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Managing soil erosion by water from marginal acidic soil employing traditional methods is difficult, if not impossible. The ability of Sedum sediforme (Rupestria group) to germinate, grow, and establish good ground cover under harsh environmental conditions induced us to assess its effectiveness as surface cover on an acid soil taken from mountain cuts (non-agricultural field) in Yamaguchi prefecture, Japan. This soil is widely used for road embankments in this prefecture. Two rainfall intensities, 30 and 60 mm h-1, were tested for 2 h and 1 h, respectively, on sedum grown in soil plots measuring 50 × 30 × 5 cm at three levels of vegetation cover: bare soil, 25% cover, and 75% cover. Under both simulated rainfall intensities, the sediment concentration, total soil loss, and total splashed soil decreased significantly with increasing vegetation cover. The dissipation of the raindrop impact energy by sedum cover was among the main factors contributing to the improvement of aggregate size distribution of the sediment and the total splashed soil and consequently a decrease in the seal formation on the soil surface. Compared with the bare soil, cumulative soil loss decreased by 77% and 73% under 30 and 60 mm h-1 rainfall intensities, respectively. The total splashed soil under sedum cover decreased by 30% as compared to that from the bare soil. The mean weight diameter of the surface soil aggregate increased significantly with increasing sedum cover. This is attributed to its ability to effectively protect the soil surface, thereby reducing soil aggregate breakdown and detachment, and consequently soil erosion.

Water availability is a critical determinant for the growth and ecological distribution of terrestrial plants. Although some xerophytes are unique regarding their highly developed root architecture and the successful adaptation to arid environments, virtually nothing is known about the molecular mechanisms underlying this adaptation. Here, we report physiological and molecular responses of wild watermelon (Citrullus lanatus sp.), which exhibits extraordinarily high drought resistance. At the early stage of drought stress, root development of wild watermelon was significantly enhanced compared with that of the irrigated plants, indicating the activation of a drought avoidance mechanism for absorbing water from deep soil layers. Consistent with this observation, comparative proteome analysis revealed that many proteins induced in the early stage of drought stress are involved in root morphogenesis and carbon/nitrogen metabolism, which may contribute to the drought avoidance via the enhancement of root growth. On the other hand, lignin synthesis-related proteins and molecular chaperones, which may function in the enhancement of physical desiccation tolerance and maintenance of protein integrity, respectively, were induced mostly at the later stage of drought stress. Our findings suggest that this xerophyte switches survival strategies from drought avoidance to drought tolerance during the progression of drought stress, by regulating its root proteome in a temporally programmed manner. This study provides new insights into the complex molecular networks within plant roots involved in the adaptation to adverse environments.

This study investigated the use of woody plants by a rural community in an area of dry land Caatinga vegetation in northeastern Brazil. Information was obtained concerning this woody species with a diameter that is equal to or greater than 3 centimeters (cm) at soil level surveyed in 100 sample plots totaling 1 hectare (ha). The following question is the hypothesis we tested. Is a plant’s relative importance (as measured by its use value) related to its “apparency,” as measured by its abundance and ecological dominance? “Apparency” explains the use value of plants in four categories: medicinal, construction, fuel, and technology. The most important uses of woody plants are related to harvesting for energy and construction purposes.

Reaumuria vermiculata is a xerohalophytic perennial dwarf shrub distributed in many gypseous and saline areas in southern Tunisia. A laboratory experiment was carried out to assess the effects of temperature and salinity on germination. The germination responses of the seeds in darkness were determined under a range of salinity and temperature regimes. Temperatures between 10� C and 30� C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or a decrease in temperature from the optimal temperature (15� C). Highest germination percentages were obtained under non-saline conditions and increases in salinity inhibited seed germination. Salt stress decreased both the germination percentage and the germination speed (increase of the mean time to germinate). Seed germination decreased with an increase in NaCl concentrations at all temperatures. An interaction between salinity and temperature yielded no germination at salinity of 300 mM, whereas some seeds germinated under the optimal temperature.

Desert succulents are renowned for their rapid recovery of shoot function after periods of drought as a result of shoot succulence, root–shoot interactions, and key root properties. Near the base of the shoot, the proximal (generally older) roots appear to play a major role in the rapid uptake and delivery of water, especially after a period of soil drying when the rest of the root system has a lower hydraulic conductance. In all of the cacti, agaves, and yuccas examined to date, hydraulic conductance for the proximal root zone is unexpectedly high. Substantial water uptake by older roots of cacti is associated with much higher axial (xylem) hydraulic conductance in proximal than in distal root regions. For agaves and yuccas, proximal roots have other anatomical and physiological traits that enhance water uptake near the shoot base. Despite suberization (waxiness) of external root tissues in the proximal region, internal cell layers appear more characteristic of young root regions with living cortical cells and a high proportion of unsuberized passage cells in the endodermis. Both features may be related to the existence of a contractile root zone possessed by all members of the Agavaceae surveyed to date. Passage cells in the endodermis and aquaporins (protein water channels) in the metabolically active cortex expedite radial water transport. The radial swelling that accompanies longitudinal root contraction may also help maintain root-to-soil contact that would otherwise be diminished in dry soil. Modifications that increase axial and radial hydraulic conductance in the proximal root region suggest that water uptake by older roots is critical to the success of desert succulents.

Because of greater interest in green roofs in the United States, it is critical to increase the number and geographic range of proven plant resources for long-term survival on rooftops. Successful plant taxa for extensive green roofs must establish themselves quickly, provide high groundcover density, and tolerate extreme environmental conditions. Furthermore, dead load weight restrictions on many buildings may limit the substrate depth that can be applied. The objective of this study was to evaluate the effect of substrate depth on initial establishment and survival of 25 succulent plant taxa for green roof applications in the midwestern United States. Survival, initial growth, and rate of coverage were compared for plants grown in three substrate depths (2.5, 5.0, and 7.5 cm) on 24 roof platforms. Plant coverage was determined from image analysis of weekly digital photographs. Results indicate deeper substrates promote greater survival and growth; however, in the shallowest depth of 2.5 cm, several species continued to persist. Of the 25 species initially planted, only 47% survived in the deepest substrate of 7.5 cm. Recommended species at the depths tested for climates similar to southern Michigan include Phedimus spurious Raf. ‘Leningrad White’, Sedum acre L., S. album L. ‘Bella d'Inverno’, S. middendorffianum L., S. reflexum L., S. sediforme J., and S. spurium Bieb. ‘Summer Glory’. Subsidiary species that are present at specific substrate depths but may not exhibit an ability to cover large areas include S. dasyphyllum L. ‘Burnatii’, S. dasyphyllum L. ‘Lilac Mound’, S. diffusum W., S. hispanicum L., and S. kamtschaticum Fisch. The primary deterrent for these subsidiary species was little to no survival at 2.5 cm. Deeper substrates promoted greater survival and growth for nearly all species tested.

