Nitrogen addition decreases seed germination in a temperate steppe

Area of Science:

• Ecology
• Environmental Science
• Botany

Background:

• Seed germination and seedling establishment are critical for plant community dynamics under global change.
• Nitrogen (N) deposition is a major global change factor, often causing species richness loss in grasslands.
• The specific effects of N addition on seed germination remain largely uninvestigated.

Purpose of the Study:

• To investigate the impact of varying levels of Nitrogen (N) addition on seed germination and seedling establishment in a semi-arid grassland.
• To understand how N enrichment influences the densities and richness of different plant functional groups and dominant species.

Main Methods:

• A pot incubation experiment was conducted in a Mongolian Plateau semi-arid grassland.
• Nitrogen was added at rates of 0, 5, 10, 20, 40, and 80 g N/m².
• Seed germination and seedling densities of 20 species were monitored from May to October 2016.

Main Results:

• Nitrogen addition significantly decreased the densities of dominant species like *Stipa krylovii*, *Leymus chinensis*, and *Artemisia frigida*.
• Seedling densities of the overall community, perennial forbs, perennial grasses, and annuals/biennials were suppressed by N addition.
• Species richness of the community, perennial forbs, and annuals/biennials declined sharply with increasing N levels, while perennial grass richness remained unchanged. The Shannon-Wiener diversity index also decreased.

Conclusions:

• Nitrogen enrichment significantly affects seed germination and reduces the successful establishment of seedlings into adult plants.
• These findings provide insights into how atmospheric N deposition contributes to species loss in grassland ecosystems.