The ‘New Wave’ in plant demographic inference: more loci and more individuals

Plant population genetic surveys are starting to take full advantage of technological advances in genotyping methods and of methodological advances in demographic inference. In this issue of Molecular Ecology, Keller et al. (2010) illustrate this trend with a particularly convincing study of rangewide genetic variation in a North American poplar, using both SNP and sequence data. They first investigate population genetic structure by estimating the most likely number of genetic clusters using a more formal approach than most other studies to date. They proceed by estimating gene flow among the inferred populations and by testing predictions on the distribution of low frequency alleles derived from recent work on range expansions.     

High value of short rotation coppice plantations for phytodiversity in rural landscapes

The demand for wood from short rotation coppice (SRC) plantations as a renewable energy source is currently increasing and could affect biodiversity in agricultural areas. The objective was to evaluate the contribution of SRC plantations to phytodiversity in agricultural landscapes assessed as species richness, species–area relationships, Shannon indices, detrended correspondence analysis on species composition, Sørensen similarities, habitat preference proportions, and species proportions found in only one land use. Vegetation surveys were conducted on 12 willow (Salix spp.) and three poplar (Populus spp.) coppice sites as well as on surrounding arable lands, grasslands and forests in central Sweden and northern Germany. SRC plantations were richer in plant species (mean: 30 species per 100 m²) than arable land (10), coniferous forests (13) and mixed forests in Germany (12). Comparing SRC plantations with other land uses, we found lowest similarities in species composition with arable lands, coniferous forests and German mixed forests and highest similarities with marginal grassland strips, grasslands and Swedish mixed forests. Similarity depended on the SRC tree cover: at increased tree cover, SRC plantations became less similar to grasslands but more similar to forests. The SRC plantations were composed of a mixture of grassland (33%), ruderal (24%) and woodland (15%) species. Species abundance in SRC plantations was more heterogeneous than in arable lands. We conclude that SRC plantations form novel habitats leading to different plant species composition compared to conventional land uses. Their landscape‐scale value for phytodiversity changes depending on harvest cycles and over time. As a structural landscape element, SRC plantations contribute positively to phytodiversity in rural areas, especially in land use mosaics where these plantations are admixed to other land uses with dissimilar plant species composition such as arable land, coniferous forest and, at the German sites, also mixed forest.     

Removal of nitrogen and phosphorus by Eucalyptus and Populus at a tertiary treated municipal wastewater sprayfield

Various progenies of Eucalyptus grandis and E. amplifolia, and clones of Populus deltoides, were evaluated for plant removal of nitrogen (N) and phosphorus (P) for 26 months at a municipal waste spray field in north Florida. Tertiary treated wastewater containing 2.73 mg L(-1) nitrate N and 0.30 mg L(-1) total P was applied using sprinkler irrigation (93.8 m3 ha(-1) d(-1)) to fast growing trees utilized for bioenergy. Eucalyptus amplifolia and E. grandis survived and grew very poorly as the result of severe winter injury in two successive years and were not evaluated for nutrient removal. Survival and growth of P. deltoides demonstrated suitability for phytoremediation, and selected clones were evaluated for biomass and nutrient content. Removals of total N (TN) and total P (TP) were greatest for main stem (36% and 44%, respectively) and foliage (44% and 36%, respectively). Low biomass producing clones generally had higher nutrient concentrations, but high biomass producing clones removed more TN and TP. Approximately 789 kg ha(-1) TN and 103 kg ha(-1) TP were removed by the highest biomass producing P. deltoides clone, representing 215% of N and 615% of P inputs.     

Phytoremediation of chlorpyrifos by Populus and Salix

Chlorpyrifos is one of the commonly used organophosphorus insecticides that are implicated in serious environmental and human health problems. To evaluate plant potential for uptake of chlorpyrifos, several plant species of poplar (Populus sp.) and willow (Salix sp.) were investigated. Chlorpyrifos was taken up from nutrient solution by all seven plant species. Significant amounts of chlorpyrifos accumulated in plant tissues, and roots accumulated higher concentrations of chlorpyrifos than did shoots. Chlorpyrifos did not persist in the plant tissues, suggesting further metabolism of chlorpyrifos in plant tissue. To our knowledge, this work represents the first report for phytoremediation of chlorpyrifos using poplar and willow plants.     

