Inorganic chemical investigations in the Forest Biosphere Reserve near Kalinin,USSR

To get a first impression of the degree of pollution in the Forest Biosphere Reserve 350 km northwest of Moscow, samples of Polytrichum commune and peat profiles were measured by ICP/MS after decomposition by high-pressure ashing. Comparing the results with data found in similar systems in Central Europe the Forest Biosphere Reserve can be described than medium-polluted by heavy metals. Pb shows lower values as in comparable systems in Germany, due to the fact of lower traffic density in Sowjetunion. The status of the nutritional elements Ca, Mg and K is in the same order of magnitude as found in German forest ecosystems.     

Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability

Summary Centaurea maculosa seedlings were grown in pots to study the effects of root herbivory by Agapeta zoegana L. (Lep.: Cochylidae) and Cyphocleonus achates Fahr. (Col.: Curculionidae), grass competition and nitrogen shortage (each present or absent), using a full factorial design. The aims of the study were to analyse the impact of root herbivory on plant growth, resource allocation and physiological processes, and to test if these plant responses to herbivory were influenced by plant competition and nitrogen availability. The two root herbivores differed markedly in their impact on plant growth. While feeding by the moth A. zoegana in the root cortex had no effect on shoot and root mass, feeding by the weevil C. achates in the central vascular tissue greatly reduced shoot mass, but not root mass, leading to a reduced shoot/root ratio. The absence of significant effects of the two herbivores on root biomass, despite considerable consumption, indicates that compensatory root growth occurred. Competition with grass affected plant growth more than herbivory and nutrient status, resulting in reduced shoot and root growth, and number of leaves. Nitrogen shortage did not affect plant growth directly but greatly influenced the compensatory capacity of Centaurea maculosa to root herbivory. Under high nitrogen conditions, shoot biomass of plants infested by the weevil was reduced by 30% compared with uninfested plants. However, under poor nitrogen conditions a 63% reduction was observed compared with corresponding controls. Root herbivory was the most important stress factor affecting plant physiology. Besides a relative increase in biomass allocation to the roots, infested plants also showed a significant increase in nitrogen concentration in the roots and a concomitant reduction in leaf nitrogen concentration, reflecting a redirection of the nitrogen to the stronger sink. The level of fructans was greatly reduced in the roots after herbivore feeding. This is thought to be a consequence of their mobilisation to support compensatory root growth. A preliminary model linking the effects of these root herbivores to the physiological processes of C. maculosa is presented.     

Physiological responses of Uroleucon jaceae (L.) to seasonal changes in the quality of its host plant Centaurea jacea L.: multilevel control of adaptations to the life cycle of the host

Summary Exploiters of short-lived plants have evolved strategies in response to physiological changes that occur during the development of their hosts. The ability to adapt to host quality changes is necessary particularly if the mobility of an animal is poor or risk-constrained. In the plant-aphid system Centaurea jaceae-Uroleucon jaceae, the responses of the aphid to the seasonal changes in its host plant grown in poor and good quality soil were investigated. Coarse- and fine-tuned physiological reactions were observed in discrete aphid generations which were reared on plants grown either in a growth chamber or in a greenhouse. The number of ovarioles and developmental time depended on extrinsic factors (length of photoperiod) not directly related to plant quality. The reproductive investment of the aphids was also independent of their total dry weight. However, within the gonadal system high correlations were found at the embryonic level (e.g. the number of sclerotized embryos or the length of the oldest embryos per ovariole were highly correlated with gonadal dry weight). Aphids which were living on the 4-leaf stage of high-quality host plants showed a significantly higher investment in their gonads than aphids feeding on senescenting hosts. Factor analysis corroborated that aphids reared on poor-quality hosts revealed no grouping of variables measured, whereas those which were reared on high-quality plants showed clustering in respect of somatic (tibia length, dry weight of soma) and gonadal (number of sclerotized and unsclerotized embryos, length of the oldest embryos, ovariole number, gonad dry weight) factors. Three different levels of adaptive response to plant quality are distinguished: individual response to host quality, maternal influences on offspring and response to changes not specific to habitat (photoperiod). These different levels of regulation are thought to enable the aphids to adapt to a host of a given nutritional quality and anticipate deteriorating habitat quality simultaneously. It is concluded that physiological constraints in aphids are only revealed when aphids are exposed to severe nutritional stress for several generations.     

