Scientists and the local government have great concerns about the climate change and water resources in the Badain Jaran Desert of western China. A field study for the local water cycle of a lake-desert system was conducted near the Noertu Lake in the Badain Jaran Desert from 21 June to 26 August 2008. An underground wet sand layer was observed at a depth of 20–50 cm through analysis of datasets collected during the field experiment. Measurements unveiled that the near surface air humidity increased in the nighttime. The sensible and latent heat fluxes were equivalent at a site about 50 m away from the Noertu Lake during the daytime, with mean values of 134.4 and 105.9 W/m² respectively. The sensible heat flux was dominant at a site about 500 m away from the Noertu Lake, with a mean of 187.7 W/m², and a mean latent heat flux of only 26.7 W/m². There were no apparent differences for the land surface energy budget at the two sites during the night time. The latent heat flux was always negative with a mean value of –12.7 W/m², and the sensible heat flux was either positive or negative with a mean value of 5.10 W/m². A portion of the local precipitation was evaporated into the air and the top-layer of sand dried quickly after every rainfall event, while another portion seeped deep and was trapped by the underground wet sand layer, and supplied water for surface psammophyte growth. With an increase of air humidity and the occurrence of negative latent heat flux or water vapor condensation around the Noertu Lake during the nighttime, we postulated that the vapor was transported and condensed at the lakeward sand surface, and provided supplemental underground sand pore water. There were links between the local water cycle, underground wet sand layer, psammophyte growth and landscape evolution of the mega-dunes surrounding the lakes in the Badain Jaran Desert of western China.

The Turpan Basin is located in the arid zone of northwestern China and is a typical closed inland basin surrounded by high mountains. It is one of the most arid regions in the world and, as a result, the groundwater in this area is very important for both domestic and agricultural uses. In the present study, the relationships of major elements (K⁺, Na⁺, Ca²⁺, Mg²⁺, HCO³⁻, SO₄²⁻ and Cl⁻) and environmental isotopes (δ¹⁸O, δ²H and T) in groundwater were analyzed to investigate the evolution of the regional hydrochemistry within the Turpan Basin. The hydrochemistry results demonstrate that groundwater with high total dissolved solids (TDS) concentration is dominated by sodium chloride (Na-Cl) and sodium sulfate (Na-SO4) type water, whereas that with low TDS concentration (typically from near mountain areas) is dominated by calcium bicarbonate (Ca-HCO3) type water. The evolution of groundwater hydrochemistry within the Turpan Basin is a result of calcium carbonate precipitation, evaporation concentration, cation exchange and dissolution of evaporites (i.e. halite, mirabilite and gypsum). Furthermore, evaporite dissolution associated with irrigation practice plays a key role in the groundwater salinization, especially in the central part of the basin. Environmental isotopes reveal that the groundwater is recharged by precipitation in the mountain areas and fast vertical infiltration of irrigation return flow. In the southern sub-basin the shallow groundwater and the deep groundwater is separated at a depth of about 40 m, with substantial differences in terms of hydrochemical and isotopic characteristics. The results are useful for decision making related to sustainable water resource utilization in the Turpan Basin and other regions in northwestern China.

Dew is an important supplement water source in arid and semi-arid areas. In order to determine the dew formation on different kinds of soils associated with various shrub species and microhabitats, we performed measurement of accumulated dew formation amount and duration in October 2009 in a revegetation-stabilized arid desert ecosystem in Shapotou area, northern China. The results indicated that the accumulated dew formation amount was four times larger at open spaces as compared to under the canopy, and it was nearly twice as much under living Artemisia ordosica plants (L.A.) as compared to under living Caragana korshinskii plants (L.C.). The opposite characteristics were found for dew duration between different microhabitats. Dew amounts at different vertical heights around the shrub stands were in the order of 50 cm above the canopy>the canopy edge>under the canopy. Dew amount continued to increase after dawn, and the proportion of average accumulated dew amount after dawn ac-counting for the average maximum amount increased from above the canopy to under the canopy. Dew formation duration after sunrise accounted for more than 50% of the total formation duration during the day time. Contrary to the distribution characteristics of dew amount, dew duration after dawn and total dew formation duration during the day time were both highest under the canopy, followed by at the canopy edge and then at 50 cm above the canopy. The portion of dew duration after dawn accounting for the total dew duration during the day time increased from above the canopy to under the canopy. From these results, we may conclude that dew availability as a supple-mental water resource for improving the microhabitats in water-limited arid ecosystems is position dependent es-pecially for the plant microhabitats at different stands layers.

