Effects of water stress on photosynthetic activity,dry mass partitioning and some associated metabolic changes in four provenances of neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis> A. Juss)

Chlorophyll (Chl) content, dry mass, relative water content (RWC), leaf mass per area (LMA), proline (Pro) content, malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (POD) activity, P _N-PAR response curves and gas exchange were studied to determine the effects of water stress on photosynthetic activity, dry mass partitioning and metabolic changes in four provenances of neem (Azadirachta indica A. Juss). The results indicated that provenance differences existed in the adaptation response to water stress that included changes to growth strategies coupled with ecophysiological and metabolic adjustments. As water stress increased, stomatal conductance (g _s), net photosynthetic rate (P _N), transpiration rate (E), and leaf RWC decreased while LMA increased in all provenances. Dry mass was reduced in droughted plants and the percentage increased in dry mass allocated to roots, and enzyme activities of SOD and POD were highest in neem originating from Kalyani (KA) provenance and lowest in neem originating from New Dehli (ND) provenance. In contrast, water stress increased MDA content least in KA and most in ND. Furthermore, neem originating from ND also had the greatest decrease in Chl a/b ratio while the ratio was least affected in neem originating from KA. These findings suggest neem originating from KA may have more drought resistance than neem originating from ND. The data from P _N-PAR response curves are less clear. While these curves showed that drought stress increased compensation irradiance (I _c) and dark respiration (R _D) and decreased saturation irradiance (I _s) and maximum net photosynthetic rate (P _max), the extent of decline in P _max was provenance dependent. P _max under non-waterlimiting conditions was higher in neem originating from Jodhpur (MA) (about 14 μmol m⁻² s⁻¹) than in the other three provenances (all about 10 μmol m⁻² s⁻¹), but mild water stress had minimal effect on P _max of these three provenances whereas P _max of MA provenance declined to 10 μmol m⁻² s⁻¹, i.e. a similar value. However, under severe water stress P _max of MA and KA provenances had declined to 40% of non-stressed values (about 6 and 4 μmol m⁻² s⁻¹, respectively) whereas the decline in P _max of neem originating from Kulapachta (KU) and ND provenances was about 50% of nonstressed values (about 5 μmol m⁻² s⁻¹). These data suggest the P _N responses of KU and ND provenances are most tolerant, and KA and MA least tolerant to increasing water stress, but also suggest MA provenance could be the most desired under both non-water-limiting and water-limiting conditions due to highest P _max in all conditions.     

不同种源油松幼苗的光合色素和非结构性碳水化合物对模拟氮沉降的短期响应

以不同种源(内蒙NM、北京BJ和山西SX)的3年生油松幼苗为研究对象,研究不同种源油松幼苗的光合色素以及非结构性碳水化合物(NSC)对氮沉降增加的短期响应。实验中设置5个氮处理:CK(0 kg hm-2a-1)、N1(15 kg hm-2a-1)、N2(25 kg hm-2a-1)、N3(50 kg hm-2a-1)、N4(150 kg hm-2a-1)。研究结果表明:(1)不同生长季,3个种源油松幼苗的光合色素对氮沉降增加的响应存在差异,但是只有BJ种源油松幼苗的叶绿素含量在生长季中期受到了氮沉降增加的显著促进作用,并在N4水平下达到最大值。(2)氮沉降的增加促进了3个种源油松幼苗NSC的转移和消耗,在生长季初期和中期,随着氮沉降水平的升高,3个种源油松幼苗的可溶性糖(SS)含量、淀粉(ST)含量以及总非结构性碳水化物(TNC)含量呈不同程度的降低。生长季末期,3个种源油松幼苗的SS和TNC明显积累。N4水平抑制了NM种源油松幼苗SS和BJ种源油松幼苗ST的累积,促进了NM种源油松幼苗ST含量和BJ种源油松幼苗SS含量的提高。氮沉降的增加显著抑制了SX种源油松幼苗NSC的积累,延长了幼苗的生长期,推迟了幼苗进入休眠的时间。     

Photosynthetic Response to Soil Water Contents of an Annual Pioneer C4 Grass (Agriophyllum squarrosum) in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and leaf water potential (Ψ_l) of an annual pioneer C₄ grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P _N, E, and g _s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P _N, E, and g _s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψ_l increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P _N, E, and g _s kept increasing even after this SWC. This might indicate that the adjustment of Ψ_l response to the changes of SWC lagged that of the photosynthetic parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tolerance to Water Stress in Tomato Cultivars

