Research advances on drought resistance mechanism of plant species in arid zones of China

Drought and shortage of water resources, which restrict the economy, society development and environmental protection, are key factors in arid zones of China. In the arid zones of Western China, researching plant drought resistance mechanism, selecting plant species with higher drought resistance, and developing water-saving techniques, are important for environmental improvement and economic development. This paper reviews research advances on drought resistance mechanism of plant species, based on research of morphological, physiological, and ecological adaptation mechanism of plant species under drought stress, such as anatomical structure of root systems and leaves, photosynthesis, antioxidant enzyme system, malondialdehyde （MDA）, osmotic adjustment, endogenous hormone, drought-induced proteins and δ^13C. Finally, this paper points out the key field of future research.

Effects of grazing intensity on seed production of Caragana stenophylla along a climatic aridity gradient in the Inner Mongolia Steppe,China

As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities （fenced, mild grazing and severe grazing） across a climatic aridity gradient （semi-arid, arid, very arid and intensively arid zones） in the Inner Mongolia Steppe, northern China during 2012-2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number seed weight and seed yield were lower in the low precipitation year （2013） than in the high precipitation year （2012）. As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.

Water use efficiency in an arid watershed: a case study

Integrated Water Resource Management （IWRM） becomes increasingly important in arid watersheds, where water resources are scarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valley in Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water for nearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation and water use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differ- ences in efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e., higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sec- tors downstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies and higher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impact of improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits, except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed to compensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of the current agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are low- ered to such levels that make annual recharge insufficient.

Effect of Bentonite on the Sandy Soils of Arid Regions： Study of Behavior of an Association of Wheat and Chickpea

The sandy soils of Mostaganem plateau are vety, poor in clay. They are characterized by very low fertility and water holding capacity. The addition of bentonite to these soils and the cultivation of durum wheat, in combination with the chickpeas, are two eco-physiological strategies to rehabilitate their agricultural suitability. This study was conducted on two plant species： a local variety of durum wheat （Waha） and a legume, chickpea （variety ILC 3279）, on a substrate bentonite at 10% dose. For each stage of growth measurements of stem height, leaf area and plants vegetative nitrogen content were quantified. Changes in total nitrogen content of durum wheat grown in substrates amended with 10% bentonite or not during the development of durum wheat in monoculture and in association with the chickpeas were analyzed. The results showed that the total nitrogen content of durum wheat was significantly higher at three leaves and tailoring stages, when durum wheat was associated with chickpea in the same soil. However, the results showed no difference during the lifting and two leaves stages. There was also a positive effect of treatment at 10% of bentonite on the plant total nitrogen content regardless of the stage and the culture system.

Water Losses in Arid and Semi-Arid Zone:Evaporation, Evapotranspiration and Seepage

The primary purpose of this study was to assess water losses by evapotranspiration, evaporation and seepage in arid zone.Normally, evaporation and seepage are the main causes of water losses.For modeling water losses,a combination of Genetic Programming(GP),Penman-Monteith(PM) and Penman combination model for measurement of evapotranspiration,evaporation and seepage has been developed.The results were found to be varying depending on how the evaporation and seepage phenomena are modeled.These results show that that there is an improvement in reducing evapotranspiration,evaporation and seepage losses in arid and semi-arid region.

Effects of vegetation cover on recruitment of Ulmus pumila L. in Horqin Sandy Land, northeastern China

Understanding the effects of vegetation cover on seedling survival is helpful for promoting vegetation restoration in environmentally fragile zones. This study was conducted in the desertified, moving sand dunes of Horqin Sandy Land, Inner Mongolia, northeastern China. We hyphothesized that （1） seed density （i.e., number/m2） increases as vegetation cover increases, and （2） there will be more surviving seedlings in locations with higher vegetation covers. Total vegetation cover and initial densities of seeds, germinated seeds and surviving seedlings of Ulmus pumilia were evaluated under various vegetation covers in trying to clarify the effects of vegetation cover on the early stages of the plant life history. In agreement with the first hypothesis, initial seed densities were greater （P〈0.05） under higher vegetation covers. The relationship between vegetation cover and initial seed density was represented by a quadratic regression, where a threshold occurred with a vegetation cover of 36% （P〈0.05）. The higher total vegetation covers, however, did not result in increased densities of germinated seeds （P〉0.05）, which on average represented 16.7% of initial seed densities. Even more, three months after the study initiation, total vegetation covers were similar （P〉0.05） at all positions in the dunes, and they determined a similar number （P〉0.05） of surviving seedlings at those positions （i.e. the second hypothesis had to be rejected）. The mean number of seedlings that survived at all positions was only 4.5% of germinated seeds. The number of surviving elm seedlings （0 to 1.7 seedlings/m2） under various vegetations covers （12.2% to 20.8%） at all dune positions by late summer would most likely not contribute to vegetation restoration in the study area.

