The Arctic terrestrial ecosystems are undergoing rapid climate change, causing shifts in the dynamics of soil nitrogen (N), a pivotal but relatively underexplored component. To understand the impacts of climate change on soil labile N pools, we performed meta- and decision-tree analyses of 391 observations from 38 peer-reviewed publications across the Arctic, focusing on experimental warming and snow addition. Soil dissolved organic nitrogen (DON), ammonium (NH4+ ), and nitrate (NO3 ) pools under experimental warming exhibited overall standard mean differences (SMDs) ranging from -0.08 to 0.02, with no significance (P > 0.05); however, specific conditions led to significant changes. The key determinants of soil labile N responses to warming were experimental duration and mean annual summer temperature for DON; annual precipitation, soil moisture, and sampling timing for NH+4 ; and soil layer for NO3 . Snow addition significantly increased all labile N pools (overall SMD = 0.23-0.36; P < 0.05), influenced by factors such as sampling timing and vegetation type for DON; experimental duration and soil moisture for NH+4 ; and soil pH for NO3 . By consolidating and reprocessing datasets, we not only showed the overall responses of soil labile N pools to climate manipulation experiments in Arctic tundra ecosystems but also identified key determinants for changes in soil N pools among environmental and experimental variables. Our findings demonstrate that warming and snow-cover changes significantly affect soil labile N pools, highlighting how the unique environmental characteristics of different sites influence terrestrial N cycling and underscoring the complexity of Arctic N dynamics under climate change.

Changing precipitation patterns and global warming have greatly changed winter snow cover, which can affect litter decomposition process by altering soil microenvironment or microbial biomass and activity. However, it remains unknown how and to what extent snow cover affects litter decomposition during winter and over longer periods of time. Here, we conducted a meta-analysis to synthesize litter decomposition studies under different levels of snow cover. Overall, deepened snow significantly enhanced litter decomposition rate and mass loss by 17% and 3%, respectively. Deepened snow enhanced litter carbon loss by 7% but did not impact the loss of litter nitrogen or phosphorus. Deepened snow increased soil temperature, decreased the frequency of freeze-thaw cycles, and stimulated microbial biomass carbon and bacterial biomass during winter, but had no effect on these parameters in summer. The promoting effect of deepened snow cover on litter decomposition in winter is mainly due to its positive effect on microbial decomposition by increasing soil temperature and reducing freezethaw cycles exceeded its negative effect on physical fragmentation of litter by reducing freeze-thaw cycles. Our findings indicate that the changes in winter snow cover under global change scenarios can greatly impact winter litter decomposition and the associated carbon cycling, which should be taken into consideration when assessing the global carbon budget in modeling.