The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), osmotic adjustment, and crop water stress index (CWSI) were investigated. Osmotic adjustment was the highest in cv. Arka Meghali, followed by cv. RFS-1. CWSI was lowest in cv. Arka Meghali and highest in cv. Pusa Ruby. Significant reduction in g _s, E, and P _N was observed in all the cultivars. The maximum reduction in E was observed in cv. Arka Saurabh during the fruiting stage (62.4 %) and maximum reduction in P _N at the flowering stage in Pusa Ruby (53.1 %). Maximum P _N was observed in Arka Meghali under water stress. The values of internal CO₂ concentration (C _i) did not follow the decrease in g _s which might be taken as an indication of mesophyll (non-stomatal) limitation to P _N. Magnitude of P _N decrease accompanying g _s reductions varied in the four cultivars. Arka Meghali which had highest rate of gas exchange efficiency (P _N/g _s) under water deficits can be recommended for rainfed cultivation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determinant of photosynthetic capacity in rice leaves under ambient air conditions

At the grain-filling stage, net photosynthetic rate (P _N), stomatal conductance (g _s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P _N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P _N value. The differences in g _s and CE were similar. P _N, g _s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P _N and CE was much higher than that between P _N and g _s in both cases, and P _N was negatively correlated with intercellular CO₂ concentration (C _i). Hence the carboxylation activity or activated amount of ribulose-1,5-bisphosphate carboxylase/oxygenase rather than g_s was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P _N was positively correlated with g _s, but negatively correlated with C _i. Thus g _s is not the determinant of the photosynthetic capacity in rice leaves.The study was supported by the State Key Basic Research and Development Plan (No.G1998010100).     

Photosynthesis,transpiration, and water use efficiency of <Emphasis Type="Italic">Leymus dasystachys</Emphasis> on the Hunshandake desert

Net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) declined from upper leaves to the lower ones during dry and rainy seasons, indicating that long-term carbon budget should take into account P _N variations for different leaf types. Relatively greater P _N in the dry season suggested that this species is more able to maintain higher P _N under drought, but the relatively higher E in the dry season might reduce water use efficiency (P _N/E) for the species. Significant correlations between P _N and g _s indicated that g _s may be the critical factor for P _N variability in the desert region.     

Diurnal and seasonal trends in photosynthetic performance of <Emphasis Type="Italic">Dalbergia sissoo</Emphasis> Roxb. and <Emphasis Type="Italic">Hardwickia binata</Emphasis> Roxb. from a semi-arid ecosystem

Diurnal and seasonal trends in net photosynthetic rate (P _N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P _N in D. sissoo ranged from 21.40±2.60 μmol m⁻² s⁻¹ in rainy season I to 13.21±2.64 μmol m⁻² s⁻¹ in summer whereas in H. binata it was 20.04±1.20 μmol m⁻² s⁻¹ in summer and 13.64±0.16 μmol m⁻² s⁻¹ in winter. There was a linear relationship between daily maximum P _N and g _s in D. sissoo but there was no strong linear relationship between P _N and g _s in H. binata. In D. sissoo, the reduction in g _s led to a reduction in both P _N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in g _s causes an increase of P _N and E with a significant moderate WUE.     

