Relative DNA content of human euchromatin and heterochromatin after G, C and Giemsa 11 banding.

Human chromosomes and interphase nuclei labeled with 3H-thymidine and treated with the ASG and trypsin technique for G banding show no DNA loss. However, after G 11 and C banding significantly more DNA is removed from euchromatin than from constitutive heterochromatin.     

Forest biomass,soil and biodiversity relationships originate from biogeographic affinity and direct ecological effects

Ecosystem biomass, soil conditions and the diversity of different taxa are often interrelated. These relationships could originate from biogeographic affinity (varying species pools) or from direct ecological effects within local communities. Disentangling regional and local causes is challenging as the former might mask the latter in natural ecosystems with varying habitat conditions. However, when the species pool contribution is considered in statistics, local ecological effects might be detected. In this study we disentangle the indirect effects of the species pool and direct ecological effects on the complex relationships among wood volume, soil conditions and diversities of different plant and fungal groups in 100 old‐growth forest sites (10 × 10 m) at the border of boreal and nemoral zones in northern Europe. We recorded all species for different vegetation groups: woody and herbaceous vascular plants, terricolous and epiphytic bryophytes and lichens. Fungal communities were detected by DNA‐based analyses from soil samples. Above‐ground wood volume was used as a proxy of biomass. We measured soil pH and nutrient content and obtained modelled climate parameters for each site. Species pool effect was considered by dividing sites into boreal and nemoral groups based on community composition. In order to disentangle direct and indirect effects, we applied variation partitioning, and raw and partial correlations. We found many significant positive relationships among studied variables. Many of these relationships were associated to boreal and nemoral species pools, thus indicating that biogeographic affinity of interacting plants and fungi largely defines forest diversity and functioning. At the same time, several relationships were significant also after considering biogeography: woody plant and ectomycorrhizal fungi diversities with wood volume, many plant and fungal groups with each other, or with soil conditions. These direct ecological interactions could be considered in forestry practices to achieve both economic gain and maintenance of biodiversity.     

The partitioning of carbohydrates and the biomass of leaves in Populus tremula L . canopy

 This study was aimed at making a quantitative evaluation of the biomass, carbohydrates and mineral nutrients partitioning in the canopy of aspen (Populus tremula L.) growing in a forest stand. Tree canopy biomass was divided into ten equal horizontal layers and the material for the study was sampled from all canopy layers. The results indicated that the specific leaf mass and the dry matter content increased but the area of leaves decreased toward the top of the canopy. The content of the non-structural carbohydrates depended largely on the position of the leaves in the canopy and the N, P and K contents in the leaves, reaching a maximum in the upper canopy layers better exposed to light. Regression analysis showed a linear relationship between the leaf mass per area and the percentage of dry matter on the one hand and the content of carbohydrates, N, P and K in the canopy on the other. Received: 11 March 1997 / Accepted: 16 June 1997     

Climate change at northern latitudes: rising atmospheric humidity decreases transpiration, N-uptake and growth rate of hybrid aspen

At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (Populus tremula L.×P. tremuloides Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008-2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect - inhibition of above-ground growth rate - was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO(3) (-) in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO(2) concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.     

Functional and structural analysis of acetylcholine receptor-rich membranes after negative staining

Phosphotungstate (pH 7.4) used for negative staining of membranes from Torpedo electric tissue rich in acetylcholine receptor does not affect binding properties and cation permeability of the receptor and its ion channel. Uranyl salts, frequently used for negative staining, precipitate the receptor-rich membranes making measurements of ligand binding and ion-permeability regulation impossible. The gross ultrastructure in the two stains is not significantly different, but for future high-resolution electron microscopy aiming at visualizing structural details of functional receptor molecules it is necessary to resort to a stain preserving native and active receptor. Uranyl salts are not applicable for this purpose. The electron micrographs obtained with phosphotungstate reveal two distinct structures in the receptor-rich membrane: a closed ring ('doughnut') and an open ring ('horseshoe'), with a ratio of abundance of about 3:2.     

Length of human C-bands in relation to the degree of chromosome condensation

Summary The C-band length of human chromosome 1 in prophase and prematurely condensed interphase chromosomes is relatively shorter than in metaphase chromosomes. However, even in chromosomes with the same degree of contraction the absolute length of the C-band varies considerably. This allocyclic behaviour of human constitutive heterochromatin has to be kept in mind if C-bands of different individuals are compared.Sponsored by the Deutsche Forschungsgemeinschaft (Sp 144)     

Partitioning of carbohydrates and biomass of needles in Scots pine canopy

The study was aimed at the quantitative evaluation of the temporal and spatial partitioning of non-structural carbohydrates and needle biomass in a canopy of Scots pine (Pinus sylvestris L.) growing in a Myrtillus site type forest stand (predominant in Estonia). The tree canopy was divided into ten equal layers and the material for the spatial partitioning of the investigated characteristics was sampled from all layers. Our findings revealed a significant variation in morphology and in the partitioning of carbohydrates in needles in different layers of the canopy. The study of the temporal dynamics of carbohydrates showed that starch content in needles started to increase in early spring before budbreak, which was accompanied by a decline in soluble carbohydrates. In October, the starch content of needles was low, but the concentration of soluble sugars started to increase attaining a maximum in winter. Regression analysis indicated that before budbreak, the partitioning of soluble sugars in different canopy layers was relatively weakly correlated with the height of the layer; however, a strong correlation was observed for starch. In autumn, when the growth of trees stopped and daily temperatures decreased, the allocation of soluble sugars was correlated with the height of the canopy layer.