Physiological tools for irrigation scheduling in grapevine (Vitis vinifera L.)

www.elsevier.com/locate/agee

Agriculture, Ecosystems and Environment 106 (2005) 159–170

Physiological tools for irrigation scheduling in

grapevine (Vitis vinifera L.)

An open gate to improve water-use efficiency?

J. Cifre, J. Bota, J.M. Escalona, H. Medrano, J. Flexas*

Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears,

Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Balearic Islands, Spain

Abstract

Grapevine is a traditionally non-irrigated crop that occupies quite an extensive agricultural area in dry lands and semi-arid

regions. Recently, irrigation was introduced to increase the low land yield, but a good compromise between grape quality and

yield is of major importance for the achievement of high-quality products as wine. Therefore, water-use-efficient irrigation and

regulated deficit irrigation programs need to be developed to improve water-use efficiency, crop productivity and quality in semi-

arid crops.

In the present review, current knowledge on grapevine responses to water stress is summarised. Based on this knowledge, the

usefulness of different physiological parameters is discussed, and current knowledge on their applicability for water stress

detection and irrigation management in grapevines is reviewed. Partial root drying (PRD) and regulated deficit irrigation (RDI)

programs are proposed as the most promising tools for such purpose. Among RDI programs, several parameters are proposed as

putative indicators of irrigation convenience and dosage. These are sap flow (measured by sap flow meters), trunk growth

variations (measured by linear transducers of displacement, LTDs), canopy temperature (assessed by infrared thermometry),

reflectance indices (measured by spectroradiometers or specifically designed instruments) and chlorophyll fluorescence

(measured by either active or passive fluorometers). Advantages and disadvantages of all these tools are discussed.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Grapevines; Water stress; Water-use efficiency; Irrigation scheduling; Physiological indicators; Sap flow; Remote sensing;

Reflectance indices; Chlorophyll fluorescence; Infrared thermometry; Linear transducers of displacement

1. Introduction

Water is the most limiting resource in the

Mediterranean region. Rainfall is scarce and irregu-

* Corresponding author. Tel.: +34 971 172365;

fax: +34 971 173184.

E-mail address: [email protected] (J. Flexas).

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

doi:10.1016/j.agee.2004.10.005

larly distributed along the year, and climate change

models predict even more arid conditions for the near

future (Ragab and Prudhomme, 2002). Therefore,

increasing water-use efficiency (WUE) should be a

key issue for research (Al-Kaisi and Yin, 2003) and it

is currently a priority for the United Nations policy,

what is called the ‘Blue Revolution’ and summarised

as ‘more crop per drop’ (Annan, 2000).

.

J. Cifre et al. / Agriculture, Ecosystems and Environment 106 (2005) 159–170160

Grapevine (Vitis vinifera L.) is a traditionally non-

irrigated crop that occupies quite an extensive

agricultural area in dry lands and semi-arid regions.

Recently, irrigation was introduced to increase the low

land yield. Grapevine is cultivated to obtain table

grape, raisins or wine. In the latter case at least, a good

compromise between grape quality and yield is of

major importance for the achievement of high-quality

premium wines. In the case of producing grapevines,

even when a certain variability in the water-use

efficiency is present (Bota et al., 2001), the wine-

market-oriented production is restricted for the

necessity of the highest grape quality standards as

well as for certain regional authorised varieties, which

commonly offer the tipicity of wine characteristics

(‘Denominaciones de Origen’, ‘Appellations d’Ori-

gine Controlees’, etc.). Therefore, for grapevine as for

other extensive crops irrigation remains up to now the

most likely way to reduce drought impacts on yield.

Hence, water-use-efficient irrigation or regulated

deficit irrigation (RDI) programs would still be one

of the most desirable tools to improve water-use

efficiency and crop productivity in semi-arid areas

(Boyer, 1996).