Response of ants to grazing disturbance at the central Monte Desert of Argentina: community descriptors and functional group scheme

Livestock ranching is one of the main productive activities in arid regions of the world.Grazing produces changes in animal as well as plant communities(e.g.richness,abundance and species dominance relationships).Ants are good biological indicators due to the environmental fidelity of some of their community parameters.We described the functional structure of the ant community in the central Monte of Mendoza,Argentina,and examined the effect of grazing using richness,diversity and the functional group scheme.We used pitfall traps to sample ants at a reserve with 30-year cattle exclusion and at an adjacent ranch.Eleven of the 27 recorded species showed significant differences in their abundance and two species were absent at the ranch.While richness and diversity did not reflect these differences,functional groups did.Hot Climate Specialists were more abundant at the ranch while Cryptic Species and Generalized Myrmicinae increased at the reserve.This study supports the utility of the functional group scheme to study the effects of grazing disturbance in ant communities of arid regions.

A method to estimate aquifer artificial recharge from a hill dam in Tunisia

in arid and semi-arid areas, artificial recharge is a key technology in groundwater resources management, and a reliable estimate of artificial recharge is necessary to its sustainable development. Several methods are available to estimate the artificial recharge; however, most of them require field data or model parameters, thus limiting their applications. To overcome this limitation, we presented an analytical method to estimate the artificial recharge through monitoring the water release by piezometer and analysing the controlling factors of the artificial recharge from a hill dam in Tunisia. A total of 97 measurements of water flow in the streambed recorded from 4 gauging stations were analysed. Results indicated that the average infiltration velocity ranged from 0.043 to 0.127 m/d and the infiltration index varied from 7.6 to 11.8 L/（s.km）. Pearson＇s correlation coefficient analysis shows that the infiltration index, the stream gradient, the thickness of unsaturated zone, the number of infiltration pond, the stream geometry, and the water flow rate were found to be the main factors in determining the infiltration. The high correlation coefficients （0.908 for the number of infiltration pond and 0.999 for the stream geometry） mean that the number of infiltration pond and the stream geometry are the most influential factors. Time variations of groundwater level were used to analyze the recharge effects on the piezometry of aquifer. The analysis showed that during the artificial recharge, the water table increased at a rate of 5 mm/d and that the increase was limited to the area surrounding the recharge site. Based on the results of the study, building infiltration ponds along streambed and improving the potential of rainwater harvesting over the study area are recommended.

Some Phenomena of the Interaction Between Vegetation and a Atmosphere on Multiple Scales

This article studies the response of the distribution pattern and the physiological characteristics of the ecosystem to the spontaneous precipitation and the interaction between vegetation and the atmosphere on multiple scales in arid and semi-arid zones, based on measured data of the ecological physiological parameters in the Ordas Plateau of northern China. The results show that the vegetation biomass and the energy use efficiency of photosynthesis are especially sensitive to the annual precipitation; strong and complex interactions exist between the vegetation and the atmosphere on multiple scales leading to supernormal thermal heterogeneity of the underlying surface, the strong vortex movement and turbulence. This study can facilitate understanding of the land surface processes and the influences of global climate change as well as human activities on the human environment in the arid and semi-arid zones. It also aids in improving the parameterization schemes of turbulent fluxes of a heterogeneous underlying surface for land surface processes in climate models.

Effects of temperature and water limitation on the germination of Stipagrostis ciliata seeds collected from Sidi Bouzid Governorate in Central Tunisia

Most ecological studies in North Africa reveal a process of continuous degradation of rangeland ecosystems as a result of overgrazing. This degradation appears across the decreasing of perennial grass diversity. Indeed, the majority of steppe ecosystems are characterized by a low density of perennial grass species at present. This study evaluated the effects of temperature and water limitation on the seed germination of Stipagrostis ciliata（Desf.） de Winter, a perennial grass species. The seeds were collected from the Bou Hedma Park, Sidi Bouzid Governorate, Central Tunisia. The thermal time and hydrothermal time models were used to describe the seed germination of S. ciliata under different water potentials and temperatures. The germination response of S. ciliata seeds in darkness was evaluated over a range of temperatures（15°C, 20°C, 25°C, 30°C and 35°C） and across a wide range of osmotic potentials（0.0, –0.2, –0.6, –1.2, –1.6 and –2.0 MPa） of the polyethylene glycol（PEG6000） solutions at each temperature level. Among the tested temperatures, 25°C was found to be the optimal temperature to the germination of S. ciliata seeds. The final germination percentage（75.2%） was obtained with distilled water. The progressive decrease of osmotic potential of the PEG6000 solutions inhibited the seed germination. However, the number of days to first germination was increased with a reduction of osmotic potential. A significant positive relationship was identified between final germination percentage of S. ciliata seeds and osmotic potential of the PEG6000 solutions, with R^2 ranging from 0.5678 to 0.8761. Furthermore, a high degree of congruency between predicted and observed germination time course curves was observed. In general, S. ciliata exhibits a significant adaptation capacity for water limitation and high temperature in arid ecosystems.

