Spatial and temporal variability of soil water in drylands: plant water potential as a diagnostic tool

Arid and semi-arid regions are characterized by low rainfall and high potential evaporative demand. Here, water is the major limiting factor for plant growth and productivity. Soil and surface hydrology properties （e.g. field capacity, infikration rates） effectively control the water re-distribution in the ecosystem, a fact that is aggravated in arid environments. Information of the spatial and temporal accessibility of soil water in desert ecosystems is limited. The purpose of the studies is the application of plant water potential to estimate the spatial and temporal variations of soil water availability in different arid ecosystems of the Negev （Israel） and southern Morocco. As model plants the evergreen shrubs Retama raetam, Thymelaea hirsuta and trees （Acacia tortilis） were chosen. Seasonal and spatial variations of the pre-dawn water potential （ψpd） were examined as diagnostic tool to determine water availability on the landscape level. The seasonal differences in the pre-dawn water potential were less pronounced on the dune compared to the interdune. This showed a better water availability on the dune slope. Also in the investigated wadis systems spatial differences of the water potential could be detected and related to the vegetation pattern.     

Spatial variability of nutrient stocks in the humus and soils of a forest massif (Fougères, France)

In this study, the spatial distribution of nutrient stocks (K, Ca, Mg and P) was examined in humus and soils at the forest massif scale (Fougères forest, France). A random stratified sampling plan including 100 sampling points was used and three potential variation factors of nutrient stocks were tested: age of stand, type of stand (broad-leaved or coniferous trees) and type of soil. Sampling classes were then compared and the variation factors were examined. Results demonstrated that nutrient stocks in the humus were not influenced by the cited factors and only the type of soil influenced nutrient stocks in soils. In fact, stocks of exchangeable elements in soils were much higher in Colluviosols-Fluviosols which show redoximorphic characteristics, and available phosphorus stocks were lower than in Alocrisols-Neoluvisols. Moreover, a low variability of nutrient stocks was observed in Alocrisols-Neoluvisols as opposed to Colluviosols-Fluviosols, which may suggest the existence of other variation factors not taken into account in this study (hydromorphic gradient, type and age of stand in hydromorphic zones).     

The potential of Vachellia kosiensis (Acacia kosiensis) as a dryland forestry species in terms of its water use,growth rates and resultant water-use efficiency§

The potential of the country’s numerous indigenous tree species to address challenges facing the commercial forestry industry in South Africa is under-explored. Relevant issues include the rising demand for timber and non-timber forest products due to population and economic growth, minimal available land for expanding traditional commercial forestry operations, and known streamflow reduction impacts associated with introduced plantation tree species. However, little is known about the water use and corresponding growth rates of indigenous tree species, and consequently their potential as an alternative form of forestry and sustainable resource use. In this study, the water use, growth rates and resultant water-use efficiency of Vachellia kosiensis (Acacia kosiensis) (dune sweet thorn) were quantified within a mature stand of these trees situated on rehabilitated dune mining land in the Richards Bay area of South Africa. Hourly sap flow rates were measured over a two-year period in five trees, and tree heights and stem circumferences were recorded periodically throughout the monitoring period, to derive biomass increments. Rates of growth and water use were used to calculate water-use efficiency, defined as mass of utilisable (stem) wood produced per unit of water transpired. Results were compared with similarly sampled data for introduced plantation species, including Eucalyptus, Pinus and Casuarina. Results showed that the indigenous V. kosiensis trees used less than half the water used by introduced plantation species. The growth rates of individual V. kosiensis trees were unable to compete with introduced species; however, their higher tree density nevertheless yielded a mean annual increment of 10.3 m³ ha^?1 y^?1 (7.2 t ha^?1 y^?1). Furthermore, their correspondingly low water-use rates indicated that the indigenous trees had similar biophysical water-use efficiency values compared with genetically improved introduced tree species and highlighted their potential as an attractive land-use option in appropriate locations within water-constrained or dryland areas.     

Cloning of a flower-specific expression promoter from Arabidopsis thaliana and its plant expression vector construction

Given the sequence of Chs gene promoter from Arabidopsis thaliana reported in GenBank (AF248988), a pair of specific     

Structural quality of soil in plantation： a case study on the mixed plantation of Alnus cremastogyne and Cupressus funebris in upper reaches of Yangtze River

In process of ecological construction in typical region of upper reaches of Yangtze River, China, the mixed plantations at the ages of 10-20 present a trend to be pure forests and degeneration. Soil samples including stratified soil and total soil were taken from 4 typical profiles in the mixed plantation ofAlnus cremastogyne and Cupressus funebris in Yanting County in central Sichuan, China. Soil indices of the plantation were compared with those of natural forest in Gongga Mountain in the same region, The results revealed that structural quality of soil in plantation was significantly lower than that in natural forests. The degradation of structural quality of soil in plantation was one of key factors for plantation degeneration, The degradation causes of structural quality of soil were analyzed. Aanthtopogenic disturbance and absence of effective protection and scientific management are the main reason for degradation of structural quality of soil in plantation. The main countermeasures, e.g. foresl reservation, ecological rehabilitation, litter horizon rebuilding as well as organic fertilizer application, were proposed to improve the structural quality of soil in plantation.     

Effects of water stress on water use efficiency and water balance components of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> and <Emphasis Type="Italic">Caragana intermedia</Emphasis> in the soil–plant–atmosphere continuum

Hippophae rhamnoides (Sea buckthorn) and Caragana intermedia (Intermediate peashrub), which are nitrogen-fixing and perennial temperate shrubs, are extensively used in the agroforestry systems in the loess areas of China. In this study, artificially controlled water gradient experiments were carried out with both shrubs, based on four levels of water supply (normal precipitation, slight drought, drought, and extreme drought). The results showed significant impacts of drought on net photosynthesis rate, biomass accumulation, and biomass allocation in both species. Water use efficiency (WUE) varied with different species, scales, and water stress intensities. WUE at the leaf scale (WUEi) was highest under moderate water stress, while the WUE at the community scale (WUEb) decreased with increasing water stress. We observed alteration in the diel and seasonal transpiration of both species in response to water stress. The night-time transpiration accounted for a small but significant proportion of the water balance, and its importance tended to increase with increasing drought. Both species experienced water deficits under all treatments. Soil moisture of H. rhamnoides declined more severely than that of C. intermedia. The ratio of transpiration to evapotranspiration (T/ET) ranged from 50 to 80% for both species in the growing season. The T/ET and WUEi of H. rhamnoides were comparatively smaller under severe water stress but increased under moist conditions. Our data suggest that H. rhamnoides uses water resources more efficiently under favorable water conditions, and C. intermedia shows competitive advantages under drought conditions. Moreover, possible strategies to maintain water balance in the water-limited agroforestry systems are discussed.     

Covariation between plant biodiversity and soil systems in a European beech forest and a black pine plantation: the case of Mount Faito,(Campania,Southern Italy)OA

Both climate and land-use changes, including the introduction and spread of allochthonous species, are forecast to affect forest ecosystems. Accordingly, forests will be affected in terms of species composition as well as their soil chemical and biological characteristics. The possible changes in both tree cover and soil system might impact the amount of carbon that is stored in living plants and dead biomass and within the soil itself. Additionally, such alterations can have a strong impact on ...