Clay Addition to Sandy Soil Reduces Nutrient Leaching—Effect of Clay Concentration and Ped Size

Leaching of nutrients, particularly in sandy soil with low nutrient and water holding capacity (WHC), is a major threat to marine and fresh water pollution. Addition of clay soil to sandy soil could be an option to increase water and nutrient holding capacity of sandy soils, but the effect of clay soil addition may depend on the form in which the clay soil is added and the addition rate. Clay soil was added to sandy soil at rate of 10 or 20% (w/w) finely ground (<2 mm) or 2 and 5 mm peds with and without nitrogen (N) and phosphorus (P) fertilizer equivalent to 60 kg N ha^?1 and 15 kg P ha^?1. The clay sand mixture for each treatment was weighed (30 g) in cores with nylon mesh at the bottom. The soils were incubated at 80% WHC for 7 weeks. To obtain leachate, 20 mL reverse osmosis (RO) water was added every week to each core. Leachate was analysed for inorganic N, P, and pH. Soil was analyzed for N, P, and pH before and after the leaching. Clay addition significantly reduced the leaching of N and P compared to sandy soil alone, with greatest reduction by finely ground clay soil and least with 5 mm peds. Compared to sandy soil alone, 83% more N was retained in clay-amended soil and P retention was doubled. This study showed that addition of finely ground clay soil can substantially reduce N and P leaching and thereby increase fertilizer retention compared to sandy soil alone.     

Type of organic carbon amendment influences pH changes in acid sulfate soils in flooded and dry conditions

Purpose

Acid sulfate soils (ASS) are common in wetlands and can pose an environmental threat when they dry because oxidation of pyrite may cause strong acidification. Addition of organic matter can stimulate sulfate reduction during wet periods and minimize acidification during dry periods. However, the effect of the organic amendment may depend on its composition.

Materials and methods

Three wetland acid sulfate (sulfuric, hypersulfidic, and hyposulfidic) soils collected from different depth in one profile were used. The soils, unamended or amended with 10 g C kg^?1 as glucose, wheat straw, pea straw, or Phragmites litter, were incubated for 18 weeks under flooded conditions (“wet period”) followed by 10 weeks during which the soils were maintained at 100 % of maximum water-holding capacity (“dry period”).

Results and discussion

During the wet period, the pH decreased in the control and with glucose to pH 3–4, but increased or was maintained in residue-amended soils (pH at the end of the wet period about 7). In the dry period, the pH of the control and glucose-amended soils remained low, whereas the pH in residue-amended soils decreased. However, at end of the dry period, the pH was higher in residue-amended soils than in the control or glucose-amended soils, particularly with pea straw (C/N 50).

Conclusions

Amendment of acid sulfate soils with plant residues (particularly those with low to moderate C/N ratio) can stimulate pH increase during flooding and reduce acidification under oxidizing conditions.

     

C. Veröffentlichungen aus dem Institut 1989

Das Institut Im Jahre 1989

C. Veröffentlichungen aus dem Institut 1989     

Interactions between soil micro- and mesofauna and plants in an ecofarming system

Interactions between crops and soil micro- and mesofauna within the root zone were investigated under field conditions on sandy loam on a larger spatial scale and in columns in the laboratory on a smaller spatial scale. During the vegetation period of summer wheat from April to July 1999 soil samples were taken monthly directly from the root zone within plant rows and between plant rows hardly penetrated by roots. Abundances of Enchytraeidae, Collembola, soil flagellates, enzyme activities and contents of total carbon and nitrogen were determined. Additionally, a laboratory experiment was carried out with soil columns. Soil from the field was defaunated and inoculated with soil fauna (Enchytraeidae, Collembola, earthworms) in different combinations. Furthermore, summer wheat was sown. Enzyme activities, soil flagellate abundance and contents of total carbon and nitrogen were measured after 2, 6 and 14 weeks. Our field results revealed considerable interactions between plant roots, sampling date and soil layer affecting Enchytraeidae and Collembola. Within plant rows flagellate numbers correlated higher with N_t and C_t than between plant rows. In the laboratory close relationships between soil fauna as well as enzyme activities and nutrients contents were found within the root zone.     

Arabidopsis type I metacaspases control cell death

Metacaspases are distant relatives of animal caspases found in protozoa, fungi, and plants. Limited experimental data exist defining their function(s), despite their discovery by homology modeling a decade ago. We demonstrated that two type I metacaspases, AtMC1 and AtMC2, antagonistically control programmed cell death in Arabidopsis. AtMC1 is a positive regulator of cell death and requires conserved caspase-like putative catalytic residues for its function. AtMC2 negatively regulates cell death. This function is independent of the putative catalytic residues. Manipulation of the Arabidopsis type I metacaspase regulatory module can nearly eliminate the hypersensitive cell death response (HR) activated by plant intracellular immune receptors. This does not lead to enhanced pathogen proliferation, decoupling HR from restriction of pathogen growth.     

