1 Introduction

The peach palm native to Amazonian is presently the main species of heart-of- palm producer in many Brazilian regions. According to data from the Brazilian Institute of Statistics and Geography (IBGE) (2016), São Paulo State (SP) stands out as one of the main Brazilian heart-of-palm producers. About 80% of the production is concentrated in the region named Vale do Ribeira-SP (LUPA 2008). Due to the tradition in heart-of-palm production and mainly to the climatic conditions (rainfall of 1600 mm year−1, with regular rainfall distribution throughout the year) this region presents ideal characteristics for rain-fed cultivation. However, an increase in peach palm plantations in non-traditional production regions, generally under water restriction (rainfall index below 1400 mm year−1, with rainfall concentrated in the spring/summer and dry winter seasons) requires the use of irrigation.

The soil water availability plays a crucial role in the production of peach palm because 90% of the heart-of-palm is composed of water (Ferreira and Graner 1982), and most of its roots occupy the upper soil layer (Bovi et al. 1999). According to Clement and Bovi (2000), due to the precocity and abundant tillering of the species, which allow constant cuts of heart-of-palms, the clump is always in vegetative stage. Abiotic factors, such as light, temperature, water and fertilizers should be optimized to maximize yield and to increase the useful economic life of the crop. With the expansion of the crop area and its migration to drought-prone areas, there is a high probability that, at least during certain periods of the year, water deficit situations will occur, causing production losses. In this context, it seems necessary to know the effects of soil water deficit on the physiology of this species and, consequently, to provide technical knowledge for peach palm irrigation.

There is an intricate relationship between rainfall and air temperature and, on the other hand, between photosynthesis (PN), stomatal conductance (gs), leaf water potential (ψleaf), chlorophyll fluorescence emission, which have influence on crop yields (Ball et al. 1994). Differently to what occurs in native habitats, in the state of São Paulo the peach palm experiences a climate seasonality with consequences for PN and vegetative growth. Regarding the later, Tucci et al. (2007) observed lower growth rates in the winter and higher ones in the summer; additionally, PN was lower in winter months (Tucci et al. 2010), what was attributed to low night temperatures throughout the winter.

In comparison to other palms of economic importance, such as coconut palm (Gomes and Prado 2007) and oil palm (Dufrêne and Saugier 1993; Suresh et al. 2012), little is known about gas exchange in peach palms (Tucci et al. 2010) and even less under soil water deficit conditions. A study addressing gas exchange in peach palm seedlings under water deficit conditions was performed on still biphid-leaves (Oliveira et al. 2002), but it is known that the stomatal frequency of biphid-leaves differs from those of adult, pinnate leaves of this species (Tucci et al. 2000). In addition, there are few studies using other heart-of-palm producers under soil water deficit, such as açaí palm (Euterpe oleracea Mart.; Calbo and Moraes 2000) and buriti palm (Mauritia vinifera Mart.; Calbo and Moraes 1997). More recently, others palms native to Brazil, such as Syagrus coronata (Mart.) Becc. (Arecaceae), showed robust stomata control and no photochemical damage under soil water deficit, and after rehydration it showed a rapid photosynthetic capacity recovery (Medeiros et al. 2015). Under field conditions, this same species exhibited lower sensitivity to drought, showing higher PN and water use efficiency during the dry season of the Northeastern semi-arid region of Brazil (Oliveira et al. 2016).

We investigated the photosynthetic performance of the peach palm, native to the Amazonian region, when cultivated under water deficit conditions at subtropical environment. The effects of soil water deficit on leaf water potential, gas exchange, chlorophyll fluorescence, as well as the performance of the species throughout the rewatering period were evaluated.

2 Materials and methods

2.1 Plant material and cultivation conditions

The experiment was carried out at Instituto Agronômico (IAC), Campinas, SP, Brazil (SP), at 22°54′S; 47°05′W, 674 m of altitude above sea level. One-year-old peach palm, Bactris gasipaes Kunth (Arecaceae), obtained from seeds of the Yurimaguas region, Peru, were transplanted, under greenhouse conditions, to 80 L-plastic pots (0.7 m in height, 0.4 m in diameter; 115 kg of substrate), where they were irrigated daily and grew for nine months. The pots, with one plant each, were arranged in four lines of ten plants each, with 2 m between lines and 1 m between plants on lines. Evaluations were carried out in plants of the central lines. A mixture of soil, cattle manure and sand (1:1:1) was used as substrate, and the plants were fertilized according to both the results of the chemical analysis of substrate and to recommendations by Bovi and Cantarella (1996). A more detailed description of substrate, fertilization and plant nutritional status evaluations are described by Tucci et al. (2007). At the beginning of the experiment, plants averaged 171.3 cm in height. The measurements were performed for 21 days, during April, 2002.

