Accumulation of glomalin-related soil protein benefits soil carbon sequestration: Tropical coastal forest restoration experiences

Many tropical coastal areas experience severe soil erosion due to heavy rainfall, especially after deforestation. Glomalin-related soil protein (GRSP), the product of arbuscular mycorrhizal fungi (AMF), improves soil structure and soil organic carbon (SOC) sequestration with vegetation restoration. Therefore, the contribution of GRSP to soil property improvement in a tropical coastal area was studied for four different restoration practices: a barren land (BL, unrestored control), a Eucalyptus exserta planted forest (EF), a mixed broadleaved forest (MF), and a secondary natural forest (SF). Results showed that vegetation restoration practices increased easily-extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) by 3.9-12.3- and 1.9-4.6-times, respectively, compared with BL. The proportions of EE-GRSP/SOC and T-GRSP/SOC were 1.6%-2.0% and 6.5%-15.8%. The concentrations of GRSP, SOC, and the GRSP/SOC ratio were similar or greater under MF than under SF. C-13 NMR analysis showed that the relatively easily degradable O-alkyl-C of SOC was significantly higher under MF than under EF and SF, while the recalcitrant aromatic-C or alkyl-C were highest under SF or EF, respectively. A significantly positive relationship was found between the GRSP/SOC ratio and aromatic-C, and between GRSP and soil aggregate stability. Our study indicates that GRSP contributes to a large proportion of SOC, and benefits SOC sequestration through increasing soil aggregate stability and recalcitrant SOC. Among these artificial or naturally growing forest areas, a mixed forest restoration practice with native tree species provides a promising restoration strategy for heavily eroded land restoration, in particular improving soil aggregation and SOC sequestration.