The recent generalisation of vine irrigation in

countries with dry summer has lead to some

controversy, due to the not fully understood relation-

ships between grapevine photosynthesis and fruit

yield and quality. Irrigation substantially increases

photosynthesis, and grape yield is increased by 1.5–4-

fold, depending on the irrigation timing, the amount of

water applied, the cultivar, the environmental condi-

tions and other cultural practices (Bravdo et al., 1985;

Hepner et al., 1985; Matthews et al., 1987; Schultz,

1996; Williams, 1996; Escalona et al., 2003). On the

other hand, it seems that, up to a certain amount of

added water, no effects are observed on grape and

wine quality, even when grape yield is increased

(Bravdo et al., 1985; Hepner et al., 1985; Medrano et

al., 2003; Escalona and Medrano, personal commu-

nication). However, larger amounts of water, although

further increasing grape yield, have a negative effect

on quality, mainly due to colour losses, low sugar

content and acidity imbalances (Bravdo et al., 1985;

Hepner et al., 1985; Matthews et al., 1990; Cacho et

al., 1992; Esteban et al., 1999, 2001). Therefore, a

deep knowledge of the mechanisms that regulate plant

carbon assimilation and partitioning under different

water regimes is of great interest in the frame of

precision agriculture, since these mechanisms play an

important role in the regulation of the fragile balance

between grape yield and quality. Eventually, this will

lead to the description of physiologically based

criteria for irrigation scheduling.

The aim of the present work is to review recent

contributions on the effects of soil water availability

on grapevines and to show the potential interest of

some physiological indicators of grapevine water

status which could better assess the irrigation schedule

and dosage for a sustainable, water-use-efficient

production of high-quality grapevines.

2. Stomatal responses of grapevines

to soil water deficit

It has been known for many years that soil water

deficit reduces photosynthesis (Kriedemann and

Smart, 1971; Liu et al., 1978), vegetative growth

(Matthews et al., 1987; Schultz and Matthews, 1988a),

and reproductive growth and yield in grapevines

(Kliewer et al., 1983; Bravdo et al., 1985; Hepner et

al., 1985; Matthews and Anderson, 1988, 1989).

Stomatal closure is among the first processes

occurring in the leaves in response to drought. A good

relationship between stomatal conductance (gs) and

leaf water potential and/or water content has been

observed in some grapevine genotypes and conditions

(Liu et al., 1978; Gamon and Pearcy, 1990; Rodrigues

et al., 1993; Naor et al., 1994), but not in many others

(Quick et al., 1992; Naor and Wample, 1994; Poni et

al., 1994; Bota et al., 2001; Flexas et al., 2002a;

Medrano et al., 2002; Schultz, 2003). The latter

represent a near-isohydric behaviour, which implies

that the same minimum leaf water potential can be

achieved at midday irrespective of soil water status.

This fact makes midday leaf water potential a poor

indicator of water stress, in contrast with pre-dawn

leaf water potential or the stem water potential that

may serve as good indicators (Schultz, 1998; Escalona

et al., 1999; Chone et al., 2001). Differences between

near-isohydric and anisohydric V. vinifera L. cultivars

seem to be related to differences in hydraulic

architecture (Schultz, 2003).

Whatever the regulation mechanisms of plant water

relations, tight stomatal closure occur at relatively low

J. Cifre et al. / Agriculture, Ecosystems and Environment 106 (2005) 159–170 161

Fig. 1. The relationship between daily maximum stomatal conduc-

tance in grapevines (V. vinifera L.) growing outdoors in Mallorca,

and submitted to different water supply. Triangles are values for 22

different varieties grown in pots without rootstock, as described by

Bota et al. (2001); open circles are values for potted plants of the

variety Tempranillo, grafted on rootstock R-110 and grown as

described by Flexas et al. (1999); closed circles are values from

a 10-year study in two varieties, Tempranillo and Manto Negro,

grafted on rootstock R-110 and growing in a commercial vineyard,

as described by Medrano et al. (2003). All data are average values of

6–8 replicates.

soil water deficit in many grapevine cultivars, leading

to a rapid reduction of gs as pre-dawn leaf water

potential decreases (Fig. 1, r2 = 0.50, see also Schultz,

2003). This fine regulation of stomatal conductance

depends on some hydraulic conductance variations

and on synthesis of abscisic acid (ABA) in the roots,

which is transported to leaves (Lovisolo et al., 2002).

