4.2. Soil enzyme activity of different type vegetations
Our study shows that different vegetation types affect soil enzyme
activity differently (Fig. 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 (Fig. 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 (Fig. 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.
Catalase can decompose hydrogen peroxide into molecular oxygen and water
to prevent cells from being damaged by reactive oxygen species
(Bartkowiak & Lemanowicz, 2017). In this study, we found no significant
difference in soil catalase activity under different vegetation types.
This may be due to less rainfall in this area, and small differences in
soil microbial activity (MBC, Fig. 2) and soil properties (bulk density
and porosity, Table 2), leading to there was no significant difference
in soil catalase activity. Furthermore, microbial communities, litter
decomposition, and soil pH are also important factors affecting soil
catalase activity (BrzeziĆska et al., 2005; Gu et al., 2009; Kannan and
Wei, 2008).
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 (Fig. 3A) and sucrase (Fig. 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
(Fig. 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 (Fig. 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 (An, Huang, &
Zheng, 2009), 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 (Fig. 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). These results suggests that
the effects of vegetation on soil enzyme activities are different under
different soil types and environmental conditions.