4.2. Soil enzyme activity of different type vegetations
Our study shows that different vegetation types affect soil enzyme
activity differently (Figure 3). Urease, a key enzyme that regulates
soil nitrogen transformation, comes mainly from plants and microbes and
plays a key role in nutrient cycling(Zhao, Li, & Wang, 2012). Soil
urease activity in XS vegetation is higher than in the others (Figure
2C). The high urease activities in XS vegetation may be due to both
microbial growth and stimulation of microbial activity by enhanced
resource availability(Li et al., 2014). At the same time, higher soil
nutrients (Table 2) and SOC contents (Figure 2D) provide microorganisms
with a rich source of nitrogen and carbon, which significantly adds to
the nutrients accumulated by transformation (Cui et al., 2019).
Improving the physical properties of soil creates an environment that
benefits microorganisms(Iovieno, Morra, Leone, Pagano, & Alfani, 2009)
and increases urease activity.
We found that the different vegetation types do not significantly affect
soil catalase activity, which could be related to the metabolic activity
of aerobic organisms(Brzezińska, Włodarczyk, Stępniewski, & Przywara,
2005). It can decompose hydrogen peroxide into molecular oxygen and
water to prevent cells from damage by reactive oxygen species
(Bartkowiak & Lemanowicz, 2017). As such, we observed no significant
change in catalase activity in adverse environments.
Soil amylase and cellulose enzymes are responsible for the rate and
course of plant material decomposition and plant debris
degradation(Piotrowska, 2014).Significant differences in soil amylase
and sucrase activities were observed under the four vegetation types (P
< 0.05). The activities of amylase (Figure 3A) and sucrase
(Figure 3D) in GL vegetation in the 0-20 cm layer were significantly
higher than in the other three vegetation types. In the 20-40 cm layer,
the soil amylase activity in the HR vegetation was the highest, while
there was no significant difference in the other three vegetation types.
The soil sucrase in the XS vegetation was significantly higher than that
in the other three vegetation types. Because there are more types of
vegetation and litter on the surface of GL, the content of SOC fractions
is higher (Figure 2), and soil organic matter has a higher input
capacity, which affects the community structure and growth of
rhizosphere soil microorganisms (Prescott, 2010). GL vegetation is also
dominated by low, herbaceous vegetation (Table 1). The shade effect of
this vegetation is small, and soil temperature is higher than in the
other three vegetation types, resulting in higher soil amylase and
invertase activities in GL vegetation. The higher MBC, POC contents
(Figure 2A, C), and total porosity (Table 2) in the 20-40 cm layer of HR
vegetation provide a source of oxygen for microbial activity, while the
root system of GL vegetation is mainly concentrated in the 0-20 cm
layer, meaning that amylase in HR vegetation is more active in the 20-40
cm layer.
In all four vegetation types, the
soil amylase, urease, and sucrase activities were greater in the upper
layer than in the lower layer, while the soil catalase activity did not
change significantly. Due to the high SOC content (Figure 2), there are
sufficient nutrient sources to facilitate the growth of microorganisms.
In addition, higher surface temperatures and better ventilation enable
soil microorganisms to quickly grow and metabolize(Chen, Shang, Cai, &
Zhu, 2019). The underground biomass in the 20-40 cm soil layer was
reduced, which reduces the source of soil nutrients, while this
reduction of SOC content and plant roots often leads to a decrease in
enzyme activity (Xiao, Huang, & Lu, 2015). The effects of vegetation on
soil enzyme activities (i.e., amylase, catalase, urease and sucrase) are
different under different soil types and environmental conditions.