Low water stress conditions in table olive trees (Olea europaea L.) during pit hardening produced a different response of fruit and leaf water relations

Elsevier Editorial System(tm) for Agricultural Water Management Manuscript Draft Manuscript Number: Title: LOW WATER STRESS CONDITIONS IN TABLE OLIVE TREES (OLEA EUROPAEA L.) DURING PIT HARDENING PRODUCED A DIFFERENT RESPONSE OF FRUIT AND LEAF WATER RELATIONS. Article Type: Research Paper Keywords: Leaf conductance; osmotic adjustment; regulated deficit irrigation; water potential. Corresponding Author: Dr. Alfonso Moriana, Corresponding Author's Institution: University of Seville First Author: José Dell'Amico Order of Authors: José Dell'Amico; Alfonso Moriana; Mireia Corell; Ignacio Girón; Donaldo Morales; Arturo Torrecillas; Félix Moreno Abstract: The scarcity of water for agricultural use is producing a generalization of deficit irrigations in most of the fruit trees. Regulated deficit irrigation in olive trees is scheduled with a period of water stress during the pit hardening phase with low or, even, no decrease in yield. During this phenological stage, fruit is a great sink of assimilates and competes with vegetative growth, producing a significant change in the water relation of the tree. The aim of this work is to study the water relations in leaves and fruits in a period of drought during the phenological stage of pit hardening in a mature (43 yearold) table olive orchard. Water relations of leaves and fruits were compared between a Control of fully irrigated trees and Stressed trees (with a period of drought from 1 week after the beginning of pit hardening until 1 week before harvest). The water stress conditions were considered as low level, according with the stem water potential data. Leaf water relations were quickly affected with a reduction of midday stem water potential and turgor pressure at 14 days after the beginning of the drought (DABD). Leaf osmotic adjustment was measured only at the end of the drought cycle (63 DABD). On the other hand, fruit water relations were affected slowly and only osmotic potential was reduced at 14 DABD. Such variations produced a change in the source of water flow from xylem to phloem according to the variations in leaf-fruit water potential. The pattern of adaptation of leaves and fruit during the drought cycle and the relationship between them is discussed. Suggested Reviewers: David Pérez-López [email protected] Facundo Vita [email protected] Ricardo Gucci [email protected] Opposed Reviewers: B. Clothier Editor Agricultural Water Management Dear Dr.Clothier: We should be grateful if you would consider the attached manuscript entitled “LOW WATER STRESS CONDITIONS IN TABLE OLIVE TREES (OLEA EUROPAEA L.) DURING PIT HARDENING PRODUCED A DIFFERENT RESPONSE OF FRUIT AND LEAF WATER RELATIONS.” for publication in the Special Issue RH Sevilla 2012 of Journal Agricultural Water Management. All the authors have read the manuscript and approved it for publication. Sincerely yours Alfonso Moriana Cover Letter Highlights Water stress produced changes in the water relations of fruit and leaves. Leaf turgor pressure decreased earlier than stomata closure and osmotic adjustment. Fruit turgor pressure was less affected than leaf turgor pressure. *Highlights (for review) 1 LOW WATER STRESS CONDITIONS IN TABLE OLIVE TREES (OLEA 1 EUROPAEA L.) DURING PIT HARDENING PRODUCED A DIFFERENT 2 RESPONSE OF FRUIT AND LEAF WATER RELATIONS. 3 4 J. Dell’Amicoa, A. Morianab,*, M. Corellb, I.F. Girónc, D. Moralesa, A. 5 Torrecillasd,e, F. Morenoc 6 7 aInstituto Nacional de Ciencias Agrícolas, Cuba 8 bEscuela Técnica Superior de Ingeniería Agronómica. University of Seville, Carretera 9 de Utrera Km 1, 41013 Sevilla, Spain 10 cInstituto de Recursos Naturales y Agrobiología (CSIC), P.O. Box 1052, E-41080 11 Sevilla, Spain 12 dDpto. Riego. Centro de Edafología y Biología Aplicada del Segura (CSIC). P.O. Box 13 164, E-30100 Espinardo (Murcia), Spain 14 eUnidad Asociada al CSIC de Horticultura Sostenible en Zonas Áridas (UPCT-CEBAS), 15 Paseo Alfonso XIII s/n. E-30203 Cartagena (Murcia), Spain 16 *Corresponding author: [email protected] Phone: (+34)954486456; Fax: 17 (+34)954486436 18 19 20 21 22 *Manuscript Click