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).