Effects of agricultural management on Si cycling in Italian paddy fields

Silicon (Si) is a beneficial nutrient for rice plants; it improves their resistance against biotic and abiotic stresses. Recent research showed that Si availability in soils is, on a large geographic scale, determined by stocks of weatherable silicate minerals. However, also on the smaller regional scale, pronounced differences in Si uptake of rice plants were observed. The reasons for these differences are not yet clear. They might include effects of agricultural management, such as crop residue recycling and irrigation. Here, we test the long-term effects of four different agricultural management practices in Vercelli (Northwest Italy), where one rice crop per year is cultivated from May to September. The experimental platform was installed in 2003 on a Haplic Gleysol known to be under continuous rice cultivation for the last 30 years and having low plant-available Si concentration. The following management practices were considered (i) tillage and crop residue incorporation in spring (ii) post-harvest rice straw burning and tillage in spring, (iii) tillage and crop residue incorporation in autumn, and (iv) tillage and crop residue incorporation in spring followed by dry seeding and delayed flooding. After seven years, in 2010, topsoil and plants were sampled at five points of time during the cropping season. We will examine plant-available Si concentrations in soil and Si uptake by rice. Results will be presented at the conference; they will reveal whether farmers are able to actively improve Si supply to rice plants by their agricultural management

Testing hypotheses on interlinks between silicon and organic matter cycling in rice ecosystems

Recent studies demonstrated that sufficient Si supply enhances the resistance of rice plants against biotic and abiotic stresses. The mechanisms by which Si supports the stress resistance are still under debate. One hypothesis assumes that phytoliths exert similar eco-physiological functions as organic structural compounds. The formation of amorphous Si oxide bodies (`phytoliths`) within the plant tissue, therefore, represents an energy-saving alternative to synthesis of organic structural compounds, such as cellulose and lignin. Hence, Si availability may interact with the recycling of organic matter because rates of plant litter decomposition are regulated by contents of structural organic compounds. We currently test the hypothesis using a large set of rice straw samples collected at 70 paddy fields in Vietnam and the Philippines. Due to the differing portions of weatherable silicate minerals in soil, Si availability varies largely between the fields; the Si concentrations in the straw samples, thus, range from 1.6 to 10.7%. The Si concentrations are significantly negatively related to carbon concentrations, which range from 31.1 to 42.5% (the R2 of the linear relationship is 0.83). In turn, no relationships between Si and nitrogen concentrations were found. These findings support the assumption that Si substitutes N-poor structural compounds in rice plants. Currently, we apply cupric oxide oxidation analysis to the straw samples in order to test for relationships between concentrations Si and lignin. The results will be included into the proposed presentation

Информационная система образовательного отдела администрации города Юрги

Sintered targets of Al2O3 are removed by CO(2-) and excimer laser radiation and deposited as thin films onto steel and silicon substrates. Micro Raman spectroscopy and atomic force microscopy are used to characterize the morphological and structural properties of the films. Mechanical properties are investigated by nanoindentation measurements and a laser-acoustic method, optical properties are studied by ellipsometry. Al2O3 films deposited using CO2-laser radiation show an inhomogeneous surface structure with droplets embedded in a matrix, whereas the films deposited using excimer laser radiation are smooth, which is explained by different material removal mechanisms. The microhardness (i.e. ratio of indentation load to residual area of the indent) of the amorphous matrix structure is about 8 GPa, the crystalline droplets are softer at about 2 GPa. Varying the processing gas pressures in the range of 0.0 1 -0.6 mbar yields a change in the index of refraction of the films, which is clo se to the bulk value for gas pressures < 0.1 mbar. The decrease of the index of refraction is caused by a lowered film density, correlating with a lowered mean energy,of the particles impinging on the substrate, which is calculated. The results show the possibility of scaling-up the pulsed laser deposition process for industrial applications by use of C02-laser radiation

Complete nucleotide sequence and structural organization of pPB1, a small Lactobacillus plantarum cryptic plasmid that originated by modular exchange

