Making Eden Read online

  M A K I NG E DE N

  For Juliette and Joshua

  and

  My parents and their insistence on the holiday diaries

  1

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  botany /’bot(ə)ni/ n. 1. the study of the physiology, structure, genetics, ecology, distribution, classification, and economic importance of plants. 2. The plant life of a particular area or time. botanic /bə’tanɪk/ adj. botanical /bə’tanɪk(ə)l/ adj.

  botanically /bə’tanɪk(ə)li/ adv. botanist n. [botanic via French botanique or Late Latin botanicus from Greek botanikos, from botaneˉ ‘plant’: botany is from botanic]

  OED

  PREFACE

  My ancestors farmed the south-east corner of England for three centuries,

  tending to sheep on the lowland pastures of the Kent marshes, reclaimed

  from the clutches of the English Channel by the Romans and later the Saxons.

  Another branch of the family has been cultivating pasture and dairy cattle on the farmlands of Essex since before the last world war. The poet John Betjeman

  (1906–1984), a fine chronicler of life in England (whose statue, incidentally, can be found inside St Pancras Station), wrote of the vanished beauty of nearby Romney

  Marsh ‘where the roads wind like streams through pasture, and the sky is always

  three-quarters of the landscape’.

  For the farming community, life was harder and less romantic than Betjeman’s

  take on things. Shepherds tended large flocks of sheep that grazed hundreds of

  acres of pasture. Shearing, lambing, rescuing animals from drainage ditches, building pens, and treating wounds were routine matters for them. They holed up at

  night in simple huts, each a basecamp for storing tools and medicines that offered few comforts and afforded minimal protection from the severe winds that raced in

  unchecked from the sea. Peripatetic shepherding—one man, his dog, a hut, and

  large flocks of sheep—was a hard way to make a living and produced a tough breed

  of men. Their lives depended on a collective wisdom, knowledge handed down

  from one generation to the next, that ensured stocking densities were adjusted

  and flocks moved to the best pastures available as the seasons turned.

  The shepherd’s livelihood depended on getting things right for the landowner

  by understanding how pastures fattened the white woolly grazing herbivores.

  The payoff came when the fattened animals were sent to the London meat market

  and the wool sold to the Wealden cloth industry or smuggled to the European

  mainland. Wool was a valuable commodity in those days, and the marsh men

  were quite prepared to risk a jail sentence for the monetary rewards to be had

  from smuggling and selling fleeces abroad, especially to France. Romney Marsh

  viii a preface

  sheep keepers maintained the pastoral economy in this way for over 500 years

  and surviving huts can still be found dotted across the region, relicts of times past.

  My grandfather’s tools hang up in the shed I can see from my office window

  and connect the past with the present. The handles worn smooth by over five

  decades of hard labour on the marshes remind me of his understanding between

  plants, stock, and the land. He understood that the grazing pastures of Kent fuel the rural economy of the county and have done so for centuries, and this regional situation is really a parable for how the whole planet operates. Plants are the food stock of the biosphere and everything else follows from there. Without plants,

  there would be no us.

  Over 7 billion people (and rising) depend on plants for healthy, productive,

  secure lives, but few of us stop to consider the origin of the plant kingdom that turned the world green and made our lives possible. The origin of humans is frequently considered in books and TV documentaries, but not the origin of land

  plants. And as the human population continues to escalate, our survival depends

  on how we treat the plant kingdom and the soils that sustain it. The evolutionary history of our land floras, the story of how plant life conquered the continents to dominate the planet, is fundamental to our own existence.

  This, then, is the subject of Making Eden. Building on the foundations established by generations of scientists, it reveals the hidden history of Earth’s sun-shot greenery and considers its future prospects as we farm the planet to feed the

  world. Our evolutionary journey stretches back over half a billion years with

  twists and turns decoded from clues encrypted in fossils, DNA molecules, and the

  ecology of the plant kingdom. It is a story of how plant life on land originated

  from freshwater algal ancestors, how it inhaled, diversified, and spread out to conquer the continents, slowly air-conditioning the planet. Finally we are glimpsing answers to the question of origins that have haunted botanists ever since Darwin.

