Topography mediates contrasting patterns of glomalin-related soil protein and its contribution to soil organic carbon in a tropical montane rainforest

Background and aims

Glomalin-related soil protein (GRSP), is a metabolite exuded by the extraradical hyphae of arbuscular mycorrhizal fungi (AMF), which enhances soil structure and consequently is often associated with improved fertility in forest soils. This study investigates how topography and local environmental conditions influence GRSP and its ratio with soil organic carbon (GRSP/SOC) to support forest management and carbon stock conservation.

Methods

In a 60-ha Jianfengling tropical montane rainforest plot, we investigated the spatial patterns of GRSP and GRSP/SOC across ridges, slopes, and valleys. Using a Random Forest model that accounted for spatial autocorrelation, we assessed how GRSP and GRSP/SOC varied with respect to topography, plant diversity, and soil physicochemistry.

Results

GRSP and GRSP/SOC exhibited strong spatial autocorrelation, with contrasting topographic trends: GRSP peaked in ridges but was lowest in valleys, whereas GRSP/SOC was highest in valleys. Soil total nitrogen, available phosphorus, and pH were key predictors of GRSP in ridges, while pH was the critical predictor of GRSP/SOC in valleys. Notably, total tree diversity—but not AMF-associated tree abundance or biomass— was significantly correlated with the relative contribution of easily extractable GRSP to SOC.

Conclusions

Topography strongly influences the spatial distribution of GRSP and GRSP/SOC in tropical montane rainforests, with divergent patterns between these metrics. Total tree diversity, rather than AMF tree diversity, better predicts GRSP/SOC variations, evidence of important feedbacks between plant communities and the potential to sequester carbon in soil. These findings highlight the need to integrate landscape heterogeneity and biodiversity into forest carbon management strategies.