Xin-ping Wang

Association between Vegetation Patterns and Soil Properties in the Southeastern Tengger Desert, China

Transitional zones or ecotones between biomes are commonly observable changes in structure and pattern of plant communities. However, there is little understanding of the key soil factors that allow dominant species (woody and herbaceous) from adjacent communities to coexist in transitional zones and how species respond to changes in soil conditions. The objective of this study was to examine the relationship between patterns of shrub and herb species in relation to soils in sandy desert-steppified desert transitional zone. Five transects with a total of 100 quadrats were distributed in different sites to survey vegetation and collect soil samples. The results indicate that fine-textured soil was highly correlated with the percentage of cover and biomass for both shrub and herbaceous species. Shrub cover was positiely correlated with soil moisture at 0.6–1.5 m depth (P < 0.01), but was only weakly negatively correlated with bulk density, sand content, pH, and water content in 0–0.6 m of soil layer. Species richness, cover, and biomass for herbaceous species were positively correlated with the percent content of clay, organic matter, and total N. The results of stepwise regression analysis show that soil moisture, texture, and nutrient are highly correlated with the structure and pattern of vegetation.

Physiological responses and tolerance mechanisms to Pb in two xerophils: Salsola passerina Bunge and Chenopodium album L.

Lead (Pb) has great toxicity to human beings and other livings. Although there are varied ways to rehabilitate the Pb contaminated area, phytoremediation of Pb pollution in arid lands is still a difficult task, it is therefore urgent to find and identify Pb tolerant plants in arid areas. The physiological responses and tolerance mechanisms to Pb stress (expressed as the Pb concentration, e.g., 0, 50, 150, 300, 600, 800, 1000 mg/L) were investigated for the xerophils Salsola passerina Bunge and Chenopodium album L. Results indicated that S. passerina exhibited higher Pb tolerance than Ch. album in terms of the seed germination rate, bio-activities of SOD and POD, and lower MDA production. There were two ways for S. passerina to reduce Pb toxicity in organism level, e.g., cell wall precipitation and state transfer of free Pb into anchorage. These findings demonstrate that S. passerina is a Pb tolerant species and may have potential application in phytoremediation of Pb contaminated arid lands.

Water balance change for a re-vegetated xerophyte shrub area

Abstract Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.

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.

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%.

Effects of altered precipitation regimes on plant productivity in the arid region of northern China

Abstract Climate change scenarios have predicted significant alterations in precipitation patterns over most of the mid-latitude land areas by the end of this century, but the degree to which altered precipitation regimes influence terrestrial ecosystem function in arid regions is uncertain. Precipitation is a primary climatic factor that regulates ecosystem function in arid regions. Based on remote sensing and meteorological data from 2000 to 2013, we analysed the spatiotemporal variations in annual net primary productivity (NPP) for different land cover types in the arid region of northern China and quantified the effects of growing season precipitation (GSP) and seasonal distribution of precipitation (SDP) on NPP variability by using the ecological process Carnegie–Ames–Stanford Approach (CASA) model. Our results suggested that significant NPP increases were found in most of the vegetated areas, especially in grasslands and shrublands. Responses of NPP to precipitation variability were related to land cover types. Grassland and shrubland were most responsive to precipitation variability followed by croplands and forests. Increased precipitation increased NPP, and NPP responded more strongly to higher precipitation than lower precipitation. We also found that increased precipitation concentration decreased NPP. GSP and SDP accounted for approximately 67% and 21%, respectively, of the variability in NPP. We concluded that growing season precipitation and its seasonal distribution were dominant factors controlling inter-annual variability in NPP in the arid region of northern China. Other factors, such as plant functional trait, antecedent soil moisture and human activities, might mediate NPP responses to precipitation variability through interaction with water availability. Our studies have implications for assessing and predicting vegetation responses to future climate change.

