Effects of Solidago canadensis L. on mineralization-immobilization turnover enhance its nitrogen competitiveness and invasiveness

Abstract

The effects of exotic plants on soil nitrogen (N) transformations may influence species invasion success. However, the complex interplay between invasive plant N uptake and N transformation in soils remains unclear. In the present study, a series of 15N-labeled pot experiments were carried out with Solidago canadensis L. (S. canadensis), an invasive plant, and the Ntrace tool was used to clarify the preferred inorganic N form and its effects on soil N transformation. According to the results, nitrate-N (NO3−-N) uptake rates by S. canadensis were 2.38 and 2.28 mg N kg−1 d−1 in acidic and alkaline soil, respectively, which were significantly higher than the ammonium-N (NH4+-N) uptake rates (1.76 and 1.56 mg N kg−1 d−1, respectively), indicating that S. canadensis was a NO3−-N-preferring plant, irrespective of pH condition. Gross N mineralization rate was 0.41 mg N kg−1 d−1 in alkaline soil in the presence of S. canadensis L., which was significantly lower than that in the control (no plant, CK, 2.44 mg N kg−1 d−1). Gross autotrophic nitrification rate also decreased from 5.95 mg N kg−1 d−1 in the CK to 0.04 mg N kg−1 d−1 in the presence of S. canadensis in alkaline soil. However, microbial N immobilization rate increased significantly from 1.09 to 2.16 mg N kg−1 d−1, and from 0.02 to 2.73 mg N kg−1 d−1 after S. canadensis planting, in acidic and alkaline soil, respectively. Heterotrophic nitrification rate was stimulated in the presence of S. canadensis to provide NO3−-N to support the N requirements of plants and microbes. The results suggested that S. canadensis can influence the mineralization-immobilization turnover (MIT) to optimize its N requirements while limiting N supply for other plants in the system. The results of the present study enhance our understanding of the competitiveness and mechanisms of invasion of alien plants.