Rob D. Smissen

Root traits are multidimensional: specific root length is independent from root tissue density and the plant economic spectrum

Summary Root, stem and leaf traits are thought to be functionally coordinated to maximize the efficiency of acquiring and using limited resources. However, evidence is mixed for consistent whole-plant trait coordination among woody plants, and we lack a clear understanding of the adaptive value of root traits along soil resource gradients. If fine roots are the below-ground analogue to leaves, then low specific root length (SRL) and high tissue density should be common on infertile soil. Here, we test the prediction that root, stem and leaf traits and relative growth rate respond in unison with soil fertility gradients. We measured fine root, stem and leaf traits and relative growth rate on individual seedlings of 66 tree species grown in controlled conditions. Our objectives were (i) to determine whether multiple root traits align with growth rate, leaf and stem traits and with each other and (ii) to quantify the relationships between community-weighted mean root traits and two strong soil fertility gradients that differed in spatial extent and community composition. At the species level, fast growth rates were associated with low root and stem tissue density and high specific leaf area. SRL and root diameter were not clearly related to growth rate and loaded on a separate principal component from the plant economic spectrum. At the community level, growth rate was positively related to soil fertility, and root tissue density (RTD) and branching were negatively related to soil fertility. SRL was negatively related and root diameter was positively related to soil fertility on the large-scale gradient that included ectomycorrhizal angiosperms. Synthesis. Root, stem and leaf tissue traits of tree seedlings are coordinated and influence fitness along soil fertility gradients. RTD responds in unison with above-ground traits to soil fertility gradients; however, root traits are multidimensional because SRL is orthogonal to the plant economic spectrum. In contrast to leaves, trees are not constrained in the way they construct fine roots: plants can construct high or low SRL roots of any tissue density. High RTD is the most consistent below-ground trait that reflects adaptation to infertile soil.

A review of genetic analyses of hybridisation in New Zealand

Abstract Hybridisation between related taxa has a range of possible biological consequences, ranging from the production of sterile offspring, through introgression of alleles into populations, to the formation of new species. Examples of plant and animal species hybridising with related taxa abound in the New Zealand region. We review New Zealand examples of hybridisation that have been verified with chromosomal, protein or DNA data. Contemporary hybridisation has been studied at hybrid zones where distinct populations meet and mate in a defined and stable zone of contact. The role of human habitat modification is highlighted with examples of recent range changes that have led to hybridisation and subsequent conservation problems. Hybridisation can result in the swamping of endangered species, although it can also act as a bridge for the transfer of adaptations among lineages. Historical hybridisation in New Zealand has been examined with phylogenetics and there are many examples of organelle introgression or capture. The origin of new species of New Zealand stick insects, ferns and daisies via hybridisation has been demonstrated with cytogenetic and DNA sequence evidence. Thus the importance of hybridisation in the evolution of New Zealands flora and fauna is highlighted.

Phylogenetic analysis of ITS sequences suggests a Pliocene origin for the bipolar distribution of Scleranthus (Caryophyllaceae)

Scleranthus is a genus of about 12 species of herbaceous plants or subshrubs native to Eurasia and Australasia. Here Scleranthus is shown to consist of European and Australasian clades, which diverged within the last 10 million years. Biogeographic implications of this dating and alternative hypotheses explaining the disjunct north-south distribution of the genus, are discussed. The trans-Tasman distributions of S. biflorus and S. brockiei are of recent origin and therefore consistent with long-distance dispersal rather than vicariance explanations. Morphological and ITS sequence data sets are significantly incongruent and trees derived from them differ over relationships among Australasian species. Hybridisation and introgression or lineage sorting are invoked to explain this discordance. Within the family Caryophyllaceae, Scleranthus ITS2 sequences have greater similarity to sequences from representatives of the subfamilies Alsinoideae and Caryophylloideae than to sequences from representatives of the subfamily Paronychioideae. SB01 Phy loal Scl R. D. S

Phylogenetic implications of trans-specific chloroplast DNA sequence polymorphism in New Zealand Gnaphalieae (Asteraceae)

Abstract.The New Zealand endemic species of Gnaphalieae (Asteraceae) present a bewildering array of morphological forms recalcitrant to phylogenetic analysis using molecular or traditional characters. The chloroplast psbA-trnH intergenic spacer is highly variable in this group, with substitutions distinguishing 18 cpDNA haplotypes distributed among samples of Raoulia species and those of related genera. A subset of haplotypes was combined with sequences of the more slowly evolving trnL intron and trnL-trnF intergenic spacer region and subjected to median network and parsimony analyses. Although a number of chloroplast lineages were resolved, these do not correspond with taxonomic units, nor with groups supported by analysis of morphological characters, nor with groups indicated by nuclear rDNA ITS sequences. These data, considered in the context of morphological character state distribution in the group, suggest a complex set of interrelationships among extant species and genera as currently circumscribed. General implications for phylogeny reconstruction are discussed.

