Osmotic adjustment of sugar beets in response to soil salinity and its influence on stomatal conductance,growth and yield

Sugar beets were grown in tanks filled with loam and clay, and were irrigated with waters of three different levels of salinity. Osmotic adjustment was determined by analyzing the pressure-volume curves at three growth stages. Sugar beets showed osmotic adjustment in two ways: with their phenological development and towards salinity. Owing to the latter adjustment sugar beets are able to maintain the turgor potential at the same value for lower values of the leaf water potential, to maintain stomatal conductance and photosynthesis and finally their production under severe water stress.Salinity affected the pre-dawn leaf water potential, stomatal conductance and evapotranspiration on both soils, but leaf area and yield only on loam.Soil texture affected stomatal conductance, evapotranspiration, leaf area and yield. As the latter was about 35% lower on clay, whereas the evapotranspiration decreased 10 to 15%, the water use efficiency was about 25% lower on clay compared with loam.     

Effect of salinity on water stress, growth, and yield of maize and sunflower

Maize and sunflower were grown in tanks filled with loam and clay, and were irrigated with water of three different levels of salinity. Predawn leaf-water potential and stomatal conductance were used as parameters for water stress. The predawn leaf-water potential of maize was higher than that of sunflower, but the effect of salinity and soil texture on the predawn leaf-water potential was the same for both crops. The stomatal conductance of sunflower was much higher and more severely affected by salinity and soil texture than the stomatal conductance of maize.

Although salinity had a more serious effect on the development of leaf area and canopy dry matter of sunflower, its effect on evapotranspiration and grain yield was the same for both crops. Soil texture had a stronger effect on the development of leaf area and canopy dry matter of sunflower, which also appeared in the evapotranspiration and grain yield, indicating that sunflower is more sensitive to drought than maize.     

Effects of frequency of irrigation and gypsum treatment on leaf water potential and leaf stomatal conductance of lucerne (Medicago sativa L.) grown on a heavy clay soil

Summary Concurrent diurnal measurements of water potential, osmotic potential and conductance were made on leaves of lucerne grown under weekly (W) and fortnightly (F) irrigation on gypsum-treated (G) and untreated soil (C). Measurements were made throughout the period of vegetative growth.Leaf water potentials were lower both at dawn and in the afternoon under fortnightly as compared to weekly irrigation. Gypsum application led to a slower decline in water potential under fortnightly irrigation, although the effect was small compared with more frequent irrigation. Stomatal conductance was reduced under treatments F_G and F_C during the later stages of vegetative growth, coinciding with leaf water potentials of less than c. –1.6 MPa.The relationship between leaf water potential and turgor potential changed with time such that positive turgor was maintained as leaf water potential declined. Turgor maintenance was achieved through a decrease in leaf osmotic potential. These data suggest that lucerne is capable of osmotic adjustment.Stomatal conductance declined rapidly below a leaf turgor potential of c. 0.1 MPa. It is hypothesised that osmotic adjustment enabled stomatal adjustment, which contributed to continued assimilation despite increasing soil moisture deficits.     

Salinity effect on crop development and yield,analysis of salt tolerance according to several classification methods

