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• Background and Aims Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious roots (aquatic roots) are commonly formed in flooding-tolerant plant species and are generally assumed to be beneficial for plant growth by supporting water and nutrient uptake during partial flooding. However, the actual contribution of these roots to plant performance under flooding has hardly been quantified. As the investment into aquatic root development in terms of carbohydrates may be costly, these costs may - depending on the specific environmental conditions - offset the beneficial effects of aquatic roots. This study tested the hypothesis that the balance between potential costs and benefits depends on the duration of flooding, as the benefits are expected to outweigh the costs in long-term but not in short-term flooding. • Methods The contribution of aquatic roots to plant performance was tested in Solanum dulcamara during 1-4 weeks of partial submergence and by experimentally manipulating root production. Nutrient uptake by aquatic roots, transpiration and photosynthesis were measured in plants differing in aquatic root development to assess the specific function of these roots. • Key Results As predicted, flooded plants benefited from the presence of aquatic roots. The results showed that this was probably due to the contribution of roots to resource uptake. However, these beneficial effects were only present in long-term but not in short-term flooding. This relationship could be explained by the correlation between nutrient uptake and the flooding duration-dependent size of the aquatic root system. • Conclusions The results indicate that aquatic root formation is likely to be selected for in habitats characterized by long-term flooding. This study also revealed only limited costs associated with adventitious root formation, which may explain the maintenance of the ability to produce aquatic roots in habitats characterized by very rare or short flooding events. [ABSTRACT FROM AUTHOR]

1. When range shifts or invasions of plant species are studied, it is important to know whether large-scale spatial variation in a species’ demography can be ignored or approximated by variation observed over smaller spatial scales. 2. Here, we studied the population dynamics of three similar (as shown by elasticity analysis) short-lived perennial plant species in multiple sites in different European countries over 2 years. We constructed a total of 40 transition matrices and analysed the spatio-temporal variation in the projected population growth rate (λ) with spatially nested life table response experiments (LTRE). 3. All species ( Carlina vulgaris, Tragopogon pratensis and Hypochaeris radicata) showed considerable life-history variation among regions on top of variation among sites within regions. 4. Net variance contributions (NVC), a novel LTRE statistic, revealed that in each species, variation in one group of vital rates contributed most to variation in λ among regions as well as among sites. However, that most important type of vital rates differed between species: plant growth in C. vulgaris, flower head production in T. pratensis and establishment probability of seedlings in H. radicata. The rankings of the NVCs of other vital rates varied between site and region effects, suggesting that buffering through negative vital rate correlations varies over different spatial scales, while the identity of the main contributor to λ variation is more constant. 5. Temporal effects were smaller than spatial effects, but the LTREs showed strong interactions between time and space (region or site), suggesting that the effect of, e.g. climate fluctuations are not synchronized throughout the distribution of a species. 6. Synthesis. This study shows that the life histories of plant species are distinguishable even when mean elasticity values show only small differences, and that life histories vary over the distribution range of a species. Demographic differences over large spatial scales can therefore only be partly substituted by small scale spatial variation in modelling studies on the population dynamics of a species across its entire distribution. [ABSTRACT FROM AUTHOR]

We report on two experiments with oilseed rape ( Brassica napus L.) to test if partial root-zone drying techniques improve yield in a crop in which vegetative and reproductive growth overlap (indeterminate growth habit), and to investigate what plant morphological responses contribute to the yield that is realized. Deficit irrigation resulted in smaller plants with smaller yields but larger seeds compared to treatments with shallow groundwater (first experiment) and with fully watered conditions (second experiment). Different partial root-zone drying treatments (water supply patterns) under deficit irrigation, however, had little effect on plant growth and yield components (number of branches, branch lengths, number of pods, etc.). Our results suggest that partial root-zone drying doesn’t work well with oilseed rape. Detailed measurements of soil water contents and root distribution indicate that roots were extremely plastic, effectively foraging for water, and these root responses may have overwhelmed physiological effects of partial root drying on the shoot. Furthermore, in crops with indeterminate growth with a short vegetative growth phase, partial root-zone drying may be ineffective in enhancing the major yield components. Further reasons for the lack of success are discussed. [ABSTRACT FROM AUTHOR]

