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New Phytol. (1999), 141, 369–371

Book reviews

Rothschild’s Reserves. Time and fragile nature. By

M ROTHSCHILD and P MARREN.

27±5¬21±5 cm. Pp. xv­242 with 101 plates.

Rehovot, Israel : Balaban, 1997. Price p}b: £15.00,

ISBN 0 86689 048 3.

This book is a tribute to Charles Rothschild, who virtually

invented nature conservation in Britain. In the words of

the authors, his plan was to protect and preserve the varied

habitats of rare and dwindling species by setting up a

nationwide network of nature reserves. Two thirds of this

admirable book consist of descriptions of the fate of each

of the 182 English reserves which Charles Rothschild

listed for preservation. The initial chapters include a

biographical sketch of Charles Rothschild, who was clearly

a delightful person as well as a visionary naturalist. They

show how he set up the Society for the Promotion of

Nature Reserves in 1912 and with the help of its members

obtained the information he required to select his list of

282 sites in the British Isles worthy of preservation. His

great efforts to get support from Government, local

authorities and voluntary bodies are described. He was

largely thwarted by the exigencies of the First World War

and the excessive caution of all whom he approached. He

died in 1923, his dream unfulfilled.

The accounts of what has happened to Rothschild’s

Reserves and some of their rare species during the last 82

years make sad reading and show how the two destructive

forces of development and neglect have contributed to the

destruction or serious deterioration of over 40% of the

sites. I know many of the sites described, and a present-

day view supports nearly all the assessments. Perhaps

rather too little has been made of successful efforts by the

conservation organizations who now manage over half

Rothschild’s Reserves. Deterioration of habitats and hence

loss of species in the countryside surrounding most of the

Rothschild sites must indirectly have had deleterious

effects on the flora and fauna of the sites, as they

increasingly became islands in a sea of intensively farmed

land. This point needs to be emphasized. With these small

reservations, the assessment can be accepted as an

extremely valuable account of what happened between the

time Charles Rothschild and his helpers in the SPNR

made their survey and the time when his daughter Miriam,

and Peter Marren and their helpers made theirs. The

comparisons are particularly valuable because of the length

of time between the two surveys. While loss through

development is usually all too obvious, that through

neglect is insidious, because it is slow and can easily go

unrecognized, even by observers on the spot.

It took 35 years for Charles Rothschild’s scheme to be

put into action by the newly formed Nature Conservancy.

It is depressing how long it took for the British public,

which included numerous naturalists and biologists, to act.

There are signs that we are also being too slow in reacting

to the destruction of habitat which continues today.

Perhaps the main value of this book is to emphasize the

importance of nature reserves in today’s world. If only

Charles Rothschild’s advice had been taken 80 years ago

the situation today would be enormously better than it is.

So long as modern agriculture and forestry provide so few

habitats for our native flora and fauna, nature reserves are

absolutely crucial in maintaining populations of species

now largely banished from farm and forest land. They will

provide the sources from which the wider countryside can

be recolonized, if and when changed conditions allow.

Conservation agencies, both governmental and voluntary,

should be urged not to let up on acquiring and managing

new nature reserves. Regrettably, the pace seems to be

slackening; it should be increased. More nature reserves

would be the most fitting memorial to Charles Rothschild,

the pioneer.

Rothschild’s Reserves is beautifully illustrated with

photographs taken in the past and the present (in colour).

It should be read by all who are concerned with nature

conservation today.

N M

The phytogeography of northern Europe. By E

DAHL. 25 cm¬19 cm. Pp. xii­297 with 82 text-

figures. Cambridge, UK: Cambridge Univeristy

Press, 1998. Price h}b: £60.00, ISBN 0 521 38358

7.

Eilif Dahl, who died in 1993, had a botanical carreer

spanning some 50 years. His wide-ranging interests

included floristics, lichens, ecophysiology, plant geogra-

phy, Quaternary history and climatology. When his

account of the mountain vegetation of Rondane in southern

Norway was published in 1957, it was rapidly recognized

as a classic. Many of his interests are apparent in The

phytogeography of northern Europe, which he wrote in the

last few years of his long life but did not quite complete. A

planned chapter on aquatic plants is missing. The

published version has been assembled by his widow Gro

Gulden, with assistance from John Birks. Inevitably, it

contains imperfections due to the author’s death, but is

presented to the public with the comment that an imperfect

work published is more valuable than a perfect work

unpublished.

Dahl was a champion of the nunatak hypothesis, the

theory that species survived the Pleistocene glaciations in

ice-free refugia, even in northern Europe. It is contrasted

by his editors with the alternative tabula rasa hypothesis,

that the flora of northern Europe is almost entirely

composed of immigrants from unglaciated areas from the

south, west and east of the ice. The theory of ice-free

refugia pervades Dahl’s treatment of endemism. Endemics

remain in their refugia because of ecological rigidity,

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370 Reviews

whereby populations surviving in limited refuges for long

periods ‘become ecologically specialized, show little mor-

phological variation, and are unable to invade new

territories as they become available’.