Variation of albedo to soil moisture for sand dunes and biological soil crusts in arid desert ecosystems

Surface albedo plays a crucial role in the energy balance of soils. The surface albedo and surface soil moisture of bare sand and biological soil crusts (BSCs) were concurrently observed on field plots of shifting sand dune and in revegetated desert ecosystems at Shapotou, northwestern China, to study relationships between surface albedo, solar elevation angle, and surface soil moisture. Results indicated that rainfall exerted a remarkable lowering effect on the variation of surface albedo by increasing surface soil moisture. Surface albedo was an exponential function of solar elevation angle, and the normalized surface albedo (solar elevation angle effect was removed) decreased exponentially with the increase of surface soil moisture. Sand surface had a higher albedo (0.266) than BSCs (0.226) when the surfaces were very dry. However, sand surface albedo became increasingly lower than that of BSCs when the surfaces were in wet conditions and when the soil moisture exceeded a critical value. The changes in soil surface albedo from sand dune to BSCs after revegetation in shallow soil profiles associated with the variation of the surface soil moisture can be seen as an indicator of the degree of sand dune stabilization when compared with the original shifting sand dune soil.

Diurnal Relationship Between the Surface Albedo and Surface Temperature in Revegetated Desert Ecosystems, Northwestern China

Quantification of the relationship between surface albedo and surface temperature was done by analyzing measured diurnal variations of surface albedo and surface temperature on the biological soil crusts and sand dunes within vegetation-stabilized desert ecosystems. The surface albedos and surface temperatures of sand dunes and biological soil crusts were measured concurrently over field plots of the moving sand area and the artificially revegetated area established in 1964 in Shapotou area, on the southeastern edge of the Tengger Desert. Results indicated that the diurnal variation of surface albedo for both dry surfaces showed an upward-facing parabolic curve on clear days and was symmetrical at about local noon. Whereas, the diurnal trend of surface temperature was opposite to that of surface albedo in the daytime and asymmetrical at about local noon times. Thereby, the data were empirically divided into forenoon and afternoon data with respect to local noon to analyze the relationship between surface albedo and surface temperature. A highly correlated negative linear relationship was found in the two time periods, respectively, and we proposed an empirical model between surface albedo and surface temperature based on that relationship. The model results indicate a good potential application for using the surface temperature to specify surface albedo.

Regional sea-surface temperatures explain spatial and temporal variation of summer precipitation in the source region of the Yellow River

ABSTRACT The summer precipitation (June–September) in the source region of the Yellow River accounts for about 70% of the annual total, playing an important role in water availability. This study divided the source region of the Yellow River into homogeneous zones based on precipitation variability using cluster analysis. Summer precipitation trends and teleconnections with global sea-surface temperatures (SST) and the Southern Oscillation Index (SOI) from 1961 to 2010 were investigated by Mann-Kendall test and Pearson product-moment correlation analysis. The results show that the northwest part (Zone 1) had a non-significantly increasing trend, and the middle and southeast parts (zones 2 and 3) that receive the most precipitation displayed a statistically significant decreasing trend for summer precipitation. The summer precipitation in the whole region showed statistically significant negative correlations with the central Pacific SST for 0–4 month lag and with the Southern Indian and Atlantic oceans SST for 5–8 month lag. Analyses of sub-regions reveal intricate and complex correlations with different SST areas that further explain the summer precipitation variability. The SOI had significant positive correlations, mainly for 0–2 months lag, with summer precipitation in the source region of the Yellow River. It is seen that El Niño Southern Oscillation (ENSO) events have an influence on summer precipitation, and the predominant negative correlations indicate that higher SST in equatorial Pacific areas corresponding to El Niño coincides with less summer precipitation in the source region of the Yellow River. Editor Z.W. Kundzewicz; Associate editor D. Gerten

Diurnal and seasonal variations of surface albedo in a spring wheat field of arid lands of Northwestern China

Surface albedo greatly affects the radiation energy balance of croplands and is a significant factor in crop growth monitoring and yield estimation. Precise determination of surface albedo is thus important. This study aimed to examine the influence of growth stages (tillering, jointing, heading, filling and maturity) on albedo and its diurnal asymmetry by measuring diurnal albedo variations. Results indicated that the daily mean surface albedo generally exhibited an increased tendency during tillering to heading but decreased after heading. Surface albedos were much higher in the morning than the corresponding values of the same solar elevation angles in the afternoon when the solar elevation angle was less than 40°, indicating a diurnal asymmetry in surface albedo. However, less difference was found in surface albedos between forenoon and afternoon when the solar elevation angle was greater than 40°. Dew droplets on the leaf surface in the morning were assumed to be the main factor resulting in the diurnal asymmetry in albedo of spring wheat.