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Agriculture, Ecosystems and Environment 106 (2005) 253–259

Optimization of irrigation water use in grapevines using the

relationship between transpiration and plant water status

A. Patakasa,*, B. Noitsakisb, A. Chouzouric

aDepartment of Natural Resources and Enterprise Management, University of Ioannina, G, Seferi 2, 30100 Agrinio, GreecebLaboaratory of Range Science, Aristotle University of Thessaloniki, P.O. 236, 54006 Thessaloniki, Greece

cInstitut fur Weinbau and Rebenzuchtung, Fachgebiet Weinbau, Forchungsanstalt, von Lade Strasse 1, D-65366 Geisenheim, Germany

Abstract

The study was carried out in order to evaluate the thresholds of grapevine internal water status as well as to propose an

irrigation management technique that permits the uninterrupted photosynthetic process under drought conditions. The

relationships between water relation, gas exchange parameters and sap flow measurements were examined in field grown

grapevines (Vitis vinifera L., cv. Malagouzia) subjected to various levels of water stress. The differences in stem water potential

were greater between the treatments compared to leaf water potential indicating that stem water potential represents a more

reliable indicator of plant water status. Stomatal conductance and photosynthetic rate were significantly lower in stressed

treatments while stomatal sensitivity to changes in vapor pressure deficit seems to be higher in stressed than in well-watered

treatment. Maximum diurnal sap flow rates were recorded early in the morning in all treatments and decreased in water stressed

treatments over the stress cycle. The SFTi/SFT1 ratio (SFT1 = mean daily sap flow of the fully irrigated plants; SFTi = mean sap

flow of the stressed plants) also decreased in water stressed treatments. The close relationship between the SFTi/SFT1 ratio and

stem water potential values could be used in developing a sap flow based technique for automatically controlling the irrigation

system in field grown grapevines.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Grapevines; Photosynthesis; Sap flow; Water potential; Water use

1. Introduction

Water stress is considered to be the most important

factor limiting plant growth and production in the

Mediterranean zone (Patakas and Noitsakis, 2001;

* Corresponding author. Tel.: +30 2641039545;

fax: +30 2310998886.

E-mail addresses: apatakas@cc.uoi.gr, patak@agro.auth.gr

(A. Patakas), noits@for.auth.gr (B. Noitsakis),

achouzou@fa-gm.de (A. Chouzouri).

0167-8809/$ – see front matter # 2004 Elsevier B.V. All rights reserved

doi:10.1016/j.agee.2004.10.013

Patakas et al., 2002). Grapevines grown in this region

are often exposed to water stress conditions due to high

evaporative demand and low water availability in the

soil. It is generally assumed that drought induces plant

water deficits which result in stomatal closure. One of

the primary processes affected by drought is photo-

synthesis, a fact due primarily to stomatal closure which

decreases water loss but also carbon flux to the sites of

carboxylation (Flexas et al., 1998; Escalona et al.,

2002). Thus, monitoring of plant water status in field

.

A. Patakas et al. / Agriculture, Ecosystems and Environment 106 (2005) 253–259254

grown grapevines is considered of great interest, as it

would allow the diagnoses of the onset and severity of

water stress so as to schedule irrigation according to the

actual plant needs.

Changes in plant water status could be described by

using a sensitive physiological indicator, which

integrates both soil and climatic conditions. The

pressure chamber is considered to be a reliable method

for determining the water status of field grown grape-

vines (Patakas et al., 1997). Use of the pressure chamber

technique can provide values of various parameters

such as stem and leaf water potential, both pre-dawn

and during the day (Greenspan et al., 1996). However,

the values of these parameters are difficult to be

assessed continuously over long periods. This dis-

advantage could be overcome by establishing a quanti-

tative relationship between plant water status and other

physiological parameters, which can be monitored

more easily. Sap flow measurements are considered to

be an accurate method of determining grapevine trans-

piration rates (Lascano et al., 1992; Eastham and Gray,

1998; Braun and Schmid, 1999a; Escalona et al., 2002).

The validity of this technique for detailed plant phy-

siological investigation in grapevines has been widely

questioned mainly due to the time lag between trans-

piration and calculated sap flow (Braun and Schmid,

1999b). However, when integrating sap flow measure-

ments over longer time period intervals much of this

error canceled out thereby increasing the accuracy of

this method up to 95% of the actual transpiration

(Kostner et al., 1998; personal unpublished data).

