Microcalorimetry, plate count and PCR–denaturing gradient gel electrophoresis
(DGGE) were employed to investigate microbial diversity and activity in soils from
the Red Soil Experimental Station of the Chinese Academy of Agricultural
Sciences, Hunan Province, China, where a wheat–corn rotation with 12 fertilization
treatments was established in 1990. Fertilization greatly increased microbial
biomass carbon (C) and nitrogen (N) (Cmic and Nmic) as well as the activities of
phosphatase, urease, invertase, protease, catalase and dehydrogenase. Manure
alone (M) enhanced the number of denitrifying and aerobic bacteria by 54.4%
and 20.5%, respectively, whereas fallow (H) increased the number of aerobic
cellulose decomposing bacteria by 31.4%. Fallow and soils amended with mineral
fertilizers plus pig manure or straw increased both the DGGE band patterns and
the Shannon index compared with mineral fertilizers or the control. Mineral
treatments with lower bacterial numbers enhanced the values of the peak time
(tmax) more than did organic treatments. The peak height (Pmax) was positively
correlated (Po0.01), with soil enzymes, Cmic and Nmic, and the number of
microorganisms, whereas the peak time (tmax) was negatively connected
(Po0.01) with these parameters. The microbial growth rate constant (k) was
linked to bacteria (Po0.01), actinomycetes (Po0.05) and catalase (Po0.05).
The total heat evolution (Q) had no relationships with any soil microbial properties
(except for catalase).We propose that Pmax and tmax could be used as indices of
soil microbial activity, while the values of k and Q are poor indicators. |
