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1. chinaXiv:201912.00009 [pdf]

Effects of temperature and light on seed germination of ephemeral plants in the Gurbantunggut Desert, China: implications for vegetation restoration

CHEN Yanfeng; CAO Qiumei; LI Dexin; LIU Huiliang; ZHANG Daoyuan
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light. Therefore, research on the effects of temperature and light on seed germination is extremely meaningful for vegetation restoration, especially in desert ecosystems. Seeds of 28 ephemeral plants collected from the Gurbantunggut Desert of China were incubated at different temperatures (5°C/1°C, 15°C/5°C, 20°C/5°C, 25°C/10°C and 30°C/15°C) in 12-h light/12-h darkness or continuous darkness regimes, and the responses of seed germination to temperature and light and the germination speed were studied in 2016. Results showed that seed germination percentage of the 28 ephemeral plants significantly differed to temperature and light. We classified the studied plants as the following groups based on their responses to temperature: 1 low temperature responsed plants, 12 moderate temperature responsed plants, 7 high temperature responsed plants, 4 non-responsed plants and 5 plants of no germination. It should be noted that Corispermum lehmannianum Bunge is sensitive to both moderate and high temperatures. There were 4 groups of plant in response to light, i.e., 7 light responsed plants, 10 dark responsed plants, 6 light non-responsed plants and 5 plants of no germination. Based on seed germination speed of the 28 ephemeral plants, we divided them into 4 patterns of germination, i.e., very rapid, moderately rapid, moderate and slow. Combining variations of temperature, precipitation and sand dune types in the study area, we suggested that very rapid and moderately rapid germinated plants could be used to moving sand dunes in early spring during vegetation restoration, moderate germinated plants could be used to semi-fixed sand dunes in late autumn, and slow germinated plants could be used to sand plain in summer. Thus, seedling establishment and vegetation restoration would be improved by considering seed germination characteristics of these ephemeral plants in the Gurbantunggut Desert, China.

submitted time 2019-12-06 From cooperative journals:《Journal of Arid Land》 Hits433Downloads100 Comment 0

2. chinaXiv:201912.00019 [pdf]

Water transport and water use efficiency differ among Populus euphratica Oliv. saplings exposed to saline water irrigation

ZHOU Honghua; CHEN Yaning ; ZHU Chenggang; YANG Yuhai; YE Zhaoxia
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Populus euphratica Oliv. is a unique woody tree that can be utilized for vegetation restoration in arid and semi-arid areas. The effects of saline water irrigation (0.00, 2.93, 8.78 and 17.55 g/L NaCl solutions) on water transport and water use efficiency (WUE) of P. euphratica saplings were researched for improving the survival of P. euphratica saplings and vegetation restoration in arid and semi-arid areas of Xinjiang, China in 2011. Results showed that hydraulic conductivity and vulnerability to cavitation of P. euphratica saplings were more sensitive in root xylem than in twig xylem when irrigation water salinity increased. Irrigation with saline water concentration less than 8.78 g/L did not affect the growth of P. euphratica saplings, under which they maintained normal water transport in twig xylem through adjustment of anatomical structure of vessels and kept higher WUE and photosynthesis in leaves through adjustment of stomata. However, irrigation with saline water concentration up to 17.55 g/L severely inhibited the photochemical process and WUE of P. euphratica saplings, resulting in severe water-deficit in leaves and a sharp reduction in water transport in xylem. Thus, it is feasible to irrigate P. euphratica forest by using saline groundwater for improving the survival of P. euphratica saplings and vegetation restoration in arid and semi-arid areas of Xinjiang, China.

submitted time 2019-12-06 From cooperative journals:《Journal of Arid Land》 Hits175Downloads94 Comment 0

3. chinaXiv:201910.00056 [pdf]

Wind regime for long-ridge yardangs in the Qaidam Basin, Northwest China

GAO Xuemin; DONG Zhibao; DUAN Zhenghu; LIU Min; CUI Xujia; LI Jiyan
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Yardangs are typical aeolian erosion landforms, which are attracting more and more attention of geomorphologists and geologists for their various morphology and enigmatic formation mechanisms. In order to clarify the aeolian environments that influence the development of long-ridge yardangs in the northwestern Qaidam Basin of China, the present research investigated the winds by installing wind observation tower in the field. We found that the sand-driving winds mainly blow from the north-northwest, northwest and north, and occur the most frequent in summer, because the high temperature increases atmospheric instability and leads to downward momentum transfer and active local convection during these months. The annual drift potential and the ratio of resultant drift potential indicate that the study area pertains to a high-energy wind environment and a narrow unimodal wind regime. The wind energy decreases from northwest to southeast in the Qaidam Basin, with the northerly winds in the northwestern basin changing to more westerly in the southeastern basin. The strong and unidirectional wind regime for the long-ridge yardangs in the northwestern Qaidam Basin results from the combined effects of topographic obstacles such as the Altun Mountains and of the interaction between the air stream and the yardang bodies. Present study suggests that yardang evolution needs such strong and unidirectional winds in high- or intermediate-energy wind environments. This differs from sandy deserts or sandy lands, which usually develop at low- or intermediate-energy wind environments. Present study clarifies the wind regime corresponding to the long-ridge yardangs' development, and lays firm foundation to put forward the formation mechanisms for yardangs in the Qaidam Basin.

