Lichao Liu

Distribution, biomass, and dynamics of roots in a revegetated stand of Caragana korshinskii in the Tengger Desert, northwestern China

A field experiment was conducted to investigate root distribution, biomass, and seasonal dynamics in a revegetated stand of Caragana korshinskii Kom. in the Tengger Desert. We used soil profile trenches, soil core sampling, and minirhizotron measurements to measure root dynamics. Results showed that the roots of C. korshinskii were distributed vertically in the uppermost portion of the soil profile, especially the coarse roots, which were concentrated in the upper 0.4xa0m. The horizontal distribution of the root length and weight of C. korshinskii coarse roots was concentrated within 0.6 and 0.4xa0m of the trunk, respectively. The lateral distribution of fine roots was more uniform than coarse roots. Total-root and fine-root biomasses were 662.4xa0±xa045.8 and 361.1xa0±xa010.3xa0gxa0m−2, accounting for about two-thirds and one-third of the total plant biomass, respectively. Fine-root turnover is closely affected by soil water, and both of these parameters showed synchronously seasonal trends during the growing season in 2004 and 2005. The interaction between fine-root turnover and soil water resulted in the fine-root length densities and soil water content in the 0- to 1.0-m soil layer having similar trends, but the soil water peaks occurred before those of the fine-root length densities.

Ecological restoration and recovery in the wind-blown sand hazard areas of northern China: relationship between soil water and carrying capacity for vegetation in the Tengger Desert

The main prevention and control area for wind-blown sand hazards in northern China is about 320000 km2 in size and includes sandlands to the east of the Helan Mountain and sandy deserts and desert-steppe transitional regions to the west of the Helan Mountain. Vegetation recovery and restoration is an important and effective approach for constraining wind-blown sand hazards in these areas. After more than 50 years of long-term ecological studies in the Shapotou region of the Tengger Desert, we found that revegetation changed the hydrological processes of the original sand dune system through the utilization and space-time redistribution of soil water. The spatiotemporal dynamics of soil water was significantly related to the dynamics of the replanted vegetation for a given regional precipitation condition. The long-term changes in hydrological processes in desert areas also drive replanted vegetation succession. The soil water carrying capacity of vegetation and the model for sand fixation by revegetation in aeolian desert areas where precipitation levels are less than 200 mm are also discussed.

Sand sea activity and interactions with climatic parameters in the Taklimakan Sand Sea, China

An analysis is undertaken of the temporal and spatial variability of climatic parameters including precipitation, potential evaporation and wind regimes that control the aeolian activity in the Taklimakan Sand Sea. Mobility index is calculated according to the mode that Lancaster (J. Arid Environ. 14 (1988) 233) suggested. Our results show that there are apparent temporal and spatial variations for this mobility index. The annual aeolian activity varies in phase with the number of windy days, precipitation and potential evaporation. Dune development is highly consistent with distribution of the mobility index. The mobility index shows that the Taklimakan Sand Sea experienced high aeolian sand activity during the 1960s and mid-1980s, and then related sand transport was reduced from the mid-1980s to the late 1990s. The mobility index cycle cannot be obtained because the available meteorological data cover only short periods. Such an approach will require longer research combined with field observations of sand movement.

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 10u2009days under four UV-B treatments (2.75, 3.08, 3.25 and 3.41u2009Wu2009m(-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.

Distribution and Seasonal Dynamics of Roots in a Revegetated Stand of Artemisia ordosica Kracsh. in the Tengger Desert (North China)

In revegetated desert areas, roots are critical for plant growth and community stability. A field study was conducted to investigate the distribution and dynamics of roots in a revegetated stand of Artemisia ordosica Kracsh. in the Tengger Desert during the growing seasons of 2004 and 2005. Seven trenches 1.2 m wide and 1.0 m deep were excavated around stems to determine the coarse root length and weight. Soil cores, spaced from the stem at an interval of 0.2, 0.4, 0.6, 0.8, and 1.0 m, were designed to take fine root samples, and minirhizotrons were buried at intervals of 0.2, 0.5, and 1.0 m away from the stem to measure the fine root number and length. The results showed that the root systems of A. ordosica is distributed vertically in the uppermost soil profile, especially for coarse roots, which were concentrated in the 0.2-m soil profile. The horizontal distribution of A. ordosica coarse roots was limited to a range of 0.6 m and 0.4 m away from the trunk for root length and weight, respectively. Fine roots were distributed uniformly in comparison with coarse roots. The total root biomass and fine root biomass were 0.42 and 0.26 kg m−2, which accounted for about 80% and 50% of the total biomass, respectively. The growth and distribution of fine roots were mainly related to soil water content. Peak values in both soil water content and fine root length were observed twice, in 2004 and 2005. The peak value of soil water content was observed 1 month prior to that of fine root length density. The fine roots were abundant 1 month later, when the volumetric soil water content reached 2.75%.