The publication is a synthesis of previous publications on the results of a long-term lysimeter experiment. From 1989 to 1998, the experimental variables were soil salinity and soil type, from 1999 onwards, soil salinity and crop variety. The plant was studied during the whole growing period by measuring the saline stress and analyzing its effect on leaf area and dry matter development and on crop yield. Salinity affected the pre-dawn leaf water potential, stomatal conductance, evapotranspiration, leaf area and yield.The following criteria were used for crop salt tolerance classification: soil salinity, evapotranspiration deficit, water stress day index. The classification according to soil salinity distinguished the salt tolerant group of sugar beet and wheat, the moderately salt sensitive group comprising broadbean, maize, potato, soybean, sunflower and tomato, and the salt sensitive group of chickpea and lentil. The results for the salt tolerant and the moderately salt sensitive groups correspond with the classification of Maas and Hoffman, excepted for soybean.The evapotranspiration deficit criterion was used, because for certain crops the relation between yield and evapotranspiration remains the same in case of drought and salinity. This criterion, however, did not appear useful for salt tolerance classification.The water stress day index, based on the pre-dawn leaf water potential, distinguished a tolerant group, comprising sugar beet, wheat, maize, sunflower and potato, and a sensitive group, comprising tomato, soybean, broadbean, chickpea and lentil. The classification corresponds with a difference in water use efficiency. The tolerant crops show a more or less constant water use efficiency. The sensitive crops show a decrease of the water use efficiency with increasing salinity, as their yield decreases stronger than the evapotranspiration. No correlation could be found between osmotic adjustment, leaf area and yield reduction. As the flowering period is a sensitive period for grain and fruit formation and the sensitive crops are all of indeterminate flowering, their longer flowering period could be a cause of their greater sensitivity.The tolerant group according to water stress day index can be divided according to soil salinity in a salt tolerant group of sugar beet and wheat and a moderately sensitive group, comprising maize, sunflower and potato. The difference in classification can be attributed to the difference in evaporative demand during the growing period.The sensitive group according to water stress day index can be divided according to soil salinity in a moderately sensitive group, comprising tomato, soybean and broadbean, and a salt sensitive group of chickpea and lentil. The difference in classification can be attributed to the greater salt sensitivity of the symbiosis between rhizobia and grain legume in the case of chickpea and lentil.     

Response of sorghum to moisture stress using line source sprinkler irrigation I. Plant-water relations

The response of sorghum (Sorghum bicolor L.) to moisture stress during the post-rainy season was studied at ICRISAT research center on a medium deep Alfisol using a line source sprinkler irrigation system. Changes in soil moisture content, stomatal conductance, leaf-water potential and leaf temperature of sorghum as a function of distance away from the line source sprinkler system were monitored throughout the season. Use of the line source technique facilitated the imposition of a range of moisture stress levels as indicated by increased water use by sorghum closer to the line source compared with the crop farther away from the line source. Canopy response measured in terms of stomatal conductance, leaf-water potential, and leaf temperature clearly reflected the gradient in moisture stress perpendicular to the line source.     

Influence of water stress on kiwifruit growth

Summary An irrigation experiment was conducted on young kiwifruit vines over two seasons to examine effects of water stress on fruit development. Vines were grown outdoors in a sandy, rooting medium enclosed within a polythene-lined trench with removable surface covers to enable strict control of the water supply. Measurements of fruit growth, leaf water potential, and stomatal conductance were made throughout the season in conjunction with periods of water stress imposed at different times, and for varying durations. Fruit development was very responsive to water stress with mean fruit size per vine at harvest varying from 60 to 130 cm³ as a result of various stress treatments. Fruit expansion ceased when predawn leaf water potentials fell below –0.1 MPa. Upon rewatering, leaf turgor was regained within 24 h even after severe, prolonged stress. Any turgor loss associated with fruit softening was quickly made up, and thereafter fruit growth continued at the same rate concurrently exhibited on continuously well-watered vines. Suggesting that stomatal conductance did not follow the rapid recovery of leaf water potentials and fruit expansion may be more closely linked to water supply than to the concurrent rate of photosynthesis. Despite the large range in mean fruit size, the shape of the fruit size distribution at harvest was not affected by water stress and it is concluded that harvest yields can be adequately modelled by assuming a normal distribution with a fixed standard deviation.     

