Arbuscular mycorrhizal fungi enhance tolerance of vinca to high alkalinity in irrigation water

This study was conducted in order to determine if inoculation with arbuscular mycorrhizal fungi (AMF) would enhance the tolerance of vinca plants to high levels of alkalinity, induced by KHCO₃, in irrigation water. AMF-inoculated and non-inoculated plants were irrigated with water containing varying HCO₃⁻ concentrations: 0, 2.5, 5, 7.5, 10, and 15 mM. Increased HCO₃⁻ concentration inhibited plant growth, specifically at concentrations ≥7.5 mM. Leaves were more affected by high HCO₃⁻ concentration than other plant parts. In non-inoculated plants, a visual evaluation of quality demonstrated that acceptable quality was produced when irrigation water contained ≤2.5 mM HCO₃⁻, but AMF-inoculated plants of good quality were produced when irrigation water contained ≤7.5 mM HCO₃⁻. In general, AMF alleviated HCO₃⁻ stress, as indicated by greater plant growth and ranking of quality. However, AMF-inoculated plants irrigated with 0 mM HCO₃⁻ exhibited reduced growth when compared to non-inoculated plants. Bicarbonate did not affect leaf Fe concentration, indicating that vinca may be a Fe efficient plant. Plants inoculated with AMF exhibited an enhanced leaf P concentration and content, which was related to an increase in the activity of the soluble alkaline phosphatase. Plants inoculated with AMF exhibited increased leaf concentration and content of Mn, Zn, Cu, B, and Mo, and increased antioxidant activity under high concentrations of HCO₃⁻. In conclusion, the tolerance of vinca to alkalinity in irrigation water can be enhanced by AMF inoculation, thus, allowing for irrigation with water of high alkalinity.     

磁化水灌溉对冬枣生长及品质的影响

以‘沾化冬枣1号’和‘沾化冬枣2号’为试材,利用磁化处理的淡水和地下浅表层微咸水灌溉,通过对枣吊、叶片及果实的生长和养分含量测定分析,探究磁化水灌溉对枣生长及品质的影响。结果表明：（1）磁化水灌溉处理能显著提高叶片叶绿素含量和鲜质量,果实有机酸、维生素C、花青素含量,并且大幅度提高果实的耐贮性。（2）沾化冬枣1号经磁化（进口磁化器A400p）淡水灌溉处理,相比淡水对照枣吊长度与直径提高了11.375%和15.810%,单叶面积提高了12.418%,单果质量、含水量、果实横径和纵径分别提高了23.779%、2.377%、3.650%和5.071%;沾化冬枣2号经磁化（进口磁化器A400p）淡水灌溉处理,枣吊长度与直径提高了23.602%和13.710%,单叶面积与叶片厚度提高了23.622%和13.825%,单果质量和还原糖含量提高了12.526%和12.110%。（3）利用磁化（自主研发磁化器DS-948-1）地下浅表层微咸水灌溉处理沾化冬枣2号,与微咸水对照相比,果实含水量和还原糖含量分别提高了4.386%和9.158%。（4）灌溉水经磁化处理后,冬枣叶片矿质元素N、P、Cu含量提高（P < 0.05）。磁化水灌溉处理有效促进了沾化冬枣的枝叶和果实生长发育,提高了果实的品质和耐贮性。     

Application of secondary-treated effluents for cultivation of sunflower (Helianthus annuus L.) and celosia (Celosia argentea L.) as cut flowers

