M.F. Ortuño

Comparative growth and water relations of Cistus albidus and Cistus monspeliensis plants during water deficit conditions and recovery

Four month old Cistus albidus and Cistus monspeliensis plants growing in a growth chamber were submitted to two consecutive cycles, during which irrigation water was withheld for 7 days before being reconnected and the plants rewatered to run off (WD treatment). Control treatment plants were irrigated daily. At the end of the second dry period the treated plants were submitted to control plant conditions for 15 days. C. monspeliensis plants withstood the water deficit better than C. albidus, mainly due to its capacity to recover a water deficit situation. C. monspeliensis plants show net assimilation rate (NAR) levels above those of the control plants during the recovery period. In C. albidus the main growth limiting factor was the cellular expansion, whereas in C. monspeliensis photosynthesis was the limiting factor. Both species developed complementary avoidance mechanisms based on stomatal closure, a reduction in leaf area and root hydraulic conductivity, and epinasty. C. monspeliensis plants showed good osmotic adjustment in response to water deficit, which enabled it to avoid decreased leaf turgor potential and partial dehydration. After the water deficit, the mobilisation of accumulated organic solutes may also have contributed to the increased relative growth rate and NAR during the recovery period.

Grapevine varieties exhibiting differences in stomatal response to water deficit

Knowledge on variety traits and physiological responses to stress is still scarce in Vitis vinifera L., limiting the optimisation of irrigation and breeding for high water use efficiency. We have characterised five grapevine varieties using thermal imaging, leaf gas exchange, leaf morphology and carbon isotope composition. Plants of the varieties Aragonez, Trincadeira, Cabernet Sauvignon, Syrah and Touriga Nacional were grown in field conditions. Two experiments were performed. In Experiment I (2006), vines of Aragonez and Trincadeira were either well irrigated (WI, 80% ETc), non-irrigated but rain fed (NI) or subjected to regulated deficit irrigation (RDI, 40% ETc) and studied along the summer season. In Experiment II (2006 and 2007), vines of the five varieties were subjected to RDI (30-40% ETc) and studied at veraison. In Experiment I, leaf temperature (Tleaf) correlated negatively with stomatal conductance (gs) and leaf water potential (Ψpd). The inverse relationship between gs and Tleaf was highly significant in the afternoon. In Experiment II, the different genotypes showed different Tleaf for similar Ψpd. Stomatal density did not correlate with gs suggesting that varieties have different stomatal control. Our results show that combined measurements of canopy temperature and Ψpd can aid in better understanding of stomatal regulation in different grapevine varieties. Such variation in stomatal regulation should be taken into account in determining irrigation strategies.

Analysis of carbohydrates in Lupinus albus stems on imposition of water deficit, using porous graphitic carbon liquid chromatography-electrospray ionization mass spectrometry

This work reports the development and application of a negative ion mode online LC-ESI-MS method for studying the effect of water deficit on the carbohydrate content of Lupinus albus stems, using a porous graphitic carbon (PGC) stationary phase and an ion trap mass spectrometer. Using this method, separation and detection of several water soluble carbohydrates, ranging from mono-, di-, and oligosaccharides (raffinose, stachyose, and verbascose) to sugar alcohols was achieved in approximately 10 min. This on-line PGC-LC-ESI-MS method shows good linearity with correlation coefficients R(2)>0.99, selectivity, short analysis time, and limits of detection (LOD) ranging from 0.4 to 9 pmol for sugars and 4-20 pmol for sugar alcohols. This PGC-LC-ESI-MS method is sensitive and allowed us to detect even small alterations in carbohydrate levels in L. albus stems that resulted from a mild/early water deficit (nmol g(-1)DW). This paper describes details of our method and its application to the quantitative analysis of water soluble underivatised carbohydrates extracted from L. albus stem tissues that have been subjected to early and severe water deficit conditions, followed by a rewatering period.

Maximum daily trunk shrinkage and stem water potential reference equations for irrigation scheduling of lemon trees

Measurements of midday stem water potential (ψstem) and maximum daily trunk shrinkage (MDS) were done over a 3-year period in adult Fino lemon trees (Citruslimon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that reference equations can be obtained for MDS and ψstem by pooling data across several seasons using crop reference evapotranspiration (ETo), daily mean vapor pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo in the case of ψstem. The best predictor of MDS under non-limiting soil water conditions was Tm, suggesting that MDS reference values can be obtained by means of easy and cheap measurements. MDS and ψstem values were not influenced significantly by yield or crop load variations between years. A negative linear relationship between MDS and ψstem was found, pointing to an unchanging radial hydraulic conductivity in the bark tissues and suggesting that the MDS is controlled by water potential.

