Rapid evolution of leaf physiology in an introduced beach daisy.

Photosynthesis is a key biological process. However, we know little about whether plants change their photosynthetic strategy when introduced to a new range. We located the most likely source population for the South African beach daisy Arctotheca populifolia introduced to Australia in the 1930s, and ran a common-garden experiment measuring 10 physiological and morphological leaf traits associated with photosynthesis. Based on predictions from theory, and higher rainfall in the introduced range, we hypothesized that introduced plants would have a (i) higher photosynthetic rate, (ii) lower water-use efficiency (WUE) and (iii) higher nitrogen-use efficiency. However, we found that introduced A. populifolia had a lower photosynthetic rate, higher WUE and lower nitrogen-use efficiency than did plants from Arniston, South Africa. Subsequent site visits suggested that plants in Arniston may be able to access moisture on a rocky shelf, while introduced plants grow on sandy beaches where water can quickly dissipate. Our unexpected findings highlight that: (1) it is important to compare introduced species to their source population for an accurate assessment of evolutionary change; (2) rainfall is not always a suitable proxy for water availability and (3) introduced species often undergo evolutionary changes, but without detailed ecological information we may not be able to accurately predict the direction of these changes.

Water availability affects seasonal CO2 -induced photosynthetic enhancement in herbaceous species in a periodically dry woodland.

Elevated atmospheric CO2 (eCO2 ) is expected to reduce the impacts of drought and increase photosynthetic rates via two key mechanisms: first, through decreased stomatal conductance (gs ) and increased soil water content (VSWC ) and second, through increased leaf internal CO2 (Ci ) and decreased stomatal limitations (Slim ). It is unclear if such findings from temperate grassland studies similarly pertain to warmer ecosystems with periodic water deficits. We tested these mechanisms in three important C3 herbaceous species in a periodically dry Eucalyptus woodland and investigated how eCO2 -induced photosynthetic enhancement varied with seasonal water availability, over a 3 year period. Leaf photosynthesis increased by 10%-50% with a 150 µmol mol-1 increase in atmospheric CO2 across seasons. This eCO2 -induced increase in photosynthesis was a function of seasonal water availability, given by recent precipitation and mean daily VSWC . The highest photosynthetic enhancement by eCO2 (>30%) was observed during the most water-limited period, for example, with VSWC <0.07 in this sandy surface soil. Under eCO2 there was neither a significant decrease in gs in the three herbaceous species, nor increases in VSWC , indicating no "water-savings effect" of eCO2 . Periods of low VSWC showed lower gs (less than ≈ 0.12 mol m-2  s-1 ), higher relative Slim (>30%) and decreased Ci under the ambient CO2 concentration (aCO2 ), with leaf photosynthesis strongly carboxylation-limited. The alleviation of Slim by eCO2 was facilitated by increasing Ci , thus yielding a larger photosynthetic enhancement during dry periods. We demonstrated that water availability, but not eCO2 , controls gs and hence the magnitude of photosynthetic enhancement in the understory herbaceous plants. Thus, eCO2 has the potential to alter vegetation functioning in a periodically dry woodland understory through changes in stomatal limitation to photosynthesis, not by the "water-savings effect" usually invoked in grasslands.

Phosphorus recycling in photorespiration maintains high photosynthetic capacity in woody species.

Leaf photosynthetic CO2 responses can provide insight into how major nutrients, such as phosphorus (P), constrain leaf CO2 assimilation rates (Anet). However, triose-phosphate limitations are rarely employed in the classic photosynthesis model and it is uncertain as to what extent these limitations occur in field situations. In contrast to predictions from biochemical theory of photosynthesis, we found consistent evidence in the field of lower Anet in high [CO2] and low [O2 ] than at ambient [O2 ]. For 10 species of trees and shrubs across a range of soil P availability in Australia, none of them showed a positive response of Anet at saturating [CO2] (i.e. Amax) to 2 kPa O2. Three species showed >20% reductions in Amax in low [O2], a phenomenon potentially explained by orthophosphate (Pi) savings during photorespiration. These species, with largest photosynthetic capacity and Pi > 2 mmol P m(-2), rely the most on additional Pi made available from photorespiration rather than species growing in P-impoverished soils. The results suggest that rarely used adjustments to a biochemical photosynthesis model are useful for predicting Amax and give insight into the biochemical limitations of photosynthesis rates at a range of leaf P concentrations. Phosphate limitations to photosynthetic capacity are likely more common in the field than previously considered.

Bad mommies: socio-cognitive judgments of single mothers with alcohol use disorder.

Gender disparity persists in the United States; women are still paid less than men and are also subject to discrimination in the workplace based on the fact that they may become mothers. Further, there is evidence to indicate that single mothers are judged more harshly than their married mother counterparts and single fathers. As a form of amelioration, some women self medicate with alcohol and according to the CDC), alcohol use disorder (AUD) is on the rise for women. Although there is research on gender disparity, the motherhood penalty, and AUD, there are no experiments testing socio-cognitive judgments on those combined factors and specifically examining what we term "the single motherhood penalty". Therefore, in two experiments using between-participants designs, participants rated a picture of a person (female or male) paired with a brief description where marital status (single or married) and type of ailment (alcohol or physical) was manipulated. In Experiment 1, a passive AUD manipulation did not show a clear single motherhood penalty. In Experiment 2, the results of an active AUD manipulation supported the predicted single motherhood penalty (Experiment 2a), but did not show an analogous single fatherhood penalty (Experiment 2 b). These findings are the first to offer empirical evidence that socio-cognitive judgments might perpetuate the interplay of the single motherhood penalty and AUD.

