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 nitrogen 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 in
each type of vegetation, except for MBC. 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. Correlation
analysis showed that the MBC has a significant effect on catalase
activities, that POC significantly affected urease and sucrase
activities, and that SOC displayed an extremely significant effect on
urease and sucrase activities. Lastly, vegetation types and hydrological
conditions could have profound effects on the soil organic carbon
fractions and enzyme activities. In conclusion, the type of vegetation
was an important factor influencing the kind of soil enzyme activity and
carbon fractions on the Loess Plateau. As such, more long-term studies
are needed to better understand the mechanism of SOC dynamics across the
different types of vegetation on the Loess Plateau.