Floristic geobotanical and bioecological research on Tuva's fallow vegetation

The article presents the results of long-term research on the vegetation of Tuva’s fallow ecosystems. Systematization of the floral complex of fallow lands (246 species, 130 genera and 32 families) according to the degree of their adventization show that about half of its composition (48-55%) are strictly fallow plants with a high proportion (up to 30% or more) of invasive plants. The fraction of accidental fallow species in cenoflora is not numerous and ranges from 7.6 to 15% in various natural and climatic regions of Tuva. Based on 120 geobotanical descriptions we have identified 20 associations, 6 formations and 4 florocenotypes. So, weedy florocenotypes includes 2 formations - Artemisia and Cannabis. Re-establishment of vegetational cover of fallow lands shows changes in the structure of communities. A small-weedy stage has been revealed, and phytocenoses of the rhizome stage with the dominance of Elytrigia repens, Leymus chinensis often get the signs of a stable derivative. It is established that fallow succession contributes to the accumulation of humus in the soil, and Artemisia fallow makes the most positive effect. In addition, the amount of humus is concentrated in the horizon of 10-20 cm, this layer contains the main mass of wheat grass rhizomes, which decomposition biosynthesizes soil ulmin. Due to the influence of fallow vegetation the content of humus increases, and agronomically valuable soil particles are formed. The research has revealed that saprophytes dominates indegradation of litter, their population varies from 105 to 107 cells/g. Aerobic and facultative anaerobic bacteria participate in decomposition. The highest rate of protein degradation we reveal in the early autumn period, and cellulose - in the summer. Bioecological studies of ecosystem engineers have shown that they are indicators of changes in environmental conditions. The most informative are species with eurytopic ecology (Artemisia glauca and Heteropappus altaicus), characteristic for communities of all stages of fallow succession. Thus, as aridity increases, the changes in pigment composition of leaves are observed according to the stages of demutation. The same species at different recovery stages have different pigment contents: leaves of Heteropappus altaicus in the weedy stage contains 0.76 ± 0.04 mg/g, in the rhizome stage - 0,83 ± 0,04 mg / g, in the stage of loose bunch - 0. 73 ± 0.03 mg / g of wet weight.