As an important parameter in the soil erosion model, soil surface roughness (SSR) is used to quantitatively describe the micro-relief on agricultural land. SSR has been extensively studied both experimentally and theoretically; however, no studies have focused on understanding SSR on the Loess Plateau of China. This study investigated changes in SSR for three different tillage practices on the Loess Plateau of China and the effects of SSR on runoff and erosion yield during simulated rainfall. The tillage practices used were zero tillage (ZT), shallow hoeing (SH) and contour ploughing (CP). Two rainfall intensities were applied, and three stages of water erosion processes (splash erosion (I), sheet erosion (II) and rill erosion (III)) were analyzed for each rainfall intensity. The chain method was used to measure changes in SSR both initially and after each stage of rainfall. A splash board was used to measure the splash erosion at stage I. Runoff and sediment data were collected continuously at 2-min intervals during rainfall erosion stages II and III. We found that SSR of the tilled surfaces ranged from 1.0% to 21.9% under the three tillage practices, and the order of the initial SSR for the three treatments was ZT<SH<CP. For the ZT treatment, SSR increased slightly from stage I to III, whereas for the SH and CP treatments, SSR decreased by 44.5% and 61.5% after the three water erosion stages, respectively, and the greatest reduction in SSR occurred in stage I. Regression analysis showed that the changes in SSR with increasing cumulative rainfall could be described by a power function (R²>0.49) for the ZT, SH and CP treatments. The runoff initiation time was longer in the SH and CP treatments than in the ZT treatment. There were no significant differences in the total runoff yields among the ZT, SH and CP treatments. Sediment loss was significantly smaller (P<0.05) in the SH and CP treatments than in the ZT treatment.

Short-term nitrous oxide (N₂O) pulse emissions caused by precipitation account for a considerable portion of the annual N₂O emissions and are greatly influenced by soil nitrogen (N) dynamics. However, in Chinese semiarid temperate steppes, the response of N₂O emissions to the coupling changes of precipitation and soil N availability is not yet fully understood. In this study, we conducted two 7-day field experiments in a semiarid tem-perate typical steppe of Inner Mongolia, China, to investigate the N₂O emission pulses resulting from artificial pre-cipitation events (approximately equivalent to 10.0 mm rainfall) under four N addition levels (0, 5, 10, and 20 g N/(m²•a)) using the static opaque chamber technique. The results show that the simulated rainfall during the dry period in 2010 caused greater short-term emission bursts than that during the relatively rainy observation period in 2011 (P<0.05). No significant increase was observed for either the N₂O peak effluxes or the weekly cumulative emissions (P>0.05) with single water addition. The peak values of N₂O efflux increased with the increasing N input. Only the treatments with water and medium (WN10) or high N addition (WN20) significantly increased the cumula-tive N₂O emissions (P<0.01) in both experimental periods. Under drought condition, the variations in soil N₂O effluxes were positively correlated with the soil NH4-N concentrations in the three N input treatments (WN5, WN10, and WN20). Besides, the soil moisture and temperature also greatly influenced the N2O pulse emissions, particu-larly the N₂O pulse under the relatively rainy soil condition or in the treatments without N addition (ZN and ZWN). The responses of the plant metabolism to the varying precipitation distribution and the length of drought period prior to rainfall could greatly affect the soil N dynamics and N2O emission pulses in semiarid grasslands.

