Response of Pinus pinaster Ait. provenances at early age to water supply. I. Water relation parameters

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Response of Pinus pinaster Ait. provenances at early

age to water supply. I. Water relation parameters

Manuel Fernández, Luis Gil, José A. Pardos

To cite this version:

Original

article

Response

of Pinus

_pinaster

Ait.

_provenances

at

_early

age

to water

supply.

I. Water

relation

parameters

Manuel Fernández Luis

_Gil,

José A. Pardos*

Unidad de Anatomía,

Fisiología

y Genética, ETS de

Ingenieros

de Montes, Ciudad Universitaria s/n,

Universidad Politécnica de Madrid, 28040 Madrid,

Spain

(Received 8 December _1997; revised 11 March 1998;

_accepted

17

_August

₁₉₉₈₎

Abstract - The seasonal evolution of tissue water relations was assessed in

_{1-year-old seedlings}

of four Pinus _{pinaster Ait.}

prove-nances

_growing

in a _{nursery and}

_subjected

to two water

_{supply regimes. Seedlings}

were also submitted to water stress

_cycles

in a

controlled environment chamber. Water relation parameters were deduced from

_{pressure-volume}

curves.

_Significant

differences were

found between water

_{supply regimes}

and measurement dates and sometimes among provenances. For the lowest water

_availability

treatment, osmotic

potential

at full _turgor decreased

_by

0.4 MPa in some _{provenances, whereas well-watered}

_seedlings

showed almost no osmotic

_adjustment.

Provenances

_originating

from hotter sites demonstrated a

_larger

and more

_rapid

acclimation to water stress _{conditions than provenances from colder sites. Osmotic}

_adjustment,

as an initial or short-term reaction,

together

with

longer-term

_changes

in cellular

_elasticity,

are both observed in P. _{pinaster in response} to water

_shortage.

These

_{physiological adaptations}

complement

known

_{morphological adaptations}

to

_drought

stress in this

_species.

With _caution, assessment of these parameters in young

seedlings

can be used as a tool for

_early

selection and

_prediction

of future

_performance

under conditions of water limitations.

(© Inra/Elsevier, Paris.)

maritime

_pine

/ _early selection / water relation _parameter

Résumé -

Réponse

au stress

_hydrique

_{des provenances de Pinus}

_pinaster

Ait. à un

_{âge précoce.}

I. Paramètres

_hydriques.

L’évolution saisonnière des relations

_hydriques

a été déterminée chez _{quatre provenances de semis d’un} an de Pinus _{pinaster Ait,}

installées en

_pépinière

et soumises à deux

_{régimes d’arrosage.}

Des semis étaient aussi soumis à des

_cycles

de stress

_hydrique

dans

une chambre climatisée. Les

_paramètres

des relations

_hydriques

ont été déduits de courbes

_{pression-volume.}

Des différences

signifi-catives ont été trouvées entre les différents _types

_d’arrosage

et aussi entre dates de mesure et provenances. En ce

_qui

concerne le

trai-tement

_{correspondant}

au stress

_hydrique

le

_{plus important,}

on a _{constaté que le}

_{potentiel osmotique}

à

_pleine

_turgescence diminuait de

0,4 MPa chez certaines provenances alors

qu’il n’y

avait

_pratiquement

_pas

_{d’ajustement osmotique}

chez les semis bien arrosés. Les provenances

originaires

des stations les

_plus

chaudes ont montré une acclimatation

_{plus grande}

et

_{plus rapide}

aux conditions de

sécheresse que les provenances des stations

plus

froides. En

_réponse

à la sécheresse il a été observé chez Pinus _pinaster un

ajuste-ment

_osmotique,

réaction à court terme, avec un

_changement

à

_long

terme de l’élasticité cellulaire. Ces

adaptations physiologiques

complètent

des connaissances

_{déjà acquises}

sur les

_{adaptations morphologiques}

à la sécheresse chez ces

_espèces.

