[Effects of revegetation on soil nitrogen-fixation and carbon-fixation microbial communities in the Horqin Sandy Land, China]. / 科尔沁沙地植被重建对土壤固氮和固碳菌群的影响.

To determine the diversity of nitrogen-fixing and carbon-fixing microbial groups in aeolian sandy soil and the effects of sand-fixation plantation type on the structures of two microbial groups in the Horqin Sandy Land, we selected six representative sand-fixation vegetations with the same age, including Caragana microphylla, Artemisia halodendron, Salix gordejevii, Hedysarum fruticosum, Populus simonii, and Pinus sylvestris var. mongolica as well as their adjacent natural Ulmus pumila open forest as test objects to investigate the diversities and structures of nifH- and cbbL-carrying microbial communities in soil by high-throughput sequencing technique. The results showed that vegetation type significantly affected soil physical and chemical properties, microbiological activities, diversities and the main compositions of nitrogen-fixing and carbon-fixing microbial communities. The diversity of soil nitrogen-fixing microbial communities under S. gordejevii and P. simonii plantations and that of carbon-fixing microbial communities under P. sylvestris var. mongolica and P. simonii plantations were significantly higher than those of other plantations. Skermanella, Bradyrhizobium, Azospirillum, and Azohydromonas were dominant nitrogen-fixation genera, with the average relative abundance of 22.3%, 21.5%, 20.8%, and 17.8%, respectively. Soil carbon-fixation microbial communities were dominated by Pseudonocardia, Bradyrhizobium, Cupriavidus, and Mesorhizobium, with relative abundance of 22.4%, 18.5%, 10.5%, and 6.0%, respectively. Soil nitrogen-fixing microbial community under C. mirophylla plantation and carbon-fixing communities under S. gordejevii and P. simonii plantations were very close to those of natural U. pumila open forest. Soil organic matter, NH4+-N, and total phosphorus were the direct determining factors for nitrogen-fixing microbial community, while pH, soil moisture, and available phosphorus were main factors influencing carbon-fixing microbial community. These observations potentially provide the scienti-fic foundations for evaluating the ecological benefits of revegetation practice in sandy lands.

[Soil microbes functional diversity in sand-fixing Caragana microphylla communities in Horqin Sandy Land].

Aimed to understand the soil microbes functional diversity in sand-fixing Caragana microphylla communities in Horqin Sandy Land, the soil microbial carbon sources metabolism diversity in 9-, 16-, and 26-yr-old C. microphylla plantations, natural C. microphylla community, and mov-ture, the average well color development (AWCD) and the capabilities of soil microbes in metabo-lizing carboxylic acids, carbohydrates, polymers, amino acids, amines, and aromatics were obvi-ously higher in moving sand dune than in the plantations. The carbon source types metabolized by soil microbes increased with the increasing age of the plantations, and the carbon source metabolic pattern of the soil microbes in 26-yr-old C. microphylla plantation was similar to that in natural C. microphylla community. The functional diversity and evenness index of soil microbes decreased after the establishment of C. microphylla on moving sand dune, whereas the functional diversity of soil microbes increased with increasing age of C. microphylla plantation.

[Comparison of the methods for extracting and purifying microbial total DNA from an aeolian sandy soil].

In order to select and establish an appropriate method for extracting and purifying the microbial total DNA from an aeolian sandy soil, six extraction methods (five direct methods and one indirect method) and two purification methods were examined, with the quantity and quality of extracted and purified total DNA compared. All the six extraction methods could extract the total DNA with a length of approximately 23 kb, among which, the improved SDS high salt extraction method (using 40% PEG8000 and 4 mol x L(-1) NaCl to precipitate DNA) was the best. This method could have a yield slightly less than that obtained by using kits, and the extracted DNA had the highest purity after purification, being available in 16S rDNA PCR amplification. Among the purification methods, the effect of agarose gel electrophoresis plus minicolumn was satisfactory, with most of the purified total DNA being able to be PCR-amplified and meet the requirements of the purity of DNA in the follow-up molecular operations.

[Amelioration effect of sand-fixing Hedysarum fruticosum plantations on soil nutrient contents and biological activities].

With adjacent semi-moving dune as the control, this paper studied the effects of 5-, 10- and 22-year old Hedysarum fruticosum plantations on the nutrient status, microbial biomass, and enzyme activities at the soil depths 0-10, 10-20 and 20-30 cm. The results showed that with the establishment of H. fruticosum plantation on moving dune, soil C, N, P and K contents and biological activities increased obviously with the increasing age of the plantation, and the increment was much higher at 0-10 cm than at 10-20 and 20-30 cm. At 0-30 cm, soil C/N increased from 7.3 to 8.5, and microbial biomass C, N and P as well as the activities of urease, protease, saccharase, phosphomonoesterase, dehydrogenase, polyphenol oxidase and nitrate reductase all increased. Among the test enzyme activities, saccharase activity had the most significant increase, with its value at 0-10 cm being 49.7-284.5 times of the control. There were significant positive correlations between soil microbial biomass C, N and P and organic C, total N and total P, respectively, and between soil microbial biomass and enzyme activities.