Is there silicon in flowers and what does it tell us?

The emergence of flowers marked an important development in plant evolution. Flowers in many species evolved to attract animal pollinators to increase fertilisation chances. In leaves, silicon (Si) discourages herbivores, for example by wearing down mouthparts. Flowers are essentially modified leaves and hence may also have the capacity to accumulate Si. If Si in flowers discourages animal visitors as it does in leaves, Si accumulation may be disadvantageous for pollination. Whether flowers accumulate Si, and what the implications may be, was not known for many species. We analysed leaves and flowers of different taxa, separated into their different anatomical parts. Flowers mostly have low Si concentrations in all parts (mean ± SE of BSi in mg g-1 was 0.22 ± 0.04 in petals, 0.59 ± 0.24 in sepals, 0.14 ± 0.03 in stamens, 0.15 ± 0.04 in styles and stigmas and 0.37 ± 0.19 in ovaries for a subset of 56 species). In most cases, less Si was accumulated in flowers than in leaves (mean ± SE of BSi in mg g-1 was 1.51 ± 0.55 in whole flowers vs. 2.97 ± 0.57 in leaves in 104 species) though intriguing exceptions are found, with some species accumulating more Si in flowers than leaves. The large variation in concentration among flowers across the taxa examined, with a particularly high concentration in grass inflorescences, tantalisingly suggests differences in the use of Si for flowers across plant groups. We conclude that the study of the functions of Si for flowers warrants more attention, with pollination strategy a potential contributing factor.

Why do plants silicify?

Despite seminal papers that stress the significance of silicon (Si) in plant biology and ecology, most studies focus on manipulations of Si supply and mitigation of stresses. The ecological significance of Si varies with different levels of biological organization, and remains hard to capture. We show that the costs of Si accumulation are greater than is currently acknowledged, and discuss potential links between Si and fitness components (growth, survival, reproduction), environment, and ecosystem functioning. We suggest that Si is more important in trait-based ecology than is currently recognized. Si potentially plays a significant role in many aspects of plant ecology, but knowledge gaps prevent us from understanding its possible contribution to the success of some clades and the expansion of specific biomes.

Evidence for shifts to faster growth strategies in the new ranges of invasive alien plants.

SUMMARY: Understanding the processes underlying the transition from introduction to naturalization and spread is an important goal of invasion ecology. Release from pests and pathogens in association with capacity for rapid growth is thought to confer an advantage for species in novel regions.We assessed leaf herbivory and leaf-level traits associated with growth strategy in the native and exotic ranges of 13 invasive plant species from 256 populations. Species were native to either the Western Cape region of South Africa, south-western Australia or south-eastern Australia and had been introduced to at least one of the other regions or to New Zealand. We tested for evidence of herbivore release and shifts in leaf traits between native and exotic ranges of the 13 species.Across all species, leaf herbivory, specific leaf area and leaf area were significantly different between native and exotic ranges while there were no significant differences across the 13 species found for leaf mass, assimilation rate, dark respiration or foliar nitrogen.Analysis at the species- and region-level showed that eight out of 13 species had reduced leaf herbivory in at least one exotic region compared to its native range.Six out of 13 species had significantly larger specific leaf area (SLA) in at least one exotic range region and five of those six species experienced reduced leaf herbivory. Increases in SLA were underpinned by increases in leaf area rather than reductions in leaf mass.No species showed differences in the direction of trait shifts from the native range between different exotic regions. This suggests that the driver of selection on these traits in the exotic range is consistent across regions and hence is most likely to be associated with factors linked with introduction to a novel environment, such as release from leaf herbivory, rather than with particular environmental conditions.Synthesis. These results provide evidence that introduction of a plant species into a novel environment commonly results in a reduction in the top-down constraint imposed by herbivores on growth, allowing plants to shift towards a faster growth strategy which may result in an increase in population size and spread and consequently to invasive success.

Is plant ecology more siliceous than we realise?

Although silicon occurs in all plants, it is an element that is largely overlooked by many plant ecologists and most plant-related research on silicon comes from agronomy, archaeology, palaeontology and biogeochemistry. Plant silicon has many functions, acting biochemically as silicic acid and physically as amorphous silica. It contributes to cell and plant strength and enables plants to respond adaptively to environmental stresses. Consequently, plant silicon can increase plant fitness in many fundamental aspects of ecology, including plant-herbivore interactions, light interception, pathogen resistance and alleviation of abiotic stresses. Here, we provide an ecological perspective to research outcomes from diverse disciplines, showing that silicon is an important element in plant ecology that is worthy of greater attention.