Dynamics of species diversity and weeds abundance in the Yakutsk city agricultural fields

Research studied the species composition, abundance of weed species of agrocenoses in Yakutsk and their dynamics depending on weather conditions. A total of 41 agricultural fields were surveyed with plantings of potatoes, cabbage, root crops, green crops and rye. The studies were carried out in 2018- 2021. The growing seasons of all the years of the study were characterized by high aridity, only May 2018 and 2019 rated wet. A total of 28 species belonging to 12 families and 24 genera have been recorded. The leading families in terms of the number of genera and species are Asteraceae, Brassicaceae, Poaceae, and Polygonaceae. The number of weed species in agrocenoses has a descending direction: green cropsrye - potatoes - root crops - cabbage. More than half of the total species composition (18 species) of weeds was noted singly or in small quantities. Potato fields stand out noticeably against the general background - almost all 11 noted species are found here singly, their species composition easily changes annually, some species are replaced by others. At the same time, resistant weed species have been identified, which from year to year, without reducing their abundance, are successfully renewed. They are constant in all agrocenoses of Chenopodium album and Elytrigia repens. In rye crops, Mulgedium tataricum was found, which was not previously noted in the territory of Yakutia. Among the weeds, the proportion of annual plants is high; long-rhizomatous grasses predominate in the spectrum of perennial grasses. In the composition of the studied weed flora, the participation of a foreign component is high (50 %), among them two-thirds are annual plants. The most active species are Fallopia convolvulus, Thlaspi arvense. The species diversity of weeds in cultures depends on the temperature and humidity conditions. In very dry years, there was a noticeable decrease in the total number of species, as well as changes in the spectrum of biomorphs - the dominance of annual species decreases, the proportion of long-rhizomatous perennials increases.