Avec

_précaution,

la détermination de ces

_paramètres

chez de

_jeunes

semis _peut être utilisée comme un outil pour une sélection

_précoce

et la

_prédiction

des

_performances

futures en situation de limitation en eau. _{(© Inra/Elsevier, Paris.)}

pin maritime / sélection

_précoce

/

_paramètres

de relation hydrique

*

Correspondence

and

_reprints

1. INTRODUCTION

Pinus

_pinaster

is

_widely

distributed in the

Mediterranean basin. Natural

_populations

as well as

plantations

occupy more than 1.4 million ha in

_Spain.

New

_plantations

are

_being

established in the Iberian

Peninsula and more are

_planned

for the near future

_[10].

However,

water

_supply

affects survival and

_growth

in

some

_plantations

_especially

if

_appropriate

_provenances are not used. Limited research has shown the _presence of

some differences in _response to water stress between provenances

[18, 37].

Nguyen

and Lamant

[30]

observed

differences in osmotic

_adjustment

between _provenances;

however,

more research is needed

_[26].

The historic

_necessity

to

_complete

a

_{breeding cycle}

in

order to select and _propagate

_{high yielding}

trees may be

shortened

_through

_early

selection

_[11].

This not

_only

reduces the

_waiting

time but allows the selection

intensi-ty to be increased and even leads to a

_{higher heritability}

because of the lower environmental variation

_[19].

In

fact,

for many

species

early

selection revealed the

exis-tence of

_genetic

differences in

_growth

rate and the

occur-rence, in some

_genotypes,

of a better

_adaptation

and a

higher

yield

under water stress conditions

[8].

A com-mon

_{experimental approach}

consists of

_{submitting plants}

to a _{range of} water

_{supply regimes,}

and to evaluate

mor-phological, physiological

and

_genetic

_parameters

in

order to establish a

_{ranking regarding}

the taxons

(species,

provenances,

genotypes)

under

_study

_[23].

Exposure

to

_drought

induces some

_acclimation;

how-ever,

_plants

need to detect small decreases in soil

mois-ture content and react

_quickly

to avoid harmful

dehydra-tion

_[33].

_{This response is}

_likely

under moderate

_genetic

control

_[29].

The _parameters deduced from

_{pressure-volume}

curves

(osmotic

potential

at full

_turgor

and at turgor

loss,

rela-tive water content at _turgor

loss,

bulk

_elasticity

modulus,

apoplastic

water)

provide

some information on a

_plant’s

capacity

(such

as

_{osmoregulation,}

cellular

_elasticity,

cel-lular water

_relations)

to maintain

_growth

and to avoid

damage

due to water stress

_[6].

The _present work

_analyses

the _responses of several

ecologically

distant provenances of P.

_pinaster

to water

availability

in terms of tissue water relation

_parameters.

Seedlings

are

_subjected

to a _{range of} water

_supply

regimes

under _nursery and

_growth

chamber

conditions,

in order to establish criteria for

_early

selection and

suit-ability

for afforestation on

_droughty

sites.

2. MATERIALS AND METHODS

During

April

1994,

seeds from the three Iberian

provenances

(Oria [Or],

Arenas de San Pedro

[Ar]

and

San Leonardo de

_Yagüe

[SL])

and two _open

_pollinated

families of one French _provenance

_{(Landes [Ld])}

were

collected

_(figure

_1,

table

_I)

and

_germinated

on moist

per-lite at 20 °C and 14 h

_photoperiod.

After

_germination,

seedlings

were taken to _open air under translucid cover

and sown in containers filled with 230 mL of sand:black

peat mixture

(2:1 v/v).

A weather station recorded air

temperatures

(figure

2).

All

_seedlings

were watered twice a week for 2 months. A

_{fungicide (Captan}

0.1

_%)

was

systematical-ly

sprayed

on the

_plants.

After 2

months,

two different

water

_supply

_regimes

were

_applied:

once a week

_(R1)

and _every 2nd week

_(R2)

to field

_capacity.

The

experi-mental

_design

consisted of 12

_completely

randomised blocks with 15

_plants

_per

block,

provenance and water

supply regime - altogether

1 440

_seedlings.