Two genetic and ecological groups of Nostoc commune in Victoria Land, Antarctica, revealed by AFLP analysis

Microscopy, DNA sequencing, and amplified fragment length polymorphism (AFLP) were used to examine variation within Nostoc commune from collections between 72 and 78°S in Victoria Land, Antarctica. Although there is considerable bias of collected material towards southern latitudes, and this material varies greatly in age (collected between 1984 and 2004), an important new phylogeographic pattern was found. DNA sequencing of the tRNAleu(UAA) region, used recently to define form species N. commune, revealed little variation between collections. AFLP analysis, however, split the collected material according to habitat (irrigated soil communities versus ponds), rather than latitude. These results suggest that environmental factors linked to latitude are not the greatest drivers of genetic variation in Victoria Land. These may operate at a lower level but would require intensive sampling within narrowly defined habitat types at a range of latitudes to uncover. We advocate extensive sampling across local environmental gradients based on water availability, comparative culturing, and development of sequence characterised amplified regions (SCARs) across a range of latitudes in future seasons of the Latitudinal Gradient Project.

Use of ISSR profiles and ITS-sequences to study the biogeography of alpine cushion plants in the genus Raoulia (Asteraceae)

AbstractNuclear ITS sequences and ISSR profiles provide evidence that Raoulia rubra is endemic to the Tararua Range in the southern part of the North Island of New Zealand. Populations in the South Island previously ascribed to R. rubra are better ascribed to R. eximia. Our findings suggest that glaciation of the central mountains of the South Island during the last ice age have had a major impact on the evolution of the South Island cushion Raoulia species in New Zealand. However, simple hypotheses accounting for the effect of Pleistocene climate change are insufficient to explain patterns of endemism in the group.

Phylogeny and biogeography of Craspedia (Asteraceae: Gnaphalieae) based on ITS, ETS and psbA-trnH sequence data

A phylogenetic analysis based on a combined dataset of three genes, nuclear 18S rDNA and plastid rbcL and atpB, indicates that the enigmatic Neotropical genus Metteniusa is a member of the lamiid (euasterid I) clade. The genus appears as an isolated taxon near, but perhaps not related exclusively to, Oncothecaceae, which supports its recognition as a separate family.

Intraspecific Relationships among Wood Density, Leaf Structural Traits and Environment in Four Co-Occurring Species of Nothofagus in New Zealand

Plant functional traits capture important variation in plant strategy and function. Recent literature has revealed that within-species variation in traits is greater than previously supposed. However, we still have a poor understanding of how intraspecific variation is coordinated among different traits, and how it is driven by environment. We quantified intraspecific variation in wood density and five leaf traits underpinning the leaf economics spectrum (leaf dry matter content, leaf mass per unit area, size, thickness and density) within and among four widespread Nothofagus tree species in southern New Zealand. We tested whether intraspecific relationships between wood density and leaf traits followed widely reported interspecific relationships, and whether variation in these traits was coordinated through shared responses to environmental factors. Sample sites varied widely in environmental variables, including soil fertility (25–900 mg kg–1 total P), precipitation (668–4875 mm yr–1), temperature (5.2–12.4 °C mean annual temperature) and latitude (41–46 °S). Leaf traits were strongly correlated with one another within species, but not with wood density. There was some evidence for a positive relationship between wood density and leaf tissue density and dry matter content, but no evidence that leaf mass or leaf size were correlated with wood density; this highlights that leaf mass per unit area cannot be used as a surrogate for component leaf traits such as tissue density. Trait variation was predicted by environmental factors, but not consistently among different traits; e.g., only leaf thickness and leaf density responded to the same environmental cues as wood density. We conclude that although intraspecific variation in wood density and leaf traits is strongly driven by environmental factors, these responses are not strongly coordinated among functional traits even across co-occurring, closely-related plant species.

DNA fingerprinting supports hybridisation as a factor explaining complex natural variation in Phormium (Hemerocallidaceae)

Abstract Analysis of AFLP profiles from 47 wild‐sourced plants of Phormium from New Zealand and Norfolk Island reveals two major genetic groups corresponding with the two currently recognised and sympatric species (P. cookianum and P. tenax). In addition, plants from a number of coastal sites, a putative F1 hybrid, and some plants identified a priori as P. cookianum display AFLP profiles consistent with a hybrid origin. These putative hybrid plants have varying genomic composition, and some were collected from morphologically uniform populations. Others depart from the intermediate morphology expected of F1 hybrids. Therefore, introgression between P. cookianum and P. tenax and the existence of stabilised hybrid derivatives appears likely. Some degree of geographic structuring of genetic diversity is evident in both species.

When do plant radiations influence community assembly? The importance of historical contingency in the race for niche space

Plant radiations are widespread but their influence on community assembly has rarely been investigated. Theory and some evidence suggest that radiations can allow lineages to monopolize niche space when founding species arrive early into new bioclimatic regions and exploit ecological opportunities. These early radiations may subsequently reduce niche availability and dampen diversification of later arrivals. We tested this hypothesis of time-dependent lineage diversification and community dominance using the alpine flora of New Zealand. We estimated ages of 16 genera from published phylogenies and determined their relative occurrence across climatic and physical gradients in the alpine zone. We used these data to reconstruct occupancy of environmental space through time, integrating palaeoclimatic and palaeogeological changes. Our analysis suggested that earlier-colonizing lineages encountered a greater availability of environmental space, which promoted greater species diversity and occupancy of niche space. Genera that occupied broader niches were subsequently more dominant in local communities. An earlier time of arrival also contributed to greater diversity independently of its influence in accessing niche space. We suggest that plant radiations influence community assembly when they arise early in the occupancy of environmental space, allowing them to exclude later-arriving colonists from ecological communities by niche preemption.