Aims Prunus mongolica is a xeric shrub, a landscape plant, a water and soil conservation plant, and an ancient species in the desert and desert steppe of the Mongolian Plateau, China. It tolerates extreme aridity and poor soil, growing strongly in desert where annual rainfall is 200 mm and annual evaporation is 3 400-4 000 mm. Study of P. mongolica is useful for understanding plant succession on the Mongolian Plateau and for sustaining and restoring the local ecosystem. Methods The Abbe refractometer method, the natural dehydration method and the PV technique were used to analyze the hydrological characteristic of P. mongolica. Important findings The relative water content, saturation water content, critical saturation deficit and water potential of P. mongolica seedling leaves were 69%, 117%, 48% and -0.85 MPa, respectively. The relative water content, critical water content and leaf water potential of P. mongolica seedlings exposed to drought stress decreased to 48%, 39% and -1.97 MPa, respectively, but the saturation water content and the ratio of bound water/free water increased to 187% and 11.94, respectively. The natural dehydration experiment indicated that P. mongolica seedlings reached equilibrium after 102 h in normal condition, but the dehydration rate decreased and the dehydration equilibrium time was delayed after 3 d of drought stress. This proved that the water-holding ability of P. mongolica increased after drought stress. In comparing the dehydration rates of the xerophytic P. mongolica and the mesophytic P. pedunculata, we discovered that the dehydration tolerance capacity of P. mongolica was higher than that of P. pedunculata. Analysis of PV curve showed that osmotic potential (Ψπ100) of water saturation and osmotic potential (Ψπ0) at turgor loss point of P. mongolica seedling were -2.49 MPa and -3.11 MPa, respectively. The fact that the difference of Ψπ100 and Ψπ0 was very large and the values very low showed that P. mongolica had strong ability to regulate turgor pressure. The ratio of bound water/free water was relatively high (7.76), and the modulus elasticity of cell wall was 4.18 MPa. The low leaf water potential and low osmotic potential of P. mongolica were beneficial for absorption of water from soil depths. Our results indicated that P. mongolica was a strong xerophyte in terms of hydrology. Its high ratio of bound water and free water, low osmotic potential at saturation water content, osmotic potential at turgor loss point and low modulus elasticity of cell wall were the physiological fundamentals of its dehydration tolerance.

Trotz großer klimatischer Unterschiede zwischen Burkina Faso und Deutschland gibt es 20 Arten, die in beiden Ländern spontan vorkommen, das sind immerhin 1 % der Flora von Burkina Faso und 0,15 % der Flora Deutschlands. Mehrheitlich handelt es sich dabei um Arten der Ruderal- und/oder Segetalflora (16 Arten), die restlichen sind Wasser- bzw. Röhrichtpflanzen. Vom heutigen Standpunkt aus betrachtet, sind die meisten der 20 Arten Kosmopoliten. Obwohl das Klima von Burkina Faso semi-arid ist, gehört keine der Arten zur Gruppe der Sklero- oder Xerophyten. Dementsprechend sind in Burkina Faso alle mehr oder weniger an wenigstens temporär überflutete Standorte oder an feuchte Böden gebunden. 15 der 16 Ruderalen werden in Deutschland dagegen als Indikatoren intermediärer bis trockener Standorte bewertet., Flora et Vegetatio Sudano-Sambesica, Vol 18 (2015)

Restinga formations grow on sandy spits of coastal plains, an environment whose conditions limit the growth and development of vegetal species. Studies on restinga gradients are good examples of how plants acclimate to restrictive environments. This work compares three woody species co-occurring in four vegetations of a restinga from Southern Brazil. It pinpoints morpho-anatomical attributes that favor the survival of species faced with spatial variability of soil and light conditions. Results indicate that they respond differently to environmental variables on different scales. The plastic response of morphological attributes is more marked than that of anatomical ones. Varronia curassavica and Dodonaea viscosa showed more xeromorphic features on the more stressful restinga formations while Symphyopappus casarettoi varied between xerophyte to mesophyte forms along the gradient. Individual height, fresh and dry leaf masses, leaf area, specific leaf mass and area, leaf density, and water content are particularly noteworthy. These responses are strategies allowing the studied species to survive in restinga environment with highly variable soil nutrient, water availability, and light conditions. The environmental conditions are important features that modulate de plant morphology along the gradient. Keywords: coastal vegetation, leaf morphology, leaf anatomy, light and soil conditions. Restinga (o cordón litoral) es una formación que se desarrolla en cordones arenosos de planícies litorales. Este ambiente presenta condiciones limitantes al crecimiento y desarrollo de las especies vegetales. Estudios en gradientes de restinga son buenos ejemplos de como las plantas se aclimatan a las condiciones ambientales restrictivas. Este trabajo tuvo como objetivo comparar tres especies leñosas co-ocurrentes en cuatro fisonomías de una restinga del sur de Brasil, buscando conocer los atributos morfo-anatómicos que favorecen la sobrevivencia de estas especies frente a la heterogeneidad espacial de las condiciones de suelo y luz. Los resultados indican que las variables ambientales fueron percibidas en diferentes escalas por las especies. Varronia curassavica y Dodonaea viscosa mostraron características más xeromórficas en las formaciones de restinga más estressantes, mientras que Symphyopappus casarettoi varió entre formas xerofíticas a mesofíticas a lo largo del gradiente. Atributos morfológicos presentaron respuesta plástica mas acentuada que los anatómicos, destácandose la altura de los individuos, las masas foliares frescas y secas, el área foliar, el área y la masa específica foliar, la densidad foliar y el contenido de agua. Tales características representan estrategias que permiten a las especies estudiadas sobrevivir en ambientes de restinga con elevada variación en la disponibilidad de nutrientes, agua del suelo y condiciones de luminosidad. Las condiciones ambientales son características importantes que modulan la morfología de la planta de lo largo del gradiente.

The aim of research to determine the type of stomata in the leaves of plants Xerophyte euphorbia (Euphorbia splendens), mesofit plant Hibiscus (Hibiscus rosasinensis), as well as hidrofit kale plant (Ipomoea aquatica). The research methods is descriptive qualitative to describe and interpret the type of stomata on the leaves. Type of stomata on the leaves of Xerophyte is anomositik. Mesofit plant hibiscus (Hibiscus rosasinensis) has a parasitic type of stomata. Hidrofit plant (Ipomoea aquatica) is anisositik, that is cells surrounded cover three neighboring cells that are not as great.

Background and aims Thiophores, which are typically desert gypsophytes, accumulate high (2-6 % S dry weight) sulphur concentrations and may possess unique tolerance to environmental stress factors, e.g. sulphate/metal toxicity, drought and salinity. Little is known of the prevalence of the behaviour or the associated physiological aspects. The aim of this study was to (a) determine the prevalence of thiophore behaviour in a group of Australian xerophytes; (b) identify elemental uptake/storage characteristics of these thiophores; and (c) determine whether the behaviour is constitutive or environmental. Methods The elemental composition of soils and the foliage of 11 species (seven genera) at a site in the Tanami Desert (NT, Australia) was compared and 13 additional Acacia species from other locations were examined for elevated calcium and sulphur concentrations and calcium-sulphur mineralization, thought to be particular to thiophores. Key results Acacia bivenosa DC. and 11 closely related species were identified as thiophores that can accumulate high levels of sulphur (up to 3·2 %) and calcium (up to 6.8 %), but no thiophores were identified in other genera occupying the same habitat. This behaviour was observed in several populations from diverse habitats, from samples collected over three decades. It was also observed that these thiophores featured gypsum (CaSO4·2H2O) crystal druses that completely filled cells and vascular systems in their dried phyllode tissues. Conclusions The thiophores studied exhibit a tight coupling between sulphur and calcium uptake and storage, and apparently store these elements as inorganic salts within the cells of their foliage. Thiophore behaviour is a constitutive trait shared by closely related Acacia but is not highly prevalent within, nor exclusive to, xerophytes. Several of the newly identified thiophores occupy coastal or riparian habitats, suggesting that the evolutionary and ecophysiological explanations for this trait do not lie solely in adaptation to arid conditions or gypsiferous soils.

Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide as this economically important legume forage is sensitive to these kinds of abiotic stress. In this study, transgenic alfalfa lines expressing both tonoplast NXH and H(+)-PPase genes, ZxNHX and ZxVP1-1 from the xerophyte Zygophyllum xanthoxylum L., were produced via Agrobacterium tumefaciens-mediated transformation. Compared with wild-type (WT) plants, transgenic alfalfa plants co-expressing ZxNHX and ZxVP1-1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water-deficit) in the greenhouse. The growth performance of transgenic alfalfa plants was associated with more Na(+), K(+) and Ca(2+) accumulation in leaves and roots, as a result of co-expression of ZxNHX and ZxVP1-1. Cation accumulation contributed to maintaining intracellular ions homoeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when subjected to NaCl or water-deficit stress. Furthermore, the transgenic alfalfa co-expressing ZxNHX and ZxVP1-1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water-use efficiency than WT plants. Our results indicate that co-expression of tonoplast NHX and H(+)-PPase genes from a xerophyte significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and restoring saline and arid marginal lands as well as improving forage yield in northern China.

The Algerian Sahara Desert which occupies more than 80% of the Algerian territory represents an ecosystem generally hostile to the spontaneous survival of living organisms. There are always geomorphologic patterns (camel pastures) relatively favourable to the proliferation of a very scattered plant species that are well adapted to the desert conditions. The dromedary is the only domestic species able to thrive under such conditions and benefit from this type of vegetation, which constitutes its main dietary source. The nutritional study of these plants shows a chemical composition reflecting the conditions of the desert. It is characterized by richness in parietal compounds and crude fibre (up to 75 and 50%) and general low content in total nitrogenous matter (4 %). However, a large variability between species related mainly to their different ecotypes and secondly to their soil conditions is observed. The in vitro digestibility is variable also depending on the species studied (22 to 37%), and its values are positively correlated with TNM and negatively with parietal compounds. Besides, the time study allows observing high contents in parietal compound in summer and relatively high contents in TNM in spring, so engendering the best digestibility in spring and lowest in summer.

Opuntia (prickly pear) is a genus of xerophyte belonging to the Cactaceae family, growing abundantly in the arid parts of the world. Owing to high nutritional value in terms of dietary fiber, polyunsaturated fatty acid, minerals, protein and an assortment of other phytochemicals, Opuntia fruits are gaining popularity. Validation of health benefits viz. antioxidant, anti-inflammatory, antidiuretic, hypocholesterolemic, antidiabetic, antiproliferation, immunostimulatory and antiulcerogenic activity have further consolidated their position in emerging nutraceutical sector. Though at infancy, the Opuntia fruit-based foods are garnering consumer approval and are expected to contribute significantly to functional food processing. This chapter explores the proven biological potentials and suggests future scopes.

Plants that use fog as an important water-source frequently have a rosette growth habit. The performance of this morphology in relation to fog interception has not been studied. Some first-principles from physics predict that narrow leaves, together with other ancillary traits (large number and high flexibility of leaves, caudices, and/or epiphytism) which constitute the "narrow-leaf syndrome" should increase fog-interception efficiency. This was tested using aluminum models of rosettes that differed in leaf length, width and number and were exposed to artificial fog. The results were validated using seven species of Tillandsia and four species of xerophytic rosettes. The total amount of fog intercepted in rosette plants increased with total leaf area, while narrow leaves maximized interception efficiency (measured as interception per unit area). The number of leaves in the rosettes is physically constrained because wide-leafed plants can only have a few blades. At the limits of this constraint, net fog interception was independent of leaf form, but interception efficiency was maximized by large numbers of narrow leaves. Atmospheric Tillandsia species show the narrow-leaf syndrome. Their fog interception efficiencies were correlated to the ones predicted from aluminum-model data. In the larger xerophytic rosette species, the interception efficiency was greatest in plants showing the narrow-leaf syndrome. The adaptation to fog-harvesting in several narrow-leaved rosettes was tested for evolutionary convergence in 30 xerophytic rosette species using a comparative method. There was a significant evolutionary tendency towards the development of the narrow-leaf syndrome the closer the species grew to areas where fog is frequently available. This study establishes convergence in a very wide group of plants encompassing genera as contrasting as Tillandsia and Agave as a result of their dependence on fog.

Nitraria retusa (Nitrariaceae) is a true xerophyte plant grows in most deserts of Egypt, especially in wadies habitat and dry salt marshes. This study aims to evaluate any possible genetic diversity among samples of Nitraria retusa grown under different habitats using Random Amplified Polymorphic DNA (RAPD) markers, protein electrophoresis and isozyme electrophoresis. For such goal, the ecological aspects of the selected habitats were investigated with the view of finding correlations among these markers and some ecological parameters. Five collected samples of Nitraria retusa were collected from Wadi Hof (sunny and shady), Oyun Musa, Kattamyia and Hammam Faraon. The obtained results showed that differences in the levels of genetic variations detected by the tested markers agree with those observed at the morphological levels. The data obtained from the tested primers resulted in PCR amplified products that differentiate the shady sample of Wadi Hof (with broad leaves) from the other investigated samples. Thus, the results obtained from the present study consider DNA and protein fingerprints for the studied populations.

This study was performed to investigate the capacity of the woody perennial Cratylia mollis, a legume endemic to the semi-arid region of the North–East of Brazil, to nodulate, and obtain N from BNF using the 15N natural abundance technique. To estimate the 15N abundance of the N-derived from soil, the leaves of several (4–6) non-legume and non-nodulating legume species growing in close proximity to the Cratylia were analysed for δ15N. The δ15N values of these reference plants were high (from +9 to +16‰) and showed relatively small differences between species at each site/sampling time. At the irrigated site at both samplings, and at the non-irrigated site sampled in the rainy season, the 15N abundance of the Cratylia mollis leaves was far lower (+1 to +5‰) strongly suggesting that the legume obtained large proportional contributions from BNF. As was to be expected, no nodules were found on the Cratylia plants at the non-irrigated site in the dry season, and the 15N abundance of the Cratylia mollis plants were very similar to that of the reference plants, consistent and nodulation and BNF being limited by water deficit at this time.