Evolution cannot fill gaps rapidly. Species are con-

strained by both primary factors (limits given the available

gene resource) and secondary factors (temporary limits

that can be overcome by microevolution). ‘There is no

known instance where it can be convincingly demonstrated

that a new amphimictic vascular plant species has evolved

by purely genetic processes other than alloploidy during

the last 18000 years’.

The book is full of interesting ideas. It is a reminder that

many fashionable notions are not new and that there are

alternatives to current fashion. The climatic requirements

of plants were seen by Dahl not so much as complex

multidimensional realized niches in climate space, but as

limits beyond which species may not transgress. In a

greenhouse world, limits might be more suitable than

realized niches for predicting effects of climate change,

because new climates might lack current analogues.

A major problem in interpreting climatic limits is that

much of the evidence is correlative. Only rarely can good

evidence of causality be established. It requires both a

strong correlation and a physiological mechanism. Dahl

studied the effect of high summer temperature on arctic

and alpine species, noting that both poor competitive

ability and a physiological intolerance of high temperatures

play a part. Another well studied limiting factor is the

requirement of trees for summer warmth. Most phyto-

geographers measure summer warmth by a simple heat

sum, for example, the annual sum of day-degrees with a

base of 0°C or 5°C. Dahl used a far more complicated

heat sum, based on the respiration of a theoretical spruce

tree with an Arrhenius response of Q"!

¯ 2±65 and a lower

temperature threshold of 2±8°C. This ‘respiration sum’

takes no account of the direct effects of solar radiation,

but does allow for diurnal variation in air temperature. It

will probably never be popular; but one is challenged to

ask why not.

Other geographical limits are less well understood.

According to Dahl, the apparent requirement of many

boreal species for a cold winter still lacks an obvious

physiological mechanism, but is probably related in some

way to the stability of the winter climate. The seeds of

Picea abies need snow cover to survive the winter. Many

other boreal plants are likely to be exhausted in an oceanic

climate by spring frosts or futile winter growth. This

limitation, however, is, at least partly, a secondary factor,

which can be overcome by the evolution of local races.

Plants of Kobresia simpliuscula from the relictual popu-

lation in England can be grown out of doors in Copenhagen

while those originating from Greenland require an arctic

glasshouse.

Dahl used four major limiting factors, winter cold,

maximum summer temperature, respiration sum and

summer drought, to define floristic elements in northern

Europe. While his definitions are interesting, they retain

some curious inconsistencies. It is puzzling to find a

‘British-Mediterranean’ sub-element of the Atlantic el-

ement but no Mediterranean–Atlantic component of the

Norwegian flora. The distribution map of the lichen

Degelia atlantica, extending from Norway to Tunisia and

southern Greece, shows just such a species.

Although phytogeography is a relatively slow-moving

subject, the book is somewhat dated, employing methods

from about 30 years ago. An account of the energy balance

of a wet surface is written mainly in units of calories per

square centimetre per minute – inconvenient for a modern

reader, who would prefer watts per square metre. Many of

the data used to estimate limiting climatic factors were

captured by manual methods, rather than from electronic

databases. Appendix 2, stretching to 73 pages, is dull. It

lists distributional data and limiting climatic factors for the

vascular plants of northern Europe. For many whole

genera, e.g. Koeleria and Alopecurus, the only information

given is whether the species are indigenous to the British

Isles or Fennoscandia or both.

Because of its high price, idiosyncrasies and inconsis-

tencies, The phytogeography of northern Europe cannot be

recommended as a standard text for undergraduate

courses. Brimming with original ideas and stimulating

theories, it is a valuable source for research workers, a

challenge for bright students and a fitting memorial to a

lifetime’s work. Those who brought the book to fruition

have done phytogeography a good service.

M H

Opportunities for biological nitrogen fixation in rice

and other non-legumes. Ed. by J. K. LADHA, F. J.

DE BRUIJN and M. A. MALIK. 26±5¬19±5 cm.

Pp. vii­216 with numerous test-figures and

tables. Dordrecht, The Netherlands: Kluwer

Academic Publishers, 1997. Price h}b: £85.00,

ISBN 0 7923 414 2; p}b: ISBN 0 7923 4748 X.

This volume contains 20 chapters, varying in length from

four to 18 pages, based on papers given at a workshop held

in conjunction with the 7th International Symposium on

Nitrogen Fixation with Non-Legumes, in October 1996 in

Faisalabad, Pakistan. All contributors were invited and

given remits which had been agreed at a previous meeting

held at IRRI in the Philippines. They thus form a more

coherent whole than the proceedings of many conferences.

All have been published in a special volume of Plant and

Soil and subjected to a refereeing process.

The first chapter sets the scene and outlines four areas

identified in the first workshop as worthy of exploration.