2.2 Greenhouse environmental conditions

Temperature and relative humidity conditions inside the greenhouse were monitored by temperature sensors, LI-1000-16, and data were stored by a data logger LI-1000, both from LI-COR Inc., Lincoln, NE, USA. Average data were recorded every 30 min. The maximum photosynthetic photon flux density (PPFD), monitored by a quantum sensor (LI-190, LI-COR Inc., Lincoln, NE, USA), was 1400 µmol m−2 s−1. It is worth mentioning that throughout the experiment the days were clear and sunny. The nighttime period was of 11:30 h  (7:00 p.m. until 06:30 a.m). Air temperature (Tair) measured with a dry- and a wet-bulb thermometer and data were used for calculating the air vapor pressure deficit (VPDair) (Buck 1981), whereas the vapor pressure difference between the leaf and the air (VPDleaf–air) was measured using the relative humidity and Tleaf, both measured with an infrared gas analyzer.

2.3 Experimental design and water regimes

The experiment was arranged in a completely random design with five control plants and five plants submitted to soil water deficit. The five control plants were well-irrigated daily so as to allow the soil to remain at field capacity of water retention. Water deficit was imposed by withdrawing water until the 13th day of study, when leaves were wilted on this day irrigation was re-established (to field capacity of water retention) for 8 days more.

2.4 Soil and plant water status

Soil water content was evaluated throughout the experiment at 10:00 a.m. by time domain reflectometry (TDR) using the soil moisture analyzer Trase System I (SoilMoisture Equipment Corp., Goleta, CA, USA). Soil water content was transformed into soil water potential (ψsoil) by means of calibration curves established in the same pots, full of substrate, according to Arruda et al. (2002). Measurements were taken at 0.3 m depth in pots of both treatments.

Plant water status was monitored by leaf water potential (ψleaf) at 5:30 a.m. and 1:30 p.m., using a pressure chamber (PMS mod. 1002, PMS Instrument Co., Albany, USA). Measurements were performed on sunlit leaves, on the terminal portion of leaflets from the medium part of the third younger completely-expanded leaf (+3 leaf), according to Tomlinson’s criteria (Tomlinson 1990).

2.5 SPAD readings

Soil and plant analyses development (SPAD) values were evaluated by means of a chlorophyll meter SPAD-Meter, Minolta 502, Japan. The equipment provides data corresponding to the intensity of the green color of the leaves, that is, an estimation of the total chlorophyll content of leaves. Measurements were performed twice, being the first at the imposition of treatments and the second at 13 day of study, corresponding to the maximum water deficit, always measured at 4 p.m. These measurements were performed in the middle of the +2 leaf, the second fully-expanded leaf from the top of the plant. On each leaflet, the SPAD readings were performed in the middle, and also on the proximal and distal part of it.

2.6 Gas exchange

The following variables were evaluated by means of a portable IRGA equipment model LCA-4 working in connection with the module Leaf Microclimate Control System, both from ADC, BioScientific Ltd., England: net CO2 assimilation (PN), transpiration rate (E), stomatal conductance (gs) and intercellular CO2 partial pressure (Ci). The water use efficiency (PN/E) and apparent carboxilation efficiency (PN/Ci) were calculated. The chamber was coupled to the portable light unity, which allows the measurements to be performed at a fixed photosynthetic photon flux density (PPFD). Gas exchange measurements were performed every 2 days at the beginning of the experiment, and daily after the 1st week, twice a day: at 8:00 a.m. and at 2:00 p.m., under natural Tair and CO2 partial pressure of 36.0 ± 0.7 Pa, under a constant PPFD of 1400 μmol m−2 s−1, which corresponded to the maximum PPFD observed inside the greenhouse. Measurements were performed on the medium portion of +2 leaves. Five plants per treatment were evaluated.

