- Email: [email protected]
Plant physiological ecology: Field methods and instrumentation
TREE vol. 5, no. 3, March 1990
provided that the stress is sufficiently intense to produce an effect3. The FA of sternopleural chaeta number in Drosophila melanogaster has been shown to be far higher at 30°C than at 25”C, especially in flies derived from young females4. The high variability at 30°C might be expected, since this is an extreme stress effectively at the limits of survival when slight changes in microenvironment may have major effects. At 25”C, FA increased with maternal age, a result consistent with many observations of decreased developmental stability with maternal age, especially in mice and our own species. In another series of experiments5, where higher sternopleural chaeta FA was found at 30°C than at 25”C, flies with specificabnormalities, including crumpled and curled wings, commonly occurred at 30°C. Fly weight was reduced only slightly, indicating that death may have been due to a generally poor developmental stability, resulting from the upsetting of underlying metabolic processes by the extreme temperature. These experiments show that FA assessments provide an epigenetic measure of stress. The expectation is for increasing FA away from an optimum, especially at stress levels approaching lethality, where major abnormalities may occur. It is at these levelsthat normal development is upset at the molecular, chromosomal and developmental levels - a conclusion appearing in early recombination studies of D. melanogaster, where major increases in FAoccurred in the narrow range from 29°C to 31°C (Refs 68). Because of this narrow
range, the detection of environmental effects in the field will be difficult, requiring conditions of relatively severe stress. One approach is to seek out ecologically marginal situations where severe stress conditions are most likely to occur. For example, the FA of a set of six characters in Rocky Mountain populations of the butterfly Caenonympha tullia was greatest at high altitudes subjected to climatic extremesg. In the muskrat, Ondantra zibethicus, harsh environmental conditions appeared to be associated with increased FA’O, and fish examples involving stresses have been summarized several times’. It is not, however, surprising that a number of field studies are inconclusive, but conclusions contrary to FA as a measure of environmental (and genomic) stress appear to be lacking. This indeterminacy is predictable, since sample sizes may be inadequate, the trait invariant, or the environmental perturbation insufficiently extreme. It may well be that in a conservation context’, major damage will have been done by the time an effect is clearly detectable at the morphological level. It is possible that easily demonstrable morphological effects will only appear at the stage of observable major metabolic effects, such as altered adenylate charges3s1’. Afurther complication is that some specific stresses may not affect FA. For example, a chemical stress, phenyl-thio-urea (PTU), reduced fly weight substantially and increased its variabiIity5, but had little effect upon FA. It is therefore a stress with little effect on the developmental stability
of flies, being a stress affecting fly weight but not the variability of the morphological structure of the fly. Presumably, the difference lies in the fact that temperature is a generalized stress and, at certain limits, the basic physiology of the organism becomes restrictive with multiple consequences; PTU, on the other hand, is a specific chemical inhibitor whose effects involve far fewer metabolic pathways. In summary, FA may provide an indicator of stress, but attention to the intensity and the nature of the stress is always necessary; it will not be useful in all situations’. Peter A. Parsons Deptof Zoology, University of Adelaide, Adelaide, SA 5001, Australia References 1 Leary, R.F. and Allendorf, F.W. (1989) Trends Ecol. Evol. 4,214-217 2 Palmer, A.R. and Strobeck, C. (1986) Annu. Rev. Ecol. Syst. 17, 391-421 3 Parsons, P.A. in Ecology and Evolution ofDrosophila (Barker, Jr2.F. and Starmer. W.T.. eds). Plenum (in oress) 4 Parsons, P.A. (1962) J. Exp. 6/o/. 39; 251-260 5 Parsons, P.A. (1961) Heredity 16, 455473 6 Parsons, P.A. (1987) Evol. Biol. 21, 31 l-347 7 Plough, H.H. (1917) J. Exp. Zoo/. 24, 148-209 8 Parsons, P.A. (1988) Biol. J. Linn. Sot. 35,49-68 9 Soul& M. and Baker, B. (1968) Heredity 23,61 l-614 10 Pankokoski, E. (1985) J. Mammal. 66, 52-57 11 Hoffmann, A.A. and Parsons, P.A. (1989) Viol. J. Linn. Sot. 37, 117-136
