Soil Organic Carbon Mineralization in Tropical Grasslands: Role of Perennial Grass Species and Rhizodeposition
摘要
The tropical grasslands of Kaziranga National Park (KNP), Assam, India, regardless of being a key terrestrial carbon reservoir, yet there is limited research on how different grass species govern soil organic carbon (SOC) mineralization. To address this knowledge gap, the present study evaluates the species-specific influence of four dominant perennial grass species on soil physicochemical, biological properties, and root exudation, with a special focus on SOC mineralization. Additionally, δ13C analysis of SOC is used to trace vegetation contributions and historical shifts in vegetation. Four prevalent grass species- Pennisetum purpureum, Saccharum spontaneum, Imperata cylindrica, and Vetiveria zizanioides were selected to investigate their role in SOC dynamics. Incubation experiments were carried out for 120 days to study the SOC mineralization potential in soil samples collected during the monsoon season (August 2024). I. cylindrica exhibited the highest potentially mineralizable carbon (483.0), followed by S. spontaneum (475.0). Whereas V. zizanioides and P. purpureum were 20.3% and 17.8% lower than highest value, respectively. Rhizodeposition varied significantly among all four grass species. V. zizanioides contributed highest amount of carbohydrates (25.9 mg kg− 1) while P. purpureum provided highest amino acid (0.104 mg kg− 1) and organic acid (1.53 mg kg− 1) contents. SOC under S. spontaneum recorded δ13C of -24.9‰, indicating a dominant C3 signature with recent vegetation shift towards C4, whereas P. purpureum (-15.4‰) implicated long-term C4 vegetation dominance. This study highlights functional roles of the studied grass species in shaping SOC dynamics. S. spontaneum and V. zizanioides exhibited stronger potential for long-term carbon sequestration, while P. purpureum and I. cylindrica contributed more to short-term carbon storage.