No description available.

This thesis focuses on the impact of elevated ozone (O3) and/or nitrogen (N) on semi-natural vegetation, with an emphasis on C-partitioning within and between plant and soil. The project reports several studies allied to the exploration of the impacts of elevated O3 and N employing short-term studies in laboratory-based controlled-environment chambers and solardomes plus long-term studies at free-air O3 fumigation sites in the Swiss Alps and at Keenley Fell, Northumberland, UK. A solardome study indicated that both the grass Dactylis glomerata, and the forb Ranunculus acris exhibited increased senescence, and reduced C-allocation below-ground, when exposed to elevated [O3]. Furthermore, N exacerbated the O3-induced reduction in the root biomass of D. glomerata. This finding led to a mechanistic exploration of C-partitioning in response to short-term (three week) exposure of D. glomerata to a combination of elevated O3 and N inputs in self-built fumigation chambers. Plants were pulse-labelled with 14C, and the fate of the recent photosynthate then traced in nine plant and soil C-pools. The study revealed a reduction in below-ground respiration (incorporating root and soil microbial respiration) in high N treated plants, and a significant antagonistic interaction between O3 and N effects on soil microbial biomass. To relate the findings to below-ground responses in an intact ecosystem, impacts of long-term O3 and N exposure on soil microbial community diversity and C metabolism were investigated in a sub-alpine grassland. Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis and Community Level Physiological Profiling (CLPP) using 14C labelled root exudate substrates and leaf litter, revealed no effects of O3 and N on the soil bacterial diversity, and limited impacts on C substrate turnover. Moreover, in a long-term study on a traditional UK haymeadow, three years of elevated O3 and N inputs did not result in significant changes in above-ground biomass of any plant functional group. However, a significant O3 x N interaction on below-ground biomass of the sward was observed with reduced root biomass in high [O3] plots. The variation in cover of individual plant species was not explained by either O3 or N when analysed by redundancy analysis (RDA). Overall, this study suggests that N deposition subtly modifies vegetation responses to O3 stress and highlights the potentially significant role played by rising levels of N deposition and O3 as drivers of changes in carbon allocation in the natural environment. Key words: Ozone; nitrogen; carbon allocation; grassland; microbial diversity

The pattern of the deposition of lead (Pb) from motor exhausts on roadside vegetation from nine verges in rural Leicestershire is described. This is shown to be a function of proximity to traffic, reactions of airborne Pb with time and predominant wind characteristics. Splash from vehicles enhances Pb deposition next to the road. Most Pb is bound by grass from solution. Live and dead grass are shown to have markedly different capacities to bind Pb, and this is attributed to the condition of the cuticle and the ability of Pb-rich solutions to penetrate intercellular spaces. The Pb content of both states of grass are shown to undergo seasonal changes, with a winter peak and summer low. This is a function of precipitation and standing time of the grass. A mean estimate of 5.2 g of Pb/m2/year is added to the soil on a site with 7000vehicles/16h day, m from the road. Input increases with precipitation and splash. The invertebrate community of six verges were sampled with pitfall traps and Tullgren extractions, and their diversities compared. No decline in diversity could be attributed to Pb, though a greater diversity was apparent at a site which had been left unmown. Snails and Sminthurid collembolans may avoid areas of high Pb contamination, though woodlice numbers were low at all sites. The sexes of the woodlouse Porcellio scaber are shown to differ in their Pb and Ca content, and an interaction in the uptake of the two metals is shown in both P. scaber and juveniles of the snail Helix aspersa. It is suggested that the digestive diverticula may be the main site of Pb and Ca absorption in both species. Toxicological experiments dosing P. scaber with sub-lethal levels of Pb could show no effect on the rate of oxygen consumption or fecundity. No increase in mortality in either P. scaber or H. aspersa could be attributed to a high Pb diet. The distribution of Pb in the tissues of adult H. aspersa is found to correspond to that of marine molluscs. Few effects on the biotic components of roadside verges have been found, though it is suggested that Pb-tolerant plants may increasingly dominate the vegetation.

No description available.

