Flow variability maintains the structure and composition of in‐channel riparian vegetation

1. Naturally variable river flows are considered to be important for structuring riparian vegetation. However, while the importance of floods for the ecology of riparian vegetation is well recognised, much less is known about the importance of small fluctuations in river flows. 2. We investigated the effect of water supply diversion weirs on the riparian vegetation of upland streams. These weirs remove within‐channel fluctuations in flow but do not prevent large floods downstream. We surveyed the in‐channel and banktop vegetation of five streams, three of which were regulated by weirs and two of which acted as controls. 3. Unexpectedly, we observed greater species richness within the channel downstream of the weirs. This was because of increased numbers of exotic and terrestrial (‘dry’) plant species. Grass cover was also greater downstream of the weirs. There were no significant differences in the banktop vegetation between the upstream and downstream sites of the regulated streams. 4. Our results highlight the role of within‐channel flow variability in maintaining the composition of vegetation within the stream channel. We suggest that greater species richness does not necessarily indicate a less‐disturbed environment. Rather, a greater number of ‘dry’ species is indicative of the impacts of flow regulation. 5. Small fluctuations in river flows are probably necessary to protect the ecosystem structure and function of regulated streams. It is recommended that variable within‐channel flows be provided in regulated streams.     

Ceratophyllum demersum hampers phytoplankton development in some small Norwegian lakes over a wide range of phosphorus concentrations and geographical latitude

1. Data on submerged and floating-leafed macrophytes, phytoplankton, nutrients (N, P) and calcium were collected from twenty-four small lakes ( 1 km²) over a wide range of latitudes in Norway. The majority of the investigated lakes were mesotrophic or eutrophic, and most of the lakes were markedly affected by diffuse and point-source runoff from agriculture. According to their macrophyte species composition, the majority of the lakes can be classified as Potamogeton lakes or Chara lakes, or a combination of these.
2. This study is consistent with the 'two alternative stable states' hypothesis. We observed clearwater lakes with dense macrophyte cover over a wider range of total P concentration than has been reported previously: from 30 to more than 700 mg P m^–3. The clearwater state was only observed in lakes with mean depths of less than 1.9 m.
3. Most clear lakes with high cover of submerged vegetation showed indications of N limitation.
4. In this study nearly all the macrophyte-dominated lakes with P concentrations above 30 mg m^–3 had dense stands of Ceratophyllum demersum (L.). This indicates that Ceratophyllum may also play an important role in stabilizing and maintaining a clearwater state at high P concentrations.     

Absolutes und relatives Wachstum bei Ammonoideen

The following basic growth parameters of the ammonoid shell are analysed: radius of the coiling spiral; whorl width; plane of cross-section; umbilical spiral. The absolute growth of these parameters follows a general growth formula which is based on the probability theory (time-dependent stochastic processes). The in crease of all basic parameters is ruled by analogous formulas which are derived from the general growth formula; the increase of the coiling spiral results in the geometrical figure of a logarithmic spiral, because this is the only one that meets the conditions of the general growth formula. The relative growth can be described as a morphogenetic program that is subdivided in presumably three formally connected subprograms. Each subprogram is defined by specific allometry and integration constants.
Folgende Grundparameter des Wachstums von Ammonoideen-Gehäusen werden analysiert: Radius der äuβeren Spirale, Windungsbreite, Querschnittsfläche, Nabelspirale. Das absolute Wachstum dieser Parameter folgt einer allgemeinen Wachstumsformel, die sich aus der Wahrscheinlichkeitstheorie (zeitabhängige stochastische Prozesse) ergibt. Die Zunahme aller Grundparameter folgt analogen Formeln, die sich aus der allgemeinen Wachstumsformel ableiten lassen; das Anwachsen des äuβeren RadiS führt zur geometrischen Figur einer logarith-mischen Spirale, da nur diese der allgemeinen Wachstumsformel genügt. Das relative Wachstum läβt sich als ein morphogenetisches Wachstumsprogramm beschreiben, das sich in vermutlich drei formal miteinander verknüpfte Unter-programme aufteilt. Jedes Unterprogramm ist durch spezifische Allometrie- und Integrationskonstanten festgelegt.     

Chenopodium necrosis: a distinctive strain of tobacco necrosis virus isolated from river water

A distinctive strain of tobacco necrosis virus (TNV) of unknown source was repeatedly isolated from water of the River Avon (Warwickshire) and two of its tributaries (R. Swift and R. Alne) using a technique developed for the concentration and isolation of water-borne bacteriophages. The same strain was isolated from the rivers Cam and Thames and from Lake Esthwaite (Cumbria) together with tomato bushy stunt virus. The TNV strain, designated Chenopodium necrosis (TNV-CN) was mechanically transmissible to C. amaranticolor and C. quinoa in both of which it caused local lesions and systemic infection. TNV-CN caused no infection when inoculated to tobacco (Nicotiana tabacum cv. White Burley) plants. The virus was not adsorbed to soil, could be isolated from leachate of soil in which systemically infected C. quinoa were grown and C. quinoa plants became infected when grown in soil watered with suspensions of the virus. The virus was not transmitted by Myzus persicae but was vectored by the zoospores of a lettuce isolate of Olpidium brassicae. TNV-CN was infective after 10 min at 85 °C., 3 wk at 20 °C and when diluted to 10^-8 but not 10^-9. Purified virus preparations contained c. 26 nm isometric virus particles. TNV-CN contained single-stranded RNA (mol. wt 1·5 × 10⁶) and one protein (mol. wt c. 26·4 × 10³) which co-electrophoresed in polyacrylamide gels with the protein of the D strain of TNV (TNV-D). Analytical centrifugation of TNV-CN indicated a single component virus with the same sedimentation coefficient (s₂₀, w= 115S) and buoyant density (1·385) in a CsCl gradient as those of TNV-D. TNV-CN and TNV-D were indistinguishable serologically.     