Three times

_(June,

2nd

week;

July,

3rd

week;

and

September,

2nd

_week),

four

_plants

_{per provenance} and

water

_{supply regime}

were removed

_just

before

_watering

and used for the

_{pressure-volume analysis.}

Water poten-tial was measured

_using

a _{pressure chamber}

_(PMS

Instruments Co.

_{Corvallis, OR, USA)}

_according

to

Ritchie and

_Hinckley

[34].

Pressure-volume curves were

constructed

_following

the

_technique

of Koide et al.

_[22].

as follows: Five-cm

_long

shoot _segments from the apex

of the

_plants

were

_removed,

their basal ends were

_placed

into distilled water and were allowed to

_rehydrated

for 12 h in closed tubes in a cool dark humid chamber. As a

result,

a water

_potential

value between -0.02 to -0.05

MPa was achieved. At this

_point,

the shoot

_segments

were allowed to

_dry

under ambient conditions in the

lab-oratory

(at

a

_nearly

constant

_temperature

of

_{20 °C). Then,}

at

_intervals,

fresh

_weight

and water

_potential

were

mea-sured. Curves with oversaturation

_points

were less than 5

% of the

_samples;

in these cases the

_points

in the

_plateau

region

were omitted and the curves were corrected

according

to Kubiske and Abrams

_[24].

The

_following

parameters were then calculated: osmotic

potential

at full

turgor (Ψπ100) and at

_turgor

loss

_(Ψπ0)

and the osmotic

amplitude

for _turgor maintenance

_{(ΔΨπ =}

Ψπ100

apoplastic

water at full _turgor to

_{dry weight}

ratio

(Wap/DW),

maximum

_elasticity

modulus

_(ϵmax)

and

weight

at full

_turgor

to

_{dry weight}

ratio

_(TW/DW).

At the same

_time,

_height

_(H),

_dry

_weight

_(DW)

after 48 h at 70

°C,

projected

needle area

_(PNA),

_specific

leaf area

_(SLA,

m

2

needles

/g

needles

),

_predawn

and

_midday

water

potentials (Ψpd,

Ψn)

and gas

exchange

parameters (net

photosynthetic

and

_{transpiration}

rates

_{[A, E]}

and

stom-atal conductance to water vapour

[gw])

were

recorded,

immediately

before the next

_irrigation,

on ten

_plants

per

provenance and water

_supply

_{regime. Projected}

needle

area was measured with a leaf area meter

_(Delta

T

Devices

_Cambridge,

_{UK). A,}

_{E and gw} were measured

with a

_portable

infrared gas

_analyser

_{(LCA-4, ADC,}

Hoddesdon,

England)

between 1200 and 1400

hours,

and

expressed

and

_analysed

on a

_projected

needle surface

basis.

On 1

_May

1995,

18

_seedlings

of each _Iberian

prove-nance were taken to a

_growth

chamber and watered twice

a week until 16 June. Chamber conditions were 22 °C,

65 % relative

_humidity

_(RH)

and 200

_μmol·m

_-2

_·s

_-1

max-imum

_{photosynthetic}

active radiation

_(PAR)

_during

the

light period

(14 h)

and 17

°C,

75 % RH in the dark. Plants were submitted to consecutive

_cycles

of

_drought,

each

_cycle

_ending

as soon as

_predawn

water

_potential

was between -1.2 and -1.5 MPa. The

_plants

were then

watered

_again

to field

_capacity

and a new

_cycle

was

begun.

Three times

_{(19 June,}

21

_July

and 7

_September)

four

_plants

_per treatment were

_again

removed and

pres-sure-volume curves were constructed.

Variance

_{analysis using}

a BMDP2V statistic

_package

(BMOP

Statistical Software

_{Inc., Cork, Ireland)}

was

applied

to the data in order to discriminate _among

prove-nances,

_watering

treatments, measurement dates and

blocks. The

_Tukey

HSD

(Honest

Significant

Difference)

for means

_comparison

was

_applied

whenever differences were

_significant

_(P

<

_0.05).

3. RESULTS

3.1. Plants at the _nursery

The block effect was not

_{statistically significant}

for

any water relation or _gas

_exchange

_parameter

_(P

>

_0.20),

so this was excluded from the statistical

_analysis

present-ed henceforth.

