Guodong Cheng

Permafrost and climatic change in China

The permafrost area in China is about 2.15×106 km2, and is generally characterized by altitudinal permafrost. Permafrost in China can be divided into latitudinal and altitudinal types, the latter can be further divided into plateau and alpine permafrost. Altitudinal permafrost also can be divided into five thermal stability types. The permafrost environment has changed significantly since the Late Pleistocene. In northeastern China, the southern limit of permafrost extended to 41–42°N during the last glaciation maximum; in the Holocene megathermal, it retreated northward. The ice wedges and permafrost formed during the Late Pleistocene are still present in the northern part of the Da-Xinganling Mountains. The inactive ice wedges at Yitulihe indicate a cooling and subsequent permafrost expansion during the Late Pleistocene. The lower limit of altitudinal permafrost in western China has elevated from 800 to 1500 m since the last glaciation maximum. Compared with that in northern Europe and North America, latitudinal permafrost in northeastern China is less sensitive to climatic warming, but altitudinal permafrost, especially permafrost on the Qinghai–Tibet Plateau (QTP), is sensitive to climatic warming. Since the early 20th century, significant permafrost degradation has occurred and is occurring in most permafrost regions in China. Due to the combined influence of climatic warming and increasing anthropogenic activities, substantial retreat of permafrost is expected on the QTP and in northeastern China during the 21st century. Permafrost degradation has and will cast great influence on engineering construction, water resources and environments in the cold regions of China. The wetlands in the cold regions of China emit significant amounts of CH4 and N2O to the atmosphere and uptake atmospheric CO2 at a considerable rate, which might contribute to the global atmospheric carbon budget and feedback to climatic systems. However, uncertainties about permafrost changes, rates of changes and their environmental impacts are still large and call for intensive studying.

The effect of enhanced ultraviolet-B radiation on growth, photosynthesis and stable carbon isotope composition (δ13C) of two soybean cultivars (Glycine max) under field conditions

Abstract Two Chinese cultivars of Glycine max , namely Heidou and Jindou, were exposed to ambient and supplemental levels of ultraviolet-B (UV-B) radiation simulating a 24% depletion in stratospheric ozone over a 9-week growing period at an outdoor experimental site. Enhanced UV-B irradiation significantly reduced leaf, stem and root biomass, and plant height in the Heidou cultivar. These changes were associated with a diminished photosynthetic (net CO 2 ) rate, stomatal conductance, transpiration rate and water use efficiency, and accompanied by decreased foliar chlorophyll a and b, and total carotenoid concentrations and elevated foliar flavonoid levels. In contrast, the Jindou cultivar displayed only a significantly reduced stem mass and stomatal conductance, but no changes in pigment composition under elevated UV-B. The greater tolerance of elevated UV-B exposures by the Jindou cultivar was attributed partly to its higher foliar flavonoid content, smaller leaf size, thicker leaf cuticle and scabrous (hairy) lamina. Nevertheless both the Heidou cultivar and the less UV-B sensitive Jindou cultivar displayed an altered carbon isotope composition (δ 13 C) in their tissues following exposure to elevated UV-B. Such carbon isotope composition changes in plant tissues suggested a means of early detection of photosynthetic disruption in plants with anticipated increase in UV-B due to stratospheric ozone depletion.

A model for simulating the response of runoff from the mountainous watersheds of inland river basins in the arid area of northwest China to climatic changes

A model for simulating the response of monthly runoff from the mountainous watersheds to climatic changes is developed. The model is based on the modifications to the HBV runoff model, and therefore represents the characteristics and runofF generation processes of inland river basins in the arid area of northwest China. Talcing the mountainous watershed of an inland river, the Heihe River originating from the Qilian Mountains and running through the Hexi Corridor as an example, the monthly runoff changes under different climate scenarios are simulated. The simulation indicates that, during the years fmm 1994 to 2030, if the annual mean air temperature increases by 0.5°C, and precipitation keeps unchanged, then the runoff of May and October will increase because of the increase of the snow melt runoff, but the runoff of July and August will decrease to some extent because of the increase of evaporation, and as a result, the annual runoff will decrease by 4%. If the precipitation still keeps unchanged, and the air temperature increases by 1.0°C, in addition to the increase of runoff of May and June, the runoff of July and August will decrease in a larger amount, making the annual runoff decrease by 7.11%. If the air temperature keeps unchanged, the increase of annual precipitation by 10% will cause the increase of runoff by 5.27%; while the increase of precipitation by 20% will cause the increase of runoff by 12.35 %. When the air temperature increases by 0.5°C: and the precipitation increases by 10%, the mnoff will increase only by 1.62%.

Influences of local factors on permafrost occurrence and their implications for Qinghai-Xizang Railway design

Through man-made disturbance experiments, the corresponding relationships between suspended particulate matter (SPM) and wind speed in different lake areas were simu lated, the physicochemical formal transformation and biological mineralizing and decaying processes of phosphorus in SPM were studied, the contribution of phosphorus transformation to phosphorus loading of the water of Lake Taihu was quantitatively estimated. The results show that about 0.44 ta-1 loading in Lake Taihu mainly comes from phosphorus-releasing action of SPM in physicochemical transformed to soluble reactive phosphorus (SRP), and the contribution mainly from biological mineralizing and decaying was about 425.8ta-1, which is equal to 15.0% of the total external loading of Lake Taihu, namely 4.7–7.5 times as much as SRP loading entering the lake by the rivers; thus it is the important source in dynamical internal loading of the lake. The determining factors for dynamical internal loading in lakes are organic phosphorus content in suspended solid and its biological transition availability.

