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) (C(mic) and N(mic)) 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 (t(max)) more than did organic treatments. The peak height (P(max)) was positively
correlated (P<0.01), with soil
enzymes, C(mic) and N(mic), and the number of
microorganisms, whereas the peak time (t(max)) was negatively connected (P<0.01) with these parameters. The
microbial growth
rate constant (k) was linked to
bacteria (P<0.01),
actinomycetes (P<0.05) and
catalase (P<0.05). The total heat evolution (Q) had no relationships with any soil
microbial properties (except for
catalase). We propose that P(max) and t(max) could be used as indices of soil
microbial activity, while the values of k and Q are poor indicators.
