Desert Abiotic Carbon Sequestration Weakening by Precipitation

Synergistic effects of clays and cyanobacteria on the accumulation dynamics of soil organic carbon in artificial biocrusts

Biocrusts are the primary organic carbon reservoirs in desert areas, in which inorganic clays potentially playing significant roles; however, the specific details of these roles remain largely unclear. In this study, typical 1:1 type (kaolin) and 2:1 type (montmorillonite, MMT) clay minerals were added to artificial biocrusts to investigate their effect on the acquisition performance of soil organic carbon (SOC). After 84 days of cultivation, the enhancement effects of kaolin and MMT were significant, resulting in SOC increments that were 5.03 times and 4.08 times higher than those of the Algae group (without clay). Notably, the two types of clay exhibited different advantages in SOC accumulation. Due to its larger external specific surface area and higher cation exchange capacity, MMT contributes more effectively to SOC stability. Specifically, the mineralization quotient (qM), hot-water extractable organic carbon (HWEOC), and molecular structural stability of SOC in the MMT group were 0.3, 0.34, and 1.31 times those of the Algae group, respectively. In contrast, kaolin was more favorable for microbial growth and SOC formation due to its higher dissolved organic carbon (DOC) content. Microbial biomass carbon (MBC), chlorophyll-a (Chl-a), photosynthetic performance index (PIABS), and Shannon index in the kaolin group were 5.67, 2.44, 11.95, and 1.82 times those of the Algae group, respectively. These findings highlighted the synergistic effect for SOC accumulation of clay and cyanobacteria in artificial biocrust systems, clarified the specific roles of two typical clay minerals, and offered new insights for accelerating the restoration of nutrient-limited areas such as deserts.

Measurement and characteristics of radon flow in an extremely arid region based on a closed-system earth-air model

Radon (222Rn) is a radioactive gas that occurs naturally in the soil and is harmful to the environment and health. However, the measuring the amount of radon flowing is challenging. This study reveals the mechanism responsible for radon transportation and concentration variation, the main driving forces acting, and the key factors operating in the vadose zone. In this study, two separate holes were used to monitor the amount of earth-air and radon flowing in and out of the soil in the extremely arid region in China where the Mogao Grottoes are located. Using a closed-system model, the quantity, characteristics, and regularity of the flow of earth-air and radon were thus determined on daily and yearly timescales. The same patterns of variation in earth-air flow and radon concentration were found at the two sites, both depending on the variation in the atmospheric pressure (AP). When the AP decreases, earth-air flows out from the soil with a high radon concentration. Conversely, when the AP increases, earth-air enters into the soil with a low radon concentration. Thus, radon is continuously emitted from the soil. The concentration of radon in the earth-air is proportional to the rate of flow of earth-air and therefore increases as the AP decreases. The radon emission also varies with the seasonal variation in temperature and AP, which is high in summer and low in winter. On a daily timescale, the radon varies in a bimodal manner. Therefore, the net amount of radon emitted from the soil is positively correlated with the amplitude of the AP fluctuation, temperature, soil porosity, and thickness of the vadose zone. The atmospheric pumping is the main driving force responsible for the radon emission. However, the surface closure, landform, cracks, faults, grain size, pore structure, soil adsorption, basal uranium/radium, salts, wind, lunar cycle, latitude and altitude have important effects on the number of radon emission. As such, it provides a scientific basis for the effective utilization of radon and prevention of its emission from soil.