Book Reviews Ecophysiological Techniques Plant Physiological Ecology: Field Methods and instrumentation edited by R.W. Pearcy, J. Ehleringer, H.A. Mooney and P.W. Rundel, Chapman & Hall, 1989. f52.00 hbk (xi + 457 pages) ISBN 0 4 12 23230 8 This book is an excellent compendium of information about a wide range of methodology related to plant physiological ecology. It is carefully written, well edited and nicely produced, its structure equally appropriate for dipping into and for reading at length. The chapters, most of which are very readable, cover topics from photosynthesis to root systems, from methods for quantifying canopy structure to those for 98
assessing plant nutrient status. The methodology covered ranges from the classical (growth analysis, foliar nutrient analysis, gravimetric soilmoisture measurements) to high technology (controlled-environment gas-exchange systems, chlorophyll fluorescence, stable-isotope techniques), and most chapters provide clear guidelines for choosing from within this range. This is an important reference book that should be on as many shelves as its high price will allow. If the book has a problem, it lies in the differences in depth and approach among the diverse chapters. Some, like the one on photosynthesis, amount almost to technical manuals with detailed descriptions of instru-
mentation, specifications and discussions of technical pitfalls. Other chapters provide less technical detail but more background on the applicability of different methods to different questions, not just to different types of measurement. A few, like those on data acquisition, nutrient use and energy balance, provide useful information about variability and sampling design; those on nutrient use and Crassulacean Acid Metabolism are outstanding for their thorough review of the subjects, with examples of the application of particular methods to specific ecological questions. This latter approach helps to avoid the problems of many methodological books, which end up presenting
‘REE vol. 5, no. 3, March
7990
the methodology as if it were the goal, rather than the means, of advances in research. By following the development of new methods, this book allows us to see the development of key questions in plant physiological ecology. These questions are of two kinds: first, there is an increasing focus on finding physiologically based answers to ecosystem-level questions; secondly, there are ever more detailed investigations of the functioning of individual plants, organs, tissues and cells in natural environments. The ecosystem-level questions are several. How is the productivity of an ecosystem determined? What resources are limiting? How do the components of the ecosystem interact? The approaches to answering these questions are at the same time increasingly physiological and increasingly integrative. Individual productivity and its limitation are examined in detail using controlledenvironment and field studies of photosynthesis, growth, water and nutrient relations. Modelling approaches allow the extension of such results to the ecosystem level with increasing accuracy, due to the development of improved methods for quantification of canopy structure; and some methods, such as eddy correlation’,* approaches to en-
ergy balance, directly produce field measurements that constitute integrated responses over large areas. Stable- and radioactive-isotope techniques allow the determination of the importance of different ecosystem processes3, and of the role of the individual in these processes and in interactions with other individuals4. At the other end of the spectrum, interest in achieving a detailed understanding of the physiological processes of plants in the field has led to the development of field extensions of laboratory methods. Heat-pulse techniques measure water flux within Isotope techindividual plants5. niques allow us to examine the allocation of carbon to different plant organ@. Pressure probes to measure the water status of cells’ may eventually be suitable for use in the field. Chlorophyll fluorescence techniques to assess levels of damage to photosystem function8 are beginning to make the transition from the laboratory to the field. Other questions that are fundamental to plant physiological ecology and its methodology include those of how to define different types of plant ‘stress’ or physiological damage. It is also of increasing interest to be able to determine the costs of survival in terms of energetic and resource investment in structures, growth and
defense, and consequently to assess the losses due to herbivory. Such stresses and costs can affect plant reproduction and fitness as well as competitive interactions. Clearly, to some degree all plant ecology is ultimately physiological, and this book is potentially very useful to all plant ecologists.