submitted time 2019-10-26 From cooperative journals:《Journal of Arid Land》 Hits1454Downloads154 Comment 0

4. chinaXiv:201910.00057 [pdf]

Spatio-temporal variation of soil moisture in a fixed dune at the southern edge of the Gurbantunggut Desert in Xinjiang, China

ZHU Hai; HU Shunjun; YANG Jingsong; Fidele KARAMAGE; LI Hao; FU Sihua
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Soil moisture is critical for vegetation growth in deserts. However, detailed data regarding the soil moisture distribution in space and time in the Gurbantunggut Desert of China have not yet been reported. In this study, we conducted a series of in situ observation experiments in a fixed sand dune at the southern edge of the Gurbantunggut Desert from February 2014 to October 2016, to explore the spatio-temporal variation of soil moisture content, investigate the impact of Haloxylon ammodendron (C. A. Mey.) Bungeon soil moisture content in its root zone, and examine the factors influencing the soil moisture spatial pattern. One-way analysis of variance, least significant difference tests and correlation analysis were used to analyze the data. The results revealed that the soil moisture content exhibited annual periodicity and the temporal variation of soil moisture content throughout a year could be divided into three periods, namely, a moisture-gaining period, a moisture-losing period and a moisture-stable period. According to the temporal and spatial variability, the 0–400 cm soil profile could be divided into two layers: an active layer with moderate variability and a stable layer with weak variability. The temporal variability was larger than the spatial variability in the active layer, and the mean profile soil moisture content at different slope positions displayed the trend of decreasing with increasing relative height and mainly followed the order of interdune area>west and east slopes>slope top. The mean profile soil moisture content in the root zone of dead H. ammodendron individuals was significantly higher than that in the root zones of adult and young individuals, while the soil moisture content in the root zone of adult individuals was slightly higher than that in the root zone of young individuals with no significant difference. The spatial pattern of soil moisture was attributable to the combined effects of snowfall, vegetation and soil texture, whereas the effects of rainfall and evaporation were not significant. The findings may offer a foundation for the management of sandy soil moisture and vegetation restoration in arid areas.

submitted time 2019-10-26 From cooperative journals:《Journal of Arid Land》 Hits1561Downloads168 Comment 0

5. chinaXiv:201811.00111 [pdf]

Microbial adaptation to long-term N supply prevents large responses in N dynamics and N losses of a subtropical forest

Han, Xiaodge; Shen, Weijun; Zhang, Jinbo; Muller, Christoph
Subjects: Biology >> Biochemistry

Atmospherically-deposited nitrogen (N) can stimulate complex soil N metabolisms and accumulations over time. Whether long-term (decadal) N deposition effects on soil N transformations and functional microbes differ from the short-term (annual) effects have rarely been assessed. Here we conducted a laboratory 15N tracing study with soil samples from a short-term (one year) N addition site and a long-term (12 years) site in a subtropical forest. The effects of simulated N deposition on soil N2O emissions, N transformation rates and microbial nitrifying and denitrifying genes were determined. Our results showed that: (1) long-term N addition did not change soil N2O fluxes significantly in comparison to the short-term N addition. Denitrification, heterotrophic nitrification and autotrophic nitrification contributed 53%, 23% and 18% to total N2O emissions, respectively. (2) Autotrophic nitrification was the dominant N transformation process, except for the high-N treatment at the long-term site. The magnitude of soil N transformation rates was significantly different among N addition treatments but not between short- and long-term N addition sites. However, long-term N addition changed the responses of specific N transformation rates to N addition markedly, especially for the rates of nitrification, organic N mineralization to NH4+, NO3- immobilization and dissimilatory NO3- reduction to NH4+ (DNRA). (3) Responses of ammonia oxidizing archaea and bacteria (AOA and AOB) were stronger than denitrifying N2O-producers (nirK) and denitrifying N2O-reducers (nosZ) at the long-term site compared to the short-term site. (4) The close correlations among N2O flux, functional genes and soil properties observed at the short-term site was weakened at the long-term site, posing a decreased risk for N losses in the acid subtropical forest soils. There is evidence for an adaptation of functional microbial communities to the prevailing soil conditions and in response to long-term natural and anthropogenic N depositions.