In this study we have examined the effects of irrigation with municipal secondary-treated effluents on growth of sunflower (Helianthus annuus L.) and celosia (Celosia argentea var cristata L.) plants for cut flower production. The applied treated effluents contained higher levels of Na (∼X6), Cl (∼X4.5), N–NH₄ (30–50 mg/l), B, HCO₃, P, K, and Fe than the potable water. The effect of the two types of irrigation water on the chemical composition of soil and leaves, flower yield and postharvest performance was examined. Our results demonstrate higher accumulation of Cl, Na, B, and NO₃ in soils irrigated with effluents as compared to potable water only in the 40–60 cm soil layer. Phosphorus accumulated to higher levels in the upper soil layer (0–20 below ground), as well as in the lower soil layer, irrigated with effluents. SAR levels as well, were higher under irrigation with the treated effluents in the soil until 40 cm below ground indicating higher Na absorption in comparison to Ca and Mg. In both sunflower and celosia, boron accumulated to higher levels in leaves of plants irrigated with effluents. In addition, under irrigation with effluents, celosia accumulated higher levels of N and Mn and sunflower higher levels of P and lower levels of Fe. Despite these differences in mineral contents, the quality of the irrigation water did not affect cut flower yield. In both species spike length, receptacle size, number of flowers and flower weight were not affected. However, flowers’ quality, examined during vase life, was compromised by irrigation with the effluents. Celosia leaves appeared more yellow and sunflower petal edges became browner. Nevertheless, leaf yellowing in celosia occurred mainly on the lower leaves of the stem, which can be removed to maintain high commercial value. The reduction in sunflower quality as well, will most likely not pose any commercial problem since these negative symptoms appeared at a late stage of vase life. Overall, our results demonstrate that secondary-treated municipal effluents can be used for production of sunflower and celosia for cut flowers, in the northern-eastern part of the ‘Negev’ desert in Israel. Due to the high SAR values of the water, and in order to avoid damage to the soil structure, dilution of this water should be considered for commercial growth.     

Daily and seasonal variation of water relationship in sugar apple (Annona squamosa L.) under different irrigation regimes at semi-arid Brazil

In the northeast of Brazil the drought period determines the yield period of the sugar apple (Annona squamosa L.). As a result, the use of irrigation is essential to stagger production over the course of the year. The results shown here represent an analysis of water status levels in sugar apples in daylight and seasonal periods in semi-arid regions. Two plant groups were studied: one without irrigation and the other with irrigation during drought months. This study showed that younger leaves displayed greater stomatal conductance and transpiration. In drought months, even in irrigated plants, the high air moisture deficit had a strong influence on the stomatal closure, which did not translate into a reduction in transpiration. Over the same period, the leaf water potential was −1.8 and −2.9 MPa at mid-day in irrigated and non-irrigated plants, respectively, and only the irrigated plants could recover their leaf hydration level at night. With a water deficit, plants showed greater control of transpiration through stomatal closure, with a linear relationship between stomatal conductance and transpiration.     

A comparative study of young ‘Thompson Seedless’ grapevines (Vitis vinifera L.) under drip and furrow irrigation. II. Growth, water use efficiency and nitrogen partitioning

The response of 3-year-old grapevines (Vitis vinifera L. cultivar ‘Thompson Seedless’) to furrow and drip irrigation was quantified in terms of water status, growth, and water use efficiency (WUE). Drip irrigation was applied daily according to best estimates of vineyard evapotranspiration while furrow irrigations were applied when 50% of the plant available soilwater content had been depleted. Drip and furrow irrigated vines showed similar water status (midday leaf water potential, Ψ₁) and shoot growth patterns throughout the season. Dry weight partitioning was not significantly different between treatments but root mass was somewhat larger for the furrow than drip irrigated vines. Nitrogen concentrations of the fruit and roots were significantly (P < 0.05) less for the drip irrigated vines when compared with the furrow treatment. Similar WUE (kg water kg⁻¹ fresh fruit wt.) were obtained for both treatments indicating that furrow irrigation was as efficient as drip irrigation under the conditions of this study. The data indicate that drip irrigation may increase the potential for control of vine growth by making vines more dependent on irrigation and N fertilization than furrow irrigation.     

Effect of two irrigation rates on yield,incidence of blossom-end rot,mineral content and free amino acid levels in tomato cultivated under drip irrigation using saline water