gredients. The Introduction promises contributions from astronomers, chemists, geologists, philosophers, physicists, anthropologists, behaviourists, biochemists, cell and developmental biologists, ecologists, geneticists, molecular biologists, palaeontologists, physiologists, systematists and others. To fulfil this promise the book goes from cosmology to cultural evolution, taking in genome structure, the cell, and the plant and animal kingdoms on the way. Winston Churchill once rejected a pudding because it ‘lacked a theme’, and there is a certain culinary confusion on the menu here as well. However, not much gets left out taphonomy to tit-for-tat behaviour, phenetics to Pangaea, extinctions to exon shuffling and Australopithecus to adaptive landscapes all find a place. The treatment is admirably up to date, although this does mean that the author has occasionally leapt on to passing bandwagons that came to a halt before getting anywhere. There is nothing more tired than yesterday’s slang, and it is already odd to see terms such as punctuated equilib-
rium and developmental constraint presented as if they are live issues in evolutionary biology. The breadth of the book means that it is shallow in parts: which is perfectly acceptable in a textbook. However, it is locally hard to follow and even sloppy, and that is certainly not acceptable. For example, after quoting Fisher’s succinct comment on natural selection as a mechanism for generating improbability, this is explained as ‘those inherently better fit are more likely to predominate because of the nature of their inheritance, not because of deliberate action by the totality which we refer to as nature’. What can that mean? The discussion of modes of selection is also confused, with stabilizing and purifying selection treated as effectively interchangeable; selection against heterozygotes presented as a means of maintaining polymorphism; and the distinction between group and kin selection not clearly made. There are arithmetical errors in the treatment of inbreeding; and the Hardy-Weinberg theorem is derived in a baffling way. It is particularly odd to read in an account of speciation
Valerie Kapos BotanyDept,Universityof Cambridge, Cambridge CB23EA,UK
References 1 Shuttleworth,
W.J. (1988) Proc. R. Sot. London Ser. 6 233,321-346 2 Shuttleworth, W.J. et al. (1984) Q.J.R. Meteorol. Sot. 110, 1143-l 162 3 Medina, E., Montes, G., Cuevas, E. and Rokzandic, Z. (1986) J. Trap. Ecol. 2, 207-217 4 Caldwell, M.M., Eissenstat, D.M. and Richards, J.H. (1985) Science 229, 384-386 5 CermBk, J., Jenik, J., Kutera, J. and tidek, V. (1984) Oecologia 64, 145-151
6 Mordacq, L., Mousse&, M. and Deleens. E. (1986) Plant Cell Environ. 9. 735-739 7 Cosgrove, D.J., van Volkenburgh, E. and Cleland, R.E. (1984) Wanta 162, 46-54 8 Winter, K., Osmond, C.B. and Hubick, K.T. (1986) Oecologia 68, 224-230
Eclectic Evolution Processand Pattern in Evolution by Charlotte J. Avers, Oxford University Press, 1989. f28.00 (xvi + 590 pages) ISBN 0 19 505275 7 There are lots of books about evolution, but very few evolution textbooks. Because they cannot leap into the past, evolutionists - be they muscular Darwinist, stark theoretician, or just plain daft - have never hesitated to leap into print. Bookshop shelves are crowded with convincing but contradictory treatments of what evolution is all about. This confuses today’s students whose academic diet, largely limited as it is to boil-inthe-bag biology, has taught them to prefer pabulum to polemic. What undergraduates need to reassure them that the molecules they study were probably not created on October 28th 4004 BC is evolution with most of the bones taken out: a terse, simple and even bland account which explains just why -to quote a famous phrase - ‘nothing in biology makes sense except in the light of evolution’. Aversstrivesfor blandness but fails because of the richness of her in-
99
provided that the stress is sufficiently intense to produce an effect3. The FA of sternopleural chaeta number in Drosophila melanogaster has been shown to be far higher at 30°C than at 25”C, especially in flies derived from young females4. The high variability at 30°C might be expected, since this is an extreme stress effectively at the limits of survival when slight changes in microenvironment may have major effects. At 25”C, FA increased with maternal age, a result consistent with many observations of decreased developmental stability with maternal age, especially in mice and our own species. In another series of experiments5, where higher sternopleural chaeta FA was found at 30°C than at 25”C, flies with specificabnormalities, including crumpled and curled wings, commonly occurred at 30°C. Fly weight was reduced only slightly, indicating that death may have been due to a generally poor developmental stability, resulting from the upsetting of underlying metabolic processes by the extreme temperature. These experiments show that FA assessments provide an epigenetic measure of stress. The expectation is for increasing FA away from an optimum, especially at stress levels approaching lethality, where major abnormalities may occur. It is at these levelsthat normal development is upset at the molecular, chromosomal and developmental levels - a conclusion appearing in early recombination studies of D. melanogaster, where major increases in FAoccurred in the narrow range from 29°C to 31°C (Refs 68). Because of this narrow
range, the detection of environmental effects in the field will be difficult, requiring conditions of relatively severe stress. One approach is to seek out ecologically marginal situations where severe stress conditions are most likely to occur. For example, the FA of a set of six characters in Rocky Mountain populations of the butterfly Caenonympha tullia was greatest at high altitudes subjected to climatic extremesg. In the muskrat, Ondantra zibethicus, harsh environmental conditions appeared to be associated with increased FA’O, and fish examples involving stresses have been summarized several times’. It is not, however, surprising that a number of field studies are inconclusive, but conclusions contrary to FA as a measure of environmental (and genomic) stress appear to be lacking. This indeterminacy is predictable, since sample sizes may be inadequate, the trait invariant, or the environmental perturbation insufficiently extreme. It may well be that in a conservation context’, major damage will have been done by the time an effect is clearly detectable at the morphological level. It is possible that easily demonstrable morphological effects will only appear at the stage of observable major metabolic effects, such as altered adenylate charges3s1’. Afurther complication is that some specific stresses may not affect FA. For example, a chemical stress, phenyl-thio-urea (PTU), reduced fly weight substantially and increased its variabiIity5, but had little effect upon FA. It is therefore a stress with little effect on the developmental stability
