Dongwei Gui

Characterizing variations in soil particle size distribution in oasis farmlands-A case study of the Cele Oasis

Characterizing soil particle size distributions (PSD) and their variation is an important issue in environmental research. In this study, fractal theory was used to analyse the soil PSD and its variations in the Cele Oasis, which is located at the southern margin of the Tarim Basin. The characteristics of the soil PSD were then evaluated to identify the primary factors that influence soil PSD. The results showed that the fractal dimension (D) values ranged from 2.11 to 2.27, and that there were significant differences among groups. Furthermore, the D values showed a significant positive correlation with fine particles (<50 @mm) and soil organic matter contents. According to a comparative analysis of D values, the utilization years of farmlands had a significant influence on PSD, while the difference in the spatial distribution of farmlands did not. These results indicated that long-term and effective tillage management of the farmlands will be beneficial to keeping and improving the states of the soil PSD and other soil properties.

Distribution pattern of plant species diversity in the mountainous Region of Ili River Valley, Xinjiang

In this paper, detrended canonical correspondence analysis was performed to analyze the relationships between diversity indices and environmental gradients, generalized additive model was employed to modal the response curves of diversity indices to the elevation, based on data from field investigation in the mountainous region of the Ili River Valley and a survey of 94 sample plots. Two hundred fifty-nine plant species were recorded in the 94 sample plots investigated, up to 235 species all appeared in the herb layer, and the species of woody plants were very limited. The communities with a complicated vertical structure presented higher values of indices. The distribution pattern of plant species diversity on the northern slope was affected by such factors as elevation, slope aspect, slope gradient, total nitrogen, total potassium, soil water content, organic matter, and that on the southern slope was mainly affected by such factors as slope gradient, elevation, available phosphorus, and soil water content. On the northern slope, Patrick index and Shannon–Wiener index of the plant communities presented a bimodality pattern along altitude; Simpson index and Pielou index showed a partially unimodal pattern. On the southern slope all the distribution pattern of species diversity indices showed two peaks, though Patrick index’s bimodality pattern was not an obvious one. These altitudinal patterns were formed by the synthetic action of a variety of environmental factors with elevation playing an important role.

Vegetation fractional coverage change in a typical oasis region in Tarim River Watershed based on remote sensing

Vegetation fractional coverage (VFC) is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing (RS). In this paper, the author conducted a case study of the delta oasis of Weigan and Kuqa rivers, which is a typical saline area in the Tarim River Watershed. The current study was based on the TM/ETM+ images of 1989, 2001, and 2006, and supported by Geographic Information System (GIS) spatial analysis, vegetation index, and dimidiate pixel model. In addition, VBSI (vegetation, bare soil and shadow indices) suitable for TM/ETM+ images, constructed with FCD (forest canopy density) model principle and put forward by ITTO (International Tropical Timber Organization), was used, and it was applied to estimate the VFC. The estimation accuracy was later proven to be up to 83.52%. Further, the study analyzed and appraised the changes in vegetation patterns and revealed a pattern of spatial change in the vegetation coverage of the study area by producing the map of VFC levels in the delta oasis. Forest, grassland, and farmland were the three main land-use types with high and extremely-high coverage, and they played an important role in maintaining the vegetation. The forest area determined the changes of the coverage area, whereas the other two land types affected the directions of change. Therefore, planting trees, protecting grasslands, reclaiming farmlands, and controlling unused lands should be included in a long-term program because of their importance in keeping regional vegetation coverage. Finally, the dynamic variation of VFC in the study area was evaluated according to the quantity and spatial distribution rendered by plant cover digital images to deeply analyze the reason behind the variation.

Root characteristics of Alhagi sparsifolia seedlings in response to water supplement in an arid region, northwestern China

The effect of variation in water supply on woody seedling growth in arid environments remain poorly known. The subshrub Alhagi sparsifolia Shap. (Leguminosae), distributed in the southern fringe of the Taklimakan Desert, Xinjiang, northwestern China, has evolved deep roots and is exclusively dependent on groundwater, and performs a crucial role for the local ecological safety. In the Cele oasis, we studied the responses of A. sparsifolia seedling roots to water supplement at 10 and 14 weeks under three irrigation treatments (none water supply of 0 m3/m2 (NW), middle water supply of 0.1 m3/m2 (MW), and high water supply of 0.2 m3/m2 (HW)). The results showed that the variations of soil water content (SWC) significantly influenced the root growth of A. sparsifolia seedlings. The leaf area, basal diameter and crown diameter were significantly higher in the HW treatment than in the other treatments. The biomass, root surface area (RSA), root depth and relative growth rate (RGR) of A. sparsifolia roots were all significantly higher in the NW treatment than in the HW and MW treatments at 10 weeks. However, these root parameters were significantly lower in the NW treatment than in the other treatments at 14 weeks. When SWC continued to decline as the experiment went on (until less than 8% gravimetric SWC), the seedlings still showed drought tolerance through morphological and physiological responses, but root growth suffered serious water stress compared to better water supply treatments. According to our study, keeping a minimum gravimetric SWC of 8% might be important for the growth and establishment of A. sparsifolia during the early growth stage. These results will not only enrich our knowledge of the responses of woody seedlings to various water availabilities, but also provide a new insight to successfully establish and manage A. sparsifolia in arid environments, further supporting the sustainable development of oases.

