Peter Bannister

Altitudinal variation in stomatal conductance, nitrogen content and leaf anatomy in different plant life forms in New Zealand

SummaryThis study is part of a series of investigations on the influence of altitude on structure and function of plant leaves. Unlike most other mountain areas, the Southern Alps of New Zealand provide localities where physiologically effective moisture stress occurs neither at high nor at low elevation, but the changes in temperature and radiation with elevation are similar or even steeper than in most other regions. In comparison with results from other mountains, where moisture may impair plant functioning at low elevation, this study allows an estimation of the relative role of water for the expression of various leaf features typically associated with alpine plants. Maximum leaf diffusive conductance (g), leaf nitrogen content (LN), stomatal density (n) and distribution, as well as area (A), thickness (d) and specific area (SLA) of leaves were studied. Three different plant life forms were investigated over their full altitudinal range (m): trees, represented by Nothofagus menziesii (1,200 m), ericaceous dwarf shrubs (1,700 m), and herbaceous plants of the genus Ranunculus (2,500 m). In all three life forms g, LN, and n increased, while SLA and A decreased with elevation. Recent investigations have found similar trends in other mountains from the temperate zone, but the changes are larger in New Zealand than elsewhere. Herbs show the greatest differences, followed by shrubs and then trees.It is concluded that g is dependent upon light climate rather than water supply, whereas SLA and related structural features appear to be controlled by the temperature regime, as they show similar altitudinal changes under different light and moisture gradients. The higher leaf nitrogen content found at high elevations in all three life forms, suggests that metabolic activity of mature leaves is not restricted by low nitrogen supply at high altitude. In general, the leaves of herbaceous plants show more pronounced structural and functional changes with altitude than the leaves of shrubs and trees.

Will loss of snow cover during climatic warming expose New Zealand alpine plants to increased frost damage

If snow cover in alpine environments were reduced through climatic warming, plants that are normally protected by snow-lie in winter would become exposed to greater extremes of temperature and solar radiation. We examined the annual course of frost resistance of species of native alpine plants from southern New Zealand that are normally buried in snowbanks over winter (Celmisia haastii and Celmisia prorepens) or in sheltered areas that may accumulate snow (Hebe odora) and other species, typical of more exposed areas, that are relatively snow-free (Celmisia viscosa, Poa colensoi, Dracophyllum muscoides). The frost resistance of these principal species was in accord with habitat: those from snowbanks or sheltered areas showed the least frost resistance, whereas species from exposed areas had greater frost resistance throughout the year. P. colensoi had the greatest frost resistance (−32.5°C). All the principal species showed a rapid increase in frost resistance from summer to early winter (February–June) and maximum frost resistance in winter (July–August). The loss of resistance in late winter to early summer (August–December) was most rapid in P. colensoi and D. muscoides. Seasonal frost resistance of the principal species was more strongly related to daylength than to temperature, although all species except C. viscosa were significantly related to temperature when the influence of daylength was accounted for. Measurements of chlorophyll fluorescence indicated that photosynthetic efficiency of the principal species declined with increasing daylength. Levels of frost resistance of the six principal alpine plant species, and others measured during the growing season, were similar to those measured in tropical alpine areas and somewhat more resistant than those recorded in alpine areas of Europe. The potential for frost damage was greatest in spring. The current relationship of frost resistance with daylength is sufficient to prevent damage at any time of year. While warmer temperatures might lower frost resistance, they would also reduce the incidence of frosts, and the incidence of frost damage is unlikely to be altered. The relationship of frost resistance with daylength and temperature potentially provides a means of predicting the responses of alpine plants in response to global warming.

The vegetation of roadside verges with respect to environmental gradients in southern New Zealand

. A survey of the vegetation of roadside verges was made across the southern part of the South Island of New Zealand. Samples were taken at 10-km intervals along selected roads providing a climatic range from the suboceanic conditions of the east coast into semi-arid Central Otago, and from Central Otago through the Southern Alps to the hyper-oceanic areas of high rainfall on the west Coast. The variation in the floristic composition is associated mainly with variation in rainfall, continentality, altitude, soil acidity, soil organic matter, and presence of forest. Sites in the arable and pastoral regions on the eastern side of the Southern Alps support a herbaceous vegetation consisting mostly of exotic species of European origin, with a few native grasses scattered through the drier and less fertile sites. A greater proportion of native species is found at higher altitudes. Roadside vegetation in the area of high rainfall to the west is characterized by indigenous ferns and woody species, although vegetation adjacent to cleared areas is more similar to that on roadsides adjacent to farmland on the east coast. The pattern of distribution of both native and exotic species is strongly related to altitudinal and climatic gradients, and the environmental responses of the exotic species are similar to those recorded in Europe. This suggests a colonization of all available sites by the exotic species, despite the relatively short time since their introduction to New Zealand, rather than an incomplete invasion.