Grapevines were among the first plant species in

which a direct role of ABA in stomatal closure was

demonstrated (Loveys and Kriedemann, 1974; Liu et

al., 1978; Loveys, 1984; Loveys and During, 1984).

More recently, Correia et al. (1995) were able to

demonstrate that the maximum daily stomatal con-

ductance (but not its diurnal fluctuation) was

determined by the xylem ABA concentration in

field-grown grapevines. In addition, it has been shown

that partial root drying in grapevines induces stomatal

closure and shoot growth reduction without modifying

leaf water status, a process in which a five-fold

increase in leaf ABA content is involved (Dry and

Loveys, 1999; Dry et al., 2000a, 2000b; Stoll et al.,

2000). On the basis of these observations, it is likely

that root ABA synthesis in response to drought

controls to some extent the stomatal responses in

grapevines, although this could also be modulated by

osmotic adjustment, xylem hydraulic conductivity,

and environmental factors such as air humidity

(During, 1987; Naor et al., 1994; Lovisolo et al.,

2002).

In summary, the tight regulation of stomatal closure

in grapevines in response to very mild soil water

deficits makes stomatal conductance itself a more

precise indicator of water stress than common water

relations’ parameters.

3. Downregulation of photosynthesis under

drought in grapevines

A close, curvilinear correlation between stomatal

conductance (gs) and net photosynthesis (AN) has been

described in grapevines, as in other species (Fig. 2A,

r2 = 0.89, see also Chaves et al., 1987; During, 1987;

Naor and Wample, 1994; Escalona et al., 1999; Flexas

et al., 2002a). Due to this correlation and to the fact

that stomatal closure is among the first events to occur

under drought, it was assumed that the drought-

induced decrease of photosynthesis was mediated by

stomatal closure (Kriedemann and Smart, 1971).

Under mild water stress, it is likely that grapevine

photosynthesis is depressed almost exclusively by

stomatal closure, as indicated by increased water-use

efficiency (i.e., the ratio of photosynthesis to

transpiration or stomatal conductance to water vapour,

see Fig. 2B). This is presumably a general feature for

most species. However, under more severe water stress

situations, non-stomatal inhibition of photosynthesis

has been described (Chaves, 1991; Cornic, 2000;

Flexas et al., 2004).

Flexas et al. (2002a) have recently shown that

drought-induced changes in many photosynthetic

parameters are more related to variations in maximum

daily gs than to variations in the most commonly used

water status parameters, like leaf water potential or

relative water content. In fact, using gs as an

integrative parameter reflecting the severity of water

stress, different grapevine cultivars (Flexas et al.,

2002a) or even different C3 species (Flexas and

Medrano, 2002; Medrano et al., 2002) followed a very

similar pattern of downregulation of different photo-

synthetic parameters in response to progressive soil


Fig. 2. The relationship between (A) net CO2 assimilation (AN) and

stomatal conductance and (B) intrinsic water-use efficiency (AN/gs)

and stomatal conductance in grapevines (V. vinifera L.) growing

outdoors in Mallorca, and submitted to different water supply.

Symbols as in Fig. 1. All data are single values, taken during the

central hours of the day (i.e., at saturating light).

water depletion. In the case of grapevines, this

observation is consistent with the above-described

near-isohydric behaviour of many drought-adapted

cultivars and with the suggestion that ABA-induced

stomatal closure (and not decreased leaf water status)

is the most immediate leaf response to drought.

Using gs as an integrative parameter for the degree

of drought, three phases of photosynthesis response

can be differentiated along a water stress gradient, that

are shared by different grapevine cultivars (Flexas et

al., 2002a; Medrano et al., 2002):

(1) A
phase of mild water stress is defined for a
decreasing range of gs from 0.5–0.7 to 0.15 mol

H2O m�2 s�1. This is characterised by a relatively

small decline of AN, which results in a progressive

increase of intrinsic water-use efficiency (AN/gs)

and a decline of sub-stomatal CO2 concentration

(Ci, Flexas et al., 2002a). As a consequence of

decreased CO2 availability in the mesophyll, the

rate of photorespiration increases, which enables

the maintenance of the thylakoid electron trans-

port rate (ETR, Flexas et al., 1999, 2000, 2002a).

