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In order to elucidate the activity and ecological distribution of arbuscular mycorrhizal (AM) fungi in Saibei desert steppe, we sampled soil from three different sites at Erniudian,Shangduzhen and Qinggeletu in Saibei desert steppe in June 2013. Roots of Caragana korshinskii and rhizosphere soil were collected from each site at five depths in the soil profile: 0-10, 10-20, 20-30, 30-40 and 40-50 cm, respectively. The results indicated that C. korshinskii formed strong symbiotic relationship with AM fungi. AM fungal spore density and colonization rates were significantly affected by sampling sites and soil depths. The highest spore density occurred at the 0-10cm layer and gradually decreased with soil depths. Hyphal colonization rate was the highest in samples collected at Shangduzhen among the three sites. However, vesicular colonization was the lowest in samples from Qinggeletu, and there were no significant differences among soil layers. Arbuscular colonization differed among the three sites. Both the total colonization rates and colonization intensity of AM fungi http: / / www.ecologica.cn in root samples from Shangduzhen were the highest compared to the other two sites, respectively. Spore density strongly correlated with soil organic C, total N, easily extractable glomain (EEG) and total extractable glomalin (TG) (all P < 0郾 01) , soil pH (P<0郾 05) , and negatively correlated with available P (P<0郾 01). Hyphal colonization rate had negative correlation with soil pH, available P, total N and acid phosphatase (all P< 0郾 05). Vesicular and arbuscular colonization rates were strongly correlated with available N and alkaline phosphatase (all P<0郾 01). EEG and TG had significant positive correlation with available N, total N, alkaline phosphatase and acid phosphatase (all P<0郾 01) , urease (P < 0郾 05) , but had no significant correlation with available P. Principal component analysis showed that acid and alkaline phosphatase, TG, total N and organic carbon were the key factors affecting soil nutrient status. The average contents of TG and EEG were 3.19 mg / g and 1.17 mg / g accounting for 7.77% and 3.83% of the total soil organic carbon, and 20郾 81% and 9.57% of the total soil nitrogen, respectively. Multiple linear regression analysis showed significant linear correlation between TG or EEG and soil organic C and total N, respectively. The results suggest that AM fungal colonization and glomalin are useful indicators for evaluating soil quality and function of desert ecosystem on the basis of its relationship with AM fungal distribution, soil nutrient dynamics, carbon and nitrogen cycle.

Desertification is the most severe problem in grasslands and sandlands in north China. In the desertified grassland, seed germination and seedling growth are affected by many ecological factors, such as drought, high temperature, sand burial, and wind and water erosion. In Inner Mongolia grassland of north China, sand burial is a common phenomenon caused by moving sand dunes. Plant shoots, seeds, and seedlings of sand dune plants are often buried by sand. Thus, plants must tolerate sand burial to survive and reproduce in sand dune habitats. Clonal plants, especially guerilla ones, can invade open patches through clonal growth, which may greatly affect soil nutrition status and microbial communities of the invaded sites. Previous study indicated that clonal growth and integration play an important role in their clonal expansion, such as in supporting the survival of new ramet on sand dunes. Psammochloa villosa produces linear monopodially growing rhizomes and it mainly relies on clonal growth to sustain and renew its populations. Hedysarum laeve is one of the arid鄄active and sand鄄fixation plants which can not only conserve soil, but also block the wind, reduce soil erosion, and thus maintain the balance and stability of arid areas. Dark septate endophytes (DSE) , a miscellaneous group of ascomycetes, colonize root tissues intracellularly and intercellularly without causing apparent negative effects on the host http: / / www.ecologica.cn plant. DSE fungi exhibit a broad range of host plants. DSE may benefit their host plants by facilitating the uptake of water and mineral nutrients from soil, and suppressing infection by plant pathogens. To investigate the effects of the growth of clonal plants on the activities of DSE and soil physical and chemical properties of invaded sites in Inner Mongolia, China, soil samples (0-50 cm depth) were collected under two guerilla鄄type, rhizomatous clonal plants, H. laeve and P. villosa, in June, August and October in 2013, respectively. The results showed that the clonal plants gradually invaded the bare spaces of community from June to October. The number of invaded community of P. villosa was higher than that of H. laeve. DSE colonization in roots of H. laeve community declined gradually with the sampling time. The highest colonization rate was found in roots sampled in June. In contrast, DSE colonization of P. villosa increased with the sampling time with the peak colonization rate in October. The invasion of clonal plants significantly increased the content of soil available nutrition, such as available N and P, which became more suitable for the growth of clonal plants. DSE colonization rate in H. laeve root systems in the bare spaces positively correlated with soil pH and electrical conductivity. Whilst for P. villosa, DSE colonization rate had strong negative correlation with soil pH, but had positive correlation with soil electrical conductivity, available N and available P, respectively. We concluded that the invasion of clonal plants greatly affected DSE colonization and...

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