Long-term changes in microbial community structure in soils subjected to different fertilizing practices revealed by quinone profile analysis

Abstract

Quinone profile analysis of stored air-dried soils gave an approximation of the long-term changes in the microbial community structure in four soils subjected to different types of fertilizer application from 1987 to 1997: unfertilized soil (NF-soil), soil amended with chemical fertilizers (CF-soil), soil amended with chemical fertilizers and 40 t ha-1 y-1 of farmyard manure (CF+ FYM-soil), and soil amended with 400 t ha-1 y-1 of farmyard manure (FYM-soil). The carbon content increased, and the soil pH remained higher in the soils receiving farmyard manure. Principal component analysis of the quinone profiles of the soils indicated that the microbial community structure showed a high similarity among the four soils before the onset of cultivation and changed to a different community structure specific to the respective fertilizing practices except for the NF-soil. The specific quinone profile became stable after two cropping seasons in the FYM-soil, after 10 cropping seasons in the CF+ FYM-soil and after 15 cropping seasons in the CF-soil, respectively. The quinone profile of the NF-soil did not become stable, and no specific profile was developed. The specific quinone profiles in the FYM- and CF+ FYM-soils were both characterized by large mole fractions of menaquinone with seven isoprenoid units (MK-7). Farmyard manure itself contained a large mole fraction of MK-7. It was suggested that the amount of MK-7 increased due to the application of farmyard manure. MK-7 indicates the presence of Gram-positive bacteria with low guanine plus cytosine contents such as Bacillus and Gram-negative bacteria of the Cytophaga-Flavobacterium complex. The specific quinone profile in the CF-soil was characterized by the presence of menaquinone with seven isoprenoid units dihydrated (MK-7(H2)and MK-7(H4). Although Brevibacterium and Kocuria contain MK-7(H2), no microorganisms are known to have MK- 7(H.) as major quinone. The common major quinones were MK-8, MK-10(H4) and a mixture of MK-8(H4) and MK-9, suggesting the predominance of Grampositive bacteria in all the soils. Mole fractions of Ubiquinone with 8 isoprenoid units (Q-8) and Q-10 increased at various times in all the soils, indicating the sporadic growth of Gram-negative bacteria.