Combined Effects of Nitrogen Deposition and Water Stress on Growth and Physiological Responses of Two Annual Desert Plants in Northwestern China

Water and N are essential requirements for plant growth and survival. The photosynthetic rate, chlorophyll content, and concentrations of sugars, proline, and soluble proteins vary in plants subject to different moisture conditions and nutritional status. Annual plants play an important role in some desert ecosystems; their occurrence affects both the vegetative productivity of deserts and the stability of sand dunes. However, few studies have analyzed the combined effects of soil water and N input on growth and physiological responses of annual plants in desert ecosystems. Different responses of annual plants to N deposition and water have the potential to change the biodiversity of plant communities within a short period of time and also increase the dominance of alien, annual plants.

Malcolmia africana and Bassia hyssopifolia are two desert plants native to northwestern China; both species are common in Central Asian desert ecosystems.  M. africana is considered to be an ephemeral, since its life cycle is completed within two to three months (short vegetative period). B. hyssopifolia an annual, lives approximately one to two months longer than M. africana (long vegetative period). Both germinate in spring, after which there is a rapid increase in shoot system biomass.

Therefore, M. africana and B. hyssopifolia were selected to determine the combined effects of nitrogen deposition and water stress on their growth and physiological responses. The results showed that nitrogen addition and water stress significantly affected growth of both species. Root weight, leaf number, average leaf area, total biomass, and the shoot/root ratio increased with N addition. For both species, increasing N levels were correlated with higher concentrations of chlorophyll and soluble proteins, higher net photosynthetic rates, and lower content of soluble sugars and proline. M. africana was more sensitive to water stress than B. hyssopifolia, but few differences were observed between the species in their response to N addition. The negative effects of water stress on growth and physiological responses were partly compensated by increased N supply. Overall, the results suggest that N deposition could lead to an increase in annual plant growth in northwestern China.

This study was jointly financed by the National Basic Research Program, the National Natural Science Foundation of China and the Key Knowledge Innovation Project of the Chinese Academy of Sciences. The result has been published on Environmental and Experimental Botany, 2011, 74: 1-8. This paper is also archived at http://www.sciencedirect.com/science/article/pii/S0098847210002613.