Rhizome development ofPhragmites australis in a reed community

Variations in the height, shoot density, biomasses of above- and below-ground parts and rhizome distributions ofPhragmites australis were investigated along a line-transect in a reed community at Yufutsu Mire, Hokkaido. Relationships of performance of the reed plants to soil conditions and species compositions were also examined. Three types of rhizome development were recognized in reed plants; (1) the central part of the reed community, characterized by well developed rhizomes and dense aerial shoots, (2) the intermediate part, characterized by development of rhizomes along both the peat and surface layers and very dense aerial shoots, and (3) the marginal part, characterized by development of rhizomes only along the peat layer and sparse aerial shoots. Observation showed that rhizomes in the surface layer actively produced aerial shoots, whereas rhizomes in the peat layer contributed to the spreading of their distribution range. With the growth of rhizomes, organic debris originating from dead rhizomes and roots accumulated in the mineral soil to promote organic soil formation. In dense parts of the reed stand, species composition was poor because of the shading and litter accumulation by reed plants. The effects of microtopography and water level on the establishment of reed seedlings were also considered.     

Growth and production ofPhragmites australis in Lake Vechten (the Netherlands)

Summary A study was carried out on several production characteristics ofPhragmites australis stands in Lake Vechten, the Netherlands. The aim was to quantify the role of this plant species in the lake's primary production and nutrient cycles (C, N and P).Maximum biomass values of 1247 and 286 g org.wt.m^–2 were measured in, respectively, shoots and underground organs in August. The shoot: root ratio was always>1. Plant litter accumulated particularly in spring and autumn. The relative growth rates of early shoots differed from those determined for the whole vegetation, indicating shoots of different ages in the latter. This was confirmed by counting the number of plants.The chemical composition of the plants changed with season. A carbon peak as high as 50.94% org.wt. was found in spring, which coincided with a nitrogen peak of 2.88% org. wt. At the end of the season N dissapeared faster from the shoots than C, whereas P declined from spring onwards.The production ofPhragmites contributed in 1979 for 5.8% to the lake's total primary production expressed in C, whereas the share of the total macrophytic unit amounted to 8.7%.The potential role ofPhragmites in the lake's nutrient cycles was largely due to nutrient leakage and decomposition.     

The density of stomata in leaves of different ecotypes ofPhragmites communis

In two investigated ecotypes ofPhragmites communis differences in the density and the total number of stomata in the leaves in sites with one ecotype only and in sites with both ecotypes were established. These characteristics did not differ significantly between the sites. The gradients of the density of stomata in successive leaves increased from the base to the apex of the shoot. The differences between the types are due to the high inserted leaves. The gradients were found in a leaf blade; their shape was influenced by the habitats.     

Factors affecting iron plaque on the roots ofPhragmites australis (Cav.) Trin. ex Steudel

Phragmites australis (the common reed) was collected at six sites in southern Québec and Ontario, Canada, in order to study the accumulation of iron plaque on the roots. The deposition of iron oxides on roots ofP. australis did not correlate directly with soil measurements; however, the amounts of iron-bound-to-carbonates fraction of the soil/sediment, responsible for the iron plaque accumulation, correlated with the % of water, % of organic matter, % of clay and pH of the substrate. Plants located very near flowing water accumulated more iron plaque on the roots than plants in other habitats through the summer; it is hypothesized that carbonates associated with iron come from the flowing water. In wetlands or sites near flowing water, most root iron was found on the surface, as iron plaque, while there was more iron inside the root in dry environments. Radial oxygen loss from the roots is probably the most important source of oxygen for the oxidation of iron.     