2.7 Chlorophyll a fluorescence

Chlorophyll a fluorescence emission was evaluated on the same leaflets at 7:00 a.m. and 1:30 p.m. A portable modulated fluorometer was used (PAM-2000, Heinz Walz GmbH, Effeltrich, Bayern, Germany), following the saturation pulse method (Bilger et al. 1995). Maximal quantum yield (FV/FM, where FV = FM-F0) of photosystem II (PSII) was calculated from the maximum (FM) and the minimum (F0) fluorescence signals, measured at 7:00 a.m., after overnight dark-acclimation, and after 30 min of dark-acclimation during diurnal period. The minimum initial fluorescence (F0) was determined under non-photosynthetic conditions under a low-intensity measuring beam. Five plants per treatment were measured.

2.8 Statistics

The experiment was arranged in a completely randomized design and data was subjected to the analysis of variance (ANOVA), considering the treatments as the source of variation. Regression analyses and curve fitting were done with the program Origin 6.0 (OriginLab Corp., Northampton, USA).

3 Results

3.1 Environmental conditions

During the study, air temperature in the greenhouse varied from 17.8 to 22.3 °C in the morning period and from 28.6 and 34.2 °C at 2:00 p.m. Leaf temperature varied from 30.2 to 34.6 °C in the morning period for plants under water deficit and from 29.4 to 32.5 °C for control plants. At 2:00 p.m. it varied from 34.5 and 41.0 °C for plants under water deficit and from 34.3 to 40.2 °C for control plants (Fig. 1a, b). The minimum air temperature during the experiment was observed on the 6th day at 6:30 a.m. corresponding to 16.7 °C (data not shown).

Fig. 1
figure 1

Average air (Tair) and leaf temperatures (Tleaf) (a, b), vapor pressure deficit (VPDair) and leaf–air vapor pressure difference (VPDleaf–air) (c, d) for control and treated plants at 8:00 a.m. (a, c) and 2:00 p.m. (b, d). Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration

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VPDair varied from 0.08 to 0.24 kPa in the morning (Fig. 1c, d). At 2:00 p.m. it was slightly higher, varying from 0.64 to 1.50 kPa, whereas VPDleaf–air varied from 1.73 to 3.15 kPa for plants under water deficit and from 1.86 to 2.89 kPa for control plants. At 2:00 p.m. VPDleaf–air varied from 2.20 to 3.83 kPa for plants under water deficit and from 1.94 to 3.51 kPa for control plants (Fig. 1c, d).

3.2 Soil and plant water status

For the control plants, the average ψsoil value was − 0.016 MPa (Fig. 2). On the other hand, soil under water deficit showed ψsoil of − 0.21 MPa 3 days after the beginning of water withdrawing and − 0.63 MPa on the day of maximum water deficit, and after rewatering values reached values close to those exhibited by the control.

Fig. 2
figure 2

Soil water potential (ψsoil, MPa) for control and treated plants at 9:00 a.m. Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration. Each symbol represents the mean value of five plants (± SE)

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Predawn ψleaf of control plants varied from − 0.3 to − 0.2 MPa, whereas plants under soil water deficit showed the lowest ψleaf at the 13th day of experiment, corresponding to − 1.6 MPa. Twelve hours after rewatering this value reached − 0.6 MPa, when leaves had already recovered their turgidity. In the following 24 h ψleaf recovered the value observed at predawn for control plants (Fig. 3a).

Fig. 3
figure 3

Leaf water potential (ψleaf, MPa) for control and treated plants at 5:30 a.m (a) and at 1:30 p.m. (b). Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration. Each symbol represents the mean value of five plants (± SE)

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ψleaf of control plants was lower at 1:30 p.m. than at 5:30 p.m., varying from − 1.4 to − 0.8 MPa. ψleaf decreased over water deficit period, being lower than those of the control plants, reaching − 1.7 MPa 13 days after water withdrawal. Nevertheless, ca. 20 h after rewatering ψleaf reached − 0.5 MPa, indicating rehydration in relation to the control plants, which showed a ψleaf of − 1.2 MPa. Thereafter, at 1:30 p.m., ψleaf of control plants remained lower than those that had been under water deficit (Fig. 3b).

3.3 SPAD readings

Initially, plants of both treatments showed SPAD values of 62.0 and 61.9, respectively. On the day of maximum water deficit, SPAD values were 62.7 e 58.8 for control and water deficit plants, respectively, with no significant difference between them.

