the Cologne‐Bonn region, W Germany, in 2005 and in 2013. We then related these changes to soil management data and humus balances obtained from farmers' surveys. As we expected that changes in SOC concentrations might at least in part be minor, we fractionated soils from 38 representative sites according to particle size in order to obtain C pools of different stability. We found that SOC concentrations had increased significantly in the topsoil (from 9.4 g kg^?1 in 2005 to 9.8 g kg^?1 in 2013), but had decreased significantly in the subsoil (from 4.1 g kg^?1 in 2005 to 3.5 g kg^?­1 in 2013). Intriguingly, these changes were due to changes in mineral‐bound SOC rather than to changes in sand‐sized organic matter pools. As bulk density decreased, the overall SOC stocks in the upper 60 cm exhibited a SOC loss of nearly 0.6 t C (ha · y)^?1 after correction by the equivalent soil mass method. This loss was most pronounced for sandy soils [?0.73 t SOC (ha · y)^?1], and less pronounced for loamy soils [?0.64 t SOC (ha · y)^?1]; silty soils revealed the smallest reduction in SOC [?0.3 t SOC (ha · y)^?1]. Losses of SOC occurred even with the overall humus balances having increased positively from about 20 kg C (ha · y)^?1 (2003–2005) to about 133 kg C (ha · y)^?1 (2005–2013) due to an improved organic fertilization and intercropping. We conclude that current management may fail to raise overall SOC stocks. In our study area SOC stocks even continued to decline, despite humus conservation practice, likely because past land use conversions (before 2005) still affect SOC dynamics.