Field water relations of a compass plant, Lactuca serriola L.

Abstract Field water relations of Lactuca serriola serriola and L. serriola integrifolia were examined. Leaf conductance to water vapour was high early in the morning and declined rapidly during the midday hours. Leaf water potentials decreased to their minima early in the morning and remained low all day. Afternoon recovery of leaf conductance occurred occasionally. Leaf conductance was shown to have a linear response to vapour concentration difference. No differences were seen between L. serriola serriola and L. serriola integrifolia. The pattern of diurnal gas-exchange activity appeared to be complemented by the pattern of intercepted solar irradiance which results from the compass plant leaf orientation observed in L. serriola.     

The effects of irrigation regimes on the water use,dry matter production and physiological responses of paddy rice

In most cases, rice production is associated with flooding irrigation and the efficiency of irrigated water use (WUEi) is generally lower for production of rice than for other crops. We have examined the effects of various irrigation regimes on water consumption in a well-puddled paddy field, as well as on dry matter production, grain yield and physiological responses of the plants. Four sets of conditions were studied, with two replications, in the well-puddled paddy field: Continuous flooding irrigation treatment (CSF); three intermittent irrigation treatments, designated II-0, II-1 and II-2, in which plants were re-irrigated when the water potential of the soil fell below 0, –10, and –20 kPa at a depth of 5 cm, respectively. Water consumption was lower during II-0 than during CSF because the percolation rate was reduced by the reduction in the hydraulic head of the ponded water. Intermittent irrigation led to the repeated shrinking and swelling of soil during II-1 and II-2 and, therefore, soil cracks developed rapidly. Since they became the major routes of water percolation, these soil cracks increased water consumption during II-1 and II-2 above that during CSF and II-0. There were no significant differences in dry matter production and grain yield between CSF and II-0, but both were significantly greater than in the case of II-1 and II-2. Therefore, WUEi increased in the following order: II-0, CSF, II-2, II-1, although the difference was very small between II-1 and II-2. A lower crop growth rate (CGR) resulted from a decrease in the net assimilation rate (NAR) during II-1 and II-2, and there was also a reduction in the leaf area index (LAI) during II-2. Early senescence with ripening and water stress around midday decreased the rate of photosynthesis in leaves, causing the lower NAR. These physiological responses of the plants were responsible for the reduction on the dry matter production and grain yield in the intermittent irrigation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Properties of peat-based casing soils and their influence on the water relations and growth of the mushroom (Agaricus bisporus)

Different combinations of peat and chalk or lime sources with differing moisture contents were used to determine how specific physical and chemical properties of the casing soil relate to the growth and water relations of the mushroom. The peat types varied in terms of decomposition and extraction method; the lime addition varied in terms of rate and type (chalk or sugar beet lime). During the colonisation of the casing soil before fruiting, the extension growth rate of mushroom mycelium was most closely correlated (negatively) with the volumetric moisture content of the casing soil. Scanning electron microscopy showed that mycelium growing at a lower casing soil matric potential (Ψ_m) had a much finer and branched structure than mycelium growing at a higher Ψ_m. Across all the peat and lime source treatments, a relationship was found between the mean Ψ_m of the casing soil and mushroom yield, with an optimum Ψ_m of -7.9 to -9.4 kPa. Mushrooms are produced in ‘flushes’ at about 8-day intervals and during the development of each flush of mushrooms, there was a significant decrease in casing soil Ψ_m . This decrease (to below -40 kPa) was greatest in the second flush, which was the highest yielding. There were no relationships between mushroom yield and casing soil osmotic potential Ψ_π within the range -93 to -154 kPa or any of the other chemical properties and water and air holding characteristics of the casing soils which were determined. Across different casing soil treatments, mushroom dry matter content was negatively correlated with mushroom yield and positively correlated with mushroom tissue osmotic potential. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modelling crop growth and biomass partitioning to shoots and roots in relation to nitrogen and water availability,using a maximization principle

Many crop models relate the allocation of dry matter between shoots and roots exclusively to the crop development stage. Such models may not take into account the effects of changes in environment on allocation, unless the allocation parameters are altered. In this paper a crop model with a dynamic allocation parameter for dry matter between shoots and roots is described. The basis of the model is that a plant allocates dry matter such that its growth is maximized. Consequently, the demand and supply of carbon, nitrogen, and water is maintained in balance. This model supports the hypothesis that a functional equilibrium exists between shoots and roots.This paper explains the mathematical computation procedure of the crop model. Moreover, an analysis was made of the ability of a crop model to simulate plant dry matter production and allocation of dry matter between plant organs. The model was tested using data from a greenhouse experiment in which spring wheat (Triticum aestivum L.) was grown under different soil moisture and nitrogen (N) levels.Generally, the model simulations agreed well with data recorded for total plant dry matter. For validation data the coefficient of determination (r²) between simulated and measured shoot dry weight was 0.96. For the validation treatments r² was slightly lower, 0.94. In addition to dry matter production the model succeeded satisfactorily in simulating the dry weight of different plant organs. The response of simulated root to shoot ratio to the level of soil moisture was mainly in accordance with the measured data. In contrast, the simulated ratio seemed to be insensitive to the changes in the levels soil N concentration used in the experiment.The data used in the present study were not extensive, and more data are needed to validate the model. However, the results showed that the model responses to the changes in soil N and water level were realistic and mostly agreed with the data. Thus, we suggest that the model and the method employed to allocate dry matter between roots and shoots are useful when modelling the growth of crops under N and water limited conditions.     

