Distribution and accumulation mechanism of microbial necromass carbon in global grassland ecosystems

• The MNC content of desert and desert steppe was lower, but the contribution to SOC was higher. • FNC was the main contributor of SOC in different grassland types. • MAP and soil clay was the vital factor affecting FNC and BNC in desert and desert steppe. • TN was the major factor affecting FNC and BNC in typical steppe and meadow steppe. Microbial necromass carbon (MNC) plays a vital role as a contributor to the persistent soil carbon pool in terrestrial ecosystems. However, the distribution and accumulation mechanism of MNC in various grassland types have not been quantified globally. To address this gap, we collected data from 565 observations sourced from 61 peer-reviewed articles, and classified grasslands into different types based on their geographic coordinates, including Desert (D), Desert steppe (DS), Typical steppe (TS) and Meadow steppe (MS). Our results revealed that the MNC content of TS (16.44 mg·g −1 ) and MS (14.99 mg·g −1 ) were significantly higher than the D (2.19 mg·g −1 ) and DS (7.59 mg·g −1 ) ( P ＜0.05), while the contribution of MNC to SOC in D (47.00 %), DS (51.91 %) and TS (56.16 %) were significantly higher than the MS (38.69 %) ( P ＜0.05). Additionally, the contribution of fungal necromass carbon (FNC) (30.87 %) to SOC was higher compared to bacterial necromass carbon (BNC) (17.56 %) in different grassland types, which suggested that FNC plays a dominant role in MNC accumulation. Moreover, our results showed that the FNC, BNC and MNC of D is more susceptible to environmental and soil factors than the other grassland types. Annual average precipitation and soil clay was the main factor affecting FNC and BNC in D and DS, while total nitrogen was the main factor affecting FNC and BNC in TS and MS. In summary, our findings contribute to better understanding of the stabilization mechanism of microbial-derived carbon in different grassland types and provide a foundation for validating the ’carbon pump theory’ of grassland ecosystems.