3.4 Gas exchange

On the first day of experiment PN was ca. 11 µmol m−2 s−1 for both treatments. In the morning period, 3 days after water withdrawal, PN of plants that had been submitted to water deficit decreased to 3.9 µmol m−2 s−1, reaching values close to zero on the 10th day, maintaining these values until the day of maximum water deficit (Fig. 4a). After rewatering, PN increased gradually, reaching 52% of the control 4 days after rewatering and the same values exhibited by the control plants after 3 days more. Significant differences between treatments (P < 0.01) were observed from the third day after water suppression until the 6th day after rewatering. At 2:00 p.m., the control plants showed PN varying from 4.1 to 6.8 µmol m−2 s−1, whereas plants submitted to water deficit showed PN values of 4 µmol m−2 s−1 at the beginning of the study; after 3 days, PN of plants submitted to water deficit decreased to nearly zero until the 2nd day after rewatering (Fig. 4b). After the 4th day of re-irrigation, PN values increased to those exhibited by the control plants.

Fig. 4
figure 4

CO2 assimilation rate (a, b), stomatal conductance (c, d), transpiration rate (e, f) and intercellular CO2 partial pressure (g, h) for control and treated plants at 8:00 a.m. (a, c, e, g) and 2:00 p.m (b, d, f, h). Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration. Each symbol represents the mean value of five plants (± SE)

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Both gs and E (Fig. 4c–f) showed a response pattern that was similar to PN. At 8:00 a.m., it was possible to observe significant difference in gs between treatments (P < 0.05) from the third day after water suppression to the 6th day after rewatering (Fig. 4c). At 2:00 p.m., gs values of control plants were lower than those measured in the morning, remaining below 0.18 mol m−2 s−1 (Fig. 4d).

At 8:00 a.m., Ci was lower for water deficit plants than the control up to the 8th day after water suppression and also soon after rewatering (Fig. 4g). In contrast, at 2:00 p.m., Ci of water deficit plants remained higher than that of control plants from the 6th day after water suppression up to when water was replaced (Fig. 4h).

At 8:00 a.m., water use efficiency (PN/E) (Fig. 5a) was higher (P ≤ 0.05) for plants under water deficit 3 days after water suppression, then it decreased to values that were lower than the control plants from the 10th to the 14th day. At 2:00 p.m., PN/E of plants submitted to water deficit remained lower than that exhibited by the control plants until 3 days after rewatering (Fig. 5b).

Fig. 5
figure 5

Values of water use efficiency (a, b) and apparent carboxylation efficiency (c, d) for control and treated plants at 8:00 a.m. (a, c) and 2:00 p.m. (b, d). Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration. Each symbol represents the mean value of five plants (± SE)

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At 8:00 a.m., values of the apparent carboxylation efficiency (PN/Ci) of control plants varied from 0.42 to 0.32 µmol m−2 s−1 Pa−1, whereas plants under water deficit showed significant decrease (P ≤ 0.05) 3 days after water suppression, reaching values of 0.01 µmol m−2 s−1 Pa−1 from the 10th day after water suppression until the end of the water withdrawal. After rewatering, values of PN/Ci increased and reached values exhibited by the control plants 7 days after rewatering (Fig. 5c). At 2:00 p.m., control plants showed values of PN/Ci that were lower than those observed in the morning (Fig. 5d). In plants under water deficit, PN/Ci remained near zero throughout the days of water suppression, recovering to the values shown by the control plants 3 days after rewatering.

The relationship between PN and gs (Fig. 6a) was explained by an exponential function (R2 = 0.99), whereas the relationship between PN and PN/Ci was explained by a linear equation (R2 = 0.98) (Fig. 6b). It is worth mention that both relationships were fitted to data from morning and afternoon periods both for control and under deficit plants. The relationships between PN and ψleaf at 5:30 a.m. (R2 = 0.64), and between PN and VPDleaf–air (R2 = 0.43) were adjusted by linear functions only for morning data (Fig. 6c, d) for plants under water deficit.

