Global Synthesis of Fertilisation-Induced Changes in the Microbial Entombing Effect.

The microbial entombing effect refers to the accumulation and stabilisation of microbially derived carbon (C) in soils following the sustained production of microbial biomass and necromass. Fertilisation practices modify soil microbial activity and C cycling and consequently influence the microbial entombing effect, which has implications for global C sequestration. We conducted a global meta-analysis to evaluate the impact of fertilisation practices on the microbial entombing effect, focusing on microbial necromass C (MNC), microbial biomass C (MBC) and the microbial necromass accumulation coefficient (NAC = MNC/MBC) across 319, 1665 and 199 paired datasets, respectively. Overall, fertilisation increased MNC by 16.6%, primarily because of an overall increase in MBC (31.9%) rather than an increase in NAC. Inorganic fertiliser application resulted in a higher accumulation of MNC (14.7%) and MBC (24.9%) in croplands than in forests and grasslands. Combining nitrogen (N) and phosphorus (P) fertilisers with straw (NPS) exhibited the highest potential for global MNC accumulation (14,900 Tg), exceeding the global average by 10.6% under fertilisation. Combining N and P fertilisers with manure (NPM) resulted in the highest global MBC (660 Tg) and NAC (35.3). These findings highlight the necessity of combined organic-inorganic fertilisation strategies to enhance soil C sequestration by increasing the contribution of the microbial entombing effect. While mean annual temperature (MAT) played a key role in determining MBC, the initial pH (ipH) and initial soil organic C (iSOC) were the dominant factors influencing the microbial entombing effect. In alkaline soils, particularly those in Central and Western Asia, NPS and NPM fertilisation exhibited the greatest potential for enhancing MNC and NAC, respectively. This study provides mechanistic insights into the impacts of fertilisation on the microbial entombing effect and highlights the critical need for site-specific management to optimise soil C sequestration.