There seems to be a trade-off between height growth and mechanical stability in plants growing in crowded habitats. Watari et al. measure extension growth and mechanical properties of internodes in Xanthium canadense plants grown at different densities and show that tissue stiffness (Young’s modulus of elasticity) and strength (modulus of rupture) play crucial roles in maintaining stability in herbaceous species that lack the capacity for secondary growth. This differs from woody species where diameter growth has been considered more important.
Sex allocation can vary widely among flowers on a plant and among plants within a population. Austen and Weis develop a numerical model and use it to demonstrate that the widespread tendency towards declining fruit set from first to last flowers on plants may contribute to temporal variation in allocation optima. Temporal trends in relative pollen and ovule investment measured in Brassica rapa, however, do not match the predicted trends in functional gender, but some findings of the model, namely decreasing male reproductive success with later flowering onset, may nonetheless apply in this taxon.
Miscanthus sinensis is a perennial C4 grass that is one parent of the economically important hybrid biomass species, M. ×giganteus. Clark et al. evaluate 620 M. sinensis accessions from most of its native range with >20 000 nuclear and plastid markers, and identify six genetic groups. They find that coastal south-east China was a refugium of M. sinensis during the last glacial maximum, and that the species recolonized Japan prior to recolonizing similar latitudes in mainland Asia. Ornamental cultivars originate almost exclusively from southern Japan, and many marketed as M. sinensis have hybrid ancestry from M. sacchariflorus.
The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared to actinomorphic flowers. By using data on 43 species from two contrasting communities, Lázaro and Totland show that zygomorphic species that are highly dependent on pollinators and ecologically specialized are less variable in flower size than ecologically generalist and selfing zygomorphic species. However, these relationships are not found in actinomorphic species. The results suggest that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species’ dependence on pollinators.
Olearia flocktoniae (Asteraceae) is an endangered shrub that was passively translocated from its natural ecosystem where it has since gone extinct. Gross and Mackay use two decades of demographic monitoring and a seed bank study in a sensitivity analysis in order to reveal vulnerabilities in the life cycle. They find that seed production is high but populations are short-term persistent (<5 years) due to transient seed banks and poor survivorship of seedlings. Seedling establishment is promoted by soil disturbance and only populations that have been disturbed annually survived the full 20 years of the study. They conclude that active management is thus required to keep this species from extinction.
Salvia (Lamiaceae) is the largest genus in the mint family, and phenotypic diversity of the genus in Africa is largely the result of repeated colonizations of the continent from different sources. Will and Claßen-Bockhoff produce a phylogenetic reconstruction and suggest that parallel character evolution is the rule rather than the exception in Old World Salvia. Notable examples are given by papery, conspicuously coloured calyces and repeated switches from bee- to bird-pollination. Different staminal lever types also evolved in parallel and should not be used any longer for characterizing major clades.
Changes occurring in the macromolecular traits of wood cell wall components of elm (Ulmus species) following an attack by Ophiostoma novo-ulmi (Dutch elm disease) are poorly understood. Ďurkovič et al. examine two elm hybrids with contrasting survival strategies upon infection with the current prevalent strain of the disease (ssp. americana × novo-ulmi) and find that the syringyl-to-guaiacyl ratio in lignin affects the degradability of cellulose by cellulolytic enzymes. When infected, the hybrids respond to medium-molecular weight cellulose degradation with the biosynthesis of high-molecular weight macromolecules of cellulose, resulting in an increase in values for the degree of polymerization and polydispersity. However, only guaiacyl-rich lignin in the tolerant hybrid is involved in a successful defence against the fungus.
Actinidia chinensis var. deliciosa (kiwifruit) is a functionally dioecious species with a highly successful reproductive performance that is impaired by a short effective pollination period. Ferradás et al. look for features of programmed cell death (PCD) in the stigmatic arms and find that in the secretory tissues cell organelles disintegrate sequentially while progressive vacuolization is detected. At the same time, chromatin condensation, nuclear deformation and DNA fragmentation and degradation are observed. These features are are evident in pollinated flowers by the second day after anthesis, but only by 4 days after anthesis in non-pollinated flowers, which corresponds to the effective pollination period. The results indicate that PCD might be accelerated by pollination, suggesting its involvement during the progamic phase.
Plants use diffuse light more efficiently than direct light, but it is often difficult to quantify this experimentally because of confounding effects such as differences in light intensity. Li et al. combine greenhouse studies with model simulations to examine photosynthesis in tomato (Solanum lycopersicum) crops, and conclude that higher production in diffuse light results primarily from a more homogeneous horizontal and vertical light distribution. In addition, plants acclimate to a high level of diffuseness by gaining a higher photosynthetic capacity of leaves in the middle of the crop and a higher leaf area index. Diffuse light also results in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance is high.
Microbial dinitrogen (N2) fixation has been reported as an additional N source for terrestrial carnivorous plant species. Sirová et al. assess the importance of fixed N in the nutrition of rootless, aquatic, carnivorous Utricularia species (bladderworts), and find that although traps harbour abundant N2-fixing micro-organisms and provide conditions highly suitable for N2-fixation, the fixation rates are low and plant uptake of fixed N is negligible. High mineral N concentrations in the traps, resulting from rapid turnover of organic matter, seem to inhibit the N2-fixation process, and thus they conclude that it is unlikely to contribute significantly to the N nutrition of aquatic carnivorous plants under their typical growth conditions.