Anthropogenic Nitrogen Inputs Promote Plant Nitrate Utilization of Polluted Forests

Abstract Artificial nitrogen (N) additions and climate changes have been shown to affect plant N utilization and soil N availability, yet it remains uncertain if and how plant N utilization changed with anthropogenic N pollution under the real climatic backgrounds in forest ecosystems. By investigating concentrations and natural 15 N abundance of leaf N, soil nitrate (NO 3 − ) and reduced N (Red‐N, sum of ammonium and extractable organic N) among forests under natural N deposition and climates in East Asia, we first quantitatively analyzed soil N‐source contributions to plants and their environmental responses on a regional scale. Plants preferentially utilized NO 3 − (54 ± 18%) over Red‐N (46 ± 18%), despite NO 3 − was four times less than Red‐N in soils. Increased N deposition, rather than climates, was the main factor enhancing soil NO 3 − availability and plant NO 3 − uptake. This work provides valuable evidence for optimizing forest management to enhance plant N sequestration and mitigate soil N losses.