Density dependent interactions between VA mycorrhizal fungi and even-aged seedlings of two perennial Fabaceae species

Summary The interaction of density and mycorrhizal effects on the growth, mineral nutrition and size distribution of seedlings of two perennial members of the Fabaceae was investigated in pot culture. Seedlings of Otholobium hirtum and Aspalathus linearis were grown at densities of 1, 4, 8 and 16 plants per 13-cm pot with or without vesicular-arbuscular (VA) mycorrhizal inoculum for 120 days. Plant mass, relative growth rates, height and leaf number all decreased with increasing plant density. This was ascribed to the decreasing availability of phosphorus per plant as density increased. O. hirtum was highly dependent on mycorrhizas for P uptake but both mycorrhizal and non-mycorrhizal A. linearis seedlings were able to extract soil P with equal ease. Plant size distribution as measured by the coefficient of variation (CV) of shoot mass was greater at higher densities. CVs of mycorrhizal O. hirtum plants were higher than those of non-mycorrhizal plants. CVs of the facultatively mycorrhizal A. linearis were similar for both mycorrhizal and non-mycorrhizal plants. Higher CVs are attributed to resource preemption by larger individuals. Individuals in populations with high CVs will probably survive stress which would result in the extinction of populations with low CVs. Mass of mycorrhizal plants of both species decreased more rapidly with increasing density than did non-mycorrhizal plant mass. It is concluded that the cost of being mycorrhizal increases as plant density increases, while the benefit decreases. The results suggest that mycorrhizas will influence density-dependent population processes of faculative and obligate mycorrhizal species.     

The influence of plant architecture on the foraging efficiencies of a suite of ladybird beetles feeding on aphids

By manipulating plant variety and predator species, we investigated the interactions of plant and predator traits in determining predation effectiveness. The predators were all coccinellid adults (Hippodamia convergens, Hippodamia variegata, Coccinella apunctata, and Coccinella septempunctata) and the prey were cabbage aphids (Brevicoryne brassicae). Foraging behavior of the four predators was observed on four crucifers that differed widely in their structures and surface textures (Brassica oleracea caulorapa, Brassica campestris, Brassica juncea crispifolia, and Hirschfeldia incana). Predation rates were significantly influenced by plant variety, a result we attribute to direct effects of plant morphology on predator mobility, falling frequency, and prey accessibility. Predation rates did not vary significantly among the ladybirds, although the four species did exhibit distinct foraging strategies as measured by time spent actively foraging, the rate of encountering aphids, and the fraction of aphids encountered that were consumed. The coccinellids also differed in their propensity for flying away from the plant, and in the frequency with which they fell from the plant. We did not detect any significant interaction effects between plant and predator species, suggesting that the main effects of plant and predator species may overwhelm their interactions in this kind of system. Our results suggest that the level of predation upon herbivorous insects may depend more upon plant architecture than on the particular species of natural enemies present.     

