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The influence of light reduction on the growth and phenolic compounds contents in Scots pine trees and seedlings was studied. Results of the first experiment in field conditions show that shade causes an increase of phenolic compounds and in the second experiment with seedlings under controlled shading conditions the results were opposite. It is suggested that the factor insolation should be paid more attention during the studies on the influence of pollution on the content of phenolic compounds.
Quercus robur seedlings are very often infested by oak powdery mildew caused by Erysiphe alphitoides. This disease attacks primary leaves with high insolation. In our experiment seedling growth in different light conditions was observed. Seedlings were derived from intact seeds or from seeds where the distal ends of acorns were cut off. Acorns were sown in pots at four light conditions (2%, 8% and 30% light transmittance and in full sunlight). For half of the seedlings we reduced the influence of powdery mildew by using a fungicide. Height of seedlings, shoot dry mass and the degree of damage caused by Erysiphe alphitoides were measured. The highest damages were in full light conditions and the lowest in the 30% light treatment. The influence of acorn reduction on powdery mildew infection was not significant (p=0.0763), however, in the full light conditions the seedlings from cut acorns were ca. 30% less damaged. The cutting of acorns also alters the height of seedlings and shoot mass. The tallest seedlings were from cut seeds growing in the 30% light treatment. The influence of the fungicide was lowest in the 30% light treatment where the decrease in damage was only ca. 10%. For nursery practice we can say that oak seedling production from cut off acorns under 30% light transmittance should give the best results of seedling growth even without the fungicide application.
Artificial defoliation is often used in studies of induced defense reactions of plants to damage by arthropods. However, little is known about the role of various external factors that may determine the nature of inducible defenses. Here we tested whether light level under which plants grow could affect the natural invasion of two-spotted spider mite (Tetranychus urticae Koch) with a broad range of host plants. For this study we used two host species that differ widely in shade tolerance: shade-adapted Norway maple (Acer platanoides L.) and sun-adapted European mountain ash (Sorbus aucuparia L.). The purpose of this study was to explore mite invasion and to test whether prior simulated defoliation, light conditions and host species differences in secondary defense metabolites (soluble phenolics) play a role in the pattern of invasion. One-year-old maple and ash seedlings growing in pots were placed into two shade houses that produced a treatment with 5% light transmittance, and the second group of seedlings was placed in full sunlight. The experiment was carried out in a location chronically affected by spider mite presence. The defoliation was performed in mid-May by manual removal of 0 (control), 25, 50, 75 and 100% of leaves. Natural two-spotted spider mite invasion took place in mid-July and was observed only on seedlings growing in the shade. Mites were found on leaves of almost all seedlings. However, the intensity of feeding damage to leaves was related to the level of earlier defoliation. Control and slightly to moderately (25–50%) defoliated seedlings of both species were most affected by spider mites. Mite feeding behavior was directly linked to changes in concentration of leaf carbon and phenolic compounds. Carbon content was positively correlated with the percent of seedlings damaged by spider mites in both tree species (R² > 0.80; P <0.05). The highest concentration of phenolic compounds was observed in leaves of seedlings subjected to 50 and 75% defoliation. Our results indicated that two-spotted spider mites preferred plants grown in a shade environment and within these plants favored leaves which are high in carbon and low in phenolic compounds. Both plant species were able to survive early season leaf damage inflicted by spider mites. Inducible phenolic compounds were among defensive secondary metabolites contributing to low spider mite success in plants recovering from artificial spring defoliation.
Mistletoe is semiparasite adversely affecting the functioning of their hosts especially at water management level. So far, there have been no reports about the impact of mistletoe on seeds from any host. The aim of the work was to evaluate the effect of the presence of mistletoe on the quality of the seeds of Scots pine (Pinus sylvestris). Unopened cones from infected and uninfected trees were collected in April 2015 in the Excluded Seed Stand in Bolewice Forest District (52°23‵54.347‵N; 16°05‵01.978‵E). Measurements of cones and seeds were made. Some seeds were used for pot experiment, where the seedlings were planted from May to October 2015. On the second part of the seeds in the end of July and August germination tests were made. The size and mass of the cones, the number and weight of seeds, and the height and weight of the seedlings were lower for the material collected from the mistletoe trees. The differences were not large but statistically significant (tabs. 1 and 2). The results showed that mistletoe has a negative impact on the parameters of cones, seedlings and seeds quality.
Carbon assimilated during photosynthesis is allocated to basic needs, such as growth, defense, and storage of nutrients. The aim of this study was to explore potential relationships between carbon allocation and light conditions during growth, including shade tolerance of species. We studied species that represent light-demanding (Sorbus aucuparia, Betula pendula), intermediate (Carpinus betulus, Quercus robur), and shade-tolerant (Acer platanoides, Fagus sylvatica) trees. We exposed seedlings to two light treatments (full sunlight and shade), and explored how these conditions affect plant growth and biomass allocation, as well as the levels of phenolic compounds, nonstructural carbohydrates, carbon, and nitrogen. We hypothesized that light-demanding species invest less carbon in chemical defenses against pathogens and/or herbivores compared to shade-tolerant species. On the other hand, light-demanding species showed the greater part of assimilated carbon allocate to growth processes. As a result, the stem diameter above the root collar, the mass of leaves, stems, coarse, and fine roots were larger under full-sunlight conditions in all species, except for greater height of A. platanoides and Q. robur under shade conditions. Leaves from full light were characterized by lower nitrogen content, higher carbon and phenolic contents, and a higher carbon/nitrogen ratio compared with leaves from seedlings grown in shade. In the case of shade-tolerant species, a trade-off mechanism can be proposed that such species restrict their usual allocation of carbon to defense and radial growth, while instead of investing it in increasing their heights and storage capacities. According to the light-demanding species, it was not possible to identify a trade-off mechanism and how carbon allocationis restricted upon exposure to shade conditions, except for the reduced allocation to the root mass.
Future climatic warming may modifyinsect development, sex ratio, quantitative changes in populations that could affect the frequency of outbreaks. Here we analyzed the influence of temperature on larval growth and development in the gypsy moth (Lymantria dispar L.). The larvae were reared at three constant temperatures: 15, 20 or 25°C, and fed with leaves of the English oak (Quercus robur L.). Larval mortality, duration of development (DD), relative growth rate (RGR), total mass of food eaten (TFE), and pupal mass (PM) were estimated. Larval mortality was lowest at 20°C, higher at 25°C, and highest at 15°C. DD significantly decreased with increasing temperature and depended on sex. The influence of temperature on the shortening of DD was stronger in males than in females. RGR significantly depended on temperature and was the highest at 25°C, and lowest at 15°C. At 15°C, RGR did not change markedly with time. In contrast, RGR at 20°C was characterized bya continuous decreasing trend. At 25°C, RGR was very high for 2 weeks but quickly declined afterwards. Temperature did not affect the TFE. PM was significantly correlated with temperature and sex. PM of females was higher at 20°C than at 15 and 25°C, in contrast to that of males, which was similar at 20 and 25°C, and higher than at 15°C. For larval growth and development, the most favourable was the medium temperature (20°C). The least favourable temperature for females was 25°C, for males 15°C. The results suggest that global warming may modifythe future sex ratio of gypsy moths that may affect insect development and outbreaks.
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