3.3 Factors affecting SMB
Accurately predicting SMBC and SMBN response to drought requires more
comprehensive insights into the influence of edaphic properties and
environmental conditions. In our study, we found the amount of SMBC and
SMBN varied significantly among drought types (Fig. 2 ). Recent
study suggested that increasing drought and global change have
pronounced negative effects on the SMB in terrestrial ecosystems (Wan et
al., 2021), which was in line with our results. Thakur et al. (2015)
found that soil microbes were sensitive to soil water content, even in a
short-term drought, microbial physiology and plant diversity would
change a lot. Similarly, drought’s legacy effect to shrubland lasting
for two years after the drought ended has been observed by Hinojosa et
al. (2019) in a post-fire experiment, drought mainly did have an
important impact on soil processes. The amount of SMBC increased but
SMBN decreased with drought, and in total the drought decreased the
amount of SMB (Hinojosa et al., 2019).
In our study, pH insignificantly affected the amount of SMBC and SMBN
but had a significantly negative correlation with the ratio of SMBC to
SMBN (Table 1). The soil pH has been regarded as a crucial factor for
the growth of soil microbial communities. A study found that bacteria
grow better in slightly alkaline soil, while most fungi prefer acidic
soil (Ma et al., 2016). The mainstream view is that compared to
bacteria, fungi characterized by higher growth efficiency and slower
degradation rate. Thus, the soil rich in fungi would accumulate higher
contents of SMBC and SMBC than which rich in bacteria (Six et al.,
2006). Several publications confirmed that soil pH was the main factor
regulating the microbial community structure and biomass content (Liu et
al., 2014; Cao et al., 2017). Moreover, Cao et al., 2017 showed pH was a
significant driver to regulate the size and abundance of the microbial
community and Mendes confirmed that pH had a strong relationship with
the bacterial community structure in south-eastern region of the Amazon
(Mendes et al., 2015).
Temperature played an important role in soil microbes carbon and
nitrogen cycling. Moreover, opposite responses along temperature
gradient were observed in our results, temperature had a positive
correlation with the amount of SMBC but was negative with SMBN
(Table.1). The results were not totally consistent with a prior study
that SMBC and SMBN showed positive response (3.61% and 5.85%
respectively) to warming (Xu et al., 2017). Water loss due to rising
temperature might inhibit microbial growth, which eventually decrease
the contents of SMBC and SMBN, especially in water-limited ecosystem
(i.e., grassland). Therefore, the influence of temperature on microbes
has both direct and indirect effects, and the final change of microbial
biomass was the result of multiple processes. In general, it was
difficult to summarize a universally suitable law about the microbes’
adaptation to temperature. The main reasons for this finding were,
firstly, the increase of temperature would enhance the activity of soil
microbes, which would promote the development of more organisms, then
increase the soil microbial biomass of the community. However,
increasing temperature can contribute to greater decomposition of SOC,
and cause the loss of soil carbon pool. SOC was the main nutrient source
for soil microbes, and the loss of SOC directly leads to the decrease of
nutrient source for microbes. Altogether, these finding emphasized the
importance of environmental factors in regulating the microbes.