3.3. Relationships between soil CO2 flux,
temperature, moisture and
SOC
The soil temperature was not significantly different in land-use types
and profiles (Table 2). From Sep.2012 to Sep.2013, soil temperature
reduced and then climbed up. where the change range of the temperature
in shallow layers (5-20cm) was larger than it in deep layers (80-200cm),
but this fluctuation of the deep layers presents an obvious hysteretic
nature compared with shallow layers (Fig.2B). We used the exponential
model to fit the relationship between soil CO2 flux (F)
and soil temperature (T), and calculate the temperature sensitivity
coefficient (Q10), significant correlation was found
between CO2 flux and temperature(P < 0.01)
(Fig.5). Sensitivity of soil CO2 flux to temperature in
deep layers was generally higher than that in shallow layers.
Soil moisture was significantly different in land-use types and profiles
(P<0.01), and and interaction effect existed between them
(Table 2). The change trend of moisture in crop land was more
complicated. On the contrary, certain difference appeared in moisture
among Robinia pseudoacacia of stand ages. The moisture of shallow
soil layers (5-20cm) decreased and then increased with the seasons,
while a slow increase trend took place in deep soil layers (80-200cm).
There was a quadratic function relation between soil CO2flux (F) and soil moisture (M) (Fig.6). On the basis of the coefficient
of determination(R2), correlation between soil
CO2 flux and soil moisture in shallow layer (5-20cm) was
stronger than that in deep layer (80-200cm).
The soil organic carbon was significantly different in different soil
profile depths (P<0.01). The organic carbon content in the
deep layers (80-200 cm) was significantly lower than that in the shallow
layer (5-20 cm). As the main substrate in the process of soil carbon
emission, soil organic carbon (SOC) has an important impact on soil
CO2 flux. Correlation analysis was carried out between
soil CO2 flux and concentration of soil organic carbon
in different land-use types and profiles (Table 3). The results showed
that correlation at depth of 20cm and 140cm were significant
(P<0.05), and it was extremely significant at depth of
200cm(P<0.01), but there was no significant correlation at
depth of 5cm and 10cm.