不同种源花榈木苗期生长及生理特性比较

为了解不同种源花榈木在贵阳的生长特性和差异,该文通过对10个种源地花榈木进行育苗试验,测定其两年生实生苗的苗高、地径、生物量、叶片光合参数、光合色素、硝酸还原酶活性、硝态氮含量和根系活力,并进行差异性分析。结果表明:(1)10个种源花榈木净光合速率、气孔导度、胞间CO₂浓度、蒸腾速率和水分利用效率差异显著(P<0.05),表明不同种源花榈木光合特性及光能利用效率具有较大差异,浙江杭州和浙江永康花榈木是具有较高光合生长潜力的种源。(2)种源间的叶绿素含量、硝酸还原酶、硝态氮、根系活力存在显著差异,福建建瓯种源的叶绿素a、叶绿素b含量和叶绿素总量最高,能够将光合原初反应过程中积蓄的光能进行高效地传递,促进碳的同化; 贵州花溪种源硝酸还原酶活性最大,硝态氮含量最高,对氮元素的利用能力较强,能够促进植物蛋白质、氨基酸和叶绿素等的合成; 贵州望谟种源根系活力最大,吸收养分的能力强。(3)各种源间苗高、地径和生物量的分配存在显著差异,浙江杭州种源的植株枝叶繁茂、根系发达,生长表现好,安徽黄山种源的植株矮小,生长表现较差; 浙江杭州种源将生物量更多分配在根和叶,提高其根系吸收养分和叶片获取光能的能力,安徽黄山种源总体生物量积累最少,长势最差。(4)通过主成分分析法对各种源的花榈木适应性进行综合评价,结果显示浙江杭州种源>贵州黎平种源>浙江永康种源>贵州望谟种源>福建建瓯种源>贵州凯里种源>贵州石阡种源>贵州花溪种源>贵州平塘种源>安徽黄山种源。综上结果表明,浙江杭州、贵州黎平和浙江永康种源花榈木对贵阳地区立地环境具有较强的适应能力和生长潜力。     

Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in P _N and g _s were not evident for the well-irrigated plants. With the lower water availability, midday reductions in P _N and g _s were much more marked and the duration of the depression was longer. Additionally, the P _N-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.     

Modelling Diurnal Courses of Photosynthesis and Transpiration of Leaves on the Basis of Stomatal and Non-Stomatal Responses,Including Photoinhibition

A mathematical model for photoinhibition of leaf photosynthesis was developed by formalising the assumptions that (1) the rate of photoinhibition is proportional to irradiance; and (2) the rate of recovery, derived from the formulae for a pseudo first-order process, is proportional to the extent of inhibition. The photoinhibition model to calculate initial photo yield is integrated into a photosynthesis-stomatal conductance (g _s) model that combines net photosynthetic rate (P _N), transpiration rate (E), and g _s, and also the leaf energy balance. The model was run to simulate the diurnal courses of P _N, E, g _s, photochemical efficiency, i.e., ratio of intercellular CO₂ concentration and CO₂ concentration over leaf surface (C _i/C _s), and leaf temperature (T ₁) under different irradiances, air temperature, and humidity separately with fixed time courses of others. When midday depression occurred under high temperature, g _s decreased the most and E the least. The duration of midday depression of g _s was the longest and that in E the shortest. E increased with increasing vapour pressure deficit (VPD) initially, but when VPD exceeded a certain value, it decreased with increasing VPD; this was caused by a rapid decrease in g _s. When air temperature exceeded a certain value, an increase in solar irradiance raised T ₁ and the degree of midday depression. High solar radiation caused large decrease in initial photon efficiency (). P _N, E, and g _s showed reasonable decreases under conditions causing photoinhibition compared with non-photoinhibition condition under high irradiance. The T ₁ under photoinhibition was higher than that under non-photoinhibition conditions, which was evident under high solar irradiance around noon. The decrease in C _i/C _s at midday implies that stomatal closure is a factor causing midday depression of photosynthesis.     

Gas exchanges of an endangered species Syringa pinnatifolia and a widespread congener S. oblata

Net photosynthetic rate (P _N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g _s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g_s. Unlike S. oblata, the maximal photosynthetic rate (P _max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P _N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.This revised version was published online in March 2005 with corrections to the page numbers.     

Photosynthetic photon flux density,carbon dioxide concentration,and vapor pressure deficit effects on photosynthesis in cacao seedlings

Independent short-term effects of photosynthetic photon flux density (PPFD) of 50–400 μmol m⁻² s⁻¹, external CO₂ concentration (C _a) of 85–850 cm³ m⁻³, and vapor pressure deficit (VPD) of 0.9–2.2 kPa on net photosynthetic rate (P _N), stomatal conductance (g _s), leaf internal CO₂ concentration (C _i), and transpiration rates (E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 μmol m⁻² s⁻¹ increased P _N by about 50 %, but further increases in PPFD up to 1 500 μmol m⁻² s⁻¹ had no effect on P _N. Increasing C _a significantly increased P _N and C _i while g _s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P _N, but the slight decrease in g _s and the slight increase in C _i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P _N. The unusually small response of g _s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange characteristics (g _s, C _i, E) among the three cacao genotypes under any measurement conditions.     

