A comparison of diatom phosphorus transfer functions and export coefficient models as tools for reconstructing lake nutrient histories

1. We compared the baseline phosphorus (P) concentrations inferred by diatom‐P transfer functions and export coefficient models at 62 lakes in Great Britain to assess whether the techniques produce similar estimates of historical nutrient status. 2. There was a strong linear relationship between the two sets of values over the whole total P (TP) gradient (2–200 μg TP L^?1). However, a systematic bias was observed with the diatom model producing the higher values in 46 lakes (of which values differed by more than 10 μg TP L^?1 in 21). The export coefficient model gave the higher values in 10 lakes (of which the values differed by more than 10 μg TP L^?1 in only 4). 3. The difference between baseline and present‐day TP concentrations was calculated to compare the extent of eutrophication inferred by the two sets of model output. There was generally poor agreement between the amounts of change estimated by the two approaches. The discrepancy in both the baseline values and the degree of change inferred by the models was greatest in the shallow and more productive sites. 4. Both approaches were applied to two lakes in the English Lake District where long‐term P data exist, to assess how well the models track measured P concentrations since approximately 1850. There was good agreement between the pre‐enrichment TP concentrations generated by the models. The diatom model paralleled the steeper rise in maximum soluble reactive P (SRP) more closely than the gradual increase in annual mean TP in both lakes. The export coefficient model produced a closer fit to observed annual mean TP concentrations for both sites, tracking the changes in total external nutrient loading. 5. A combined approach is recommended, with the diatom model employed to reflect the nature and timing of the in‐lake response to changes in nutrient loading, and the export coefficient model used to establish the origins and extent of changes in the external load and to assess potential reduction in loading under different management scenarios. 6. However, caution must be exercised when applying these models to shallow lakes where the export coefficient model TP estimate will not include internal P loading from lake sediments and where the diatom TP inferences may over‐estimate TP concentrations because of the high abundance of benthic taxa, many of which are poor indicators of trophic state.     

The Effects of Inhibition of Cotyledon Photosynthesis on Seedling Development in Cucumis sativus L.

The period during which cucumber cotyledons function purelyas storage organs is very brief and this role is supplementedand superseded shortly after emergence by their photosyntheticfunction. Inhibition of cotyledon photosynthesis by DCMU duringthe early post emergence phase prevented further plumule developmentalthough some cotyledon expansion still took place before seedlingdeath occurred. Seedlings did not survive DCMU application tothe cotyledons if the treatment was made before the first leafwas expanded. Reduction of the incident light intensity at the cotyledon surfaceto about 10 per cent of the control reduced the rate of growthof the seedlings but they did not die. Shading one cotyledonsubstantially reduced the weight and area of that cotyledonand of the seedling as a whole. There was little indicationthat the untreated cotyledon either increased its photosyntheticrate or its output of photosynthate-nor did it supply the inhibitedcotyledon with assimilates. There was some indication that sucroseapplied to the cotyledon surface was able to compensate forlight to a small extent especially when only one cotyledon wasshaded. However, in full light, sucrose tended to be inhibitory. After emergence cotyledon reserves are sufficient only for limitedcotyledon development. Survival and growth of the seedling beyondthis stage is dependent upon cotyledon photosynthesis.     

A comparison of visualization techniques for recording arbuscular mycorrhizal colonization

The extent of arbuscular mycorrhizal colonization was assessed in 10 field-collected plant species, representing three annual forbs, three perennial forbs, three perennial grasses and one annual grass. Each root system of each plant was split into four portions, and for each portion, mycorrhizal structures were revealed with epifluorescence microscopy (under which only arbuscules are generally visible) and three commonly used stains (Chlorazol Black E, Acid Fuchsin and Trypan Blue). The aim of the study was not to evaluate the efficacy of each method, but to compare results obtained by each under standard laboratory conditions. The recorded colonization levels of arbuscules, total arbuscular mycorrhizal fungal material and total fungal (arbuscular mycorrhizal+non-arbuscular mycorrhizal) material differed significantly between visualization methods in a number of species. However, there were also interactions between stain and plant species, indicating that the performance of a stain is dependent on the plant species being examined. In some cases (e.g. Plantago lanceolata ), each visualization method produced the same colonization level, while in others (e.g. Dactylis glomerata ), each method gave a different result. These data therefore suggest that the level of mycorrhizal colonization recorded in any particular plant species at a particular time is dependent on the technique employed.     

Some Effects of Potassium Deficiency on Seedling Development

Seedlings with leaf-like photosynthetic cotyledons such as Cucumissativus, Sinapis alba and Trifolium pratense have higher growthrates and a greater requirement for an external supply of potassiumthan hypogeal species (Pisum sativum, Vicia faba) or epigealspecies with very fleshy cotyledons (Phaseolus vulgaris, Lupinusalbus, Lupinus angustifolius). The initial stages of seedlingdevelopment in the latter two groups involve mainly transferof reserves from cotyledons to axis and a relatively small increasein total seedling dry weight takes place during the first 2to 3 weeks. Potassium may be drawn either from the supply already presentin the cotyledons or from an external source. Species with expandingphotosynthetic cotyledons utilize the reserve potassium duringcotyledon development and it is not transported to the epicotyl.Thus, in these species an external supply of potassium is essentialfor full development of the photosynthetic system and the roots.In species whose cotyledons are not major photosynthetic organsthe reserve potassium is transported from the cotyledons tothe developing axis. In these species culture in a nutrientsolution deficient in potassium or in distilled water increasesroot dry weight but reduces plumule weight (although to a lesserextent than in species with leaf-like cotyledons). In general,the response of seedlings to culture in a nutrient solutiondeficient in potassium was very similar to culture in distilledwater only. Thus, although all the species studied had similar levels ofpotassium in the seed (µg potassium/mg dry weight) itssite of utilization differs. It appears that seedlings withleaf-like cotyledons are more susceptible during early seedlinggrowth to deficiencies in external factors, such as potassium,than are species with fleshy cotyledons.     