Isohydrodynamic behavior in deficit-irrigated Cabernet Sauvignon and Malbec and its relationship between yield and berry composition

Cabernet Sauvignon and Malbec grapevines were irrigated at 70 or 23 % of estimated crop evapotranspiration throughout berry development over four growing seasons. Stomatal behavior was characterized by relating predawn leaf water potential and mid-morning stomatal conductance to mid-morning leaf water potential. Seasonal average weekly midday leaf water potential was lower in Cabernet Sauvignon than Malbec despite similar irrigation amounts. Both cultivars exhibited anisohydric behavior with midday leaf water potential decreasing linearly with declining predawn leaf water potential (r ² = 0.51) and stomatal conductance (r ² = 0.42). However, both cultivars utilized hydrodynamic mechanisms to maintain a soil-to-leaf water potential gradient of ?0.62 (±0.03) MPa under standard irrigation and ?0.75 (±0.04) MPa under reduced irrigation. Berry fresh weight and titratable acidity decreased, and the concentration of total anthocyanins increased in both cultivars in response to decreases in midday leaf water potential. The slope of regression equations for seasonal mean midday leaf water potential was used to estimate cultivar-specific levels of water stress associated with changes in berry weight and berry composition at fruit maturity.     

Response of two varieties of lentil to soil salanity

Two varieties of lentil were grown in tanks filled with clay, and were irrigated with waters containing three different levels of salinity. Salinity affected the germination and survival of the seedlings; the pre-dawn leaf-water potential and maximum osmotic adjustment; the development of leaf area, dry matter and number of flowers, and, finally, the yield.Lentil has a high water-use efficiency, about 2 kg m⁻³ under non-saline conditions, much higher than legumes such as broadbean and soybean. The crop, however, is much more salt sensitive and can only be grown on non-saline soils. At an EC_e of 2 dS/m, the limit between non-saline and slightly saline soils, the yield reduction is about 20% and at an EC_e of 3 dS/m it is 90–100%.The salt tolerance classification, made after a greenhouse experiment with nutritive solutions, was not confirmed by the experiments reported here.     

Simulation of possible adaptive mechanisms in crops subjected to water stress

Summary The dynamics of stress development in crops involves a decrease in turgor potential of leaves which causes decreases in leaf expansion, photosynthesis, and transpiration. A study was conducted to evaluate the effectiveness of three possible adaptive mechanisms in maintaining turgor potential and growth. These mechanisms — osmotic adjustment, increased root growth, and increased stomatal resistance at full turgor — were examined by a simulation experiment using a dynamic model of the soil-crop-atmospheric system. Osmotic adjustment was found to be ineffective in maintaining turgor for crops grown in a sandy soil because of the rapid development of stress. When a ten-day drying cycle was simulated for a clay soil, cumulative transpiration, photosynthesis and growth were increased by osmotic adjustment, indicating an improved ability of the crop to maintain turgor under the simulated conditions for the clay soil. increased stomatal resistance was ineffective for the simulated conditions because of a concomitant decrease in photosynthetic rate. Increased soil volume occupied by roots was found to be the most effective adaptive mechanism for maintaining turgor, transpiration, photosynthesis and growth of crops in both soil types.Contribution from Department of Agricultural Engineering, Institute of Food and Agricultural Sciences, University of Florida. Supported in part by Grant No. FL-AGO-1911 Cooperative Research, United States Department of Agriculture. Florida Agricultural Experiment Station Journal No. 2657     

水分和锌对番茄叶水势、光合特性及蒸腾效率的影响

通过盆栽试验,研究了3个土壤水分水平W1、W2、W3和2个锌溶液水平Z0、Z1对番茄叶水势、光合特性及水分利用效率的影响。结果表明,随着土壤水分的增加,番茄叶水势升高,晴朗天气中午12:00时W3处理叶水势可达-1.52 MPa;W3处理叶面积、光合速率、蒸腾速率和气孔导度分别比W1与W2高出25.7%与10.0%、19.6%与4.2%、20.7%与9.3%、26.6%与15.8%;叶面喷施锌不同程度的提高了叶片光合速率、蒸腾速率和气孔导度,在W2适宜水分下,三者分别提高9.1%、2.9%和7.3%;土壤水分的提高使植株的蒸腾效率增加,在W1、W2条件下叶面喷锌显著提高了叶片蒸腾效率。     