Moreover, sap flow can be monitored continuously thus

providing a continuous record of plant water losses and

requirements in response to environmental variables.

The aim of our study was to evaluate a quantitative

direct relationship of grapevine transpiration to plant

water status that might be used to schedule irrigation

so that plant water status can be maintained above

certain thresholds in field grown grapevines.

2. Materials and methods

2.1. Experimental site

The experiment was conducted during the summer

of 1999 and 2000 in the vineyard of Gerovassileiou

which is located in Epanomi, 25 km south-west from

Thessaloniki. The vineyard occupied almost 40 ha, and

the soil, according to FAO classification for soil types, is

a calcaric regosol. The climate is typical Mediterranean

with mild rainy winters and long, hot and dry summers.

The experimental vines (Vitis vinifera L. cv., Mala-

gouzia) were 10 years old grafted on 110R (V. ber-

landieri � V. rupestris) rootstocks and were occupied a

3 ha plot of the vineyard. The plants were trained in a

bilateral cordon, 2.50 m apart, with a 1.20 m within-

row spacing. The main wire was 0.40 m above the soil

surface and the shoots were maintained on a vertical

plane by three wires, the highest of which was located

1.50 m above the soil surface. All vines were uniformly

pruned and were irrigated with a drip irrigation system.

From the beginning of summer (June 1999), the

experimental plot was divided into three equal subplots

(T1–T3). Two of them (T2, T3) were subjected to

repeated deficit irrigation cycles during the summer

period while the third (T1) was irrigated daily to 100%

of evapotranspiration. The water applied in T1 was

considered sufficient to fully satisfy the needs of the

vines (fully irrigated treatment). The duration of each

deficit irrigation cycle was 12 days and the amount of

irrigation applied was programmed using two reduction

percentages: 50% and 80% of the daily evapotranspira-

tion (ETc) for T2 and T3 subplots, respectively. ETc was

calculated using the equation

ETc ¼ KcET0

where ET0 was the reference crop evapotranspiration

and Kc was the crop coefficient (Doorenbos and Pruitt,

1984). ET0 was computed from wind speed, incoming

solar radiation, air temperature and specific humidity

values, measured using an automatic weather station

(Metos compact, Pessl Instruments GmbH) locating in

the experimental field. In all treatments, irrigation water

was supplied daily. At the end of each cycle, additional

irrigation equal to 50% and 80% of ETc for T2 and T3

treatments, respectively, was applied with the objective

of replenishing the evapotranspiration losses of the

previous days. The recovery of plants was followed

by a new deficit irrigation cycle of equal duration.

2.2. Sap flow, gas exchange and water potential

measurements

In order to estimate the transpiration rate of the

grapevines, it was assumed that sap flow equals total

A. Patakas et al. / Agriculture, Ecosystems and Environment 106 (2005) 253–259 255

Fig. 1. Diurnal changes in stem water potential (A) and leaf water

potential (B) in all treatments at a randomly selected day at the end

of a deficit irrigation cycle. Each symbol represents the mean

� standard errors of six replicates.

transpiration. Sap flow was measured using the Granier

system (Granier, 1985, 1987), as it has the advantage of

allowing continuous measurements which the semi-

continuous heat pulse system does not have. The sap

flow measurements, according to Granier system, were

based on the temperature differences between two

cylindrical probes with a diameter of 2 mm and a length

of 15 mm, which were installed radially into the stem at

a vertical distance of 100–150 mm. In our experiment,

sap flow was measured on three selected plants per

treatment of similar leaf area (LAI = 1.5). The latter

was measured using a LAI-2000 Plant Canopy

Analyzer (Li-Cor, Lincoln, NE, USA) (Patakas and

Noitsakis, 1999). The installation of sap flow sensors in

each plant was made according to Braun and Smith

(1999). Measurements were taken at 20 s intervals and

their average stored every 15 min on a data logger. Sap

flow measurements (litre per hour or day) were

converted to dimensional unit (millimetre per hour or

day) according to the plant leaf area (3 m2). Changes in

the sap flow in the stressed treatments during a deficit

irrigation cycle was expressed using the SFTi/SFT1 ratio

where SFT1 is the mean daily sap flow of the fully

irrigated plants and SFTi the mean sap flow of the

stressed plants.