The plants in the Gurbantunggut Desert located in Xinjiang, China are drought adapted species and grow in generally nutrient-poor soils. A survey was conducted in the desert to determine the arbuscular mycorrhizal (AM) status associated with the desert plants which belong to 23 species from 11 families of annuals and perennials. Roots from all plants were examined for the presence of internal and external hyphae, vesicles and coils/arbuscules to determine the status and extent of mycorrhizal colonization. Of the plant species surveyed, 14 (61%) were found to form AM associations, 5 (22%) were possible AM colonized species, and 4 were non-mycorrhizal plants. The proportions of annuals and shrubs forming AM were significantly lower than those of perennials and herbs, respectively. Spore density varied from 5 to 21 per 20 g in soil of root zone. 14 AM fungal taxa in 3 genera were isolated and identified, 10 of which belonged to Glomus, 3 to Acaulospora, and 1 to Archaeospora. Glomus was the dominant genus in all genera identified. G. deserticola and G. etunicatum were the most common taxa isolated, with occurrence frequencies of 77.4% and 74.8%, and relative abundances of 14.4% and 15.5%, respectively.

The effects of salinity and nitrogen (N) on growth and the role of NO3- in osmotic adjustment in the leaf-succulent euhalophyte Suaeda physophora and the stem-succulent xerophyte Haloxylon persicum were evaluated. Seedlings were exposed to 1 or 300 mm NaCl in 0.05, 1 or 10 mm NO3- -N treatments for 24 d. At 10 mm NO3-, 300 mm NaCl had no adverse effect on the concentration of NO3-, the content of organic N, and the estimated contribution of NO3- to osmotic potential in leaves of S. physophora, but markedly reduced these in stems of H. persicum. At 300 mm NaCl, more NO3- but less Cl- and Na+ were involved in osmotic adjustment in leaves of S. physophora compared with that in stems of H. persicum. The contribution of NO3- to osmotic potential was much higher in S. physophora, but lower in H. persicum, than that of amino acids at 300 mm NaCl. The nutritional and osmotic roles of NO3- -N seem to be more important in the euhalophyte S. physophora than in the xerophyte H. persicum under saline conditions. These characteristics may determine the natural distributions of the two species in saline or arid environments.

The expansion of the Prosopis genus from the Chaco region towards drier and colder areas would involve several morphological and physiological adaptations that allow these species to occupy different ecological niches. Prosopis argentina and Prosopis alpataco (Fabaceae, Mimosoideae) are good examples of shrubs adapted to highly stressed environments.Prosopis genus from the Chaco region towards drier and colder areas would involve several morphological and physiological adaptations that allow these species to occupy different ecological niches. Prosopis argentina and Prosopis alpataco (Fabaceae, Mimosoideae) are good examples of shrubs adapted to highly stressed environments.Prosopis argentina and Prosopis alpataco (Fabaceae, Mimosoideae) are good examples of shrubs adapted to highly stressed environments. P. argentina reaches its ecological optimum in sandy soils while P. alpataco attains it in clayish, saline and periodically flooded soils. We analysed the effects of water stress on the early seedling growth of P. argentina and P. alpataco; in addition we discussed the importance of these effects in the ecological success of these species. We used a completely randomized experimental design with two fixed factors: species (P. argentina and P. alpataco), and two levels of water supply (350 and 1400 mm). Water stress produced a detrimental effect in the seedling growth of both species, which was evident from the reduction in leaf area, seedling height, and above-ground and root biomass. However, plant growth in P. alpataco was more strongly affected by water stress than it was in P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.reaches its ecological optimum in sandy soils while P. alpataco attains it in clayish, saline and periodically flooded soils. We analysed the effects of water stress on the early seedling growth of P. argentina and P. alpataco; in addition we discussed the importance of these effects in the ecological success of these species. We used a completely randomized experimental design with two fixed factors: species (P. argentina and P. alpataco), and two levels of water supply (350 and 1400 mm). Water stress produced a detrimental effect in the seedling growth of both species, which was evident from the reduction in leaf area, seedling height, and above-ground and root biomass. However, plant growth in P. alpataco was more strongly affected by water stress than it was in P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.P. argentina and P. alpataco; in addition we discussed the importance of these effects in the ecological success of these species. We used a completely randomized experimental design with two fixed factors: species (P. argentina and P. alpataco), and two levels of water supply (350 and 1400 mm). Water stress produced a detrimental effect in the seedling growth of both species, which was evident from the reduction in leaf area, seedling height, and above-ground and root biomass. However, plant growth in P. alpataco was more strongly affected by water stress than it was in P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.P. argentina and P. alpataco), and two levels of water supply (350 and 1400 mm). Water stress produced a detrimental effect in the seedling growth of both species, which was evident from the reduction in leaf area, seedling height, and above-ground and root biomass. However, plant growth in P. alpataco was more strongly affected by water stress than it was in P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.P. alpataco was more strongly affected by water stress than it was in P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.P. argentina, as suggested by the significant species-irrigation interactions (Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.Po0:05) found in the height and biomass variables. The proportional growth (biomass reach in water stress in relation to control treatment) was lower in P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features.P. alpataco (0.14) than in P. argentina (0.32). These results indicate that P. argentina has a greater tolerance to water deficit during plant establishment. Our results, and the morphological feature of each species , are consisten with the previous findings that have described P. argentina as a xerophyte able to cope with harsh sand.dune conditions, and P. alpataco as a phreatophytic species with more mesomorphic features. Fil: Villagra, Pablo Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias; Argentina Fil: Cavagnaro, Juan Bruno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias; Argentina

Velvet mesquite [Prosopis velutina Woot., Syn.: P. juliflora (Swartz) DC. var. velutina (Woot.) Sarg.] has become more popular in arid landscapes of the southwestern U.S., but little information on N requirements during the seedling stage is available. In addition to optimize growth of seedlings, minimizing N in runoff during production is an important consideration. Experiments were conducted to determine how biomass production and N leaching were affected first by different ratios of ammonium and nitrate N in sand culture and second by different N concentrations when seedlings were grown in two substrates. Mesquite seedlings produced the greatest biomass after 120 days when fertigated with a solution of 33 NO3–: 67 NH4+. Loss of N through leachate was 40% greater when NH + 4 comprised two thirds or more compared to one third or none in the fertigation solution. Nitrogen in leachate was highest after 16 weeks of treatment, coinciding with the reduced growth rate of seedlings. The second experiment utilized either sand or commercial growing media and a fertigation solution of 33 NO3–: 67 NH4+. Fertigation with 200 mg·L–1 N after 60 days in either substrate produced greatest biomass, while rates of 25, 50, or 100 mg·L–1 N produced about half of that biomass. With few exceptions, less N in either form was found in leachate when seedlings were grown in media and were fertigated with the two higher N rates compared to seedlings grown in sand at the two higher N rates. Plant morphology, biomass accumulation, photosynthate allocation, and the fate of N in the growing substrate and in leachate were strongly affected by the choice of growing substrate.

