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Biological soil crusts occur in dry land worldwide. However, studies on the carbon exchange of crusts with different histories of crust development are rare, especially in terms of the responses of carbon exchange to increasing atmospheric CO2 concentrations and decreasing water contents of crust organisms. In this study, we classified sites in Shapotou in the Tengger Desert as recent (site revegetated in 1981 in mobile sand dunes) and old (site revegetated in 1956) successional stages, and systematically analyzed the changes in the carbon exchange of cyanobacterial-algal crusts developed in the two sites to dehydration, air temperature (15 and 25 °C), and CO2 concentration (200–2000 ppm). The old crusts had a higher carbon exchange rate than the recent crusts during dehydration, and the maximum carbon exchange rates were 3.49 and 2.45 µmol · m−2 · s−1 for the old and recent crusts, respectively, at an approximately 60% water content of dry crust organisms. The carbon exchange rate was higher at 25°C than at 15°C for both crusts. No difference in the CO2 saturation points between the two crusts and between the two temperatures was observed, however, the saturation point significantly increased with the increase in the water content of the crust organisms, from 224 to 1384 ppm, when the water content of the crust organisms was increased from 20% to 100%. The water content of the crust organisms was the regulating factor for the carbon exchange rate of both the old and recent cyanobacterial-algal crusts. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes. [Copyright &y& Elsevier]

Biological soil crusts are widespread in arid and semiarid regions. They are one of the major components of desert ecosystems, and their importance has been demonstrated by numerous researchers. However, little research has been carried out on the relationship between biological soil crusts and the diversity of desert insects. In this study, psammophilous Caragana korshinskii-Artemisia ordosica communities occurring on semifixed dunes and fixed dunes in the Shapotou region at the southeastern fringe of the Tengger desert are investigated. Observation sample plots and the survey quadrats were arranged in the vegetation areas with different types and coverage of biological soil crusts. The insects were surveyed in 10 m × 10 m quadrats and caught by a sampling frame and net-trap methods. The insect number was recorded and samples were collected for identification. The results show that as compared to the un-crusted vegetation area, the presence of biological soil crusts in the Tengger desert significantly increases the diversity and abundance of insect species. Diversity and abundance in the quadrats mainly covered by moss and lichen crusts are significantly higher than those in the quadrats mainly covered by cyanobacteria and algal crusts. The contribution of biological soil crusts to the diversity of insect species may be attributed to the stabilized soil surface providing suitable habitats and some food sources for the insects. [ABSTRACT FROM AUTHOR]