Tables II and III illustrate the mean values of water

potential

and other

_{morphological}

_{and gas}

_exchange

parameters. Water

_potential

_{and gas}

_exchange

rate values

were not

_{significantly}

different _{among provenances;}

however,

provenances showed differences in

growth

and

SLA. Arenas, Oria and Landas provenances stand out

because of their

_growth

for the R1 treatment. For

R2,

the Landas families lost the

_potential

of biomass

_production

they

showed under

_high

water

_{availability.}

Survival rate

was

_higher

than 97 % for all provenances for the R 1

treatment and in the _{range of 67-80}

%,

according

to

(16 %)

occurred

_{during July,}

the

_period

of

_highest

water stress.

Table IV shows the mean values for the

_majority

of

water relation

_parameters,

and table V _presents the levels

of

_{significance,}

_taking

into account the effect of

prove-nance, water

supply

treatment, measurement date and their interaction. The differences between provenances

or between dates with

_regard

to water relation

parame-ters derived from

_{pressure-volume}

curves were _greater

for the R2 than for the R1 treatment, with the

exception

of RWC0. The Landes _provenance showed the

_highest

tissue water content ratio

_(TW/DW),

the water accumu-lation was greatest in the

_symplast.

For the R2 treatment,

there were

_only

small _{differences between provenances}

during

June and

_September

for

_{&Psi;&pi;100; however,}

_during

July

&Psi;&pi;100

_(figure

₃₎

was

_{significantly}

lower in the Oria and _{Arenas provenances}

_(Or

= -1.70 _±

0.07;

Ar = -1.52

±

_0.07;

SL = -1.13 _± 0.06 and Ld = -1.18 _± 0.07

_MPa).

Similar results were noted for &Psi;&pi;0. The exposure to water stress in June led later in

_July

to decreases in

&Psi;&pi;100, &Psi;&pi;0,

&epsiv;max and TW/DW

ratio,

whereas &Delta;&Psi;&pi; increased. From

_July

to

_September

the

_previously

men-tioned water relation _{parameters changed} but in the

opposite

direction from that noted from June to

_July.

Nevertheless,

for most of the _parameters the initial June values were not reached

_{by September.}

For _{all the}

prove-nances, the decrease in TW/DW value from June to

September

was not due to a concomitant

_drop

in

Wap/DW

(table IV); therefore,

it was

_likely

due to a decrease of

_symplastic

water content.

3.2. Growth chamber

experiment

Table VI shows the measured water _relation parame-ters and their

_significance

level based _upon

_analysis

of

variance

_(ANOVA).

Differences between _provenances

were not

_significant

for _{any parameter}

_(0.122

<

P <

0.888),

neither was the interaction of provenance x

date

_(0.124

< P <

_0.917).

_Only

date was observed to

The first _response to water stress

_cycles

_(from

_day

1

to

₃₂₎

was a

_significant

decrease of &Psi;&pi;100 and &Psi;&pi;0 and

an increase of &Delta;&Psi;&pi;.

_Changes

in

_RWC0,

&epsiv;max, TW/DW and

_Wap/DW

were not

_significant

until the third

mea-surement

_(day

_80),

then an increase of TW/DW and a

decrease of

_Wap/DW

were observed.

_Figure

4 illustrates

a Höfler

_diagram

for one of the three _provenances

_(SL).

Diagrams

for the other _provenances were

_quite

similar.

4. DISCUSSION

In

_general,

water

_potential

and _gas

_exchange

values from this

_study

were similar to those from other studies of

_{pine species}

_{[7, 15].}

For the R1 treatment, mean

val-ues were not

_{significantly}

different _{among provenances.}

Predawn water

_{potential dropped}

to -0.5 MPa after

7

_days

without water.

_{Although Tschaplinski}

et al.

[39]

observed that such

_predawn

values can affect

_plants,

P.

pinaster

showed no effect and continued to _grow. In

addition,

values of noon or minimum water

_potential

indicated no stress. Under water

_shortage

conditions

(R2),

water stress was

_high

and

_predawn

water

_potential

approached

the survival threshold. Differences _among provenances were not

_significant.

