Nitrogen saturation in temperate forest ecosystems has been a topic of extensive research, with initial hypotheses suggesting that chronic nitrogen additions would lead to increased nitrate mobility, soil acidification, and forest decline. These hypotheses were based on the idea that nitrogen additions would initially be taken up by plants, with minimal microbial uptake, and that as nitrogen availability increased, microbial processes such as nitrification would become more significant. However, recent studies have shown that nitrogen retention in these ecosystems is highly efficient, with significant amounts of added nitrogen being retained in soil organic matter rather than being lost through leaching or other processes. The research has revealed that nitrogen saturation is a complex process involving multiple mechanisms, including microbial immobilization, abiotic incorporation into soil organic matter, and mycorrhizal assimilation. These mechanisms help explain the high retention efficiency observed in many forest ecosystems, even under conditions of high nitrogen deposition. The findings also suggest that the initial assumptions about the role of microbial processes in nitrogen retention may not fully account for the observed patterns, and that other factors, such as the presence of mycorrhizal fungi, may play a more significant role in nitrogen retention. The study also highlights the importance of land-use history in determining the response of forest ecosystems to nitrogen deposition. Forests with a history of agricultural use or other disturbances may be more nitrogen limited and may require higher nitrogen inputs to reach saturation. This suggests that the response of forest ecosystems to nitrogen deposition is not uniform and can vary significantly depending on the specific conditions of the site. Overall, the research indicates that nitrogen saturation in temperate forest ecosystems is a complex and multifaceted process, with multiple mechanisms contributing to the retention of added nitrogen. These findings have important implications for understanding the long-term effects of nitrogen deposition on forest ecosystems and for developing strategies to mitigate the potential negative impacts of nitrogen saturation.Nitrogen saturation in temperate forest ecosystems has been a topic of extensive research, with initial hypotheses suggesting that chronic nitrogen additions would lead to increased nitrate mobility, soil acidification, and forest decline. These hypotheses were based on the idea that nitrogen additions would initially be taken up by plants, with minimal microbial uptake, and that as nitrogen availability increased, microbial processes such as nitrification would become more significant. However, recent studies have shown that nitrogen retention in these ecosystems is highly efficient, with significant amounts of added nitrogen being retained in soil organic matter rather than being lost through leaching or other processes. The research has revealed that nitrogen saturation is a complex process involving multiple mechanisms, including microbial immobilization, abiotic incorporation into soil organic matter, and mycorrhizal assimilation. These mechanisms help explain the high retention efficiency observed in many forest ecosystems, even under conditions of high nitrogen deposition. The findings also suggest that the initial assumptions about the role of microbial processes in nitrogen retention may not fully account for the observed patterns, and that other factors, such as the presence of mycorrhizal fungi, may play a more significant role in nitrogen retention. The study also highlights the importance of land-use history in determining the response of forest ecosystems to nitrogen deposition. Forests with a history of agricultural use or other disturbances may be more nitrogen limited and may require higher nitrogen inputs to reach saturation. This suggests that the response of forest ecosystems to nitrogen deposition is not uniform and can vary significantly depending on the specific conditions of the site. Overall, the research indicates that nitrogen saturation in temperate forest ecosystems is a complex and multifaceted process, with multiple mechanisms contributing to the retention of added nitrogen. These findings have important implications for understanding the long-term effects of nitrogen deposition on forest ecosystems and for developing strategies to mitigate the potential negative impacts of nitrogen saturation.