The osmotic adjustment traits of Suaeda physophora (euhalophyte), Haloxylon ammodendron (xero-halophyte) and Haloxylon persicum (xerophyte) were investigated both in field and under controlled conditions. The results showed that percentage of inorganic solutes in total solutes was over 90%, while the estimated contribution of Na+ to Ψs was over 50% for the two halophytic species, in field condition. The percentages of inorganic solutes and organic solutes were 66% and 34%, respectively, and the estimated contribution of Na+ to Ψs was less than 18%, while the estimated contribution of soluble sugars to Ψs was over 20% in H. persicum, in field condition. The estimated contribution of proline to Ψs was less than 0.2% for all species both in field and under salt stress in a greenhouse experiment. The estimated contribution of NO3− to Ψs was less than 4% for all species in field condition. In greenhouse experiment, the concentration of NO3− was higher under various NaCl treatments than that in control condition for S. physophora; the estimated contribution of NO3− to Ψs was over 7% in S. physophora, and it was higher than that in other species at various treatments. In conclusion, inorganic ions especially Na+ were more important in osmoregulation for S. physophora and H. ammodendron to adapt to saline and arid environment, while organic solutes, especially soluble sugars played more important role in drought adaptation in the xerophyte, H. persicum. Proline did not play an important role in osmoregulation for all species both in field and controlled conditions. NO3− played more important role in osmoregulation in S. physophora and H. ammodendron cultured in full-strength Hoagland's nutrient solution under NaCl treatments compared with that growing in saline soils in field condition.

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.

Sclerophylly is a common feature of vegetation on infertile soils, and its adaptive significance has been linked to nutrient-use efficiency by protection of leaves to maximise carbon gain. However, there has been little investigation of how the leaf mechanical properties that contribute to the phenomenon of sclerophylly vary along nutrient gradients. In this paper, we investigate how leaf mechanical properties vary among plants on three contrasting soil types (grey sand, laterite soil, and soil overlying dolerite) in a Mediterranean climate in southwestern Australia. Most species were sclerophyllous, but there was 5-fold variation in leaf mass per unit area (LMA) and 17- to 473-fold variation in mechanical properties among species. Species growing on laterite and/or sand (low-nutrient soils) had higher punch strength, work (a measure of toughness) to punch, specific (per unit leaf thickness) work to punch, work to shear, specific work to shear, and flexural stiffness (EI W) than those on dolerite soils (higher in nutrients). There were few differences in mean values of leaf mechanical properties between the two low-nutrient soils, possibly because the lower concentration of nutrients in the sand is balanced by the greater soil volume than the laterite soil (higher concentration of nutrients, but shallower). There were also few differences in leaf properties between plants of the same species growing on contrasting soil types. There was some variation among sclerophyllous species in their mechanical characteristics, but overall, EI W provided the strongest contribution to sclerophylly, explaining up to 81% of the variation in LMA. There was no evidence of differences among soil types in the relationships of mechanical properties with LMA, and therefore, no evidence of variation in the mechanical constitution of sclerophylly among soil types.

The effects of available soil N and P and the effect of simulated browsing (leave removal) on foliar condensed tannin (CT) concentration were tested on young Colophospermum mopane (J. Kirk ex Benth) J. Leonard (Mopane) plants. Although clear differences in growth occurred between different levels of soil N, no differences in foliar CT concentration were found. Changes in available soil P and physical damage did not affect the plant growth or chemical composition. The complete absence of response of CT concentration to physical damage and soil nutrients may be related to the age of the trees in this study. It is proposed that existing theories on the interaction between soil properties and carbon based defences in trees are expanded, to include the potential responses of young trees to different soil nutrient levels.

The Dune System of Donana National Park (SW Spain) exhibit a mosaic of environmental characteristics, with different plant communities, all under the same Mediterranean climate, creating an interesting field laboratory for the study of plant responses to stressing conditions. Fourteen woody plant populations were selected, belonging to either xerophytic or hygrophytic plant communities on stabilised dunes, where topography causes differences in soil water availability. Plants were tagged and morphological and ecophysiological measurements were recorded in winter and summer of 1999. Seasonal differences in ecophysiological measurements together with morphological variables were used as plant traits to identify the main adaptive responses of the species. Cluster analysis of traits separated three groups of plant strategies: spiny legume species; sclerophyll, and semideciduous species. In addition, another two kind of strategies have been found in the semideciduous group of species, those withstanding water shortages, attaining very negative water potentials, low photochemical efficiency, and leaf proline accumulation in summer, as opposed to those tolerating water deficit, with moderate seasonal differences in water potential, proline content and photochemical efficiency. The results of this study indicate that legume species behave as a different functional group and drought-semideciduous species present different adaptive responses under the same environmental stress. Ecophysiological measurements must be used as plant traits to detect functional groups under Mediterranean climate.

The present communication is a first-time report on the analyses of n-alkane profile of epicuticular wax extracted from the mature leaves of Nyctanthes arbor-tristis L. during a calender year. The composition of n-alkanes revealed hentriacontane (n-C31), tritriacontane (n-C33), tetratriacontane (n-C35) and nonacosane (n-C29) as the major constituents with tritriacontane (n-C33) being the dominant constituent. The cumulative percentage of these four odd-numbered alkanes also showed phenological variation being highest during the fruit ripening stage (average value 63.29%) followed by the flowering stage (mean value 60.74%). The values remained moderate on an average of 54.31% for the rest of the year. This study also confirms the xerophytic feature of the plant having higher proportion of longer carbon chain n-alkanes greater than C31 (dominant peaks are of C33 and C35).

Many terrestrial ecosystems are nutrient limited. Koerselman and Meuleman (1996) proposed critical foliar N:P values that could predict wetland nutrient deficiencies (N:P 16, P limitation). Although critical N:P values have potential as ecological and diagnostic tools, species differences in N and P requirements must be tested. The objectives of our experiments were 1) to determine if two desert species share critical N:P values, and 2) to assess the N:P tool's applicability in a non-wetland system. We studied two common, co-occurring North American desert shrubs, Chrysothamnus nauseosus spp. consimilis and Sarcobatus vermiculatus. Based on leaf N and P concentrations, effective mycorrhizal status, and leaf N:P, we predicted Chrysothamnus would be N limited and Sarcobatus would be P limited. During the 2000 and 2001 growing seasons, juvenile shrubs received N, P, N+P, or control treatments. To assess interaction with water limitation, other shrubs were irrigated and fertilized in 2001 (N+IR, P+IR, N+P+IR, control IR). Contrary to the predicted N limitation in Chrysothamnus, stem growth was 1.7-fold greater in P+IR plants relative to IR controls, although without irrigation Chrysothamnus did not respond to P addition. Also, contrary to the predicted P limitation in Sarcobatus, stem growth was 2.7-fold and 1.5-fold greater in N and N+IR plants, respectively, relative to their controls. Leaf N was significantly higher in N-treated Sarcobatus, both with and without irrigation. Our study suggests species-specific critical N:P values and that the N:P tool does not effectively predict desert shrub nutrient limitations. Species adapted to low nutrient conditions may not respond to increased nutrient availability due to water and nutrient co-limitation, lack of plasticity, or lower tissue nutrient requirements.