Plant root exudates contain various organic and inorganic components that include glucose, citric and oxalic acid. These components affect rhizosphere microbial and microfaunal activities, but the mechanisms are not fully known. Studies concerned from degraded grassland ecosystems with low soil carbon (C) contents are rare, in spite of the global distribution of grasslands in need of restoration. All these have a high potential for carbon sequestration, with a reduced carbon content due to overutilization. An exudate component that rapidly decomposes will increase soil respiration and CO₂ emission, while a component that reduces decomposition of native soil carbon can reduce CO₂ emission and actually help sequestering carbon in soil. Therefore, to investigate root exudate effects on rhizosphere activity, citric acid, glucose and oxalic acid (0.6 g C/kg dry soil) were added to soils from three biotopes (grassland, fixed dune and mobile dune) located in Naiman, Horqin Sandy Land, Inner Mongolia, China) and subjected to a 24-day incubation experiment together with a control. The soils were also analyzed for general soil properties. The results show that total respiration without exudate addition was highest in grassland soil, intermediate in fixed dune and lowest in mobile dune soil. However, the proportion of native soil carbon mineralized was highest in mobile dune soil, reflecting the low C/N ratio found there. The exudate effects on CO₂-C emissions and other variables differed somewhat between biotopes, but total respiration (including that from the added substrates) was significantly increased in all combinations compared with the control, except for oxalic acid addition to mobile dune soil, which reduced CO₂-C emissions from native soil carbon. A small but statistically significant increase in pH by the exudate additions in grassland and fixed dune soil was observed, but there was a major decrease from acid additions to mobile dune soil. In contrast, electrical conductivity decreased in grassland and fixed dune soil and increased in mobile dune. Thus, discrete components of root exudates affected soil environmental conditions differently, and responses to root exudates in soils with low carbon contents can differ from those in normal soils. The results indicate a potential for, e.g., acid root exudates to decrease decomposition rate of soil organic matter in low carbon soils, which is of interest for both soil restoration and carbon sequestration.

 Litter decomposition is the fundamental process in nutrient cycling and soil carbon (C) sequestration in terrestrial ecosystems. The global-wide increase in nitrogen (N) inputs is expected to alter litter decomposition and，ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels (low N with 50 kg N/(hm²•a) (LN), medium N with 100 kg N/(hm²•a) (MN), and high N with 200 kg N/(hm²•a) (HN)) and three N addition forms (ammonium-N-based with 100 kg N/(hm²•a) as ammonium sulfate (AS), nitrate-N-based with 100 kg N/(hm2•a) as sodium nitrate (SN), and mixed-N-based with 100 kg N/(hm²•a) as calcium ammonium nitrate (CAN)) compared to control with no N addition (CK). The results indicated that the litter mass remaining in all N treatments exhib¬ited a similar decomposition pattern: fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period (120–1,200 days). The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I (<398 days) and a linear decay function in phase II (>398 days). The three N addition levels exerted insignificant effects on litter decomposition in the early stages (<398 days, phase I; P>0.05). However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively (P<0.05). AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period (P>0.05). The effects of these two N addition forms differed greatly from those of CAN after 746 and 1,053 days, respectively (P<0.05). During the decomposition period, N concentrations in the decomposing litter increased whereas C concentrations decreased, which also led to an exponential decrease in litter C:N ratios in all treatments. No significant effects were induced by N addition levels and forms on litter C and N concentrations (P>0.05). Our results indicated that exogenous N additions could exhibit neutral or inhibitory effects on litter decomposition, and the inhibitory effects of N additions on litter decomposition in the final decay stages are not caused by the changes in the chemical qualities of the litter, such as endogenous N and C concentrations. These results will provide an important data basis for the simulation and prediction of C cycle processes in future N-deposition scenarios.

Caragana microphylla Lam., a leguminous shrub species, plays an important role in revegetation in the degraded ecosystems of the Horqin Sandy Land, northeastern China. Large areas planted with this shrub have been artificially established as sand binders for soil protection, which might change the composition of soil bacterial communities with the development of sand dune stabilization. In this paper, we investigated the diversity and composition of native soil bacterial communities in the C. microphylla plantation for sand fixation using polymerase chain reaction with denaturing gradient gel electrophoresis (PCR-DGGE) to understand the influence of this plantation on sandy soil ecosystem development. We collected soil samples from plantations with an age sequence of 0, 9, 16, and 26 years, as well as from the natural community, to identify the differences among soil bacterial communities. The result showed that bacterial abundance and community composition in the sandy land were affected by the age of the C. microphylla plantation. Moreover, bacterial diversity decreased with increasing plantation age, and the composition of the bacterial community in the 26-year plantation was similar to that in the natural community. Phylogenetic analysis of bands excised from the DGGE gels showed that members of alpha Proteobacterium,
gamma Proteobacterium, Gemmatimonadetes and Chloroflexi were dominant in the sandy land. The stabilization of moving sand dune and development of sand-fixed plantation resulted in an increase of soil fertility, which could drive the structural evolvement of soil bacterial community, and it needs over 20 years for the soil bacterial community to form a stable structure, similar to the case for the natural vegetation.

