Zhi-Shan Zhang

Measurement of rainfall interception by xerophytic shrubs in re-vegetated sand dunes

Abstract More than 40 years of re-vegetation using mainly xerophytic shrubs Artemisia ordosica Krasch. and Caragana korshinskii Kom. at Shapotou Desert Experimental Research Station near Lanzhou, China has resulted in established dwarf-shrub and herbaceous cover on sand dunes. Precipitation, as the sole source of water replenishment in the semiarid area, plays a pertinent role in sustaining the desert ecosystem. A field study was conducted to (a) measure interception loss on shrub canopies during individual rainfall events, (b) determine the canopy storage capacity of individual plants, and (c) explore the relationship between interception and rainfall parameters. The total rainfall and its respective partitions as throughfall were determined and the interception losses in the studied ecosystem were quantified. Interception loss was shown to differ among the xerophyte taxa studied. During the growing seasons, the average shrub community interception loss is 6.9% and 11.7% of the simultaneous overall precipitation, for A. ordosica and C. korshinskii, respectively. Taking into account the observed rainfall conditions and vegetation cover characteristics, it was concluded that the interception loss was 2.7% of the total annual precipitation verified in the period for the A. ordosica community with an average cover of 30%, canopy projection area of 0.8 m2 and canopy storage capacity of 0.75 mm. In contrast, interception loss for the C. korshinskii community was 3.8% with an average cover of 46%, canopy projection area of 3.8 m2 and canopy storage capacity of 0.71 mm. For individual plants of both shrubs, the proportion of interception loss to gross rainfall decreased notably as the rainfall intensity increased between 0 and 2 mm h−1, while it tended to remain constant at about 0.1–0.2 for A. ordosica and 0.1–0.3 for C. korshinskii when the rainfall intensity was >2 mm h−1.

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.

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%.

Carbon fixation and its influence factors of biological soil crusts in a revegetated area of the Tengger Desert, northern China

Biological soil crusts (BSCs) are an important type of land cover in arid desert landscapes and play an important role in the carbon source-sink exchange within a desert system. In this study, two typical BSCs, moss crusts and algae crusts, were selected from a revegetated sandy area of the Tengger Desert in northern China, and the experiment was carried out over a 3 year period from January 2010 to November 2012. We obtained the effective active wetting time to maintain the physiological activity of BSCs based on the continuous field measurements and previous laboratory studies on BSCs photosynthesis and respiration rates. And then we developed a BSCs carbon fixation model that is driven by soil moisture. The results indicated that moss crusts and algae crusts had significant effects on soil moisture and temperature dynamics by decreasing rainfall infiltration. The mean carbon fixation rates of moss and algae crusts were 0.21 and 0.13 g C/(m2·d), respectively. The annual carbon fixations of moss crusts and algae crusts were 64.9 and 38.6 g C/(m2·a), respectively, and the carbon fixation of non-rainfall water reached 11.6 g C/(m2·a) (30.2% of the total) and 8.8 g C/(m2·a) (43.6% of the total), respectively. Finally, the model was tested and verified with continuous field observations. The data of the modeled and measured CO2 fluxes matched notably well. In desert regions, the carbon fixation is higher with high-frequency rainfall even the total amount of seasonal rainfall was the same.

Gross rainfall amount and maximum rainfall intensity in 60-minute influence on interception loss of shrubs: a 10-year observation in the Tengger Desert

In water-limited regions, rainfall interception is influenced by rainfall properties and crown characteristics. Rainfall properties, aside from gross rainfall amount and duration (GR and RD), maximum rainfall intensity and rainless gap (RG), within rain events may heavily affect throughfall and interception by plants. From 2004 to 2014 (except for 2007), individual shrubs of Caragana korshinskii and Artemisia ordosica were selected to measure throughfall during 210 rain events. Various rainfall properties were auto-measured and crown characteristics, i.e., height, branch and leaf area index, crown area and volume of two shrubs were also measured. The relative interceptions of C. korshinskii and A. ordosica were 29.1% and 17.1%, respectively. Rainfall properties have more contributions than crown characteristics to throughfall and interception of shrubs. Throughfall and interception of shrubs can be explained by GR, RI60 (maximum rainfall intensities during 60 min), RD and RG in deceasing importance. However, relative throughfall and interception of two shrubs have different responses to rainfall properties and crown characteristics, those of C. korshinskii were closely related to rainfall properties, while those of A. ordosica were more dependent on crown characteristics. We highlight long-term monitoring is very necessary to determine the relationships between throughfall and interception with crown characteristics.

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.

Divergent variations in concentrations of chemical elements among shrub organs in a temperate desert.

Desert shrubs, a dominant component of desert ecosystems, need to maintain sufficient levels of nutrients in their different organs to ensure operation of various physiological functions for the purpose of survival and reproduction. In the present study, we analyzed 10 elements in leaves, stems, and roots of 24 dominant shrub species from 52 sites across a temperate desert ecosystem in northwestern China. We found that concentrations of all 10 elements were higher in leaves than in stems and roots, that non-legumes had higher levels of leaf Na and Mg than did legumes, and that Na was more concentrated in C4 leaves than in C3 leaves. Scaling relationships of elements between the photosynthetic organ (leaf) and non-photosynthetic organs (stem and root) were allometric. Results of principal components analysis (PCA) highlighted the important role of the elements responsible for osmoregulation (K and Na) in water utilization of desert shrubs. Soil properties and taxonomy explained most variation of element concentrations in desert shrubs. Desert shrubs may not be particularly susceptible to future change in climate factors, because most elements (including N, P, K, Ca, Mn, Zn, and Cu) associated with photosynthesis, osmoregulation, enzyme activity, and water use efficiency primarily depend on soil conditions.

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.

Topographic differentiations of biological soil crusts and hydraulic properties in fixed sand dunes, Tengger Desert

Biological soil crusts (BSCs) play an important role in surface soil hydrology. Soils dominated with moss BSCs may have higher infiltration rates than those dominated with cyanobacteria or algal BSCs. However, it is unnown whether improved infiltration in moss BSCs is accompanied by an increase in soil hydraulic conductivity or water retention capacity. We investigated this question in the Tengger Desert, where a 43-year-old revegetation program has promoted the formation of two distinct types of BSCs along topographic positions, i.e. the moss-dominated BSCs on the interdune land and windward slopes of the fixed sand dunes, and the algal-dominated BSCs on the crest and leeward slopes. Soil water retention capacity and hydraulic conductivity were measured using an indoor evaporation method and a field infiltration method. And the results were fitted to the van Genuchten-Mualem model. Unsaturated hydraulic conductivities under greater water pressure (<-0.01 MPa) and water retention capacities in the entire pressure head range were higher for both crust types than for bare sand. However, saturated and unsaturated hydraulic conductivities in the near-saturation range (>-0.01 MPa) showed decreasing trends from bare sand to moss crusts and to algal crusts. Our data suggested that topographic differentiation of BSCs significantly affected not only soil water retention and hydraulic conductivities, but also the overall hydrology of the fixed sand dunes at a landscape scale, as seen in the reduction and spatial variability in deep soil water storage.