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.
The relative ability of different plant taxa to invade new biogeographic regions successfully is dependent upon a number of biological and physical factors, one of which is the reproductive system, which directly influences population structure, gene flow and evolutionary potential. Considering seed formation, plants can reproduce through sex (selfing and outcrossing) or apomixis (asexual reproduction through seed.
St. John’s wort (Hypericum perforatum) is such an invasive species which is indigenous to central and eastern Europe; it is self-compatible and can reproduce through sex or apomixis. H. perforatum has successfully invaded North America since the first record of introduction in Lancaster, Pennsylvania in 1793. Its high genotypic plasticity in conjunction with variable levels of facultative apomixis are hypothesized to have contributed to its rapid spread throughout the continent. For example, in an analysis of multiple phenotypic traits, Maron et al. (2004) demonstrated that the introduction of H. perforatum into North America was accompanied by rapid climatic adaptation.
Using an analysis of a collection of European native and North American invasive accessions, a recent paper in Molins Annals of Botany examines biogeographic differentiation in both natural and introduced populations, and test whether variation in apomixis traits is correlated with the propensity for H. perforatum to invade novel environments.
Molins, M.P., Corral, J.M., Aliyu, O.M., Koch, M.A., Betzin, A., Maron, J.L., & Sharbel, T.F. (2014) Biogeographic variation in genetic variability, apomixis expression and ploidy of St. John’s wort (Hypericum perforatum) across its native and introduced range. Annals of Botany, 113 (3): 417-427 doi: 10.1093/aob/mct268.
St. John’s wort (Hypericum perforatum) is becoming an important model plant system for investigations into ecology, reproductive biology and pharmacology. This study investigates biogeographic variation for population genetic structure and reproduction in its ancestral (European) and introduced (North America) ranges. Over 2000 individuals from 43 localities were analysed for ploidy, microsatellite variation (19 loci) and reproduction (flow cytometric seed screen). Most individuals were tetraploid (93 %), while lower frequencies of hexaploid (6 %), diploid (<1 %) and triploid (<1 %) individuals were also identified. The presence of pure and mixed populations representing all three genetic clusters in North America demonstrates that H. perforatum was introduced multiple times onto the continent, followed by gene flow between the different gene pools. Taken together, the data presented here suggest that plasticity in reproduction has no influence on the invasive potential of H. perforatum.
Understanding the species composition of pollen on pollinators has applications in agriculture, conservation and evolutionary biology, but current identification methods cannot always discriminate taxa at the species level. Kron et al. test the use of flow cytometry to characterize pollen loads from individual bees, using DNA content as a species marker, and find that they are able to quickly measure DNA contents for nuclei from hundreds to thousands of pollen grains per bee. They observe differences in pollen load diversity between bumble-bees and honey-bees and find evidence of between-cytotype pollinator movement in a population of Solidago. This technique provides a new tool to complement other methods for examining pollinator behaviour.