Unraveling the paradox: Increased glomalin accumulation amid declining mycorrhizal biomass across a two-million-year dune chronosequence

Background and aims

Arbuscular mycorrhizal fungi (AMF) are integral to the global carbon and nutrient cycles, primarily through the production of glomalin-related soil protein (GRSP), which contributes significantly to soil organic carbon (SOC) accumulation and ecosystem stability. However, the distribution pattern and environmental controls of GRSP during long-term ecosystem development are poorly understood.

Methods

Here, we investigated the dynamics of GRSP and its contribution to SOC accumulation along a 2-million-year chronosequence at Jurien Bay, south-western Australia, a biodiversity hotspot with severe phosphorus (P) deficiency.

Results

Our results revealed a progressive decline in AMF biomass with increasing soil age along the chronosequence, driven by P depletion and a reduction in the relative dominance of mycorrhizal plants (indicated by their relative canopy cover). Paradoxically, GRSP concentrations, especially easily-extractable GRSP (EE-GRSP), increased significantly along the chronosequence and peaked in the most weathered and severely P-impoverished soils. In addition, GRSP contributed up to 142 ± 15 mg SOC g⁻¹, with increased production and stability facilitated by interactions with soil acidity, fine texture, nutrient stoichiometry, and mycorrhizal plant richness (the number of plant species that can form a symbiosis with AMF).

Conclusions

These results demonstrate that GRSP dynamics is primarily determined by AMF turnover, mycorrhizal plant species richness, and nutrient limitation, underscoring its critical role in SOC accumulation under nutrient-depleted conditions. This study advances our mechanistic understanding of AMF-mediated soil processes, with implications for sustainable land management and climate change mitigation in nutrient-limited yet biodiverse ecosystems.