Summary

An experiment investigated the effects of two rates of irrigation, one of which reflected a substantial degree of water stress, on the mineral content, free amino acid levels and incidence of blossom-end rot (BER) in tomato (Lycopersicon esculentum Mill. `Durinta'). The plants were grown in the open with drip irrigation using saline water from a well (mean EC_w 5.2 dS m²¹). The yield per plant was higher and fewer fruit were affected by BER in the treatment involving the higher level of irrigation. The fruit of the first and fifth truss, and the leaves immediately above, were analysed for their macronutrient, micronutrient and free amino acid content. The macronutrient leaf and fruit content hardly showed any difference, only the N concentration in fruit being significantly affected in the water stressed plants, in which the levels were higher. The Ca concentration in the stylar portion of mature fruit, which is related with the incidence of BER, was not significantly affected by the level of irrigation. As regards micronutrients, only the Fe (in leaf and fruit of the first truss), Cu (in leaf of the first truss), Zn (in leaf and fruit of the first truss, and leaf of the fifth truss) and Mn (in leaf of the first truss) concentrations differed significantly. The total free amino acid leaf content was similar in both irrigation treatments. However, the total free amino acid content of fruit, significantly those of the first truss, was higher in the less irrigated treatment. The amino acids: aspartic acid (only from the first.truss), glutamic acid, proline and alanine had high concentrations in the fruit of the less irrigated plants, while the g-aminobutyric acid and phenylalanine (only from the fifth truss) concentrations were higher in fruit of the more irrigated plants.     

Effects of deficit irrigation strategies on cluster microclimate for improving fruit composition of Moscatel field-grown grapevines

The grapevine plays a very important role in the economic, social and cultural sectors of many regions; however vineyards are often grown in regions under stressful conditions and thus they are vulnerable to climate change. The objective of this research was to investigate the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative growth, plant microclimate, berry composition and yield components, compared to conventional deficit irrigation (DI, 50% ETc), full irrigation (FI, 100% of ETc) and non-irrigated vines (NI). The study was undertaken in mature ‘Moscatel’ grapevines (Vitis vinifera L.) grown in Pegões, South of Portugal. Compared to the other irrigated treatments, PRD vines showed a better microclimate at the cluster zone with higher incident photosynthetic photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry temperatures were higher than those of denser ones (DI and FI). Compared to the conventional irrigation technique the better microclimate observed in PRD vines was a consequence of a reduction in vine growth, where lower values of leaf layer number, leaf area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we observed a tendency to a development of a deeper root system, while DI and FI showed a more homogeneous root distribution throughout the different soil layers. PRD showed an improvement in berry quality with higher values of flavour precursors, and total phenols concentration without any significant yield reduction compared to DI and FI.     

The effect of waste water irrigation on the extra virgin olive oil quality from the Tunisian cultivar Chemlali

The availability of fresh water is very scarce in the Middle East and North Africa. Yet consequently, brackish water or recycled wastewater can be used for irrigation, minimising the exploitation of natural water resources. The aim of this work was to study how irrigation with treated wastewater (TWW) over 4 years affects some parameters of “Chemlali” olive oil quality. Two treatments were considered: trees irrigated with treated wastewater and others cultivated in rain-fed conditions. Results showed that irrigation with TWW over 4 years did not affect free acidity, and specific ultraviolet absorbance at K₂₃₂ and K₂₇₀. For both the crop seasons the mean values of these parameters were lower than the upper limits established for “extra virgin” olive oil. However, irrigation with TWW cumulatively increased palmitic, palmitoleic, linoleic and linolenic acid contents and decreased oleic acid rates. A significant decrease of total phenol contents was also observed at the end of experimental period.     

Effect of combined water and salinity stress factors on evapotranspiration of Sedum kamtschaticum Fischer in relation to green roof irrigation

In dryland areas, secondarily treated municipal wastewater could be used in extensive green roof systems. In this study, the effects of water and salt stress on a crassulacean acid metabolism (CAM) plant, Sedum kamtschaticum Fischer, was evaluated under intermittent saline irrigation. The salinity of irrigation water varied from 6.0 to 18.0 dS m^?1. A reduction in soil water content and an increase in soil water electrical conductivity (EC) were observed during the irrigation interval (5–17 d) as a result of evapotranspiration (ET). The effect of soil water potential (SWP) on reduction of the ET ratio (ET_r) was successfully described with an equation that could be applicable to a wide range of soil salinities and water contents, to estimate ET. In this study, the stress factor was defined as the integration of solute potential, and matric potential less soil water content for optimum growth (less than ?0.1 MPa) with elapsed time. The stress factor rapidly reduced total ET in CAM plants but effectively increased water-use efficiency (WUE). Thus, by using CAM plants for green roofs under intermittent saline irrigation, the need for irrigation water is reduced without a considerable loss of plant biomass.     