灌水处理对冬小麦生理生长特性等的影响研究

通过对冬小麦不同生育期进行有限灌溉的大田试验,研究不同水分处理对冬小麦的土壤水分变化、株高、叶面积指数、光合特性、产量以及水分利用效率的影响。结果表明:①灌水量越大,含水量变化的土层深度越大;并且土层深度越大,含水量的变化越小。②开花期灌水对缺水处理叶面积指数和株高的补偿效应明显。③各处理的光合特性日变化趋势一致,蒸腾速率和气孔导度日变化趋势均是双峰曲线,光合速率日变化趋势均是单峰曲线,均有"午休"现象。④开花水有利于籽粒的形成,只灌开花水也可获得较高产量。但产量与总灌水量之间呈抛物线关系。⑤单叶和产量水平的水分利用效率均随灌水量的不同而不同。总灌水量越大,叶片水分利用效率越大,灌溉水利用效率越低,水分利用效率越低。⑥综合考虑,全生育期只灌1次75 mm开花水的处理最合理。     

盐胁迫下水氮处理对小桐子生理特性的影响

为研究盐胁迫条件下不同水氮处理对小桐子幼树生理特性的影响,采用3个灌水水平(灌水处理的每次灌水量分别为T1:3.2 L/株,T2:5.4 L/株,T3:9.6 L/株),4个施氮水平(NZ:0 g,NL:10 g,NM:30 g,NH:50 g),共12个处理,6次重复,进行温室小区试验.结果表明:盐胁迫下适当增加灌水量可以有效提高小桐子的净光合速率;在盐胁迫且不施氮条件下,与T1相比T2和T3能促进小桐子的光合特性、叶水势增加;适宜的土壤水氮调控有助于增加小桐子的光合作用;在盐胁迫与灌水量相同处理条件下,与NZ相比,NL,NM,NH下的小桐子的光合作用显著,且叶水势减小.与T3NH比,T3NM的净光合速率、蒸腾速率、气孔导度、叶水势分别显著提高4.98%,6.01%,9.14%,22.97%.在盐胁迫下,有利于小桐子生理特性的最优处理是T3NM.     

温室滴灌条件下水分亏缺对番茄生长及生理特性的影响

为确定温室滴灌条件下番茄高产高效的适宜土壤水分控制指标,采用小区试验方法,在温室滴灌条件下研究了不同时期水分亏缺对番茄生长发育及生理特性的影响。研究结果表明,任何生育阶段发生水分亏缺均会降低番茄叶片光合速率及气孔的开度,进而影响干物质的累积和运转,但不同时期水分亏缺的影响形式及程度有所不同;苗期水分亏缺会抑制番茄的正常生长发育,但水分过高会使植株徒长,不利于光合产物向产量的运移;开花坐果期水分亏缺不仅抑制了番茄的生长发育,而且降低了干物质的累积,并最终影响到产量的形成;成熟采摘期水分亏缺会加速番茄植株的老化,降低最终干物质量,对番茄产量的形成影响最为明显。在不影响番茄植株正常生长发育及生理需水情况下,适度水分亏缺(T1处理)可实现高产与高效用水的统一。     

Whole-tree water balance and indicators for short-term drought stress in non-bearing ‘Barnea’ olives