In an investigation of succulence as an adaptation to water‐stressed desert environments, we studied the anatomy of photosynthetic succulent stems in 28 species from Apocynaceae, Asclepiadaceae, Asteraceae, Crassulaceae, Didieriaceae, Euphorbiaceae, Geraniaceae, and Vitaceae. Only species with enlarged pith or cortex were examined, not species with enlarged parenchymatous wood. The numbers of species with particular characters are as follows: pith is the most voluminous tissue—5 species; cortex is the most voluminous tissue—22; cortical bundles present—0; medullary bundles present—4; palisade cortex present—16; epidermis with thick or lignified walls—0; epidermis outer wall somewhat thickened—6; multiple epidermis present—0; cuticle >2 μm thick—4; cuticle

More than 40 years of revegetation using mainly Artemisia ordosica, Hedysarum scoparium, and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou has established a dwarf-shrub and herbaceous cover on the stabilized sand dunes. The evapotranspiration (ET) of the xerophyte dwarf-shrub A. ordosica plant vegetation was measured by the autoweighing lysimeter method during the growing seasons from 1990 to 1995, and 2002 on the southeast edge of the Tengger Desert at Shapotou, China. The study showed that the average ET rates were 0.88 mm d(-1), and they varied from 0.6 mm d(-1) to 1.31 mm d(-1) during the 7-year experimental period from 1990 to 1995, and 2002. The ratios of ET/Precipitation (P) varied from 69.8% to 120.9% with an average of 90.9%. The higher ET/P value in 1991 was associated with the properties of intra year distribution of rainfall events, and resulted in soil moisture depletion. The correlation between the accumulative P and the accumulative ET was quite high. For the years 1990, 1993, and 1995, the relationship between the accumulative ET and the accumulative P had a closed linear relationship, resulting from the higher intensity of monthly P exceeding 40% of the overall P during the growing season. Whatever the variation in the monthly P, statistics showed that the relationship between the accumulative P and ET could be expressed as an equation, ET=0.8003 P+5.8914, with a correlation coefficient of R-2=0.9035. Results suggest that in areas similar to Shapotou it is practical to establish an artificial protection belt using xerophytic shrubs.

The success of the desert shrub Larrea tridentata (creosotebush) has been largely attributed to temperature acclimation and stomatal control of photosynthesis (A) under drought stress. However, there is a paucity of field data on these relationships. To address this void, we conducted a joint field and modelling study that encompassed a diverse set of environmental conditions. At a Larrea-dominated site in southern New Mexico we manipulated soil moisture during the growing season over a 2-year period and measured plant pre-dawn water potential (Ψ pd ), stomatal conductance (g) and A of individual shrubs. We used these data to develop a semi-mechanistic photosynthesis model (A-Season) that explicitly couples internal CO 2 (C;) and g. Vapour pressure deficit (VPD) and Ψ pd affect instantaneous in a manner that is consistent with a biophysical model of stomatal regulation of leaf water potential. C i is modelled as a function of g, derived from a simplification of a typical A-C i curve. After incorporating the effects of growing temperature on stomatal behaviour, the model was able to capture the large diurnal fluctuations in A, g and C i and the observed hysteresis in g versus C i dynamics. Our field data and application of the A-Season model suggest that dogma attributed to Larrea's success is supported with regard to stomatal responses to VPD and Ψ pd , but not for mechanisms of temperature acclimation and CO 2 demand.

Structural characteristics of the mesophyll were studied in five boreal grass species experiencing a wide range of light and water supply conditions. Quantitative indices of the palisade and spongy mesophyll tissues (cell and chloroplast sizes, the number of chloroplasts per cell, the total cell and chloroplast surface area per unit leaf surface area) were determined in leaves of each of the species. The cell surface area and the cell volume in spongy mesophyll were determined with a novel method based on stereological analysis of cell projections. An important role of spongy parenchyma in the photosynthetic apparatus was demonstrated. In leaves of the species studied, the spongy parenchyma constituted about 50% of the total volume and 40% of the total surface area of mesophyll cells. The proportion of the palisade to spongy mesophyll tissues varied with plant species and growth conditions. In a xerophyte Genista tinctoria, the total cell volume, cell abundance, and the total surface area of cells and chloroplasts were 30–40% larger in the palisade than in the spongy mesophyll. In contrast, in a shade-loving species Veronica chamaedris, the spongy mesophyll was 1.5–2 times more developed than the palisade mesophyll. In mesophyte species grown under high light conditions, the cell abundance and the total cell surface area were 10–20% greater in the palisade mesophyll than in the spongy parenchyma. In shaded habitats, these indices were similar in the palisade and spongy mesophyll or were 10–20% lower in the palisade mesophyll. In mesophytes, CO2 conductance of the spongy mesophyll accounted for about 50% of the total mesophyll conductance, as calculated from the structural characteristics, with the mesophyll CO2 conductance increasing with leaf shading.

Diaspore characteristics of 22 families, including 102 genera and 150 species (55 represented by seeds and 95 by fruits) from the Gurbantunggut Desert were analyzed for diaspore biological characteristics (mass, shape, color, and appendage type). The diaspore mass and shape were significantly different in phylogeny group (APG) and dispersal syndromes; vegetative periods significantly affected diaspore mass, but not diaspore shape; and ecotypes did not significantly affect diaspore mass and shape, but xerophyte species had larger diaspore mass than mesophyte species. Unique stepwise ANOVA results showed that variance in diaspore mass and shape among these 150 species was largely dependent upon phylogeny and dispersal syndromes. Therefore, it was suggested that phylogeny may constrain diaspore mass, and as dispersal syndromes may be related to phylogeny, they also constrained diaspore mass and shape. Diaspores of 85 species (56.67%) had appendages, including 26 with wings/bracts, 18 with pappus/hair, 14 with hooks/spines, 10 with awns, and 17 with other types of appendages. Different traits (mass, shape, color, appendage, and dispersal syndromes) of diaspore decided plants forming different adapted strategies in the desert. In summary, the diaspore characteristics were closely related with phylogeny, vegetative periods, dispersal syndromes, and ecotype, and these characteristics allowed the plants to adapt to extreme desert environments.

Although Artemisia ordosica Krasch. and Sabina vulgaris Ant. are the dominant shrub species in the Mu-us desert ecosystem, they differ in their botanical traits. We investigated the spatial patterns of soil properties using geostatistical analysis to examine the effect of plant species on these spatial patterns. Comparison among three microsite types (under A. ordosica, under S. vulgaris, and the opening between vegetation) showed that A. ordosica generally had less effect than S. vulgaris on local soil properties. The long life-span, prostrate life-form, and evergreen leaf-habit of S. vulgaris may lead to a higher accumulation of organic and fine materials under S. vulgaris. The range of spatial autocorrelation found in the mass of organic matter on the soil surface was smaller than that of the coverage of S. vulgaris (11.5 m) which corresponded to the canopy patch size of this species, and was longer than the canopy patch size of A. ordosica. The ranges of total C and N, and pH (11.7–15.6 m) were similar to that of S. vulgaris. The range of available P (106.3 m) was comparable to that of the coverage of A. ordosica (86.2 m) considered to be the scale of the distribution of this species. The ranges of silt+clay and exchangeable K, Ca, and Mg (31.0–46.7 m) were not related to plant presence, and were similar to that of topography (43.1 m).