Water status indicators of lemon trees in response to flooding and recovery

Potted 2-year-old lemon trees [Citrus limon (L.) Burm. fil, cv. Verna] grafted on sour orange (C. aurantium L.) rootstock were subjected to flooding for 3 d. Control plants were irrigated daily to field capacity. Continuously (sap flow, trunk diameter fluctuations) and discretely (predawn and midday leaf water potential, leaf conductance) measured plant-based water status indicators were compared. The sensitivity of the maximum daily trunk shrinkage signal intensity to flooding and its behaviour during the recovery period demonstrated that this indicator is more feasible than the others for use in automatic irrigation. The responses to flooding of continuously and discretely measured plant-based water status indicators were very similar to those observed in response to drought stress indicating that it necessary to use soil water measurement automatic sensors to detect the cause of the stress. The results underlined the robustness of the compensation heat-pulse technique for estimating instantaneous and daily transpiration rates on flooding stress and recovery.

Initial water deficit effects on Lupinus albus photosynthetic performance, carbon metabolism, and hormonal balance: metabolic reorganization prior to early stress responses

The early (2-4 d) effects of slowly imposed soil water deficit on Lupinus albus photosynthetic performance, carbon metabolism, and hormonal balance in different organs (leaf blade, stem stele, stem cortex, and root) were evaluated on 23-d-old plants (growth chamber assay). Our work shows that several metabolic adjustments occurred prior to alteration of the plant water status, implying that water deficit is perceived before the change in plant water status. The slow, progressive decline in soil water content started to be visible 3 d after withholding water (3 DAW). The earliest plant changes were associated with organ-specific metabolic responses (particularly in the leaves) and with leaf conductance and only later with plant water status and photosynthetic rate (4 DAW) or photosynthetic capacity (according to the Farquhar model; 6 DAW). Principal component analysis (PCA) of the physiological parameters, the carbohydrate and the hormone levels and their relative values, as well as leaf water-soluble metabolites full scan data (LC-MS/MS), showed separation of the different sampling dates. At 6 DAW classically described stress responses are observed, with plant water status, ABA level, and root hormonal balance contributing to the separation of these samples. Discrimination of earlier stress stages (3 and 4 DAW) is only achieved when the relative levels of indole-3-acetic acid (IAA), cytokinins (Cks), and carbon metabolism (glucose, sucrose, raffinose, and starch levels) are taken into account. Our working hypothesis is that, in addition to single responses (e.g. ABA increase), the combined alterations in hormone and carbohydrate levels play an important role in the stress response mechanism. Response to more advanced stress appears to be associated with a combination of cumulative changes, occurring in several plant organs. The carbohydrate and hormonal balance in the leaf (IAA to bioactive-Cks; soluble sugars to IAA and starch to IAA; relative abundances of the different soluble sugars) flag the initial responses to the slight decrease in soil water availability (10-15% decrease). Further alterations in sucrose to ABA and in raffinose to ABA relative values (in all organs) indicate that soil water availability continues to decrease. Such alterations when associated with changes in the root hormone balance indicate that the stress response is initiated. It is concluded that metabolic balance (e.g. IAA/bioactive Cks, carbohydrates/IAA, sucrose/ABA, raffinose/ABA, ABA/IAA) is relevant in triggering adjustment mechanisms.

Establishing maximum daily trunk shrinkage and midday stem water potential reference equations for irrigation scheduling of early maturing peach trees

Measurements of midday stem water potential (Ψstem) and maximum daily trunk shrinkage (MDS) were taken over a 4-year period in early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on GF-677 rootstock. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that seasonal reference equations can be obtained for MDS and Ψstem using crop reference evapotranspiration (ETo), daily mean vapour pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo and VPDm in the case of Ψstem. In this way, VPDm was seen to be the best predictor of MDS and Ψstem, without both were influenced significantly by yield or crop load variations between years. When the postharvest regression between MDS or Ψstem and the meteorological parameters mentioned were broken down into early and late postharvest periods, the correlation coefficients improved and were closely related to the presence or absence of sugar-demanding sinks, such as active root growth. A negative linear relationship between MDS and Ψstem was found, pointing to unchanging radial hydraulic conductivity in the bark tissues and suggesting that MDS depends to a great extent of the water potential.