submitted time 2018-11-22 Hits951Downloads456 Comment 0

6. chinaXiv:201810.00184 [pdf]

Simulating hydrological responses to climate change using dynamic and statistical downscaling methods: a case study in the Kaidu River Basin, Xinjiang, China

BA Wulong; DU Pengfei; LIU Tie; BAO Anming; LUO Min; Mujtaba HASSAN; QIN Chengxin
Subjects: Geosciences >> History of Geosciences

Climate change may affect water resources by altering various processes in natural ecosystems. Dynamic and statistical downscaling methods are commonly used to assess the impacts of climate change on water resources. Objectively, both methods have their own advantages and disadvantages. In the present study, we assessed the impacts of climate change on water resources during the future periods (2020–2029 and 2040–2049) in the upper reaches of the Kaidu River Basin, Xinjiang, China, and discussed the uncertainties in the research processes by integrating dynamic and statistical downscaling methods (regional climate models (RCMs) and general circulation modes (GCMs)) and utilizing these outputs. The reference period for this study is 1990–1999. The climate change trend is represented by three bias-corrected RCMs (i.e., Hadley Centre Global Environmental Model version 3 regional climate model (HadGEM3-RA), Regional Climate Model version 4 (RegCM4), and Seoul National University Meso-scale Model version 5 (SUN-MM5)) and an ensemble of GCMs on the basis of delta change method under two future scenarios (RCP4.5 and RCP8.5). We applied the hydrological SWAT (Soil and Water Assessment Tool) model which uses the RCMs/GCMs outputs as input to analyze the impacts of climate change on the stream flow and peak flow of the upper reaches of the Kaidu River Basin. The simulation of climate factors under future scenarios indicates that both temperature and precipitation in the study area will increase in the future compared with the reference period, with the largest increase of annual mean temperature and largest percentage increase of mean annual precipitation being of 2.4°C and 38.4%, respectively. Based on the results from bias correction of climate model outputs, we conclude that the accuracy of RCM (regional climate model) simulation is much better for temperature than for precipitation. The percentage increase in precipitation simulated by the three RCMs is generally higher than that simulated by the ensemble of GCMs. As for the changes in seasonal precipitation, RCMs exhibit a large percentage increase in seasonal precipitation in the wet season, while the ensemble of GCMs shows a large percentage increase in the dry season. Most of the hydrological simulations indicate that the total stream flow will decrease in the future due to the increase of evaporation, and the maximum percentage decrease can reach up to 22.3%. The possibility of peak flow increasing in the future is expected to higher than 99%. These results indicate that less water is likely to be available in the upper reaches of the Kaidu River Basin in the future, and that the temporal distribution of flow may become more concentrated.

submitted time 2018-10-29 From cooperative journals:《Journal of Arid Land》 Hits3165Downloads479 Comment 0

7. chinaXiv:201810.00188 [pdf]

Seasonal differences in climatic controls of vegetation growth in the Beijing–Tianjin Sand Source Region of China

SHAN, Lishan; YU, Xiang; SUN, Lingxiao; HE, Bin; WANG, Haiyan; XIE, Tingting
Subjects: Geosciences >> History of Geosciences

Launched in 2002, the Beiing–Tianjin Sand Source Control Project (BTSSCP) is an ecological restoration project intended to prevent desertification in China. Evidence from multiple sources has confirmed increases in vegetation growth in the BTSSCP region since the initiation of this project. Precipitation and essential climate variable-soil moisture (ECV-SM) conditions are typically considered to be the main drivers of vegetation growth in this region. Although many studies have investigated the inter-annual variations of vegetation growth, few concerns have been focused on the annual and seasonal variations of vegetation growth and their climatic drivers, which are crucial for understanding the relationships among the climate, vegetation, and human activities at the regional scale. Based on the normalized difference vegetation index (NDVI) derived from MODIS and the corresponding climatic data, we explored the responses of vegetation growth to climatic factors at annual and seasonal scales in the BTSSCP region during the period 2000–2014. Over the study region as a whole, NDVI generally increased from 2000 to 2014, at a rate of 0.002/a. Vegetation growth is stimulated mainly by the elevated temperature in spring, whereas precipitation is the leading driver of summer greening. In autumn, positive effects of both temperature and precipitation on vegetation growth were observed. The warming in spring promotes vegetation growth but reduces ECV-SM. Summer greening has a strong cooling effect on land surface temperature. These results indicate that the ecological and environmental consequences of ecological restoration projects should be comprehensively evaluated.

