Dynamics of the aboveground phytomass of the Ob floodplain meadows in the area of the Tomsk carbon polygon (Kaibasovo)

At the Kaibasovo site (Tomsk carbon polygon), during 2017-2021, studies of multi-year changes in the vegetation of the floodplain meadows of the Ob river were carried out on 4 permanent sample plots to determine the effect of weather conditions and floods on the formation of aboveground phytomass. 
The research area is located within the southern taiga subzone of the forest zone and belongs to the northern part of the Shegarsky section of the floodplain. Permanent sample plots were laid out on relief elements of different flooding conditions - high ridges, their slopes, and depressions. Grass, forb and sedge phytocenoses were studied. In the phase of maximum development of the herbage, geobotanical descriptions and sampling of aboveground phytomass (including litter and rags) were carried out. Descriptions were made on an area of 100 m2, the herbage was mowed from squares of 0.25 m2 four times. Under field conditions, the mowing was sorted by types, dried and weighed. The productivity of the herbage was determined by summing up the masses of particular types. Further, the average indicators of phytocenosis such as the composition of dominant species, the total number of species, the composition and ratio of various fractions (agrobiological and ecological groups) were determined in terms of 1 m2 of aboveground mass. 
Weather conditions and meadow flooding regime for the growing seasons of 2017-2021 were characterized on the basis of data from the Molchanovo meteorological station and the Nikolskoe gauging station. We took into account the average ten-day and monthly values of temperature and precipitation as well as HTC for the entire growing season. This provided the possibility to select wet and dry, warm and relatively cold seasons as a basis for analyzing the phytomass dynamics. Based on the results of a general evaluation of hydroclimatic conditions, 2017-2018 have been assessed as warm, humid, mid-water, 2019 - extremely dry and hot, when the floodplain was not flooded, 2020 - slightly dry mid-water, 2021 - cold and dry with a relatively high flood. 
It was found that the dynamics of the meadow vegetation of the Kaibasovskiy section of the Ob floodplain is determined by the influence of the weather conditions of the current and previous years, the nature of the flood, and characterized by changes in the above-ground mass, the ratio of dominant species, the composition of ecological and biological groups of species in the herbage. 
The change in the state of the cereal community, developed on a high ridge, was due to the dynamics of weather conditions. The range of productivity changes over the years was the smallest. This was due to the good adaptability of the phytocenosis provided by a variety of vegetatively mobile long-rhizome grasses from the ecological groups of xeromesophytes, mesophytes and eumesophytes. The state of the other three communities studied was determined not only by weather conditions, but also by a more important factor such as flooding of meadows during seasonal floods. Their productivity turned out to be generally higher and the range of fluctuations in the amount of aboveground phytomass over the years was wider (on average, twice). 
The study of the relationship between the productivity of the herbage and the destruction of the aboveground part of the mortmass and hydroclimatic conditions showed that at all altitudinal levels of the floodplain in arid conditions, there is a decrease in the mass of the herbage of meadows and the accumulation of dead plant residues. The aboveground phytomass of the communities of the upper and middle altitude levels increases with the increase in environmental humidity, while the total aboveground mass increases, but the proportion of dead plant matter decreases. 
The increase of aboveground phytomass of sedge phytocenoses of medium-low and low levels occurs in humid, warm, mid-water years, while an increase in the abundance of moisture-loving grasses and sedges in the herbage is observed. The accumulation of the amount of dead plant matter is also observed in years with prolonged stagnation of water. The decomposition of litter and rags is most active in humid and warm spring.