Heterodichogamy, a dimorphism in which two morphs coexist in a population and undergo synchronous reciprocal sex changes, is an extremely rare and poorly understood sexual system. Fukuhara and Tokumaru study Platycarya strobilacea (Juglandaceae) and demonstrate that it is heterodichogamous based on observations of inflorescence architecture, sexual expression and pollination biology. Pollination by thrips is suggested by their frequent presence with attached pollen grains, the scarcity of other insect visitors, the synchronicity of thrips number in male spikes with the maturation of female flowers, and the morphological characters shared with previously reported thrips-pollinated plants.
Many aquatic species with stylar polymorphisms have the capacity for clonal and sexual reproduction. Haddadchi et al. study differences between a monomorphic population of Nymphoides montana and polymorphic populations. They find that very few seeds are produced in the monomorphic population due to dysfunctional pollen and ovules, and that stigma–anther separation is minimal. ISSR results show that the monomorphic population is one large, single-ramet genotype, unlike the multi-genotypic fertile polymorphic populations. Evolutionary loss of sex in a clonal population in which a mating morph is absent is evident, and under these conditions clonal growth may assure reproduction and expand the population via spreading stolons.
Traits affecting the form and function of fine roots in woody plants show complex phenotypic variation. Lee et al. manipulate root segments of 2-year-old Acer rubrum and Quercus rubra seedlings in order to compare functional traits and trait plasticities in fine root tissues with natural and reduced levels of colonization by microbial symbionts. They find negligible plasticity for root diameter, branching intensity and nitrogen concentration across both species between levels of colonization. Roots with reduced colonization have decreased tissue density and increased specific root length, but species differences are significant and greater than treatment effects in traits other than tissue density. If common, such a result would greatly simplify and strengthen ecosystem- and community-level investigations that require information about the costs and benefits of constructing and maintaining fine root tissues.
Biomass allocation patterns are important to ecosystem carbon cycles, and differ among species and in response to nutrient availability. Zhou et al. examine responses of ephemeral and annual plant species to different levels of nitrogen application in a desert environment, and find that compared to annuals, ephemerals grow more rapidly, increase shoot and root biomass with increasing nitrogen application rates and significantly decrease root/shoot quotients. However, an isometric log shoot vs. log root scaling relationship is maintained across all species. The results contribute to understanding how native species respond to N pollution and highlight that different life history strategies respond differently to nitrogen application.
In some species, epicotyl dormancy break in seeds that have deep simple epicotyl morphophysiological dormancy requires a certain root length to be attained, but the mechanisms associated with this are unclear. Hao et al.study seeds of Tibetan peony (Paeonia ludlowii) and find that a root length of ≥6 cm is necessary before dormancy can be released by cold stratification. They determine that root length increases the ratio of GA3/ABA of the epicotyl in the seeds, with ABA accumulation decreasing with increasing root length. They conclude that the epicotyl becomes sensitive to cold stratification once a certain ratio is reached.
Knowledge about the interacting effects of various global-change drivers on sexual reproduction of plants, one of their key mechanisms to cope with change, is limited. Gruwez et al. study common juniper (Juniperus communis), a poorly regenerating and hence threatened species, to determine the impact of various factors associated with global change on key stages in reproduction. They find that negative effects of increasing temperature and atmospheric depositions on seeds mostly became visible after embryo development, when seeds are ripe and ready for dispersal. However, damaging influences begin during the development of the gamethophytes and around the fertilization period. They suggest that the failure of natural regeneration in many European juniper populations may be attributable to climate warming as well as high atmospheric deposition of nitrogen and sulphur.
Shining a laser onto biological material produces light speckles, and patterns of such biospeckle activity reflect changes in cell biochemistry, developmental processes and responses to the environment. Ribeiro et al. use a portable laser and a digital microscope to observe in situ biospeckle activity in roots of Zea mays, Jatropha curcas and Citrus limonia, and find that when a root encounters an obstacle the intensity of biospeckle activity decreases abruptly throughout the root system. The response becomes attenuated with repeated thigmostimuli. The data suggest that at least one component of root biospeckle activity results from a biological process, which is located in the zone of cell division and responds to thigmostimuli. The methodology presented is relatively inexpensive and portable, the analysis can be automated and the technique provides a rapid and sensitive functional assay.
Annual plants must increase root water uptake during development to match an increasing transpirational water loss by the shoot. Suku et al. study barley (Hordeum vulgare) plants during the early stages of vegetative development (9–28 d old) to determine by what means root water uptake is increased. They analyse individual roots, entire root systems and intact plants using a range of experimental approaches and find that although root hydraulic conductivity (representing root water uptake properties and including aquaporin function) increases in younger plants, the main means by which water uptake is increased during development is via an increase in root surface area.
Soybean (Glycine max) is a typical short-day plant and several loci controlling flowering have been characterized. Whilst genes have been identified for loci E1 to E4, their degree of natural variation is unknown. Tsubokura et al. determine the sequences of these genes and their flanking regions for 39 accessions by primer walking, and perform systematic discrimination among alleles using DNA markers. Allelic combinations at the E1 to E4 loci are found to be associated with ecological types and about 62–66 % of variation of flowering time can be attributed to the loci. The results therefore suggest the existence of unidentified genes for flowering in soybean.
Ipomopsis aggregata and I. tenuituba are two sister species that frequently produce natural hybrids. Bischoff et al. study floral scent in parental species and natural hybrids to explore potential scent mediation of prezygotic and postzygotic reproductive isolation. They find that there is qualitative overlap in the floral bouquets, yet the quantitative emission rates differ. A striking difference is the compound indole, emitted almost exclusively by I. tenuituba at night. Emissions by hybrids are highly variable, and not generally intermediate between the parents, although indole emissions are intermediate. The indole signal could potentially serve as a hawkmoth attractant that mediates reproductive isolation both before and after hybrid formation.