Leaf Gas Exchange of Pachyrhizus ahipa and P. erosus Under Water and Temperature Stress

Gas exchange, water relations, and leaf traits were studied in the tuberous-root producing legumes ahipa (Pachyrhizus ahipa) and yambean (P. erosus) under different environmental conditions. Differences in leaf traits (hairiness, leaf area, areal leaf mass, stomatal density) and paraheliotropism were found between ahipa and yambean. Under sufficient water supply, the increase in air temperature and decrease in air humidity increased stomatal conductance (g _s) and net photosynthetic rate (P _N) in yambean but reduced them in ahipa. In a drying soil (14 d after irrigation), inter-specific variation in gas exchange was only observed in the early morning, and yambean showed a greater sensitivity to water restriction than ahipa. High g _s at low humidity increased P _N of P. erosus but resulted in lower water-use efficiency (WUE). However, long-term WUE, estimated by leaf carbon isotope discrimination, showed little variation between species. Daily-irrigated ahipa and yambean grown in the greenhouse did not show significant differences in gas exchange. However, leaf temperature was significantly greater in yambean than in ahipa while a steepper relationship between E and P _N and g _s was observed in ahipa.     

Gas Exchange Characteristics and Water Relations in Some Elite Okra Cultivars Under Water Deficit

Thirty-days-old plants of two cultivars of okra (Hibiscus esculentus L.), Sabzpari and Chinese-red, were subjected for 30 d to two water regimes (100 and 60 % field capacity). Leaf water potential and osmotic potential of both lines decreased significantly with the imposition of drought. Both the leaf pressure potential and osmotic adjustment were much lower in Chinese-red than those in Sabzpari. Chlorophyll (Chl) b content increased, whereas Chl a content remained unchanged and thus Chl a/b ratios were reduced in both lines. Drought stress also caused a significant reduction in net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and water use efficiency (WUE) especially in cv. Sabzpari. The lines did not differ in intrinsic WUE (P _Ng_s) or intercellular/ambient CO₂ ratio. Overall, the growth of two okra cultivars was positively correlated with P _N, but not with g _s or P _N/E, and negatively correlated with osmotic adjustment.     

Physiological divergences between two rhizomatous grasses from a desertification steppe,North China

The inter-and intra-specific physiological differences, e.g. rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), and water use efficiency (WUE), were compared between two grasses, Calamagrostis epigeios (L.) Roth. and Psammochloa villosa (Trin.) Bor., and between their leaf types in a desertification steppe in North China. The two species had a similar habitat, but differed in leaf area and rhizome depth. Leaf P _N, E, and g _s for P. villosa were significantly greater than those for C. epigeios in the growing season, but WUE for the former species was only 50 and 80 % of that for the latter one in dry and rainy seasons, respectively. In general, leaf P _N, E, g _s, and WUE for both vegetative and reproductive shoots of the two species exhibited little variations between leaf types or with leaf age, even though there were some remarkable differences between dry and rainy seasons. The mean leaf P _N and E in reproductive shoots of P. villosa were significantly lower than those in its vegetative shoots in rainy season, while these differences were much smaller for those of C. epigeios. P. villosa with deeper rhizome roots has relative higher leaf P _N, E, and g _s, but a smaller WUE in the arid desertification steppe region.     

Elevation provenance affects photosynthesis and its acclimation to temperature in the high-Andes alpine herb Phacelia secunda

• We analysed whether Phacelia secunda populations from different elevations exhibit intrinsic traits associated with diffusive and biochemical components of photosynthesis, and if they differ in acclimation of photosynthesis to warmer temperatures. We hypothesized that P. secunda will have similar photosynthetic performance regardless of altitudinal provenance and that plants from high elevations will have a lower photosynthetic acclimation capacity to higher temperature than plants from low elevations.
• Plants from 1600, 2800 and 3600 m a.s.l. in the central Chilean Andes were collected and grown under two temperature regimes (20/16 °C and 30/26 °C day/night). The following photosynthetic traits were measured in each plant for the two temperature regimes: A_N, g_s, g_m, J_max, V_cmax, Rubisco carboxylation k_cat^c.
• Under a common growth environment, plants from the highest elevation had slightly lower CO₂ assimilation rates compared to lower elevation plants. While diffusive components of photosynthesis increased with elevation provenance, the biochemical component decreased, suggesting compensation that explains the similar rates of photosynthesis among elevation provenances. Plants from high elevations had lower photosynthetic acclimation to warmer temperatures compared to plants from lower elevations, and these responses were related to elevational changes in diffusional and biochemical components of photosynthesis.
• Plants of P. secunda from different elevations maintain photosynthetic traits when grown in a common environment, suggesting low plasticity to respond to future climate changes. The fact that high elevation plants had lower photosynthetic acclimation to warmer temperature suggests higher susceptibility to increases in temperature associated with global warming.

