Yigang Hu

Soil-Plant Relationships in the Hetao Irrigation Region Drainage Ditch Banks, Northern China

Species-environment relationships is a central issue in ecology and important to plant reconstruction and management in degraded ecosystems. We explored how the interactions among soil nutrients, salinity, and ion ratios influence vegetation distribution in the Hetao Irrigation Region drainage ditch banks. Twoway indicator species analysis (TWINSPAN) techniques and Canonical Correspondence Analysis (CCA) were used to classify the vegetation and to examine the relationships between vegetation and soil chemical properties. The plant communities of Saussurea salsa–Phragmites australis–Sonchus arvensis and Leymus chinensis–Sonchus arvensis occurred within 161 of a total 245 plots. Edaphic factors exerted the strongest influence on vegetation patterns and distributions, with available soil nutrient content being identified as the dominant factor, followed by soil salinity and soil pH. Maintaining soil nutrient and salinity at moderate levels is an efficient approach to prevent species loss in the drainage ditch banks.

Soil respiration sensitivities to water and temperature in a revegetated desert

Soil respiration in water-limited ecosystems is affected intricately by soil water content (SWC), temperature, and soil properties. Eight sites on sand-fixed dunes that revegetated in different years since 1950s, with several topographical positions and various biological soil crusts (BSCs) and soil properties, were selected, as well as a moving sand dune (MSD) and a reference steppe in the Tengger Desert of China. Intact soil samples of 20 cm in depth were taken and incubated randomly at 12 levels of SWC (0 to 0.4 m3 m−3) and at 9 levels of temperature (5 to 45°C) in a growth chamber; additionally, cryptogamic and microbial respirations (RM) were measured. Total soil respiration (RT, including cryptogamic, microbial, and root respiration) was measured for 2 years at the MSD and five sites of sand-fixed dunes. The relationship between RM and SWC under the optimal SWC condition (0.25 m3 m−3) is linear, as is the entire range of RT and SWC. The slope of linear function describes sensitivity of soil respiration to water (SRW) and reflects to soil water availability, which is related significantly to soil physical properties, BSCs, and soil chemical properties, in decreasing importance. Inversely, Q10 for RM is related significantly to abovementioned factors in increasing importance. However, Q10 for RT and respiration rate at 20°C are related significantly to soil texture and depth of BSCs and subsoil only. In conclusion, through affecting SRW, soil physical properties produce significant influences on soil respiration, especially for RT. This indicates that a definition of the biophysical meaning of SRW is necessary, considering the water-limited and coarse-textured soil in most desert ecosystems.

Species Composition and Species Richness in the Hetao Irrigation Region Drainage Ditches, Northern China

Drainage ditches play an important role in maintenance of plant species diversity. We investigated plant species composition and diversity, and soil and water chemical properties in drainage ditches in the Hetao Irrigation Region of northern China. We compared species composition similarity within the same and among different drainage areas, and compared diversity of plant species, among different ditch sizes and slope positions. We identified a total of 70 plant species, which belonged to 64 genera and 30 families in the drainage ditch. The most frequent family was Compositae representing 15.7% of the total flora; Phragmites australis (Cav.) Trin. ex Steud was the most widespread species with a frequency of more than 60% in all plots. The highest similarity values occurred in lateral ditches within the same drainage areas, and in main ditches among different drainage areas. The coefficient of variation of total salt in soil was closely related to species similarity in all ditches. Ditch size and position were significantly correlated with the indexes of species diversity. Higher plant α-diversity occurred in smaller ditches and tended to be the highest at the transition zone and on the slope of the ditches. The response of species composition and diversity to environmental factors was significant for saline concentrations. Reducing the current water and soil saline contents, while maintaining current slope soil nitrogen content was suggested as an optimal way of maintaining high species diversity.

Effects of Vegetation Reclamation on Temperature and Humidity Properties of a Dumpsite: A Case Study in the Open Pit Coal Mine of Heidaigou

Vegetation cover greatly influences the microclimate of a landscape, which plays an important role in ecosystem function and health. The following study examines the influence of different vegetation types on the microclimate of a surface mine reclamation site. Average soil and air temperatures are significantly lower, while relative humidity is significantly higher in re-vegetated areas of a surface mine dumpsite in the Heidaigou. Vegetation recovery, particularly an increase in herbaceous vegetation cover, is expected to significantly reduce temperature and increase relative air humidity, improving the microclimate of the dumpsite in arid and semi-arid regions.

Evolution of soil respiration depends on biological soil crusts across a 50-year chronosequence of desert revegetation

ABSTRACT Despite intensive study in recent decades, soil respiration rate (Rs) and its evolution accompanying vegetation succession remain perplexing. Using a 50-year chronosequence of sand-fixing revegetation in the Tengger Desert of China, we took intact soil columns of 20 cm in depth, incubated them at 12 levels of soil water content (0–0.4 m3 m−3) and at nine temperatures (5–45°C) in a growth chamber, and measured Rs. The results showed that Rs increased rapidly 15 to 20 years following revegetation but stabilized after 25 years. Rs for soils covered with moss crusts were markedly higher than those covered with algal crusts. Further, Rs correlated significantly with sand content (negatively) and fine particle contents (positively), and increased exponentially with increased soil organic matter (SOM) and total nitrogen (TN) contents. Soil texture had a stronger influence on Rs than did SOM and TN. Also, Rs increased linearly with increased coverage and depth of biological soil crusts, which had a more pronounced influence on Rs than did soil physicochemical properties. Our results suggest that the capacity of carbon sequestration likely increases during the 50-year period after revegetation because the linear increase in SOM outweighs the limited sigmoidal increase in Rs.

Effects of drainage water on plant diversity and distribution of agricultural drainage ditch beds in an arid irrigated area of Northwestern China

Agricultural drainage ditches are essential to sustaining food production in arid irrigation regions, with various sizes and drainage characteristics as important buffer ecotones in agricultural areas. Bed vegetation and water properties were investigated in 39 agricultural drainage ditches in the Lingwu District of Ningxia Yellow River Irrigation Area in Northwestern China. The results showed that water depth, width, and velocity generally increased with larger ditch size. Water salinity was higher in drainage ditches (>1 g/L) than in croplands, canals, and the Yellow River. Total nitrogen and total phosphorus were at high levels: ∼1.6 and ∼0.1 mg/L, respectively. Forty plant species belonging to 19 families and 31 genera were identified, with higher plant richness and diversity found in smaller sized drainage ditches. Macrophytes dominated the bed vegetation with a mean vegetative coverage of >30% in all-sized ditches, and Phragmites australis occurred with the most frequency. Water depth and salinity were considered as the primary factors affecting the distribution of vegetation in drainage ditch beds. The study suggests that practical conservation of smaller sized drainage ditches is conducive to increasing the plant diversity of agricultural landscapes.