Soil and vegetation dynamics were examined along roads abandoned for 5, 10, 21, 31, 55 and 88 years in southern Nevada in an attempt to elucidate factors controlling desert succession. None of the measured soil or vegetation parameters varied significantly with road age. Differences were found, however, between soils and vegetation on roads vs. nearby controls, and soils differed between roads created by surface vehicular traffic and bulldozing. Studies of recovery following disturbance in deserts must take into account natural patterns of plant and soil heterogeneity and initial disturbance type.

Summary The pattern of protein ubiquitination during the course of an imposed water deficit in the xerophytic species Festuca novae-zelandiae was determined in leaf tissues at three developmental stages (the leaf base (LB) comprising the meristematic and elongating tissues, the immature lamina (IL) and the mature lamina ML)). Using SDS-PAGE and anti-ubiquitin monoclonal antibody recognition, changes in the pattern of protein ubiquitination were observed in the IL and ML, specifically in the later stages of the water deprivation time-course with evidence for enhanced conjugation of three polypeptides of 18 Ku, 26 Ku and 29 Ku. These differences were not observed in the LB tissue, or in leaf extracts from water-sufficient plants. These observations support the concept of preferential protection for the leaf meristematic and elongating regions in xerophytic species during a water deficit.

Soil microarthropods were sampled in plots centered on creosotebushes (Larrea tridentata) and in plots centered on mesquite (Prosopis glandulosa) coppice dunes. Nine plots in each area were covered by rain-out shelters with greenhouse plastic roofs which excluded natural rainfall and nine plots received natural rainfall. There were differences in the abundance of several mite taxa in soils from the mesquite coppice dune plots. Some taxa (Stigmaeidae, Nanorchestidae, and Entomobryidae) occurred in significantly lower numbers in the soils of the drought plots. Other taxa (Tarsonemidae and Cunaxidae) were more abundant in the drought plots in the mesquite coppice dunes. There were no significant differences in the abundance of any of the dominant taxa of soil microarthropods in the drought and control plots centered on creosotebush. In the creosotebush habitat, there were significantly fewer Prostigmata in the plots exposed to drought. In an area with both creosotebush and mesquite, there were no significant differences in microarthropod population responses to drought and in recovery from drought. The differences in responses of soil microarthropods to drought in creosotebush and mesquite habitats are attributed to the differences in soil stability, litter accumulations, and microclimate associated with the shrubs.

The content of the secondary metabolites anthrone C-glycosides (barbaloin, homonataloin and nataloin) in Aloe mutabilis leaves are the highest in the upper third of each leaf. The content of these phenolic metabolites is also higher in young leaves than in older leaves, and higher in plants grown in shade than in direct sunlight. There are also significant monthly differences in the content of these metabolites, which are more pronounced in young leaves than in old leaves. We hypothesize that the higher content of these compounds in the periphery of the leaves and plants is a defense strategy against leaf-eaters.

Characteristics of chlorophyll (Chl) among species growing in desert areas receiving high intensities of insolation were investigated. Generally, chlorophyll content in xerophytes is low; perennials, except succulents and halophytes, have higher contents than annuals. This decreased Chl content is compensated for by an increased Chl stability index (CSI). Moreover, the difference between the Chl a / b ratio in fresh and heated leaves is decreased in plants with a high CSI, where a positive difference refers to destruction of Chl a and a negative difference to destruction of Chl b .A significant correlation between both Chl content and CSI with water content, soluble proteins, Mg 2+ , K + and iron was found, with the sign of the correlation dependent on the importance of the constituents to Chl content and CSI in the studied species.

Seed germination behaviour of the chenopodAgriophyllum squarrosumin the moving dunes of the Tenggeli Desert was studied. The response of seed germination with time, expressed as the proportion of seed germinated per day, presented a unimodal continuous process. Seeds began to germinate in less than 3 h and the germination rate peak was reached 7 days after watering. All seeds eventually germinated. Seeds were collected in 1993 and 1994, so the maternal plants had different growing periods, with different plant sizes and germination times. Germination in sand was tested in the second year and showed that there is no innate dormancy ofA. squarrosumduring the growing season. The mechanism for long-term survival ofA. squarrosumin temperate sand dunes is discussed.

Desert succulents resume substantial water uptake within 1‐2 d of the cessation of drought, but the changes in root structure and hydraulic conductivity underlying such recovery are largely unknown. In the monocotyledonous leaf succulent Agave deserti Engelm. substantial root mortality occurred only for lateral roots near the soil surface; nearly all main roots were alive at 180 d of drought. New main roots were initiated and grew up to 320 mm at soil water potentials lower than ‐ 5·0 MPa, utilizing water from the shoot. The hydraulic conductivity of distal root regions decreased 62% by 45 d of drought and 70% thereafter. After 7 d of rewetting, root hydraulic conductivity was restored following 45 d of drought but not after 90 and 180 d. The production of new lateral roots and the renewed apical elongation of main roots occurred 7‐11 d after rewetting following 180 d of drought. Hydraulic conductivity was higher in the distal region than at midroot and often increased again near the root base, where many endodermal cells lacked suberin lamellae. Suberization and xylem maturation were influenced by the availability of moisture, suggesting that developmental plasticity along a root allows A. deserti to capitalize on intermittent or heterogeneous supplies of water.

In the arid sand dune ecosystem of Nizzana, northwestern Negev, Israel, three perennial species were investigated for concentrations of the elements C, N, S, P, Ca, Mg, K, Na and Cl. From the dune tops (crests) to the dune valleys six different ecotopes (habitats) were discerned where the sampling took place. The soil conditions are known due to previous investigations of H.-P. Blume and his coworkers. The species Anabasis articulata and Cornulaca monacantha (both Chenopodiaceae) showed considerable variation of element contents according to the ecotopes. In some ecotopes of the dune valleys they showed higher contents of sodium and chloride than in the ecotopes of the proper dune, and by Na/K ratios of > 1 they indicated slightly halophytic character. The glycophyte Thymelaea hirsuta (Thymelaeaceae) exhibited very low element concentrations which practically did not change between the ecotopes. The conclusion was drawn that Thymelaea is characterized by a higher selectivity of ion uptake than the two other species. Elementgehalte von mehrjahrigen Pflanzenarten in der Sandwuste bei Nizzana (Israel) In den ariden Sanddunen-Okosystemen bei Nizzana, nordwestlicher Negev, Israel, wurden drei mehrjahrige Arten auf die Konzentrationen der Elemente C, N, S, P, Ca, Mg, K, Na und Cl untersucht. Von den Dunenrippen (-kammen) bis in die Dunentaler wurden 6 Okotope (Habitate) unterschieden, in denen die Proben genommen wurden. Die Bodenverhaltnisse dieser Okotope waren durch die vorhergegangenen Untersuchungen von H.-P. Blume und seiner Mitarbeiter bekannt. Die Arten Anabasis articulata und Cornulaca monacantha, beide Fam. Chenopodiaceae, wiesen eine erhebliche Variabilitat der Elementkonzentrationen je nach den Okotupen auf. In einigen Okotopen der Dunentaler nahm ihr Na- und Chloridgehalt zu, und mit Na/K-Verhaltnissen > 1 zeigten sie einen leicht halophytischen Charakter. Der Glykophyt Thymelaea hirsuta (Fam Thymelaeaecue) besas sehr geringe Elemenlgehalte, die sich auch in den verschiedenen Okotopen kaum unterschieden. Es wurde die Schlusfolgerung gezogen, das sich Thymelaea durch eine starker selektive Ionenaufnahme auszeichnet als die beiden anderen Arten.