Studies on the reflectance spectral features of saline soil along the middle reaches of Tarim River: a case study in Xinjiang Autonomous Region, China

There has been growing interest in the use of reflectance spectroscopy as a rapid and inexpensive tool for soil characterization. In this study, 53 soil samples were collected from the oasis in the Weigan and Kuqa River delta along the middle reaches of Tarim River to investigate the level of soil chemical components in relation to soil spectral. An approach combining spectral technology and multi-variant statistical analysis was used to determine the reflectance spectral features of saline soil. The spectral data was first pretreated to remove noises and absorption bands from water, which eliminated influence from instrument errors and other external background factors. Several spectral absorption features were calculated for several saline soil samples to confirm that soil at the same salinity level had similar absorption spectral properties. Secondly, a correlation relationship between reflectance spectra and salinity factors was estimated by bivariate correlation method. Fourteen salinity factors including eight major ions and soil electrical conductivity (EC), soil salt content (SSC), pH, and total dissolved solid (TDS) in the saline soil were evaluated. Datasets of the salinity factors that correlated significantly with field data measurements of reflectance rate and the corresponding spectrum data were used to construct quantitative regression models. According to the multiple linear regression analysis, SSC, SO42−, TDS, and EC had a correlation coefficient at 0.746, 0.908, 0.798, and 0.933 with the raw spectral data, respectively, which confirmed strong correlation between salinity factors and soil reflectance spectrum. Findings from this study will have significant impact on characterization of spectral features of saline soil in oasis in arid land.

Responses of root growth of Alhagi sparsifolia Shap. (Fabaceae) to different simulated groundwater depths in the southern fringe of the Taklimakan Desert, China

Alhagi sparsifolia Shap. (Fabaceae) is a spiny, perennial herb. The species grows in the salinized, arid regions in North China. This study investigated the response characteristics of the root growth and the distribution of one-year-old A. sparsifolia seedlings to different groundwater depths in controlled plots. The ecological adaptability of the root systems of A. sparsifolia seedlings was examined using the artificial digging method. Results showed that: (1) A. sparsifolia seedlings adapted to an increase in groundwater depth mainly through increasing the penetration depth and growth rate of vertical roots. The vertical roots grew rapidly when soil moisture content reached 3%–9%, but slowly when soil moisture content was 13%–20%. The vertical roots stopped growing when soil moisture content reached 30% (the critical soil moisture point). (2) The morphological plasticity of roots is an important strategy used by A. sparsifolia seedlings to obtain water and adapt to dry soil conditions. When the groundwater table was shallow, horizontal roots quickly expanded and tillering increased in order to compete for light resources, whereas when the groundwater table was deeper, vertical roots developed quickly to exploit space in the deeper soil layers. (3) The decrease in groundwater depth was probably responsible for the root distribution in the shallow soil layers. Root biomass and surface area both decreased with soil depth. One strategy of A. sparsifolia seedlings in dealing with the increase in groundwater depth is to increase root biomass in the deep soil layers. The relationship between the root growth/distribution of A. sparsifolia and the depth of groundwater table can be used as guidance for harvesting A. sparsifolia biomass and managing water resources for forage grasses. It is also of ecological significance as it reveals how desert plants adapt to arid environments.

Effects of cutting and burning on regeneration of Alhagi sparsifolia Shap. on the southern fringe of the Taklamakan Desert, North-west China

Indigenous vegetation such as Alhagi sparsifolia Shap. (Fabaceae) has been severely damaged in recent years because of the growing population and increasing land use on the southern margin of the Taklamakan Desert. Alhagi sparsifolia plays an important role in supporting the fragile ecosystem in the oasis foreland as it has multiple ecological and economic functions. Cele Oasis, located on the southern rim of the Taklamakan Desert, was used to investigate the impact of human disturbance on regeneration of A. sparsifolia in the oasis–desert ecotone. Observations of A. sparsifolia in response to cutting and burning were conducted in 2010 and 2011. The results showed that burning in spring significantly decreased height and biomass in comparison to cutting in the fall. Moreover, biomass was decreased by spring burning more than by spring cutting. Burning in spring is no advantage for the growth and survival of A. sparsifolia. Cutting in fall appears to be a useful treatment for increasing the production from and survival of A. sparsifolia that could facilitate the sustainable development of the Cele Oasis.