Stomata

closed,

as is

made evident

_by

the values recorded for _gas

_exchange

parameters, and

_growth

was restricted. The restriction of

growth

due to lack of available water is a well-known

general

response of

plants

[5];

such observations have been made in

_1-year-old

P.

_pinaster

_[16].

For

compari-son, threshold values of water

_potential

that result in

stomata closure and a decrease in

_{photosynthesis}

of

some Pinaceae

_species

are listed: -1.3 MPa for Pinus

pinaster [9],

-1.2 MPa for Cedrus

atlantica, -1.5

MPa

for

_Pseuotsuga

menziesii

(Mirb.) Franco,-1.9

MPa for

Pseudotsuga

macrocarpa

[12], -1.5

MPa for Larix occi-dentalis Nutt.

[17],

-1.75 MPa for Pinus banksiana Lamb. and Picea

_glauca

_(Moench)

Voss.

_[15].

For the R1 treatment, differences between prove-nances are small with

_regard

to water relation

_parameters

derived from

_{pressure-volume}

curves. Pressure

_potential

was

_{always positive}

(&Psi;P

>

_0),

since water

_potential

val-ues close to _turgor loss were never measured in

_spite

of

the

_high

summer _{temperatures. Very} low water

_potential

values

_{(-2.5 MPa)}

on 27

_July

for the

_R2,

_suggested

that

many

plants

had exceeded the

turgor

loss

_point.

As a

consequence, an increase in

_mortality

was observed.

However,

most of the

_plants

had recovered 24 h after

watering.

For Cedrus atlantica and Pinus

_nigra,

a

_drop

of

_&Psi;pd

below -3.0 and -2.5

MPa,

respectively,

reduces the

_possibility

of

_surviving

and if -4.5 and -3.0 MPa are

reached,

recovery is

impossible

[21].

Under water

_shortage

conditions

_(R2),

differences

between provenances, water

_supply

treatments as well as

between dates were obvious. Water stress

_cycles

led to

changes

in water relation _parameters of

_plant

tissues. This is in _agreement with other studies of several conifer

species

[1, 4, 13, 35, 36, 38,

40,

41, 42, 43].

The

decrease of

&Psi;&pi;100, &Psi;&pi;0,

&epsiv;max and

TW/DW,

parallel

to

the increase of

&Delta;&Psi;&pi;,

indicate the

_development

of

strate-gies

of acclimation to water stress conditions.

However,

the _response of &epsiv;max cannot be

_generalised

since it is

possible

to find

_plants,

resistant or hardened to

_dryness,

with

_higher

&epsiv; values

_{[35]; therefore,}

&epsiv;

_performance

depends

on the

_species

_[13].

As water stress abates from

July

to

_September,

water relation parameters tend to

recover to values linked with

_periods

of active

_growth.

Such reversible

_changes

have been described for other conifers

_{[4, 32, 43].}

When

_comparing

_{the reaction of the provenances} to water stress,

changes

in &Psi;&pi;100 and &Psi;&pi;0 _suggest a more

rapid

response in the Arenas and Oria provenances. Lower &Psi;&pi;100 and &Psi;&pi;0 values would indicate a _greater

ability

to absorb water to maintain

_turgor

when

_plant

water

_potential

decreases.

At the

_beginning

of the season

_symplastic

water

con-tent of leaves is almost twofold their

_{dry weight}

and this

ratio decreases

_{during July,}

as leaves mature and

_dry

matter increases. It is also

_possible

that in water-stressed

plants symplastic

volume diminishes as cellular

_integrity

is lost and the

_permeability

of the membranes is reduced

[4, 32].

A modification of this

_pattern

was shown

_{by Joly}

and Zaerr

_[20]

for several

_populations

of

_Pseudotsuga

menziesii

(Mirb)

Franco under water stress: in

_spite

of

the decrease in the ratio of

_symplastic

water to

_dry

weight,

the

&Psi;&pi;100,

RWC0 and TW/DW values were not

modified

_by

water

_supply

or stress

_intensity

and no

In the

_growth

_chamber,

a

_change

in

_{&Psi;&pi;100,}

&Psi;&pi;0 and

&Delta;&Psi;&pi; was _{the first response}

_(days

1 to

₃₂₎

to water stress.

