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 (Corg), microbial carbon (Cmic), and potentially mineralizable carbon (Cpm). The highest values of microbial indicators and carbon content were observed in the upper 30 cm, with a maximum in the upper 10 cm. Corg 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 Cmic stock to the Corg 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 Cpm 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 Cpm 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), Cmic 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.