外来植物入侵对土壤氮有效性的影响

外来植物入侵对土壤氮循环和氮有效性的影响是入侵成功或进一步加剧的重要原因。通过对比相同研究地点入侵区域和无入侵区域的土壤原位氮状态差异, 探讨了外来植物入侵对土壤氮有效性的影响程度和生理生态学机制。基于107篇相关研究文献数据的整合, 发现植物入侵区域相对于无入侵区域土壤总氮、铵态氮、硝态氮、无机氮、微生物生物量氮含量显著增加, 增幅分别为(50 ± 14)%、(60 ± 24)%、(470 ± 115)%、(69 ± 25)%、(54 ± 20)%。土壤硝态氮含量增幅较大反映硝化作用增强, 这可能增加入侵植物硝态氮利用以及喜硝植物的共存。温带地区植物入侵后土壤的硝态氮含量增幅显著高于亚热带地区。固氮植物入侵后土壤的总氮和无机氮含量增幅均显著高于非固氮植物入侵。木本和常绿植物入侵后土壤的总氮含量增幅分别高于草本和落叶植物入侵; 而土壤铵态氮含量的增幅没有显著差异且与固氮入侵植物占比无明显关系; 然而硝态氮含量的增幅普遍较高且与固氮入侵植物占比显著正相关。外来入侵植物固氮功能以及凋落物质量和数量是影响土壤氮矿化和硝化过程的关键因素。该研究为理解外来植物入侵成功和加剧的机制以及入侵植物功能性状与土壤氮动态之间的关系提供了新的见解。

Effects of exotic plant invasion on soil nitrogen availability

Aims Exotic plant invasion has been a global eco-environmental issue, which declines biodiversity and influences ecosystem structure and function. Over the past decades, more and more studies showed that influences of exotic plant invasion on soil nitrogen (N) cycles, and soil N availabilities can facilitate the success and aggravation of invading plants.Methods Based on differences in soil N contents between invaded and uninvaded areas in natural ecosystems at the same study sites, this study explored magnitudes and ecophysiological mechanisms of soil N variations under exotic plant invasion.Important findings Based on the data integrated from 107 papers, we found that contents of soil total N, ammonium-N, nitrate-N, inorganic N, microbial biomass N under exotic plant invasion were increased by (50 ± 14)%, (60 ± 24)%, (470 ± 115)%, (69 ± 25)%, (54 ± 20)% respectively relative to those under no invasion. The increment in the soil nitrate-N pool was highest, suggesting higher nitrification rate, which potentially promoted plant nitrate-N utilization and the coexistence of nitrate-preferring species. The increment of soil nitrate-N pool under invasion was higher in the temperate zone than the subtropical zones significantly. Invasion of N₂-fixing plants caused obviously larger increments of soil total N and nitrate-N contents compared to invasion of non-N₂-fixing plants. The invasion of woody and evergreen invasive plants caused larger increments of soil total N than herbaceous and deciduous plants, respectively. The increases in soil ammonium-N under invasion did not differ substantially among different life forms and showed no clear relationship with the percentage of N₂-fixing plants. Differently, soil nitrate-N showed much larger increments under invasion and showed positive linear relationship with the percentage of N₂-fixing invasive plants. The N₂-fixing function, litter quality and quantity of invasive plants are important factors regulating soil N mineralization and nitrification under invasion. This study provides novel insights into the mechanisms underlying the success and aggravation of plant invasion and into the relationships between soil N dynamics and plant functional traits in ecosystems under exotic plant invasion.