8-year nitrogen addition shaped discriminatingly microbial community interaction networks inhabiting Korean pine litter over decomposition process

Litter decomposition associated microbial community plays a crucial role in nutrient cycling and soil fertility. A higher nitrogen-deposition ecosystem with flexible nutrient features in litter and environmental variable may disrupt this process and involved with microbial succession. Yet, little know about the specific links between microbial traits and the dynamic decomposition process under nitrogen addition, particularly in-situ habitant. This study investigates the decomposition process of in-situ litter on Korean pine (Pinus Koraiensis) plantations under long-term nitrogen addition, including litter nutrient content dynamics, environmental factors and microbial community succession inhabiting litter. The findings show that the impact of nitrogen addition on nutrient contents and environmental factors over decomposition time is complex. In the middle and late stages of litter decomposition, high nitrogen significantly reduced litter pH. Additionally, high nitrogen addition alters the available phosphate release pattern over time. The impact of nitrogen addition on microbial community composition and assembly will be strongly stage-dependent. In the early stage, bacterial community assembly under nitrogen addition was still primarily driven by stochastic processes (dispersal limitation). However, high nitrogen addition shifted the bacterial community assembly from being dominated by deterministic processes (heterogeneous selection) to stochastic processes (drift) in the middle and late stages. During the late stage, nitrogen addition changes the core bacterial and fungal compositions. while it does not affect the predominance of stochastic processes in fungal community assembly (dispersal limitation and drift). Furthermore, the impact of nitrogen addition on bacterial and fungal co-occurrence networks is inconsistent. Bacteria are more sensitive to nitrogen addition than fungi. High nitrogen addition decreased bacterial stability over time, while high nitrogen addition promoted fungal stability, but suppressed fungal niche differentiation in the late stage. In conclusion, these findings demonstrated that the impact of nitrogen addition on litter nutrient content, environmental factors and associated microbial traits like assembly processes and co-occurrence networks is restricted to high nitrogen addition and the late stage of decomposition.