4.3. Relationship between soil carbon fraction and enzyme
activity
Enzymes participate in the transformation process of soil nutrients.
Enzyme activity plays a vital role in soil microbial activity and soil
quality (Ebhin Masto, Chhonkar, Singh, & Patra, 2006). Under stable
organic nutrient conditions, soil enzyme activity is typically higher,
and increased mineralization of the soil’s nutrients creates a more
favorable environment for nutrient cycling (Roldán, Salinas-García,
Alguacil, & Caravaca, 2005). The results of this study demonstrate that
catalase activity was significantly related to MBC content, and can
reflect the changing process of MBC. Both urease activity and invertase
activity displayed significant positive correlations with organic carbon
and total N content. Urease and invertase activity can reflect the
decomposition of organic matter and nitrogen in soil and can be used as
important indicators of soil fertility. In sum, enzyme activity and
carbon fraction influence each other’s conversion and circulation of
nutrients (Qi et al., 2016; S. Zhao et al., 2016).
5. Conclusions
This study analyzed the responses of soil organic carbon fractions and
related enzyme activities to different vegetation types in the northern
Loess Plateau. Our results demonstrated that the content of soil SOC,
EOC and POC were greater in the upper layer than in the lower layer,
except for MBC. This variation was similar for different vegetation
types. Vegetation types effected on soil organic carbon fractions
differently. The maximum MBC content in the upper soil was observed in
HR vegetation, the maximum EOC content was observed in GL vegetation,
and the soil POC and SOC contents of SX vegetation were significantly
higher than in the other three vegetation types. Moreover, the type of
vegetation significantly influenced soil enzyme activities, except for
catalase. For all four vegetation types, the soil amylase, urease, and
sucrase were all significantly higher in the upper than in the lower
layer. In contrast, the soil catalase displayed no significant
difference between soil layers. In addition, we also found that the MBC
significantly impacted catalase activities, POC significantly impacted
urease and sucrase activities, and SOC significantly impacted urease and
sucrase activities. Considering that the related effects of vegetation
environment on litter decomposition and soil microbial community
structure will jointly affect the soil carbon dynamics under human
disturbance, more long-term research is needed to better understand the
dynamic mechanism of soil organic carbon fractions after returning
farmland to forest.