This study examines the hypothesis that soil respiration can always be interpreted purely in terms of biotic processes, neglecting the contribution of abiotic exchange to CO₂ fluxes in alkaline soils of arid areas that characterize 5% of the Earth’s total land surface. Analyses on flux data collected from previous studies suggested reconciling soil respiration as organic (root/microbial respiration) and inorganic (abiotic CO₂ exchange) respiration, whose contributions in the total CO₂ flux were determined by soil alkaline content. On the basis of utilizing meteorological and soil data collected from the Xinjiang and Central Asia Scientific Data Sharing Platform, an incorporated model indicated that inorganic respiration represents almost half of the total CO₂ flux. Neglecting the abiotic module may result in overestimates of soil respiration in arid alkaline lands, which partly explains the long-sought “missing carbon sink”

The soil properties in arid ecosystems are important determinants of vegetation distribution patterns. Soil organic carbon (SOC) content, which is closely related to soil types and the holding capacities of soil water and nutrients, exhibits complex variability in arid desert grasslands; thus, it is essentially an impact factor for the distri-bution pattern of desert grasslands. In the present study, an investigation was conducted to estimate the spatial pattern of SOC content in desert grasslands and the association with environmental factors in the diluvial-alluvial plains of northern Qilian Mountains. The results showed that the mean values of SOC ranged from 2.76 to 5.80 g/kg in the soil profiles, and decreased with soil depths. The coefficients of variation (CV) of the SOC were high (ranging from 48.83% to 94.67%), which indicated a strong spatial variability. SOC in the desert grasslands of the study re-gion presented a regular spatial distribution, which increased gradually from the northwest to the southeast. The SOC distribution had a pattern linked to elevation, which may be related to the gradient of climate conditions. Soil type and plant community significantly affected the SOC. The SOC had a significant positive relationship with soil moisture (P<0.05); whereas, it had a more significant negative relationship with the soil bulk density (BD) (P<0.01). However, a number of the variations in the SOC could be explained not by the environmental factors involved in this analysis, but rather other factors (such as grazing activity and landscape). The results provide important references for soil carbon storage estimation in this study region. In addition, the SOC association with environmental variables also provides a basis for a sustainable use of the limited grassland resources in the diluvial-alluvial plains of north-ern Qilian Mountains.

 Studies on carbon dioxide (CO₂) emissions at provincial level can provide a scientific basis for the optimal use of energy and the formulation of CO₂  reduction policies. We studied the variation of CO₂ emissions of primary energy consumption and its influencing factors based on data in Xinjiang Uygur autonomous region from 1952 to 2008, which were calculated according to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Xinjiang’s CO2 emission process from 1952 to 2008 could be divided into five stages according to the growth rates of total amount of CO₂  emissions and CO₂ emission intensity. The impact factors were quantitatively analyzed using Logarithmic Mean Divisia Index (LMDI) method in each stage. Various factors, including government policies and technological progress related to the role of CO₂  emissions, were comprehensively analyzed, and the internal rela-tionships among various factors were clarified. The results show that the contribution rates of various impact factors are different in each stage. Overall, economic growth and energy consumption intensity were the main driving factors for CO₂  emissions. Since the implementation of the birth control policy, the driving force of population growth on the increase in CO₂  emissions has slowly weakened. The energy consumption intensity was further affected by the industrial structure and energy consumption intensity of primary, secondary and tertiary industries, with the energy consumption intensity of the secondary industries and the proportion of secondary industries being the most important factors affecting the energy consumption intensity. Governmental policies and technological progress were also important factors that affected CO₂  emissions.