     

Growth and Leaf Gas Exchange Characteristics in Dalbergia sissoo Roxb. and D. latifolia Roxb. Under Water Deficit

Forty two-month-old plants of Dalbergia sissoo and D. latifolia were subjected for 56 d to water deficit induced by withholding water. Drought stress caused a significant reduction in plant height, stem diameter, net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) in both species, but the reduction was greater in D. sissoo than in D. latifolia. Water use efficiency (P _N/E) was adversely affected due to water stress only in D. latifolia, and intrinsic water use efficiency (P _N/g _s) was increased in both species. There was a slight effect of water stress on variable to maximum fluorescence (F_v/F_m) (quantum yield of photosystem 2) in both species, but the species did not differ significantly in this attribute.     

Single leaves photosynthetic characteristics of two insect-resistant transgenic cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) varieties in response to light

How the photosynthetic characteristics of insect-resistant transgenic cotton (Gossypium hirsutum L.) respond to light or whether this genetic transformation could result in unintended effects on their photosynthetic and physiological processes is not well known. Two experiments were conducted to investigate the shapes of net photosynthetic rate (P _N), stomatal conductance (g _s), apparent light use efficiency (LUE_app) and water use efficiency (WUE) light-response curves for single leaves of Bt (Bacillus thuringiensis) and Bt+CpTI (cowpea trypsin inhibitor) transgenic cotton plants and their non-transgenic counterparts, respectively. Results showed that the significant difference in response of P _N and WUE to light between transgenic cotton and non-transgenic cotton occured but not always throughout the growing season or in different experiments or for all transgenic cotton lines. It was highly dependent on growth stage, culture condition and variety, but no obvious difference between any transgenic cotton and non-transgenic cotton in the shapes of g _s and LUE_app light-response curves was observed in two experiments at different growth stages. In the field experiments, transgenic Bt+CpTI cotton was less sensitive to response of P _N to high irradiance at the boll-opening stage. In pot experiments, WUE light-response curves of both Bt transgenic cotton and Bt+CpTI transgenic cotton progressively decreased whereas non-transgenic cotton slowly reached a maximum at high irradiance at boll-opening stage. We supposed that culture environment could affect the photosynthesis of transgenic cotton both directly and indirectly through influencing either foreign genes expression or growth and physiological processes.     

Growth and photosynthetic responses in Jatropha curcas L. seedlings of different provenances to watering regimes

Seedlings from four provenances of Jatropha curcas were subjected to 80, 50, and 30% of soil field capacity in potted experiments in order to study their responses to water availability. Our results showed that with the decline of soil water availability, plant growth, biomass accumulation, net photosynthetic rate, stomatal conductance (g_s), and transpiration rate (E) decreased, whereas leaf carbon isotope composition (δ¹³C), leaf pigment contents, and stomatal limitation value increased, while maximal quantum yield of PSII photochemistry was not affected. Our findings proved that stomatal limitation to photosynthesis dominated in J. curcas under low water availability. The increase of δ¹³C should be attributed to the decrease in g_s and E under the lowest water supply. J. curcas could adapt to low water availability by adjusting its plant size, stomata closure, reduction of E, increasing δ¹³C, and leaf pigment contents. Moreover, effects of provenance and the interaction with the watering regime were detected in growth and many physiological parameters. The provenance from xeric habitats showed stronger plasticity in the plant size than that from other provenances under drought. The variations may be used as criteria for variety/provenance selection and improvement of J. curcas performance.     

Peanut Photosynthesis Under Drought and Re-Watering

The photosynthetic response of three Arachis hypogaea L. cultivars (57-422, 73-30, and GC 8-35) grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (g _s), transpiration rate (E), and net photosynthetic rate (P _N) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUE_i) and photosynthetic capacity (P _max) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained g _s, E, and P _N activities. Twenty-four hours after re-watering, the electron transport rates and RuBPCO activity strongly increased. P _N and P _max fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented.