Data from: Increased nitrogen input enhances Kandelia obovate seedling growth in the presence of invasive Spartina alterniflora in subtropical regions of China

Mangroves in China are severely affected by the rapid invasion of the non-native species Spartina alterniflora. Although many studies have addressed the possible impacts of S. alterniflora on the performance of mangrove seedlings, how excessive nitrogen (N) input due to eutrophication affects the interactions between mangrove species and S. alterniflora remains unknown. Here, we report the results from a mesocosm experiment using seedlings of the native mangrove species Kandelia obovata and the exotic S. alterniflora grown in monoculture and mixed culture under no and nitrogen (N) addition treatments for 18 months. Without N addition, the presence of S. alterniflora inhibited the growth of K. obovata seedlings. Excessive N addition significantly increased the growth rate of K. obovata in both cultures. However, the positive and significantly increasing relative interaction intensity index (RII) suggested that the invasion of S. alterniflora could favour the growth of K. obovata under excessive N input. Our results imply that excessive N input in southeastern China can increase the competitive ability of mangrove seedlings against invasive S. alterniflora.

中国红树林正受到外来物种互花米草（Spartina alterniflora）的快速入侵，遭受严重影响。尽管已有诸多研究探讨了互花米草对红树林幼苗生长的潜在影响，但富营养化引发的过量氮（N）输入如何调控红树林物种与互花米草之间的种间相互作用，目前仍不明晰。本研究开展了为期18个月的中宇宙实验（mesocosm experiment），以本土红树林物种秋茄（Kandelia obovata）与外来入侵种互花米草为实验材料，设置单种、混种两种种植模式，以及无氮添加、氮添加两种处理方案。结果显示，无氮添加条件下，互花米草的存在会抑制秋茄幼苗的生长；而过量氮添加则显著提升了两种种植模式下秋茄的生长速率。但相对相互作用强度指数（relative interaction intensity index, RII）呈现正向且显著升高的变化趋势，表明在过量氮输入条件下，互花米草的入侵反而会促进秋茄的生长。本研究结果暗示，中国东南部地区的过量氮输入，可提升红树林幼苗对抗入侵种互花米草的竞争能力。