Insert Fig. 5
Importantly, there were still variations when considering specific
LUCCs. This variation was observed in different LUCCs within the same
soil layer and in different layers within specific LUCC (Fig. 4, Fig.
5). On the one hand, all specific LUCCs showed significant SOC loss at
different sampling depths after deforestation, except for the 0-40 cm
(lnRR = 0.21, 95%CI : [-0.49, 0.14]) and 0-60 cm
profiles (lnRR = -0.13, 95%CI : [-0.50, 0.46]) under
the grassland transformed from the native forest (Fig. 3a). On the other
hand, the response SOC storage to specific LUCC varied with the sampling
depths. Generally, the lost SOC in shallow
sampling
(0-20 and 0-30 cm) was higher than that of deeper sampling (Fig.4 and
Table 3). Overall, the lost SOC nearly 50.0% in shallow sampling (i.e.,
0-20 cm, 0-30 cm) after deforestation, and less than 40.0% in deeper
sampling (i.e., 0-40 cm, 0-60 cm, 0-100 cm). Similarly, there was no
apparent loss of TN storage for the 0-40 cm profile after transforming
from native forest to grassland. Other specific LUCCs resulted in
significant lost TN storage at all sampling depths. On average, the loss
efficiency of TN storage were 43.5%, 42.3%, 38.1%, 34.3% and 33.7%
respectively, in the 0-20, 0-30, 0-40 and 0-60 cm profiles, showing a
clear decreasing trend with depths. Therefore, these data implied that
the response of SOC and TN to deforestation was
pronounced
in the surface layers.
In our study, we found that land restoration benefited for SOC and TN
gains (Table 3, Fig. 5), but the effect magnitude showed large variation
between LUCCs. Except for the slight loss after recovering from farmland
to plantation, other LUCCs increased the SOC storage. Notably, the
restoration from cropland to native forest significantly increased SOC
for all sampling depths (Fig. 3) and the gained effect of other LUCCs
decreased with sampling depths. Similarly, the increased TN storage by
land restoration differed among different LUCCs. The increased of TN
storage from cropland to native forest and other types (mainly
indicating that grassland to native forest) was satisfactory.