  In some respects, Making Eden can be regarded as the prequel to my previous book, The Emerald Planet (2007), which actually had rather little to say about how plant life on land got going and sustains the diversity of life there. Instead, it offered a closely argued case for recognizing plants as a ‘geological force of

  nature’, drivers of changes, sculpting continents, and changing the chemistry of

  the atmosphere and oceans, to set the agenda for life on Earth. It was a long overlooked story that went on to sow the seeds for the three-part BBC2 television

  series How to Grow a Planet (2012).

  preface a ix

  But now the stage is set for Making Eden. My hope in writing this book is that it might at least give readers pause for thought before dismissing botany as boring

  and irrelev
ant. I also hope that it might persuade readers to think of plants, and the scientists who study them, in an entertaining new light. Steve Jones, a leading geneticist at University College London, and one time regular science columnist

  for the Daily Telegraph, wrote an article a few years ago entitled ‘Where have all the botanists gone, just when we need them?’ He rightly pointed out the central role

  of plants in the challenges facing humanity, and the challenges facing the subject of botany, writing ‘why do students find the vegetable world so boring when without it we would perish?’ Plants and botanists are in need of greater advocacy.

  Ultimately, I hope readers may come to appreciate that botany is an astonishing

  and deeply engaging field of scientific enquiry, with immediacy to all life on Earth.

  d.b.

  Sheffield, 2018

  ACKNOWLEDGEMEN TS

  I am fortunate to be located in an outstanding academic department at the

  University of Sheffield, with many talented and generous colleagues. I offer

  sincere thanks to Jonathan Leake, Charles Wellman, Sir David Read, Colin

  Osborne, Ben Hatchwell, David Edwards, Jon Slate, and Pascal Antoine Christin,

  who all read and commented on various drafts, as well as shared and discussed

  ideas with me. The department houses a ‘writer in residence’ scheme funded by

  the Royal Society of Literature: conversations with successive incumbents, Fiona

  Shaw and Frances Byrnes, about writing and readers proved enlightening.

  I offer warm thanks to the following colleagues from other institutes who

  kindly took the time to read and comment on early and late-breaking drafts of

  chapters, or have discussed issues that arose: Phil Donoghue, Burkhard Becker,

  Yves Van de Peer, Doug Soltis, David Hibbett, Steve Banwart, Chuck Delwiche,

  Jane Langdale, Nick Harberd, Jill Harrison, Lawren Sack, Peter Franks, Alistair

  Hetherington, Dominique Bergmann, Joe Berry, Ralf Reski, John Bowman, Stefan

  Rensing, Kevin Newsham, Chris Berry, Bill Stein, Linda VanAller Hernick, Frank

  Mannolini, Martin Bidartondo, Jeff Duckett, Dana Royer, Christine Strullu-

  Derrien, and Jim Hansen. All of these individuals helped sharpen my thinking.

  John Bowman and Stefan Rensing kindly shared copies of their unpublished

  manuscripts on the genomes of Marchantia and Chara, respectively. David Malloch helpfully discussed his mycological thinking with me, and both he and David

  Hawksworth provided the back-story on Kris Pirozynski and a picture or two.

  Peter Raven generously agreed to be interviewed and treated me to a memorable

  lunch in St Louis made unforgettable by his compelling narrative on the state of

  the planet, and plant life in particular. Paul Kenrick at the Natural History Museum, London, kindly provided a valuable critique on a late, nearly complete draft of the manuscript and caught some crucial errors. I thank all of these people whose

  work has helped shape and improve the text. Of course, any errors are my own

  responsibility.

  xii a ack now ledgements

  We all need great mentors, no matter which walk of life we choose. In having

  the late William (Bill) Chaloner FRS (22 November 1928–13 October 2016) as a

  mentor for nearly two decades, I was fortunate to have had one of the best. Bill

  died before I completed this book, but had already offered me his encouraging,

  critical comments on several chapters. This book is dedicated to Bill’s memory; a man who really did ‘leave an afterglow of smiles when life is done’. In 1970, Bill published an influential academic paper entitled ‘The rise of the first land plants’

  ( Biological Reviews, 45, 353–77) in which he dealt with ‘the facts from which a hypothesis of evolutionary progression may be constructed’. Nearly 50 years on,

  I realize that I have unconsciously written my own update on that same thesis.

  Financial support for my research group over the past decade has been pro-

  vided by the Royal Society, the Leverhulme Trust, and the Natural Environment

  Research Council, UK, for which I am most grateful.

  Sincere thanks must go to my patient and enthusiastic editor, Latha Menon,

  whose editorial comments and wise suggestions improved the text. My gratitude

  too, to Jenny Nugée, and the rest of the Oxford University Press team, who effi-

  ciently took the book through the publication process.

  Writing this book has taken quite some time, which in one way has been help-

  ful because the suspicion is that a long manuscript improves with a long gestation time. But the down side is the steeply rising forbearance required of my wife,

  Juliette, who additionally provided title inspiration. So there comes a point, after so many years, when you have to get on with it. Joshua’s imminent arrival helped

  daddy get a move on, so that we can all spend more time together growing apples,

  walking, bird watching, and learning how to fish. I thank Juliette and Joshua for their patience, love, and support, and look forward to our fun times together now that this is done.