Efficient inhibition of the Alzheimer's disease beta-secretase by membrane targeting

beta-Secretase plays a critical role in beta-amyloid formation and thus provides a therapeutic target for Alzheimer's disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a beta-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active beta-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting beta-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.     

Protein adsorption on and swelling of polyelectrolyte brushes: A simultaneous ellipsometry-quartz crystal microbalance study

With a coupled spectroscopic ellipsometry-quartz crystal microbalance with dissipation (QCM-D) experimental setup, quantitative information can be obtained about the amount of buffer components (water molecules and ions) coupled to a poly(acrylic acid) (PAA) brush surface in swelling and protein adsorption processes. PAA Guiselin brushes with more than one anchoring point per single polymer chain were prepared. For the swollen brushes a high amount of buffer was found to be coupled to the brush-solution interface in addition to the content of buffer inside the brush layer. Upon adsorption of bovine serum albumin the further incorporation of buffer molecules into the protein-brush layer was monitored at overall electrostatic attractive conditions [below the protein isolectric poimt (IEP)] and electrostatic repulsive conditions (above the protein IEP), and the shear viscosity of the combined polymer-protein layer was evaluated from QCM-D data. For adsorption at the "wrong side" of the IEP an incorporation of excess buffer molecules was observed, indicating an adjustment of charges in the combined polymer-protein layer. Desorption of protein at pH 7.6 led to a very high stretching of the polymer-protein layer with additional incorporation of high amounts of buffer, reflecting the increase of negative charges on the protein molecules at this elevated pH.     

Simple linear relationship between dry matter,specific gravity,and tissue specific gravity in a diploid potato breeding population

Summary Two hundred clones were randomly selected in 1988 and in 1989 from a hybrid population ofSolanum phureja andSolanum stenotomum to determine the relationship between specific gravity (SG) and percent dry matter (%DM), and between tissue specific gravity (TSG) and %DM. The objectives were: (1) to determine the dry matter prediction equation for a diploid potato population, (2) to determine whether estimates of %DM and efficiency of selection for %DM could be improved by measuring TSG, and (3) to determine the influence of year on the estimates. In 1988 the prediction equation for the relationship between %DM and SG was %DM=198.71 (SG-191.30,r=0.85. Ranges and means for the variables were: (1) %DM: 16.99–32.67, mean 25.16; (2) SG: 1.054–1.122, mean 1.089. In 1989 the relationship of %DM and SG was predicted as %DM=194.46(SG)-187.53,r=0.87; whereas the relationship of %DM and TSG was predicted as %DM=196.77(TSG)-192.91,r=0.87. Ranges and means for the variables were: (1) %DM: 10.68–34.57, mean 21.32; (2) SG: 1.030–1.122, mean 1.074; (3) TSG: 1.046–1.141, mean 1.089. Slopes were not significantly different between any of the prediction equations, but intercepts were significantly different. Estimates of %DM were not improved by measuring TSG. Year did influence the relationship between %DM and SG.     

Evaluation of sodium percarbonate as a bath treatment for amoebic gill disease in Atlantic salmon

Amoebic gill disease (AGD), caused by Neoparamoeba perurans, is a major health challenge for Atlantic salmon aquaculture globally. While freshwater bathing for 2 hr is effective in reducing infection severity, there is need for more rapid and lower cost alternatives. To this end, a combination of sodium percarbonate (SPC) in freshwater was examined for its treatment efficacy. Initial in vitro studies showed a reduction in amoeba viability when exposed for 30 min to freshwater containing >500 mg/L SPC. Subsequently, AGD‐affected salmon were bathed for 30 min in 16°C freshwater containing 100, 500 or 1,000 mg/L SPC, or for 2 hr in 16°C freshwater to mimic industry practice. Treatment at the highest SPC concentration caused extensive gill damage and substantial mortality. Neither occurred to a significant extent at lower SPC concentrations. Gill pathology of surviving fish 10 days post‐treatment (dpt) was comparable to or more severe than pre‐treatment, and significantly (p < .001) more severe than in 2 hr freshwater bathed fish. N. perurans DNA was confirmed by qPCR in all treatment groups at 10 dpt. The data indicate that a 30‐min exposure to SPC in freshwater is not a suitable alternative to existing freshwater treatment of AGD.