Dissolved and colloidal phosphorus fluxes in forest ecosystems—an almost blind spot in ecosystem research

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L^?1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m^?2 a^?1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.     

Genetische Variabilität

Zusammenfassung Für die Pflanzenzüchtung ist die genetische Variabilität eine entscheidende Voraussetzung. Sie basiert auf Genmutationen, Chromosomenmutationen, Introgressionen, Autopolyploidie, Alloplasmie, transponiblen DNA-Elementen und der Kombination. Diese Variabilitätskomponenten werden charakterisiert. Außerdem wird anhand von Beispielen ihr Einfluß auf die Entwicklung der Kulturpflanzen demonstriert.Um effektiv in der Pflanzenzüchtung arbeiten zu können, bedarf es der Analyse von genetischer Variabilität. Dies geschieht mit Hilfe von Kreuzungsexperimenten und Parameterschätzungen. In zunehmendem Maße werden auch Marker bei der Analyse eingesetzt.Einen wichtigen Faktor zur zielgerichteten Beeinflussung der genetischen Variabilität stellt die Selektion dar. Sie führt zur Einschränkung der Kombination. Die Selektion ist für die Entwicklung von Sorten notwendig. Sie hat aber auch eine Verarmung an genetischer Information zur Folge.Für den weiteren Fortschritt in der Pflanzenzüchtung gilt es, eine genügende genetische Variabilität zu gewährleisten. Dazu bedarf es auch Maßnahmen zu ihrer Erhaltung. Genetische Variabilität muß außerdem verstärkt charakterisiert und analysiert werden.

---

Genetic variability

Summary Genetic variability is a decisive prerequisite to plant breeding. It is based on gene mutations, chromosome mutations, introgressions, autopolyploidy, alloplasmy, transposible DNA elements and recombinations. These components of the genetic variability are illustrated and examples are given to demonstrate their contributions to the evolution of crop plants.Effective plant breeding requires the analysis of the genetic variation. It is analysed by hereditary studies and parameter estimations. The utilization of markers is continuously increasing in studies of the genetic variation.Selection is an important factor to a purposive influence on the genetic variability and leads to a restriction of the recombinations. Selection is necessary for the development of varieties but results also in an impoverishment of genetic information.For the continuous progress in plant breeding an adequate genetic variability is to secure. That includes also activities to its conservation. Furthermore the characterization and analysis of the genetic variability has to be intensified.

---

. , , , , , . . , . , , . . . . . . , , . . . .

     

Die Typen der Ringfasziation und die Röhrenverbänderung beiPrimula

Zusammenfassung Zunächst werden die bisher bekannten Ringfasziationen in drei Gruppen eingeteilt, nämlich den Normal-Typus, auch Kanal- oderOenothera-Typus genannt, zu welchem der überwiegende Teil der Ringfasziationen gehört, der Trichter- oderPisum-Typus und schließlich der Röhren- oderPrimula-Typus. Ringfasziationen werden stets durch Invaginationen gebildet. Es werden Angaben zur Morphologie und vor allem zur Anatomie der röhrigen Fasziation vonPrimula malacoides gemacht. Der innere Leitbündelring hat keine Verbindung zum äußeren Leitbündelring und zum Wurzelsystem; beiPrimula hat das innere System jedoch Verbindung mit der Tracheidenplatte im Boden der Röhren.

---

The types of ring-fasciation and tube-fasciation inPrimula

Summary At first the ring fasciation as hitherto known are divided in three groups, namely the normal type, named also the channal- orOenothera-type, to which belong the prevailing parts of such fasciations, the funnal- orPisum-type and finally the tupe- orPrimula-type. Ring fasciations are always formed by invagination. It becomes some statements on morphology and above all on anatomy ofPrimula malacoides. The inner ring of leading elements has no joining to the outer ring of leading elements of the root system; inPrimula the inner ring however has joining with the plate of tracheids in the bottom of the tube.

---

Primula

: , Oenothera, ; Pisum , , Primula. . , , Primula malacoides. , , Primula

     

Probing high-barrier pathways of surface reactions by scanning tunneling microscopy

The ability of scanning tunneling microscopy to probe the pathways of thermally activated high-barrier surface processes is frequently limited by competing low-barrier processes that can confuse measurement of the true initial and final configuration. We introduce an approach to circumvent this difficulty by driving the surface process with nanosecond laser heating. The method is applied to determine the pathway of recombinative desorption in the H/Si(001) system. The observed configuration of dangling bonds after laser heating reveals that the desorbed hydrogen molecules are not formed on single dimers, but rather from neighboring silicon dimers via an interdimer reaction pathway.     

Einfluß der Fließstreckenlänge auf die Bodenumlagerung innerhalb einer erosionsgeschützten Kleinparzelle

Dependence of erosion from flow length within an erosion-protected plot On an Udalf derived from loess different micro-reliefs were formed to reduce erosion. Their effects on the spatial distribution of sand contents on bare soil after one vegetation period are described. At first erosion caused residuals of sand on unflooded areas and corresponding accumulation of finest material on flooded ones. Beds without flow barriers showed reduced clay and silt contents in the upper layer of about 2 mm. On beds with small dams there were no soil losses from the catchment areas between these flow barriers visible. Secondly the enriched sand was moved, too. This occured widely on flat beds. Within catchment areas there were only very small deposits of removed sand in front of the dams. In conclusion: Within the limits of a chosen risk, artificial microreliefs reduce completely erosion damages.     

Fenbendazole. I. Structure-activity relationships

Substitution of alkyl benzimidazol-2-ylcarbamates by phenoxy- or phenylthio-groups in the 5-position results in an increase in anthelmintic activity. The biological spectrum is altered by substitution of the phenyl ring. A sulphonic ester substituent in the 5-position of the benzimidazole nucleus also increases anthelmintic activity.     

Influence of mechanical and thermal treatment of animal feed on the true digestibility of amino acids. 2. True digestibility of amino acids in treated horse beans]

Trials were performed to investigate in which way mechanical and/or thermal treatment of horse beans would have an effect on the harmful components that were shown to be present in horse beans. In the course of these trials amino acids from heat-treated horse beans (variety Fribo) were analyzed for their true digestibility. Apart from heat-treated horse beans the investigation included undecorticated and decorticated beans and a mixture of horse beans with spring barley.