A floristic framework of Australian rainforests

In the first comprehensive floristic classification of Australian rainforests and monsoon forests, fresh insights made possible by the use of floristic as distinct from structural data are outlined. A set of 561 individual communities, on sites ranging from North Queensland westwards to the Kimberley region and southwards to Tasmania, is defined by the presence or absence of 1316 tree species, or 406 genera. The data have been subjected to numerical classification, first with respect to species, then to genera. The species classification first divides into three ‘ecofloristic regions’: A, temperate (microtherm) and subtropical (mesotherm) humid evergreen rainforests; B, tropical (megatherm) humid evergreen grading into highly seasonal raingreen (monsoon) forests; and C, subtropical (mesotherm) moderately seasonal humid/subhumid raingreen forests. The sites are further divided into eight ‘ecofloristic provinces’, for each of which a core area is identified and the ten most common diagnostic tree species listed for selected floristic elements, whose ecological relationships are briefly described. Gradients of quantitative thermal-moisture indices are added to standard climatic typology to provide a more flexible identification of local climates that characterize community-types of each province across a wide latitudinal/altitudinal range. Community disjuncts and outliers of a particular province are interpreted as the results of past environmental sifting (in which ecological factors are not entirely determinate), of previously more continuous rainforest vegetation. The genera classification first divides into humid eastern coastal and subhumid western and subcoastal sites, then four thermal types, and finally nine groups of floristic ‘paleo-provinces’. Where the species and genera classifications are not in substantial agreement, a wide-ranging generic element across the provinces in northern and northeastern Australia is interpreted in paleogeographic terms. The relict distribution of existing community types, as the result of climatic sifting of ancient floral stocks, is discussed in support of emerging ideas about the autochthony of Australian rainforests, especially those tropical types that are not intrusive. It is argued that the unique ecological relationships of Australian rainforests justify the most conservative uses of the relatively small remaining areas.     

Invertebrate colonization of a new, man-made stream in southern Sweden

SUMMARY.

• 1 The invertebrate colonization of a man-made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby.
• 2 The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream.
• 3 Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant.
• 4 The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last.
• 5 After a year, the community structure in Flugströmmen closely resembled that in lake-outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another.
• 6 The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.

     

The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley

Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m^–2 s^–1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m^–2s^–1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm^–2 after 8 h at 975 µE m^–2s^–1) but starch was also of significance (20 mg dm^–2after 8 h at 975 µE m^–2 s^–1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m^–2 s^–1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 15–20 mg dm^–2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m^–2s^–1 the sucrose level rose to only 10 mg dm^–2. Herethere was no discernible delay in the depletion of sucrose orstarch.     

Inhibition of photosynthetic electron transport and formation of inactive chlorophyll in winter stressed Pinus silvestris

Kinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochrome f have been studied in chloroplasts isolated from active and winter stressed Pinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochrome f and P700 was observed. Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll. Low-temperature fluorescence emission spectra were recorded when either chlorophyll a (433 nm) or chlorophyll b (477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyll a fraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyll a antennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophyll a/b complex is relatively resistant to winter stress.     

Phycochromes b and d: their occurrence in some phycoerythrocyanin-containing blue-green algae (cyanobacteria)

Abstract
Phycochromes b and d, two types of photoreversibly photochromic pigments previously extracted from the blue-green alga Tolypothrix distorta , which contains phycoerythrocyanin, have now been found in three Anabaena strains also containing phycoerythrocyanin. Tests for the presence of phycochromes b and d in a number of blue-green algae lacking phycoerythrocyanin have been negative. The possibility that phycochrome b-type absorbance changes are due to changes in the α-subunit of phycoerythrocyanin is discussed.     

Some effects of humidity on the light reaction of photosynthesis in the lichens Cladonia impexa and Collema flaccidium

Luminescence and fluorescence were measured at different relative humidities in the lichen Cladonia impexa Harm. Both parameters showed a constant value at relative humidities lower than 80%: thereafter they increased. Low relative humidity was found to decrease energy transfer from chlorophyll b to chlorophyll a. inhibit electron transport, lower electron holding capacity on the reduced side of photosystem two and impair far-red-induced afterglow, reflecting photophosphorylation. In Collema flaccidium Ach. Ach. energy transfer from the accessory pigments phycocyanin and phycoerythrin to chlorophyll a was only possible at high relative humidity. The results are interpreted as due to conformational changes caused by changed water content in the lichen.