Bodenkennwerte und Ertrage von Nährstoffmangelvarianten und nach temporärer düngung von Mangelvarianten im Thyrower Statischen Nährstoffmangelversuch

Langjährig unterlassene Kalkung führte bei mineralisch (NPK) und mit Stallmist gedüngtem Boden in den letzten 20 Versuchsjahren zu pH‐Werten von 4,2 bis 3,6. Die Relativerträge nahmen im Vergleich zur mineralischen Volldüngung (NPKCa) ab. Diese Abnahme war von der Pflanzenart abhängig und bei Sommergerste deutlicher als bei Kartoffeln und Mais. Kalkung des mit NPK gedüngten Bodens erhöhte die Erträge bei Mais bereits im ersten Jahr, bei Gerste und Kartoffeln erst nach mehreren Jahren auf das Niveau der Vergleichsvariante. Bei einer Umstellung von Stallmist auf Stallmist + NPKCa glichen sich die Erträge von Mais und Sommergerste im gleichen Jahr, bei Kartoffeln erst nach mehreren Jahren dem langjährig mit Stallmist + NPKCa gedüngten Prüfglied an.

Im langjährig ungedüngten Boden fielen pH‐Wert, K_DL und P_DL in den letzten 20 Versuchsjahren ebenfalls deutlich ab (pH 3,6 bis 4,1; K_DL 2,2 bis 5,0 und P_DL 3,5 bis 5,5 mg/100 g Boden). In deren Folge und durch N‐Mangel kam es bei Gerste zum Totalausfall und bei Mais nahezu zum Totalausfall. Bei Kartoffeln lag der Ertrag noch bei 15% der Vergleichsvariante NPKCa. Eine Düngung der Mangelparzellen mit NPKCa ließ den pH‐Wert bereits im ersten Jahr, K_DL und P_DL erst nach mehrmaliger Düngung in den anzustrebenden Bereich ansteigen. Eine Angleichung der Erträge an die Erträge des durchgehend mit NPKCa gedüngten Prüfgliedes dauerte drei bis vier Jahre.     

Suitability of plant physiological methods to estimate the transpiration of agricultural crops

Transpiration is the main part of the water balance in the system soil-plant during the vegetation period. Its determination or calculation is essential for modeling of soil moisture content or solute transport. Transpiration is difficult to quantify because it is influenced by the atmosphere, the soil, and the plants. This paper describes the potential and limitations of plant physiological methods (sap flow, gas exchange, leaf water potential) to estimate the transpiration. A weighable lysimeter was used as reference method. Results are shown for corn [Zea mays L.] and rape [Brassica napus L.]) for the years 1998 and 1999. At days without rain the diurnal transpiration rates, determined by the plant physiological methods and by the lysimeter differ by less than 12%. The results demonstrate that the plant physiological methods applied are important for an understanding of the complex transpiration process. Limitations lie in the difficulties in up-scaling, and the impossibility of measurements of the absolute actual transpiration rates of agricultural crops for longer periods like months or years.     

N-(pyrid-3-yl)thioureas and derivatives as acaricides. II. Quantitative structure-activity relationships and chemodynamic behaviour

The biological activity of a series of N-(pyrid-3-yl)thioureas and -carbodiimides, analogues of the insecticide/acaricide diafenthiuron, towards the carmine spider mite (Tetranychus cinnabarinus Boisd.) and the two-spotted spider mite (T. urticae Koch) was analysed using QSAR methodology. A canonical correlation analysis allowed for the establishment of a prediction model and the identification of outliers within that model. The chemodynamic behaviour of certain compounds in the two series, including these outliers, determined by using photochemical experiments in the laboratory as well as in the glasshouse, was shown to be responsible for anomalous results obtained in the biological tests. It was found from the above study that the biological activity towards both spider mite species is extremely sensitive to the kinetics of formation of the carbodiimides from the corresponding thioureas and to the photostability of the former. The results obtained with a thiourea which underwent no appreciable photochemical transformation into the corresponding carbodiimide supported the hypothesis that the thioureas are also in-vivo propesticides of the acaricidal carbodiimides.     

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Ohne Zusammenfassung     

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba)

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.     

The herbicide binding niche of photosystem II-a model

The Q_B binding niche of photosystem II is also the binding site for many different herbicides. In order to understand the mode of binding of the herbicides, a 3-dimensional model of the binding niche was constructed. The model was based upon a comparison of the known structure of the Q_B binding niche in purple bacteria with sequence and mutant data of the D-1 protein of photosystem II. Plastoquinone builds up hydrogen bonds to phenylalanine 265 backbone amide nitrogen, to serine 264 hydroxyl, and to histidine 215 delta-1 nitrogen. In addition to these hydrogen bond donors and acceptors, herbicides can build up hydrogen bonds to backbone carbonyl of alamine 263 and to serine 268 hydroxyl. This is supported by binding data of inhibitors in Chlamydomonas reinhardtii chloroplasts of wild type and of five D-1 protein mutants (Ser264 Ala, Ala251 Val, Phe255Tyr, Val2191le, Leu275Phe).