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Deserts are groundwater-dependent ecosystems. Modern rainfall appears to recharge groundwater in the deserts, but direct observations are lacking. Desert pavements (DPs) and gilgai microtopography are typical landform in arid deserts. Here, we investigated whether DPs and gilgai microtopography resulted in groundwater recharge. We used photos and videos, measurements of water table fluctuations, and groundwater hydrochemistry. Research findings showed that DPs and gilgai microtopography formed and captured runoff after a heavy rain. The rise of both water table and trace ion concentration in groundwater demonstrated that gilgay microtopography recharge groundwater by collecting rainfall after a heavy rain in the arid Gobi Desert. We concluded that DPs and gilgai synergistically captured rainfall and then recharged groundwater in arid Gobi Deserts. This study provides evidence to support the viewpoint of groundwater recharge by rainfall in arid deserts. [ABSTRACT FROM AUTHOR]

Background: Disturbance is a key driver of changes in terrestrial ecosystems, especially in water limited regions. In the desert ecosystem of Northwest China, shrubs are often foraged by camels and this causes the shrubs lost their aboveground tissues. Although the aboveground tissue could recover after the disturbance, the mechanisms of resprouts' recovery after the disturbance are still poorly understood. We investigated the morphological and physiological characteristics and root water uptake sources of resprouts and non-disturbed seedlings of four desert shrub species that were often foraged by camels. Results: The results showed that the resprouts grew rapidly after the removal of aboveground tissue. The height and aboveground biomass of resprouts reached the level of 5-year-old seedlings following a growing season. Compared to un-disturbed seedlings, higher leaf water potential, leaf hydraulic conductance and photosynthesis rate were observed in resprouts, indicating that resprouts grew rapidly after disturbance. Furthermore, we found that the root water uptake source did not change after disturbance. This indicated that the roots of resprouts kept intact water uptake capacity after disturbance, which could keep supplying sufficient water to the aboveground tissue. Due to the removal of aboveground tissue of the resprouts, the water demand of aboveground tissue decreased, which induced an imbalance of water supply from roots to demand of aboveground tissues of resprouts. This explained the improved physiological performance and rapid recovery of resprouts after disturbance. Conclusions: The imbalance of water supply to demand contributes to the rapid recovery of desert shrubs after disturbance. The findings provide insight into the eco-physiological mechanism for the maintenance of desert ecosystems that are facing disturbance. [ABSTRACT FROM AUTHOR]

Succulent xerophytes (SX) and less succulent xerophytes (LSX) are able to accumulate inorganic ions and synthesize organic solutes (OS) to adapt to drought stress. Silicon (Si) is one of the five beneficial elements for plants and its importance to SX has been confirmed. In the study, the features of main osmolytes and Si were studied in SX and LSX species, and the coupling effects of inorganic ions were investigated in the SX H. ammodendron and LSX C. korshinskii. Results showed that SX and LSX had the common adaptive characteristic of preferentially accumulating inorganic ions rather than OS for drought resistance, and the total amount of osmotica in SX was 2.36‐times higher than that in the LSX. The greatest contribution to drought resistance was K+ (29.7%), the lowest was Na+ (2.4%) in LSX, while the greatest contribution was Na+ (41.7%), the total OS was the lowest (2.4%) in SX. The coupling effects of inorganic ions played vital important roles in drought resistance of the SX and LSX. The better coupling ratios of NaCl, NH4NO3, CaCl2, MgCl2 and Na2SiO3 in H. ammodendron were 20:5:20:40:10 and 40:10:60:10:7.5 (g kg−1 dry soil), and the better coupling ratios of KNO3, CaCl2, MgCl2 and K2SiO3 in C. korshinskii were 20:10:20:10 and 40:20:60:5 (g kg−1 dry soil). Findings suggested that the rational coupling of inorganic ions can be utilized as mineral compound fertilizers to restore and reconstruct degraded vegetations in semiarid areas. [ABSTRACT FROM AUTHOR]

