Flooding tolerance in four 'Garrigue' landscape plants: implications for their future use in the urban landscapes of north-west Europe?

Within a changing climate, Mediterranean ‘Garrigue’ xerophytes are increasingly recommended as suitable urban landscape plants in north-west Europe, based on their capacity to tolerate high temperature and reduced water availability during summer. Such species, however, have a poor reputation for tolerating waterlogged soils; paradoxically a phenomenon that may also increase in north-west Europe due to predictions for both higher volumes of winter precipitation, and short, but intensive periods of summer rainfall. This study investigated flooding tolerance in four landscape ‘Garrigue’ species, Stachys byzantina, Cistus × hybridus, Lavandula angustifolia and Salvia officinalis. Despite evolving in a dry habitat, the four species tested proved remarkably resilient to flooding. All species survived 17 days flooding in winter, with Stachys and Lavandula also surviving equivalent flooding duration during summer. Photosynthesis and biomass production, however, were strongly inhibited by flooding although the most tolerant species, Stachys quickly restored its photosynthetic capacity on termination of flooding. Overall, survival rates were comparable to previous studies on other terrestrial (including wetland) species. Subsequent experiments using Salvia (a species we identified as ‘intermediate’ in tolerance) clearly demonstrated adaptations to waterlogging, e.g. acclimation against anoxia when pre-treated with hypoxia. Despite anecdotal information to the contrary, we found no evidence to suggest that these xerophytic species are particularly intolerant of waterlogging. Other climatic and biotic factors may restrict the viability and distribution of these species within the urban conurbations of north-west Europe, but we believe increased incidence of flooding per se should not preclude their consideration.

Managing the nutrition of plants and people

One definition of food security is having sufficient, safe, and nutritious food to meet dietary needs. This paper highlights the role of plant mineral nutrition in food production, delivering of essential mineral elements to the human diet, and preventing harmful mineral elements entering the food chain. To maximise crop production, the gap between actual and potential yield must be addressed. This gap is 15–95% of potential yield, depending on the crop and agricultural system. Current research in plant mineral nutrition aims to develop appropriate agronomy and improved genotypes, for both infertile and productive soils, that allow inorganic and organic fertilisers to be utilised more efficiently. Mineral malnutrition affects two-thirds of the world's population. It can be addressed by the application of fertilisers, soil amelioration, and the development of genotypes that accumulate greater concentrations of mineral elements lacking in human diets in their edible tissues. Excessive concentrations of harmful mineral elements also compromise crop production and human health. To reduce the entry of these elements into the food chain, strict quality requirements for fertilisers might be enforced, agronomic strategies employed to reduce their phytoavailability, and crop genotypes developed that do not accumulate high concentrations of these elements in edible tissues.

Pollinator community responses to the spatial population structure of wild plants: A pan-European approach

Land-use changes can alter the spatial population structure of plant species, which may in turn affect the attractiveness of flower aggregations to different groups of pollinators at different spatial scales. To assess how pollinators respond to spatial heterogeneity of plant distributions and whether honeybees affect visitation by other pollinators we used an extensive data set comprising ten plant species and their flower visitors from five European countries. In particular we tested the hypothesis that the composition of the flower visitor community in terms of visitation frequencies by different pollinator groups were affected by the spatial plant population structure, viz. area and density measures, at a within-population (‘patch’) and among-population (‘population’) scale. We found that patch area and population density were the spatial variables that best explained the variation in visitation frequencies within the pollinator community. Honeybees had higher visitation frequencies in larger patches, while bumblebees and hoverflies had higher visitation frequencies in sparser populations. Solitary bees had higher visitation frequencies in sparser populations and smaller patches. We also tested the hypothesis that honeybees affect the composition of the pollinator community by altering the visitation frequencies of other groups of pollinators. There was a positive relationship between visitation frequencies of honeybees and bumblebees, while the relationship with hoverflies and solitary bees varied (positive, negative and no relationship) depending on the plant species under study. The overall conclusion is that the spatial structure of plant populations affects different groups of pollinators in contrasting ways at both the local (‘patch’) and the larger (‘population’) scales and, that honeybees affect the flower visitation by other pollinator groups in various ways, depending on the plant species under study. These contrasting responses emphasize the need to investigate the entire pollinator community when the effects of landscape change on plant–pollinator interactions are studied.

