Growth Efficiencies ofDiverse Pinus taeda families

as affected byGenetics of the Root system

James E. Grissom and Steven E. McKeandDepartment of Forestry

North Carolina State University,Raleigh, NC, U.S.A.

Objectives

Evaluate genetic effects of Roots upon Aboveground Growth process

Determine whether Root system can alter Stemwood production; under what conditions

Identify physiological traits related to Root effects on Stemwood production

Materials and Methods

Loblolly pine seedlings from 2 contrasting provenances;10 OP families; 5 from fast-growing (ACP) prov. and 5 from slow-growing (LPT) prov.

total 1800 seedlings

Grafted reciprocally (fast type onto slow type, and vice versa)

All possible combinations of genotypes

Grafted at 12 weeks of age (June 1997)

Out-planted at 40 weeks of age (January 1998),on a sandy infertile site in Scotland County, NCPlanted in split plot layout, of 6 blocks, full set of 150 trees per sub-plot ;

half of the plots were fertilized by hand, twice each year.

Fertilizer applications:Elemental dosage (kg/ha)

Month N* P K Fe B Cu ZnMarch 50 23 40 0.5 -- -- --June 50 23 40 0.5 0.1 0.2 0.2

* N - total 10% composed of 6% urea + 4% ammoniacal

Methods

After two growing seasons, in early October 1999,

Tree heights and diameters were measured,

Roots were dug up and seedlings harvested.

Methods

Total numbers of harvested seedlings:

Type Fast-grow Slow-grow GRAFTED 260 260NON-GRAFTED 40 40

300 + 300

Roots were washed, dried and weighed.

Stems, branches and leaves were separately dried in 70oC oven for 72 hours, and then weighed.

Methods

Leaf Physiology:

Methods

Gas Exchange Instantaneous Portable Photosynthesis

System (Li-Cor LI-6400)

Carbon isotope Integral Mass spectrometry

composition (Finnigan Isotope Ratio Mass Spec.)

Weather Data:

13.1”

7.9”

-5.2”

-10

-5

0

5

10

15

NormalMay-Aug.

ActualMay-Aug.

Deficit

During Summer of 1999, moderate droughtoccurred in central North Carolina:

TotalRainfall(inches)

0

300

600

900

1200

Rootstock type

Fast Slow

= SLOW

= FAST

Fast Slow

Total

Biomass

(g)

|-- Fast --| |-- Slow --| Top (scion)

Total Plant Biomass, Grafted Trees,Fertilized treatment, aged 2 years

450

300

150

0

150

300

450

600

750

900

Rootstock type

Mas

s (g

)For Fast-growing seedling top:

Fast Slow

Above-ground

Below-ground 450

300

150

0

150

300

450

600

750

900

Rootstock type

Ma

ss

(g

)

= SLOW= FAST

For Slow-growingseedling top:

Fast Slow

Biomass Allocation :

Stem Growth Efficiencies, Grafted treesFertilized treatment

0.0

0.2

0.4

0.6

0.8

1.0

Fast Slow

Rootstock

FAST SLOW

Fast Slow

|-- Fast ---| Top |-- Slow --| Stem mass

Leaf mass

ANOVA:Source P-value

Top (scion) 0.01

Rootstock 0.09

(g/g)

Water Use Efficiency of shoot of Fast-growing family is Raised when grown on Slow-growing Rootstock.

Ph

oto

syn

thet

ic

Rat

e ( u

mo

l/m2/s

ec)

Leaf Water Conductance ( mol /m 2/sec)

Steeper slope means greater efficiency

Rootstock type:

SLOW FAST

4

5

6

7

8

9

10

0.06 0.08 0.10 0.12 0.14 0.16

Carbon Isotope Discriminationby Graft Class, Fertilized treatment

18

19

20

21

22

FAST SLOW

Fast Slow

Rootstock

Fast Slow

|-- Fast ---| Top |-- Slow ---|ANOVA:Source P-value

Top (scion) 0.035

Rootstock 0.006

(%o)

Growth Efficiency vs.Carbon Isotope Discrimination

0.5

0.6

0.7

0.8

0.9

1

19.0 19.5 20.0 20.5 21.0

C Isotope Discrimination (%%)

Gro

wth

Eff

icie

ncy

s:Fastr:Slow

FastFast

SlowSlow

SlowFast

Higher Water Use Efficiency (?)

Summary of Important Results

Rootstocks can substantially impact allocation of mass to aboveground parts, including the main stem.

When fertilized, fast-growing provenance attains large mass both above- and below-ground, even when grafted to a slow-growing counterpart.

Biomass Allocation

Summary of Important Results

Stem Growth Efficiency is affected more by Scion stock, but Water Use Efficiency is affected more by Root stock.

Efficiency of Foliage

Conclusions

Genetic factors in Roots can alter Growth Efficiency, when soil nutrients are adequate for growth.

Growth Efficiency appears related to Water Use Efficiency, among genetic families.

Carbon isotope (13C) content in leaves shows promise as a physiological marker for “Efficiency of Foliage”.