here to download Manuscript: DellAmico et al.doc Click here to view linked References 2 Abstract 23 The scarcity of water for agricultural use is producing a generalization of deficit 24 irrigations in most of the fruit trees. Regulated deficit irrigation in olive trees is 25 scheduled with a period of water stress during the pit hardening phase with low or, 26 even, no decrease in yield. During this phenological stage, fruit is a great sink of 27 assimilates and competes with vegetative growth, producing a significant change in the 28 water relation of the tree. The aim of this work is to study the water relations in leaves 29 and fruits in a period of drought during the phenological stage of pit hardening in a 30 mature (43 year-old) table olive orchard. Water relations of leaves and fruits were 31 compared between a Control of fully irrigated trees and Stressed trees (with a period of 32 drought from 1 week after the beginning of pit hardening until 1 week before harvest). 33 The water stress conditions were considered as low level, according with the stem water 34 potential data. Leaf water relations were quickly affected with a reduction of midday 35 stem water potential and turgor pressure at 14 days after the beginning of the drought 36 (DABD). Leaf osmotic adjustment was measured only at the end of the drought cycle 37 (63 DABD). On the other hand, fruit water relations were affected slowly and only 38 osmotic potential was reduced at 14 DABD. Such variations produced a change in the 39 source of water flow from xylem to phloem according to the variations in leaf-fruit 40 water potential. The pattern of adaptation of leaves and fruit during the drought cycle 41 and the relationship between them is discussed. 42 43 Keywords: Leaf conductance, osmotic adjustment, regulated deficit irrigation, water 44 potential. 45 46 3 1. Introduction 47 Water is a scarce natural resource which is very important in agricultural practices. 48 Although irrigated lands are around 17% of the total agricultural surface, they provide 49 more than 40% of the total production (Fereres and Evans, 2006). However, the increase 50 of water scarcity in arid and semi-arid zones, the competition with other social uses 51 (such as sanitary, landscape uses) and the general feeling that irrigated agriculture is an 52 over-exploited system, are producing a decrease in the availability of water resources 53 for agricultural use. Regulated deficit irrigation (RDI) is a practice which was suggested 54 around the early 80’s in peach trees (Chalmer et al., 1981) and consists of a reduction of 55 water applied during the most drought resistant phenological stages without a yield 56 penalty. From the first work in peach orchards, RDI has been a common research line in 57 most fruit trees (Bebohudian and Mills, 1997). Therefore, in most of the species the 58 drought sensitivity to water stress has been well described (Bebohudian and and Mills, 59 1997). 60 The water deficit schedule in olive trees is traditionally based on severe water 61 withdrawal around the beginning of massive pit hardening (Goldhamer 1999; Moriana 62 et al 2003). During this period of time, the fruit development alters all the water 63 relations of the tree in conditions of high fruit load (Martín-Vertedor et al., 2011). The 64 effect of water stress in leaf water relations has been widely described for olive trees 65 (Bongi and Long, 1987; Angelopoulos et al., 1996; Fernández et al., 1997; Dichio et al., 66 1997, 2003 and 2006; Moriana et al., 2002) but little is known about fruit. The olive is a 67 very drought resistant fruit tree, in which water stress produces leaf osmotic adjustment 68 (Dichio et al., 1997, 2003 and 2006), strong stomatal control (Angelopoulos et al., 1996, 69 Moriana et al., 2002) and a high level of dehydration (Moriana et al., 2002). 