Annual and seasonal changes of the air temperature with altitude in the Upper Dades valley, High Atlas, Morocco

The purpose of this study is to determine the size of air temperature changes with altitude in the mountains of the arid zone, on the example of the Upper Dades valley(High Atlas, Morocco). The air temperature change with altitude was determined on the basis of 5 years data from three meteorological stations. The analysis was carried out on an annual and seasonal basis. The annual and daily variations of thermal gradients between pairs of stations were also determined. It was found that the average thermal gradient in the Upper Dades valley was-1.02℃ per 100 m. The highest values of the thermal gradient occur in winter and the lowest in summer. In winter,the thermal gradient was characterized by the greatest variability. Minima of the daily variation of air temperature gradients were observed in early morning hours and maxima around midday. In the lower part of the valley, air temperature inversion frequently developed between 10 AM and 3 PM UTC.The obtained results show high thermal gradients in the mountains of the arid zone, with their annual amplitude increasing in the lower parts of the valley.The instantaneous values of the gradients were significantly modified by the supply of latent heat and the occurrence of dust storms. It has been shown that the advection factor plays an important role in shaping large gradient values. The study contains novel results of thermal gradient measurements in high mountains of arid zone.

Water conservation in the Arab region: a must for survival

The Arab region covers an area over 13 million square kilometers in size, with almost 90% of its area classified as arid or ex- tremely arid with very little precipitation, extremely high evaporation and almost no vegetation cover. The region is classified in many international reports as the poorest region in the world in the context of renewable water resources and critical water scarcity which hinders the socio-economfic development of many countries in this region. The rapidly increasing population has reduced the per capita share of renewable water to less than the poverty line of 1,000 m3/（capita＇a） and, in some Arab countries, to less than the extreme poverty line of 500 m3/（capita＇a）. This has led to over-exploitation of non-renewable groundwater and desalination of salty water in many countries with considerable costs and contamination of many renewable sources. Atmospheric processes re- sponsible for aridity in the Arab region are projected to intensify due to climate change, resulting in an alarming decrease in pre- cipitation and increase in evaporation rates. Many concerned entities in the region consider water security as a key element for food security and ultimately political stability. Hence, various efforts have been exerted to identify key problems and suggested solutions. The Arab Water Ministers Council of the Arab League, as well as Reports of the Arab Forum for the Environment and Development （AFED） and the recommendations of the 13th Regional Meeting of the Arab National Committees of the Interna- tional Hydrological Programme of UNESCO （niP）, have all made similar recommendations on the need to address the issues of water scarcity in the Arab region which will be further discussed in this paper. However, none of these reports focused on ＂Water Conservation＂ as an equally important action for coping with water scarcity in the region. There are many definitions for ＂Water Conservation＂ in the scientific literature, including huge water savings from irrigation, industrial use, and domestic use as well as methods and approaches for augmenting water supply through non-conventional practices such as water harvesting and waste water reuse. In this paper, a review is provided for definitions, methods and impacts of water conservation and its role in alleviat- ing water scarcity in the Arab region.

A method of characterizing land-cover swap changes in the arid zone of China

Net area change analysis can dramatically underestimate total change of land cover, even sometimes seriously misinterpret ecological processes of the ecosystem, especially in arid or semiarid zones. In this paper, a suite of indices are presented to characterize land-cover swaps that may seriously damage the ecosystem in arid or semiarid zones, based on swap-change areas extracted from remotely sensed images. First, swap percentage of total area and swap intensity of total changes were used to determine the status of land-cover swap change in an area. Then, dominated swap category and individual swap- change intensity for a land-cover category were used to determine flagged land-cover swap-change categories. Finally, swap-change mode and Pielou＇s index were used to determine the land-cover swap-change processes of dominant categories. A case study is conducted using this approach, based on two land-cover maps in the 1980s and 2000 in Naiman Qi, Tongliao City, Inner Mongolia, China. This study shows that the approach can clearly quantify the severity and flagged classes of land-cover swap-change and reveal their relationship with ecological processes of the ecosystem. These results indicate that the approach can give deep insights into swap change, which can be very valuable to land-cover policy making and management.