Godley review: A touch of frost? Cold hardiness of plants in the southern hemisphere

Abstract This review contrasts the frost resistance of plants from the Southern Hemisphere with that of the Northern Hemisphere and is principally concerned with plants from New Zealand, Australia, and South America. It gives a brief overview of methods for determining frost resistance in the field and in controlled environments with intact or excised plant parts. It considers various methods of determining frost resistance and the expression of critical temperatures causing damage, and discusses the problems of using excised plant parts and freezing of tissues. This review, however, is not principally concerned with physiological aspects of frost resistance, but more with biogeographic aspects of the environment and quantification of the relationships between frost resistance and temperature related factors such as altitude and latitude. It gives examples of differences in frost resistance between the two hemispheres and attributes these to the contrast between the climates of largely continental land masses in the Northern Hemisphere and the oceanic environment of the Southern Hemisphere. Furthermore, it also shows similarities between the frost resistance of plants from the Southern Hemisphere during the growing season and the maximum frost resistance of tropical alpine species and further similarities between species on oceanic islands in both hemispheres. Comprehensive lists of species’ frost resistance are included in tables and appendices.

Carbon and nitrogen isotope ratios, nitrogen content and heterotrophy in New Zealand mistletoes

The carbon isotope ratio (δ13C) of New Zealand mistletoes (–29.51±0.10‰) and their hosts (–28.89±0.12‰) is generally more negative, and shows less difference between mistletoes and their hosts, than found in previous studies. In 37% of the examined pairs, the δ13C of mistletoes was less negative than that of their hosts. These reversals were not associated with the relative position (proximal or distal) of the host material with regard to the mistletoe. Differences between host and mistletoe tended to be greater on hosts with less negative δ13C. Both nitrogen content and isotope ratio (δ15N) of the mistletoe leaves were strongly correlated with those of their hosts. Nitrogen contents of mistletoe leaves were similar to those of their hosts at low nitrogen contents but proportionately less on hosts with a high nitrogen content, whereas δ15N of mistletoes was consistently similar to that of their hosts. The δ13C of mistletoes was related to both host nitrogen content and δ15N, but δ13C in host tissue was related to neither, suggesting that the mistletoes derived both nitrogen and carbon from their hosts. The δ13C of both hosts and mistletoes were significantly related to leaf conductance and carbon dioxide concentration but relationships with transpiration and water use efficiency were not significant. In all cases there was no clear separation between the responses of hosts and mistletoes. This may be related to the similarity of stomatal conductance, transpiration and photosynthesis in the studied mistletoes and their hosts and is consistent with the small differences in δ13C between mistletoes and hosts found in this study. Consequently, the estimation of mistletoe heterotrophy from carbon discrimination is confounded, as the small difference between host and mistletoe carbon discrimination could equally well result from either similarities in photosynthesis and water relations or heterotrophic assimilation of host-derived carbon. The differences between our study and previous studies (which are mostly from seasonally dry or semi-arid to arid environments) may be related to the temperate environment in which these mistletoes grow. Water is freely available so that the mistletoe is able to obtain sufficient water and dissolved nutrients without having to maintain the high transpiration rate and low water potentials that are needed to extract water from a water-stressed host. Similarly, mistletoe photosynthesis is less inhibited by water stress. The physiological similarities between mistletoe and hosts from a temperate environment are reflected in their similar δ13C values.

