The effects of well-developed biological soil crusts on vascular plants in a temperate desert of Northwestern China: Negative or positive?

Background/Question/Methods: The interaction between crusts and vascular plants is controversial. We hypothesize that it will be different effects of BSCs on vascular plants during their different life stages, and will be different due to different species of vascular plants. We conducted a series of shadow experiments to examine the effects of biological soil crusts on seed germination of Haloxylon persicum, Ephedra distachya, Ceratocarpus arenaarius, Ma1colmia africana and Lappula semiglabra.

Results/Conclusions: The results show that the effects of biological soil crusts on seed germination of target species were variable under both moist and dry conditions. The presence of crusts significantly reduced germination of Ceratocarpus arenaarius and Malcolraia africana compared with surfaces from which the crusts had been removed. But there was no significant effect on germination of the other species under dry conditions. Under moist conditions, seed germination of Haloxylon persicum, Ceratocarpus arenaarius and Lappula semiglabra was significantly lower on crusts than on the surface devoided of crust, and there was no significant effect for Ephedra distachya and Maleolmia Africana. In general, biological soil crusts affected the germination of some vascular plants, but whether the effect was negative or positive depended on water condition and biological characteristics of the seeds. We also found that, after seed germination, biological soil crusts significantly accelerated the growth rate of seedlings in all five species, but increased biomass accumulation only in herbaceous species, not in shrub species. Crusts also promoted early flowering and fruiting in herbaceous species, which could be beneficial to rapid establishment of herb communities before environmental resources become more available in other seasons. Crusts also influenced nutrient uptake by plants, especially N. The influence on uptake of other nutrients was species-specific. Therefore, biological soil crusts may be important in maintaining desert plant diversity.