Verification of a mathematical growth model ofPhragmites australis using field data from two scottish lochs

A growth model ofPhragmites australis was verified using two independent sets of published field data. The model simulates the growth pattern of a well-established, monospecific stand ofP. australis in the absence of genetic diversity and environmental stresses of mainly nutrient and water deficiency. The model formulated using first order differential equations was combined with plant phenology and comprises five subroutines in which photosynthetically active radiation, shoot, root, rhizome and new rhizome biomass are calculated. Using the model, experimental results were reproduced within reasonable limits having concordance correlation coefficients of more than 0.75 for 70% of the output parameters, which was the main objective of the study. The modelled efficiencies of PAR were 7.15% and 3.09%, as opposed to 7.7% and 2.53% in experimental estimations, for Loch of Forfar and Loch of Balgavies, respectively. Production and seasonal fluxes of dry matter ofP. australis in Scottish lochs were estimated using the modelled quantities for the 1975 growing season in g m⁻². They showed that 31% and 37% of total net photosynthate translocated to rhizomes before shoot senescence began in Loch of Forfar and Loch of Balgavies, respectively. Also in both lochs approximately 45% of total downward translocation came from accumulated shoot dry matter during senescence, while the rest came from photosynthesis before the shoots started to senesce.     

Catalytic decomposition of cellulose under biological conditions

1. The catalytic decomposition of undegraded cellulose in the form of cotton fibres is described with hydrogen peroxide at 0·4–0·04% (w/v) concentration in the presence of ferrous salts at pH3–5. 2. Complete solubilization of 5mg. of cotton fibres occurred in about 7 days in the presence of 0·4% hydrogen peroxide and 0·2mm-ferrous sulphate at the optimum pH4·2–4·3. 3. With 0·4% hydrogen peroxide the most rapid decomposition of cellulose was confined to ferrous sulphate concentrations of approx. 2–0·02mm. If the concentrations of the reagents were decreased in proportion extensive breakdown occurred but much more slowly. 4. In the primary stages of breakdown cotton fibres were disintegrated to very short fibres. These were subsequently solubilized, but there was little accumulation of soluble material. Organic matter was lost from solution as the reaction progressed. 5. Other naturally occurring cellulose-containing materials, such as grass, straw, hay and sawdust, were also disintegrated and solubilized by hydrogen peroxide and ferrous sulphate.     

Probable effects of algal bloom on the growth ofPhragmites australis (Cav.) Trin. ex Steud.

The effects of blue-green algal blooms on an emergent reed plant,Phragmites australis (Cav.) Trin. ex Steud., were investigated in a eutrophic lake in central Japan. The plants showed conspicuous withering of bottom leaves in spring of 1982, after an early occurrence of the bloom. In June, the plants in the area of algal infestation had about half the shoot length and dry weight of normalP. australis without the algal infestation. Reductions in water transparency, dissolved oxygen in bottom water and redox potentials of surface soil corresponded to the presence of algal bloom and plant damage.     

Predatory behaviour ofScatophaga stercoraria under laboratory conditions

Laboratory experiments tested the effectiveness ofScatophaga stercoraria (L.) as a predator of various insect species. Photophases, ages and gender of predators and effects of dung presence on predation rates were compared for either sex using counts of prey cadavers, behavioral observations and oviposition rates. Males consistently killed more prey than females, but longer photophases did not significantly increase daily predation rates. Nine to 10-day-old flies approaching sexual maturity achieved highest predation rates. Dung was found to affect predatory behaviour but not cumulative predation. Predatory behaviour of sexually mature males was more affected than female behaviour by the presence of dung, whereas sexually immatures flies showed no response to dung presence. Preconditioning ofS. stercoraria adults using 3 prey species of different sizes did not affect the prey chosen in subsequent random choice experiments. Larger prey species such asMusca domestica (L.) orDelia antiqua (Meigen) were preferred toDrosophila sp. by both sexes ofS. stercoraria. This species may be a useful predator for future integrated pest management techniques in vegetable crops or control of house flies in barns.      