Pre-conditioning ornamental plants to drought by means of saline water irrigation as related to salinity tolerance

This study examines the feasibility of using saline irrigation water for commercial pot cultivation of three ornamentals: Calceolaria hybrida, Calendula officinalis and Petunia hybrida. Two saline treatments were assayed: irrigation with low saline tap water (electrical conductivity = 1.16 dS m⁻¹), and irrigation with a high saline solution of NaCl 100 mM + CaSO₄ 10 mM + MgSO₄ 2.5 mM (electrical conductivity = 12.5 dS m⁻¹). When the control plants reached marketable size the watering was stopped and the plant response to drought was studied. Petunia and Calceolaria were tolerant to salinity. Petunia saline-treated plants reduced their growth slightly and increased N and chlorophyll contents in the leaves. Calceolaria experienced a strong reduction in growth and a delay in flowering but no toxicity symptoms or mortality was recorded. These species were moderate NaCl accumulators. Calendula was sensitive to salinity: 16% of the plants died and the surviving ones experienced a heavy reduction of growth, a decrease in chlorophyll and a large accumulation of NaCl in the leaves. Saline pre-conditioned plants of Calceolaria and Petunia were tolerant to drought. In these plants, leaf water content and, specifically, leaf relative water content were sustained longer than in non-pre-conditioned plants throughout the drought period. In Calendula, leaf relative water content decreased at the same rate in pre-conditioned and non-pre-conditioned plants. Consequently, salinization did not confer drought resistance upon this species. Possible factors determining the tolerance to drought in saline pre-conditioned plants are discussed.     

Deficit irrigation as a strategy to control growth in ornamental plants and enhance their ability to adapt to drought conditions

The shortage of water in many parts of the world has led to the development of new irrigation strategies such as regulated deficit irrigation and sustained deficit irrigation. Water deficit induces different morphological and physiological responses in ornamental plants, but the application of irrigation strategies can obtain quality plants well adapted to the environment. Deficit irrigation controls plant growth, and can be considered a sustainable technique which avoids the use of plant growth regulators. In addition, root system morphology can be modified by water stress to improve the ability to extract water from the soil and strengthen a plant’s physical support. In addition, the application of deficit irrigation during nursery period is a technique frequently used to harden plants before transplanting. Water deficit affects morphological and physiological aspects that might provide a capacity to adapt to adverse conditions. All these features contribute to increasing water use efficiency and the root to shoot ratio and root density, promoting the more rapid establishment of ornamental plants in garden or landscape settings. In view of the results obtained, it is possible to apply and validate the most appropriate irrigation strategy for each species and to obtain the full benefits of applying deficit irrigation.

Abbreviations: DI, Deficit irrigation; ETc, Crop evapotranspiration; gs, stomatal conductance; Pn, Net photosynthesis; RDI, Regulated deficit irrigation; SLA, Specific leaf area; WUE, Water use efficiency     

Comparison of growth,leaf water relations and gas exchange of Cistus albidus and C. monspeliensis plants irrigated with water of different NaCl salinity levels

Four-month-old potted Cistus albidus and Cistus monspeliensis plants growing in a greenhouse were submitted to saline stress from 9 August to 2 December, using irrigation water containing 0, 70, and 140 mM NaCl. C. monspeliensis plants are more tolerant to saline irrigation water than C. albidus plants, mainly due to their capacity to resist stress with a lower plant biomass and canopy area; furthermore, they showed no leaf necrosis symptoms. Under saline stress conditions the main growth limiting factor in both species was photosynthesis. Both Cistus species responded to saline stress by developing avoidance and tolerance mechanisms. The avoidance mechanisms took place at a morphological and physiological level. Morphologically, the reduction in the canopy area can be considered a mechanisms for regulating water loss via transpiration. Treated C. monspeliensis plants showed a greater capacity to absorb water and were able to conserve it more efficiently than C. albidus plants. Tolerance mechanisms included Na⁺ and Cl⁻ inclusion and osmotic adjustment. However, the reaction of each species to osmotic adjustment was different, because in C. monspeliensis plants the osmotic adjustment was unable to prevent a decrease in leaf turgor. The curvilinear relationship between P_n and g_l observed in C. monspeliensis plants indicated stomatal limitation of photosynthesis below a leaf conductance of about 160 mmol m⁻² s⁻¹. In C. albidus plants, a linear relationship between photosynthesis and leaf conductance rather a curvilinear model was significant, indicating limitation of the photosynthetic capacity.     