70 4 Expansion of fruit requires, among other factors, an adequate flow of water to 71 the organ and sufficient turgor to drive cell enlargement. Berges and Selles (1993) in 72 peach fruit suggested that the water flow into the fruit was the sum of xylem and 73 phloem water transport. Therefore, changes in phenological stages and/or water status 74 of the tree may change the water pathway, in addition to fruit transpiration. Greenspan 75 et al (1994 and 1996) reported a change in the water transport to the grape berry with 76 the phenological stage of the fruit. During pre-veraison the net inflow corresponds to 77 xylem, while in post-veraison it changes to the phloem (Greenspan et al., 1994 and 78 1996). In olive trees, Proietti et al. (1999) reported a decrease in the photosynthesis 79 activity of fruits from the beginning of fruit development until 6-8 weeks after 80 polinisation. Drought sensibility of fruit changes with different phenological stages 81 (grape, Greespan et al., 1996; strawberry, Pomper and Breede, 1997). Water stress 82 conditions increase the maximum daily shrinkage at the beginning of fruit growth (pre-83 veraison in grape and green-white stage in strawberry) but do not change around 84 ripening (post-veraison in grape and red stage in strawberry). A significant osmotic 85 adjustment of strawberry fruits during the green-white phenological stage is reported, 86 but not in the red fruit stage (Pomper and Breen, 1997). 87 The aim of this work is to study the water relations of fruit and leaves at pit 88 hardening in adult olive trees, under field conditions. Since this is the period of time 89 when water deficit restrictions are common, the response of water relation to a cycle of 90 water stress during this phenological stage was described. RDI works report that 91 moderate water stress conditions during pit hardening do not reduce yield. Therefore, 92 our hypothesis is that fruits would present higher drought resistance than leaves. 93 94 5 2. Material and Methods 95 2.1. Description of the experiment 96 Experiments were conducted at La Hampa, the experimental farm of the Instituto de 97 Recursos Naturales y Agrobiología (CSIC). This orchard is located at Coria del Río 98 near Seville (Spain) (37º17’’N, 6º3’W, 30 m altitude). The sandy loam soil (about 2 m 99 deep) of the experimental site was characterized by a volumetric water content of 0.33 100 m3 m-3 at saturation, 0.21 m3m-3 at field capacity and 0.1 m3m-3 at permanent wilting 101 point, and 1.30 (0-10cm) and 1.50 (10-120 cm) g cm-3 bulk density. The experiment 102 was performed on 43-year-old table olive trees (Olea europaea L cv Manzanillo) during 103 2011. Tree spacing followed a 5 m x 5 m square pattern. Pest control and fertilization 104 practices were those commonly used by the growers and no weeds were allowed to 105 develop within the orchard. Irrigation was carried out during the night by drip using one 106 lateral pipe per tree row and five emitters per plant, delivering 8 L h-1 each. Irrigation 107 requirements were determined according to daily reference evapotranspiration (ETo) 108 and a crop factor based on the time of year and the percentage of ground area shaded by 109 the tree canopy (Fernández et al., 1998). 110 Trees were irrigated with 100% of ETc in order to obtain non-limiting soil water 111 conditions until the beginning of pit hardening. The beginning of the pit hardening was 112 estimated according to Gijón et al. (2010) around day of the year (DOY) 157. One week 113 later (DOY 165) irrigation was withdrawn to three lines of olives. Measurements were 114 made in 4 olives irrigated at 100% ETc during all the experiment (Control trees) and 4 115 olives in the central line of the plot where irrigation was withdrawn (Stressed trees). All 116 the measurements were made in these 4 trees per treatment. The drought cycle was 117 performed for 63 days and then trees were irrigated with the same amount of water than 118 6 Control trees. The experiment was stopped 7 days after the recovery because the harvest 119 had taken place. 120 2.2 Measurements 121 Micrometeorological 30 min data, namely air temperature, solar radiation, relative 122 humidity of air and wind speed at 2 m above the soil surface were collected by an 123 automatic weather station located some 40 m from the experimental site. Daily 124 reference evapotranspiration (ETo) was calculated using the Penman-Monteith equation 125 (Allen et al., 1998). The meteorological data in the period of the experiment is presented 126 in Figure 1. Maximum temperatures varied from 26.8 ºC (19 days after the beginning of 127 the drought period (DABD)) to 38.5 ºC (66 DABD) (Figure 1a). Mean and minimum 128 temperatures were parallel to the maximum data. Minimum temperatures varied from 129 15.3 ºC (24 DABD) to 24.4 ºC (67 DABD) (Figure 1a). The values of the potential 130 evapotranspiration varied from 7.2 mm day-1 (2 DBAD) to 3.5 mm day-1 (68 DABD), 131 though most of the data were between 5.5 to 7 mm day-1 (Figure 1b). Only one event of 132 rain was measured during the experiment at 48 DABD (2 mm). 