Defence dichotomy: coping with herbivores in air and water (Review)
Plant defence against herbivores is a crucial theme in the evolution of both plants and animals, yet it is expressed very differently in water and on land. Spines, hairs, and distance signalling are common in land plants but very rare in submerged aquatic plants. To account for this hitherto unrecognized dichotomy, Vermeij (pp. 1099–1109) suggests that animal sensory capacities are in part to blame. Herbivores, pollinators and plant dispersers on land often rely on long-range visual or olfactory signals, whereas aquatic herbivores do so on a much smaller scale, all because of the contrasting properties of air and water. Both contact and long-range defences of plants are much more developed in land plants, whose ecological connections with animals are far more complex than in water. Host specialization by small herbivores is very high on land, but generally less in marine ecosystems, especially in the tropics.
Temperature requirements of pollen germination shape species distributional ranges
Although plant distribution patterns are well documented, our understanding of the ecophysiological mechanisms that control the geographical ranges of plant species remains poor. Using a largely ignored method, the performance of the male gametophyte in vitro, Rosbakh and Poschlod (pp. 1111–1120) assessed whether the thermal range of pollen germination and tube growth control species distribution ranges along an elevational gradient. They found a strong and positive relationship between temperature conditions at collection sites and the minimum temperature for both pollen germination and pollen tube growth. In addition, a significant correlation between maximum temperature of pollen tube growth and temperature of flowering month was apparent.
Enhanced water stress tolerance of plum plants transformed with cytosolic ascorbate peroxidase genes
Cytosolic antioxidant enzymes are a target to give durable resistance to water stress in commercial plum trees. Diaz-Vivancos et al. (pp. 1121–1131) show improved tolerance to moderate or severe drought in transgenic lines, correlating with reduced leaf-drop, better photosynthetic performance (PSII quantum yield) and a tighter control of water use efficiency. The two lines transformed with multiple copies of superoxide dismutase and ascorbate peroxidase genes suggested an enhanced capacity to cope with drought-induced oxidative stress. The transformed lines may be a valuable rootstock for improving plum crop yields in adverse environments.
Selection and evolution of flower colour
We currently know little about the evolution of flower colour when multiple pigment families are present. Ellis and Field (pp. 1133–1140) examined the patterns of evolutionary transitions between anthocyanin-pigmented (red, pink, blue and purple) and yellow flowers in the tribe Antirrhineae. A phylogenetic comparative analysis points to selection for either yellow or anthocyanin pigmentation at different times. Nevertheless, these transitions are constrained to move through an unpigmented intermediate step. These findings suggest fluctuating selection favouring flowers with a single pigment over those with zero or two pigments.
Photosynthesis in midrib and interveinal lamina
Except in C4 plants, photosynthetic activity is attributed mainly to leaf mesophyll cells, and photosynthesis in veins of C3 and CAM (Crassulacean acid metabolism) plants is usually neglected. Kuźniak et al. (pp. 1141–1151) studied the photosynthesis-related properties of the midrib and the interveinal lamina cells in leaves of Mesembryanthemum crystallinum, a C3-CAM intermediate plant. The vascular system of C3- and CAM-performing plants contained photosynthetically-competent parenchyma cells but with limited photosynthetic activity. The midrib chloroplasts resembled those in the bundle sheath of C4 plants. The authors propose different metabolic roles for midrib chloroplasts in C3 and CAM plants of M. crystallinum.
Response of desert moss to increasing nitrogen deposition
Syntrichia caninervis dominates species in moss crusts in many northern hemisphere desert ecosystems, which are facing disturbance from increasing N deposition. Zhang et al. (pp. 1153–1161) give evidence from simulated N deposition experiments suggesting that low amounts of added N increase shoot length and leaf size of S. caninervis, whereas high doses reduce almost all growth parameters. Moss shoot density increased but population biomass decreased with high N. Responses of physiological parameters were similar to the growth indices. Therefore, low amounts of added N (0–0.5 g N m–2 year–1) may enhance moss growth and vitality, while higher amounts have detrimental effects.
Tree crown architecture and ice accretion
Despite a longstanding interest in tree species’ vulnerability to ice storms, analyses of the influence of crown structure on within-crown variation in ice accretion are rare. Nock et al. (pp. 1163–1173) test the hypothesis that intra-crown ice accretion can be predicted by a measure of sheltering by neighbouring branches. Empirical results and simulations confirmed a key role for crown architecture in determining intra-crown ice accretion. As suspected, droplets are attenuated by passage through the crown, and thus higher branches accumulate more ice. This is the first step in developing a modelling approach to investigating intra-crown and inter-specific variation in freezing rain damage.
