root traits governed by biological and environmental...

Root traits governed by biological and environmental factors

Louise Comas

Breeding for root traits: a new frontier

Critical functions

Functional traits still poorly understood

Dynamic

High C costsDon Tremain, Tree with rootsGetty Collection

Talk outline Plant strategies belowground: root trait

evolution

Effects of plant management and environment on root dynamics & functioning

(UC Davis walnut research & breeding program)

(USDA corn & sunflower water deficit research )

Root system structure

1st order

2nd

(3rd)

Coarse roots (structural support, plumbing)

Fine roots (physiologically active, ephemeral)

Evolved plant strategies below ground

What can we learn from natural selection?

Mature tree traits

SRL

(m g

-1)

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

QAQR

AS

AN

FG

BL

CG

CO

PV

PS

Fast Slow

SR

L (m

g-1

)

0

50

100

150

200

250

300 (a)

SRLFast > Slow

(P<0.05)

Seedling traits

• faster root proliferation• more soil explored

Root morphology

Comas et al. 2002; Comas & Eissenstat 2004

PV0.00

Aceraceae Fagaceae PinaceaeAN AS TCQR QA

Fast-growing seedlings

Fast Slow

Consistency Index = 0.44

= m g-1SRL

- Unordered linear parsimony- Square-root reconstruction- Tree based on APGII 2003

Comas & Eissenstat 2009

Comas et al 2012 IJPSCenozoicPaleo-geneCretaceousTriassicPermianCarboniferous

Paleozoic Mesozoic

Jurassic Neo-gene

Cenozoic

300 200 100 0 MY

0.13-0.400.40-0.680.68-0.960.96-1.241.24-1.511.51-1.791.79-2.072.07-2.352.35-2.622.62-2.902.90-3.18

Phylogenetic pattern

Distance from each node to root of the tree (MY)

0 100 200 300 400

Diam

eter (m

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4Paleozoic Mesozoic Cen.

Comas et al 2012 IJPS

Evolution in root diameter

R2 = 0.83P < 0.05

Lower [CO2]Greater stom. densityHigh leaf vein density

Thinner roots = less cortex for less impedance to water movement?

Roo

t len

gth

dens

ity

(cm

/cm

3 )

6

4

2

20 40 60 80 100 SRL (m/g)

Comas et al 2012 IJPS, data from Withington et al 2006

Trade-offs between morphology & RLD

R2 = 0.69P < 0.05

Conclusions• Within close relatives, longer SRL and thinner

roots allow fast-growing species to exploit soil pockets more quickly (with higher costs but faster returns on these costs)

• Root morphology more ‘hard-wired’ than physiology

• Evidence suggests that angiosperms evolved thinner roots with longer SRL, potentially to increase water uptake & transport, and out compete plants in upland habitats

NE US vineyards• Juice grape production

• Lake Erie region, NY

• Soil: Chenango gravelly loam

• Training: high-wire bilateral cordon

• Minimal pruning to reducecosts and raise crop yield

• Issues with alternate-bearing vines

Vitis labruscana Bailey cv Concord

Effects of plant management and environment on root dynamics & functioni

Balanced growth theory - does irrigation compensate for root growth?

Irrigated vs non-irrigated?

Competing sinks - do roots compete with fruit for plant carbon?

Minimal vs heavy pruning? Timing?

Questions

• Roots compete with fruit for plant carbon

• Root growth is bimodal - major root flush in spring with a smaller root flush in fall

Conventional wisdom in grape

Mullins MG, Bouquet A. Williams LE. 1992. Biology of the Grapevine.

• 25-yr-old vines, treatments initiated in 1991

• Completely randomized block design; 2x2 factorial

• experimental unit = 5 vines plus 2 as buffer

• study duration = 4 years (1997-2000)

• roots observed with minirhizotrons

xx

xx

xx

xx

xx

xx

xx

xx

Block 4Block 1

Block 3Block 2

xx

xx x

x

xx

xx

xx x

x

xx

xx

xx x

x

xx

xx

xx x

x

xx

xx

xx x

x

xx

xx

xx x

x

xx

xexperimental vinesbuffer vinesroot tubes

Experimental layout

Record images: every 2 wks (active vines)1x per month (dormant)

Minirhizotrons

Root production

Ave

rage

tota

l roo

t pro

duct

ion

(mm

cm

-2 y

r-1)

0.0

0.5

1.0

1.5

2.0

2.5

NI Irr NI Irr

Dry years Wet years

Comas et al. 2005 New Phytologist

Root distribution in dry years

1997

1998

Dep

th (c

m)