Climate warming and nitrogen (N) deposition change ecosystem processes, structure, and functioning whereas the phosphorus (P) composition and availability directly influence the ecosystem structure under condi-tions of N deposition. In our study, four treatments were designed, including a control, diurnal warming (DW), N deposition (ND), and combined warming and N deposition (WN). The effects of DW, ND, and WN on P composition were studied by ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy in a temperate grassland region of China. The results showed that the N deposition decreased the soil pH and total N (TN) concentration but increased the soil Olsen-P concentration. The solution-state ³¹P NMR analysis showed that the DW, ND and WN treatments slightly decreased the proportion of orthophosphate and increased that of the monoesters. An absence of myo-inositol phosphate in the DW, ND and WN treatments was observed compared with the control. Furthermore, the DW, ND and WN treatments significantly decreased the recovery of soil P in the NaOH–EDTA solution by 17%–20%. The principal component analysis found that the soil pH was positively correlated with the P recovery in the NaOH–EDTA solution. Therefore, the decreased soil P recovery in the DW and ND treatments might be caused by an indirect influence on the soil pH. Additionally, the soil moisture content was the key factor limiting the available P. The positive correlation of total carbon (TC) and TN with the soil P composition indicated the influence of climate warming and N deposition on the biological processes in the soil P cycling.

Soil enzyme activity plays an important role in the conversion of soil organic carbon into inorganic carbon, which is significant for the global carbon cycle. In this study, we investigated the soil enzyme activities of two ligninolytic enzymes (peroxidase and polyphenol oxidase) and five non-ligninolytic enzymes (α-1,4-glucosidase (AG); β-1,4-glucosidase (BG); N-acetyl-β-glucosaminidase (NAG); β-D-cellobiosidase (CBH); and β-xylosidase (BXYL)) in four plant communities of the Sangong River basin in Fukang, North Xinjiang, China. The four typical plant communities were dominated by Haloxylon ammodendron, Reaumuria soongonica, Salsola passerina, and Tamarix rarmosissima, respectively, with saline soils of varied alkalinity. The results showed that the soil peroxidase activity decreased seasonally. The activities of the five non-ligninolytic enzymes decreased with increasing soil depths, while those of the two ligninolytic enzymes did not show such a trend. In the four plant communities, BG had the highest activity among the five non-ligninolytic enzymes, and the activities of the two ligninolytic enzymes were higher than those of the four non-ligninolytic ones (AG, NAG, CBH, and BXYL). The community of H. ammodendron displayed the highest activity with respect to the two ligninolytic enzymes in most cases, but no significant differences were found among the four plant communities. The geometric mean of soil enzyme activities of the four plant communities was validated through an independently performed principal component analysis (PCA), which indicated that different plant communities had different soil enzyme activities. The correlation analysis showed that soil polyphenol oxidase activity was significantly positively correlated with the activities of the five non-ligninolytic enzymes. The soil pH value was positively correlated with the activities of all soil enzymes except peroxidase. Soil microbial carbon content also showed a significant positive correlation (P<0.01) with the activities of all soil enzymes except polyphenol oxidase. The results suggested that the H. ammoden-dron community has the highest ability to utilize soil organic carbon, and glucoside could be the most extensively utilized non-ligninolytic carbon source in the saline soil of arid areas in Xinjiang.
Keywords: soil enzyme activity; saline soil; Haloxylon ammodendron; Reaumuria soongonica; Salsola passerina; Tamarix rarmosissima

Nutrient resorption is an important conservation mechanism for plants to overcome nutrient limitation in the less fertile area of desertified land. In the semi-arid Horqin Sandy Land of Northern China, the shrub Artemisia halodendron usually colonizes into the bare ground of severely desertified land as a pioneer species. It is, therefore, expected that A. halodendron will be less dependent on current nutrient uptake through efficient and proficient resorption of nutrients. In this study, we found that averaged nitrogen (N) and phosphorus (P) concentrations in senesced leaves significantly varied from 12.3 and 1.2 mg/g in the shifting sand dune to 15.9 and 1.9 mg/g in the fixed sand dune, respectively, suggesting that foliar N and P resorption of A. halodendron were more proficient in the shifting sand dune. In particular, positive relationships between nutrient concentrations in senesced leaves and soil nutrient availability indicate that A. halodendron in infertile habitats is more likely to manage with a low level of nutrients in senesced leaves, giving this species an advantage in infertile soil. Moreover, foliar N- and P-resorption efficiencies and proficiencies showed limited inter-annual variability although annual precipitation varied greatly among 2007–2009. However, N and P resorption of A. halodendron were not more efficient and proficient than those previously reported for other shrubs, indicating that the pioneer shrub in sand dune environments does not rely more heavily than other plants on the process of resorption to conserve nutrients. Incomplete resorption of nutrients in A. halodendron suggests that senesced-leaf fall would return litter with high quality to the soil, and thereby would indirectly improve soil nutrient availability. The restoration of desertified land, therefore, may be accelerated after A. halodendron pioneers into shifting sand dunes.

