Journal of Conference Abstracts

Microbial Activity and Biomass in Native and Agricultural Ecosystems of Gray Forest Soil

Ilya V. Yevdokimov (ilya@issp.serpukhov.su), Alla A. Larionova (ilya@issp.serpukhov.su) &
Sergey A. Blagodatsky (blag@issp.serpukhov.su)

Institute of Soil Science and Photosynthesis, Russian Academy of Science, 142292, Pushchino, Moscow Region, Russia.

Gray forest soils sampled from forest, artificial meadow, and wheat-rotation sites were analysed for microbial biomass and available C. Soil microbial biomass was measured by fumigation-extraction (Brookes et al., 1985; Vance et al., 1987), rehydration-extraction (Blagodatsky et al., 1987), substrate-induced respiration (SIR; Anderson & Domsch, 1978), and kinetic (Panikov & Sizova, 1996) methods. Available C was assessed by a modified Wright-Hobbie method (Panikov et al., 1992) and by chemical analysis of salt extracts from fresh soil.

Data on microbial biomass C and N obtained using fumigation-extraction and rehydration-extraction methods were similar. A conversion factor of kc=0.25 instead of the commonly used kc=0.38, and a variable instead of constant kn, were preferable for gray forest soil. Microbial biomass C and N values were 2-4 times larger for soil sampled in April than for soil sampled in November. Data on microbial C determined by the SIR method were much the same as those obtained by the kinetic approach.

Total SOM showed a two-fold decrease in C content following land conversion to agriculture. In contrast to crop management, artificial grassing resulted in C accumulation in soil. In spite of considerable variability in soil respiration rate, microbial C, microbial N, and available C that were related to differences in sampling time, storage conditions, pattern of the experiment, measuring approach, etc., all four variables measured were correlated with SOM content and exhibited the same tendency: the highest values were obtained for the forest soils and the lowest for the arable soils.

The percentage of active microbial biomass, assessed by kinetics of microbial growth on glucose, and maximal specific growth rates of microbial populations, were highest in the arable soils. Low values of the Michaelis constant Ks in arable soils, but not in meadow or forest soils, indicate a high affinity of the microbial community in arable soils for glucose. These features of microbial growth suggest that the microbial population in crop soil grows usually on temporary batch inputs of easily decomposable carbohydrates. In Meadow and forest soils, organic substrates other than glucose seem to be the usual substrates for microbial degradation. Estimates of available C concentrations determined by the Wright-Hobbie method were much lower than soluble C concentrations determined by salt extraction, probably because soluble C substances represent both available C substrates and a pool of some other metabolites.

The significant increase in microbial biomass resulting from artificial grassing or arable soils, as well as characteristics of microbial growth on glucose, indicate that this management practice favors the development of a microbial population that is similar to the microbial community of native forest soils.

References

Anderson, J.P.E. & Domsch, K.H., Soil Biol. Biochem. 10, 215-221 (1978).

Blagodatsky, S.A., Blagodatskaya, Ye.V., Gorbenko, A. Yu. & Panikov, N.S., Soviet Soil Sci. 19, 119-126 (1987).

Brookes, P.C., Landman, A., Pruden, G. & Jenkinson, D.S., Soil Biol. Biochem. 17, 8837-843 (1985).

Panikov, N.S., Blagodatsky, S.A., Blagodatskaya, J.V. & Glagolev, M.V., Biol. Fertil. Soils 14, 280 287 (1992).

Panikov, N.S. & Sizova, M.V., J. Microbiol. Meth. 24, 219-230 (1996).

Vance, E.D., Brookes, P.C. & Jenkinson, D.S., Soil Biol. Biochem. 19, 703-707 (1987).