Characterization of three hormone mutants of Nicotiana plumbaginifolia: evidence for a common ABA deficiency

Summary Various auxin-resistant Nicotiana plumbaginifolia mutants have already been isolated, including 1217 which shows cross-resistance to paclobutrazol. Recently, a cytokinin-resistant mutant, CKR1, has been characterized and has been shown to be affected in abscisic acid (ABA) biosynthesis. We have isolated a new mutant, Esg152, which was selected on the basis of its early germination. In each of these mutants, resistance is due to a recessive nuclear mutation at a single locus. Complementation analysis indicated that mutants I217, CKR1 and Esg152 belong to the same complementation group. They have a similar phenotype, which includes a reduction in seed dormancy and an increased tendency to wilt. These mutants display an increased auxin tolerance and enhanced root formation when leaf or hypocotyl sections are cultivated on auxin. By immunoenzymatic methods, we show that the endogenous levels of ABA are significantly lower than in the wild-type. We have assigned the symbol aba1 to the recessive alleles of the locus affected in the three mutants. The complexity of hormonal interactions is discussed briefly emerging from a consideration of this class of mutants.     

The stability of foreign protein production in genetically modified plant cells

Summary The stability of foreign protein production in genetically engineered plant cells was studied. A cultured tobacco cell line was transformed with a chimeric molecule carrying a bacterial gene, ß-glucuronidase (GUS), under plant regulatory sequences. The specific GUS activity was monitored for 294 days with ten independently transformed cell lines either in the presence or the absence of selectable antibiotics. Specific GUS activity was stably maintained in five lines. About a two-to four-fold increase in the GUS activity was observed from three cell lines. The remaining two cell lines lost the activity within the first 70 to 210 days. The presence of antibiotics did not significantly alter the stability of the foreign protein production in all cell lines examined.     

A synecological investigation of Matteuccia struthiopteris — dominanted stands in Western Norway

This investigation is based on phytosociological and ecological analyses of stands dominated by M. struthiopteris within its main distributional area in Western Norway. The distribution and floristical composition of such stands are related to different environmental parameters such as regional climate, soil and topography. The data are analysed by numerical methods, of which two-way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA), and simple discriminant functions (DISCRIM) are the most useful. Few stands occur in areas where the mean July temperature is below 12.0 °C, and where the mean January temperature is higher than 0 °C. The soil is rich in metal cations, with a base saturation mostly higher than 50% in the B-layer. Based on a TWINSPAN classification of the 230 investigated stands, 9 different groups (types) are distinguished. Many stands have a tree layer of Alnus incana, while stands with a canopy of Betula pubescens, Fraxinus excelsior and Ulmus glabra are considered to be marginal sites for M. struthiopteris. The types described are interpreted as belonging to the Pruno padi-Alnetum incanae, Alno incanae-Fraxinetum excelsioris and Alno incanae-Ulmetum glabrae associations within the Alno-Ulmion alliance. The floristic composition of the quadrats is highly correlated with the altitude/temperature gradient. The other important factor is interpreted to be soil moisture. Soil richness is poorly correlated with the floristic composition of the different stands. Several stands represent a regeneration stage after cessation in cultivation, while others appear to have been very little influenced by human activity.     

Variation in tissue element concentrations in Quercus ilex L. over a range of different soils

In order to study the variability in nutrient concentrations in four tissues of Q. ilex in relation to soil properties, we selected fifteen stands in both Quercus ilex forests and Q. ilex-Pinus halepensis mixed forests. These stands had developed on soils derived from eight different parent materials. Three soil groups were differentiated according to their chemical properties: calcareous soils, siliceous soils, and volcanic soils. Across sites, nutrient concentrations were generally less variable in current-year tissues than in older tissues. Nitrogen and potassium showed the lowest variability among sites, their concentrations in current-year leaves ranging from 1.17% to 1.39% for N and from 0.53% to 0.68% for K. There were few statistically significant correlations between tissue element concentrations, the most frequent being the antagonistic relationship between calcium and magnesium. Nitrogen concentration in current-year leaves was negatively correlated with soil chemical fertility (nitrogen, phosphorus and potassium). This may reflect a nutritional imbalance between nitrogen and other nutrients, some of which may be more limiting than nitrogen to Q. ilex growth in Catalonia forests. Negative correlations were also found between plant magnesium and soil calcium, and positive correlations between plant calcium and soil calcium.