Effect of biological soil crusts on microbial activity in soils of the Tengger Desert (China)
Introduction
Arid and semiarid lands account for as much as 33–40% of Earth's terrestrial surface, and are expanding rapidly (Billings et al., 2003). Vegetation cover in these areas is patchy and discontinuous due to combined impacts of harsh environmental factors such as prolonged drought, high temperatures and high soil erosion rates. Nevertheless, biocrusts are able to adapt successfully to these adverse environments, colonize the bare disaggregated geological substrate (Li, 2012) and cover as much as 70% of the interspaces between the sparse vegetation in these areas (Steven et al., 2014). Numerous studies have examined the ecosystem functions of biocrusts in desert ecosystems, such as fixing of C and N, improving soil structure, enhancing soil stability, modifying soil temperature, moisture and local hydrology, reinforcing plant colonization and promoting soil invertebrate and microbial diversity (Belnap and Lange, 2003, Bowker et al., 2013, Darby et al., 2010, Liu et al., 2013, Neher et al., 2009).
Soil microbes, as an important biological component of soils, have a function in soil formation and soil remediation processes, through the decomposition of organic matter, formation of humus, and nutrient cycling. Soil basal respiration is mostly associated with activity of microbes, therefore it indicates the potential mineralization rate of soil organic matter by soil microbes from a desert ecosystem (Pell et al., 2006). The ratio of basal respiration to microbial biomass carbon (metabolic quotient: qCO2), provides a method to relate both the amount and activity of soil microbes (Anderson and Domsch, 1990). Soil basal respiration, qCO2 and enzyme activity provide a measure of microbial activity, which is a sensitive indicator of soil quality changes in response to environmental changes (Creamer et al., 2014, Raiesi and Beheshti, 2015, Wardle and Ghani, 1995). Recent studies have examined the relationship between biocrusts and soil microbial activity. For example, Bastida et al. (2014) found that the values of soil basal respiration and enzyme activities were higher in biocrusts than in soil beneath biocrusts in south-east Spain. Miralles et al., 2012a, Miralles et al., 2012b found that the values of soil basal respiration and the activities of arylsulphatase, β-glucosidase, casein-protease, cellulase and phosphomonoesterase were higher in soil beneath biocrusts than in bare substrate of the Tabernas Desert. Yu and Steinberger (2012) reported that the values of soil basal respiration were two-fold higher in biocrusts-covered interdune than in playa in the western Negev Desert. Studies by Zhang et al. (2012) and Liu et al. (2014) showed that soil catalase, urease, dehydrogenase and sucrase activities were high beneath biocrusts compared with bare soil without crust. It is also suggested that the successional stages of crusts could influence soil basal respiration and enzyme activities such as catalase, urease, dehydrogenases, sucrase and nitrogenase (Liu et al., 2014, Miralles et al., 2012b, Wu et al., 2009).
Although the influence of biocrusts on soil basal respiration, qCO2 and enzyme activity has been studied, few studies have specifically examined how the soil microbial activity parameters respond to differences in successional stages of crusts, such as those in restored sand dunes in the Tengger Desert. Moreover, less is known about the effects of biocrusts on qCO2 and enzyme activity at different soil depths and in different seasons. The present study aims to clarify functions of biocrusts in soil processes based on soil basal respiration, qCO2 and enzymatic activities. Firstly, we determined the impacts of biocrusts on soil basal respiration, qCO2 and enzyme activities in the study area and secondly, showed how these parameters varied with successional stages of crusts. Thirdly, we examined how these parameters changed after trampling disturbance. Finally, we studied the spatial and temporal variations of soil basal respiration, qCO2 and enzyme activities under biocrusts in the study area.
Section snippets
Study area
The field sites (i.e., revegetated and natural vegetated) were located in the desert steppe region at the Shapotou Desert Research and Experiment Station, bordering the Tengger Desert, northern China (37°32′N, 105°02′E) at an elevation of 1300 m a.s.l. The sites are representative of the transition zone between desertified steppe and sand dunes. The climate is tropical dry with an average precipitation and potential evaporation of approximately 186 and 3000 mm yr−1, respectively. Average annual
Effects of biocrusts on soil physicochemical properties
Both cyanobacteria–lichen and moss crusts affected soil texture, resulting in an increase in the content of soil clay and silt and reduction in the content of sand in 0–30 cm soil in comparison with bare soil (Table 1). Soil organic C, total N, available N, total P, available P and pH were higher beneath biocrusts than in bare soil at the depth of 0–30 cm (Table 1). These soil physicochemical properties markedly varied with the successional stage of crusts, the restoration age and soil depth (
Effects of biocrusts on soil basal respiration, qCO2 and enzyme activities
The biocrusts in vegetated areas enhanced soil physicochemical properties, basal respiration and the activity of soil alkaline phosphatase, protease and cellulase, and reduced qCO2. These results are similar to the findings of Miralles et al., 2012a, Miralles et al., 2012b and Bastida et al. (2014), who found that soil basal respiration and several hydrolase enzyme activities were higher in biocrusts than in bare substrata in south-east Spain. High soil basal respiration under biocrusts
Conclusions
Biocrusts strongly increased soil basal respiration and activities of soil alkaline phosphatase, protease and cellulase, and reduced qCO2 in vegetated areas of the Tengger Desert. Severe trampling of biocrusts markedly reduced soil basal respiration and activities of soil alkaline phosphatase, protease and cellulase, and enhanced qCO2 in 0–15 cm soil layer in the study areas. The successional stage of crusts and the restoration age also highly affected soil basal respiration, qCO2 and enzyme
Acknowledgements
This research was funded by China National Funds for Regional Science (grant No. 41261014) and the China National Funds for Young Scientists (grant No. 41401341).
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