Intensified risk to ecosystem productivity under climate change in the arid/humid transition zone in northern China

Assessing the climate change risk faced by the ecosystems in the arid/humid transition zone(AHTZ)in northern China holds scientific significance to climate change adaptation.We simulated the net primary productivity(NPP)for four representative concentration pathways(RCPs)using an improved Lund-Potsdam-Jena model.Then a method was established based on the NPP to identify the climate change risk level.From the midterm period(2041–2070)to the long-term period(2071–2099),the risks indicated by the negative anomaly and the downward trend of the NPP gradually extended and increased.The higher the scenario emissions,the more serious the risk.In particular,under the RCP8.5 scenario,during 2071–2099,the total risk area would be 81.85%,that of the high-risk area would reach 54.71%.In this high-risk area,the NPP anomaly would reach–96.00±46.95 gC·m-2·a-1,and the rate of change of the NPP would reach–3.56±3.40 gC·m-2·a-1.The eastern plain of the AHTZ and the eastern grasslands of Inner Mongolia are expected to become the main risk concentration areas.Our results indicated that the management of future climate change risks requires the consideration of the synergistic effects of warming and intensified drying on the ecosystem.

Superficial Color Patches as a Visual Diagnostic Criterion for Agricultural Management

Soil management matters in semiarid lands are key to have acceptable yields and to preserve diversity. After the major agricultural intensification underwent in the semiarid lands of Monegros, NE Spain, custom tailored tools are needed to reconcile agriculture with habitats conservation. The objectives of this study were to quantify the effect of soil properties of two distinctly colored soils, white patches （WP） and dark patches （DP）, dominant in the arid landscape of the central Ebro Basin, Spain on winter cereal grain yield and to prove that superficial soil color could be used as a visual diagnostic criterion for evaluation of agricultural practices in arid lands. Significant differences between WP and DP soils were found in gypsum, carbonate contents, available water holding capacity and infiltration rate. The grain yield ranged from 51 to 5 713 kg ha-1. Significantly lower yields （P 〈 0.01） and precipitation-use efficiency （P 〈 0.05） were attained in the WP soils for the three seasons studied. This difference increased with the average rainfall due to the significantly lower soil water infiltration （P 〈 0.01） and water holding capacity （P 〈 0.05） found in the gypseous soils. Our results show that mapping the soil surface color at farm scale can be a low=cost tool for optimizing agricultural practices and recovering the natural vegetation. This approach can be advantageous in similar arid or semiarid environments around the world.

Thermoregulatory value of cracking-clay soil shelters for small vertebrates during extreme desert conditions

Deserts exhibit extreme climatic conditions.Small desert-dwelling vertebrates have physiological and behavioral adaptations to cope with these conditions,including the ability to seek shelter.We investigated the temperature(T)and relative humidity(RH)regulating properties of the soil cracks that characterize the extensive cracking-clay landscapes of arid Australia,and the extent of their use by 2 small marsupial species:fat-tailed and stripe-faced dunnarts(Sminthopsis crassicaudata and Sminthopsis macroura).We measured hourly(over 24-h periods)the T and RH of randomly-selected soil cracks compared to outside conditions,during 2 summers and 2 winters.We tracked 17 dunnarts(8 Sminthopsis crassicaudata and 9 Sminthopsis macroura)to quantify their use of cracks.Cracks consistently moderated microclimate,providing more stable conditions than available from non-crack points,which often displayed comparatively dramatic fluctuations in T and RH.Both dunnart species used crack shelters extensively.Cracks constitute important shelter for small animals during extreme conditions by providing a stable microclimate,which is typically cooler than outside conditions in summer and warmer in winter.Cracks likely play a fundamental sheltering role by sustaining the physiological needs of small mammal populations.Globally,cracking-clay areas are dominated by agricultural land uses,including livestock grazing.Management of these systems should focus not only on vegetation condition,but also on soil integrity,to maintain shelter resources for ground-dwelling fauna.

The New Progresses in Coupling Relations of Mountain-oasis-desert System

In this paper, the concepts and principles of mountain-oasis-desert system （MODS） are put forward according to the natural geographical situations in arid zone of western china, The spatiotemporal characteristics and dynamic changes of typical MODS, the process of material circulation, energy transform and information transmission among MODS and the mechanism of MODS interaction and symbiosis are analyzed. The foundation and frame of the coupling type are determined by landform types and climate characteristics： the spatial pattern of the coupling type is determined by the hydrological characteristics; the vegetation type reflects the appearance of the coupling type; the soil state restdcta the function of the coupling type and the human activities influence the development course of the coupling type. Interface course of MODS is closely related to such medium as water, soil, air, etc., and water is the major medium during the course of material circulation, energy transform and information transmission. The disorder of water salt, water heat and water land restricts the stability of water ecosystem.