Effects of microbiotic crusts on evaporation from the revegetated area in a Chinese desert

Conflicting views exist on the evaporative effects of microbiotic crusts. The effects of microbiotic crusts on evaporation were studied using a microlysimeter under different simulated precipitation. The results show that under minor precipitation, the microbiotic crusts generally act as a retarding factor for evaporation, prolonging water retention in the surface layer in comparison with sandy soil, whereas under abundant precipitation, the crusts result in less infiltration and a greater total water loss through evaporation. It is possible that microbiotic crusts act as a major environmental driver in the succession of restored vegetation through their influence on evaporative water loss.

Mechanical Disturbance of Microbiotic Crusts Affects Ecohydrological Processes in a Region of Revegetation-fixed Sand Dunes

ABSTRACT Microbiotic crusts (MC), also called biological soil crusts or cryptogamic crusts, are formed by cyanobacteria, fungi, blue-green algae, lichens, and mosses, and are widespread in arid and semiarid zones such as the area of sands fixed in place by revegetation near Shapotou at the southeastern edge of Chinas Tengger Desert. We studied mechanically disturbed and 40-year-old intact MC in this area using a series of soil hydrological experiments and ecological investigations to examine the ecohydrological responses after mechanical disturbance of the MC. Once the MC was disturbed, the MC layer became ore primitive or disappeared entirely, resulting in a 32.8% decrease in the fine particles content of the upper soil layers, a 28.7% increase in soil albedo and a 168.9% decrease in the topsoils water-retention capacity. These changes greatly altered soil hydrological processes in the disturbed soils: the steady-state infiltration rates in the upper soil layer increased by 693%, the precipitation recharge layer deepened, and the surface evaporation rate decreased by 20.3%. Moreover, the disturbance increased storage of plant-available water in the herbaceous rooting zone and improved the environment for germination and subsequent growth of annual herb species, as shown by a notable increase in the coverage, density, frequency, and biomass of annual plants. We conclude that MC represent a major component of Shapotous regional ecosystem and that disturbance will significantly alter local ecohydrological processes.

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.

Winter snowfall can have a positive effect on photosynthetic carbon fixation and biomass accumulation of biological soil crusts from the Gurbantunggut Desert, China

Winter snowfall is an important factor in the growth and development of biological soil crusts (BSCs) in temperate desert regions of China. In this study, intact algae, lichen, and moss crusts from the Gurbantunggut Desert were collected and exposed to five experimental treatments—snow removal (0S), snow decrease to half that of ambient conditions (1/2S), ambient snow (S), snow increase to 1.5 times that of ambient conditions (3/2S), and snow increase to twice that of ambient conditions (2S)—to evaluate the effect of snowfall on the ecophysiological parameters of the BSCs during the melt and at the end of the growing period. The results clearly identified differences in physiological and ecological indexes between snowfall manipulation treatments in March, and further found that the values of most of the ecophysiological indexes were influenced by snow removal/reduction treatments, the type of BSC and their interaction effect. The chlorophyll fluorescence parameters, chlorophyll content, and the rates of photosynthesis and respiration of all three types of crust declined because of decreased soil water content with decreased snow cover, and this effect would likely be even greater under conditions of decreased precipitation. The rates of photosynthesis and respiration of the main types of BSC were changed by variations in the winter snowfall, and confirmed the existence of long-term snowfall impacts on photosynthetic carbon fixation and biomass accumulation. These results provide a foundation for future studies to assess the potential effects of snowfall on the carbon sequestration of BSCs from arid and semi-arid regions.