Density and distribution of Badgers in south-west England–a predictive model

This paper describes a predictive model for estimating the density and distribution of Badger social groups, in the south-west of England, based on habitat characteristics. Main sett density was used as an index of Badger social group density, and a preliminary study to define the different types of Badger sett observed in the field and to establish a relationship between main sett density and social group density is also described. The habitat characteristics that emerged as having the most influence on Badger social group density were the 'diggability' of the soils, the topography of the area, altitude, the length of hedgerows and the number of woodland units greater than 1 ha. The application of the model is briefly discussed.     

Effects of Potassium Deficiency on Cotyledon Photosynthesis and Seedling Development in Cucumis sativus L.

Seedlings of Cucumis sativus L. grew much less vigorously whencultured in potassium-deficient nutrient solution than in fullnutrients. The poorer growth was attributed to reduced CO₂ fixationby the cotyledons, which form the bulk of the photosyntheticsurface at this stage, and to a much lower level of export ofphotosynthetic products from the cotyledons. The magnitude ofthese effects increased as the seedlings aged and they werea major factor in the poorer development of the plumule in potassium-deficientplants. Electron microscopic examination of the cotyledons shows thatthe lower ¹⁴CO₂ fixation in potassiumstarved seedlings is associatedwith poorly-defined granal stacks and a proliferation of intergranalthylakoids. In plants grown in full nutrients the incorporationof radiocarbon into a cell wall fraction and into other insolublecomponents of the cell increased with cotyledon age whereasin potassium-deficient seedlings there was an increase in thepercentage of the total radiocarbon in the soluble fraction.This suggests either that the incorporation of photosyntheticproducts into cellular components was inhibited or that theability of the cotyledon to translocate photosynthetic productsto the rest of the seedling was reduced in plants grown in potassium-deficientconditions.     

Graph theory, tionary trees and classification

Many methods have been used for analysing information about organisms in order to understand tionary relationships and/or to determine classifications. The reationship between some of these methods is illustrated for the character state matrix, incompatibility and similarity matrices, minimal unrooted and rooted trees, and tionary classifications. Existing methods of determining the shortest possible tree are described. In addition a new method of building a minimal tree is introduced which starts with the largest possible subset (clique) of characters that is compatible for all pairs of characters. The remaining characters are ranked in order of their increasing number of incompatibilities. These characters are added singly, a tree constructed and then tested for minimality by previously described methods for partitioning characters into subsets. The procedure is repeated at least until the tree can no longer be proved minimal. The relationship between trees and tionary and phylogenetic classifications has been neglected but three methods are metioned and a new criterion suggested. It is suggested that graph theory, rather than statistics, is better suited for the primary analysis of comparative data.     

Estimating the impact of past persecution and habitat changes on the numbers of Badgers Meles meles in Britain

Data from a Badger sett survey undertaken in the mid-1980s were used to calculate the effects of past persecution and land-use changes on Badger numbers. The current British Badger population was estimated to be 41,894 ± 4404 social groups; if the effects of past persecution were eliminated, the population could be 43,437 ± 4731 social groups, an increase of 3.7%. Most of this increase relates to persecution in Norfolk and Suffolk last century. In Britain the Badger population is largely confined to those areas which are intensively managed, and the numbers and distribution of Badgers reflect patterns of agricultural activity. However, over-intensive use of the landscape is detrimental to Badger numbers. To quantify the impact of land-use changes on the British Badger population, a number of habitat features favourable to Badgers were identified; 1-km squares that contained five or more such features had significantly higher mean Badger densities. If all the 1-km squares were managed to include five or more of the habitat features favoured by Badgers, and the effects of persecution were eliminated, the Badger population could be 58,284 ± 5640 social groups, an increase of 39%. The absence of semi-natural broadleaved woodlands in a 1-km square had the greatest effect in reducing Badger numbers, and tree-planting schemes may be beneficial in providing potential new sett sites. However, Badgers are poor colonists, and the construction of artificial setts and the translocation of displaced social groups of Badgers will greatly facilitate the colonization process. The value of such an approach for predicting the effects of future land-use policy on Badgers and other species, and for managing the British wildlife resources, is discussed.     

A cladistic analysis of wax scales (Hemiptera: Coccoidea: Coccidae: Ceroplastinae)

Seven genera of wax scales (Ceroplastinae) have been accepted as valid by some or all coecidologists: Ceroplastes Gray, Ceroplastidia Cockerell, Cerostegia De Lotto, Gascardia Targioni Tozzetti, Paracerostegia Tang, Vinsonia Signoret and Waxiella De Lotto. The status of most these genera is controversial. The present study reviews the taxonomic history of wax scales and presents a new classification based on cladistic analysis of morphological data from the adult females of eighty-three species. The analysis indicates that the wax scales form a monophyletic group, that Waxiella is monophyletic but that Ceroplastidia, Gascardia and Vinsonia are not, and fails to support the generic status of Cerostegia and Paracerostegia. Apart from the type species of Vinsonia , which was placed as a sister to the rest of wax scales, the only other species assigned to Vinsonia and most species of all other genera fall within Ceroplastes in the cladogram. Recognition of any of these genera renders Ceroplastes paraphyletic or polyphyletic. Thus, cladistically, the wax scales should be classified into one genus, Ceroplastes.