Diversity and distribution of alkaliphilic psychrotolerant bacteria in the Qinghai-Tibet Plateau permafrost region.

The Qinghai–Tibet Plateau represents a unique permafrost environment, being a result of high elevation caused by land uplift. And the urgency was that plateau permafrost was degrading rapidly under the current predicted climatic warming scenarios. Hence, the permafrost there was sampled to recover alkaliphilic bacteria populations. The viable bacteria on modified PYGV agar were varied between 102 and 105xa0CFU/g of dry soil. Forty-eight strains were gained from 18 samples. Through amplified ribosomal DNA restriction analysis (ARDRA) and phylogenetic analyses, these isolates fell into three categories: high Gxa0+xa0C gram positive bacteria (82.3%), low Gxa0+xa0C gram positive bacteria (7.2%), and gram negative α-proteobacteria (10.5%). The strains could grow at pH values ranging from 6.5 to 10.5 with optimum pH in the range of 9–9.5. Their growth temperatures were below 37°C and the optima ranging from 10 to 15°C. All strains grew well when NaCl concentration was below 15%. These results indicate that there are populations of nonhalophilic alkaliphilic psychrotolerant bacteria within the permafrost of the Qinhai-Tibet plateau. The abilities of many of the strains to produce extracellular protease, amylase and cellulase suggest that they might be of potential value for biotechnological exploitation.

Hymenobacter psychrotolerans sp. nov., isolated from the Qinghai--Tibet Plateau permafrost region

A psychrotolerant bacterium, designated strain Tibet-IIU11T, was isolated from the Qinghai--Tibet Plateau permafrost region, China. A taxonomic study was conducted using a polyphasic approach, with determination of physiological and biochemical properties and phylogenetic analysis based on 16S rRNA gene sequences. The novel isolate was found to belong to the genus Hymenobacter and was distinct from the recognized species of this genus. The major fatty acids were iso-C15 : 0 (24.5 %), summed feature 3 (C16 : 1omega7c and/or iso C15 : 0 2-OH; 20.0 %), summed feature 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B; 14.0 %), C16 : 1omega5c (12.7 %) and anteiso-C15 : 0 (8.4 %). Phosphatidylethanolamine and an unknown aminophospholipid were predominant in the polar lipid profile. The quinone system consisted exclusively of menaquinone MK-7 and sym-homospermidine was the major polyamine present. These chemotaxonomic traits are in good agreement with the characteristics of the genus Hymenobacter. The assignment of the novel isolate to this genus was further supported by a DNA G+C content of 60 mol%. On the basis of the polyphasic evidence presented in this study, it is proposed that strain Tibet-IIU11T (=DSM 18569T=CGMCC 1.6365T) represents a novel species, Hymenobacter psychrotolerans sp. nov.

Technical approaches on permafrost thermal stability for Qinghai–Tibet Railway

Widespread warm permafrost with a high ice content is a key problem for the roadbed stability of the Qinghai–Tibet Railway. A new approach is proposed to alleviate the effect of global warming and engineering construction on permafrost by cooling the roadbed and positively protecting the permafrost. Measures for cooling the roadbed by adjusting solar radiation, conduction, and convection are studied and applied to prevent ground ice from thawing and to ensure roadbed stability in permafrost regions. The results of monitoring permafrost embankments at Beiluhe and along the Qinghai–Tibet Railway show that the measures adopted for cooling the roadbed are very effective in raising permafrost table and reducing the soil temperature.

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.

The microbial diversity, distribution, and ecology of permafrost in China: a review

AbstractnPermafrost in China mainly located in high-altitude areas. It represents a unique and suitable ecological niche that can be colonized by abundant microbes. Permafrost microbial community varies across geographically separated locations in China, and some lineages are novel and possible endemic. Besides, Chinese permafrost is a reservoir of functional microbial groups involved in key biogeochemical cycling processes. In future, more work is necessary to determine if these phylogenetic groups detected by DNA-based methods are part of the viable microbial community, and their functional roles and how they potentially respond to climate change. This review summaries recent studies describing microbial biodiversity found in permafrost and associated environments in China, and provides a framework for better understanding the microbial ecology of permafrost.

Long-term thermal regimes of the Qinghai-Tibet Railway embankments in plateau permafrost regions

Ten years of ground temperature data (2003–2013) indicate that the long-term thermal regimes within embankments of the Qinghai-Tibet Railway (QTR) vary significantly with different embankment structures. Obvious asymmetries exist in the ground temperature fields within the traditional embankment (TE) and the crushed-rock basement embankment (CRBE). Measurements indicate that the TE and CRBE are not conducive to maintaining thermal stability. In contrast, the ground temperature fields of both the crushed-rock sloped embankment (CRSE) and the U-shaped crushed-rock embankment (UCRE) were symmetrical. However, the UCRE gave better thermal stability than the CRSE because slow warming of deep permafrost was observed under the CRSE. Therefore, the UCRE has the best long-term effect of decreasing ground temperature and improving the symmetry of the temperature field. More generally, it is concluded that construction using the cooling-roadbed principle meets the design requirements for long-term stability of the railway and for train transport speeds of 100 km h−1. However, temperature differences between the two shoulders, which exist in all embankments shoulders, may cause potential uneven settlement and might require maintenance.