The G−/G+ ratio exhibited a positive correlation with the soil pH
(p b 0.05). Increased soil pH and change of substrates bioavailability
by biochar induce the higher G−/G+ ratio. Higher G−/G+ ratio were observed
in higher-temperature-pyrolyzed biochar amended acidic soils
except soil S1 (Fig.4a). The easy bioavailable materials in biochar such
as hemicelluloses might be responsible for the increase G−/G+ ratio
especially at the early stage of incubation. The increased G−/G+
ratio was supported by previous study which also showed the decline
of gram-positive Acidbacteria and abundance of gram-negative
Alphaproteobacteria and Bacteroidetes (Kolton et al., 2011; Xu et al.,
2016). Other suggested a shift from acid to alkaline phosphomonoesterase
activity may suggest an ecological and functional shift towards a
more copiotrophic ecology (Jenkins et al., 2016). As the gram-negative
bacteria had not been detected in control for soil S1 at the end of the incubation,
higher aromatic structure in 500BC and 700BC stimulated the
growth of gram-positive bacteria.