Abstract:

In recent years， the artificial biological soil crusts applied in land desertification has been developed to be a technology of new and green in the environment protection particular in fixing moving sand and the study of ecological restoration of desert areas. However， the yield of desert cyanobacteria and other organisms used for the cultivation of artificial biological soil crusts is a bottleneck that limits the large-scale application of this technology. Thereby， to explore the growth characteristics of desert cyanobacteria and their effect factors， seven predominated species isolating from Tengger Desert cyanobacteria crusts， including Microcolus vaginatus and Nostoc carneum， were selected as subjects. In the condition of laboratory test， the influence of inoculum density on its growth characteristics and the changes of pH and conductivity of water environment during growth are explored. Results showed that， with the increase of the inoculum density， the growth time to enter stationary phase of M. vaginatus and N. carneum was advanced. In the early stage of growth， the dry weight of M. vaginatus was significantly higher at densities of 0.35 and 0.95 mg·L^-1 than at densities of 2.13， 6.59 and 13.42 mg·L^-1， and the opposite was true in the later stages of growth. In the early and late stages of growth， the dry weight of N. carneum in the density of 0.04-0.32 mg·L^-1 was significantly higher than that of the density of 0.86-2.59 mg·L^-1；the total mass of M. vaginatus at the density of 6.59-13.42 mg·L^-1 was significantly higher than 0.35-2.13 mg·L^-1，the total mass of Nostoc spp. was significantly higher at the density of 0.04-0.32 mg·L^-1 than 0.86-2.59 mg·L^-1，the total mass of M. vaginatus was significantly higher than Nostoc spp. under the same inoculum density. The growth of both M. vaginatus and N. carneum can increase the pH of water environment， but decrease the electrical conductivity significantly. The total mass of M. vaginatus and N. carneum showed a significant power and binomial relationship with inoculum density respectively， the pH of water environment with the dry weights of M. vaginatus and N. carneum was significantly positively correlated， and the electrical conductivity had a negative correlation with the dry weight of N. carneum. The inoculum density is an important factor affecting the growth of M. vaginatus and N. carneum. The proliferation of two species of cyanobacteria is one of the main causes of the high pH and the decrease of the electrical conductivity of water environment. Therefore， this study suggests that the inoculum density of the two desert cyanobacteria are 6.59-13.42 mg·L^-1 and 0.04-0.32 mg·L^-1 during large-scale cultivation， respectively.

Key words: biological soil crust, desert cyanobacteria, Microcolus vaginatus, Nostoc carneum, initial densities