ALBERT

Notes: Zusammenfassung. Auf einem stark verunkrauteten Feld (guter Lehmboden] wurde die Veränderung der Unkrautflora im Verlauf von 3 Jahren bei verschiedenartiger Unkrautbekämpfung (keine Unkrautbekämpfung; zweimal Blindeggen sowie Eggen im 3-Blattstadium des Getreides; chemische Unkrautbekämpfung mit DNOC) beobachtet In diesem Zeitraum ging die Gesamtverunkrautung als Folge des guten Getreidestandes auch in den Parzellen ohne Unkrautbekämpfung erheblich zurück.Durch jährlich wiederholte, intensive mechanische Unkrautbekämpfung wurde im Verlauf von 3 Vegetationsperioden die Gesamtverunkrautung gegenüber der Kontrolle etwas, der Bestand einzelner Unkrautarten wie Alopecunus myosuroides, Sinapis arvensis und Galeopsis tetrahit erheblich vermindert. Der prozentuale Anteil der grasartigen Unkräuter an der Gesamtverunkrautung entsprach bei Versuchsende dem der unbearbeiteten Parzellen.Durch chemische Bekämpfung mit DNOC wurden im Vergleich zur unbehandelten Kontrolle Sinapis arvensis, Palygonum convolvulus, Galium aparine und die Gesamtverunkrautung stark reduziert, Alopecurus myosuroides dagegen stark gefördert. Das Artenverhältnis änderte sich zugunsten der grasartigen Unkräuter.Some observations on changes in weed populations under continuous cereal cropping and with différent methods of weed control

Notes: Summary. Pot experiments on the competitive effects of charlock (Sinapis arvensis L.) on oats and wild oat (Avena fatua L.) on barley had the following results:(1) During the period up to tillering there was an appreciable effect of the weeds on crop growth with depression in plant weight of 10–15% from that in the absence of weeds.(2) The greatest competitive effect occurred up to the middle of shooting of the cereals, when there were depressions in plant weight of 25–32%.(3) After this stage, the competitive effects of the weeds were much less in pots with a high nutrient level, and at low nutrient level there was almost no competitive effect.(4) The reduction in growth at the time of weeding was somewhat less at the low nutrient level than at the high nutrient level, and it is concluded that at the high level the competitive ability of the weeds was favoured more than that of the cereal crops.(5) The cereals were not able to overcome the initial damage caused by the weeds even when the weeds were removed at the beginning of tillering. A partial recovery did how ever occur at the high but not at the low nutrient level.(6) Both combinations, oats with charlock and barley with wild oat, behaved similarly, but some differences could be observed. Compétition entre plantes cultivées et mauvaises herbes II. Action des mauvaises herbes annuelles sur les céréales

Notes: Abstract. With the aid of specifically designed potometer experiments, it is shown that, after ozone fumigation, twigs transpiring in gas exchange chambers show poor water balance in decreasing humidity. The quotient of water uptake to water loss never falls below 0.9 in healthy material because of the control capacity of the stomata. In twigs from a tree fumigated with ozone irregular and delayed stomatal closure results in values of 〈 0.5 or even lower, depending on the degree of damage. As a result, in dry air, the transpiration rates of fumigated twigs often fall far below those of the control material, even if they were higher than the latter in humid air. In analogous experiments, the difference in behaviour between twigs of densely (‘healthy’) and sparsely needled (‘damaged’) trees from the natural stand is comparable to the difference between controls and ozone-fumigated trees in most respects. In soil that is more or less dried out and after the best possible saturation of the twigs during the night, the transpiration rates of fumigated trees increase fairly strongly in the humid chamber air at dawn, but finally decrease more or less suddenly to lower values than in the controls. The results are placed in the context of the basic research on plant water relations and compared with histological changes in the stomatal apparatus after a period of fumigation as described earlier. Therefore, long-term effects of pollution can be explained as a specific distrubance of hydroregulation.

Notes: Seasonal changes of some water relations parameters of Norway spruce shoots (Picea abies [L.] Karst.) were studied during two experiments using the pressure-volume analysis. For each experiment only shoots of a single tree were used.During the first study, the course of the turgor loss point (as bulk osmotic pressure when turgor first reaches zero, πp) of shoots developed in late 1986 vegetation period, were measured in 1987. The turgor loss point decreased temporarily from –2.5 MPa at the beginning of the year to –3.3 MPa at the end of March, but then increased to the original level for the rest of the year.During the second study, water relations parameters were measured in late summer 1987 and in late winter 1988. Winter shoots at full water saturation contained up to 20% less water than in late summer. Accordingly, the bulk osmotic pressure at full water saturation (πp) decreased from –1.7 MPa in late summer to –1.9 MPa in winter, πp decreased also from –2.2 MPa to –2.8 MPa. However, the amount of osmotically active substances (mOsmol, N) remained unchanged. The relative amount of apoplastic water in the total shoot water content appeared to drop insignificantly from 17% to 15%.The results show that the decrease in πo and πp in late winter is not due to an accumulation of osmotically active substances in the vacuoles but is due to a decrease in tissue water content. The temporary reduction of the symplastic volume by deposition of osmotically inert substances seems to be the most probable cause of this phenomenon.