Spectral reflectance properties of major objects in desert oasis: a case study of the Weigan–Kuqa river delta oasis in Xinjiang, China

Aiming at the remote sensing application has been increasingly relying on ground object spectral characteristics. In order to further research the spectral reflectance characteristics in arid area, this study was performed in the typical delta oasis of Weigan and Kuqa rivers located north of Tarim Basin. Data were collected from geo-targets at multiple sites in various field conditions. The spectra data were collected for different soil types including saline–alkaline soil, silt sandy soil, cotton field, and others; vegetations of Alhagi sparsifolia, Phragmites australis, Tamarix, Halostachys caspica, etc., and water bodies. Next, the data were processed to remove high-frequency noise, and the spectral curves were smoothed with the moving average method. The derivative spectrum was generated after eliminating environmental background noise so that to distinguish the original overlap spectra. After continuum removal of the undesirable absorbance, the spectrum curves were able to highlight features for both optical absorbance and reflectance. The spectrum information of each ground object is essential for fully utilizing the multispectrum data generated by remote sensing, which will need a representative spectral library. In this study using ENVI 4.5 software, a preliminary spectral library of surface features was constructed using the data surveyed in the study area. This library can support remote sensing activities such as feature investigation, vegetation classification, and environmental monitoring in the delta oasis region. Future plan will focus on sharing and standardizing the criteria of professional spectral library and to expand and promote the utilization of the spectral databases.

Stoichiometry in aboveground and fine roots of Seriphidium korovinii in desert grassland in response to artificial nitrogen addition

Nitrogen (N) input by atmospheric deposition and human activity enhances the availability of N in various ecosystems, which may further affect N and phosphorus (P) cycling and use by plants. However, the internal use of N, P, and N:P stoichiometry by plants in response to N supply, particularly for grass species in a desert steppe ecosystem, remains unclear. In this work, a field experiment was conducted at an infertile area in a desert steppe to investigate the effects of N fertilizer addition rates on the stoichiometry of N and P in a dominant grass species, Seriphidium korovinii. Results showed that for both aboveground and fine roots of S. korovinii, N inputs exponentially increased the N concentration and N:P ratios while P concentrations decreased. Meanwhile, the relationships between N and P concentrations for both aboveground and fine roots were significantly negative. Furthermore, while the N concentrations in the plants were relatively low, P concentrations were higher than the global means, resulting in a relatively low N:P ratio. These results suggest that the stoichiometric characteristics of N were different from that of P for this desert plant species. Results also show that the intraspecific variations in the main element traits (N, P, and N:P ratios) were consistent at the whole-plant level. Our results also suggest that N should be part of any short-term fertilization plan that is part of a management strategy designed to restore degraded desert grassland. These findings highlight that nutrient addition by atmospheric N deposition and human activity can have significant effects on the internal use of N and P by plants. Therefore, establishing a nutrient-conservation strategy for desert grasslands is important.

Characteristics of the clonal propagation of Alhagi sparsifolia Shap. (Fabaceae) under different groundwater depths in Xinjiang, China

Clonal reproduction of plants commonly occurs in arid areas because seedling establishment is rare in such severe environments. The features of clonal architecture differ not only among plant species but also within the same species growing in different environments. The characteristics of clonal propagation of Alhagi sparsifolia Shap. (Fabaceae), growing on the margins of Cele Oasis on the southern rim of the Taklamakan Desert, were investigated in September 2010. The study was conducted on three sites with different groundwater depths (2.5, 4.5, and 11.0 m). The results showed that the root suckering depth and the ability to expand and the biomass of coarse lateral roots of A. sparsifolia significantly increased when the groundwater depth increased. Moreover, the vegetative regeneration capacity of A. sparsifolia significantly declined with increasing groundwater depth, and the canopy cover at the site with a groundwater depth of 2.5 m was significantly greater than at the other two sites. There was no difference in aboveground biomass at the three sites. In such hyper-arid environments with a scarcity of soil nutrients, it was demonstrated that groundwater depth plays an important role in the clonal growth and propagation traits of A. sparsifolia. Increases in the groundwater depth as a result of over-use of oasis water for irrigation could lead to reduced populations of this important species in the interfaces between oases and the surrounding desert.