Spatial patterns in a two-tiered semi-arid shrubland in southeastern Spain

Abstract. Single species and bivariate distribution patterns in a semi-arid shrubland in southeastern Spain, dominated by the tall leguminous shrub Retama sphaerocarpa, were investigated by second-order spatial analysis based on Ripley's K-function. Shrubs were significantly clumped because of a strong association of dwarf shrubs, mostly Artemisia barrelieri, under the canopy of Retama. Retama shrubs were randomly distributed, but when different size-classes were analysed separately, the pattern changed from significantly clumped to random and then to regular with increasing canopy diameter, suggesting increasing intraspecific competition with shrub size. Artemisia was significantly clumped at all scales because of aggregation under the canopy of large Retama shrubs. The association between the species became stronger with increasing canopy diameter of Retama shrubs, suggesting that facilitation prevailed over interspecific competition because of niche separation in different tiers, both above and below ground. Retama shrub size thus determined both the type of pattern for its own size class and tier, and the scale and intensity of the association with its understorey shrubs.     

能化态线粒体内膜脂流动性与能量偶联活性

本文从观察温度的影响出发,探讨了鼠肝线粒体内膜体,在琥珀酸氧化建立跨膜质子电化学梯度（ΔμＨ＾＋）时,膜脂双分子层中ＤＰＨ荧光偏振值（ｒ）的变化与膜能量偶联活性之间的相互关系。结果表明,１５￣３５℃温度内,能化引起ｒ值变化趋势相似,ｒ值变化速率随温度升高而增加,但与温度对ｒ值影响相比只是在较小的范围内变动。另一方面,１５￣３０℃温度内,随温度升高质子回漏速率加快,ＲＣＲ值和ＡＤＰ／Ｏ比值下降,但跨     

Early root growth plasticity in seedlings of three Mediterranean woody species

Using a 141 F₂ population generated from maize inbred B64 × teosinte Zea nicaraguensis cross, quantitative trait loci (QTLs) controlling aerenchyma formation in roots under non-flooding drained soil conditions were identified. Seedlings of Z. nicaraguensis formed clear aerenchyma in the cortex of adventitious roots in non-flooding conditions, whereas the maize inbred line B64 did not. In the F₂ population, the capacity to develop aerenchyma exhibited wide and continuous variation, suggesting the trait was controlled by multiple genes. A linkage map was developed using 85 SSR markers, covering 1,224 cM across all ten chromosomes. Composite interval mapping analysis revealed that four QTLs for aerenchyma formation under non-flooding conditions were located to two regions of chromosome 1 (identified as Qaer1.02-3 and Qaer1.07), chromosome 5 (Qaer5.09) and chromosome 8 (Qaer8.06-7), and these explained 46.5% of the total phenotypic variance. The multiple interval mapping approach identified additional QTLs on chromosomes 1 (Qaer1.01) and 5 (Qaer5.01). Using these results, it may be possible to use SSR markers linked to aerenchyma formation in a marker assisted selection approach to introduce aerenchyma formation in drained soil conditions into maize for the eventual development of flooding tolerant maize hybrids.     

Plasmid-based genetic modification of human bone marrow-derived stromal cells: analysis of cell survival and transgene expression after transplantation in rat spinal cord

Background

Swine is an important agricultural commodity and biomedical model. Manipulation of the pig genome provides opportunity to improve production efficiency, enhance disease resistance, and add value to swine products. Genetic engineering can also expand the utility of pigs for modeling human disease, developing clinical treatment methodologies, or donating tissues for xenotransplantation. Realizing the full potential of pig genetic engineering requires translation of the complete repertoire of genetic tools currently employed in smaller model organisms to practical use in pigs.

Results

Application of transposon and recombinase technologies for manipulation of the swine genome requires characterization of their activity in pig cells. We tested four transposon systems- Sleeping Beauty, Tol2, piggyBac, and Passport in cultured porcine cells. Transposons increased the efficiency of DNA integration up to 28-fold above background and provided for precise delivery of 1 to 15 transgenes per cell. Both Cre and Flp recombinase were functional in pig cells as measured by their ability to remove a positive-negative selection cassette from 16 independent clones and over 20 independent genomic locations. We also demonstrated a Cre-dependent genetic switch capable of eliminating an intervening positive-negative selection cassette and activating GFP expression from episomal and genome-resident transposons.

Conclusion

We have demonstrated for the first time that transposons and recombinases are capable of mobilizing DNA into and out of the porcine genome in a precise and efficient manner. This study provides the basis for developing transposon and recombinase based tools for genetic engineering of the swine genome.     

Water release through plant roots: new insights into its consequences at the plant and ecosystem level

Hydraulic redistribution (HR) is the passive movement of water between different soil parts via plant root systems, driven by water potential gradients in the soil-plant interface. New data suggest that HR is a heterogeneous and patchy process. In this review we examine the main biophysical and environmental factors controlling HR and its main implications at the plant, community and ecosystem levels. Experimental evidence and the use of novel modelling approaches suggest that HR may have important implications at the community scale, affecting net primary productivity as well as water and vegetation dynamics. Globally, HR may influence hydrological and biogeochemical cycles and, ultimately, climate.     