  CON TEN TS

  1. All flesh is grass

  1

  2. Fifty shades of green

  14

  3. Genomes decoded

  42

  4. Ancient genes, new plants

  66

  5. Gas valves

  94

  6. Ancestral alliances

  122

  7. Sculpting climate

  150

  8. Eden under siege

  172

  Simplified Geologic Timescale from the Cambrian

  199

  Endnotes

  200

  Figure credits

  243

  Plate credits

  245

  Publisher’s acknowledgements

  246

  Index

  247

  High irradiance

  Terrestrial stressors

  Drought

  Fresh water

  Algal mat

  Salt water

  Ch

  Mesostigma

  Ch

  Klebsor

  Ch

  Co

  Zygnemat

  La

  loroph

  loro

  arop

  leoc

  ndp

  ky

  mi

  hy

  haetop

  lan

  yt

  bo

  ce

  ophy

  ts

  es

  diophy

  toph

  ph

  ae

  yc

  hy

  ce

  yc

  ea

  ce

  ce

  ae

  ea

  e

  ae

  ae

  e

  KCM

  KCM

  ZCC

  Streptophytes

  Chloroplastida

  Interaction with

  substrate microbiota?

  Plate 1. Colonization of terrestrial habitats by streptophyte green algae, the group that includes all land plants. ZCC abbreviates the higher branching grades (Zygnematophyceae, Coleochaetophyceae, and Charophyceae) and KCM abbreviates the lower branching or

  basal grades (Klebsormidiophyceae, Chlorokybophyceae, and Mesostigmatophyceae).

  Plate 2. Present-day species of charophyte algae, the group which includes the freshwater ancestors of land plants. (A) Klebsormidium nitens (Klebsormidiales), (B) the stonewort Nitella hyalina (Charales), (C) Coleochaete pulvinata (Coleochaetales), and (D) Spirogyra (spiral chloroplast) and Mougeotia (flat chloroplast) (Zygnematales). Note basal branch in Mougeotia
(white arrow) and holdfasts (black arrows).

  Plate 3. The diversity of plants. (A) An assemblage of Phaeoceros (a hornwort; white arrow), Fossombronia (a leafy liverwort; red arrow), and interspersed mosses. The arrows point to the sporophytes. (B) Lycopodium digitatum, a lycopod, showing spore-bearing cones. (C) A tree fern ( Cyathea horrida), (D) the cycad Cycas revoluta, a widely cultivated cycad sometimes called ‘Sago Palm’, (E) Nymphaea hybrid, a water lily, a representative of one of the basal branches of flowering plants, and (F) Ampelopsis sp., grape family (Vitaceae) being pollinated by a wasp. Ampelopsis represents the eudicots.

  Plate 4. Coastal redwoods, the tallest trees on Earth. This titan lives in Prairie Creek Redwoods State Park, California, USA and is probably over 1500 years old. Photo composed of a mosaic of 84 images.

  Wild type “normal”

  Moss line without

  Moss line without

  Moss line without

  moss

  the SMF1 gene

  the SMF2 gene

  the SCRM gene

  (no stomata develop)

  (stomata develop)

  (no stomata develop)

  Stomata

  Plate 5. Normal moss develops stomata on its sporophytes, whereas lines lacking SMF1 and SCRM genes develop sporophytes lacking stomata. In contrast, those with the SMF2 gene develop normal stomata. The top line of images were taken with an epifluorescence microscope which causes the stomata to glow. The lower set are photos taken using a scanning electron microscope. Scale bar in all images = 50 µm.

  Plate 6. Reconstruction of the early vascular land plant Aglaophyton with images of a cross section of a rhizome and fossilized fungal structures resembling arbuscules. Top right photo (cross section): ×15 magnification; bottom photo: × 600 magnification.

  Plate 7. Exhibit of sedimentary tree stumps outside the Gilboa Museum.

  Plate 8. Reconstruction of the 385-million-year old complex forest at Gilboa, one of the first forests on Earth.

  Plate 9. Mobile truck-mounted rig for drilling rock cores at a quarry near Cairo, New York State.

  Plate 10. Rock cores of fossil soils drilled from a 385-million-year-old forest floor. Smaller image shows small tree (archaeopteridalean-type) root, termed a rhizolith, preserved as clay cast with central carbonaceous strand, surrounded by a ‘drab-halo’. Scale bar = 1 cm.