Fig. 6
figure 6

Relationships between CO2 assimilation rate and stomatal conductance in (a) (R2 = 0.99**; n = 58) and apparent carboxilation efficiency (PN/Ci) (b) (R2 = 0.98**; n = 58); and leaf water potential at 5:30 a.m. (ψleaf) (c) (R2 = 0.64**; n = 15); and leaf–air vapour pressure difference (VPDleaf–air) (d) (R2 = 0.43**; n = 11) for control and treated plants at 8:00 a.m. (a, c) and 2:00 p.m. (b, d). In c and d only PN data of 8:00 a.m. were included. Each symbol represents the mean value of 5 plants (± SE)

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3.5 Chlorophyll a fluorescence

The average values of maximal quantum yield (FV/FM) of PSII for control plants were 0.83 at 7:00 a.m. and 0.81 at 1:30 p.m. (Fig. 7a, b). At 7:00 a.m. values of FV/FM for plants under water deficit decreased from the 7th day, reaching 0.78 on the 14th day of experiment, then it increased to values that were similar to those exhibited by the control plants at the end of the study. At 1:30 p.m., on the day of maximum water deficit, FV/FM reached 0.76, and after 4 days of rewatering values were similar to those shown by the control plants (Fig. 7b).

Fig. 7
figure 7

Maximal quantum yield (FV/FM) of PSII for control and treated plants at 7:00 a.m. (a) and 1:30 p.m. (b). Day 0: all plants irrigated; days 1–13: plants submitted to water deficit. Arrows indicate the day of rehydration. Each symbol represents the mean value of five plants (± SE)

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4 Discussion

The fact that Tleaf of water deficit plants was higher than control ones could be due to the cooling effect of the higher E in control plants. As expected, ψleaf of control plants were more negative in the midday than in the predawn. Because control plants were maintained at soil field capacity, their ψleaf values being more negative than those measured in the afternoon (− 1.3 to − 0.8 MPa; Fig. 3b) could be due to the increase in Tair and Tleaf.

The linear relationships between PN and ψleaf in the predawn (Fig. 6c) and between PN and VPDleaf–air (Fig. 6d) observed only for plants under water deficit suggest higher sensitivity of PN to water deficit in the soil as well as in the air, in relation to control plants.

High differences between predawn ψleaf and ψsoil, as observed in this study for water deficit plants has already been reported in the literature. In addition to differences associated with the methods used for the estimation of ψleaf and ψsoil, when roots are under dry soil conditions, the discrepancies might be likely due to soil moisture heterogeneity, low soil and plant hydraulic conductivity and also poor soil-root hydraulic continuity (Richter 1997; Donovan et al. 2001). Other mechanisms that could contribute to predawn differences between ψleaf and ψsoil, even in plants growing in well-watered homogenous soils are nighttime transpiration, putative apoplastic solutes in intercellular spaces, and growth (Donovan et al. 2001).

The sharp decrease of PN 6 days after the beginning of treatments (Fig. 4a) demonstrates the drastic effect of the soil water deficit on the peach palm photosynthetic activity. A PN decrease of 94% was observed in the morning when the ψleaf reached − 1.1 MPa at predawn, whereas at midday, ψleaf reached − 1.4 MPa (Fig. 3). On the other hand, PN and gs showed values that were close to zero in the midday.

Regarding plants submitted to soil water deficit, a very interesting situation could be observed after rewatering. On the next day after rewatering, ψleaf reached − 0.5 MPa at midday, that is, leaves measured at midday were more hydrated than those measured at predawn on the same day (− 0.6 MPa), and also when compared to the control plants measured at midday (− 1.2 MPa). From then until the end of the experiment, control plants maintained more negative ψleaf at midday when compared to those submitted to water deficit. The fact that ψleaf still recovered during the morning hours, instead of reaching a plateau value, could suggest a very low soil-leaf hydraulic conductance, that is, one night after rehydration was not sufficient to completely recover the plant water status (Donovan et al. 2001).

After rewatering, PN, E and gs recovered slowly, nevertheless reaching values shown by the control plants only 7 days after rewatering. At both times of the day, PN recover was gs-dependent (Fig. 4a–d), reinforcing the strong stomatal control of PN usually exhibited by many species (Pinheiro and Chavez 2011). The atypical higher ψleaf values of rewatered plants at midday deserves further studies but could be partially explained by the incomplete recovery of gs and E in the morning (Figs. 3, 4), leading to conservation of water in  rewatered plants, similar to an isohydric behavior (Tardieu and Simonneau 1998; Tardieu et al. 2010). Nevertheless, after 7 days of rewatering, gas exchange values recovered to those exhibited by the control plants, although ψleaf at 1:30 p.m. had not recovered yet. These midday ψleaf differences between treatments observed at the end of the experiment could be due to the following hypothesis: once gas exchange measurements were performed only at 8:00 a.m. and 2:00 p.m., it is possible that gs of rewatered plants might have decreased at midmorning.

