Species Differences in Nitrogen Acquisition in Humid Subtropical Forest Inferred From ¹⁵N Natural Abundance and Its Response to Tracer Addition

• Main Authors: Geshere Abdisa Gurmesa, Xiankai Lu, Per Gundersen, Qinggong Mao, Yunting Fang, Jiangming Mo
• Format: Article
• Language: English
• Published: MDPI AG 2019-11-01
• Series: Forests
• Subjects: n deposition; ¹⁵n natural abundance; subtropical forest; tree species; china
• Online Access: https://www.mdpi.com/1999-4907/10/11/991

Differences in nitrogen (N) acquisition patterns between plant species are often reflected in the natural ¹⁵N isotope ratios (δ¹⁵N) of the plant tissues, however, such differences are poorly understood for co-occurring plants in tropical and subtropical forests. To evaluate species variation in N acquisition traits, we measured leaf N concentration (%N) and δ¹⁵N in tree and understory plant species under ambient N deposition (control) and after a decade of N addition at 50 kg N ha^−1 yr^−1 (N-plots) in an old-growth subtropical forest in southern China. We also measured changes in leaf δ¹⁵N after one-year of ¹⁵N addition in both the control and N-plots. The results show consistent significant species variation in leaf %N in both control and N-plots, but decadal N addition did not significantly affect leaf %N. Leaf δ¹⁵N values were also significantly different among the plant species both in tree and understory layers, and both in control and N-plots, suggesting differences in N acquisition strategies such as variation in N sources and dominant forms of N uptake and dependence on mycorrhizal associations among the co-occurring plant species. Significant differences between the plant species (in both control and N-plots) in changes in leaf δ¹⁵N after ¹⁵N addition were observed only in the understory plants, indicating difference in access (or use) of deposited N among the plants. Decadal N addition had species-dependent effects on leaf δ¹⁵N, suggesting the N acquisition patterns of these plant species are differently affected by N deposition. These results suggest that co-occurring plants in N-rich and subtropical forests vary in their N acquisition traits; these differences need to be accounted for when evaluating the impact of N deposition on N cycling in these ecosystems.