Frost Resistance and the Distribution of Conifers

The distribution of plants is well correlated with climate. For example, Koppen’s (1936) climate classification is based on major biomes which are subdivided with respect to various relationships between temperature and precipitation, whilst Thornthwaite’s (1948) classification is based on potential evapo-transpiration. The distribution of major vegetation types is explained and even predicted by such classifications. Resistance to low temperatures, however, operates at the species level, and the distribution of species is strongly related to their resistance to winter frosts (Sakai and Larcher 1987; Larcher 1995). Species from cold climates are likely to have high resistance to frost while those from warmer climates are less frost hardy. Consequently, a classification of climate that takes minimum temperatures into account is most likely to be correlated with frost resistance of species. In horticulture, the concept of plant hardiness zones is well established. These zones are based on the lowest mean air temperatures of the coldest month and, as their first usage was in the USA (Rehder 1940), are based on the Fahrenheit scale of temperature. The U.S. Department of Agriculture (USDA) refined the method and adopted 11 hardiness zones — from Zone 1 with mean minimum air temperatures of less than −50°F with incremental bands of 10°F until Zone 10 (30–40°F) and finally Zone 11 (>40°F) (see Appendix; Rehder 1940; Huxley et al. 1992).

Flowering and Shoot Extension in Heath Plants of Different Geographical Origin

(1) Plants of Calluna vulgaris, Erica cinerea and E. tetralix collected from a wide range of sites (mostly British, but including one from Spain) were grown in experimental plots in Stirling. Flowering was observed from 1972 to 1975 and shoot extension was measured in 1974. (2) In Calluna and Erica cinerea late flowering tended to be associated with a warm, southerly site of origin, and early flowering with a cooler, northern site of origin, while in E. tetralix early flowering was associated with a prostrate growth form and small shoot increments. (3) In all three species the date of flowering was positively correlated with the date at which shoots reached 50% of their maximum extension, whilst in Calluna and Erica cinerea plants with a rapid rate of extension tended to originate from cooler and more northerly climates.

Ice formation and foliar frost resistance in attached and excised shoots from seedlings and adult trees of Nothofagus menziesii

Abstract Freezing in leaves of N menziesii was monitored by experimental freezing of attached twigs and seedlings growing naturally in a forest site and compared with a routine laboratory test in which excised plant material was used. Major differences in ice nucleation were observed: ice formed in attached leaves in situ at temperatures that were on average 4°C higher than in excised leaves, in both seedlings and adult trees. Excision did not affect the symptoms of frost damage. Mean foliar frost resistance was 2°C lower in seedlings than in mature shoots, and about 1°C lower in shoots measured in situ than in excised shoots.

The frost resistance of juvenile and adult forms of some heteroblastic New Zealand plants

Abstract Many New Zea1and trees are heteroblastic, with juvenile forms that differ markedly from the fom Of the adu1t tree. Their phase change ‘Orresponds with the transition from cold air near the ground to warmer air above. Heteroblastic species, therefore, might be expected to have juvenile forms that are more frost resistant than their mature forms. Juveni1e forms of Streblus heteroPhYllus and so‐phora microphylla were more frost resistant than their mature forms and the juvenile and adult forms of the homoblastic Pittosporum eugenioides showed no consistent differences in their frost resistance. Juvenile forms of Carpodetus serratus, Hoheria angustifolia, P1agianthus regius, and Pseudopanax crassifolius were less frost resistant than their mature counte∼ms. We conc1ude that juvenile foms are not inherently more frost resistant than their equivalent mature forms and note that populations of the same species from different environments readily acquire the frost resistance appropriate to their habitat.

The winter hardening and foliar frost resistance of some New Zealand species of Pittosporum

Abstract The foliar frost resistance of Pittosporum eugenioides, P. obcordatum, P. tenuifolium, and P. crassifolium increased from -6°C to -8°C in March and April to between -9°C and -10°C in July. Leaves of P. obcordatum had the lowest frost resistance (-7°C) in April, but showed the highest resistance (<-10°C) in July. The foliar frost resistance of P. eugenioides is greater than that previously recorded, similar to that of P. crassifolium and P. tenuifolium, and is consistent with the widespread distribution of this species within New Zealand. The relatively high frost resistance of leaves of P. obcordatum is in accord with its occurrence in frost-prone habitats. Seedlings of P. eugenioides subjected to short days and night-time temperatures around 0°C became about 1°C more frost resistant than untreated seedlings in autumn (April and May). The maximum frost resistance (-11°C) attained by treated seedlings of this species was no greater than that of untreated seedlings, but was 2°C greater than that of...