In arid and semi-arid regions, freshwater scarcity and high water salinity are serious and chronic problems for crop production and sustainable agriculture development. We conducted a field experiment to evaluate the effect of irrigation water salinity and nitrogen (N) application rate on soil salinity and cotton yield under drip irrigation during the 2011 and 2012 growing seasons. The experimental design was a 3×4 factorial with three irrigation water salinity levels (0.35, 4.61 and 8.04 dS/m) and four N application rates (0, 240, 360 and 480 kg N/hm²). Results showed that soil water content increased as the salinity of the irrigation water increased, but decreased as the N application rate increased. Soil salinity increased as the salinity of the irrigation water increased. Specifically, soil salinity measured in 1:5 soil:water extracts was 218% higher in the 4.61 dS/m treatment and 347% higher in the 8.04 dS/m treatment than in the 0.35 dS/m treatment. Nitrogen fertilizer application had relatively little effect on soil salinity, increasing salinity by only 3%–9% compared with the unfertilized treatment. Cotton biomass, cotton yield and evapotranspiration (ET) decreased significantly in both years as the salinity of irrigation water increased, and increased as the N application rate increased regardless of irrigation water salinity; however, the positive effects of N application were reduced when the salinity of the irrigation water was 8.04 dS/m. Water use efficiency (WUE) was significantly higher by 11% in the 0.35 dS/m treatment than in the 8.04 dS/m treatment. There was no significant difference in WUE between the 0.35 dS/m treatment and the 4.61 dS/m treatment. The WUE was also significantly affected by the N application rate. The WUE was highest in the 480 kg N/hm2 treatment, being 31% higher than that in the 0 kg N/hm² treatment and 12% higher than that in the 240 kg N/hm2 treatment. There was no significant difference between the 360 and 480 kg N/hm² treatments. The N use efficiency (NUE) was significantly lower in the 8.04 dS/m treatment than in either the 4.61 dS/m or the 0.35 dS/m treatment. There was no significant difference in NUE between the latter two treatments. These results suggest that irrigation water with salinity <4.61 dS/m does not have an obvious negative effect on cotton production, WUE or NUE under the experimental conditions. Application of N fertilizer (0–360 kg N/hm²) could alleviate salt damage, promote cotton growth, and increase both cotton yield and water use efficiency.

Changes in both soil organic C storage and soil respiration in farmland ecosystems may affect atmospheric CO₂ concentration and global C cycle. The objective of this field experiment was to study the effects of three crop field management practices on soil CO₂ emission and C balance in a cotton field in an arid region of Northwest China. The three management practices were irrigation methods (drip and flood), stubble managements (stubble-incorporated and stubble-removed) and fertilizer amendments (no fertilizer (CK), chicken manure (OM), inorganic N, P and K fertilizer (NPK), and inorganic fertilizer plus chicken manure (NPK+OM)). The results showed that within the C pool range, soil CO₂ emission during the whole growing season was higher in the drip irrigation treatment than in the corresponding flood irrigation treatment, while soil organic C concentration was larger in the flood irrigation treatment than in the corresponding drip irrigation treatment. Furthermore, soil CO₂ emission and organic C concentration were all higher in the stubble-incorporated treatment than in the corresponding stubble-removed treatment, and larger in the NPK+OM treatment than in the other three fertilizer amendments within the C pool range. The combination of flood irrigation, stubble incorporation and application of either NPK+OM or OM increased soil organic C concentration in the 0−60 cm soil depth. Calculation of net ecosystem productivity (NEP) under different management practices indicated that the combination of drip irrigation, stubble incorporation and NPK+OM increased the size of the C pool most, followed by the combination of drip irrigation, stubble incorporation and NPK. In conclusion, management practices have significant impacts on soil CO₂ emission, organic C concentration and C balance in cotton fields. Consequently, appropriate management practices, such as the combination of drip irriga¬tion, stubble incorporation, and either NPK+OM or NPK could increase soil C storage in cotton fields of Northwest China.