It is essential to study the relationships of soil water and plants in desert areas for determining available soil water for plants, scheduling best irrigation management practices, deciding the suitable artificial vegetation density, and for selecting drought‐tolerating and water‐saving plants. In this study more than 100 lysimeters were installed to measure evapotranspiration and water‐use efficiency of five desert xerophyte species: Elaeagnus angustifolia, Hedysarum scoparium, Tamarix ramosissima, Caragana korshinskii, and Haloxylon ammodendron. The lysimeters were used to simulate evaporation of desert soils and transpiration of desert plant species with various groundwater depths and surface water supply conditions. The experimental data showed that the amount of transpiration, indexes of transpiration and evapotranspiration, and water‐use efficiency were different with different groundwater depths, plant species and plant ages. More than 80% of the total annual transpiration of the plants a...

Herbaceous mimosa (Mimosa strigillosa Torr and Gray) is a new reclamation species currently under a series of assembly and evaluation programs by the Natural Resources Conservation Service's Plant Materials Center and Stephen F. Austin State University at Nacogdoches, Texas. Two floating lysimeters were designed and installed at the Stephen F. Austin Experimental Forest, about 20 km south of Nacogdoches, Texas to study differences in evapotranspiration (ET) between the mimosa and bare ground in July–October 1993. Pan coefficients during the study period ranged from 0.40 to 0.58, and no irrigation was applied to the lysimeters in the study. Water losses to the air in area covered by herbaceous mimosa were compatible with other turfgrasses under optimum soil moisture conditions. However, under environmental stress, average daily ET for the mimosa in four summer months was 1.6 mm/day, a value only 0.4 mm/day greater than bare ground. These results agree with a previous study that the plant is a water conservation species capable of tolerating severe drought conditions.

A quantitative study of leaf anatomy of 20 species of some non-succulent perennial desert plants belonging to 12 families of the Dicotyledoneae is provided. The species were collected from natural desert habitats belonging to three phytogeographical regions of Egypt. Features representing xeromorphy include small leaf or leaflet area (18 species), pubescent surfaces (16 species), amphistomaticy, iso-bilateral leaf construction and multilayered palisade of two to four layers (18 species). Particular attention is given to quantify the palisade properties as well as the hydraulic conductance ( Kh ) of the xylem tissue supplying the transpiring areas. The ratio of the palisade cell surface area/the leaf or leaflet area ( Apal/A ) ranges from 22·6 in Astragalus spinosus to 49·6 in Zilla spinosa . Moreover, Apal/A is highly correlated with the palisade thickness ( r = 0·541, N = 100, p = 0·0001) and with the thickness of lamina. The predicted Kh of the xylem is calculated from the conduit lumen diameters using the Hagen-Poiseuille relation. Eighteen species show low predicted Kh values ranging from 0·6 to 300·5 × 10 −13 m 4 MPa −1 s −1 . The highest values of predicted Kh occur in Gomphocarpus sinaicus and Chrozophora obliqua , which have the highest leaf areas. Predicted Kh correlates very well with leaf or leaflet area supplied by the petiole or petiolule ( r = 0·685, N = 100, p = 0·0001). The efficiency of xylem conductance is further identified by calculations of the leaf specific conductance ( LSC = Kh /distal leaf or leaflet area) and the predicted maximum pressure gradients (MPa m −1 ). The measured anatomical parameters and their correlations are discussed in terms of the ecophysiological adjustments of the desert plants to their habitat.

SUMMARY Hakea psilorrhyncha R. M. Barker seedlings were subjected to a two-way interaction experiment with two levels of water availability and two levels of light. Physiological drought was imposed by adding 6000 MW polyethylene glycol (PEG), at an osmotic potential of − 0.56 MPa, in a continuous-flow drip irrigation system. Unstressed plants (-PEG) were watered with distilled water (osmotic potential of −0.01 MPa). Seedlings were grown under natural light (120–500 μmol m−2 s−1 sunlight at midday + L) or shaded (< 150 μMmol m−2 s−1 sunlight at midday; – L. Plant morphology tissue water relations and carbon isotope composition ($13C) were measured after 12 wk growth. The smallest leaves had the highest mass per unit area (LMA, an index of sclerophylly) and were present in the + PEG+ L treatment, whereas the largest, thickest leaves had the lowest density and were produced in the – PEG + L treatment. Plants in shade were smaller and less sclerophyllous. There was a linear decrease in osmotic potential at full turgor and turgor loss point, and an increase in elastic modulus and $13PC, as level of sclerophylly increased, with -PEG-L leaves at one extreme and +PEG + L at the other. We conclude that high levels of sclerophylly induced by low water availability and high light intensity are associated with substantial drought tolerance in H. psilorrhyncha.

Two shrub species, Atriplex halimus L. and Salsola vermiculata L., are considered useful for rehabilitation of degraded rangelands in west Asia and north Africa. They can be established from direct seeding and are capable of self-sowing. In this study, seed storage at different temperatures and the influence of fruiting bracts on seed germination were examined for the two species during two seasons. Fruits (utricles) were stored at 20–22°C (room temperature), 0°C or −22°C. Germination tests were carried out after 33, 56, 90, 152, 272 and 397 d in storage in the first season and after 44, 76, 104, 170, 288 and 412 d in the second season. Seeds were germinated in their fruiting bracts or after bract removal. Bract removal significantly improved seed germination of both shrubs regardless of storage temperature. For S. vermiculata the increase in germination was in the range of 1.3- to 14.7-fold compared with values for the intact fruit in Season 1 and 0.5 to 3.8 in Season 2. Similarly the ranges for A. halimus were 0.5- to 4.2-fold and 0.7- to 5.3-fold in the two seasons respectively. The effect of cold storage was greater on Salsola than on Atriplex. The reduction of the storage temperature from 21°C to 0°C and −22°C increased the longevity of S. vermiculata seeds by 2.8–46.6 times in Season 1 and by 2.9–2.6 times in Season 2. There was little or no effect on the longevity of A. halimus. A leachate prepared by soaking fruiting bracts from S. vermiculata significantly depressed germination (p < 0.01), the effect being greater on Salsola seeds (20% reduction) than on Atriplex seeds (8% reduction). A leachate from A. halimus produced a slight but non-significant reduction in germination.

Nutritional quality of cactus and other desert plants, commonly used as feed for livestock in Baja California peninsula during dry seasons, was evaluated considering their general analysis, associated digestive enzymatic activity, presence of digestive enzymatic inhibitors and lectins. Even if nutritional quality of cacti as a protein source is low with respect to other plants, their water content and nutritional quality may be important as an emergency feed for cattle. The use of Opuntia cholla instead of Ferocactus species is proposed in order to protect endangered species.