Arbuscular mycorrhizal (AM) fungi penetrate the cortical cells of the roots of vascular plants, and are widely distributed in soil. The formation of these symbiotic bodies accelerates the absorption and utilization of mineral elements, enhances plant resistance to stress, boosts the growth of plants, and increases the survival rate of transplanted seedlings. We studied the effects of various arbuscular mycorrhizae fungi on the growth and development of licorice (Glycyrrhiza glabra). Several species of AM, such as Glomus mosseae, Glomus intraradices, and a mixture of fungi (G. mosseae, G. intraradices, G. cladoideum, G. microagregatum, G. caledonium and G. etunicatum) were used in our study. Licorice growth rates were determined by measuring the colonization rate of the plants by the fungi, plant dry biomass, phosphorus concentration and concentration of secondary metabolites. We estab-lished two cloned strains of licorice, clone 3 (C3) and clone 6 (C6) to exclude the effect of genotypic variations. Our results showed that the AM fungi could in fact increase the leaf and root biomass, as well as the phosphorus concentration in each clone. Furthermore, AM fungi significantly increased the yield of certain secondary metabolites in clone 3. Our study clearly demonstrated that AM fungi play an important role in the enhancement of growth and development of licorice plants. There was also a significant improvement in the secondary metabolite content and yield of medicinal compounds from the roots.

Pappophorum vaginatum is the most abundant C₄ perennial grass desirable to livestock in rangelands of northeastern Patagonia, Argentina. We hypothesized that (1) defoliation reduce net primary productivity, and root length density and weight in the native species, and (2) root net primary productivity, and root length density and weight, are greater in P. vaginatum than in the other, less desirable, native species (i.e., Aristida spegazzinii, A.subulata and Sporobolus cryptandrus). Plants of all species were either exposed or not to a severe defoliation twice a year during two growing seasons. Root proliferation was measured using the cylinder method. Cylindrical, iron structures, wrapped up using nylon mesh, were buried diagonally from the periphery to the center on individual plants. These structures, initially filled with soil without any organic residue, were dug up from the soil on 25 April 2008, after two successive defoliations in mid-spring 2007. During the second growing season (2008–2009), cylinders were destructively harvested on 4 April 2009, after one or two defoliations in midand/ or late-spring, respectively. Roots grown into the cylinders were obtained after washing the soil manually. Defoliation during two successive years did reduce the study variables only after plants of all species were defoliated twice, which supported the first hypothesis. The greater root net primary productivity, root length density and weight in P. vaginatum than in the other native species, in support of the second hypothesis, could help to explain its greater abundance in rangelands of Argentina.

The Ulanbuh Desert borders the upper reach of the Yellow River. Every year, a mass of aeolian sand is blown into the Yellow River by the prevailing wind and the coarse aeolian sand results in serious silting in the Yellow River. To estimate the quantity of aeolian sediments from the Ulanbuh Desert blown into the Yellow River, we simulated the saltation processes of aeolian sediments in the Ulanbuh Desert. Then we used a saltation submodel of the IWEMS (Integrated Wind-Erosion Modeling System) and its accompanying RS (Remote Sensing) and GIS (Geographic Information System) modules to estimate the quantity of saltation sediments blown into the Yellow River from the Ulanbuh Desert. We calibrated the saltation submodel by the synchronous observation to wind velocity and saltation sediments on several points with different vegetation cover. The vegetation cover, frontal area of vegetation, roughness length, and threshold friction velocity in various regions of the Ulanbuh Desert were obtained using NDVI (Normalized Difference Vegetation Index) data, measured sand-particle sizes, and empirical relationships among vegetation cover, sand-particle diameters, and wind velocity. Using these variables along with the observed wind velocities and saltation sediments for the observed points, the saltation model was validated. The model results were shown to be satisfactory (RMSE less than 0.05 and |Re| less than 17%). In this study, a subdaily wind-velocity program, WINDGEN, was developed using this model to simulate hourly wind velocities around the Ulanbuh Desert. By incorporating simulated hourly wind-velocity and wind-direction data, the quantity of saltation sediments blown into the Yellow River was calculated with the saltation submodel. The annual quantity of aeolian sediments blown into the Yellow River from the Ulanbuh Desert was 5.56×106 t from 2001 to 2010, most of which occurred in spring (from March to May); for example, 6.54×105 tons of aeolian sand were blown into the Yellow River on 25 April, 2010. However, in summer and winter, the saltation process occasionally occurred. This research has supplied some references to prevent blown sand hazards and silting in the Yellow River.