Hydrogen peroxide concentrations in leaves under natural conditions

While H2O2 has been implicated in numerous plant environmental responses, normal levels and variabilities are poorly established, and estimates of leaf tissue concentrations span more than three orders of magnitude, even in a single species under similar conditions. Here, leaf tissue H2O2 contents under natural conditions are reported after determining (i) that H2O2 in extracts was stable with time, (ii) that H2O2 added to the extract was recovered quantitatively, and (iii) that the H2O2 calibration curve was unaffected (or quantifiably affected) by the extract. The broad applicability of the protocol and variability in leaf concentrations were demonstrated using tissue collected from several habitats in association with three, more extensive, experiments. The first involved nychthemeral studies of the mangrove, Rhizophora mangle L. Lowest H2O2 levels occurred in the early morning and near sunset, with higher levels both at midday and at night. Second, using five temperate species in Spring, concentrations were compared on a warm, sunny day and a cool, cloudy day. Higher concentrations were found on the warm day for Aesculus glabra Willd., Glechoma hederacea L., Plantago major L., and Viola soraria Willd., while there were no differences in Quercus macrocarpa Michx. Finally, the effects of elevated CO2 and ozone were examined in soybean, Glycine max L. Pioneer 93B15 under Free Air gas Concentration Enrichment (FACE) conditions. Both supplements led to elevated H2O2. Overall, mean leaf, midday, and mid-summer H2O2 concentrations ranged from 0.67 micromol (gFW)(-1) in mangrove to 3.6 micromol (gFW)(-1) in A. glabra Willd. Greatest within-species differences were only 2.5-fold in any of the studies.     

Carbohydrate levels in rhizomes ofPhragmites australis at an oligotrophic and a eutrophic site: A preliminary study

Seasonal dynamics of total nonstructural carbohydrates (TNC) and of carbohydrate species (starch, sucrose, glucose, fructose) were followed in rhizomes ofPhragmites australis at two sites of the T?eboň Biosphere Reserve (Czech Republic): Branná sand pit and Ro?mberk fishpond-western shore, which were classified (according to plant species composition and phosphorus availability) as oligotrophic and hyper-eutrophic, respectively.Phragmites stands at these sites were expanding and retreating, respectively. Rhizomes were sampled within terrestrial parts of the reed stands (at a water depth of about 10 cm). The levels of total non-structural carbohydrates were determined mainly by levels of starch and sucrose, while glucose and fructose were present at comparatively low levels. The most conspicuous differences between the sites were associated with autumnal and March levels of carbohydrates. In March, i.e. at the beginning of vegetative development, TNC and starch levels were lower at the hyper-eutrophic, as compared with the oligotrophic, site. Starch and TNC levels fell from August to September at the hyper-eutrophic, but not at the oligotrophic, site. At the low water depth investigated, the differences between stands in carbohydrate levels do not seem to be large enough to account solely for their different vigour. It is suggested that the effect of water depth needs to be evaluated in more detail.     

Prey selection by Chaoborus punctipennis under laboratory conditions

Equal numbers of Diaphanosoma leuchtenbergianum, Daphnia parvula, and Diaptomus pallidus were offered to individual, fourth-instar larvae of Chaoborus punctipennis. When the prey species were presented separately to the larvae, 100% of the Diaphanosoma, 67% of the Daphnia, and 57% of the Diaptomus were consumed. However, when the three species were offered to the predator concurrently, 90% of the Diaphanosoma, 10% of the Daphnia and < 1% of the Diaptomus were eaten. This strong selection for Diaphanosoma was consistent at three prey densities.     

Practical aspects of fumonisin production under laboratory conditions

Studies were performed to develop an efficient method for fumonisin toxin production in sufficient quantities for animal toxicological experiments, on the basis of three earlier published fumonisin toxin production methods. Three absolutely necessary factors were taken into account and tested in a serial experiment. TheFusarium verticillioides strain MRC 826 was directly inoculated onto soaked, autoclaved, whole maize kernels (50 g/1.71 jar). The inoculation was performed by standard spore suspension (l×l0⁶/ml), a 5/2 surface/volume culture was prepared and incubated at 25 °C for 5 weeks. To maintain the optimal a_w of approximately 1.00, the evaporated water was re-filled weekly. A final concentration of 4454±1060.9 ppm fumonisin B₁ was reached, with good repeatability. In the laboratory practice, consistent production of constant amounts of FB₁ can be obtained by applying the above settings.     

Activity rhythms in littoral Acari under laboratory conditions

Under experimental conditions, endogenous activity rhythms were found among several species of the terrestrial moiety of the littoral Acari. These rhythms correlated with both circatidal (semidiurnal) and photoperiod/temperature (diurnal) cycles. In non-littoral species, only diurnal cycles were observed. Under similar experimental conditions, members of the aquatic moiety, i.e. the family Halacaridae, showed no activity cycles, and it is thought that in these mites activity may be exogenous. It is suggested that the possession of endogenous activity cycles among the terrestrial moiety is an adaptation to prevent inundation and dislodgement by wave action, and that the aquatic moiety, which are permanently immersed, require no such adaptation, and rely upon exogenously triggered activity patterns.     