133 The daily pattern of the leaf stomatal conductance in olive trees is characterized 134 with a maximum during the morning with a decrease after that until midday when the 135 minimum value is measured (Xiloyanis et al., 1996). This maximum leaf conductance is 136 more sensitive to water stress (Moriana et al., 2002). The drought cycle was 137 characterized by weekly measurements of maximum leaf conductance (g) and midday 138 stem water potential (stem). Abaxial leaf conductance was measured in two full 139 expanded and well illuminated leaves per tree in each treatment with a steady state 140 porometer (LICOR-1600, LICOR, UK) around 10:00 GMT, when maximum values are 141 expected. Midday stem water potential in one leaf per tree was measured with a 142 13 Control trees (around 15% and 17%). However, such differences did not affect the fruit 283 volume (Table 1). Fruits in Stressed trees were bigger than Control in volume in the two 284 samples (at 49 and 63 DABD). The differences in volume were of 6% at 49 DABD and 285 11% at 63 DABD. 286 287 4. Discussion 288 The period of pit hardening in olives is very important for the physiology of the tree. 289 Fruit is a very important sink of nutrient and water from this date (Rallo and Suarez, 290 1989). Fruit development in conditions of high fruit load produced an increase in leaf 291 conductance and a decrease in water potential (Martin-Vertedor et al., 2011) and an 292 important decrease in vegetative growth even in fully irrigated conditions (Rallo and 293 Suarez, 1989). However, in our conditions, there were not clear differences between 294 leaf and fruit in Control trees. Therefore, there was not a preferential water pathway 295 during pit hardening from root to fruit in conditions of low fruit load. The osmotic 296 potential was lower and the turgor pressure higher in leaves than in fruits throughout the 297 experiment in Control trees. These conditions would be related to a preferential 298 vegetative growth respect to fruit growth, which consistent with the low fruit load 299 conditions of the experiment. 300 The water stress level obtained after 63 days of the drought period was low, due 301 to the high spring rainfalls (140 mm from April to June, last rains 30 mm at the 302 beginning of June). Although, midday stem water potential (stem) was significantly 303 lower in Stressed than Control trees, the minimum values only reached at -1.8 MPa 304 from 42 DABD. This minimum stem value is considered a low water stress level in 305 14 comparison to the values reported in the literature in this phase of fruit development 306 (i.e. potted olive, Dichio et al 1997, 2003 and 2006; field olive, Moriana et al., 2002; 307 Moriana et al., 2003; Iniesta et al., 2009). According to our results, at this level of water 308 stress the leaf osmotic adjustment was small, because significant differences in leaf 309 osmotic potential at full turgor (100 leaf) were only found at the end of the experiment. 310 On that date (63 DABD), Stressed trees presented an osmotic adjustment of 0.33 MPa, 311 which was slightly decreased after 7 days of recovery to 0.17 MPa. This result in 312 osmotic adjustment is slightly lower than the ones reported by Dichio et al (2003) in 313 low water stress potted trees, which was 0.45 MPa, but is higher than ones reported with 314 P-V curves in this work, which was 0.11 MPa. The value of osmotic adjustment after 315 the recovery (0.17 MPa) was very similar to the ones reported by Dichio et al (2006) in 316 the recovery period of potted olive trees (0.14 MPa). The delay in the recovery of 100 317 leaf is also consistent with the data reported by Dichio et al. (2006) who measured a 318 significant osmotic adjustment even 30 days after the beginning of the recovery of 319 potted olive trees. This residual osmotic adjustment may be related to an uncompleted 320 rehydration of the trees. In our results, though there were no significant differences in 321 stem, leaf conductance was slightly, but significantly, lower. The conditions of 322 completed and fast rehydration are strongly related to a high wet surface in the recovery 323 period (Pérez-López et al., 2008) that usually is not provided in field conditions. 