Abstract:

Nitrogen deposition is one of the major driving factors for biodiversity. Generally speaking, graminoids and deciduous shrubs compete more for nitrogen than forbs and evergreen shrubs. However, previous studies have mainly focused on a single life-form of plants in alpine meadows or desert steppes, ignoring the range of different life-forms across different habitats. Furthermore, there is no obvious canopy or vertical structure in these ecosystems that might exacerbate light limitation. Hence, there need to be more nitrogen experiments in other more complicated ecosystems (e.g. forest ecosystem) to better understand how nitrogen affects understory plants. We conducted an 8-year N fertilization experiment with three treatment levels (0 kg N·ha ^-1·yr ^-1, 50 kg N·ha ^-1·yr ^-1, 100 kg N·ha ^-1·yr ^-1) in the Quercus wutaishanica forest at Mt. Dongling, Beijing to study the response of temperate forest understory plants to nitrogen deposition. We found that: (1) Nitrogen addition reduced the species richness and biodiversity of understory plants and changed the species composition and community structure significantly. (2) Nitrogen addition increased richness of the shrub layer, but decreased richness of the herbaceous layer. (3) Graminoids responded negatively to nitrogen deposition, while forbs were positively affected. The study shows that richness and species composition change differently in response to nitrogen deposition for different life-forms of plants. In fact, the entire community of understory plants may shift in response to a change in soil resources (e.g. increase in nutrient contents and decrease in pH) and light availability (e.g. shrubs can access light easier than herbs).

Key words: nitrogen deposition, species richness, Quercus wutaishanica, understory plants, biodiversity