At this stage, stomatal closure is probably the only

limitation to photosynthesis.

(2) A
moderate water stress phase is characterised
by intermediate gs values (0.15 > gs > 0.05 mol

H2O m�2 s�1). During this phase, a further

reduction in AN occurs and water-use efficiency

usually increases, but it decreases in some

cultivars (e.g. Naor et al., 1994). Ci still decreases,

but ETR and the carboxylation efficiency (e; i.e.,

the initial slope of AN–Ci curve) characteristically

decline during this phase (Flexas et al., 1999,

2002a). The decline of e is dominated by

decreased mesophyll conductance at this stage

(Flexas et al., 2002a), since the activity of

photosynthetic enzymes, such as Rubisco, is

mostly unaffected (Bota et al., 2004; but see

Maroco et al., 2002). NPQ, a chlorophyll

fluorescence parameter indicative of thermal

dissipation in the antenna of photosystem II,

increases under these conditions, and steady-state

chlorophyll fluorescence (Fs) drops under high

light (Flexas et al., 2000, 2002b). Therefore, in

this phase, stomatal limitations seem dominant

and photosynthesis is rapidly reversed upon re-

watering (Flexas et al., 1999), but non-stomatal

limitations are already developing (Naor et al.,

1994; Flexas et al., 2002a, 2002b; Maroco et al.,

2002).

(3) A
phase of severe water stress takes place when gs
is very low (<0.05 mol H2O m�2 s�1). In this

stress phase, steeper reductions of AN, AN/gs, ETR

and e occur. NPQ further increases, and the

excitation capture efficiency of photosystem II

(Fv/Fm) is eventually reduced, especially during

very hot days (Flexas et al., 2002a; Medrano et al.,

2002). During this phase AN/gs decreases (During,

1987) and Ci steeply increases (Flexas et al.,

2002a), indicating that non-stomatal limitations to

photosynthesis become dominant. The rate of

photorespiration is decreased, but the ratio of

photorespiration to photosynthesis still increases,


maintaining ETR high relative to AN (During,

1988; Flexas et al., 1999, 2002a). In this phase,

photosynthesis did not recover after irrigation

(During, 1988; Quick et al., 1992), indicating that

non-stomatal inhibition is dominant. Further

decreases of e during this phase are likely to be

due to impaired Rubisco activity (Bota et al.,

2002, 2004; Flexas et al., 2002a; Maroco et al.,

2002). A general decline in the activity and

amount of photosynthetic enzymes is observed in

this phase (Maroco et al., 2002; Flexas et al.,

2004).

4. Physiological tools for water stress detection

and management of grapevine irrigation

As mentioned in previous sections, for water stress

situations characterised by gs values above 0.05–

0.1 mol H2O m�2 s�1 photosynthesis is mainly lim-

ited by stomatal closure, and a complete recovery of

the maximum AN occurred just one night after

irrigation (Flexas et al., 1999). For more prolonged

and/or more pronounced water deficits leading to

further decreases of gs, non-stomatal limitations

(metabolic and/or restricted internal CO2 diffusion)

are dominant and photosynthesis did not recover

rapidly after irrigation (During, 1988; Quick et al.,

1992). Therefore, maximising WUE implies a certain

reduction in crop yield. Interestingly, in grapevines

(see above sections), highest crop load is linked to low

grape quality. Thus, in fact, limitations to grape yield

are a common practice (if not compulsory) for a

market standard wine production and premium wines.

Thus, being an extensive crop in drought-prone areas,

irrigation would give more benefits if schedules and

dosages were oriented to maximise water-use effi-

ciency (Fereres, 2003).