Economic benefits and ecological restoration are the leading drivers of desert development through man-made oasis expansion. However, the sustainability of oasis expansion in combating desertification while promoting economic growth remains unclear, though such knowledge is critical for future desert development across the globe. To address this knowledge gap, a comprehensive assessment integrating meteorological, groundwater and remote-sensing data as well as groundwater simulation datasets was conducted to evaluate the spatial–temporal changes in the desert-oasis ecotone of northwest China over the past six decades. Desert development causes a rapid decline in the surrounding groundwater table, increases pollution in soil and groundwater and is associated with an increased frequency of strong sandstorms. Desert development seems to have improved the environment and promoted the economy, but there is a huge cost for the overexploitation of water resources and the transfer of pollution from surface to underground, which could cause deserts to degrade further. [ABSTRACT FROM AUTHOR]

Changes in spatial patterns of vegetation and their underlying hydrological mechanisms has significant implications for landscape ecological researches. However, empirical studies which test the relationships between vegetation spatial pattern and hydrology are scarce. Based on an in situ investigation and on geostatistical analysis, we described spatio-temporal changes in population characteristics in two shrub populations in the transition zone between oasis and desert in the Heihe River Basin, northwestern China. Our results showed that the density and cover of two dominant species were significantly greater in 2016 than in 2002. Total species richness also increased with time. N. sphaerocarpa population was distributed in small strips in 2002 and in big strips in 2016. R. soongorica population exhibited uniform distribution in 2002, and big-strip distribution pattern in 2016. The results of a semi-variogram analysis showed that the nugget/sill ratio of the two populations was 0.077 to 0.116 in 2002, and 0.066 to 0.144 in 2016. This indicated that the random variance of spatial heterogeneity occupied 7.7–11.6% of total spatial heterogeneity in 2002, and 6.6–14.4% in 2016. In 2002, the range values ( A 0 ), respectively for density and cover, were 33.09 and 14.7 m for N. sphaerocarpa , and 24.9 and 25.2 m for R. sphaerocarpa . In 2016, these values increased to 37.2 and 30.3 m for N. sphaerocarpa , and 57.3 and 75 m R. sphaerocarpa . This indicated that the scale of spatial heterogeneity for density and cover of the two dominant species increased from 2002 to 2016. Correlation analysis showed that summer precipitation and soil water content significantly related to total species richness. We concluded that summer precipitation was a key factor which affected population characteristics and spatial patterns. The mechanism driving this was a rise in summer precipitation leading to an increase in soil water content and, eventually, to a change in the spatial patterns of plants. [ABSTRACT FROM AUTHOR]

Nitraria tangutorum(Bobr), a typical succulent xerophyte with high level of seed dormancy, is one of the few shrubs found to date that can develop and form fixed dunes in desert regions. Our studies have demonstrated that the strong drought tolerance of the succulent xerophytes was strongly linked to high sodium (Na+) accumulation in the photosynthesizing branches (PB) as well as leaves. The study is to explore a method that can rapidly promote the seed germination ofN. tangutorum, and then investigate the positive effects of Na compound fertilizer (NaCF) on the growth and drought tolerance ofN. tangutorumand ecological environment by short-term pot experiment in a greenhouse and long-term field and pot experiment in a desert environment. The results indicate that the germination rate of seeds obtained a maximum by 69% when seeds were treated with 150 mg L−1gibberellic acid (GA3) for 48 h followed by soaking in concentrated sulfuric acid (98% H2SO4) for 55 min, and then germinated (25/5°C) in darkness for 8 d. After breaking seed dormancy, the NaCF significantly stimulated growth ofN. tangutorumand, concomitantly, improved its ability to cope with water deficit (30% of field water capacity) by increasing Na+more than Potassium (K+) accumulation for osmotic adjustment in greenhouse and desert conditions. The contribution (take the pot experiment in the desert, for example) of Na+to the osmotic potential (compared with control) varied from 13.9% in plants subjected to diammonium phosphate [(NH4)2HPO4] to, surprisingly, 63.9% in plants grown in the presence of NaCF under water deficit. The distribution characteristics of the total Na+(1620 mg) in the NaCF indicate that 691.2 mg (42.7%) is absorbed by plants, 848.8 mg (52.4%) remained in the pot and 80 mg (4.9%) leached, which accounted for 2.2% of the nursery soil, respectively. The positive effect of NaCF on the drought resistance ofN. tangutorumand the ecological environment were also confirmed in the field experiments. These findings suggest that the rapid seed germination technology ofN. tangutorumcombined with the popularization and application of NaCF can shorten the seed germination period and make the seedling establishment much easier, which may be an effective strategy to restore and reconstruct degraded vegetation in many desert regions. [ABSTRACT FROM PUBLISHER]