Mechanisms of interaction between a leguminous shrub and its understorey in a semi-arid environment

Retama sphaerocarpa shrubs in semi-and environments often have a dense understorey of annual and perennial herbs forming so-called "islands of fertility" The effect of the canopy on soil fertility and microclimate and the combined effect of canopy and litter on species diversity and productivity were assessed under Retama spliaerocarpa shrubs in a semi-and environment in southeast Spain Soil chemical properties differed significantly among three positions under the canopy, particularly between inner and outer positions The potential mineralization rate of organic matter was significantly higher in soils from an intermediate position under the canopy than in soils from either the centre and the edge Soil chemical fertility and estimated soil seed bank were highest also in soil at an intermediate position and lowest in soil from the edge The understorey flora was favoured by the lower temperature and irradiation and increased soil fertility under the shrubs canopies Species emerging from the soil seed bank separated clearly into two groups which occupied inner and outer positions under the canopy Different levels of addition of Retama litter significantly decreased species richness and the number of emerged seedlings In the field, pots placed near the centre, at an intermediate position and at the edge of the canopy of Retama shrubs differed significantly in species richness and biomass production Overall, micro-climatic conditions combined with increased chemical fertility of the soil and inhibitory effects of litter to produce a large biomass of herbs at intermediate positions between the centre and the edge of the canopy. The high proportion of litter from annual species in that position increases the mineralization rate and hence nutrient dynamics in a process which also could benefit the shrub     

Spatial pattern in Anthyllis cytisoides shrubland on abandoned land in southeastern Spain

Abstract. Univariate and bivariate distribution patterns of small shrubs on abandoned land in semi-arid southeastern Spain were investigated by second-order spatial analysis (Ripley's K-function). All shrubs (Anthyllis cytisoides and subdominant Artemisia barrelieri) were either randomly distributed or clumped at scales of 0.25 - 1.0 m. The pattern shown by A. cytisoides shrubs alone changed from clumped to random with decreasing density. Pattern analysis and demographic data suggest a successive replacement of A. barrelieri, which had high proportions (44 - 86 %) of dead shrubs, by the dominant A. cytisoides. In two of three plots there was a positive association between A. cytisoides and A. barrelieri at a scale of 0.25 - 0.5 m. In the third plot, believed to represent a more advanced stage of colonization, there was a negative association (repulsion) between the two species, presumably as a result of interspecific competition from A. cytisoides. Dead shrubs present in spring 1994 were randomly distributed in all plots. Living and dead A. cytisoides shrubs were positively associated at a scale of 0.5 m, suggesting that the shrubs died as a result of intraspecific competition in small clumps. The shrubland previously dominated by A. barrelieri is changing to A. cytisoides shrubland with increasing biomass and ground cover.     

Species Identity and Water Availability Determine Establishment Success Under the Canopy of Retama sphaerocarpa Shrubs in a Dry Environment

Seedling establishment in harsh environments is often enhanced by the proximity of adult shrubs. This information has been used in restoration work by placing seedlings of species being restored under the canopy of some shrubs. However, monitoring this process is often restricted to a single species, and comparisons with practices that protect planted seedlings against harsh conditions are scant. Similarly, few studies have supplied seedlings with water in the summer to observe the effects of water availability on the interaction. We compared sapling survival of three woody species (Olea europaea, Pistacia lentiscus, and Ziziphus lotus) under the leguminous shrub Retama sphaerocarpa and in gaps covered with piled branches that mimicked a shrub canopy. After 3 years, survival of saplings planted under Retama differed depending on species identity and water supply. Survival of Olea saplings placed under Retama shrubs was twice that under piled branches if not watered (35 ± 8 vs. 17 ± 2 %, respectively), whereas survival of saplings under Retama, if watered, was less (48 ± 11 vs. 68 ± 8%, respectively). Retama shrubs had a negative effect on Ziziphus; most saplings died under its canopy, whereas survival in piled branches ranged 10–54%. Pistacia was neither facilitated nor outcompeted by Retama. Facilitation of Olea by Retama shrubs was more apparent under dry conditions where watering increased competition and decreased facilitation. Overall, we conclude that Retama shrubs can help dry land restoration to a greater extent than artificial shade for Olea when not watered. The critical role played by water supply in determining nursing success rates warrants further study.     

Rethinking species selection for restoration of arid shrublands

Restoration is playing an increasingly important role in ecology as natural habitats become scarcer and chances to restore ecosystems damaged by human activities are more common. However, restoration of degraded Mediterranean arid ecosystems is hampered by drought and poor soils, which cause many establishment failures. To compare how species belonging to different successional stages establish in a very stressful site, we carried out a field experiment with 14 tree and shrub species differing in functional traits. After three growing seasons, mid-successional shrubs such as the leafless Ephedra fragilis and the C₄ Salsola oppositifolia, or green-stemmed legumes like Coronilla juncea, Genista umbellat, and Retama sphaerocarpa, showed survival rates up to 93%, while late-successional species like Tetraclinis articulata, Pinus halepensis, Olea europaea, and Pistacia lentiscus, frequently used and recommended in regular restoration projects, hardly reached 55%. We found that survival was highest for legumes, followed by leafless species, and C₄ shrubs, traits that are believed to maximize resource uptake in cleared and infertile areas while reducing water losses. Thus, selection of mid-successional species having such traits should be considered for successful restoration. These species would increase the success of restoration programs, but also would increase soil fertility, reduce soil erosion processes, and eventually facilitate establishment of other species, therefore accelerating secondary succession. We suggest a new approach for the restoration for arid shrublands in which species are carefully selected based on traits that best suit the environmental conditions.