These are: non-nodular associations, such as that between

sugar cane and Acetobacter diazotrophicus ; nodular asso-

ciations, such as the attempts to induce nodule like

structures on rice; transferring nif genes directly into

plants; increasing our understanding of N-use efficiency in

rice, and its relation with carbon dioxide fixation. Some of

the chapters include new information, others are es-

sentially reviews, and occasionally some new ideas emerge.

Overall, the amount of information not available elsewhere

is limited, but it is very useful to have it all included in one

volume.

The bulk of the chapters (14) are entirely or mainly on

the first two topics. Few specifically address rice, rather

they point to relevant aspects of other associations, most

notably that between Azoarcus and Kallar grass. Of those

that do address rice, Barraquio et al. report isolation inter

alia of the potential nitrogen fixing organism Herba-

spirillum seropedicae, but these workers were unable to find

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Reviews 371

evidence of nitrogen fixation. This particularly organism is

an interesting one as it can also be pathogenic, with the

borderline between pathogenesis and beneficial association

being very thin (Olivares et al., 1997). The subsequent

chapter (with the same title) by Stoltzfus et al. discusses

both natural isolates and experiments with artificial

inoculation. Again the results to date are not clear-cut.

Several papers report on studies of the mode of entry of

associative bacteria into plants, including rice. This subject

is very controversial, and at the most recent (1997)

International Nitrogen Fixing Conference, in Paris,

resulted in some extremely acrimonious debate. The

evidence presented in this volume is consistent with the

entry of bacteria via wounds where lateral roots emerge, a

route which rhizobia adopt in some legumes such as

groundnut. Some plant anatomists, most notably from

McCully’s group in Canada have claimed that this is not

possible, at least in healthy monocots. It is a pity that, in

the chapter of which she is an author, this topic was not

addressed. Otherwise, this particular chapter (Rolfe et al.)

gives a good account of the effects of bacteria on root

morphogenesis. They use the term ‘modified root out-

growths’, rather than ‘para-’ or ‘pseudo’ nodules to

describe structures induced by bacteria. Based on the

legume system, Hirsch discusses the role of phyto-

hormones in nodule morphogenesis. Since one of the ways

in which bacteria affect root growth is by production of

auxins and other plant growth promoters, this paper is

timely. Promotion of root growth per se is likely to lead to

better N uptake from soil sources, making unambiguous

determination of nitrogen fixation essential. Kennedy et al.

have developed an elegant method of demonstrating this,

by tagging the nifH gene in Azospirillum brasilense with

lacZ and following the invasion of wheat roots with this

construct. This has the added benefit of demonstrating

that low oxygen conditions are present, since nifH requires

low pO#

for its induction.

Apart from the method of entry by bacteria, there are

two other questions which currently bedevil workers in the

general area of nitrogen fixation associated with grasses.

The first of these is ‘can sufficient bacteria be housed in the

plant without causing damage?’. Whilst alluded to in a

number of chapters, this problem has still not been

rigorously tackled. The second is ‘how do the plants

obtain nitrogen fixed by the bacteria, presumably for their

own use?’. In the advanced legume symbiosis, ammonium

is transferred directly to the host for assimilation. Do

associative bacteria have to die before their fixed nitrogen

is released to the plant? This does not necessarily appear to

be the case, and two of the chapters in this volume report

work on ammonia excreting mutants of bacteria.

One of the aspects of the signalling systems in the

legume–rhizobial system which has received much at-

tention recently is the role of lipo-oligosaccharides. These

substances form part of an interesting discussion by Stacey

and Shibuya, whose main thrust is chitin recognition

systems. The authors argue that, while both rice and

legumes have sites with chitin-binding proteins, legumes

may have a second, more specific site, necessary for nodule

induction. This could be one of many fundamental

differences between legumes and monocots which chal-

lenge those trying to induce nodule-like structures on the

latter.

The final chapter, by Shantaram and Mattoo, attempts

(with a considerable degree of success) to put the previous

ones in perspective and to point the way ahead for future

work. They correctly point out that, in spite of much

effort, there has been very little recent success in improving

nitrogen fixation by legumes (e.g. by using genetically

modified rhizobia). They argue that a research programme

devoted to improving uptake and utilization of combined

N by plants in general has much to commend it.

I have not attempted to cover every single chapter in this

book. The most notable omission is the chapter of Dixon

et al. on the prospects and problems of introducing nif into

plants. I recommend readers to follow this well argued

account.

Taken overall, this volume contains a well balanced

assessment of the state-of-play on the possibilities of

exploiting nitrogen fixation in association with rice.

However, I can see no justification in Kluwer, yet again,

selling a hardback copy, at a high price, of material that has

already been published in their own journal, Plant and

Soil. Apart from the Preface, nothing is added. It would

have been relatively simple, with modern technology, to

have included an index and enhanced the value of a

separate volume.

Olivares FL, James EK, Baldani JI, Do$ bereiner J. 1997.Infection of mottled stripe disease-susceptible and resistant

sugar cane varieties by the endophytic diazotroph Herbaspiril-

lum. New Phytologist 135 : 723–737.

J. I. S