AbstractMining activities leave large areas of post‐mining lands to be reclaimed. Increases in soil C and N pools and N availability are important to successfully reestablish trees on post‐mining land. In this study, we determined C and N concentrations and natural stable isotope of 13C and 15N in soil and plant in Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) plantations 8 years after establishment on non‐mined land (NM), post‐mining land without soil amendment (NAM), and post‐mining land with soil amendment (AM) in a placer gold mining region of Northeast China. We found that the growth of Mongolian pine was significantly slower on NAM as compared with NM (decreasing by 73% in tree height and 63% in basal diameter), but tree growth improved on AM. Soil C and N concentrations, plant N concentration, and soil δ15N value decreased in the order of NM > AM > NAM, implying that soil N availability decreased in post‐mining land, but soil amendment could increase soil N availability. However, the values of δ15N in plant tissues of Mongolian pine were higher on NAM than on NM and AM, suggesting that soil inorganic N form absorbed by trees might be changed when trees were directly planted on post‐mining land with lower soil N availability. In addition, the values of δ13C in 1‐ and 2‐year‐old leaves of Mongolian pine were lowest when planted on NAM, indicating a decrease in intrinsic water‐use efficiency of Mongolian pine. Our results suggest that soil amendment helps us establish forests successfully on post‐mining lands. Copyright © 2015 John Wiley & Sons, Ltd.