Drainage-weighing lysimeters allowed monitoring of water balance components of non-bearing olive (Olea europaea cv Barnea) trees over a 3-month period including short-term events of controlled but severe water stress. The objective of the study was to evaluate a variety of soil and plant-based water status and drought stress monitoring methods on the basis of tree-scale evapotranspiration (ET). As the trees entered into and recovered from water stress, meteorological data, actual ET (ET_a), soil water content and changes in leaf turgor pressure were continuously monitored. Additionally, midday measurements of stem water potential, stomatal conductance, canopy temperature, and quantum yield of PSII photochemistry were conducted. Diurnal (dawn to dusk) measurements of all the above were made hourly on days of maximum stress. Shoot elongation rate was measured for periods of stress and recovery. Quantum yield of PSII photochemistry, stomatal conductance, and stem water potential all successfully indicated reductions in whole-tree water consumption beginning at moderate stress levels. These measured parameters fully recovered to the levels of non-stressed trees soon after water application was renewed. Shoot elongation was reduced 25-30% for the 10-day period during and following drought and recovered thereafter to levels of non-stressed trees. Whole-tree ET_a was reduced by as much as 20% even following full recovery of the leaf level parameters, suggesting reduced canopy size and growth due to the stress period. Non-destructive, continuous (turgor pressure) and remotely sensed (canopy temperature) methods showed promising potential for monitoring effects of water stress, in spite of technological and data interpretation challenges requiring further attention.     

Interactive effects of elevated CO2, nitrogen and drought on leaf area,stomatal conductance,and evapotranspiration of wheat

Atmospheric CO₂ enrichment may bring different effects on plant growth and evapotranspiration if plants are under N and water deficient conditions. In this study, spring wheat (Triticum aestivum L.) was grown in pots at two atmospheric CO₂ concentrations (ambient and elevated), two levels of soil moisture (well-watered and droughted to 45–60% of field capacity) and five nitrogen (N) fertilization treatments (0, 112.5, 225.0, 337.5, 450.0 kg hm⁻²) in growth chambers. Leaf growth, leaf area, and tiller increment were largely a function of N application and water supply. Elevated CO₂ increased 23–45% in leaf area only with the N-added treatments 55 days after sowing. Elevated CO₂ also reduced stomatal conductance more in droughted treatments (−51%) than in well-watered treatments (−41%), and more with zero N application (−60%) than with the adequate N (−35 to 44%). Evapotranspiration (ET) was also reduced by CO₂ enrichment in a similar way. Our results showed that the CO₂-enrichment-induced decrease in transpiration almost compensated for the increase in ET brought by the higher leaf area under adequate N and water supply, such that ET was similar for control and CO₂-enriched plants. Under reduced N and water supply, CO₂ enrichment had limited effect on either leaf growth or ET.     

Photosynthesis,plant growth and dry matter distribution in kiwifruit as influenced by water deficits

The effects of water deficits on photosynthesis, plant growth and dry matter accumulation and distribution in the kiwifruit, cv Hayward, grown under controlled conditions in the glasshouse were studied. Water stress was imposed by irrigating the plants with 100%, 85%, 65% and 40% of water needed to reach pot capacity in the soil. Water deficits reduced the rate of photosynthesis by up to 53–64% in relation to the control. This decline was attributed to stomatal closure, since stomatal conductance was reduced significantly, or/and to inhibition of photosynthesis at chloroplast level. Severe water stress reduced plant height by 78–84%, total dry weight by 58–66% and total leaf area by 72–77%. The root to shoot ratio was 3.5 times higher in water-stressed plants, showing that water stress in kiwifruit alters the pattern of dry matter distribution favouring the roots. The decrease in growth induced by water deficits was a consequence of a reduction in both photosynthesis and photosynthates partitioning, which adversely affects leaf area development.     