Nebkhas are important indicators of land degradation in desert steppes and play an important role in the ecological and evolutionary dynamics of desert steppe ecosystems. This study examined the relationship between the diversity of plant species and nebkha morphology during different growth stages of the nebkhas. In this study, each nebkha is defined as a self-contained unit. The species composition and vegetation patterns within each unit during different stages of formation were investigated, while also the plant species within the inter-nebkha area of the desert steppe field were examined. Results show that more than 90% of the species within the nebkha units were herbaceous. In developing nebkhas, the increase in nebkha size was associated with an increase in the herb species richness but a decrease in the overall plant density. When nebkha size was constant, similar correlations with species richness or density were found. The richness of species within the inter-nebkha area was significantly higher compared to developing nebkhas during periods of growth, but lower when nebkha development was complete and growth had stalled. The density of species was significantly higher in the nebkhas than the inter-nebkha area during all developmental periods. Thus, nebkhas provide a highly favorable condition for plant recruitment and survival when fully developed. However, when nebkhas are still forming, the inter-nebkha areas provide greater plant support. These results have important implications to biodiversity conservation in desert steppe fields. [ABSTRACT FROM AUTHOR]

Overgrazing has caused serious soil degradation, vegetation destruction, and wind erosion in temperate desert areas of northwestern China. To address this, the Livestock Enclosure Scheme was implemented in 2004 to allow for self-recovery of the overgrazed desert. The aim of this study was to investigate the effect of livestock enclosure on the restoration process by examining changes in the ecological environment of a temperate desert recovering from overgrazing. Vegetation parameters and soil properties under grazing site, 5-year fenced site, and 9-year fenced site were examined in the degraded desert in the Hexi Corridor of China. The results showed that vegetation coverage, height, plant density, richness, diversity, and litter biomass all improved after 5 years of fencing, demonstrating that short-time fencing had a positive effect on vegetation restoration in the temperate desert. Furthermore, 9 years of fencing significantly increased soil organic C (SOC), total N (TN), and total P (TP) in the 0–20 cm soil profile, while available N (AN) and available P (AP) showed the reverse trend. The values of soil C and N storage after 9 years of fencing were almost 5.55 Mg ha − 1 and 0.69 Mg ha − 1 , respectively. Enhanced vegetation caused reductions in soil water near the soil surface (0–30 cm) where vegetation uptake mainly occurred. These findings could offer insight into the development of effective strategies for protecting and enhancing the resilience of a livestock-disturbed temperate desert. [ABSTRACT FROM AUTHOR]

Afforestation is a key technique for the control of desertification and environmental deterioration in arid and semiarid regions. Therefore, it is important to quantify the influence of the succession that results from afforestation on biodiversity conservation and ecological environment. Here, we describe a case study in the sand-binding vegetation communities in China’s semiarid desert steppe in which we evaluated the effects of afforestation and key ecological processes on the community characteristics, and explored the ecological mechanism of the succession paradigm of afforestation in arid and semiarid regions. 42 species from 20 families and 40 genera along the afforestation successional gradient were collected during a comprehensive vegetation survey in 2013. The community was dominated by species in the Leguminosae, followed by the Poaceae, Compositae, and Zygophyllaceae. Our results show that the succession significantly affected community and habitat characteristics. The numbers of families, genera, and species decreased primarily during succession and then increased sharply to a maximum. Species diversity appeared to reach its maximum towards the middle of the succession, and shrubs had a greater contribution and accounted for 80.6% of the community biomass, whereas herbaceous plants contributed 64.8% of the total vegetation cover. Soil crusts significantly altered the rainfall infiltration and redistributed soil water balance, and water in the 40- to 100-cm soil layer played a decisive role in vegetation productivity and cover. Therefore, the interactional feedback between vegetation development, soil crusts and soil water was the main driver responsible for the feedback mechanism of the succession paradigm for the sand-binding vegetation communities in the semiarid desert steppe of China. [ABSTRACT FROM AUTHOR]