Effect of alleviating products with different mode of action on physiology and yield of olive under drought

Two years old self-rooted Koroneiki olive trees (Olea europaea L.) were subjected to two irrigation regimes, i.e. the fully irrigated and the severely water stressed trees, while they were treated with three alleviating products of different mode of action. The products used were the osmolyte glycine betaine, the antioxidant Ambiol and the heat and irradiance reflecting kaolin clay particles. The effects of product application and water regime on leaf characteristics, shoot and root growth, photosynthesis, leaf compatible solids (carbohydrates) concentration and yield were evaluated. All products applied, exhibited significant alleviating action, based on the relative alleviation index. Irrigated trees exhibited greater growth than drought stressed ones, while the ameliorating products maintained the water content of the leaves under drought conditions and resulted in lower leaf tissue density. On the other hand carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress, while the opposite stood for intercellular CO₂. Drought stress resulted in elevated sucrose leaf concentration, while the application of Ambiol increased stachyose concentration and that of glycine betaine did the same with the mannitol concentration. Among the alleviating products tested in this experiment Ambiol and glycine betaine had a significant positive effect on leaf water content, photosynthesis and yield under both drought and well irrigated conditions.     

Green roofs sown with an annual plant mix attain high cover and functional diversity regardless of irrigation frequency

Annual plant species have great potential on green roofs as many are highly attractive, fast and cheap to establish via sowing and can provide rapid cover and growth, which is important for ecosystem service provision. While irrigation is essential for survival and growth of annual plants in seasonally hot or dry climates, it is also important to minimize water use as availability is often limited. Therefore, we evaluated how irrigation frequency affects plant cover, species abundance, richness and diversity, plant traits and functional diversity of a 16 species mixture of Australian annual species (4 g m⁻² ~ 2100 seeds m⁻²) sown onto thirty 0.25 m² green roof modules. The experiment was carried out in Melbourne, Australia, from January (summer) to July (winter) 2020. After a 2-month irrigated establishment phase (to ensure germination and seedling establishment), three irrigation treatments (2, 4 and 6 days between irrigation) were applied to the modules for three months. Plant cover was reduced at lower irrigation frequency (6 days), but ≥ 80% plant cover was achieved in all irrigation treatments. There was no effect of irrigation frequency on species abundance and richness; however, abundance, richness and diversity reduced over time, likely due to competition effects. Plant height and leaf area were also reduced by lower irrigation frequency. At the community level, functional diversity was unaffected by irrigation frequency. Our results indicate that green roofs sown with a mixture of annual plants can achieve good plant coverage, as recommended by green roof guidelines, and maintain high diversity when minimally irrigated in their first growing season.     

Nursery inoculation of tomato with arbuscular mycorrhizal fungi and subsequent performance under irrigation with saline water