Plant response to the soil water reserve: Consequences of the root system environment

Summary The ability of water balance models based on the concept of Transpirable Soil Water to predict the occurrence of water stress and the need for irrigation was tested for several environmental conditions of the root system, to determine in which conditions errors are likely to be appreciable. The response of evapotranspiration, stomatal conductance and leaf water potential to soil water reserve was studied under three conditions: (i) in pots with maize plants, (ii) in the field with deep soil and the root system placed in favourable conditions, with wheat during a dry year and with maize during four years with contrasting climate, (iii) in the field, with soil compaction which disturbed the maize root system, decreasing its efficiency for water uptake, during four year. (i) In the pot experiment, where the volume of the Transpirable Soil Water (TSW) is well defined, the responses followed the hypothesis of water balance models. (ii) The soil depletion was higher than the calculated TSW during two dry years in the field, because of an appreciable contribution of the non-rooted soil layers to the water balance. As a consequence, evapotranspiration, stomatal conductance and predawn water potential did not decrease over the whole range of soil water reserve. Grain yield was no lower in those years than in the wet years, in spite of the fact that the soil water reserve was depleted. Thus, a water balance based on the TSW would have underestimated in these conditions the ability of plants to withdraw soil water, overestimating the necessity of irrigation. Predawn water potential gave, on the contrary, indications consistent with the responses of the stomatal conductance and the net CO₂ assimilation. (iii) The water uptake by plants would have been overestimated in the case of compacted soil. Stomatal conductance was low even for high levels of the soil water reserve, except if the densely rooted top 0.1 m layer of soil was rewatered by irrigation. Water stress could not have been diagnosed in this case from indications of soil water potential or of pre-dawn water potential. These data confirm that some knowledge of the environmental conditions of the root system is necessary to determine if errors made using water balance models are likely to be appreciable, and to know if they lead to an underestimation or overestimation of the risk of water stress.     

The influence of bearing cycles on olive oil production response to irrigation

Water requirements for olive oil production and the effects of deficit irrigation were determined while considering the relative fruit loads on trees occurring as a result of biennial bearing cycles. Two Israeli olive (Olea europaea) varieties (Barnea and Souri) were evaluated for growth and yield parameters in a 4-year field study where five relative irrigation rates were applied. Increasing irrigation increased stem water potential, vegetative growth, and olive fruit yield with the increases tapering off at application rates reaching 75–100% of potential crop evapotranspiration. Tree water status, growth, and fruit characteristic parameters were highly affected by both fruit load and by irrigation level. Oil yield increases as a function of increased irrigation were initiated for each cultivar only following an ‘off’ season when the treatments lead to higher vegetative growth. The increased oil yields as a function of increased irrigation were primarily explained by higher tree-scale capacity for carrying fruit, especially as irrigation alleviated measureable water stress. For the Barnea cultivar in ‘on’ years, a secondary effect due to increased oil per fruit as irrigation increased was evident, particularly at the higher application rates.     

水分胁迫对枇杷果实发育阶段的光合特性和果实品质的影响

以6年生大五星枇杷为试材,系统研究了果实发育阶段水分胁迫处理对枇杷叶片的光合特性和果实品质的影响,结果表明:随水分胁迫加剧,叶片的净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Cs)下降,水分利用率(WUE)提高。不同水分处理的Pn日变化曲线呈双峰型,具有明显的"午休"现象。果实的可溶性固形物、总糖、总酸的含量随水分胁迫加剧而提高。水分胁迫导致果实单果重和果实含水率显著下降。该研究为攀西干旱河谷枇杷果实发育阶段的水分管理提供决策支持。     

遮荫补灌提高陇东旱塬区小麦对干热风的抗逆适应

利用灌浆期模拟干热风胁迫,并结合遮荫补灌措施,研究干热风对小麦叶片失绿黄化特性、渗透调节物质质量分数和产量构成因子的影响。结果表明,干热风胁迫使灌浆期叶片叶绿素降解转化能力显著增强,叶片失绿黄化程度加重、渗透调节功能失衡,产量下降。遮荫或补灌均能提高小麦旗叶持绿面积、叶绿素质量分数和产量,降低叶片黄化指数、类胡萝卜素质量分数、渗透调节物质质量分数。遮荫灌水在缓解干热风对小麦抗逆伤害方面具有加性效应。因此,遮荫补灌可有效提高小麦在干热风胁迫下的抗逆适应。