Rongliang Jia

Responses of photosynthetic properties and chloroplast ultrastructure of Bryum argenteum from a desert biological soil crust to elevated ultraviolet-B radiation.

Our understanding of plant responses to enhanced ultraviolet-B (UV-B) radiation has improved over recent decades. However, research on cryptogams is scarce and it remains controversial whether UV-B radiation causes changes in physiology related to photosynthesis. To investigate the effects of supplementary UV-B radiation on photosynthesis and chloroplast ultrastructure in Bryum argenteum Hedw., specimens were cultured for 10 days under four UV-B treatments (2.75, 3.08, 3.25 and 3.41 W m(-2) ), simulating depletion of 0% (control), 6%, 9% and 12% of stratospheric ozone at the latitude of Shapotou, a temperate desert area of northwest China. Analyses showed malondialdehyde content significantly increased, whereas chlorophyll (Chl) fluorescence parameters and Chl contents decreased with increased UV-B intensity. These results corresponded with changes in thylakoid protein complexes and chloroplast ultrastructure. Overall, enhanced UV-B radiation leads to significant decreases in photosynthetic function and serious destruction of the chloroplast ultrastructure of B. argenteum. The degree of negative influences increased with the intensity of UV-B radiation. These results may not only provide a potential mechanism for supplemental UV-B effects on photosynthesis of moss crust, but also establish a theoretical basis for further studies of adaptation and response mechanisms of desert ecosystems under future ozone depletion.

Photosynthesis of two moss crusts from the Tengger Desert with contrasting sensitivity to supplementary UV-B radiation

Predicting the effects of increased ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion on temperate desert ecosystems requires better knowledge of the ecophysiological response of common moss species. The aim of the current work was to determine whether elevated UV-B radiation affected photosynthetic performance and chloroplast ultrastructure of two moss crusts and whether response differences were observed between the crusts. In laboratory experiments, Bryum argenteum and Didymodon vinealis, which show microdistributions and are dominant in soil crusts at the Tengger Desert, Northern China, were subjected to four levels of UV-B radiation of 2.75 (control), 3.08, 3.25, and 3.41 W m−2 for 10 days, simulating 0, 6, 9, and 12% of stratospheric ozone at the latitude of Shapotou, respectively. The results showed that chlorophyll a fluorescence parameters (i.e., the maximal quantum yield of PSII photochemistry, the effective quantum yield of PSII photochemistry, and photochemical quenching coefficient), pigment contents, soluble protein contents, and the ultrastructure were negatively influenced by elevated UV-B radiation and the degree of detrimental effects significantly increased with the intensity of UV-B radiation. Moreover, results indicated that B. argenteum was probably more sensitive to supplementary UV-B radiation than D. vinealis. Therefore, we propose the use of B. argenteum crusts as a bioindicator of responses to elevated UV-B radiation.

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.

Combined application of cyanobacteria with soil fixing chemicals for rapid induction of biological soil crust formation

ABSTRACT Combined applications of cyanobacteria with soil fixing chemicals were investigated to generate artificially induced biological soil crust (BSC). Polyvinyl alcohol (PVA) and Tacki-Spray (TKS7) chemicals composed of bio-polysaccharides and tackifiers were examined under laboratory conditions. Following singular applications of chemicals, the mean weight diameter values of soil treated with TKS7 were 1.4–2.5 times higher than those of soil treated with PVA and thus TKS7 was selected for further tests for application with cyanobacteria (Nostoc Vaucher ex Bornet & Flahault, Phormidium Kützing ex Gomont, and Scytonema arcangeli Bornet ex Flahault). Combined application of cyanobacteria and different concentrations of TKS7 enhanced soil aggregate stability, resulting in mean weight diameter values of 0.58–0.69 mm and was comparable to TKS7 singular application (0.18–0.40 mm). Surface hardness values were also highly improved by the combined application of cyanobacteria with TKS7 (4.5 MPa) compared to singular treatment of cyanobacteria (2.3 MPa). In addition, superabsorbent polymer (SAP) was applied as a water-holding material and nutrient supplement in soil. The SAP promoted cyanobacterial cell growth under dry conditions. Chlorophyll a content of soil was improved by the addition of SAP (CST1: 2.93 µg g−1) compared to singular treatment of cyanobacteria (C: 2.25 µg g−1). These results suggest that combined application of cyanobacteria with TKS7 and SAP can induce BSC formation faster than singular application of cyanobacteria. The novel method presented herein can be applied to restoration of degraded soils in arid and semiarid areas.

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.

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°

Hydrological response of biological soil crusts to global warming: A ten-year simulative study

Biological soil crusts across the desert regions play a key role in regional ecological security and ecological health. They are vital biotic components of desert ecosystems that maintain soil stability, fix carbon and nitrogen, influence the establishment of vascular plants, and serve as habitats for a large number of arthropods and microorganisms, as well as influencing soil hydrological processes. Changes in temperature and precipitation are expected to influence the functioning of desert ecosystems by altering biotic components such as the species composition of biological soil crusts. However, it remains unclear how these important components will respond to the prolonged warming and reduced precipitation that is predicted to occur with climate change. To evaluate how the hydrological properties of these biological soil crusts respond to these alterations, we used open-top chambers over a 10-year period to simulate warming and reduced precipitation. Infiltration, dew entrapment, and evaporation were measured as surrogates of the hydrological functioning of biological soil crusts. It was found that the ongoing warming coupled with reduced precipitation will more strongly affect moss in crustal communities than lichens and cyanobacteria, which will lead to a direct alteration of the hydrological performance of biological soil crusts. Reductions in moss abundance, surface cover, and biomass resulted in a change in structure and function of crustal communities, decreased dew entrapment, and increased infiltration and evaporation of biological soil crusts in desert ecosystems, which further impacted on the desert soil water balance.