Microbial Production and Carbon Dioxide Emission by Soils of the Chashnikovo Carbon Polygon with Various Potential for Organic Matter Mineralization

Microbial production and CO₂ emissions were studied in Albic Retisol (Loamic) and Albic Retisol (Aric, Loamic) of the Chashnikovo carbon polygon (Moscow oblast) of Lomonosov Moscow State University at the peak of vegetation activity. The objects were monitoring sites in two natural ecosystems (secondary spruce forest and mixed-grass meadow) and two agroecosystems (perennial grasses and bare fallow). The soils differed in the carbon stocks of organic matter (C_org), microbial carbon (C_mic), and potentially mineralizable carbon (C_pm). The highest values of microbial indicators and carbon content were observed in the upper 30 cm, with a maximum in the upper 10 cm. C_org stocks in the 0- to 30-cm layer were 1.1–1.3 times higher in agrosoils (72.7–75.6 t ha^–1) than in natural soils (59.4–65.0 t ha^–1) due to the difference in soil density. The contribution of the C_mic stock to the C_org stock in meadow soils and agrosoils covered by perennial grasses (1.8 and 1.4%) was higher than in forest soils and soils covered by bare fallow. The C_pm stock in natural soils (1.34 and 0.97 t ha^–1 for the 0- to 10-cm layer) was 1.3–2.3 times higher than that in agrosoils; however, the intensity of organic matter mineralization in agrosoils was 1.4–2.9 times lower than in soils of natural ecosystems. For ecosystems with similar vegetation, the effect of C_pm stocks on the value of microbial CO₂ production was shown; its proportional increase was noted. The maximum potential microbial production of CO₂ (4.8 gC m^–2 day^–1 for the 0- to 10-cm layer and 10.5 gC m^–2 day^–1 for the 0- to 30-cm layer), C_mic stock (0.50 t ha^–1), as well as CO₂ emission (11.09 ± 0.29 gC m^–2 day^–1), were characteristic of the meadow soils. In other biocenoses, microbial production of CO₂ was approximately two times lower. Since CO₂ emission, in addition to microbial respiration, was also caused by the respiration of plant roots, its minimum values were observed for agrosoils under bare fallow (5.01 ± 1.43 gC m^–2 day^–1). The CO₂ emission by forest soils and agrosoils under perennial grasses was statistically insignificantly lower compared to the meadow.