Whole plastid genomes and nrDNA of Diospyros species from New Caledonia
Some plant groups, especially on islands, have been shaped by strong ancestral bottlenecks and rapid, recent radiation of phenotypic characters. Turner et al. (pp. 1175–1185) have used complete plastid genomes and nrDNA to unravel phylogenetic relationships between 22 closely related Diospyros species from New Caledonia. The structure of the phylogenetic trees constructed indicates those species as being most probably the result of rapid radiation. A significant geographic clustering of the genetic information, especially from plastid genomes, was found. This could indicate transfer of plastid genomes due to hybridization and introgression following secondary contact.
Core business: X-ray CT toolchain for tree-ring analysis
Disentangling tree growth requires more than ring width only. Although X-ray densitometry is an established technique to determine key wood density parameters, tedious manual procedures hamper fast analyses. De Mil et al. (pp. 1187–1196) present an X-ray computed tomography toolchain to enable high-throughput density profiling of large sets of increment cores. The obtained 3D archive is analysed via software routines with which traditional tree-ring analysis as well as semi-automated density-based pattern matching can be performed. The toolchain allows fast assessment of newly sampled increment cores, without any surface treatment or visual inspection. This offers the opportunity for large-scale screening of lesser-studied tree species, and improving current chronologies with sub-annual density information.
Competition effects on plastic and genotypic responses to [CO2]
Plant–plant interactions could mediate vegetation responses to rising atmospheric CO2 concentration ([CO2]), because some plants benefit more from [CO2] elevation than others. We investigated how changes in performance due to elevated [CO2] are modified by aboveground plant–plant interactions. Van Loon et al. (pp. 1197–1207) grew Plantago asiatica seeds originating from natural [CO2] springs and from ambient [CO2] in mono-stands of both origins as well as mixtures of both origins in climate rooms under different [CO2] levels. Their results showed that plant performance to elevated [CO2] was mainly determined by plastic responses and not by genotypic responses. However, this pattern was highly modified by plant–plant interactions.
Do sequence repeats undermine plastid genome stability?
Although a few plant lineages have lost one copy of the plastid genome (plastome) inverted repeat (IR), its near ubiquity among streptophytes has fostered speculation about its functional role and consequent evolutionary significance. To evaluate hypotheses of its persistence, Blazier et al. (pp. 1209–1220) sequenced plastomes of Erodium (Geraniaceae), where several species have lost the IR structure and found that the plastomes of one derived clade surprisingly contained a large IR. Comparative analyses across the genus suggest that the IR per se does not stabilize plastome structure but rather, like bacterial endosymbiont genomes, increased proportions of non-IR recombinogenic repeats likely contribute to genomic instability in Erodium.
Soil seed bank assembly at multiple scales
In gypsum soil communities, above-ground vegetation and seed banks are tightly connected, but mechanisms involved in their organization may differ. Peralta et al. (pp. 1221–1228) investigated the effects of water addition, biological soil crust cover (BSC), above-ground vegetation and the Stipa tenacissima tussocks on soil seed banks at two spatial scales. BSC has a filtering role at fine spatial scale on seed bank structure: it decreased seed abundance and species richness in the persistent seed bank, and it determined complete seed bank species composition. The heterogeneity of BSCs promotes niche differentiation and thereby potentially enhances species coexistence and species diversity.
Gas exchange measurements on Miscanthus leaves
Miscanthus has a high yield potential, but even though it is less cold sensitive than other C4 species, it emerges later in spring than C3 species. Xiurong et al. (pp. 1229–1239) identified one Miscanthus sacchariflorus with a level of cold tolerance similar to Miscanthus × giganteus. They also found a positive linear correlation between net photosynthesis and shoot growth rate as well as specific leaf area. These are relatively easy to measure and useful for the screening of productivity and cold tolerance. The Miscanthus genotype with high cold tolerance can be useful for breeding of new interspecies hybrids or cultivation in temperate climates.
Is hyperaccumulation of nickel worthwhile in non-serpentine soils?
Ni-hyperaccumulating species produce high-Ni litters and potentially influence important ecosystem processes such as decomposition. According to the elemental allelopathy hypothesis of hyperaccumulation, the restriction of the majority of metal hyperaccumulators in metaliferous soils may be dependent on litter decomposition. Adamidis et al. (pp. 1241–1248) using for the first time mixed-species litters containing hyperaccumulated Ni: (1) indicate the presence of Ni-resistant decomposers on serpentine soil, (2) demonstrate the selective decomposition of low-Ni parts of litters on non-serpentine soils and (3) give support to the elemental allelopathy hypothesis, presenting the potential selective advantages acquired by metal hyperaccumulators through litter decomposition on serpentine soils.