1999

2000

Mean fine root production (%)0.0 0.2 0.4 0.6 0.8 1.0

0 - 20

21 - 40

41 - 60

61 - 80

81 - 110

*

**

**

0 - 20

21 - 40

41 - 60

61 - 80

81 - 110

0 - 20

21 - 40

41 - 60

61 - 80

81 - 110

0 - 20

21 - 40

41 - 60

61 - 80

81 - 110

Non-irrigatedIrrigated

(wet)

(dry)

(dry)

(wet)


Timing of root production

1997

0.00

0.02

0.04

0.06 Heav/NIHeav/IrrMin/NIMin/Irr

1998

New

root

s (m

m c

m-2

)

0.00

0.02

0.04

0.06

1999

0.00

0.02

0.04

0.06

2000

Mar Apr May Jun Jul Aug Sep Oct Nov

0.00

0.02

0.04

0.06

Comas et al. 2010 AJGWR

(wet)

(dry)

(dry)

(wet)

Root production rate


0.00

0.01

0.02

0.03

Vine phenology

Bud dev Flwr dev Frt dev Frt ripe Sht dormBud dev Flwr dev Frt dev Frt ripe Sht dorm

Rat

e of

root

pro

duct

ion

(mm

cm

-2 d

-1)

0.00

0.01

0.02

0.03

0.00

0.01

0.02

0.0319971998

1999 2000

Wet yearsDry years

Heav/NIHeav/IrrMin/NIMin/Irr

Ear dev Frt set Frt dev Frt ripe Sht dorm Ear dev Frt set Frt dev Frt ripe Sht dorm

v

vbl

bl

v

bl

vbl

(cm)

Mea

n fin

e ro

ot p

rodu

ctio

n (m

m c

m-2

d-1

)

0.0

0.5

1.0

1.5

2.0

2.5

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

Apr May Jun Jul Aug Sep Oct0.0

0.5

1.0

1.5

0 - 20

21 - 40

41 - 60

61 - 80

Apr May Jun Jul Aug Sep Oct

81 - 110

Root phenology & distribution


Minimally pruned Heavily prunedDepth

Conclusions

• No evidence of C limitations on root growth

• Amount & timing of root growth is controlled by both plant and environment (canopy development & soil moisture)

Aging effects on root function

1mm

Ephemeral fine roots

Root boxes

Whi

te ro

ots

(%)

0255075

100

% white % dark Plot 1 Zero

Root age (weeks)0 1 2 3 4 5 6 7 8 9

TTC

redu

ctio

n (A

g-1

DW

)

0

10

20

30

40

50

60

70

80

0

5

10

15

20

25

30

35

40

45

50

55

RespirationTTC reduction

Respiration (nm

ol O2 g -1 D

W s -1)

(a)

(b)


Root metabolism with age

0

20

40

60

80

100

120

140

White Brow n Black Control

TTC

redu

ctio

n (A

g-1

d.w

t.)

Root pigmentation

3902408 Jul 97 30 Mar 981 Nov 97

White Brown Black

Metabolic decline w/ pigmentation

1 mm


• Other work has shown nutrient uptake capacity declines quickly with root age (P in apple, Bouma et al 2001; N in grape, Volder et al 2005); What about water uptake?

• Young roots have high C costs but greatest nutrient acquisition capacity

• Apples vs oranges (Eissenstat 1999)

• Other environmental factors, especially temperature effects on root growth & function?

Root functioning with age

• Some broad generalizations may hold (fast growth, drought adapted = long SRL, thin diameters)

• Complexity in root functioning demands in-depth knowledge of the system breeders are breeding for

• What root traits do plants need to sustain yields under different types of drought? Different strategies for different species?

Implications & future directions

Acknowledgements

Root evolutionKevin Mueller, Univ MinnesotaLyla Taylor, Univ of SheffieldPeter Midford, NESCentHilary Callahan, Barnard/ColumbiaDavid Beerling, Univ of Sheffield

Grape ResearchDavid Eissenstat, PSUAlan Lakso, Cornell Laurie Anderson, Ohio WesleyanRick Dunst, Cornell Vineyard Lab

Funding sourcesUSDA/CSREES Eastern & Western Viticulture ConsortiumNSF IOSNESCent

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

bloomveraison

harvest

bloom

veraisonharvest

bloom

veraison

harvest

bloom

veraison

harvest

1997

0.00.20.40.60.81.01.21.41.6

1998

0.00.20.40.60.81.01.21.41.6

1999

Roo

ts p

rese

nt (

mm

cm

-2)

0.00.20.40.60.81.01.21.41.6

2000

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

0.00.20.40.60.81.01.21.41.6

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

B. Brown rootsA. White roots C. Total roots

Heav/NIHeav/Irr

Min/NIMin/Irr

(wet)

(dry)

(dry)

(wet)

Standing root populations veraison

veraison

veraison

veraison


root traits governed by biological and environmental...

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