Transpirational Water Loss in Invaded and Restored Semiarid Riparian Forests

The invasive tree, Tamarix sp., was introduced to the United States in the 1800s to stabilize stream banks. The riparian ecosystem adjacent to the middle Rio Grande River in central New Mexico consists of mature cottonwood (Populus fremontii) gallery forests with a dense Tamarix understory. We hypothesized that Populus would compensate for reduced competition by increasing its water consumption in restored riparian plots following selective Tamarix removal, resulting in similar transpiration (T) among stands. The northern study site included a Populus stand invaded by Tamarix (INV_N) and a restored Populus‐only stand (RES_N), as did a southern site (INV_S and RES_S) approximately 80 miles south. At each site, 20 × 20–m plots were established where up to 16 stems were monitored throughout the 2004 growing season using thermal dissipation sapflow sensors. Populus sapflux rates were greater in restored stands, suggesting those trees compensated for understory removal by using more water. Sapflow was scaled to estimate stand‐level T based on a quantitative assessment of sapwood basal area (A_sw) by species. Although exotic species represented 85 and 91% of the total stems in the invaded stands, it amounted to only 3% (INV_S) and 4% (INV_N) of the total A_sw, contributing proportionately less to T compared to Populus. Our results indicate that removing Tamarix from the Populus understory in this riparian forest had a minimal impact on stand water balance. Riparian restoration of the type discussed herein should focus primarily on enhancing riparian health rather than generating water.     

Linking woodland key habitat inventory and forest inventory data to prioritize districts needing conservation efforts

Woodland key habitat (WKH) inventories have been conducted in northern European countries, with the aim to create networks of minimally disturbed forest stands for protection. The goal of national forest inventory is to provide information relevant to forest management, such as on forest types, trees species composition, age structure and wood volume. The aim of this study was to link these two inventory databases to identify districts of Latvia most deficient in connectivity and habitat quality, in order to prioritize districts needing conservation effort. As an example, the area of deciduous forest with nemoral tree species (oak, ash, lime, maple and elm) and aspen was chosen. These forests provide habitat for a specific community of epiphytes. Using information in the WKH database, habitat quality in different districts of Latvia was estimated by the frequencies of occurrence of structural elements and selected indicator epiphyte species in nemoral tree species and aspen WKHs. Using digital data in the national forest inventory database, fragmentation metrics were determined for forests that, according to age and tree species composition, could potentially be nemoral tree and aspen WKHs. On a regional level, the lowest habitat quality in WKH occurred in districts that had the least fragmentation of potential WKH forest. In the less fragmented areas, the habitat quality of the existing WKH will likely increase in the future, and could be promoted by management to create structural elements typical of natural forests. The districts with the most fragmented nemoral and aspen forests, contained WKHs with the best habitat quality. A focus on protection should be given to these stands as they are the most likely to support source populations, and there is a need to improve spatial continuity of suitable tree substrate in these areas.     

Development and characterization of microsatellite markers in Populus euphratica (Populaceae)

In this study, we developed 12 microsatellite loci for Populus euphratica and checked their variability in 27 individuals. The number of alleles for 12 loci ranged from five to nine, the observed and expected heterozygosities ranged from 0.32 to 0.48 and from 0.53 to 0.67. Frequencies of null alleles of all loci are not significantly greater than zero. None of the loci showed significant deviation from Hardy-Weinberg equilibrium. No significant linkage disequilibrium was observed between pairs of studied loci. These markers are useful in studies of population genetic structure of P. euphratica.     

Inhibitory effect of Eucommia ulmoides Oliver on adipogenic differentiation through proteome analysis

Eucommia ulmoides Oliver was tested to control the differentiation of cultured human mesenchymal stem cell into adipocyte. The extent of the inhibitory effect on the conversion of adipose was measured using Oil red O staining, which stains accumulated lipid droplets in the cytoplasm of adipocyte. The adipocyte differentiation was inhibited by an extract from E. ulmoides Oliver in the concentration range 0.01–50.0 g/l. After 2D PAGE, protein spots of E. ulmoides Oliver extract treated stem cells were analyzed. Several protein spots were strongly up-regulated in E. ulmoides Oliver extract treated cells. Among them, tropomyosin was identified by MALDI-TOF. These results suggest that E. ulmoides Oliver has an inhibitory activity toward the adipose conversion, which is a major cause of obesity.     

Responses of riparian trees to interannual variation in ground water depth in a semi-arid river basin

We investigated the physiological and growth responses of native (Populus fremontii S. Wats. and Salix gooddingii Ball) and exotic (Tamarix chinensis Lour.) riparian trees to ground water availability at the free‐flowing Hassayampa River, Arizona, during dry (1997) and wet (1998) years. In the drier year, all species experienced considerable water stress, as evidenced by low shoot water potentials, low leaf gas exchange rates and large amounts of canopy dieback. These parameters were significantly related to depth of ground water (DGW) in the native species, but not in T. chinensis, in 1997. Canopy dieback was greater in the native species than in T. chinensis when ground water was deep in 1997, and dieback increased rapidly at DGW > 2·5–3·0 m for the native species. Analysis of combined data from wet and dry years for T. chinensis tentatively suggests a similar physiological sensitivity to water availability and a similar DGW threshold for canopy dieback. In 1998, shoot water potential and leaf gas exchange rates were higher and canopy dieback was lower for all species because of increased water availability. However, T. chinensis showed a much larger increase in leaf gas exchange rates in the wet year than the native species. High leaf gas exchange rates, growth when water is abundant, drought tolerance and the maintenance of a viable canopy under dry conditions are characteristics that help explain the ability of T. chinensis to thrive in riparian ecosystems in the south‐western United States.