Based on this knowledge, physiologically based

irrigation tools may attempt to maintain the plants at a

limit between water stress and excess water con-

sumption, thus making a rational use of irrigation

water. This kind of irrigation may save water with

respect to empirical irrigation, improving yield as

compared with rainfed grapevines, and maintaining

the high fruit quality. Partial root drying (PRD) and

regulated deficit irrigation (RDI) programs are

currently envisaged as the most promising irrigation

tools based on physiological knowledge of grapevine

response to water stress.

Partial root drying (PRD) consists in drip irrigation

alternating from one side of the row to the other, thus

allowing that some roots of the plants are always in

contact with drying soil. The aim of this technique is to

control excessive vegetative vigour and save irrigation

water without influencing fruit yield and quality. This

treatment induces root ABA synthesis in the dried

zone (Dry and Loveys, 1999; Dry et al., 2000a,

2000b), leading to partial stomatal closure without

reducing leaf water status. Therefore, by adjusting the

proportion of roots that are irrigated, it is possible to

maintain the plants at the inflexion point of the AN–gs

relationship, thus saving a large amount of water with

only a small reduction of photosynthesis (Stoll et al.,

2000). Trials in Australia with this type of irrigation

have shown a significant reduction in vegetative

growth while maintaining fruit yield and quality,

saving in irrigation (Dry et al., 2001).

Regulated deficit irrigation (RDI) programs consist

in continuously monitoring some physiological para-

meters indicative of vine water stress. Irrigation

should be applied only when such a parameter drops

below a certain threshold value. Although leaf water

potential has been proposed as an indicative parameter

for RDI programs in grapevines (Girona et al., 2002)

and other extensive crops (Goldhamer et al., 1999), the

near-isohydric behaviour of many cultivars will

probably preclude its use, specially to detect mild

to moderate water stress situations, in which large

reductions of photosynthesis and yield occur without

much effects on canopy water relations. Presently, and

based on the knowledge of grapevine response to

progressive water stress described on the above

sections, it seems reasonable that continuously

monitoring of some direct or indirect indicators of

crop gs or AN may allow deciding when and how much

water must be applied for a rational use of irrigation

water. To give priority to high water-use efficiency

over maximum yield, irrigation should be applied only

when the indicator parameter drops below a certain

threshold value, preferably corresponding to some gs

value between 0.05 and 0.15 mmol H2O m�2 s�1.

According to current knowledge on water stress

effects on grapevine photosynthesis, yield and quality,

maintaining grapevines at such gs range may, in

principle, allow: (1) maximum water-use efficiency,


(2) rapid reversibility of photosynthesis upon irriga-

tion, (3) relatively moderate yield loses as compared to

intensive irrigation and (4) maintenance of optimum

grape quality characters.

Several contact and remote sensing approaches

have been proposed as such indicators of gs. Among

contact approaches, the most promising are (1) sap

flow meters and (2) linear transducers of displacement

(LTDs). Among the remote sensing approaches, (3)

thermal imaging, (4) reflectance indices and (5)

chlorophyll fluorescence have been evaluated with

some success.

4.1. Sap flow meters

Sap flow measurements give reliable, direct

estimates of plant or shoot water loss without

disturbing the conditions of the leaf environment

(Shulze et al., 1985; Ansley et al., 1994; Fernandez et

al., 2001). In irrigated grapevines, sap flow measure-

ments were shown as a good tool to estimate canopy

transpiration (Yunusa et al., 2000). More recently,

Escalona et al. (2002) have demonstrated a very high

correlation between single leaf gs and the instanta-

neous sap flow in water-stressed, potted grapevines

(see also Table 1). For the total daily water

consumption, the correlation was even higher

(r2 = 0.98) and close to a 1:1 relationship. Net

photosynthesis rate was correlated as well with sap

flow values (r2 = 0.78), and this correlation increased

(r2 = 0.91) when the daily balances of both parameters

were compared. Ginestar et al. (1998) have already

started to apply sap flow measurements to establish

different irrigation coefficients to Shiraz grapevines,

obtaining a gradient of grape yield and qualities. The

main advantages of sap flow measurements may be:

