Elizabeth A. C. Price

Studies of growth in the clonal herb Glechoma hederacea. I: Patterns of physiological integration

The stoloniferous clonal herb Glechoma hederacea (Labiatae) has a decussate phyllotaxy. Each node bears two leaves which emerge from the opposite faces of a quadrangular stolon. Anatomical studies showed that the vascular tissue of the stolon is concentrated into four major bundles, and leaf traces connect each leaf of a ramet to the proximal pair of vascular bundles. These two vascular bundles also provide the vascularization for the secondary stolon developing from the axial of that leaf. Transport of resources in the vascular system was analysed using acid fuchsion dye and 14 C-labelled photoassimilate. All transport of dye in the xylem was acropetal (...)

Clonal plants and environmental heterogeneity – An introduction to the proceedings

Clonal growth is characterised by the ability of plants to produce shoot and root units (ramets) which are genetically identical to the parent, and which are potentially independent. Ramets of clonal plants are likely to experience environmental heterogeneity in the form of resource distribution patterns or exposure to other environmental factors. For certain species the key attributes of clonality that appear to confer ecological success under heterogeneous growing conditions can be fairly readily identified, but for the majority of clonal species the mechanisms that may be of particular importance are less certain. Future lines of research should continue to investigate the ecological and evolutionary implications of plant clonality in the context of realistic scales of environmental heterogeneity, as such information may be of considerable practical value.

The causes and developmental effects of integration and independence between different parts of Glechoma hederacea clones

The clonal species Glechoma hederacea shows both physiological integration and physiological independence between its ramets at different structural levels. The cause of these differences in intra-clone integration is analysed, using (1) acid fuchsin dye to reveal the vascular connections between different ramets through the xylem, (2) 14 C as marker to demonstrate and quantify photoassimilate translocation patterns in the phloem, and (3) anatomical studies. Dye movement in the xylem was strictly acropetal and highly sectorial, and the sectoriality was determined by phyllotaxy. Patterns of movement of 14 C were qualitatively similar to those of xylem-based resources, although there was some basipetal movement of photoassimilate (...)

Seasonal patterns of partitioning and remobilization of 14C in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, 14C-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of 14C allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of 14C recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of 14C exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and 14C fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this 14C was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.

The effects of competition on growth and form in Glechoma hederacea

Morphological responses to competition were analysed in Glechoma hederacea, a clonal herb with plagiotropic shoots. Ramets of clones were grown either in isolation or in competition with cut or uncut Lolium perenne swards. G. hederacea produced the same above ground biomass, but different morphologies when grown with short and tall grass. Despite considerable reductions in biomass and stolon branching when grown with competition rather than in isolation, the capacity for lateral extension of primary stolons was maintained. All other measured variables were reduced by competition, except for stolon internode length and petiole length and mass. These variables reached their greatest values in the uncut grass treatments. These responses could promote avoidance of competition by escape in both the horizontal and vertical planes; growth through vegetated sites would be rapid, and sites where competitors are absent would be occupied more densely. Reductions in PAR and in the R/FR ratio incident on the plant are both implicated in inducing these morphological changes. Differences in relative humidity, caused by the proximity of neighbours, also appeared to exert a considerable influence upon growth and morphology of G. hederacea. Connected parts of G. hederacea clones grown with and without competition developed different morphologies; each primary stolon behaved as an integrated physiological unit, developing a morphology appropriate for the conditions in which it was growing.

Studies of growth in the clonal herb Glechoma hederacea. II : The effects of selective defoliation

Defoliation of ramets in a clonal species affects the subsequent growth of newly developing parts by preventing translocation of photoassimilates. In this paper, the hypothesis is tested that the structural level at which a clone responds to such interference, and the response it displays, will be determined by the ramets which are defoliated, and by the patterns of physiological integration between its connected ramets. An experiment was carried out in which clones of Glechoma hederacea were subjected to either 0% (control), 50% or 100% leaf removal. Fifty per cent defoliation was applied in three different patterns to determine if these had different effects upon subsequent growth (...)

