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  • Author or Editor: Hui Xu x
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Water potential at soil–root interface (ψ s-r) indicates soil water availability to the plants. It is related to plant water potential and transpiration. To know the characteristics of ψ s-r, in the plants under a subirrigation system, hysteresis of ψ s-r, as well as xylem water potential (ψ x) and transpiration were examined in response to soil dehydration for Prunus × cistena grown in three soil mixes: mix 1-composted bark, peat, and sand; mix 2—peat, bark, sand, and compost; and mix 3—peat, sawdust, and sand. When the soil mixes were dried from high to low water potential (ψ s), plants grown in mix 2 maintained higher ψ s-r, as well as higher ψ x and higher transpiration. However, when the soil mixes were dehydrated from the bottom, the relationships of ψ s-r, ψ x, and transpiration to ψ s showed strong hysteresis effect. ψ s-r was always lower at a given ψ s when soil was rewetted from dry to wet conditions than when soil was dried from wet conditions. ψ x and transpiration also showed hysteresis in response to soil dehydration. The extent of hysteresis was the largest in mix 2 and the smallest in mix 3. Hysteresis of ψ X or transpiration showed a similar trend to that of ψ s-r. This suggests that ψ s-r is a good indicator of soil water availability to the plants and more directly related to ψ X and transpiration than is ψ s. The difference in hysteresis of ψ s-r among soil mixes might be related to the properties of hydraulic conductance, which are determined by the soil texture. Hence, further study is needed to elucidate the mechanism of the hysteresis phenomenon.

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Tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in peat bags, rockwool slabs, and NFT in a greenhouse to examine the effects of nutrient solution electrical conductivity (EC) and potential evapotranspiration (PET)-dependent EC variation on plant water relations. Peat bags were irrigated by a PET-dependent irrigation system. EC was varied from 1 to 4 mS·cm-1 according to PET under –5 and –9 kPa of substrate water potential setpoints (SWPS). The plants in rockwool and NFT were treated with ECs of 2.5, 4, and 5.5 mS·cm-1. Peat bags and rockwool slabs were overwatered once a week to wash out the accumulated salts. Leaf water potential (ψ1) and relative water content (θ) were measured before and after plants were overwatered. Turgor (P) and osmotic π potentials were estimated from the pressure-volume method. Before plants were overwatered, ψ1 was significantly lower in the plants with high EC and low SWPS treatments and also lower in variable EC-treated plants, but P maintained close to the control value. After plants were overwatered, ψ1 recovered close to the control level and P became higher because of the lower π in the treatments of high EC, variable EC, and/or low SWPS. At a given ψ1 the plants with high EC, variable EC, and/or low SWPS maintained higher θ. The analysis of the pressure-volume curve showed that the leaves treated with high EC, variable EC, and/or low SWPS had higher turgid water content, higher symplasmic (osmotically active) water content, lower apoplasmic (osmotically inactive) water content, and lower θ point of zero turgor (incipient plasmolysis). Maintenance of P after overwatering was directly proportional to photosynthetic capacity. We suggest that osmotic adjustment occurs in response to high EC, low SWPS, or both and that overwatering substrates and varying EC can not only avoid salinity stress, but also improve turgor maintenance.

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`Capello' tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in peat-based substrate (70% sphagnum peat and 309'. perlite, by volume) and supplied with nutrient solutions of high (4.5 mS·cm-1) or low (2.3 mS·cm-1) electrical conductivity (EC) under high (95% ± 5%) or low (55% ± 8% of capillary capacity) soil water conditions. Three weeks after treatments started, stomatal transpiration (TRst) and cuticular transpiration (TRcu) rates were measured by three methods: 1) analyzing TRst and TRcu from a water retention curve obtained by drying excised leaves in air under a photosynthetic photon flux (PPF) of 400 μmol·m-1·s-1, 2) analyzing TRst and TRcu from a transpiration decline curve obtained by measuring transpiration rates after cutting the leaf from the stem of the dehydrated plant in the gas-exchange system, and 3) measuring transpiration rates under light and in dark respectively using the gas-exchange method. TRst and TRcu were decreased by high EC and/or low soil water content. For method 1, the transpiration decline curve shows two distinct phases: the initial steep slope that indicates TRst and the gently sloped section that indicates TRcu. Both slopes were lower for high EC and/or water-stressed plants compared to the control (low EC and high soil water content). The tangent lines of these two phases of the curve intersect at one point (t, w). The value oft that indicates the time for stomatal closure was longer and the value of w that indicates the critical tissue water level for stomatal closure was lower for high EC and/or water-stressed plants. In method 2, the initial rate of total transpiration was higher in high EC and/or water-stressed plants. Leaf wax content increased, especially under high EC stress. This suggests that increased deposition of wax prevents water loss from the cuticle. A delay in complete stomatal closure, complete closure at lower RWC, and reduced TRcu or an increase in wax deposit were adaptations to water and salinity stresses in tomato plants under our controlled environmental conditions.