Observed also in

_Pseudotsuga

menziesii

[20],

this acts as

a stimulus to induce internal

_changes

in water allocation and

_elasticity

of tissues, which were then noted later

(days

32 to

_80).

Water stress induced an increase of

sym-plastic

water content, the

_opposite

response to that

observed for the R2 water

_{supply regime}

at _{the nursery.}

It can be assumed that in the

_growth

chamber

_plants

did

not _support such

_high

stress and the loss in

_integrity

of membranes was not

_approached.

In

_spite

of the differ-ences

_previously

mentioned,

the three provenances showed a similar _pattern for the water relation

parame-ters, and their

_{genetic potential}

for water stress

acclima-tion may be limited

_{by growth}

conditions. Because of the low level of radiation in the

_growth

_chamber,

osmotic

adjustment

is affected

_{[29, 41].}

The results should be

_interpreted

with some

_caution,

since the _response of the _parameters under

_{study depends}

on the season, cultural conditions, seed

origin

and

species

[4, 27, 31, 41, 42]

and even on the nature of the tissue

_sampled

from the

_plant

_[38].

Colombo

_[6],

in his work with Picea mariana, obtained similar or

_opposite

results to those of other

authors,

and he

_suggested

some

reasons to

_justify

the lack of a uniform _pattern for &epsiv;. Furthermore,

although

water deficit induces

_changes

in

water _parameters, seasonal

_changes

have been found in

well-watered

_plants

_[14].

On the other

_hand,

differences between

_populations

do exist but

_they

are so small that

genetic

correlations are difficult to demonstrate

_[42].

Under moderate water _stress,

_plants

will

_produce

as

much

_dry

matter

_(growth)

as additional water

_they

would be able to remove from the soil. This

_ability

_may be linked to low values of cellular

_elasticity

_[29],

as

occurred in

_plants

in the

_growth

chamber. Under severe

water stress, another

possibility

is that maintenance of

tissue water content would be more

_important

than

main-tenance of water

_potential.

Then,

the increase in cell

elasticity

could be the mechanism for stress acclimation if other mechanisms are limited

_[25].

This

_appeared

to

have occurred to

_plants

under the R2 water

_supply

at the nursery.

In

conclusion,

the

_following

can be

_emphasised:

i)

With

_adequate

water

_supply,

differences for most of the

water relations

_parameters

_{among provenances} are not

significant.

ii)

Restriction of water

_{supply through}

stress

cycles

causes noticeable

_changes

in water _parameters. A

drop

in

&Psi;&pi;100,

&Psi;&pi;0

_(osmotic

_adjustment),

&epsiv;max and TW/DW

_points

to acclimatisation

_{strategies by plants}

to water stress. Differences between Oria and Arenas de

San Pedro

_(provenances

from hotter sites) and San

Leonardo and the Landes

_(provenances

from colder

sites)

point

to a better or a _{faster response}

_by

the first

two _provenances to water stress. In

addition,

the lower

specific

leaf area of the Oria and _{Arenas provenances}

may be a _strategy to save water. The Arenas _provenance

stands out because of its

_growth,

whereas the Landes families lost the

_potential

of biomass

_{production they}

showed under

_high

water

_{availability.}

These results are

in _agreement with the field

_performance

at five and

eigh-teen _{years old of the} same _provenances at five

experi-mental

_plots

_{[2]; therefore,}

_they

indicate some

_validity

to

the use of water _parameters as criteria

_applied

for

_early

selection to

_1-year-old

P.

_pinaster

_seedlings.

Acknowledgements:

We thank Irena Trnkova Farrel for

_verifying

the

_English

version of this text. This

research was

_{supported by}

CEC- DG 12 Forest

_Project

Contract MA2B-CT91-0040 and the ’Ministerio de Educación y Ciencia’ of

_Spain.

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