324 This low and slow period of water stress produced a different response in leaf 325 and fruit physiology. In leaves, water potential (leaf) was more clearly reduced than in 326 fruits (fruit). Such changes meant that from 14 DABD, when a significant water stress 327 was detected (stem, was significantly lower), the difference between leaf and fruit 328 () was clearly negative. Therefore, leaf was lower than fruit. Nobel and de la 329 15 Barrera (2000) in platyopuntias plants suggested that such differences indicated that the 330 water entered the fruit via the phloem rather than the xylem. Several authors reported a 331 decrease inin daily cycles, due to the effects of water stress (vines, Greenspan et 332 al., 1996; strawberries, Pomper and Breen, 1997), though only in 333 strawberries,changes from positive to negative (Pomper and Breen, 1997). 334 However, these decreases were steady until 42 DABD when a sharp increase meant that 335  were similar to Control trees. On the date (42 DABD), minimum stem occurred and 336 probably a stomatal closure began (though the main differences in g occurred at 56 337 DABD). Therefore, the main ways for water flow in the fruit may be changed at the 338 beginning of water stress and reversible if water stress progressed. Greenspan et al. 339 (1994 and 1996) suggested that the bulk of vascular water flow changes from xylem in 340 pre-veraison to phloem in post-veraison in full irrigated grape berry. Mathews and 341 Shackel (2005) suggested that in fully irrigated prunes the relative importance of xylem 342 and phloem in the water flow to the fruit may be reversible. 343 The drought conditions, in addition, affected the components of water potential. 344 The fruit osmotic potential ( fruit) was significantly reduced from 14 DABD and the 345 leaf turgor pressure (pleaf) from 29 DABD (though it tended produce lower values 346 from 14 DABD). On the other hand, fruit turgor pressure (pfruit) and leaf osmotic 347 pressure ( leaf) were not clearly affected during the experiment. These responses 348 suggest that vegetative growth is more sensitive to water stress than fruit growth in 349 olive trees. Such drought resistance of the fruit is likely related to a fruit osmotic 350 adjustment which may be produced by an increase of the phloem flow in the fruit. 351 Pomper and Breen (1997) reported an osmotic adjustment of strawberry fruits in 352 conditions of water stress during green-white stage. In addition, these results are 353 16 consistent with the conclusion of the regulated deficit irrigation works which reported a 354 decrease in the vegetative growth with low impact on the fruit yield (i.e. Goldhamer, 355 1999; Alegre et al., 2002; Moriana et al., 2003; Lavee et al., 2007;Tognetti et al., 2006; 356 Iniesta et al., 2009). 357 The slow progress of low level of water stress permits the description of several 358 mechanisms in the water relations of leaves and fruit. Water stress induced, probably 359 first, a significant leaf dehydration (stem and leaf). Such a response likely reduced the 360 water transport to the fruit from xylem (decrease of which produced a decrease of 361 the fruit osmotic potential ( fruit) and likely fruit osmotic adjustment. Then, the fruit 362 delayed the decrease of fruit turgor pressure compared to the leaf. Because of the 363 progression of water stress, fruit water potential was affected (fruit) and also the fruit 364 turgor pressure (pfruit). This alone, or with the permanent decrease of leaf turgor 365 pressure, produced the stomatal closure. The reduction of leaf transpiration induced a 366 change in the water flow into the fruit with an increase of xylem flow and a recovery in 367 the fruit turgor pressure. Finally, a leaf osmotic adjustment at the end of the experiment 368 is likely related to the improvement of leaf turgor pressure. In the mechanism proposed 369 the level of water stress is as important as the duration, as Hsiao (1990) suggests. Olive 370 trees are considered species tolerant to high internal dehydration (Moriana et al., 2002). 