(a) the fact that they directly reflect canopy sap flow

and transpiration, therefore being directly related to

Table 1

Threshold values of sap flow, net CO2 assimilation (AN), and stomatal co

50 mm) null and minimum (around �50 mm)

Trunk

growth (mm)

Maximum daily

Sap flow (g m�2 h�1)

Daily Sap flow

(g m�2 day�1)

50 150 1174

0 83 630

�50 36 320

Values inferred from data in Escalona et al. (2002).

whole-canopy gs, and (b) the fact that they correlate

with gs at any given range of the latter, therefore

allowing a continuous monitoring of gs from full water

availability to severe water depletion. The principal

disadvantages are: (a) that the sensors are quite

expensive, thus not allowing establishing a high

number of them per field; and (b) the fact that this is a

contact or intrusive technique, which may imply some

interference with plant performance.

4.2. Linear transducers of displacement

LTDs were mainly introduced by Garnier and

Berger (1986), and envisaged as a powerful tool for

irrigation scheduling (Fereres et al., 1999; Moriana et

al., 2000). They permit the continuous measurements

of the stem diameter, which can be related to plant

growth, water-use and status. The shrinking and

swelling of the extensible plant tissues provide an

indirect measure of the transpiration streams during

daylight periods, and is related to changes in water

content and turgor potential of their cells. In spite of its

potential usefulness, little attention has been paid to

this technique in grapevine studies, although Escalona

et al. (2002) have recently demonstrated that diurnal

stem diameter variations closely track sap flow (see

also Table 1). The main advantage of this technique is

that the sensors are very inexpensive, thus allowing the

establishment of a high number of them per field. As

remarkable disadvantages, there is the fact that this is a

contact technique, which may imply some interfer-

ence with plant performance, and that any possible

correlation with gs would be somewhat indirect.

4.3. Infrared thermometry

It has been long recognised that leaf or canopy

temperature is highly dependent on the rate of

nductance (gs), at which trunk growth is either maximum (around

Leaf-level AN

(mmol m�2 s�1)

Daily carbon gain

(g m�2 day�1)

Leaf-level gs

(mol m�2 s�1)

11.1 3.4 0.15

6.9 2.6 0.09

3.7 2.1 0.02


transpiration and can therefore be used as an indicator

of stomatal opening (Sinclair et al., 1984). Accord-

ingly, infrared thermometry has been developed as a

means for irrigation scheduling (Jones, 1999; Jones et

al., 2002). The main advantages of this tool are: (a) the

potential amplitude of its fields of view, allowing

measurements at different scales ranging from single

leaves to several hectares, and (b) the fact that, in

principle, thermometric signals should correlate with

gs at any given range of the latter, therefore allowing a

continuous monitoring of gs from full water avail-

ability to severe water depletion. Riou et al. (2000)

have recently described a thermometric parameter

sensible to water stress in grapevines, and Jones et al.

(2002) have shown reasonable estimations of whole

canopy gs based on thermometric determinations. The

principal disadvantages are: (a) the possibility of

misleading interpretations whenever the temperature

sensed is biased by, for example, bare soil in the

sensor’s field of view, although recent investigations

have shown that this problem can be avoided by the

use of modern thermal imagers with associated image

analysis software (Jones et al., 2002); and (b) the fact

that scaling-up to satellite level for regional-scale

purposes would be difficult due to the strong

absorption of infrared radiation by the atmosphere.

Despite its big potential interest, much knowledge has

still to be gained prior to this tool becomes easily used

for irrigation scheduling.

4.4. Canopy reflectance indices

Different parameters reflecting changes in canopy

reflectance at different wavelengths have been used

for monitoring plant performance. The general

advantage of all these parameters or indexes is that

they are not restricted by the dimension of their field of

view, allowing measurements from small to large

scales, including airborne and satellite detection

(Gamon et al., 1990; Sellers et al., 1992; Penuelas

and Filella, 1998).