In water-limited environments, the water sources used by desert shrubs are critical to understanding hydrological processes. Here we studied the oxygen stable isotope ratios ( δO) of stem water of Nitraria sibirica as well as those of precipitation, groundwater and soil water from different layers to identify the possible water sources for the shrub. The results showed that the shrub used a mixture of soil water, recent precipitation and groundwater, with shallow lateral roots and deeply penetrating tap (sinker) roots, in different seasons. During the wet period (in spring), a large proportion of stem water in N. sibirica was from snow melt and recent precipitation, but use of these sources declined sharply with the decreasing summer rain at the site. At the height of summer, N. sibirica mainly utilized deep soil water from its tap roots, not only supporting the growth of shoots but also keeping the shallow lateral roots well-hydrated. This flexibility allowed the plants to maintain normal metabolic processes during prolonged periods when little precipitation occurs and upper soil layers become extremely dry. With the increase in precipitation that occurs as winter approaches, the percentage of water in the stem base of a plant derived from the tap roots (deep soil water or ground water) decreased again. These results suggested that the shrub's root distribution and morphology were the most important determinants of its ability to utilize different water sources, and that its adjustment to water availability was significant for acclimation to the desert habitat. [ABSTRACT FROM AUTHOR]

In the arid inland river basins of northwestern China, human activities control almost all the surface hydrologic processes. The potential effects of these altered hydrologic processes are gradually becoming clear, especially since the 2000 implementation of the integrated water resources management projects in the Shiyang River, the Heihe River, the Tarim River, and the Shuler River. While the appearance of these eco-hydrology changes and consequent environmental effects in the oasis has attracted broad attention, related research is still lacking. Eco-hydrological process changes in the desert-oasis ecotone were investigated in the Pingchuan irrigation district in the middle reaches of the Heihe River. The results showed that the annual average amount of surface water irrigation during the past 20 years has decreased by 1.498×10 m, while the annual average amount of well irrigation has increased by 1.457×10 m, since 2000, when the State Council of China approved the water diversion scheme for the Heihe River Basin. The groundwater depth before the water diversion scheme generally varied between 2.44-3.19 m (average 2.73±0.24 m), while that after the water diversion scheme has varied between 3.08-4.01 m (average 3.79±0.62 m). The distribution area of <3 m groundwater depth decreased from 3612 to 394 hm; while the distribution area of >3 m groundwater depth increased from 853 to 3843 hm. However, although the hydrologic processes changed dramatically, no significant effects on vegetation productivity in the desert-oasis ecotone were detected during the study period. [ABSTRACT FROM AUTHOR]

Soil moisture and its variations are key factors for understanding hydrological processes, which are characterized by a high temporal variability at different scales. The study was conducted at three field stations in the desert regions of northwestern China, where soil moisture measurements with gravimetric method were used to characterize the temporal stability of soil moisture using various statistical parameters and an index of temporal stability (ITS). The soils are a gray-brown desert soil at the Linze station, an aeolian sandy soil at the Fukang station, and a brown desert soil at the Cele station. Soil textures are accordingly sandy loam at Linze and Cele, and loamy sand at Fukang. The dynamic variation in soil moisture depends strongly on the rainfall pattern (amount and frequency) in these desert ecosystems. Soil moisture content is low and significantly different among the three desert ecosystems, with the maximum at the Linze station (6.61 ± 2.08 %), followed by the Cele (4.83 ± 0.81 %) and Fukang (3.46 ± 0.47 %) stations. The temporal pattern exhibits high variability because soil moisture is characterized by low temporal stability and a high coefficient of variation (CV). The standard deviation, CV, and ITS increase significantly with increasing soil moisture. Soil moisture displays a skewed frequency distribution that follows a logarithmic function at lower soil moisture but a log-normal distribution at higher values. [ABSTRACT FROM AUTHOR]

