This thesis is part of the project GA CR P504 / 11/1151 "The role of plants in the greenhouse gas balance Carex fens". The aim of this thesis is to evaluate the seasonal dynamics of Carex acuta belowground biomass in model grassland wetlands (the "wet meadows") near Třeboň. Belowground biomass of C. acuta L. was sampled using the destructive method. The samples were taken on four dates in 2014. On each date, three hummocks of C. acuta and three soil samples in their immediate vicinity were sampled on each date. Live roots had a greater dry weight than decaying roots on all sampling dates. Their total dry weight varied slightly, depending on season. The ratio of live roots to decaying roots did not differ much. The weight of live roots in hummock was almost always higher than that of the dead ones. The dry weight of living roots was always greater in the hummock than below it. Their total weight varied slightly during the year. Aquatic roots formed only a small part of the dry weight of live roots in hummocks. A greater total belowground dry weight found on 21st December 2014, in comparison with 5th August 2014, was associated with a greater amount of rhizomes of other plant species. The shoots increased their dry weight during the year. Maximum weight of tillers was recorded on 8th August 2014. There were no dead shoots on 25th March 2014. Dry weights of dead tillers were largely similar throughout the year. The volumetric soil water content (%) was usually higher in the upper soil layers. The bulk density of the soil was almost identical on all sampling sites, except for the top layer on site 1, where it was considerably lower.

My thesis is a part of the project GACR 206/06/0058 Monitoring of selected heavy metals and risk elements in a wastewater cleaning process in artificial wetlands. The goal is to evaluate temporal and spatial variability of underground biomass of Phragmites australis in the artificial wetland used for wastewater treatment in Slavošovice. The destructive method was used for the sampling. The aboveground biomass was determined from six samples taken at the inflow and six samples at the outflow. The belowground biomass (in 2008) was estimated from two samples taken at the inflow and two samples at the outflow. In 2009, the belowground biomass was determined from six samples taken from the inflow and six samples from the outflow. The analysis of the root structure was determined from 12 samples collected at the inflow and 12 samples of the outflow. The mean total aboveground biomass reached 1039 g.m-2 at the inflow and the 1749 g.m-2 at the outflow. Average total belowground biomass in 2009 reached the inflow 1718 g.m-2 and 1562 g.m-2 at the outflow. The average total length of roots growing from one node to was 284,7 m.m-2 and 324,9 m.m-2 in the inflow and outflow part, respectively. Average specific root length of the inflow was 2589,5 cm.g-1 and the outflow 2956,9 cm.g-1. The average total length of roots reaching the inflow of two kilometers and three kilometers of inflow.