Articles containing the keyword 'radiation'

Frost resistance during shoot elongation in seedlings of Norway spruce (Picea abies (L.) H. Karst.) was studied in two experiments. The aim of the first study was to evaluate the effect of varying mineral nutrition. Except for potassium, only minor differences in mineral elements concentrations were established, presumably due to low levels of irradiance and thus a low rate of dry matter production. No significant differences in frost injuries were found between the treatments in the experimental series, but the control seedlings were significantly less injured. It is assumed that poor hardiness development at the end of one growth period resulting from low levels of irradiance may decrease the frost resistance during the next shoot elongation phase. Observations from the second experiment with Norway spruce nursery stocks representing different seedling ages and production systems, support this assumption.

The PDF includes an abstract in Finnish.

• Rostad, E-mail: hr@mm.unknown

The utilization of direct radiation was studied in five model stands of Poisson-type tree distribution and cone-shaped crowns. The radiation extinction depended on the self-shading of the crown and the shading caused by other trees. The results indicate that at low sun elevation a stand populated by very narrow-crowned trees is most effective in light interception and photosynthesis. At high sun elevation a broad-crowned canopy is best illuminated and most favourable for photosynthesis. A stand with a two-storey canopy is effective in all latitudes when the crowns are moderately narrow. In two-storey canopies the foliage of the lower storey can be better illuminated than in the lower parts of the upper storey, because of the smaller self-shading in the small crowns of the lower storey. A canopy where the crown volume is concentrated on few big crowns is less effective than a canopy consisting of many small crowns.

The PDF includes an abstract in Finnish.

• Pukkala, E-mail: tp@mm.unknown
• Kuuluvainen, E-mail: tk@mm.unknown

The effect of solar radiation and air temperature on the basic density of Scots pine (Pinus sylvestris L.) wood has been investigated on the basis of material obtained from the literature. Solar radiation seemed to affect basic density during earlywood formation. Temperature had the greatest effect on basic density  in late summer. The varying effects of radiation and temperature seemed to be associated with the dynamics of the crown system of trees. Especially the capacity of the crown system to produce the amount of photosynthesis needed in tracheid growth is assumed to be of importance in controlling the variation in the basic density of Scots pine wood. Growth of thracheids from the point of view of photosynthate supply is discussed.

The PDF includes a summary in Finnish.

• Kellomäki, E-mail: sk@mm.unknown

The investigation is concerned with testing chemical totalizer of radiation (Frankfurt radiometer) for use in measuring the components of a simple energy balance (latent heat = net radiation – sensible heat) so as to gain an estimate for evaporation. The meter is based on the temperature dependence of the inversion rate of sugar solution. The relationship is exponential. It was found that radiation sums for 2–6-day periods can be reliably determined with this meter when global radiation is below 20 MJ·m^-2d^-1. Determining sensible heat is noticeably inaccurate, and hence the calculation of evaporation values, too. In comparing evaporation from different types of ground and plant cover one thus has to be content with drawing conclusions on the basis of net radiation values. The totalizer is therefore only suited to describing radiation conditions.

The PDF includes a summary in Finnish.

• Mannerkoski, E-mail: hm@mm.unknown

This study, comprising three experiments, aims to determine the effect of the geographical origin of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst.) seeds, and the duration of the time lag between the moisture treatment and subsequent irradiation on the gamma-irradiation sensitivity of seeds.

The studies showed that the greater the irradiation dose seeds were subjected to the slower the rate of germination. In general, small radiation doses (250–1,000 rad) had a stimulating effect and the final germination percentage (36–40 days) increased. However, when the level was further increased, the germination percentage decreased. Air-dry and moistened seeds withstood irradiation better than others. In a study with moistened seeds from different geographical sources, pine and spruce seeds from Northern Finland were less able to withstand irradiation than those originating from the south.

The PDF includes a summary in English.

• Lehtiniemi, E-mail: tl@mm.unknown

The study was carried out in order to find out the changes taking place in germination of seeds in certain tree species as a function of gamma irradiation, the height growth of the seedlings produced and the types of phenotypic mutants possibly found in the generation that had received radiation. The tree species studied were Pinus sylvestris L., Picea abies (L.) H. Karst., Betula verrucosa (Betula pendula Roth), B. Pubescens Ehrh., Alnus glutinosa (L.) Gaertn. and Alnus incana (L.) Moench.

Soaked seeds that had received a rather small dose of radiation germinated usually better than storage-dry seeds, B. pubescens being an exception. The damages observed in germination, height growth and the relative number of mutants were greater the higher the irradiation doses. The LD₅₀ dose (germination, 28 days) was as follows in the case of the different tree species (storage dry/soaked): P. Sylvestris 1,500-2,000/2500-3,000, P. abies 1,000-1,500/4,000-4,500, B. pendula 9,500-10,000/7,000-7,500, B. pubescens >10,000/7,500-8,000 and A. Glutinosa 10,000/8,500-9,000 rad. Mass production of different mutants of deciduous trees for ornamental purposes, for example, appears to be easy using gamma-irradiation. On the other hand, the possibility of increasing tree growth remains open for further study.

The PDF includes a summary in English.

• Lehtiniemi, E-mail: tl@mm.unknown

The relationship between canopy structure and photosynthetic radiation regime are studied in a theoretical basis. In modelling the canopy structure, a statistical approach is applied and the radiation field inside a stand is described in terms of random variables and their distribution. A comparison is made between horizontally homogenous stands and grouped forest stands in order to assess the influence of grouping of foliage on the irradiance distribution in a forest stand. Results show that grouping considerably reduces the interception of radiation and causes a large spatial variation. In coniferous stands the grouping of needles into shoots and the effect of penumbra are shown to have an important influence on the distribution of radiation on the needle area.

The PDF includes a summary in Finnish.

• Oker-Blom, E-mail: po@mm.unknown

• Palva, Helsinki University of Technology, Applied Electronics Laboratory, P.O. Box 3000, FIN-02015 HUT, Finland E-mail: lauri.palva@hut.fi
• Garam, Helsinki University of Technology, Applied Electronics Laboratory, P.O. Box 3000, FIN-02015 HUT, Finland E-mail: eg@nn.fi
• Palmroth, University of Helsinki, Dept. of Forest Ecology, P.O. Box 24, FIN-00014 University of Helsinki, Finland E-mail: sp@nn.fi
• Sepponen, Helsinki University of Technology, Applied Electronics Laboratory, P.O. Box 3000, FIN-02015 HUT, Finland E-mail: rs@nn.fi
• Hari, University of Helsinki, Dept. of Forest Ecology, P.O. Box 24, FIN-00014 University of Helsinki, Finland E-mail: ph@nn.fi