Abstract: Rainfall pulses can significantly drive the evolution of the structure and function of desert ecosystems, and understanding the mechanisms that underlie the response of desert plants to rainfall is the key to understanding the responses of desert ecosystems to global climatic change. The present study was carried out at the desert-oasis ecotone in the middle of China''s Heihe River Basin. We measured sap flow in the branches and stems of desert shrubs (Nitraria sphaerocarpa and Elaeagnus angustifolia) using sap flow gauges, and studied the response of sap velocity to rainfall pulses using the “threshold-delay” model. The results showed that the response of sap flow began about 1h earlier after rainfall, and that sap velocity increased two to threefold, compared to its pre-rainfall value. The sap velocity increased significantly, then decreased gradually, with increasing rainfall. The response of sap flow differed significantly between rainfall, species, position within species during pulse duration, and the interactive effects also differed significantly (P <0.0001). The response pattern followed the threshold-delay model, with lower thresholds of ≤5.2 and 1mm of rainfall for the stems and branches, respectively, demonstrating the importance of small rainfall events (<5mm) for plant growth and survival in desert regions. [Copyright &y& Elsevier]

• Soil quality is significantly improved by desert reclamation. • The SOC stocks show exponential change with long-term conventional cultivation. • The N:P ratio has an essential influence on SOC and nutrient stocks. Reclamation in desert-oasis areas is effective for improving land productivity and ensuring food supply. However, the understanding of the sustainable productivity of soils under long-term conventional cultivation after desert reclamation is still poor. This study was conducted to determine soil structural properties, organic carbon stocks (SOCS) and nutrient stocks under four desert reclamation ages (0, 30, 60, and 100) in the arid region of northwest China, and evaluate the influence of long-term conventional cultivation on desert soil quality. The results indicated that soil structural stability index (SI) in topsoil improved after desert reclamation, but showed a slight downward trend after 60 years of cultivation, and farmland soil in the study area was still at serious risk of degradation (SI ≤ 5 %) overall. SOCS were enlarged by 4.2 times after desert reclamation, and nitrogen stocks (NS) and phosphorus stocks (PS) were increased by 1.2–6.5 times. However, the regression analysis showed that SOCS and NS in 0–40 cm soil layer and PS in topsoil stopped increasing after about 60-year conventional cultivation. Soil stoichiometry, pH and texture were the key factors affecting SOCS, NS and PS in oasis farmlands. In summary, our study emphasized that soil quality in arid areas was greatly improved after desert reclamation, however, long-term conventional agriculture management measures limited this improvement. Therefore, long-term conventional management of agricultural land in arid areas should introduce appropriate conservation measures to achieve sustainable soil productivity. [ABSTRACT FROM AUTHOR]

A physically-based model for soil-plant-atmosphere continuum (SPAC) is parameterized and evaluated against field-measured physiological responses of a desert shrub, Haloxylon Ammodendron (HA) , to rainfall pulses in a desert environment in northwestern China. Despite its simplicity, the model was successfully employed to assess the complexity and uncertainty involved in the physiological responses of HA following pulsed rainfall events. Through modelling efforts, we report a systematic evaluation of the non-linear relationship between the physiological responses of HA and pulse magnitude or antecedent moisture. The results show that following the rainfall pulses, the modeled daily transpiration and assimilation rates either stayed the same or decreased monotonically with water stress. However, the stomatal conductance (g s) and photosynthetic rate (A n) responses were relatively weaker when compared to the increase in water potential. We found that rainfall events with <5 mm cannot induce any substantial response of A n (Δ < 4 μmol m−2s−1), and at least 13 mm of rain is required to increase A n by 10 μmol m−2s−1. Significant responses of water use efficiency (WUE) were not even discernible from viewing the simulation. Our analysis reproduced the judgements with a certain uncertainty that HA is basically a kind of drought resistant species, it tends to have a more conservative water-use strategy and thus a safer photosynthetic behavior. The inverse–texture hypothesis is much more clearly supported by the modeling experiments, suggesting that soil texture drives differences in the effects of pulses on the magnitude and sensitivity of the physiological responses of plants, and the interaction between rainfall and soil texture may lead to the preferred acquisition and use of pulsed precipitation by HA. The modelling work and findings in this study is likely to shed light on the quantitative understanding of the physiological behavior of other plants in water-limited environments. Image 1 • A physically-based SPAC model is parameterized and evaluated against field-measurements. • Rainfall events with <5 mm cannot induce any substantial response of photosynthetic rate. • At least 13 mm of rain is required to increase photosynthetic rate by 10 μmol m−2s−1. • Soil texture drives differences in the effects of pulses on the physiological responses. [ABSTRACT FROM AUTHOR]