371 Therefore, the decrease of leaf water potential (stem and leaf) is one of the most 372 important signals that likely produce changes in the water relations of the tree. Moriana 373 and Fereres (2002) in field olive trees, reported that gas exchange is less sensitive to 374 water stress than water potential at the beginning of a drought cycle. This delay between 375 the beginning of leaf dehydration and stomatal closure would provide the trees with the 376 capacity to maintain the assimilation. The closure of stomata would be produced by an 377 17 increase of the loss of hydraulic conductivity (Lo Gullo et al., 1988) from a threshold 378 water potential (as in conifers (Froux et al., 2005)). The resistance of fruits to these 379 initial conditions of water stress is consistent with their important role in the water 380 relations of the tree (Martín-Vertedor et al., 2011). 381 382 5. Conclusions 383 The water flow in the fruit during pit hardening in fully irrigated conditions is produced 384 from xylem and phloem. In conditions of low fruit load, there were clear differences 385 between the component of water potential between leaves and fruits. Osmotic potential 386 at the time of maximum leaf conductance was lower in leaves than in fruits. Turgor 387 pressure at the same time was higher in leaves than in fruits. Such differences may be 388 related to a higher vegetative growth produced by the low fruit load. 389 Low water stress conditions produced significant changes in the water relations 390 of fruit and leaves. There was a clear delay in the stomatal closure and leaf osmotic 391 adjustment that produced a decrease in the leaf turgor pressure. On the other hand, there 392 was a change in the leaf-fruit water potential that likely benefited fruit growth, with no 393 decrease in fruit turgor pressure, in comparison with leaves. This process is consistent 394 with a higher drought sensitivity of vegetative growth than fruit growth, which permits 395 the reduction of irrigation with no effect on yield. The midday stem water potential of -396 1.8 MPa is a reference of water stress levels for deficit irrigation. 397 398 Acknowledgements 399 18 This research was supported by the Spanish Ministerio de Ciencia e Innovación 400 (MICINN), (AGL2010-19201-CO4-03.) and Group AGR-151 (Junta de Andalucía).The 401 stay of D. Morales and J. Dell’Amico was supported by the AECID project 402 D/030431/10. Thanks are due to J. Rodriguez for help with field measurements. 403 404 References 405 Alegre, S., Marsal, J., Mata, M., Arbones, A., Girona, J., Tovar, M., 2002. Regulated 406 deficit irrigation in olive trees (Olea europaea L. cv. Arbequina) for oil 407 production. Acta Hortic. 586, 259-262. 408 Allen, R.G., Pereira, L.S., Raes, D., Smith. M., 1998. Crop evaportranspiration. 409 Guideline for computing crop water requirements. FAO irrigation and drainage 410 paper nº 56. Roma. FAO. 411 Angelopoulos, K., Dichio, B., Xiloyannis, C., 1996. 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Time is presented as days 514 after the beginning of drought (DABD) 515 Midday Stem Water Potential Stress Integral (MPa*day) 0 20 40 60 80 100 120 a Leaf Conductance Stress Integral (mmol m -2 s -1 * day) 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 b Fig6 Table 1. Fruit characteristics in the two surveys (49 days after the beginning of stress (DABD) and 63 DABD). Each value is the average of 10 data. Asterisk in the same column indicates significant differences (p<0.05, LSD Test). 49 DABD 63 DABD Treatment Longitud inal Diameter (mm) Tranversal Diameter (mm) L/T ratio Volumen (cm 3) Longitudi nal Diameter (mm) Tranversal Diameter (mm) L/T ratio Volumen (cm 3) Control 20.83 16.71 1.24 3.07 21.38 18.06 1.18 3.68 Estressed 21.82 16.91 1.29 3.30 23.42 18.42 1.27 4.18 LSD 0.18 * 0.11n.s. 0.007 * 0.066 * 0.208 * 0.100 * 0.009* 0.070* Table 1 Click here to download Tables: table1.docx