A long-standing question in plant ecology remains about what underlying mechanisms are responsible for the distribution of plant species across environmental gradients. Most plant ecologists agree that the answer lies within the concept of 'niche' and thus in the set of driving 'key-resources' for plant growth under specific environmental conditions. Here I examine two key soil resources: nitrogen (N) and phosphorus (P). I ask whether changes in the availability of Nand P in soils may predict changes in critical plant element ratios (i.e. C:N:P stoichiometry). Very few studies have used an 'ecological stoichiometric' approach to address whether changes in soil nutrient availability and content could explain changes in plant C:N:P tissue stoichiometry along strong soil development gradients. I address this question using four ecological successions distributed across Europe where I measured C:N:P stoichiometry of roots, stems and leaves of 72 plant species. If plant nutrient stoichiometry is determined by Nand P uptake in response to local growth conditions (i.e. pioneer vs. advanced soil development stages), I would expect soil and plant N:P ratios positively related along the soil chronosequence. Overall my results show that soil N:P ratios strongly increased along the gradient of soil development from pioneer to advanced successional stages. However, I found that neither changes in soil nutrient availability, nor total soil nutrient content or soil N:P stoichiometry were significantly related to changes in plant nutrient stoichiometry. Instead I found that plant functional group identity (i.e. legumes vs. grasses vs. forbs) has a strong control over changes in plant N:P ratios regardless of the temporal stage of the ecological succession. I have also found that carbon:nutrient ratios (either C:N or C:P) along primary successions are quite variable and are partly related to changes in soil nutrient status, plant functional group identity and plant compmiment (e.g. roots vs. leaves). The lack of any correlation between soil and plant stoichiometry could be attributed to (1) the presence of internal mechanisms of plant nutrient and carbon use efficiency, (2) belowground ecophysiological processes (e.g. root exudation), and (3) plant-microbial interactions (e.g. symbiosis) all which can affect plant nutrients uptake and nutrient reallocation within compmiments. Finally, my study shows that wild-plant species seem to have a high-degree of internal nutrient regulation (i.e. high stoichiometric homeostasis), whose underlying mechanisms need to be better understood because may be key to better understand plant distribution along environmental gradients

The use of ornamental herbaceous plants in ecologically based planting schemes (EBPS) requires selection of species which are compatible, particularly for productive environments where competition is likely to be intense. Competitor, Stress tolerator, Ruderal (CSR) theory is considered and rejected as a guide to plant selection, although some of its insights are regarded as valuable. Competition between component taxa in EBPS is considered a key issue. Researching competition for practitioners in horticulture and allied industries involves a less reductionist and a greater observational methodology than is customary amongst plant ecologists. Simple competition trials are evaluated with regard to not just their outcomes in terms of understanding competition, but also their suitability for practitioners. A system for the classification of ornamental herbaceous plants is suggested, based on easily recognised aspects of their morphology and phenology. Plant architecture, the potential to spread through ramets and an ability to exploit growing seasons of various lengths are regarded as key variables. Relationships between the suggested categories and estimates of competitive performance in garden and EBPS conditions are considered. Biomass, as represented by a combination of canopy height and spread, an ability to spread extensively through ramets and an ability to grow over a long growing season are suggested as key factors in predicting both long-term survival and competitive performance. A knowledge of plant traits is suggested as being of key importance to practitioners in predicting plant performance over time, more so than comparison of environmental conditions in the region of origin and in cultivation. The contribution of genetically derived traits to distinct growth characteristics in different growing conditions is recognised, and their relevance to practitioners working with a variety of different design methodologies is discussed.

No description available.

This thesis describes (1) a simple and effective method for growing large numbers of fern gametophytes under field conditions and (2) the application of this method to investigate the sequence and timing of events in the fern life-cycle following spore dispersal or soil disturbance at different times of the year. Long-term field experiments involving <i>Athyrium filix-femina</i>, <i>Blechnum spicant, Polystichum setiferum</i> and <i>Phyllitis scolopendrium</i> were initiated at 2 sites near Edinburgh in January and October 1988. During these experiments (which continued till January 1990) both sites experienced a series of exceptionally mild Winters. The results for the 4 species were strikingly similar. Spores sown in January germinated in the Spring and gametophytes became sexual in the following year between mid-Spring and mid-Summer. Germination was synchronous although many spores did not produce gametophytes. Gametophytes quickly became 2-dimensional; no protonemata were observed. Sex organs developed and matured rapidly and their production was continuous. Most populations consisted of male, female and bisexual gametophytes. In general, female gametophytes were larger than bisexual gametophytes and all archegoniate gametophytes were larger than male gametophytes. All archegoniate gametophytes were meristic; all male gametophytes were ameristic. Most populations were predominantly male. Female gametophytes were always more abundant than bisexual gametophytes. All bisexual gametophytes were protandrous. Fertilization was often rapid, often occurred at high frequency and was not seasonal. Polyembryony was rare. All gametophytes from the January sowing survived the Winter of 1988/'89 but male and fertilized archegoniate gametophytes began to die in the Spring or Summer of 1989. No sporelings died. All gametophytes and sporelings from the October sowing survived throughout the experiment. A third (short) field experiment involving <i>A.filix-femina</i>, <i>B.spicant</i>, <i>P.setiferum</i>, <i>P.scolopendrium</i>, <i>Dryopteris affinis</i> subsp. <i>borreri</i>, <i>Dryopteris dilatata</i>, <i>Dryopteris filix-mas</i> and <i>Pteridium aquilinum</i> was initiated in August 1989. Spores of all 8 species germinated more or less immediately but only gametophytes of <i>P.aquilinum</i> became sexual before Winter. In one population fertilization occurred before the end of the year.