submitted time 2018-10-29 From cooperative journals:《Journal of Arid Land》 Hits3640Downloads468 Comment 0

8. chinaXiv:201810.00189 [pdf]

Sap flow characteristics and physiological adjustments of two dominant tree species in pure and mixed plantations in the semi-arid Loess Plateau of China

TANG Yakun; WU Xu; CHEN Yunming
Subjects: Geosciences >> History of Geosciences

It is essential to understand the water consumption characteristics and physiological adjustments of tree species under drought conditions, as well as the effects of pure and mixed plantations on these characteristics in semi-arid regions. In this study, the normalized sap flow (SFn), leaf water potential, stomatal conductance (gs), and photosynthetic rate (Pr) were monitored for two dominant species, i.e., Pinus tabuliformis and Hippophae rhamnoides, in both pure and mixed plantations in a semi-arid region of Chinese Loess Plateau. A threshold-delay model showed that the lower rainfall thresholds (RL) for P. tabuliformis and H. rhamnoides in pure plantations were 9.6 and 11.0 mm, respectively, and the time lags (τ) after rainfall were 1.15 and 1.76 d for corresponding species, respectively. The results indicated that P. tabuliformis was more sensitive to rainfall pulse than H. rhamnoides. In addition, strong stomatal control allowed P. tabuliformis to experience low gs and Pr in response to drought, while maintaining a high midday leaf water potential (Ψm). However, H. rhamnoides maintained high gs and Pr at a low Ψm expense. Therefore, P. tabuliformis and H. rhamnoides can be considered as isohydric and anisohydric species, respectively. In mixed plantation, the values of RL for P. tabuliformis and H. rhamnoides were 6.5 and 8.9 mm, respectively; and the values of τ were 0.86 and 1.61 d for corresponding species, respectively, which implied that mixed afforestation enhanced the rainfall pulse sensitivity for both two species, especially for P. tabuliformis. In addition, mixed afforestation significantly reduced SFn, gs, and Pr for P. tabuliformis (P<0.05), while maintaining a high leaf water potential status. However, no significant effect of mixed afforestation of H. rhamnoides was observed at the expense of leaf water potential status in response to drought. Although inconsistent physiological responses were adopted by these species, the altered water consumption characteristics, especially for P. tabuliformis indicated that the mixed afforestation requires further investigation.

submitted time 2018-10-29 From cooperative journals:《Journal of Arid Land》 Hits2432Downloads315 Comment 0

9. chinaXiv:201805.00539 [pdf]

Enhancement of the Prediction Accuracy of Pole Coordinates withEmpirical Mode Decomposition

Zhao Danning; Lei Yu; CaiHongbing
Subjects: Astronomy >> Astrophysical processes

This paper is aimed at separation treatment of low- and high-frequency components in polar motion forecasting and thenimproving time-series predictions. For the purpose, the empirical mode decomposition (EMD) is employed as a filter to extract low- and high-frequency signals from original pole coordinate data. The decomposition of the pole motion observations between 1986 and 2015 from the International Earth Rotation and Reference Systems Service (IERS) C04 seriesillustrates that the low-frequency fluctuations including inter-decadal, inter-annual, Chandler and annual wobbles and shorter-period high-frequency oscillationscan be separated from the observed time-series by the EMD. On the basis of separation, the least-squares (LS) extrapolation of models for annual and Chandler wobbles and for the linear trend are used for deterministic prediction of the low-frequency fluctuations, while the autoregressive (AR) technology is applied to forecasting the high-frequency oscillations plus LS fitting residuals. Pole coordinateforecasts are calculated as the sum of LS extrapolation and AR predictions (LS+AR).We have evaluated the accuracy of our long-term predictions (up to 1 year in the future) in comparison with the IERS official predictions in terms of year-by-year statistics of 5 years. It is shown that the accuracy of the LS+AR methodcan be significantly improved using a combination of the EMD and LS+AR (EMD+LS+AR). Also, the proposed prediction strategyoverall outperforms the IERS solutions. In addition, the predictions are compared with those from the Earth Orientation Parameters Prediction Comparison Campaign (EOP PCC). The comparison demonstrates that the developed schemeis a very accurate approach to predict polar motion. According to this study, it is concluded that polar motion predictions may be enhanced through separation treatment of different time-scale fluctuations and thus such processing seems to be necessary in pole coordinate prediction.

submitted time 2018-05-28 From cooperative journals:《天文研究与技术》 Hits3812Downloads273 Comment 0

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