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Direct atom-resolved imaging of oxides and their grain boundaries

Using high-resolution transmission electron microscopy, we obtained structure images of strontium titanate (SrTiO3) with a clearly resolved oxygen sublattice along different crystallographic directions in the bulklattice and for a Sigma3 tilt grain boundary. Comparison with image simulations showed that the grain boundary contains oxygen vacancies. Measurements of atom displacements near the grain boundary revealed close correspondence with theoretical calculations.     

Driving factors of temporal variation in agricultural soil respiration

Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO₂ budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO₂ m^–2 h^–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO₂ m^–2 day^–1, while values below 300 mg CO₂ m^–2 day^–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO₂ g^–1 dry weight h^–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q₁₀ values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q₁₀ values. Within the temperature interval between 20°C and 30°C, Q₁₀ values were around 2 while the Q₁₀ values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account.     

Silicon decreases the arsenic level in rice grain by limiting arsenite transport

Silicon (Si) reduces arsenic (As) levels in rice shoot and grain. However, the underlying mechanisms remain unclear. In this study, we examined the effect of Si application to three rice paddy soils on the dynamics of Si, iron (Fe), phosphorus (P), and As in the soil solution, As accumulation in rice straw, flag leaf, husk, brown rice, and polished rice, and on As speciation in polished rice. Silicon application to soil increased the concentrations of Si, Fe, As, and P in the soil solution, while the redox potential was unaffected. Arsenic concentrations of straw, flag leaf, and husk were reduced by half by Si application, while As concentrations of brown and polished rice were decreased by 22%. The main As species in polished rice was arsenite, As(III), with a fraction of 70%, followed by dimethylarsinic acid (DMA) and arsenate, As(V), with 24% and 6%, respectively. Silicon application to the soil did not affect DMA or As(V) concentration of polished rice, while the As(III) concentration was reduced by 33%. These results confirm that Si reduces As(III) uptake and translocation into the shoot. Furthermore, data indicate that decrease of As concentration of polished rice is due to decreased As(III) transport into grain. Possible underlying mechanisms are discussed.     

Separation of metallic from semiconducting single-walled carbon nanotubes

We have developed a method to separate metallic from semiconducting single-walled carbon nanotubes from suspension using alternating current dielectrophoresis. Our method takes advantage of the difference of the relative dielectric constants of the two species with respect to the solvent, resulting in an opposite movement of metallic and semiconducting tubes along the electric field gradient. Metallic tubes are attracted toward a microelectrode array, leaving semiconducting tubes in the solvent. Proof of the effectiveness of separation is given by a comparative Raman spectroscopy study on the dielectrophoretically deposited tubes and on a reference sample.     

Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.     

Forage legumes for future dry climates: Lower relative biomass losses of minor forage legumes compared to Trifolium repens under conditions of periodic drought stress

Dairy livestock production systems rely on high‐quality forage legumes, which are widely present in grassland swards all over Europe. A future climatic scenario with higher average annual temperatures and lower precipitation is expected to affect grassland productivity in general and the productivity of the most important forage legume species Trifolium repens in particular. One way to cope with such constraints is the adoption of currently underutilized minor legume species with a higher tolerance towards drought stress. Therefore, the present study investigated legume species with lower moisture requirements than T. repens, these are Lotus corniculatus, Medicago falcata, Medicago lupulina and Onobrychis viciifolia in comparison with T. repens. Legumes were grown in containers as monocultures in a roofed open‐sided greenhouse under conditions of optimal water supply or periodic drought stress. Generally, drought stress decreased the biomass production, but species differed in their reaction. Particularly, M. lupulina and L. corniculatus had lower relative biomass losses (?26%) compared to T. repens (?43%, as averaged over drought stress periods). However, in overall biomass production T. repens still was at one level with M. lupulina and L. corniculatus under drought stress. This was related to high stomata control as indicated by the intrinsic water‐use efficiency. We conclude that there are promising future options of forage legumes as alternatives to T. repens.