Haotian Yang

Carbon sequestration capacity of shifting sand dune after establishing new vegetation in the Tengger Desert, northern China.

Reconstructing vegetation in arid and semiarid areas has become an increasingly important management strategy to realize habitat recovery, mitigate desertification and global climate change. To assess the carbon sequestration potential in areas where sand-binding vegetation has been established on shifting sand dunes by planting xeric shrubs located near the southeastern edge of the Tengger Desert in northern China, we conducted a field investigation of restored dune regions that were established at different times (20, 30, 47, and 55 years ago) in the same area. We quantified the total organic carbon (TOC) in each ecosystem by summing the individual carbon contributions from the soil (soil organic carbon; SOC), shrubs, and grasses in each system. We found that the TOC, as well as the amount of organic carbon in the soil, shrubs, and grasses, significantly increased over time in the restored areas. The average annual rate of carbon sequestration was highest in the first 20 years after restoration (3.26 × 10(-2)kg·m(-2) ·year(-1)), and reached a stable rate (2.14 × 10(-2) kg·m(-2) ·year(-1)) after 47 years. Organic carbon storage in soil represented the largest carbon pool for both restored systems and a system containing native vegetation, accounting for 67.6%-85.0% of the TOC. Carbon in grass root biomass, aboveground grass biomass, litter, aboveground shrub biomass, and shrub root biomass account for 10.0%-21.0%, 0.2%-0.6%, 0.1%-0.2%, 1.7%-12.1% and 0.9%-6.2% of the TOC, respectively. Furthermore, we found that the 55-year-old restored system has the capacity to accumulate more TOC (1.02 kg·m(-2) more) to reach the TOC level found in the natural vegetation system. These results suggest that restoring desert ecosystems may be a cost-effective and environmentally friendly way to sequester CO2 from the atmosphere and mitigate the effects of global climate change.

Water repellency of biological soil crusts and influencing factors on the southeast fringe of the Tengger Desert, north-central China.

Abstract Biological soil crusts (BSC) have key roles in hydrological and ecological processes in arid desert areas. Water repellency (WR) of BSC is an important property because it modifies the local hydrological regimes and affects ecosystem functions. However, the variations of WR in different types of BSC and the temporal variations under field condition are relatively unknown. Actual WR of four types of BSC and mobile sand were observed sequentially after heavy rainfall using the water drop penetration time test. The development of BSC on the surface of stabilized sand dune markedly promotes WR. The WR of four types of BSC variation across time was influenced by environmental factors under field conditions. The WR increased as soil moisture content or air relative humidity increased up to a level above which WR decreased. However, the peak levels varied between the different types of crusts. For surface temperature of BSC and air temperature, the WR of the four types of BSC decreased with increasing temperature. Our results demonstrate that the WR of BSC in arid desert ecosystems depends greatly on the developmental stages of the crusts, as well as environmental factors, such as antecedent topsoil moisture conditions, relative humidity, surface temperature, and air temperature.

Allometric models for estimating shrub biomass in desert grassland in northern China

ABSTRACT The development of shrub allometric models is crucial for accurate biomass assessment, as well as for scientific studies of carbon storage and carbon cycling of desert ecosystems. The aim of the present study was to construct allometric models to predict biomass using easily measured variables for xerophytic shrubs. The 12 most widespread shrub species of northern China were selected and a total of 385 individuals were harvested to obtain the weight of its components (leaves, twigs, branches, and roots), the crown area (CA) and plant height (H). Based on a high coefficient of determination (R2), a low standard error of estimate (SEE), and low Akaike information criterion (AIC) values, 72 species-specific and 24 multispecies models with CA and H as independent variables were developed. The function lnW (biomass of different components) = a + b × lnX (predictor variable) was selected as optimal model. CA was revealed as the best independent variable for the biomass of leaves and twigs, and V (CA × H) was the best predictor variable for branches, aboveground, belowground, and total biomass. In conclusion, for the first time species-specific and multispecies models were constructed with a high goodness of fit of leaves, twigs, branches, aboveground, belowground, and total biomass for 12 shrub species in northern China. Compared to multispecies models, species-specific models had improved accuracy. Since biomass quantification is the basis of carbon stocks estimation, the models presented here can be considered as alternative tool for assessing carbon storage and carbon cycling of desert ecosystems.