of flies, being a stress affecting fly weight but not the variability of the morphological structure of the fly. Presumably, the difference lies in the fact that temperature is a generalized stress and, at certain limits, the basic physiology of the organism becomes restrictive with multiple consequences; PTU, on the other hand, is a specific chemical inhibitor whose effects involve far fewer metabolic pathways. In summary, FA may provide an indicator of stress, but attention to the intensity and the nature of the stress is always necessary; it will not be useful in all situations’. Peter A. Parsons Deptof Zoology, University of Adelaide, Adelaide, SA 5001, Australia References 1 Leary, R.F. and Allendorf, F.W. (1989) Trends Ecol. Evol. 4,214-217 2 Palmer, A.R. and Strobeck, C. (1986) Annu. Rev. Ecol. Syst. 17, 391-421 3 Parsons, P.A. in Ecology and Evolution ofDrosophila (Barker, Jr2.F. and Starmer. W.T.. eds). Plenum (in oress) 4 Parsons, P.A. (1962) J. Exp. 6/o/. 39; 251-260 5 Parsons, P.A. (1961) Heredity 16, 455473 6 Parsons, P.A. (1987) Evol. Biol. 21, 31 l-347 7 Plough, H.H. (1917) J. Exp. Zoo/. 24, 148-209 8 Parsons, P.A. (1988) Biol. J. Linn. Sot. 35,49-68 9 Soul& M. and Baker, B. (1968) Heredity 23,61 l-614 10 Pankokoski, E. (1985) J. Mammal. 66, 52-57 11 Hoffmann, A.A. and Parsons, P.A. (1989) Viol. J. Linn. Sot. 37, 117-136
Book Reviews Ecophysiological Techniques Plant Physiological Ecology: Field Methods and instrumentation edited by R.W. Pearcy, J. Ehleringer, H.A. Mooney and P.W. Rundel, Chapman & Hall, 1989. f52.00 hbk (xi + 457 pages) ISBN 0 4 12 23230 8 This book is an excellent compendium of information about a wide range of methodology related to plant physiological ecology. It is carefully written, well edited and nicely produced, its structure equally appropriate for dipping into and for reading at length. The chapters, most of which are very readable, cover topics from photosynthesis to root systems, from methods for quantifying canopy structure to those for 98
assessing plant nutrient status. The methodology covered ranges from the classical (growth analysis, foliar nutrient analysis, gravimetric soilmoisture measurements) to high technology (controlled-environment gas-exchange systems, chlorophyll fluorescence, stable-isotope techniques), and most chapters provide clear guidelines for choosing from within this range. This is an important reference book that should be on as many shelves as its high price will allow. If the book has a problem, it lies in the differences in depth and approach among the diverse chapters. Some, like the one on photosynthesis, amount almost to technical manuals with detailed descriptions of instru-
mentation, specifications and discussions of technical pitfalls. Other chapters provide less technical detail but more background on the applicability of different methods to different questions, not just to different types of measurement. A few, like those on data acquisition, nutrient use and energy balance, provide useful information about variability and sampling design; those on nutrient use and Crassulacean Acid Metabolism are outstanding for their thorough review of the subjects, with examples of the application of particular methods to specific ecological questions. This latter approach helps to avoid the problems of many methodological books, which end up presenting
‘REE vol. 5, no. 3, March
7990
the methodology as if it were the goal, rather than the means, of advances in research. By following the development of new methods, this book allows us to see the development of key questions in plant physiological ecology. These questions are of two kinds: first, there is an increasing focus on finding physiologically based answers to ecosystem-level questions; secondly, there are ever more detailed investigations of the functioning of individual plants, organs, tissues and cells in natural environments. The ecosystem-level questions are several. How is the productivity of an ecosystem determined? What resources are limiting? How do the components of the ecosystem interact? The approaches to answering these questions are at the same time increasingly physiological and increasingly integrative. Individual productivity and its limitation are examined in detail using controlledenvironment and field studies of photosynthesis, growth, water and nutrient relations. Modelling approaches allow the extension of such results to the ecosystem level with increasing accuracy, due to the development of improved methods for quantification of canopy structure; and some methods, such as eddy correlation’,* approaches to en-
ergy balance, directly produce field measurements that constitute integrated responses over large areas. Stable- and radioactive-isotope techniques allow the determination of the importance of different ecosystem processes3, and of the role of the individual in these processes and in interactions with other individuals4. At the other end of the spectrum, interest in achieving a detailed understanding of the physiological processes of plants in the field has led to the development of field extensions of laboratory methods. Heat-pulse techniques measure water flux within Isotope techindividual plants5. niques allow us to examine the allocation of carbon to different plant organ@. Pressure probes to measure the water status of cells’ may eventually be suitable for use in the field. Chlorophyll fluorescence techniques to assess levels of damage to photosystem function8 are beginning to make the transition from the laboratory to the field. Other questions that are fundamental to plant physiological ecology and its methodology include those of how to define different types of plant ‘stress’ or physiological damage. It is also of increasing interest to be able to determine the costs of survival in terms of energetic and resource investment in structures, growth and
defense, and consequently to assess the losses due to herbivory. Such stresses and costs can affect plant reproduction and fitness as well as competitive interactions. Clearly, to some degree all plant ecology is ultimately physiological, and this book is potentially very useful to all plant ecologists.