Water relation parameters were measured daily

using a pressure chamber. Predawn water potential

(CPD) was measured early in the morning (06:00 am) on

six uncovered, mature fully expanded leaves of six

randomly selected plants in each treatment. Diurnal

values of leaf (CL) and stem water potential (CS) were

measured every 2 h starting at (06:00 am). Leaf water

potential (CL) measurements were also conducted on

six randomly selected leaves, which had been exposed

to direct sunlight for at least 1 h before measurements.

Stem water potential (CS) was measured simulta-

neously on adjacent non-transpiring leaves that had

been bagged with both plastic sheet and aluminum foil

for at least 1 h before measurements (Begg and Turner,

1970). Diurnal values of photosynthetic rate (PN) and

stomatal conductance (CS) were measured using a

portable gas exchange system (Li-Cor 6400, Li-Cor,

Nebraska, USA) on six leaves per treatment. Sampling

was always done in the central row of five consecutive

rows under the same treatment to avoid any border

effect.

Measurements were conducted during five deficit

irrigation cycles in 1999 and six cycles of equal

duration in 2000. Since no significant differences were

observed between the measurements the data pre-

sented here referred to a randomly selected deficit

irrigation cycle in 2000.

2.3. Experimental design and statistics

The experimental design was completely rando-

mized and statistical analysis was carried out with the

SPSS statistical computer package (SPSS for Win-

dows, Standard Version Release 6.1). Statistical

differences between treatments were analyzed by

one-way analysis of variance (ANOVA).

3. Results

Diurnal measurements of stem (CS) and leaf water

potential (CL) indicated that both parameters

decreased during the day reaching minimum values

at mid-day (Fig. 1). However, treatment differences

were greater for CS than for CL values. Furthermore,

the changes in mid-day CS over a deficit irrigation

cycle were greater than those of predawn and mid-day

CL in both the deficit irrigated treatments (T2–T3)

A. Patakas et al. / Agriculture, Ecosystems and Environment 106 (2005) 253–259256

Fig. 2. Changes in mid-day stem water potential (A), predawn leaf

water potential (B) and mid-day leaf water potential (C) in all

treatments over a deficit irrigation cycle. Each symbol represents the

mean � standard errors of six replicates.

Fig. 3. Changes in maximum daily rates of photosynthesis (A) and

stomatal conductance (B) in all treatments over a deficit irrigation

cycle. Each symbol represents the mean � standard errors of six

replicates.

Fig. 4. Relationship between maximum daily rates of photosynth-

esis and mid-day stem water potential in all treatments over a deficit

irrigation cycle.

(Fig. 2). Differences between treatments in mid-day

CS at the end of each deficit irrigation cycle were also

greater than differences in mid-day CL (Fig. 2).

Maximum diurnal values of CS and PN decreased

during the deficit irrigation cycle in T2 and T3

treatments (Fig. 3). The relationship between max-

imum diurnal values of PN and mid-day CS indicates

that photosynthesis was unaffected by water status for

water potentials greater than �0.6 MPa (Fig. 4).

The diurnal changes in sap flow over a typical

summer day indicated that sap flow increased during

the day reaching maximum values early in the

morning and then decreased in all treatments (Fig. 5).

Sap flow in the T1 treatment seemed to increase

linearly with vapor pressure deficit (VPD) which

integrates a range of environmental conditions

(Fig. 6A). In stressed plants, on the other hand,

sap flow responded to VPD in a more exponential

relationship (Fig. 6B). The SFTi/SFT1 ratio tends to

decrease in the stressed treatment during the deficit

irrigation cycle (Fig. 7). The values of the above ratio

seem also to be closely related to the mid-day CS

values (Fig. 8).

A. Patakas et al. / Agriculture, Ecosystems and Environment 106 (2005) 253–259 257

Fig. 5. Diurnal course of sap flow in all treatments at a randomly

selected day at the end of a deficit irrigation cycle.

Fig. 7. Changes in sap flow expressed as SFTi/SFT1 ratio

(SFT1 = mean daily sap flow of the fully irrigated plants; SFTi = -

mean sap flow of the stressed plants) in stressed treatments over a

deficit irrigation cycle.