Variation in root-associated phosphatase activities in wheat contributes to the utilization of organic P substrates in vitro, but does not explain differences in the P-nutrition of plants when grown in soils

To understand whether genotypic variation in root-associated phosphatase activities in wheat impacts on its ability to acquire phosphorus (P), various phosphatase activities of roots were measured in relation to the utilization of organic P substrates in agar, and the P-nutrition of plants was investigated in a range of soils. Root-associated phosphatase activities of plants grown in hydroponics were measured against different organic P substrates. Representative genotypes were then grown in both agar culture and in soils with differing organic P contents and plant biomass and P uptake were determined. Differences in the activities of both root-associated and exuded phosphodiesterase and phosphomonoesterase were observed, and were related to the P content of plants supplied with either ribonucleic acid or glucose 6-phosphate, respectively, as the sole form of P. When the cereal lines were grown in different soils, however, there was little relationship between any root-associated phosphatase activity and plant P uptake. This indicates that despite differences in phosphatase activities of cereal roots, such variability appears to play no significant role in the P-nutrition of the plant grown in soil, and that any benefit derived from the hydrolysis of soil organic P is common to all genotypes.

Effect of earthworm Eisenia fetida and wetland plants on nitrification and denitrification potentials in vertical flow constructed wetland.

The response of nitrification potentials, denitrification potentials, and N removal efficiency to the introduction of earthworms and wetland plants in a vertical flow constructed wetland system was investigated. Addition of earthworms increased nitrification and denitrification potentials of substrate in non-vegetated constructed wetland by 236% and 8%, respectively; it increased nitrification and denitrification potentials in rhizosphere in vegetated constructed wetland (Phragmites austrail, Typha augustifolia and Canna indica), 105% and 5%, 187% and 12%, and 268% and 15% respectively. Denitrification potentials in rhizosphere of three wetland plants were not significantly different, but nitrification potentials in rhizosphere followed the order of C. indica > T. augustifolia > P. australis when addition of earthworms into constructed wetland. Addition of earthworms to the vegetated constructed significantly increased the total number of bacteria and fungi of substrates (P < 0.05). The total number of bacteria was significantly correlated with nitrification potentials (r = 913, P < 0.01) and denitrification potentials (r = 840, P < 0.01), respectively. The N concentration of stems and leaves of C. indica were significantly higher in the constructed wetland with earthworms (P < 0.05). Earthworms had greater impact on nitrification potentials than denitrification potentials. The removal efficiency of N was improved via stimulated nitrification potentials by earthworms and higher N uptake by wetland plants.

Sesquiterpenoids lactones: benefits to plants and people

Sesquiterpenoids, and specifically sesquiterpene lactones from Asteraceae, may play a highly significant role in human health, both as part of a balanced diet and as pharmaceutical agents, due to their potential for the treatment of cardiovascular disease and cancer. This review highlights the role of sesquiterpene lactones endogenously in the plants that produce them, and explores mechanisms by which they interact in animal and human consumers of these plants. Several mechanisms are proposed for the reduction of inflammation and tumorigenesis at potentially achievable levels in humans. Plants can be classified by their specific array of produced sesquiterpene lactones, showing high levels of translational control. Studies of folk medicines implicate sesquiterpene lactones as the active ingredient in many treatments for other ailments such as diarrhea, burns, influenza, and neurodegradation. In addition to the anti-inflammatory response, sesquiterpene lactones have been found to sensitize tumor cells to conventional drug treatments. This review explores the varied ecological roles of sesquiterpenes in the plant producer, depending upon the plant and the compound. These include allelopathy with other plants, insects, and microbes, thereby causing behavioural or developmental modification to these secondary organisms to the benefit of the sesquiterpenoid producer. Some sesquiterpenoid lactones are antimicrobial, disrupting the cell wall of fungi and invasive bacteria, whereas others protect the plant from environmental stresses that would otherwise cause oxidative damage. Many of the compounds are effective due to their bitter flavor, which has obvious implications for human consumers. The implications of sesquiterpenoid lactone qualitiesfor future crop production are discussed.