Recalcitrant carbon components in glomalin-related soil protein facilitate soil organic carbon preservation in tropical forests

Abstract

Glomalin-related soil protein (GRSP) is known as an important microbial by-product which is crucial for preserving or accumulating soil organic carbon (SOC). However, the underlying mechanisms are not well understood. In this study, we investigated the chemical structures of GRSP and its relationship with SOC using 13C nuclear magnetic resonance (NMR) in three tropical forests. The three forests, including a planted forest (PF), a secondary forest (MF) and a primary forest (BF), were selected to represent the natural successional process after disturbance in southern China. Results showed that the average concentrations of GRSP were (3.94 ± 1.09) mg cm−3 and accounting for (3.38 ± 1.15)% of the SOC in the top 10 cm soil. NMR analysis indicated rich aromatic C (~30%) and carboxyl C (~40%) in GRSP, and abundant alkyl C (~30%) and O-alkyl C (~50%) in SOC. The recalcitrance indexes (RI), as defined as the ratio of sum of alkyl C and aromatic C over sum of O-alkyl C and carboxyl C, was (98.6 ± 18.9)%, (145.5 ± 10.9)% and (20.7 ± 0.3)% in GRSP higher than that in SOC in the PF, MF and BF, respectively. This study demonstrated that the stubborn structure of GRSP probably regulate the resistance of SOC sequestration in tropical forests, especially in the planted and secondary forests.

Soil Organic Carbon Stabilization in the Three Subtropical Forests: Importance of Clay and Metal Oxides

“…In contrast, broadleaved forest was considered to N‐saturated and phosphorus‐limited (Fang et al, ; Huang et al, ; Lu et al, ), and soil respiration of the broadleaved forest was less sensitive than the coniferous forest or the mixed forest to the high N deposition (Deng et al, ). Finally, the composition of microbial community was observed to be significantly different between the pines dominated coniferous forest and broadleaf dominated mixed forest or broadleaved forest, with arbuscular mycorrhizal fungi being dominant in the broadleaved forest and nonarbuscular mycorrhizal fungi in the coniferous forest (Liao et al, ; Zhang et al, ). This difference in microbial composition can also influence SOC stabilization through microbial by‐product, such as glomalin‐related soil protein, as shown in the soil sampled taken from three forests by Zhang et al ().…”

“…Finally, the composition of microbial community was observed to be significantly different between the pines dominated coniferous forest and broadleaf dominated mixed forest or broadleaved forest, with arbuscular mycorrhizal fungi being dominant in the broadleaved forest and nonarbuscular mycorrhizal fungi in the coniferous forest (Liao et al, 2018;Zhang et al, 2017). This difference in microbial composition can also influence SOC stabilization through microbial byproduct, such as glomalin-related soil protein, as shown in the soil sampled taken from three forests by Zhang et al (2017). As a result of the significant leaching process in fine-textured soils along vertical profile, SOC was often found to be negatively correlated with soil clay content, as SOC was typically high in soil surface and clay content was high in illuvial B horizons.…”

Assay of Glomalin Using a Quartz Crystal Microbalance Biosensor

“…The soil selected for optimization came from typical middle European arable regions and it contained glomalin in an amount 2.41 mg/g. For instance, level glomalin in soil from China was reported to be 3.94 mg/ml . The low limit of detection gives opportunity to analyze even soils with low fertility.…”

Functions and Application of Glomalin-Related Soil Proteins: A Review

“…Moreover, GRSP has a positive contribution to the soil C pools in native grasslands for a soil binding agent (Purin et al 2006). Combined with three kinds of soil samples obtained from the surface soil to the depth of 20 cm, Zhang et al (2017a) drew a linear correlation between GRSP and SOC. It is estimated that GRSP accounts for 4% to 5% of total soil C source, which was higher than the contribution of microbial biomass C in Hawaiian soils (Wu et al 2014b).…”

“…It seems that GRSP may not provide a positive contribution to the SOC pool. Recently, the chemical structure of GRSP was shown by the method of the solid-state 13 C cross polarisation magic angle spinning (Zhang et al 2017a). The result showed that GRSP had a high carboxyl C ratio (40% of total content) and relatively high aromatic hydrocarbon ratio (30% of total content) and alkyl C (20% of total content).…”