Photoinhibition of photosynthesis in willow leaves under field conditions

Chlorophyll fluorescence of leaves of a willow (Salix sp.) stand grown in the field in northern Sweden was measured on several occasions during the growing season of 1987. For leaves that received mostly full daylight, the F _V/F _P ratio declined roughtly 15% in the afternoon on cloudless days in July (F _P is the fluorescence at the peak of the induction curve obtained at the prevailing air temperature after 45 min of dark adaptation, and F _V is variable fluoresence, F _V=F _P-F _O, where F _O is minimal fluorescence). There was no decrease in the F _V/F _P ratio on cloudy days, while the effect was intermediate on changeable days. In view of this light dependence, together with the fact that the decline in the F _V/F _P ratio was paralleled with an equal decline in the corresponding fluorescence ratio F _V/F _M at 77K, and a similar decline in the maximum quantum yield of O₂ evolution, it is suggested that the decline in the F _V/F _P ratio represents a damage in photosyntem II attributable to photoinhibition. Recovery of the F _V/F _P ratio in dim light following a decline on a cloudless day took 7–16 h to go to completion; the F _V/F _P ratio was fully restored the following morning. When all active leaves of a peripheral shoot were compared, the F _V/F _P ratio in the afternoon of a day of bright light varied greatly from leaf to leaf, though the majority of leaves showed a decline. This variation was matched by a pronounced variation in intercepted photon flux density. When leaves developed in the shade were exposed to full sunlight by trimming of the stand an increased sensitivity to photoinhibition was observed as compared to peripheral leaves. The present study indicates that peripheral willow shoots experienced in the order of 10–20% photoinhibition during an appreciable part of their life. This occurred even though the environmental conditions were within the optimal range of photosynthesis and growth.Abbreviations and symbols F _O minimum fluorescence - F _P fluorescence at the peak of the induction curve obtained at normal ambient temperatures - F _V variable fluorescence - F _M maximum fluorescence obtained at 77K - PPFD photosynthetic photon flux density     

Observations on the colonization of a young polder area in the netherlands with special reference to the clonal expansion ofPhragmites australis

In 1968, the polder Zuidelijk Flevoland was reclaimed in the Netherlands. Observations on species succession were made during a period of seven years in an area later known as the nature reserve Oostvaardersplassen. Directly after reclamation, a large number of plant species were recruited. Here, only the dynamics of the three dominant species will be discussed, i.e. the annual mudflat speciesSenecio congestus, and the long-lived emergent macrophytesTypha latifolia andPhragmites australis. Small differences in elevation had a large impact on seedling recruitment. Overall,S. congestus dominated in the first year after reclamation, andT. latifolia prevailed during the second and third year. Thereafter,P. australis became dominant, despite fewer seedlings. In the first three years after reclamation, clones ofP. australis grew very slowly, afterwards they showed a constant expansion rate of ca. 4 m/yr. However, close to pools waterfowl grazing slowed down the expansion of clones. The observed spatial and temporal variation in the colonization of this young polder area can be explained by species differences in life history traits, resource capture, as well as in the susceptibility to stem-boring insects and waterfowl grazing.     

Oviposition in Culicoides impunctatus under laboratory conditions

We present a laboratory-based examination of oviposition preference in the Scottish biting midge, Culicoides impunctatus (Diptera: Ceratopogonidae). A variety of oviposition substrates were screened in no-choice and choice bioassays for efficacy in eliciting an egg-laying response. Both upper-layer photosynthetic Sphagnum spp. moss and Juncus articulatus infusions were identified as producing increased oviposition under no-choice conditions. During choice trials against a control of damp cottonwool, upper-layer Sphagnum spp. moss produced a significantly greater egg-laying response. These conclusions are interpreted in terms of possible cues involved in oviposition site selection and assessed for future use in colonisation of this troublesome species.