Among them, the simplest indexes, as the simple

ratio (SR = NIR/R, i.e., the ratio between near-

infrared to visible red) and the so-called normalised

difference vegetation index (NDVI = NIR � R/

NIR + R), correlate with the amount of green biomass

over an area and with the absorbed PPFD, and they

have even been shown to reflect stomatal conductance

and photosynthesis in unstressed plants (Sellers et al.,

1992; Penuelas and Filella, 1998). The main

disadvantage, that precludes their use for irrigation

purposes, is that they are quite static, failing to follow

gs and photosynthesis changes with developing

drought (Penuelas et al., 1994; Runyon et al., 1994).

A water index has been defined (WI = R900/R970)

that closely follows leaf water content and gs during

drought (Penuelas et al., 1993, 1994; Penuelas and

Filella, 1998). This seems a very promising tool for

drought assessment, provided that it performs better at

the canopy than at the leaf scale (Penuelas et al.,

1993). Its main disadvantage is that, because it

involves structural changes like loss of cell wall

elasticity, its variations appear only when RWC drops

below 85% (Penuelas et al., 1993). This precludes its

use for mild water stress assessment or for assessment

of plants, like many near-isohydric grapevine culti-

vars, capable of maintaining RWC within narrow

ranges.

The photochemical reflectance index (PRI = R531

� R570/R531 + R570) is strongly correlated to the

de-epoxidation state of the xanthophyll cycle (Gamon

et al., 1990; Penuelas et al., 1994; Penuelas and

Filella, 1998). PRI has been shown to correlate with

photosynthesis and gs, thus been capable to reflect

drought at the leaf level in many species (Penuelas et

al., 1998; Stylinski et al., 2002; Winkel et al., 2002),

including grapevines (Evain et al., 2004). Its principal

disadvantages are that (a) the precise PRI values as

well as their relationship to AN and gs seem dependent

on the species and/or the instrument used (Stylinski et

al., 2002; Winkel et al., 2002) and (b) on occasions it

fails to follow drought at the canopy scale, which is

probably due to leaf changes in orientation as a

consequence of wilting (Gamon et al., 1990; Penuelas

et al., 1994).

4.5. Chlorophyll fluorescence indices

Chlorophyll fluorescence indices have been pro-

posed as well as irrigation tools. With current

instrumentation, chlorophyll fluorescence can be

measured at short distances, of several meters, with

laser-based fluorometers (Flexas et al., 2000; Ounis

et al., 2001), and from airborne using sun-induced

chlorophyll fluorescence (Moya et al., 1998). How-

ever, satellite detection is theoretically possible if


Fig. 3. (A) The relationship between net CO2 assimilation (AN) and stomatal conductance. (B) The relationship between intrinsic water-use

efficiency (AN/gs) and stomatal conductance. (C) The relationship between Fs/F0 and stomatal conductance. (D) The relationship between Fs/F0

and net CO2 assimilation (AN). Data are from grapevines (V. vinifera L.) growing in a commercial vineyard in 1999 in Mallorca, and submitted to

different water supply, as described by Flexas et al. (2002a, 2002b). Circles correspond to Tempranillo, and triangles to Manto Negro. Closed

symbols are from irrigated plants, and empty symbols from non-irrigated. All data are average values of 6–8 replicates.

fluorescence is measured within the Ha Fraunhofer

band, or even within the oxygen bands, i.e. at certain

wavelengths not present in the solar spectrum due to

attenuation by the sun atmosphere (Moya et al., 1998).

Instruments are currently envisaged for this purpose

(Moya et al., 2004).

Among all chlorophyll fluorescence parameters,

steady-state chlorophyll fluorescence (Fs) normalised

to its dark-adapted state (F0) is especially remarkable,

because it can be measured by remote sensing without

depending on measuring fluorescence during saturat-

ing flashes. Passive detection is inexpensive and

non-dangerous. In addition, because of its remote

measurements, this technique causes no interference

with plant performance (Flexas et al., 2000; Moya et al.,

2004). Moreover, like reflectance indices, the measure-

ment of Fs/F0 is not restricted by the dimension of the

target or by the instrument field of view, allowing

measurements from small to large scales. All together

makes the continuous remote recording of Fs/F0 a

promising tool for plant management.

The diurnal response of Fs/F0 to light intensity

could be a sensitive indicator of water deficit. A

positive correlation is observed between Fs/F0 and

PPFD under irrigation, but an inverse correlation

develops as drought progresses, which is a character-

istic signal of water stress that can be related to a

strong increase of the non-photochemical quenching

(Cerovic et al., 1996; Flexas et al., 1999, 2000). In

addition, Flexas et al. (2002b) have shown that, at

saturating light intensity (a condition often met in

vineyards in summer), Fs/F0 directly correlates with gs

and photosynthesis in different C3 species. In grape-

vines, the relationship between Fs/F0 and gs is

curvilinear (r2 = 0.52) (Fig. 3C, see also Flexas et

al., 2002b), Fs/F0 steeply changing only when non-

stomatal limitations appear (i.e. when gs drops below

0.10–0.15 mol H2O m�2 s�1, Flexas et al., 2002b).

Thus, proper monitoring of Fs would be a useful tool

to irrigate plants only when gs drops below the

inflexion point between predominant stomatal and

non-stomatal limitations to photosynthesis, which is


Fig. 4. Relationship between Fs/F0 and stomatal conductance in

grapevine plants (V. vinifera L.) growing outdoors conditions during

summer 1999 in Mallorca, as described by Flexas et al. (1999).

Closed circles correspond to data during progressive water stress

development, and open circles correspond to recovery upon irriga-

tion of the same plants.

close to the inflexion point of the AN–gs relationship

(Fig. 3A, r2 = 0.97). On the other hand, the relation-

ship between Fs/F0 and AN is linear (Fig. 3D,

r2 = 0.57), which may be an even more interesting

feature for irrigation purposes. The large scattering

present in Fig. 3 may not preclude the use of Fs/F0 as

an indicator parameter since, as shown by Ounis et al.

(2001), scattering disappear when Fs/F0 is measured at

a larger canopy spot, instead of at leaf level. Remote

sensing instruments are currently being designed for

measuring at large canopy spots (Moya et al., 2004).

Beyond the advantages already mentioned, this

parameter is of particular interest because its

correlation to gs seems to be identical during drought

and recovery (Fig. 4, r2 = 0.80). A main disadvantage

is that, presently, no commercial instrument available

is capable of passive remote sensing of chlorophyll

fluorescence. In addition, before this technique

became useful for irrigation purposes, more studies

are needed to establish its applicability in different

crops and under different conditions.

5. Conclusions

In summary, current knowledge on physiological

responses of grapevines to water stress allows

envisaging physiologically based irrigation tools for

water-use-efficient irrigation programs. Partial root

drying (PRD) and regulated deficit irrigation (RDI)

programs are such tools. Among RDI programs,

several indicator parameters seem promising. These

are sap flow, trunk growth variations, canopy

temperature, photochemical reflectance index (PRI)

and steady-state chlorophyll fluorescence. All these

tools have yielded promising results at the ecophy-

siological level. A combination of PRD and RDI

techniques has not been tested, and could yield even

more promising results. In addition, it would be time

now to conduct a number of studies at the agronomical

level to confirm the usefulness of these approaches,

prior to their extension as common, practical tools, for

vineyard management and irrigation.

Acknowledgements

We thank Herederos de Ribas S.A. (Mallorca) for

the management of the experimental vineyard. We

gratefully acknowledge the work of many people in

field data collection and processing (especially Joana

Barcelo, Javier Gulıas, Elkadri Lefi, Bartolome

Sampol and Diego Riera). Suggestions on the manu-

script by Dr. M. Ribas-Carbo are indebted. Financial

support from CICYT-Projects AGF94-0687, AGF97-

1180 and AGL-2001-1285-CO3-01 of the Plan

Nacional (Spain) are greatly acknowledged. Finally,

we wish to express our gratitude to Dr. C. Dıez de

Bethancourt for her encouragement to work in this

field and for her advice on chemical analysis.

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Physiological tools for irrigation scheduling in grapevine (Vitis vinifera L.)

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