Analysis of plant root systems is difficult under field conditions, especially root systems of adult trees, which are large and complex and include fine absorbing roots as well as conducting coarse roots. Although coarse roots can be visualized by several methods, there are technical difficulties with root quantification. The method presented here focuses on the quantification of absorbing root surfaces through an electrical (the modified earth impedance) method. It is based on the experimentally verified fact that an applied electric current flows from the roots to the soil (or vice versa) through the same interfacial areas and predominantly in the same way as water (water solution of minerals or nutrients) flows from the soil to the tree. Based on the different conductivities of tree tissues and soil, the interfacial area, which represents the absorbing root surfaces (or root absorption zones), can be calculated. Only the theoretical description of the method is presented in this paper: the experimental verification of the method under field conditions is presented in the accompanying paper.

We validated, by means of allometric relationships and root severing experiments, the modified earth impedance method developed for measuring absorbing root surfaces. For the allometric studies, a series of 350 small and large trees of six broadleaf and coniferous species in several experimental sites was examined. We found a good linear ln-ln fit between absorbing root surface area and basal area (or stem cross-sectional area at the root collar in seedlings) over a range of stem diameters from 0.5-55 cm. The absorbing root surface area also changed consistently with crown projected area and the root-accessed area (territory) of the tree. At the whole-tree level, absorbing root surface area reached about 70 times that of basal area and 40% of crown projected area, or roughly 1/3 of the root-accessed area in Norway spruce (in this species, the ratio was relatively larger in small trees and smaller in large trees). The absorbing root surfaces of mechanically severed parts of Norway spruce root systems changed in about the same proportions as the geometrically determined parts of the severed root systems. These results are promising and support field applications of the method in biological and ecological studies.

Plasma modification of powder has recently attracted much interest because of new prospects of the interfacial properties supervision. There was mostly used the low-pressure plasma modification in fluidized bed, but for industrial-scale application the employment of mechanical stirring also appears to be very promising at the moment. It was shown that application of plasma modification methods led to substantial process time reduction. In case of the polyethylene, parts sintered from the plasma-modified polyethylene powder were characterized with high surface tension, which allowed e.g. direct painting or adhesive bonding without any additional pre-treatment. Plasma modification also significantly enhanced the adhesion of the polymer to the substrate. Adhesion and wettability measurements were carried out to reveal surface modification of plasma treatment of HDPE powders. This paper describes results of the polyethylene powder plasma treatment in microwave low-pressure plasma and discusses possibilities of its application.

Problems of the powder particles plasma modification are practically the same as in the case of solid films. Troubles of the powder treatment are related with its threedimensional character, small size of particles, treated large area and problems with powder manipulation, that also must not be neglected. For modification of polymer powder surface properties like wettability and adhesion without changing powder bulk properties there have been mostly applied methods employing low temperature (cold) plasma treatment at low pressures. Presented contribution describes design and investigation of a novel plasma reactor exploiting the dielectric barrier discharge burning in air at atmospheric pressure by ambient temperature and its usability tests. For tests HDPE powder Borealis CB 9155-01 was used. This plasma reactor is of a very simple construction in comparison with other in literature described apparatuses used for this purpose and needs no vacuum equipment. Powder capillarity tests had proved significant powder capillarity changes induced by DBD plasma modification. Modification effect reduction (aging) is remarkably small (max. reduction about 20 % in one year after the modification date), hence modification effect is very time stable.

In this article, experimental studies of the onset voltages and of the low current region of negative atmospheric corona discharge on trees are presented. Recent experiments show that the corona discharges on natural biological objects often differ from the classical discharges with metal electrodes. The onset voltage values lie in a wide range around the expected value. It has been found that the negative corona onset voltage of multiple point (such as the top of a coniferous tree) is higher than that of a single point. VA characteristics of multiple point coronas lie below those for a single point from the onset until a critical value is reached. From this point, the slope of the characteristics is steeper for the multipoint geometry. The effect of the multiple point configurations depends mainly on separation of needles. When the needles are closed together -the case of the needles of spruce or pine -the needles behave as a single needle. The difference may be caused by the presence of complex hydrocarbons released from the plants and the changes in the surrounding atmosphere.