Modelling the influence of snowfall on cyanobacterial crusts in the Gurbantunggut Desert, northern China

Biological soil crusts (BSCs) are widespread in arid and semiarid regions. They have long been regarded as a key biotic component of desert ecosystems. However, little information is available regarding the influence of snowfall on BSCs in desert ecosystems. Therefore, we conducted the present work in the largest fixed and semi-fixed desert in China, the Gurbantunggut Desert, where snowfall is a special form of precipitation, and snow cover is a prerequisite for BSC survival during the harsh winter. We investigated the effects of altered winter snowfall on biomass, chlorophyll (Chl) fluorescence, moisture content, and soluble-protein and malondialdehyde (MDA) concentrations in cyanobacterial crusts in the early (March) and late (October) periods after snowfall in 2014. The results indicated that biomass (indicated by Chl a), Chl fluorescence (i.e. maximum photochemical efficiency, fluorescence yield and rates of electron transport) and the concentration of soluble protein of cyanobacterial crusts declined as a result of lower soil water content resulting from snow removal or reduction. Increased snowfall had positive effects on physiological properties associated with photosynthesis but induced dramatic decreases in the MDA concentration in cyanobacterial crusts. In addition, photosynthesis of cyanobacterial crusts was obviously higher in the late than in the early period after snowfall, which can be attributed to increases in the cover of cyanobacteria in the crust communities. These findings provided evidence that increased snowfall in the Gurbantunggut Desert could favour and help maintain the development of BSCs.

Soil water repellency and influencing factors of Nitraria tangutorun nebkhas at different succession stages

Soil water repellency (WR) is an important physical characteristic of soil surface. It is capable of largely influencing the hydrological and geomorphological processes of soil, as well as affecting the ecological processes of plants, such as growth and seed germination, and has thus been a hot topic in recent research around the world. In this paper, the capillary rise method was used to study the soil WR characteristics of Nitraria tangutorun nebkhas. Soil water repellencies at different succession stages of Nitraria tangutorun were investigated, and the relationships between soil WR and soil organic matter, total N, and total P, soil texture, pH, and concentrations of CO32−, HCO3−, Cl−, SO42−, Na+, K+, Ca2+ and Mg2+ were discussed. Soil WR may be demonstrated at the following nebkhas dune evolvement stages: extremely degraded>degraded>stabilized>well developed>newly developed>quick sand. Apart from some soil at the bottom, the WR of other soils (crest and slope of dune) was found to be largest at the topsoil, and decreased as the soil depth increased. The results showed that multiple factors affected soil WR characteristics, e.g. WR increased significantly as the contents of soil organic matter and total N increased, but did not change as the total P content increased. Soil texture was a key factor affecting soil WR; soil WR increased significantly as clay content increased, and decreased significantly as sand content increased. Low pH was shown to be more suitable for the occurrence of soil WR. Four cations (Ca2+, Mg2+, K+ and Na+) and two anions (Cl− and SO42−) enhanced soil WR, while CO32− decreased it. HCO3− did not show any observable effect. Finally, we established a best-fit general linear model (GLM) between soil-air-water contact angle (CA) and influencing factors (CA=5.606 sand+6.496 (clay and silt)-2.353 pH+470.089 CO32−+11.346 Na+-407.707 Cl−-14.245 SO42−+0.734 total N-519.521). It was concluded that all soils contain subcritical WR (0°

Changes in winter snow depth affects photosynthesis and physiological characteristics of biological soil crusts in the Tengger Desert

Water availability is a major limiting factor in desert ecosystems. However, a winter snowfall role in the growth of biological soil crusts is still less investigated. Here, four snow treatments were designed to evaluate the effects of snow depth on photosynthesis and physiological characteristics of biological soil crusts. Results showed that snow strongly affected the chlorophyll fluorescence properties. The increased snow depth led to increased contents of photosynthetic pigments and soluble proteins. However, all biological soil crusts also exhibited a decline in malondialdehyde and soluble sugar contents as snow increased. Results demonstrated that different biological soil crusts exhibited different responses to snow depth treatment due to differences in their morphological characteristics and microhabitat. In addition, interspecies differentiation in response to snow depth treatment might affect the survival of some biological soil crusts. Further, this influence might lead to changes in the structural composition and functional communities of biological soil crusts.