In order to restore a degraded alkaline grassland, the local government implemented a large restoration project using fences in Changling county, Jilin province, China, in 2000. Grazing was excluded from the protected area, whereas the grazed area was continuously grazed at 8.5 dry sheep equivalent (DSE)/hm². In the current re-search, soil and plant samples were taken from grazed and fenced areas to examine changes in vegetation and soil properties in 2005, 2006 and 2008. Results showed that vegetation characteristics and soil properties improved significantly in the fenced area compared with the grazed area. In the protected area the vegetation cover, height and above- and belowground biomass increased significantly. Soil pH, electrical conductivity and bulk density decreased significantly, but soil organic carbon and total nitrogen concentration increased greatly in the protected area. By comparing the vegetation and soil characteristics with pre-degraded grassland, we found that vegetation can recover 6 years after fencing, and soil pH can be restored 8 years after fencing. However, the restoration of soil organic carbon, total nitrogen and total phosphorus concentrations needed 16, 30 and 19 years, respectively. It is recommended that the stocking rate should be reduced to 1/3 of the current carrying capacity, or that a grazing regime of 1-year of grazing followed by a 2-year rest is adopted to sustain the current status of vegetation and soil resources. However, if N fertilizer is applied, the rest period could be shortened, depending on the rate of application.

Arbuscular mycorrhizal fungi (AMF) are known to facilitate the growth and vigour of many plants, particularly in arid ecosystems. In a survey of AMF in a date palm plantation and two natural sites of a desert in Oman, we generated many single spore-derived cultures of AMF. We identified a number of these isolates based on spore morphotyping and molecular phylogenetic analysis using the sequence of the LSU-rDNA. Here, we presented the characteristics of four species of AMF recovered, namely Claroideoglomus drummondii, Diversispora aurantia, Diversispora spurca and Funneliformis africanum. The four species have been described previously, but for the Arabian Peninsula they are reported here for the first time. Our endeavor of isolation and characterization of some AMF habituated to arid sites of Arabia represents a first step towards application for environmental conservation and sustainable agriculture in this region.

High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, rapid socioeconomic development has increased the demand for water resources in the oases of the middle reaches of the Heihe River in northwestern China, and the lower reaches of the Heihe River have changed from a perennial river to an ephemeral stream with a decreased and degraded riparian zone. Tamarisk (Tamarix ramosissima) is the dominant shrub species of the desert riparian forest. In this study, the daily and seasonal patterns of tamarisk stem diameter growth, including the main period of tree ring formation, were examined. Observations concerning the driving forces of growth changes, along with implications for the ecology of the dendrohydrological area and management of desert riparian forests in similar arid regions, are also presented. The diurnal-seasonal activity of stem diameter and the dynamics of growth ring formation were studied using a point dendrometer and micro-coring methods during the 2012 growing season in shrub tamarisk in a desert riparian forest stand in the lower reaches of the Heihe River in Ejin Banner, Inner Mongolia of northwestern China. Generally, the variation in diurnal diameter of tamarisk was characterized by an unstable multi-peak pattern, with the cumulative stem diameter growth over the growing season following an S-shaped curve. The period from late May to early August was the main period of stem diameter growth and growth-ring formation. Among all of the hydroclimatic factors considered in this study, only groundwater depth was significantly correlated with stem diameter increment during this period. Therefore, for the dendrochronological study, the annual rings of the tamarisk can be used to reconstruct processes that determine the regional water regime, such as river runoff and fluctuations in groundwater depth. For the management of desert riparian forests, suitable groundwater depths must be maintained in the spring and summer to sustain tree health and a suitable stand structure.