Control Of Water Relations Research Articles

Involvement of root ABA and hydraulic conductivity in the control of water relations in wheat plants exposed to increased evaporative demand

We studied the possible involvement of ABA in the control of water relations under conditions of increased evaporative demand. Warming the air by 3°C increased stomatal conductance and raised transpiration rates of hydroponically grown Triticum durum plants while bringing about a temporary loss of relative water content (RWC) and immediate cessation of leaf extension. However, both RWC and extension growth recovered within 30min although transpiration remained high. The restoration of leaf hydration and growth were enabled by increased root hydraulic conductivity after increasing the air temperature. The use of mercuric chloride (an inhibitor of water channels) to interfere with the rise on root hydraulic conductivity hindered the restoration of extension growth. Air warming increased ABA content in roots and decreased it in shoots. We propose this redistribution of ABA in favour of the roots which increased the root hydraulic conductivity sufficiently to permit rapid recovery of shoot hydration and leaf elongation rates without the involvement of stomatal closure. This proposal is based on known ability of ABA to increase hydraulic conductivity confirmed in these experiments by measuring the effect of exogenous ABA on osmotically driven flow of xylem sap from the roots. Accumulation of root ABA was mainly the outcome of increased export from the shoots. When phloem transport in air-warmed plants was inhibited by cooling the shoot base this prevented ABA enrichment of the roots and favoured an accumulation of ABA in the shoot. As a consequence, stomata closed.

Functional plant ecology. 2nd edn

Pugnaire and Valladares cover all aspects of the multidisciplinary comparative science of functional plant ecology, which is centred on the study of whole plants in natural or field conditions to quantify the variation of plant functional properties and to determine the underlying laws accounting for this variation. The book opens with a chapter on ‘Methods in comparative functional ecology’, which discusses how the study of plant function has unfolded over time. The role of structure and growth form in plant performance is highlighted through the study of poikilohydrous autotrophs (e.g. lichens), which lack the control of water relations, and the maximum growth potential of species, which can be linked to the characteristics of the habitat from which the species came. Chapters on leaf arrangement and root-system structure illustrate how plant architecture is influenced by resource-capture requirements for light above ground and water/nutrients below ground. This is then developed in the following three chapters, which focus on the physiological ecology of resource relations. Studies from the Arctic, Antarctic, tropics and Mediterranean are used to exemplify the relationships between habitats and plant distribution. Five chapters on populations and communities touch on all aspects of inter- and intraspecific interactions (competition, herbivory, reproduction, etc). The book closes with a series of chapters on new approaches, including remote sensing at multiple scales and a revisit of the plant ecology strategy debate. Functional plant ecology is an updated version of the Handbook of functional plant ecology edited by Pugnaire and Valladares (1999; New York: Marcel Dekker). The layout of the second edition is much the same, except for the omission of a chapter on ‘Plant survival in arid environments’ and minor changes to the running order of the 23 remaining chapters. As a result the second edition is 177 pages shorter than its predecessor. It is a pity that useful section headings, which divided chapters into different subject topics, have been removed from the contents page as it makes the book more difficult to navigate at a quick glance than the earlier edition. However, these can soon be written in by hand! Chapters have been revised and updated to include the latest published works, although it should be noted that no new references (i.e. post 1999) are cited in four of the chapters, including the introduction. The book follows a bottom-up approach with detailed studies from plant organs up to the broadest ecosystem approaches. Studies at the lower levels of organisation are conducted with the aim of being subsequently scaled up to the level of the ecosystem. Pugnaire and Valladares have managed to pull together a wide range of subjects with the depth and breadth of a series of essays, but the accessibility of a textbook. However, the chapters are not linked as you would expect in a textbook, and the style of some of the chapters can be a bit foreboding to the uninitiated. A list of contents is presented at the start of each chapter, and where appropriate appendices are given, such as detailed information on experimental design and competition indices in the chapter on plant interactions. Effective black and white illustrations are used throughout the book, and additional colour inserts appear in the remote sensing chapter. Although costly, I think the book would have benefitted from the inclusion of more colour inserts as black and white photographs of lichens on rocks, for example, do not show the subject matter as well. The book is intended for a broad audience, ranging from specialist plant ecologists to upper-level undergraduate and postgraduate students. It will certainly be well used as a reference book on my bookshelf. In 724 pages Pugnaire and Valladares have produced a comprehensive reference for anyone interested in functional plant ecology. This timely, fully revised and updated edition, which includes work from 49 contributors, investigates the role of plant function in determining the underlying laws that shape plant communities at multiple scales. The book has an international flavour, describing studies from many different parts of the world, and is therefore globally applicable.

Studies on lichen-dominated systems. XVIII. Morphological control of evaporation in lichens

The current belief that lichens are incapable of controlling their water relations is based largely on evidence collected from experiments testing for active metabolic controls only. In this study, controlled wind tunnel experiments designed to test for any passive morphological control of evaporation in four lichen species show that such mechanisms are important to the water relations of the plants and thus suggest that the observed morphological variability in lichens is of great ecological significance.Time-dependent and moisture-content-dependent changes in evaporation rate were examined using samples of lichen thalli from a number of different arctic and subarctic populations of Alectoria ochroleuca (Hoffm.) Massal., Alectoria nitidula (Th.Fr) Vain, Cetraria nivalis (L.) Ach., and Cladina alpestris (L.) Harm. The work has shown that the observed interspecific and intraspecific variability in evaporative resistance found in these plants is influenced by three separate morphological characteristics: variability in surface area to weight ratio; variability in thallus shape; and variability in the degree of clumping of thalli. When other aspects of the ecology and physiology of the test lichens were considered, it became clear that these lichens exhibited a potential to modify their morphological characteristics over long periods of time in such a way that greater photosynthetic productivity was assured.It was concluded that although the control of water relations in lichens is of a different nature from higher plants, the control is present nonetheless.