Protected horticultural crops as well as those planted in open fields particularly in the Mediterranean region have to cope with increasing salinization of irrigation water. High salinity of the supply water has detrimental effects on soil fertility and plant nutrition and reduces crop growth and yield. This study was conducted to determine if pre-inoculation of transplants with arbuscular mycorrhizal (AM) fungi alleviates salt effects on growth and yield of tomato (Lycopersicon esculentum Mill. Cv. Marriha) when irrigated with saline water. Tomato seeds were sown in polystyrene trays with 20 cm³ cells and treated with AM fungi (AM) or without (nonAM) Glomus mosseae. Once the seedlings were reached appropriate size, they were transplanted into nonsterile soil in concrete blocks (1.6 m × 3 m × 0.75 m) under greenhouse conditions. The soil electrical conductivity (EC_e) was 1.4 dS m⁻¹. Plants were irrigated with nonsaline water (EC_w = 0.5 dS m⁻¹) or saline water (EC_w = 2.4 dS m⁻¹) until harvest. These treatments resulted with soil EC at harvest 1.7 and 4.4 dS m⁻¹ for nonsaline and saline water treatments, respectively. Root colonization with AM fungi at flowering was lower under saline than nonsaline conditions. Pre-inoculated tomato plants with AM fungi irrigated with both saline and nonsaline water had greater shoot and root dry matter (DM) yield and fruit fresh yield than nonAM plants. The enhancement in fruit fresh yield due to AM fungi inoculation was 29% under nonsaline and 60% under saline water conditions. Shoot contents of P, K, Zn, Cu, and Fe were higher in AM compared with nonAM plants grown under nonsaline and saline water conditions. Shoot Na concentrations were lower in AM than nonAM plants grown under saline water conditions. Results indicate that pre-inoculation of tomato transplants with AM fungi improved yield and can help alleviate deleterious effects of salt stress on crop yield.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Water relations and yield of lysimeter-grown strawberries under limited irrigation

The effects of partial root-zone drying (PRD), as compared to deficit irrigation (DI) and full irrigation (FI), on strawberry (cv. Honeoye) berry yield, yield components and irrigation water use efficiency (WUE_I) were investigated in a field lysimeter under an automatic rain-out shelter. The irrigation treatments were imposed from the beginning of flowering to the end of fruit maturity. In FI the whole root zone was irrigated every second day to field capacity viz. volumetric soil water content (θ) of 20%; while in DI and PRD 60% water of FI was irrigated to either the whole or one-half of the root system, respectively, at each irrigation event. In PRD, irrigation was shifted from one side to the other side of the plants when θ of the drying side had decreased to 8–11%. Compared to FI plants, leaf water potential was significantly lower in DI and PRD plants in 3 out of 10 measurement occasions, while stomatal conductance was similar among the three treatments. Leaf area, fresh berry yield (FY), individual berry fresh weight, berry water content, and berry dry weight (DW) were significantly lower in DI and PRD plants than those of FI plants; whereas the total number of berry per plant was similar among treatments. Compared with FI, the DI and PRD treatments saved 40% of irrigation water, and this led to a 28 and 50% increase of WUE_I based on berry FY and DW, respectively, for both DI and PRD. Conclusively, under the conditions of this study PRD had no advantage compared to DI in terms of berry yield and WUE_I. DI and PRD similarly decreased berry yield and yield components and thus cannot be recommended under similar conditions.     

Effects of water deficit on olive trees cv. Chemlali under field conditions in arid region in Tunisia

Water scarcity in the Mediterranean basin in addition to the extension of irrigated lands is one of the main factors limiting agricultural development. The need for supplementary irrigation of the Chemlali olive cultivar (Olea europaea L.) during summer and autumn periods was investigated. Leaf water content, gas exchange parameters, fruit development and yield in rain-fed and in irrigated plants have been monitored in 12-year-old olive trees grown under environmental conditions in semi arid regions characterized by high temperatures and high light intensity. Trees were subjected to three irrigation treatments, T0, T1 and T2 corresponding respectively to 0, 33 and 66% of crop evapotranspiration (ET_c) by a drip irrigation system. The water deficit during the summer (from June to August) led to the decrease of soil moisture, leaf water content and gas exchange parameters. Irrigated trees showed the same slow activity in the three summer months as the rain-fed trees. For all treatments, net CO₂ assimilation, stomatal conductance and transpiration rates were markedly decreased by environmental conditions (high air temperature and high light intensity) during the summer period. At the partial active growth phase of the Chemlali olive cultivar (September–November), a significant re-increase in all parameters was observed. However, net photosynthesis and stomatal conductance of control plants (T0) were, respectively, 57 and 40% lower than those of plants conducted under milder water contribution (T1). The decrease of physiological activity in irrigated plants during hot and dry (summer time) and cold (winter) seasons was a clear evidence that water supply during such periods will be without a great benefit for photosynthetic activity, and thus growth, if applied under critical conditions inducing the rest phase of the plant. The non-statistically significant slight differences as well in photosynthetic performances activities (Pn, Gs and E rates), as in olive production between the two irrigated treatments will not cover the expenses of water loss when applying irrigation at 66% of ET_c especially in arid region characterized by scant and irregular rainfall. On the light of these results, we can conclude that the irrigation of this species during the vegetative growth phase (in spring and autumn), and stopping it during the olive rest phase (in summer and winter) could be recommended at least under the experimental conditions of this study; and that the contribution of 600 mm of water per year (33% of ET_c) can respond to the needs of the Chemlali olive cultivar in a semi arid region without impairing photosynthetic activity and olive production.     