Land degradation causes serious environmental problems in many regions of the world, and although it can be effectively assessed and monitored using a time series of rainfall and a normalized difference vegetation index (NDVI) from remotely-sensed imagery, dividing human-induced land degradation from vegetation dynamics due to climate change is not a trivial task. This paper presented a multilevel statistical modeling of the NDVI-rainfall relationship to detect human-induced land degradation at local and landscape scales in the Ordos Plateau of Inner Mongolia, China, and recognized that anthropogenic activities result in either positive (land restoration and re-vegetation) or negative (degradation) trends. Linear regressions were used to assess the accuracy of the multilevel statistical model. The results show that: (1) land restoration was the dominant process in the Ordos Plateau between 1998 and 2012; (2) the effect of the statistical removal of precipitation revealed areas of human-induced land degradation and improvement, the latter reflecting successful restoration projects and changes in land management in many parts of the Ordos; (3) compared to a simple linear regression, multilevel statistical modeling
could be used to analyze the relationship between the NDVI and rainfall and improve the accuracy of detecting the effect of human activities. Additional factors should be included when analyzing the NDVI-rainfall relationship and detecting human-induced loss of vegetation cover in drylands to improve the accuracy of the approach and eliminate some observed non-significant residual trends.

Optimal use of water and fertilizers can enhance winter wheat yield and increase the efficiencies of water and fertilizer usage in dryland agricultural systems. In order to optimize water and nitrogen (N) management for winter wheat, we conducted field experiments from 2006 to 2008 at the Changwu Agro-ecological Experimental Station of the Chinese Academy of Sciences on the Loess Plateau, China. Regression models of wheat yield and evapotranspiration (ET) were established in this study to evaluate the water and fertilizer coupling effects and to determine the optimal coupling domain. The results showed that there was a positive effect of water and N fertilizer on crop yield, and optimal irrigation and N inputs can significantly increase the yield of winter wheat. In the drought year (2006–2007), the maximum yield (Y_max) of winter wheat was 9.211 t/hm² for the treatment with 324 mm irrigation and 310 kg/hm² N input, and the highest water use efficiency (WUE) of 16.335 kg/(hm²×mm) was achieved with 198 mm irrigation and 274 kg/hm² N input. While in the normal year (2007–2008), the maximum winter wheat yield of 10.715 t/hm² was achieved by applying 318 mm irrigation and 291 kg/hm² N, and the highest WUE was 18.69 kg/(hm²×mm) with 107 mm irrigation and 256 kg/hm² N input. Crop yield and ET response to irrigation and N inputs followed a quadratic and a line function, respectively. The optimal coupling domain was determined using the elasticity index (EI) and its expression in the water-N dimensions, and was represented by an ellipse, such that the global maximum WUE (WUE_max) and Y_maxvalues corresponded to the left and right end points of the long axis, respectively. Considering the aim to get the greatest profit in practice, the optimal coupling domain was represented by the lower half of the ellipse, with the Y_max and WUE_max on the two end points of the long axis. Overall, we found that the total amount of irrigation for winter wheat should not exceed 324 mm. In addition, our optimal coupling domain visually reflects the optimal range of water and N inputs for the maximum winter wheat yield on the Loess Plateau, and it may also provide a useful reference for identifying appropriate water and N inputs in agricultural applications.