Using continuously recorded trunk diameter fluctuations for estimating water requirements of lemon trees.

Adult Fino lemon trees (Citrus limon L. Burm. fil.) grafted on sour orange (Citrus aurantium L.) and irrigated above their crop water requirements (T0 treatment) were compared with plants where water was applied according to maximum daily trunk shrinkage (MDS) (T1 treatment), in order to maintain MDS signal intensity [actual (T1) MDS/control (T0) MDS] threshold values close to unity. When MDS signal intensity on at least 2 of 3 consecutive days did not exceed the signal intensity threshold value, irrigation was reduced by 10%. In contrast, when the MDS signal intensity on at least 2 of 3 consecutive days exceeded the threshold value, the irrigation rate was increased by 10%. The results indicated that lemon tree irrigation scheduling can be based on MDS measurements, avoiding the appearance of any plant water stress situation without affecting yield or fruit quality. Also, the cumulative amounts of applied water in T1 plants can be considered as an estimate of lemon tree water requirements, because they were only 9% above the estimated crop evapotranspiration (ETc) and drainage did not occur. Nevertheless, to improve the precision of irrigation management, some changes in the irrigation protocol for periods of variable evaporative demand were proposed: for instance, increasing the irrigation scheduling frequency and/or using changes in the daily irrigation rate higher than those proposed in the protocol.

Iron deficiency enhances bioactive phenolics in lemon juice

BACKGROUND This study was designed to describe the phenolic status of lemon juice obtained from fruits of lemon trees differing in iron (Fe) nutritional status. Three types of Fe(III) compound were used in the experiment, namely a synthetic chelate and two complexes derived from natural polymers of humic and lignine nature. RESULTS All three Fe(III) compounds were able to improve the Fe nutritional status of lemon trees, though to different degrees. This Fe(III) compound effect led to changes in the polyphenol content of lemon juice. Total phenolics were decreased (∼33% average decrease) and, in particular, flavanones, flavones and flavonols were affected similarly. CONCLUSION Iron-deficient trees showed higher phenolic contents than Fe(III) compound-treated trees, though Fe deficiency had negative effects on the yield and visual quality of fruits. However, from a human nutritional point of view and owing to the health-beneficial properties of their bioavailable phenolic compounds, the nutritional quality of fruits of Fe-deficient lemon trees in terms of phenolics was higher than that of fruits of Fe(III) compound-treated lemon trees. Moreover, diosmetin-6,8-di-C-glucoside in lemon juice can be used as a marker for correction of Fe deficiency in lemon trees.

Changes in growth, physiological parameters and the hormonal status of Myrtus communis L. plants irrigated with water with different chemical compositions

Myrtus communis, an important Mediterranean ornamental shrub, was used to study the effect of irrigation water with different chemical compositions in the plant response. A treatment with NaCl was used to establish the plant resistance to high salinity at long term. Plants were subjected to four irrigation treatments with drainage for three months: Control (0.8 dS m(-1)); two treatments using reclaimed water (RWs): RW1 (2.0 dS m(-1)) and RW2 (5.0 dS m(-1)); and NaCl (10.0 dS m(-1)). High levels of electric conductivity of RWs not affected plant growth, while NaCl decreased leaf dry weight. Coinciding with the accumulation of Na(+) and Cl(-) in the roots, soil water potential decreased, which hinders the mobilization of water to the leaves, decreasing leaf water potential. The osmotic adjustment in the NaCl treatment was due to Na(+) and Cl(-) ions, although the proline could contribute as an Osmo compatible solute, increasing the turgor plants. Also changes in cell walls rigidity minimize the negative effects on the water balance; however, a higher lipid peroxidation was observed in these plants. Stomatal closure was associated with a decrease in K(+) and an increase in abscisic acid. NaCl produced an increase in salicylic acid and did not affect jasmonic acid contents at the end of the experiment. Similar behavior in soil and leaf water potentials, although less pronounced than in NaCl, was shown in RW2 plants. The abscisic acid increased in the RW2 with respect to the control and a decrease in stomatal conductance was observed at the end of the experiment. Plants irrigated with RW1 behaved similarly to the control.