Effect of different drip irrigation methods and fertilization on growth,physiology and water use of young apple tree

A pot experiment was conducted to investigate the effect of three drip irrigation methods (i.e. conventional drip irrigation (CDI), both sides of the root-zone irrigated with full watering, alternate drip irrigation (ADI), both sides of the root-zone irrigated alternatively with half of the full watering, and fixed drip irrigation (FDI), only one side of the root-zone irrigated with half of the full watering) on growth, physiology, root hydraulic conductance and water use of young apple tree under different nitrogen (N) or phosphorus (P) fertilization (i.e. CK (no fertilization), N₁ (0.2 g N/kg), N₂ (0.4 g N/kg), P₁ (0.2 g P₂O₅/kg) and P₂ (0.4 g P₂O₅/kg)). Results show that compared to CDI, ADI and FDI reduced mean root dry mass, daily transpiration, root hydraulic conductance (K_r), leaf photosynthesis rate, transpiration rate and stomatal conductance of young apple tree by 6.9 and 27.7, 29.3 and 45.0, 6.8 and 37.9, 2.5 and 4.8, 32.6 and 33.0, 22.1 and 22.3%, but increased leaf water use efficiency (WUE) by 31.3 and 29.8%, respectively when they saved irrigation water by 50%. Compared to the CK, N or P fertilization significantly increased K_r, and K_r was increased with the increased N or P fertilization level. There were parabolic correlations between K_r and root dry mass, daily transpiration and stomatal conductance. Our results indicate that ADI reduced transpiration rate significantly, but it did not reduce photosynthesis rate and K_r significantly, thus alternate drip irrigation improved WUE and the regulation ability of water balance in plants.     

The Reinvigoration of Apple Trees by the Inarching of Vigorous Rootstocks

Summary

The purpose of this research was to determine if established, orchard-grown apple trees that were con®ned in root-restricting membranes received adequate water for growth when irrigated. Previous data had shown positive effects of root restriction on reducing shoot extension growth in apple. Soil matric potential (Ψ_sm), leaf stomatal conductance (g) and leaf water potentials (Ψ_l) were measured over daily cycles during the period of maximum tree water use (July and August). Measurements were also made of the Ψ_sm and fruit size throughout the growing season. Daily and seasonal Ψ_sm showed that the soil within the root restricting membranes (+R) when irrigated (+I) remained closed to field capacity (<100 HPa), which was not the case for unirrigated soil within the membranes (-I +R). Ψ_l measured before dawn, showed that similar levels of drought stress were evident between irrigated and restricted (+I +R) and unrestricted (+I -R and -I -R) trees. The Ψ_sm, and Ψ_l for trees with roots within restricting membranes were significantly more negative, in the absence of irrigation (-I +R). Measurement of g showed that root restricted trees were transpiring at similar rates in the presence of irrigation (+I +R) as unrestricted trees (+I -R) with or without irrigation. Stomatal closure could not explain the increased Ψ_l observed for the restricted irrigated (+I +R) treatment compared with unrestricted (-R) trees. A reduced stomatal aperture was the most likely explanation for the reduction in growth previously observed with the restricted unirrigated trees. Fruit size was also affected by root restriction and the effect became greater as the roots became more restricted with tree age. Similarly, there was also a negative effect, in one year, of root restriction on fruit size at harvest, even in the presence of irrigation. Data show that reductions in soil water availability, Ψ_l and g, for the root-restricted trees (+I +R), were unlikely to be the causes for the previously observed reductions in shoot growth (tree size). These results imply that other factors were in operation, among which root-synthesized chemical regulators of shoot growth are the most likely candidates.