Differential effects of fine root- and mycelium-derived carbon on soil organic carbon in response to warming in an alpine meadow

Plant carbon (C) inputs through fine roots and extramatrical mycelia (EMM) play a crucial role in driving soil organic C (SOC) pools. However, few studies have explored the distinct roles of fine roots and EMM on SOC accumulation, how these inputs drive the priming effect (PE) on native SOC decomposition, and how warming affects these processes in climate-sensitive alpine meadow ecosystems. In this study, we placed ingrowth cores with different mesh sizes (2 mm, 48 μm, and 1 μm) containing C4 soil in the field to quantify fine root- and EMM-derived C into particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) and their impact on the decomposition of native SOC in an alpine meadow in the hinterland of Qinghai-Tibet Plateau for 3 years under experimental warming (∼2.4 °C). The results showed that fine roots promote SOC accumulation, particularly as MAOC. In general, newly sequestered C derived from fine roots exceeded the loss of native C via PE induced by fine root C input. In contrast, EMM had no effect on SOC as EMM-derived C inputs were counterbalanced by native C decomposition induced by EMM. Additionally, fine root-derived new SOC and new MAOC were significantly higher than that derived from EMM, while the PE induced by fine roots and EMM showed no significant difference. These findings suggested that warming (∼2.4 °C) had no detectable effect on SOC pool, new SOC inputs, and the PE on native SOC decomposition. However, warming mitigated the loss of native POC induced by either EMM or fine roots. In summary, fine roots play a leading role in SOC accumulation and warming (∼2.4 °C) has minor effects on SOC dynamics in the alpine meadows.