Swedish University of Agricultural Sciences

About: Swedish University of Agricultural Sciences is a education organization based out in Uppsala, Sweden. It is known for research contribution in the topics: Population & Soil water. The organization has 13510 authors who have published 35241 publications receiving 1414458 citations. The organization is also known as: Sveriges Lantbruksuniversitet & SLU.

Developmental pathway of somatic embryogenesis in Picea abies as revealed by time-lapse tracking.

Abstract: Several coniferous species can be propagated via somatic embryogenesis. This is a useful method for clonal propagation, but it can also be used for studying how embryo development is regulated in conifers. However, in conifers it is not known to what extent somatic and zygotic embryos develop similarly, because there has been little research on the origin and development of somatic embryos. A time-lapse tracking technique has been set up, and the development of more than 2000 single cells and few-celled aggregates isolated from embryogenic suspension cultures of Norway spruce (Picea abies L. Karst.) and embedded in thin layers of agarose has been traced. Experiments have shown that somatic embryos develop from proembryogenic masses which pass through a series of three characteristic stages distinguished by cellular organization and cell number (stages I, II and III) to transdifferentiate to somatic embryos. Microscopic inspection of different types of structures has revealed that proembryogenic masses are characterized by high interclonal variation of shape and cellular constitution. In contrast, somatic embryos are morphologically conservative structures, possessing a distinct protoderm-like cell layer as well as embryonal tube cells and suspensor. The lack of staining of the arabinogalactan protein epitope recognized by the monoclonal antibody JIM13 was shown to be an efficient marker for distinguishing proembryogenic masses from somatic embryos. The vast majority of cells in proembryogenic masses expressed this epitope and none of cells in the early somatic embryos. The conditions that promote cell proliferation (i.e. the presence of exogenous auxin and cytokinin), inhibit somatic embryo formation; instead, continuous multiplication of stage I proembryogenic masses by unequal division of embryogenic cells with dense cytoplasm is the prevailing process. Once somatic embryos have formed, their further development to mature forms requires abscisic acid and shares a common histodifferentiation pattern with zygotic embryos. Although the earliest stages of somatic embryo development comparable to proembryogeny could not be characterized, the subsequent developmental processes correspond closely to what occurs in the course of early and late zygotic embryogeny. A model for somatic embryogenesis pathways in Picea abies is presented.

Microbial biomass and activities in soil as affected by frozen and cold storage

Abstract: When monitoring microbial biomass and activities in soil, the storage conditions of the soil samples prior to analysis may be decisive for the results. Studies made on freshly collected soils are generally preferred but these are not always possible for practical reasons, since sampling is often restricted to short periods of the year, e.g. due to climatic conditions. The most commonly used methods to store soils for microbiological analyses are refrigeration or freezing of field moist soil. There are, however, studies that warn against any kind of storage, although other studies do not indicate any drawbacks to it. We have compared the microbial biomass and activities in 12 different, annually frozen, agricultural mineral soils when fresh and when stored at +2±2°C and at −20±2°C for 1 d and for 1, 3, 6 and 13 months. The results showed that the effects of freezing generally were smaller than those of refrigeration. The biomass estimated by chloroform fumigation–extraction and biomass index estimated by substrate induced respiration differed in that chloroform fumigation extracted carbon had decreased with 27% after 3 months at +2°C, while substrate induced respiration showed only small deviations from the results from fresh soils. Basal respiration rate and potential denitrification activity showed a similar pattern, with a pronounced decrease in values for refrigerated soils. The nitrogen mineralisation capacity was the only measure that was greatly influenced by freezing. After 6 months N mineralisation in the frozen soils was 25% higher than that of the fresh soils. Potential ammonium oxidation and the degradation rate of the herbicide linuron were affected only a little or not at all by storage for 13 months. We concluded that storage at −20°C for 13 months does not affect the microflora in annually frozen soils in any decisive way. We have also discussed the possible reasons for the contradictory results between different studies made on storage effects.

Predators or prey? Spatio-temporal discrimination of human-derived risk by brown bears

Abstract: Prey usually adjust anti-predator behavior to subtle variations in perceived risk. However, it is not clear whether adult large carnivores that are virtually free of natural predation adjust their behavior to subtle variations in human-derived risk, even when living in human-dominated landscapes. As a model, we studied resting-site selection by a large carnivore, the brown bear (Ursus arctos), under different spatial and temporal levels of human activity. We quantified horizontal and canopy cover at 440 bear beds and 439 random sites at different distances from human settlements, seasons, and times of the day. We hypothesized that beds would be more concealed than random sites and that beds would be more concealed in relation to human-derived risk. Although human densities in Scandinavia are the lowest within bear ranges in Western Europe, we found an effect of human activity; bears chose beds with higher horizontal and canopy cover during the day (0700-1900 hours), especially when resting closer to human settlements, than at night (2200-0600 hours). In summer/fall (the berry season), with more intensive and dispersed human activity, including hunting, bears rested further from human settlements during the day than in spring (pre-berry season). Additionally, day beds in the summer/fall were the most concealed. Large carnivores often avoid humans at a landscape scale, but total avoidance in human-dominated areas is not possible. Apparently, bears adjust their behavior to avoid human encounters, which resembles the way prey avoid their predators. Bears responded to fine-scale variations in human-derived risk, both on a seasonal and a daily basis.

Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model

Abstract: . The riparian zone, the last few metres of soil through which water flows before entering a gaining stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis in the representation of hyporheic, riparian, and hillslope processes.

Muscle histochemical and biochemical properties in relation to meat quality during selection for increased lean tissue growth rate in pigs.

Abstract: The relationship between the histochemical and biochemical properties of muscle and the quality of meat during selection to improving the lean tissue growth rate was studied. Pigs (n = 82) from Generations 2 and 4 were randomly sampled in a selection experiment in which the genotype x protein interaction was studied. Comparisons were made of longissimus muscle (LM) and quadriceps femoris (QF) from Generations 2 and 4, and biceps femoris (BF) in the fourth generation from pigs fed a low- or high-protein diet. A higher total growth rate, lean tissue growth rate, and lean percentage were found in pigs fed the high-protein diet than in pigs fed the low-protein diet. Pigs fed the high-protein diet had a higher glycolytic capacity in all muscles than pigs fed the low-protein diet. When the meat quality traits were compared, pigs fed the high-protein diet had a lower intramuscular fat content, higher shear force value, higher protein extractability, lower light reflectance, and somewhat higher water-holding capacity. With selection, pigs became fatter on both diets. In Generation 4, glycolytic and oxidative capacity was somewhat higher in muscle tissue than in Generation 2. Muscle metabolic profile and meat quality traits differed among muscles (LM, BF, QF) but no pronounced differences were found between generations. No marked changes were observed in Type I, IIA, or IIB fibers, either between diets or between generations. The Type IIC fibers could only be identified in Generation 4.