Combined Effects of Snow Depth and Nitrogen Addition on Ephemeral Growth at the Southern Edge of the Gurbantunggut Desert

Water and nitrogen (N) are two key factors affecting plant growth in terrestrial ecosystems, and changes in the availability of water and N markedly influence plant traits. Subsequently, these changes affect ecosystem processes, especially in resource-limited arid deserts. Thus, understanding how plant communities respond to concurrent alterations in water and N availabilities under global change scenarios is important.

In the Gurbantunggut Desert in China, the germination and development of ephemerals primarily depend on the early spring snowmelt water. Nearby farms have recently increased their application of nitrogenous fertilizer. Emission from nearby cities has also enhanced local soil N levels. This potential source of N would disperse to adjacent desert ecosystems.

To explore the effects of different snow-covering depths and N addition levels on ephemerals, a bi-factor field experiment with varying snow depths and N addition levels was conducted during the snow-covering season from 2009 to 2010 at the southern edge of the Gurbantunggut Desert.

Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast, N addition sharply decreased the density of ephemerals in the same snow treatment. Meanwhile, N addition exhibited a different effect on the growth of ephemeral plants: in the 50% snow treatment, N addition limited the growth of ephemeral plants, showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth (100% and 150% snow treatments), N addition benefited the growth of the dominant individual plants. Species richness was not significantly affected by snow in the same N treatment. However, N addition significantly decreased the species richness in the same snow-covering depth. The primary productivity of ephemerals in the N addition increased with the increase of snow depth.

These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply. With plenty of water (100% and 150% snow treatments), N addition contributed to the growth of ephemeral plants; while with less water (50% snow treatment), N addition restricted the growth of ephemeral plants. The result was published in Journal of Arid Land in December 2013.