The atmospheric [CO<SUB>2</SUB>] has been rising steadily for the last 150 years, largely as a result of land-use change and anthropogenic emissions from the burning of fossil fuels. Models predict that the current concentration of atmospheric [CO<SUB>2</SUB>] will double within the next century and that temperatures will increase. Predicted increases in [CO<SUB>2</SUB>] and temperature are likely to affect plant growth, yield, biomass allocation, and bud phenology. The likely increase in the evapotranspiration potential caused by an increase in air and soil temperature could have a negative effect in particular in areas with limited water resources. The present experiments were designed to study the effects of rising [CO<SUB>2</SUB>] on the long-term growth and carbon allocation of four clones of Sitka spruce (<I>Picea sitchensis </I>(Bong.) Carr.) taken from two provenances, and the long-term interactive effects of elevated [CO<SUB>2</SUB>] and water stress on growth, plant water use and plant water relations of cherry seedlings (<I>Prunus avium </I>L.). Two-year-old saplings of four clones of Sitka spruce were grown in ten open top chambers (OTCs) at two CO<SUB>2</SUB> concentrations (~350 and ~700 μmol mol<SUP>-1</SUP>) for two growing seasons at the Institute of Terrestrial Ecology, near Edinburgh (UK). The saplings in elevated [CO<SUB>2</SUB>] were significantly larger in all respects than those grown in ambient [CO<SUB>2</SUB>]. Each clone showed a positive growth response to elevated [CO<SUB>2</SUB>] over the whole duration of the experiment. Only a few studies have been made to date on clonal plant response to elevated CO<SUB>2</SUB>, and growth different genotypes may prove to be important for forest species, particularly for forest crops. Cherry plants were grown at two CO<SUB>2</SUB> concentrations (~350 and ~700 μmol mol<SUP>-1</SUP>) for two years from seed in six OTCs within an unheated glasshouse at the University of Edinburgh. The experiment was designed to mimic the effects of natural water stress on the growth of young cherry seedlings. Elevated [CO<SUB>2</SUB>] significantly increased total dry mass production in both water regimes.

The aim of the study was to investigate factors influencing survival and growth of <i>Pinus sylvestris</i> L. at a natural tree-line. Five experimental stations were set up along an altitudinal transect from 290 m to 675 m at Creag Fhiaclach in the Cairngorm Mountains, Scotland. Three further stations were established in the University grounds at Edinburgh, two of which were inside greenhouses. Thus, a climatological gradient was obtained. Eight 2 year-old <i>Pinus sylvestris</i> of Scottish provenance were potted into pea/sand compost and placed at each of the eight stations and measurements of height extension, needle length and fascicle number were made during 1989 and 1990. Similar measurements were also made on five native trees at each station along the transect. Air and meristem temperatures were measured and monthly means calculated for all stations. Mean monthly air and meristem temperatures decreased with increasing altitude. Growth of <i>P.sylvestris</i> was found to vary with altitude and can be accounted for at least in part by temperature variation. Height extension, fascicle number, percentage needle survival and needle length decreased with increasing altitude, mean height extension and mean number of fascicles being positively correlated with mean meristem temperatures of the previous (May to June) growth season. Cuticles of needles from all trees measured along the transect were isolated by acid digestion (5% chromic acid) and no significant difference was found in cuticular weight per surface area between altitudes. Results are discussed in relation to the hypothesis of Tranquillini (1979) on the causal relationships leading to winter desiccation of shoots at alpine tree-lines. The hypothesis is considered inappropriate to Scots pine in Scotland. Needle water potential varied with altitude only in the potted trees related to their age and susceptibility to fluctuating conditions. Needle nutrient concentrations varied significantly with time, needle age and altitude, being higher in valley trees than above the tree-line. Low values were thought to be related to poor nutrient availability, restricted root growth and the effects of low temperatures. Photosynthetic rates of native <i>P.sylvestris</i> were higher in valley trees than in those above the tree-line early in the season due to a developmental lag caused by temperature. By September, rates were higher above the tree-line and plants showed an adaptation of increased quantum efficiency. Percentage needle loss over winter was similar between valley and above tree-line populations, possibly through the effect of frost acting at the lower station. The relevance of the present study is discussed in relation to other tree-lines and to future predictions of tree growth with respect to climatic warming. Suggestions for further work are proposed.