Abstract: Mycorrhizae can enhance plant nitrogen (N) acquisition and affect soil N cycling. Because tree species differ in mycorrhizae types they associated with, stand-scale soil N cycling could be influenced by tree species composition via their association with different types of mycorrhizae. We investigated the effects of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) forests on soil N cycling in subtropical forests. Total soil N and ammonium (NH₄⁺-N) contents did not differ between AM and ECM forests, whereas dissolved organic N (DON) and nitrate (NO₃^--N) were significantly higher in AM than in ECM forests (P<0.001). In particular, soil NO₃^--N was more than twice as high in AM as in ECM forests in both the organic horizon and mineral horizon. Soil NO₃^-∶NH₄⁺ ratio was greater than 1 in AM forest soil but less than 1 in ECM forest soil, indicating that plant-available N was abundant in AM forest soil. Soil net nitrification was 2.2 times higher in the AM forest than in the ECM forest and positively correlated with soil NO₃^--N content. The relatively fast soil N cycling in AM forests was attributed to the higher aboveground litter quality, soil pH, and water contents. We found that more nitrate was leached in AM forests than ECM stands, suggesting that the “mycorrhizal-associated nutrient economy” framework can also apply to subtropical forests. These results will improve our prediction of soil N cycling, aid the development of soil N cycling models under global change, and facilitate forest restoration in this subtropical region.

Key words: mycorrhizal-associated nutrient economy, inorganic nitrogen, net nitrogen transformation rate.