gredients. The Introduction promises contributions from astronomers, chemists, geologists, philosophers, physicists, anthropologists, behaviourists, biochemists, cell and developmental biologists, ecologists, geneticists, molecular biologists, palaeontologists, physiologists, systematists and others. To fulfil this promise the book goes from cosmology to cultural evolution, taking in genome structure, the cell, and the plant and animal kingdoms on the way. Winston Churchill once rejected a pudding because it ‘lacked a theme’, and there is a certain culinary confusion on the menu here as well. However, not much gets left out taphonomy to tit-for-tat behaviour, phenetics to Pangaea, extinctions to exon shuffling and Australopithecus to adaptive landscapes all find a place. The treatment is admirably up to date, although this does mean that the author has occasionally leapt on to passing bandwagons that came to a halt before getting anywhere. There is nothing more tired than yesterday’s slang, and it is already odd to see terms such as punctuated equilib-
rium and developmental constraint presented as if they are live issues in evolutionary biology. The breadth of the book means that it is shallow in parts: which is perfectly acceptable in a textbook. However, it is locally hard to follow and even sloppy, and that is certainly not acceptable. For example, after quoting Fisher’s succinct comment on natural selection as a mechanism for generating improbability, this is explained as ‘those inherently better fit are more likely to predominate because of the nature of their inheritance, not because of deliberate action by the totality which we refer to as nature’. What can that mean? The discussion of modes of selection is also confused, with stabilizing and purifying selection treated as effectively interchangeable; selection against heterozygotes presented as a means of maintaining polymorphism; and the distinction between group and kin selection not clearly made. There are arithmetical errors in the treatment of inbreeding; and the Hardy-Weinberg theorem is derived in a baffling way. It is particularly odd to read in an account of speciation
Valerie Kapos BotanyDept,Universityof Cambridge, Cambridge CB23EA,UK
References 1 Shuttleworth,
W.J. (1988) Proc. R. Sot. London Ser. 6 233,321-346 2 Shuttleworth, W.J. et al. (1984) Q.J.R. Meteorol. Sot. 110, 1143-l 162 3 Medina, E., Montes, G., Cuevas, E. and Rokzandic, Z. (1986) J. Trap. Ecol. 2, 207-217 4 Caldwell, M.M., Eissenstat, D.M. and Richards, J.H. (1985) Science 229, 384-386 5 CermBk, J., Jenik, J., Kutera, J. and tidek, V. (1984) Oecologia 64, 145-151
6 Mordacq, L., Mousse&, M. and Deleens. E. (1986) Plant Cell Environ. 9. 735-739 7 Cosgrove, D.J., van Volkenburgh, E. and Cleland, R.E. (1984) Wanta 162, 46-54 8 Winter, K., Osmond, C.B. and Hubick, K.T. (1986) Oecologia 68, 224-230
Eclectic Evolution Processand Pattern in Evolution by Charlotte J. Avers, Oxford University Press, 1989. f28.00 (xvi + 590 pages) ISBN 0 19 505275 7 There are lots of books about evolution, but very few evolution textbooks. Because they cannot leap into the past, evolutionists - be they muscular Darwinist, stark theoretician, or just plain daft - have never hesitated to leap into print. Bookshop shelves are crowded with convincing but contradictory treatments of what evolution is all about. This confuses today’s students whose academic diet, largely limited as it is to boil-inthe-bag biology, has taught them to prefer pabulum to polemic. What undergraduates need to reassure them that the molecules they study were probably not created on October 28th 4004 BC is evolution with most of the bones taken out: a terse, simple and even bland account which explains just why -to quote a famous phrase - ‘nothing in biology makes sense except in the light of evolution’. Aversstrivesfor blandness but fails because of the richness of her in-
99