The slow recovery of gs after rewatering could be attributed to ABA accumulation in leaves symplast throughout the water deficit period, extending the stomatal closing effects, once its redistribution to the guard-cells is dependent on pH gradients in different leaf compartments (Wilkinson and Davies 2002; Tardieu et al. 2010). Gomes et al. (2009) found out that ABA accumulates in dwarf coconut leaflets throughout water withdraw periods and did not decrease completely to levels exhibited by control plants after 8 days of rewatering. In orange trees, Gomes et al. (2004) also found that the soil water deficit increased leaf ABA content with consequent stomatal closure when ψleaf was lower than − 1.0 MPa, at 2:00 p.m.

The minimum ψleaf value observed at predawn was − 1.6 MPa, when PN was near zero at 8:00 a.m. on the 13th day of water deficit. In this respect, the peach palm can be considered a species showing mesophyte characteristics as far as drought tolerance is concerned, once it reaches PN zero in ψleaf between − 1.1 and − 2.5 MPa (Larcher, 2000). In other palm species under water deficit, minimum values of ψleaf when PN was close to zero were reported at the same mentioned range, varying from − 1.2 MPa for dwarf coconut (Cocus nucifera var. nana; Gomes et al. 2009) to more negative values than the observed in the present research, such as − 2.1 and − 2.5 MPa for buriti palm (Muritia vinifera; Calbo and Moraes 1997) and açaí palm (Euterpe oleracea; Calbo and Moraes 2000), respectively. Peach palm seedlings exhibiting biphid-leaves submitted to water deficit a showed a minimum value of ψleaf of − 1.9 MPa (Oliveira et al. 2002).

The importance of stomatal PN limitation during water deficit can also be verified by the PN exponential response to gs (Fig. 6a), which in the present study presented a more pronounced PN drop when gs values were lower than 0.1 mol m−2 s−1, reinforcing stomatal limitation of PN under water deficit as observed for many species (Flexas et al. 2009; Pinheiro and Chavez 2011). In peach palms Tucci et al. (2010) also reported a similar relationship between PN and gs, under conditions of seasonal variation of gas exchange.

On the other hand, the relationship between PN and PN/Ci was linear (Fig. 6b) indicating no additional increases in the apparent limitation of carboxylation under water deficit. Restriction of CO2 diffusion to the mesophilic carboxylation sites, with decreases in gs as well as in mesophyll conductance could be contributing to the down-regulation of PN and, consequently, to the decrease of PN/Ci values in low PN, as also reported for different plant species (Flexas et al. 2009; Pinheiro and Chavez 2011). In a study of gas exchange response to irradiance with Citrus species, PN/Ci values of 0.7 µmol m−2 s−1 Pa−1 decreased linearly to zero in response to gs, as stomata close under darkness (Machado et al. 2005), pointing out the gs regulation of PN and PN/Ci.

FV/FM of control plants was between 0.82 and 0.83 (Fig. 7) in early morning, which is in the range (between 0.78 and 0.83) observed by Osmond (1994) for most species. Control plants showed a midday decrease in FV/FM, reflecting photosynthetic regulatory responses to excessive PPFD. On the other hand, plants submitted to water deficit showed a minimum FV/FM value of 0.76 on the day of maximum deficit at in. After 4 days of rewatering, FV/FM values reached those exhibited by control plants. It is important to note that this minimum FV/FM value was not lower than 0.72, thus not characterizing chronic photoinhibition (Critchley 1998). The lower FV/FM values measured at midday in plants submitted to water deficit recovered to values ≥ 0.78 in the following morning, which indicate that a photoprotection or dynamic photoinhibition process has occurred (Osmond 1994), probably due to PPFD values above saturation and high air temperatures associated with the absence of PN.

In conclusion, the physiological responses of the peach palms to soil water deficit suggest a tolerance to drought, showing characteristics of mesophytes, that is, moderate decrease of ψleaf, stomatal control of water losses and consequent PN limitation, whereas the photosynthetic apparatus was maintained by photoprotection processes.