Biological invasion has become one of the most serious environmental problems around the world, even the arid areas are no exception, although which is charcteristiced by harsh natural conditions and water shortages. Biological soil crusts (BSCs), known as the ecosystem engineer, play an important role in maintaining the stability and health of native plant communities in arid ecosystems. However, it is fully unknown whether BSCs can offer some benefits in preventing exotic plant invasions. To answer this question, we conducted a greenhouse experiments to: 1. test the effects of algal crusts on seed germination and growth of exotic grass; 2. test the effects of algal crusts on the growth of an exotic plant with two native annual grasses, Eragrostis poaeoides and Artemisia capillaries. This study was conducted in the ecotone between steppe-like desert and sandy-desert (North China). Specifically, we considered Stipa glareosa as exotic grass which is widely distribute over the natural desert steppe. The experiment included three algal crust cover levels (intact, disturbed and bare soil) and four species combinations (E. poaeoides, E. poaeoides mixed with S. glareosa, A. capillaries, and A. capillaries mixed with S. glareosa).
Results/Conclusions
Preliminary analysis showed that algal crusts can significantly (P<0.001) reduce exotic grass germination, and the maximum and minimum germination rates were found in bare soil and intact algal crusts respectively. There was significant interaction between exotic grass and algal crust cover level in individual-plant aboveground biomass of native grasses (P<0.05), but lacked a significant main effect of exotic grass on the two native grasses. Thus it is suggested that the influence of exotic grass on native grasses growth depended on different algal crust cover levels. Our results indicated that the presence and expansion of BSCs on the fixed dunes can reduce the germination and biomass of exotic grass and maintain native species diversity, which could be attributed to the formation of a physical barrier and reduction of available soil water. We conclude that BSCs acting as the natural biological barrier for artificial sand-fixing vegetation can promote stability and sustainability of ecosystems in this arid area.