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.

A review of the usefulness of relative bulk density values in studies of soil structure and compaction

Abstract: The state of compactness is an important soil structure and quality attribute, and there is a need to find a parameter for its characterization that gives directly comparable values for all soils The use of some relative bulk density value for this purpose, particularly the degree of compactness (Hakansson, 1990), is discussed in this review The degree of compactness has been defined as the dry bulk density of a soil as a percent of a reference bulk density obtained by a standardized uniaxial compression test on large samples at a stress of 200 kPa The bulk density should be determined at standardized moisture conditions, to prevent problems caused by water content variations in swelling/shrinking soils The degree of compactness (D) makes results of soil compaction experiments more generally applicable Whereas the bulk density or porosity optimal for crop growth vary greatly between soils, the optimal D-value is virtually independent of soil composition Critical limits of penetration resistance (3 MPa) and air-filled porosity (10%, v/v) are similarly related to the D-value and matric water tension in most soils As the D-value increases above the optimal, the tension range offering non-limiting conditions becomes increasingly limited The D-value of the plough layer induced by a given number of passes by a certain vehicle is similar in all soils, provided the moisture conditions are comparable The degree of compactness facilitates modelling of soil and crop responses to machinery traffic Although this parameter was primarily introduced for use in annually disturbed soil layers, its use may be extended to undisturbed soil layers

Stoichiometry and Nutrition of Plant Growth in Natural Communities

Abstract: Stoichiometric relations in plants, with emphasis on C:N:P, are reviewed. Both theoretically and empirically it is found for whole plants as well as for different tissues that nitrogen concentrations increase slower than phosphorus concentrations. A lack of data prevents the establishment of relations between nitrogen and other elements. Optimal element ratios where elements are simultaneously limiting growth can be established. There is a considerable variability around these optimal ratios in observed values. Conclusions about the ecological significance of stoichiometric relations based on these observations may therefore be biased. The significance of this variability remains to be established.

Linking photoreceptor excitation to changes in plant architecture

Abstract: Plants sense neighbor proximity as a decrease in the ratio of red to far-red light, which triggers a series of developmental responses. In Arabidopsis, phytochrome B (PHYB) is the major sensor of shade, but PHYB excitation has not been linked directly to a growth response. We show that the basic helix-loop-helix (bHLH) transcription factor PIF7 (phytochrome-interacting factor 7), an interactor of PHYB, accumulates in its dephosphorylated form in shade, allowing it to bind auxin biosynthetic genes and increase their expression. New auxin synthesized through a PIF7-regulated pathway is required for shade-induced growth, linking directly the perception of a light quality signal to a rapid growth response.

Mechanism of the anticoagulant action of heparin

Abstract: The anticoagulant effect of heparin, a sulfated glycosaminoglycan produced by mast cells, requires the participation of the plasma protease inhibitor antithrombin, also called heparin cofactor. Antithrombin inhibits coagulation proteases by forming equimolar, stable complexes with the enzymes. The formation of these complexes involves the attack by the enzyme of a specific Arg-Ser bond in the carboxy-terminal region of the inhibitor. The complexes so formed are not dissociated by denaturing solvents, which indicates that a covalent bond may contribute to their stability. This bond may be an acyl bond between the active-site serine of the enzyme and the arginine of the cleaved reactive bond of the inhibitor. However, the native complexes dissociate slowly at near-neutral pH into free enzyme and a modified inhibitor, cleaved at the reactive bond. So, antithrombin apparently functions as a pseudo-substrate that traps the enzyme in a kinetically stable complex.