Insert Fig. 3
Obviously, deforestation has resulted in the loss of SOC and TN storage (lnRR < 0, P < 0.05, Fig. 3a-b). The lost SOC was mainly found in the grassland, cropland, fruit trees and other fields (grassland mainly turned into farmland), with the loss efficiency more than 50.0%. Even the farmland with the lowest loss efficiency reached 34.4%. We observed slight difference between LUCCs after deforestation (P = 0.09), and instead the response of TN storage varied greatly in different LUCCs (P = 0.02). When native forest was converted to secondary forest, the TN storage loss was highest (57.5%), while the lowest loss was noticed in the cropland (29.0%) originating from native forest. When native forest was converted to plantation and grassland, the reduction was 34.2% and 49.7%, respectively. Undoubtedly, deforestation greatly contributed to the loss of SOC and TN in the Karst areas of southwest China.
In contrast to the effect magnitude of deforestation, land restoration benefited for SOC and TN gain to some extent (Fig. 3c-d, P< 0.01). The increased SOC storage was 87.7%, 64.3% and 55.0%, respectively when the cropland was recovered to grassland, native forest and others (mainly refers to the conversion of grassland to native forest). Interestingly, insignificant gain was observed upon reverting cropland to grassland (lnRR = 0.11, P> 0.05) and fruit trees (lnRR = 0.10, P> 0.05), and even slight loss after the converting from cropland to plantation (lnRR = - 0.12, P > 0.05). The TN had similar trend as SOC, showing variations among specific LUCCs (Fig. 3, d, P < 0.01). Specifically, the TN storage increased by 109.2% (lnRR = 0.74, P< 0.05) and 94.8% (lnRR = 0.10, P < 0.05), respectively after restoring from cropland to native forest and other LUCCs (mainly grassland to native forest). Shifting from cropland to the grassland ecosystem slightly increased the TN storage (lnRR = 0.01, P > 0.05). Additionally, we observed the lost TN storage when cropland was converted to fruit trees (lnRR = -0.09, P > 0.05) and plantations (lnRR = -0.04, P > 0.05).