Causes and consequences of sectoriality in the clonal herb Glechoma hederacea

The causes of sectoriality and consequences for clone behaviour are examined using data from the stoloniferous herb Glechoma hederacea. The proximal causes of physiological integration patterns are investigated using anatomical studies, acid fuchsin dye to reveal patterns of xylem continuity between ramets, and 14C as a label to reveal quantitative photoassimilate translocation patterns in the phloem. Dye movement in the xylem was acropetal and sectorial, and the sectoriality was determined by phyllotaxy. Patterns of 14C-labelled photoassimilate allocation were qualitatively similar to those of xylem based resources, although there was some basipetal movement of photoassimilate. The patterns of physiological integration and independence between ramets are shown to be governed by rules which depend on vascular continuity and discontinuity between ramets. Physiological support to stolon apices results in acquisition of relative branch autonomy (branches become semi-autonomous integrated physiological units, IPUs). This paper evaluates whether observed physiological integration patterns may be modified by altering normal source-sink relationships or by modifying environmental conditions. An experiment using different defoliation intensities, and different defoliation patterns at the same overall intensity, demonstrated that the precise positions of leaves removed from a clone had unique consequences for its subsequent development. Individual ramets of a given clone may be located in microhabitats of differing quality. An experiment in which competition was either present or absent throughout the space occupied by the clone, or patchy in distribution, showed that G. hederacea did not respond to competition at the whole clone level. Instead, connected stolons (IPUs) responded independently to local competition. Sectoriality may promote the restriction of lethal, localised environmental factors within the affected IPU. A study investigating the uptake and translocation of zinc by clones revealed that quantified patterns of zinc distribution resembled patterns of 14C movement in the phloem, and that there was no significant transport of zinc from one stolon to another. Although sectorial patterns of resource movement in G. hederacea can be modified in the short term, in the long-term, physiological integration may not allow this species to integrate the effects of environmental heterogeneity. A mobile clonal species with a high growth rate and relatively short-lived ramets, such as G. hederacea, is likely to benefit from a semi-autonomous response to patch quality at the level of the stolon, since the alternative of widespread intra-clonal support may increase the residence time of the clone in unfavourable pathches.

Bio-indicators of nitrogen pollution in heather moorland

Heather moorlands are internationally important ecosystems that are highly sensitive to eutrophication and acidification by reactive atmospheric nitrogen (N) deposition. We used a long-term experiment simulating wet-deposition of N on heather moorland to identify potential bio-indicators of N deposition. These indicators were subsequently employed in a survey covering a N deposition gradient ranging from approximately 7 to 31kg N ha(-1) yr(-1), at selected sites throughout the UK. In this regional survey litter phenol oxidase activity and bryophyte species richness were negatively associated with N deposition. Calluna vulgaris N:P ratios and litter extractable N were positively correlated with N deposition. The use of the suite of four bio-indicators has the potential to provide rapid assessment of the extent of N saturation of heather moorland sites and moorland ecosystem functioning, and has significant advantages over reliance on single measures such as soil N status or an individual bio-indicator species.

The legacy of nitrogen pollution in heather moorlands: Ecosystem response to simulated decline in nitrogen deposition over seven years

Eutrophication and acidification of heather moorlands by chronic atmospheric nitrogen (N) pollution, is of major concern within these internationally important ecosystems. However, in the UK and Western Europe generally emissions of NO(y) and NH(x) peaked during the 20th century. Due to the history and scale of atmospheric N pollution, the legacy of these high levels of N deposition, through accumulation in soil, may hinder or prevent ecosystem recovery. Effects of N pollution on heather moorland were investigated throughout the ecosystem including; the dominant plant species, Calluna vulgaris, the bryophyte and lichen community and the soil system using a long-term experiment simulating wet N deposition. We observed an increase in C. vulgaris height, shoot extension and canopy density, litter mineral N, total N concentration, N:P and C:N ratios in response to N addition. Bryophyte species diversity, bryophyte and lichen frequency and the frequency of two individual bryophyte species (Lophozia ventricosa and Campylopus flexuosus) were significantly reduced by N addition. We developed an N recovery experiment, using a split-plot design, on the long-term N treatment plots to investigate ecosystem response to a simulated decline in N deposition. Two years after cessation of N treatment the only ecosystem component that responded to the recovery experiment was C. vulgaris shoot extension, however after seven years of recovery there were significant declines in litter total N concentration and mineral N and an increase in litter C:N ratio. Although bryophytes and lichens form a close relationship with atmospheric N deposition these organisms did not show a significant response to the N recovery experiment, two years after cessation of N treatment. These data indicate that low nutrient ecosystems, such as moorlands, have the capacity to respond to declines in N deposition however the accumulation of pollution may hinder recovery of sensitive organisms, such as bryophytes and lichens.

What are the European legal duties to conserve biodiversity in university campuses

Biodiversity is a key element of sustainable development in university campuses. However, integrating biodiversity in campuses requires strategic planning, beyond minimum compliance with protected species and habitats legislation. This leads to the questions: which university functions impact on biodiversity and what obligations are there under European environmental law for universities to consider biodiversity strategically? University functions and their consequent impacts were classified thematically into four and seven categories respectively. These categories were used to systematically search the Environmental Legislation Update Service and EUR-Lex for relevant legislation, which was also classified. Universities undertake capital projects, building alterations, grounds maintenance, and outdoor activities. These functions may cause loss, damage, disturbance, introductions, pollution to, and overuse of, biodiversity. Legislation applying to these impacts spans wildlife, plant health, planning, and pollution prevention disciplines. The interdisciplinary legal framework for biodiversity presents compliance and integration challenges, such as overlooking legislation or duplicating efforts. This article will help those involved in university management, teaching and research to identify and integrate in their work the relevant legal obligations on biodiversity.