The biomass-ratio hypothesis states that ecosystem properties are driven by the characteristics of dominant species in the community. Tardif et al. measure decomposition rates of litter from four herb species at three sites along a correlated climatic gradient of temperature and precipitation in order to test the predictive value of the hypothesis. They find that community-weighted means of monoculture values provide good predictions of mixed-species’ litter decomposition, converging to the predicted values with increasing species richness and in climates less favourable to decomposition. The results support the idea that the biomass-ratio hypothesis, operationalized as community-weighted means, could offer the opportunity to predict ecosystems processes at larger spatial scales and in a changing environment.
Elucidating the stoichiometry and resorption patterns of multiple nutrients is an essential requirement for a holistic understanding of plant nutrition and biogeochemical cycling. Liu et al. examine the relationships between resorption patterns of 13 nutrients and leaf nutrient status in eight plant functional types in the karst region of south-western China. They find that four nutrients (N, P, K and Mg) show resorption, seven (B, Ca, Cu, Fe, Mn, Mo and Zn) accumulate in senesced leaves, and two (Na and S) show no resorption or accumulation.The resorption efficiencies of N, P and K and accumulation of Ca and Zn increase with decreasing concentrations of these nutrients in green leaves. The results emphasize the fact that nutrient resorption patterns strongly depend on the element and the plant functional type.
Some tall species of Typha (cattails/bulrushes) are able to withstand hurricane-force winds. Witztum and Wayne dissect leaves of various species and examine the fibre cables – composed of long, non-lignified cells – that traverse the air chambers (lacunae). They find that the cellulose microfibrils that make up the walls of the cable-fibres are oriented parallel to the long axis of the fibres and make the cables strong under tension. Dorsal and ventral leaf surfaces and partitions contain lignified fibre bundles and vascular strands that are strong under compression, and in combination the result is a tensegrity structure that creates wind-resistant ‘multiple load paths’ through which stresses can be redistributed throughout the tall, upright leaves.
Members of the arabinogalactan protein (AGP) gene family have important functions in plant growth and development, especially in plant reproduction. Lin et al. examine expression of Brassica campestris male fertility 8 (BcMF8) in pistils of Chinese cabbage (B. campestris ssp. chinensis), and find that it encodes a putative AGP that is located in the cell wall and is expressed in pollen grains and pollen tubes. Functional interruption of BcMF8 by antisense RNA technology results in misshapen pollen with abnormal intine development and aperture formation, and a decrease in germination percentage. Where germination does occur, pollen tubes are unstable, abnormally shaped and burst more frequently relative to controls. The results suggest a crucial function of BcMF8 in modulating the physical nature of the growing pollen tube wall and in helping to maintain the integrity of the tube wall matrix.
Heteromorphy in flowers has a profound effect on breeding patterns within a species, but little is known about how it affects reproductive barriers between species. Ma et al. study a natural hybrid zone between two heterostylous primrose species, Primula beesiana and P. bulleyana, and find that all hybrid derivatives examined are backcrosses of first or later generations to P. bulleyana, and have the cpDNA of that species.Viable F1s can not be produced with P. bulleyana pollen on P. beesiana mothers. They conclude that partial ecological isolation, inhibition of heterospecific pollen and possibly complete barriers to F1 formation on P. beesiana may be enough to make F1 formation very rare in these species. The hybrid zone may thus have a finite lifespan as successive generations become more similar to P. bulleyana.
Double B-box zinc finger (DBB) proteins are recently identified plant transcriptional regulators that participate in the response to NaCl-induced stress in arabidopsis. Kiełbowicz-Matuk et al.investigate variations in a Solanum DBB protein, SsBBX24, in S. tuberosum and S. sogarandinum and find evidence of trafficking from the nucleus to the cytosol during the light period. SsBBX24 gene expression exhibits circadian cycling under control conditions, with the highest and lowest abundances of both transcript and protein occurring 8 h and 18 h after dawn, respectively. Low temperature, salinity and polyethylene glycol disturb the circadian regulation of SsBBX24 gene expression at the protein level, and the time of the day modulates the magnitude of SsBBX24 expression in response to high salt concentration. They propose that stress-dependent, post-transcriptional mechanisms alter the regulation by the circadian clock of the amount of SsBBX24 in Solanum.
In the mangrove genus Avicennia successive vascular cambia are organized in patches, creating stems with non-concentric xylem tissue surrounded by internal phloem tissue. Robert et al. monitor stem variations in A. marina trees in a natural mangrove forest over the course of one year, and find that patchiness occurs in both the radial growth and the shrinkage and swelling patterns of the stems. Radial increment is affected by fresh water availability rather than tidal inundation. They conclude that the ability to develop successive cambia in a patchy way enables Avicennia trees to adapt to changes in the prevailing environmental conditions, enhancing its survival in the highly dynamic mangrove environment.
Since the advent of molecular phylogenetics, attempts have been made to infer the evolutionary trajectories of chromosome numbers on DNA phylogenies. Sousa et al.combine cytogenetics, using fluorescent in situ hybridization (FISH), and modelling of changing chromosome numbers in a maximum-likelihood framework to study Typhonium, a genus of Araceae with 2n = 24 and 2n = 8, the lowest known count in the family. A combination of a densely sampled phylogeny, ancestral state modelling and FISH reveals that the species with n = 4 is highly derived, with the FISH data pointing to a Robertsonian fusion-like chromosome rearrangement in the ancestor of this species.
MADS-box transcriptional regulators play important roles during plant development. Sun et al. study structural and functional variation of FUL-like (AP1 subfamily), SEP-like and AGL6-like genes in the basal eudicot Epimedium sagittatum and provide a description of EsFUL-like, EsAGL2-1, EsAGL2-2 and EsAGL6-like function divergence and conservation in comparison to a selection of model core eudicots. The results highlight how organization in genomic segments containing A- and E-class genes in sequenced model species has resulted in similar topologies of AP1 and SEP-like gene trees.
Fern classification has been highly unstable in the past, largely because the morphological characters selected for emphasis in higher-level classifications have been variable. Christenhusz and Chase review the history of fern classification, and consider that some classifications based on single characteristics have been useful for identifying species but are highly artificial in terms of their views on relationships, whilst classifications using a suite of characters have been considered more ‘natural’, but with the advance of molecular phylogenetics many of these ‘natural’ groups are also been shown to be highly artificial. They highlight which groups/genera have taxonomic issues that remain to be clarified, and propose the use of broader family concepts. Progress in developing a consensus fern classification is reflected in a new proposed classification.