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Greenhouse tomato plants (cv. Capello) were grown in peat moss based substrate and treated with high and low nutrient solution electric conductivity (EC) under high (95±5%) and low (55±8%) soil water conditions. Photosynthesis (Pn) was decreased about 25% 1 day after soil water content reached 55%. However, as the soil water deficit was prolonged, the effect of water deficit diminished, with the decreasing extent of ca 15% on the 11th and 16th days from starting treatments. This suggested that tomato plants acclimated to soil water deficit. One day after soil water content reached 55%, leaf turgor potential (TP) decreased largely as leaf water potential (WP) dropped. However, as soil water level was kept constant for a period, TP recovered to a quite large extent even at the same WP level. This TP recovery accounted for the photosynthetic recovery. Drying the constantly well watered plants to the same soil water level decreased Pn to a much larger extent than did the prolonged soil water deficit. This supports the above-mentioned photosynthetic acclimation. The effects of high EC were not observed 1 day after the treatments started, but became larger and larger as the treatments were prolonged. Build-up of EC in the soil accounted for this result

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‘Akizuki’ (Pyrus pyrifolia Nakai) is a dominant Asian pear cultivar with gradually increasing cultivation area in Shandong province. However, this cultivar is found susceptible to cork spot disorder in recent years. In this study, we explored the physiological-biochemical mechanism of cork spot disorder in pear fruit, and investigated the effectiveness of spraying calcium (Ca), boron (B) solution or prohexadione calcium (P-Ca) on cork spot incidence. Cork spotted fruit had the characteristics of significantly larger fruit size with shorter fruit pedicels. Compared with normal fruit, cork spotted fruit had lower content of total soluble solids, soluble and reducing sugar, and vitamin C. In addition, cork spotted fruit accumulated much higher levels of N and Mg, and lower levels of K and P. However, Ca deficiency was not observed in cork spotted fruit, on the contrary, we determined high concentrations of Ca and free Ca2+ in disordered fruit. At the same time, the ratios of K/Ca, Mg/Ca, and (K+Mg)/Ca were significantly lower in cork spotted fruit as compared with normal fruit. Among all treatments, spraying with 3500 times dilution of P-Ca at 15-day intervals from 30 to 90 days after full bloom showed promise for reducing cork spot incidence in ‘Akizuki’ pear without affecting fruit quality attributes. This research herein reveals the physiological-biochemical characteristic of cork spot disorder, and implicates P-Ca as a potential tool to reduce cork spot incidence in Asian pear cultivar Akizuki.

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Water potential at soil-root interface (WPs-r) appears to be a good indicator of soil water availability to the plants. However, it is not easy to measure it routinely. Plant water status is more convenient to manage from bulk soil water potential (WPsoil) determination if a good relationship between WPsoil and WPs-r can be established. In order to elucidate this relationship in different substrates, three soil mixes: Mix-1) composted bark, peat, sand; Mix-2) peat, bark, sand, compost; and Mix-3) peat, sawdust, sand, were used with Prunus × cistena. Two-year-old field grown plants were placed in a greenhouse. After soil water was depleted to different levels, WPsoi1, xylem water potential (WPxylem). transpir-ation as well as stomatal conductance were measured using a portable gas exchange system. WPs-r was calculated from these measured data. Plants grown in Mix-2 kept higher WPs-r until WPsoil decreased to -24 KPa, while WPs-r in the plants grown in Mix-1 began to decrease at -5 KPa of WPsoil. Mix-3 showed a medium critical WPsoil for WPs-r to decrease. Since there was a better availab-ilty of soil water to the plants, plants in Mix-2 also showed higher WPxylem. Dynamic analysis showed that plants in Mix-2 kept better plant water status mainly by avoiding water stress. Plants in Mix-3 also avoided water stress, but it was, at least in part, attributed to less leaf area

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Floral initiation is an important transition point from vegetative growth to reproductive growth in tomatoes and is known to be affected by light intensity, temperature, and nutrients. However, the regulation between flower formation and environmental factors, including nutrient conditions, due to source–sink dynamics (supply and demand of photoassimilates) is seldom documented. To evaluate the effects of light intensity and nutrition conditions on prefloral formation and development, dynamic floral characteristics during development were fitted with sigmoidal logistic curves under four light treatments with shading nets in two nutrient conditions. Source activity and sink strength were altered, which caused differences in the floral positions, length of floral shoots, floral initiation dates, and leaf numbers under the different treatments. Accumulated light acts upstream of nutrition supply during the formation of buds and leads to the accumulation of carbohydrates in source organs. Leaf area reached ≈500 cm2, and dry matter weights reached ≈3 g in each treatment until the flowering day, revealing that some level of photoassimilates are necessary for floral initiation. Both days to flowering and bud number were highly correlated with daily light integral (DLI) from 6 to 12 days before anthesis, which means this period is important for anthesis in tomato. Our results highlight regulation of the transition from vegetative growth to reproductive growth by tomato seedlings due to environmental factors and nutrients. A better understanding of communication between source organs and sink organs during floral initiation response to different environments is expected to provide management strategies for greenhouse tomato production.

Open Access

Jinyan (Actinidia eriantha × A. chinensis) is one of the gold-fleshed kiwifruit cultivars currently being promoted in south China. However, its fruit dry matter is usually less than 16%, which seriously affects fruit quality including taste and flavor. This causes a financial loss to growers: not only are the prices paid for the fruit low because of their bad reputation for quality, but some orchards have been removed. Improvement of fruit quality is essential. In this study, a method is described for squeezing and twisting flowering shoots before flowering and removing the distal vegetative parts of flowering shoots after fruit set. The effects on fruit quality were determined. The dry matter of fruit was increased by 6.6%. Fruit size also increased as did the chlorophyll a content and the chlorophyll:carotenoid ratio. The significantly increased fruit dry matter, resulting in significant increases in fruit soluble solids concentrations (P < 0.01), thereby possibly improving fruit taste. Fruit weight, fruit length, and carotenoid and ascorbic acid concentrations were significantly enhanced in comparison with controls (P < 0.01), increasing by 20%, 7%, 12%, and 19%, respectively. However, there was no significant difference in soluble sugar concentrations, titratable acid concentrations, and the reduced chlorophyll b concentrations. This research provides a practical method to increase fruit dry matter, and hence a way to allow fruit quality to reach commercial requirements for cultivars such as Jinyan, which under previous management systems had significant shortcomings in fruit flavor and taste.

Open Access