Microbial Community Dynamics Of Biological Soil Crusts In Desert Induced By Addition Of Cellulose

At present, the problem of global desertification is grim, especially in Inner Mongolia where there are many deserted areas. Biological soil crusts (BSCs) can contain desertification, and provide a good fundamental environment for the ecosystem recovery. Cellulose degrading bacteria (CDB) are one of the main microbial physiological groups in desert soil, which play an important role in maintaining stability and repairing desert ecosystem. Past studies have proved that straw amending improved soil quality and changed the microbial community structure. However, the effects on the microbial community structure by the addition of cellulose into remains unclear.This study added different cellulose materials into BSCs and determined the shifts of total bacteria and CDB community structure by the regular sampling. Samples were divided into two fractions to be used to:one to count the numbers of total bacteria and CDB by the traditional culture methods, isolate and characterize CDB; another to extract soil DNA for PCR amplification, DGGE analysis of bacterial16S rDNA V3-V5. The results and conclusions were summarized as the followings:(1) Compared with the control, wheat straw greatly increased the numbers of bacteria and CDB, and wood flour didn’t effectively affect the number. After ten days of the addition of wheat straw, the numbers of bacteria and CDB increased sharply, that both reached the highest numbers at30days. From60days to the100days, all samples’ numbers of bacteria and CDB were Tends to be steady. At100day, the samples’numbers of bacteria and CDB by added exo-cellulose are higher than the control group.(2) Eight CDB(Marked as YD1、YD2、YD3、YD4、YD5、YD6、YD7and YD11) were isolated and identified by physiological and16S rDNA sequence analysis, they belong to Acinetobacter calcoaceticus, Pseudomonas fluorescens, Streptomyces humidus, Bacillus subtilis, Bacillus megaterium, Gordonia terrae, Arthrobacter nicotinovorans, Stenotrophomonas maltophilia, respectively, in which only YD7and YD11appeared on the count plate with exo-cellulose induced sample, but were not observed in the control. It was concluded that the addition of exo-cellulose could enrich CDB and easy the isolation of some CDB. The CMCase enzyme activity of YD4was17.5IU, which was significantly higher than other strains’. (3) Through the DGGE results and relative analysis, it could be seen that the diversity and richness of bacteria and CDB were improved by the addition of exo-cellulose and the effect of straw was much higher than wood flour. The samples were generally cluster into together based on dealing means and culturing time. The proportion of Clostridium was the highest, and so it may play an important role in degrading cellulose in BSC. Although cellulose were added and the community structure of each sample varied greatly, but the dominant groups always remained as Firmicutes and Alphaproteobacteria with minor ratio shifts in each sample.In sum from above, the addition of exo-cellulose may make crucial change in bacteria community structures and their numbers. And some cellulose degradation bacteria and other significant functional bacteria was increase in abundance and composition by induction of exo-cellulose. These functional bacteria changes contribute to the decomposition of cellulose material, which are helpful in nutrition enhancement and improve soil fertility,and healthy ecosystem recovery in desert.