A small cryptic plasmid designated pPB1 was isolated from Lactobacillus plantarum BIFI-38 and its complete 2899 bp nucleotide sequence was determined. Sequence analysis revealed four putative open reading frames. Based on sequence analysis two modules could be identified. First, the replication module consisted of a sequence coding for a replication protein (RepB) and its corresponding target site, and two putative repressor proteins (RepA and RepC). Sequence analysis indicated the possible synthesis of an antisense RNA that might regulate RepB production. A putative laggingstrand initiation site was also found, suggesting that pPB1 replicates via a rolling circle mechanism. The second module of pPB1 consisted of a sequence coding for a putative mobilization protein and its corresponding oriT site. Since the nucleotide sequence of the replication module showed 94.5% identity to the similar region on the Leuconostoc lactis plasmid pCI411, and the nucleotide sequence of the mobilization module had 97.5% identity to L. plantarum plasmid pLB4, it is concluded that pPB1 originated by modular exchange between two such plasmids by homologous recombination. Putative recombination sites where crossover might have taken place were also identifiedThis work was supported by Grant 07G/0035/2003 from the Comunidad de Madrid and RM03-002 from the Instituto Nacional de Investigación y Tecnologı´a Agraria y Alimentaria (INIA). We thank R. Gonza´lez and A.V. Carrascosa for their advice and critical reading of the manuscript. B. de las Rivas was a recipient of a postdoctoral fellowship and A. Marcobal of a predoctoral fellowship both from the Comunidad de Madrid.Peer reviewe

Температурные режимы работы твэлов реактора ИРТ-Т

Приведены результаты теплофизических расчетов активной зоны реактора ИРТ-Т. Показано, что при номинальной мощности реактора температурные режимы твэлов укладываются в предельные значения и соответствуют требованиям технического обоснования безопасности

Persistence of dissolved organic matter explained by molecular changes during its passage through soil

Dissolved organic matter affects fundamental biogeochemical processes in the soil such as nutrient cycling and organic matter storage. The current paradigm is that processing of dissolved organic matter converges to recalcitrant molecules (those that resist degradation) of low molecular mass and high molecular diversity through biotic and abiotic processes. Here we demonstrate that the molecular composition and properties of dissolved organic matter continuously change during soil passage and propose that this reflects a continual shifting of its sources. Using ultrahigh-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, we studied the molecular changes of dissolved organic matter from the soil surface to 60 cm depth in 20 temperate grassland communities in soil type Eutric Fluvisol. Applying a semi-quantitative approach, we observed that plant-derived molecules were first broken down into molecules containing a large proportion of low-molecular-mass compounds. These low-molecular-mass compounds became less abundant during soil passage, whereas larger molecules, depleted in plant-related ligno-cellulosic structures, became more abundant. These findings indicate that the small plant-derived molecules were preferentially consumed by microorganisms and transformed into larger microbial-derived molecules. This suggests that dissolved organic matter is not intrinsically recalcitrant but instead persists in soil as a result of simultaneous consumption, transformation and formation

No depth-dependence of fine root litter decomposition in temperate beech forest soils

Aims Subsoil organic carbon (OC) tends to be older and is presumed to be more stable than topsoil OC, but the reasons for this are not yet resolved. One hypothesis is that decomposition rates decrease with increasing soil depth. We tested whether decomposition rates of beech fine root litter varied with depth for a range of soils using a litterbag experiment in German beech forest plots. Methods In three study regions (Schorfheide-Chorin, Hainich-Dün and Schwäbische-Alb), we buried 432 litterbags containing 0.5 g of standardized beech root material (fine roots with a similar chemical composition collected from 2 year old Fagus sylvatica L. saplings, root diameter<2mm) at three different soil depths (5, 20 and 35 cm). The decomposition rates as well as the changes in the carbon (C) and nitrogen (N) concentrations of the decomposing fine root litter were determined at a 6 months interval during a 2 years field experiment. Results The amount of root litter remaining after 2 years of field incubation differed between the study regions (76 ± 2 % in Schorfheide-Chorin, 85 ± 2 % in Schwäbische-Alb, and 88±2 % in Hainich-Dün) but did not vary with soil depth. Conclusions Our results indicate that the initial fine root decomposition rates are more influenced by regional scale differences in environmental conditions including climate and soil parent material, than by changes in microbial activities with soil depth. Moreover, they suggest that a similar potential to decompose new resources in the form of root litter exists in both surface and deep soils