Victoria Vladimirovna Pronina

Due to the need to develop technologies for reducing carbon dioxide emissions and increasing the C-absorption
capacity of natural and anthropogenic ecosystems, the possibility of using mineral fertilizers to regulate microbial
respiration and CO2 emissions from urban lawn soils was evaluated. Th e studies were carried out on the territory of
the Botanical Garden of Moscow State University on the Lenin Hills in a small-plot experiment with the fractional
application of four types of complex fertilizers (NPKS 27:6:6:2, NPKS 21:10:10:2, NPK 15:15:15 and NPK 18:18:18
+ 3 MgO + trace elements (TE)) at doses of 60 and 120 kg N ha-1 during the growing season. Th e carbon content
of microbial biomass (Cmic) using substrate-induced respiration was studied, the basal respiration (BR) of soils was
estimated, and the emission of CO2 from soils using closed static chambers was determined. Тhe Cmic content in the
soil of the control plot in the summer period varied within 1300–1450 μg·g-1. Th e application of NPKS 21:10:10:2
and NPK 18:18:18 + 3 MgO + TE at a low dose increased the Cmic content by 12–35% for two weeks, then it decreased.
Th e application of all fertilizers for a short period increased basal respiration of soils and CO2 emission,
maximum on the 6th day. After two weeks, the increase in the intensity of BR and CO2 emission decreased or it
reached the control values (1,5 μg C-CO2·g-1·h-1 and 500 mg·CO2 ·m-2·h-1 respectively) or less. In the short term,
the lowest intensity of CO2 emission and a surge in basal respiration, along with an increase in microbial biomass,
were observed with the addition of fertilizer NPKS 21:10:10:2. The greatest change in the functioning of the soil
microbial community, revealed by the maximum qCO2, occurred with the introduction of NPKS 27:6:6:2. The dynamics
of CO2 emission from the soils of the small-plot experiment from April to October correlated with the soil
temperature (rS = 0.66, p<0.05, n=135). In all periods of the study, the minimum CO2 emissions were noted for the
plot with NPKS 21:10:10:2 fertilizer.

The methane uptake and the carbon dioxide emission by Albic Retisols (Aric) under the cultivation of green manure crops and perennial grasses, as well as the carbon accumulation in their phytomass were estimated at the «Chashnikovo» carbon supersite of the Moscow region during the summer period of 2024. White mustard, vetch-oat mixture, perennial legume-cereal grasses and giant miscanthus were studied. Greenhouse gas fluxes were measured using an automatic chamber, aboveground phytomass assessed by the mowing method, underground phytomass — by washing roots from soil monoliths. The soils absorbed atmospheric methane at the rate of 0.15 to 0.62 mg C·m‒2·day‒1. The highest total methane uptake over the summer was observed in soils under miscanthus at the rate of –0.047 g C·m‒2, it statistically significantly decreased by 1.6 times in soils under the vetch-oat mixture, by 1.8 times under perennial grasses and by 2.2 times under mustard. The total CO2 emission by soils over the summer was maximum under perennial grasses — 927.6 g C·m-2, decreased under miscanthus – 835.9 g C·m‒2, vetch-oat mixture — 737.4 g C·m‒2 and mustard — 476.6 g C·m‒2. The increased CO2 emission by soils under perennial crops is due to more active root respiration during the formation of statistically significantly greater underground phytomass compared to green manure crops.  The aboveground phytomass of giant miscanthus was more than 2 times higher compared to other plants. In total, over the growing season, the following carbon accumulation was observed in the phytomass: 536.0 g C·m‒2 in white mustard, 735.9‒755.3 g C·m‒2 in legume-cereal perennial grasses and vetch-oat mixture, 2157.7 g C·m‒2 in miscanthus. Thus, the studied Albic Retisols (Aric) acted as a weak sink of atmospheric methane and emitted carbon dioxide in an amount less than or comparable to the carbon accumulation in the phytomass of green manure crops and perennial grasses. These data are important for the development of technologies aimed at reducing greenhouse gas emissions and increasing carbon sequestration in agroecosystems.