1. Globally, both climatic patterns and nitrogen deposition rates show directional changes over time. It is uncertain how woody seedlings, which coexist with herbaceous plants in savannas, respond to concurrent changes in water and nutrient availability. 2. We investigated competition effects between herbaceous vegetation and tree seedlings ( Colophospermum mopane) under changed water and nutrient (fertilized) conditions in a garden experiment situated in a semi-arid savanna. 3. Herbaceous competition significantly suppressed woody seedling growth. The effect of herbaceous competition on woody seedling growth remained constant with both increasing water and nutrient availability. However, during a wet-season drought, herbaceous competition apparently caused premature leaf senescence in non-irrigated treatments. Fertilization exacerbated negative competition effects during the drought, while irrigation prevented leaf loss of tree seedlings in spite of herbaceous competition and fertilization. 4. Based on a conceptual model, we propose that the vigorous response of herbaceous plants to increased nutrient availability leads to faster depletion of soil water, which increasingly causes water stress in woody seedlings if the interval between watering events is prolonged, e.g. during wet-season droughts. 5. Synthesis. Our data support the notion that changes in drought frequency are of greater importance to woody recruitment success than changes in annual rainfall amount. Based on the water and nutrient interactions observed in our experiment, we suggest that the effect of increased nitrogen deposition on woody seedling recruitment is contingent on water availability. [ABSTRACT FROM AUTHOR]

1 An increasing number of studies have shown that plants produce more root mass when sharing rooting space with an intraspecific neighbour as compared with plants growing alone. This so-called self/non-self discrimination has been suggested as a mechanism by which plants may prevent wasteful competition with their own roots and enhance their competitive ability for nutrients with roots of neighbouring plants. The overproduction of root biomass is said to result in a ‘tragedy of the commons’, because it appears to occur at the expense of reproductive biomass. 2 Studies on self/non-self root discrimination have commonly used a split-root design to distinguish self from non-self competition, while keeping the total amount of nutrients available per plant the same. This design has recently been criticized because the rooting volume differs between treatments. 3 Here, we use three general hypotheses to explain the published results without invoking the mechanism of self/non-self discrimination. The hypotheses propose that differences in root mass are due to differences in rooting volume, and differences in nutrient availability determine whole plant growth. More root mass without more growth results in less reproductive biomass. 4 A reanalysis of the results of root self/non-self discrimination confirms these hypotheses. Root overproduction in the presence of another plant, as found in nearly all studies, is consistent with effects of a larger soil volume available to these plants as compared with plants growing alone. Under the same total nutrient availability, total plant weight was the same or higher when more roots were produced. Inevitably, a larger root production with the same total biomass implies that less reproductive biomass is produced. 5 Although our analysis can explain most of the results of the split-root experiments, we cannot rule out the possibility that self/non-self root discrimination did take place. We discuss a limited set of experiments for which volume effects cannot explain the results, suggesting, in fact, that direct self/non-self root interactions have operated. We suggest experimental designs that can demonstrate their ecological significance in the future. 6 We conclude that there is ample evidence that plants can sense the volume of available rooting space, and a limited number of studies on individual roots show that plant roots may sense the identity of neighbouring roots and respond accordingly. The significance of these responses for whole plant growth and reproduction in relation to well-known resource competition effects is yet largely unknown and in urgent need of further study. [ABSTRACT FROM AUTHOR]

Many studies have focused on the ecology of seed dimorphism, the production of two seed types by a single plant. Morphology and seed size are usually correlated, but how morphology affects germination percentage and seedling growth is poorly understood. Here we explicitly separate these effects for nine populations of the dimorphic species Tragopogon pratensis subsp. pratensis. Larger seeds yielded higher germination percentages, yet seed morphology had no additional direct effect on germination. Neither seed size nor seed morphology affected seedling growth. Neither germination nor seedling growth varied among populations. but seed head varied significantly. Results show that germination is mainly controlled by seed site rather than by seed morphology. This study is one of the few to distinguish explicitly between seed size and seed morphology effects on ecological characteristics and suggests that seed dimorphism may exert its ecological effects predominantly through its correlated size. [ABSTRACT FROM AUTHOR]

Plants growing at high densities express shade avoidance traits as a response to the presence of neighbours. Enhanced shoot elongation is one of the best researched shade avoidance components and increases light capture in dense stands. We show here that also leaf movements, leading to a more vertical leaf orientation (hyponasty), may be crucial in the early phase of competition. The initiation of shade avoidance responses is classically attributed to the action of phytochrome photoreceptors that sense red:far-red (R:FR) ratios in light reflected by neighbours, but also other signals may be involved. It was recently shown that ethylene-insensitive, transgenic (Tetr) tobacco plants, which are insensitive to the gaseous plant hormone ethylene, have reduced shade avoidance responses to neighbours. Here, we report that this is not related to a reduced response to low R:FR ratio, but that Tetr tobacco plants are unresponsive to a reduced photon fluence rate of blue light, which normally suppresses growth inhibition in wild-type (WT) plants. In addition to these light signals, ethylene levels in the canopy atmosphere increased to concentrations that could induce shade avoidance responses in WT plants. Together, these data show that neighbour detection signals other than the R:FR ratio are more important than previously anticipated and argue for a particularly important role for ethylene in determining plant responses to neighbours. [ABSTRACT FROM AUTHOR]