Notes: Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce (Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (Wan) as well as in the defoliated shoots (Was). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (πon and πos) was determined. The dependence of the bulk-averaged turgor pressure (Pt) on the water content and the relationship between the bulk modulus of elasticity of the needles (ɛn) and the bulk-averaged needle turgor pressure (Ptn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988.The proportion of Wan in the total needle water content (Wtn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of Was in Wts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of Wan in the total water content of the shoots (Wt) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (πos) were –1.5 MPa and –1.7 MPa. Thus πon was 0.1 MPa lower and πos 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (πo).The relation between bulk-averaged turgor pressure and water content showed that during water loss Ptn dropped more rapidly than the turgor pressure of defoliated shoots (Pts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between Ptn and Pts. The flat course of Pts seems to be the main reason for the often observed “plateau” of ψ-isotherms of whole shoots near full turgor.

Notes: Summary. Experiments were conducted between 1985 and 1988 to evaluate the effect of duration and time of solarization on the control of two broom rapes (Orobanche aegyptiaca Pers., O. crenata Forsk.) and other weeds common in the fields of faba bean (Vicia faba L.) and lentil (Lens culinaris Medik.) in West Asia. Solarization was performed by applying clear polyethylene sheet to the soil for 0, 10, 20, or 40 days in 1985/86, 0, 30, or 40 days in 1986/87 and 0, 20, 30, 40 or 50 days in 1987/88 during the hot season (July and August) and for 50 days immediately before sowing during milder weather (September and October) in 1986/87. Best control was obtained with solarization for 30–50 days in the hot season. Maximum soil temperature under polyethylene at 5 cm was 55°C in 1985, 48°C in 1986 and 57°C in 1987. Broomrape dry weight decreased in the first experiment by more than 90% in both faba bean and lentil fields. Solarization controlled broom-rape and other weeds in the following two seasons when the soil was left undisturbed during the season of the treatment.

Notes: Für die 6 untersuchten tropischen Segetalarten Ageratum conyzoides, Blechum brownei, Crassocephalum crepidioides, Mikania micrantha, Paspalum conjugatum und P. paniculatum lag die untere Temperaturgrenze bei der Keimung im Bereich von 10 bis 15(20)°C, die maximale bei ≤ 40°C, das Optimum zwischen 20 und 35°C. Ageratum conyzoides und C. crepidioides hatten etwas geringere Ansprüche an die Keimtemperatur als die übrigen Arten, was ihre vergleichsweise stärkere Verbreitung in Höhenlagen erklärt. Die Keim-temperaturen der beiden Vertreter aus den gemässigten Breiten, Alopecurus myosuroides und Chenopodium album, lagen bei 5 (Minimum), 15–25 (Optimum) bzw. 40°C (Maximum). Die Keimung von A. conyzoides, C. crepidioides und M. micrantha wurde bereits ab einem osmotischen Potential von - 1 bar negativ beeinflusst. Bei - 4,7 bar keimte von den 6 tropischen Arten nur noch P. paniculatum in geringem Umfang, während AL myosuroides und Ch. album bis -4,7 bar nicht beeinträchtigt wurden. Nach einjähriger trockener Lagerung keimten alle 6 tropischen Arten nur unter Lichteinfluss. Nach 20 Monaten keimten C. crepidioides und P. paniculatum auch in Dunkeln.

Notes: Bei Flughafer wurde der Emfluß verschiedener Applikationsorte zwischen Spitze und Basis des Sprosses auf die Penetration und Translokation von 14C-Diclofop-methyl untersucht. Die Penetration liegt an der Basis der Blattspreitc am 1. Blatt um 64% und am 2. Blatt um 95% höher als an der Spitze des jeweiligen Blattes. Die Translokation von 14C-Diclofop-mcthyl in basipeitaler Richtung ist begrenzt. Daher ist die Menge an 14C-Diclofop-methyl an der Sproßbasis, dem Hauptwirkort, um so höher, je näher das Herbizid zur Sproßhasis appliziert wird. Hinsichtlich einer möglichst optimalen Verteilung von 14C-Didofop-methyl in der Pflanze erwies sich die Applikation an die Basis del Blattsprciten als am günstigsten. Dies beruht u.a. darauf daß es bei diesem Applikationsort zu einem Einlaufen der Herbizidlösung in die Blattscheidc und infolgedessen zu einem mechanischen basipetalen Vordringen innerhalb dieser in den Bereich der mcristematischen Gewehe der Sproßbasis kommt. Als Konsequenz daraus ergibt sich die Forderung nach einer möglichst gezielten Deponierung von Diclofop-methyl in den Bereich der Sproßbasis.