4. Discussion

The significantly greater treatment differences in

CS compared to CPD and CL throughout the day and

during the deficit irrigation cycle (Figs. 1 and 2) mean

that CS values might be the best indicator of

differences in plant water status. These results agree

Fig. 6. Dependence of sap flow on vapour pressure deficit (VPD) in

well-irrigated (A) and stressed treatments (B) over a deficit irriga-

tion cycle.

with those of Garnier and Berger (1985) and

MacCutchan and Shackel (1992) who have success-

fully applied CS as a water-deficit indicator in plum

and peach orchards. On the other hand, CL measure-

ments have long been used as an index of water stress

as it reflects a combination of many factors such as

vapor pressure deficit, leaf intercepted radiation, soil

water availability, internal plant hydraulic conductiv-

ity and stomatal regulation (Patakas et al., 1997). Lack

of differences in CL values between treatments (Fig. 2)

could be attributed to the isohydric behavior of

grapevines that lead to similar values of CL in both

irrigated and stressed plants (Escalona et al., 2002).

These species maintain similar CL values through

stomatal regulation of transpiration in order to prevent

such low CL that could damage leaves (Naor and

Wample, 1994; Schultz and Matthews, 1988).

The close relationship between mid-day CS and the

PN (Fig. 4) indicates that photosynthesis is reduced

when CS values fall below critical threshold values of

�0.6 MPa independently of irrigation treatment. This

Fig. 8. Relationship between SFTi/SFT1 ratio and mid-day stem

water potential in stressed treatments over a deficit irrigation cycle.

A. Patakas et al. / Agriculture, Ecosystems and Environment 106 (2005) 253–259258

value of CS seems to represent a plant threshold that

could be used to schedule irrigation in order to

maintain plant water status within a favorable range.

Furthermore, the fact that sap flow increased linearly

in relation to VPD indicates that there was no direct

effect of VPD on stomatal control in well-watered (T1)

plants (Fig. 6A). In contrast, when water started to

become limiting, an increase in VPD seemed to lead to

stomatal closure and thus reducing sap flow of stressed

plants (Fig. 6B). Stomatal closure in response to

increasing VPD might be an effective strategy to avoid

excessive water loss under drought conditions and

prevent leaf water potential from falling to dangerous

levels (Tyree and Sperry, 1988). However, the

physiological mechanisms of stomatal response are

very complex and not fully understood. Hypotheses

involving hydraulic and/or biochemical signals have

been proposed and verified in many studies (Stoll et al.,

2000; Davies et al., 2002). In grapevines, recent studies

showed that abscisic acid levels in the leaves were much

higher under high-VPD conditions. High abcisic acid

levels may also increase the sensitivity of stomata to

VPD (Lovisolo et al., 2002). This seems to agree with

our results where abscisic acid concentrations were

significantly higher in the leaves of stressed than in the

well-irrigated plants (data not shown).

The close relationship between SFTi/SFT1 ratio and

CS values (Fig. 8), in relation with the observed

relationship between CS and PN (Fig. 4), could allow

an estimation of a critical value of the above ratio

which corresponds to the onset of photosynthesis

reduction in plants. According to this, for the values of

the SFTi/SFT1 ratio greater than 0.80 the water stress

seems to impose only a slight decrease in PN. As water

stress becomes more severe, and values of SFTi/SFT1

ratio falls to less than 0.80, the reduction in PN could

become significant. Thus, it could be assumed that

monitoring the SFTi/SFT1 ratio value could be used as

a clear and simple signal for an automatic controller

for a real-time irrigation schedule in order to improve

irrigation management in vineyards.

5. Conclusions

Irrigation is considered as very important for

grapevine production in water-short Mediterranean

region. In order to improve irrigation management in

vineyards a plant based technique capable to diagnose

the onset and severity of water stress is proposed. This

technique is based on the fact – well confirmed by our

data – that stem water potential represents a reliable

indicator of grapevines water status. However, the

disadvantage of the above parameter to be assessed

continuously over long period could be overcome by

the close relationship between mean daily sap flow

decrease and stem water potential. Our data indicated,

that using this relationship a critical value of daily sap

flow decrease could be estimated and can be used as an

accurate and simple signal for real-time irrigation

scheduling in vineyards. This approach has the

advantages that it needs only a small number of

sensors and little data processing. Possible discre-

pancies of the method due to seasonal fluctuations in

VPD and evaporative demand are expected to be

negligible due to the ability of grapevines to regulate

their transpiration rate and thus exert fine control over

transpiration under completely different evaporative

conditions (Yunusa et al., 2000). Furthermore, the

possible errors due to the tissue reactions and/or

changes in evaporative conditions are minimized since

the method only uses relative values of sap flow.

Acknowledgement

This research was financially supported in part by

Domaine Gerovassiliou, Epanomi, Greece.

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