Transfer of water from roots into dry soil and the effect on wheat water relations and growth

This investigation was performed to study the effect on plant water relations and growth when some of roots grow into dry soil. Common spring water (Triticum aestivum) plants were grown from seed in soil in 1.2 m long PVC (polyvinyl chloride) tubes. Some of the tubes had a PVC partition along their center so that plants developed a split root system (SPR). Part of the roots grew in fully irrigated soil on one side of the partition while the rest of the roots grew into a very dry (-4.1 MPa) soil on the other side of the partition. Split root plants were compared with plants grown from emergence on stored soil moisture (STOR) and with plants that were fully irrigated as needed (IRR). The experiment was duplicated over two temperature regimes (10°/20°C and 15°/25°C, night/day temperatures) in growth chambers. Data were collected on root dry matter distribution, soil moisture status, midday leaf water potential (LWP), leaf relative water content (RWC) and parameters of plant growth and yield.Some roots were found in the dry side of SPR already at 21 DAE (days after emergence) at a soil depth of 15 to 25 cm. Soil water potential around these roots was -0.7 to -1.0 MPa at midday, as compared with the initial value of -4.1 MPa. Therefore, water apparently flowed from the plant into the dry soil, probably during the night. Despite having most of their roots (around 2/3 of the total) in wet soil, SPR plants developed severe plant water stress, even in comparison with STOR plants. Already at 21 DAE, SPR plants had a LWP of -1.5 to -2.0 MPa, while IRR and STOR had a LWP of -0.5 MPa or higher. As a consequence of their greater plant water stress, SPR as compared with IRR plants were lower in tiller number, ear number, shoot dry matter, root dry matter, total biomass, plant height and grain yield and had more epicuticular wax on their leaves.It was concluded that the exposure of a relatively small part of a plant root system to a dry soil may result in a plant-to-soil water potential gradient which may cause severe plant water stress, leading to reduced plant growth and yield.     

Tissue water relations and leaf growth of tropical corn cultivars under water deficits

Abstract This study reports on the effect of water deficit on the tissue water relations and leaf growth of six corn cultivars, growing in glasshouse conditions, in order to understand growth responses to drought of tropical corn. A mild water-stress treatment was imposed slowly; plants reached a minimum pre-dawn leaf water potential of about –1.5 MPa by day 12 after watering was withheld. Analysis of the water relation characteristics of growing leaves using the pressure–volume technique demonstrated that under water deficits all the cultivars changed their moisture-release curves compared with irrigated plants. Osmotic potential at full turgor was lowered in water-stressed plants of all the genotypes and the degree of such change was between 0.34 MPa and 0.58 MPa. Thus, turgor pressure was lost at a lower water potential in water-stressed plants than in irrigated plants of all the varieties. Volumetric elastic moduli were also increased under water deficits and the increase ranged between 10% and 141% among the cultivars. In all the genotypes, the stress imposed led to a reduction of leaf area and dry matter accumulation. Leaf expansion was very sensitive to low turgor pressure and it ceased when turgor reached 0.2 MPa. Thus, varieties able to maintain a higher degree of turgor pressure (i.e. by osmotic adjustment) under water deficits may be able to prolong leaf growth.     

Effect of nitrogen on growth and water relations of radiata pine families

The effect of nitrogen fertilisation on growth, foliar nutrients and water relations of four families of radiata pine (Pinus radiata, D. Don) currently in the Australian breeding program was examined from age six to 11 years. At this stage, the stand was ready for commercial thinning. The annual rainfall at the site varied from 563 to 733 mm.Application of nitrogen fertiliser resulted in stem wood volume at age nine years of 178 m³ ha^-1 in the controls, compared with 228 m³ ha^-1 in plots treated with 600 kg N ha^-1. Pre-dawn needle water potential () measured in three consecutive summers (when rainfall ranged from 53 to 106 mm) were consistently higher (less water stress) in nitrogen fertilised than in control trees. Similarly, the water stress integral (S) decreased consistently with increasing levels of nitrogen, although total water use in fertilised trees would have been substantially higher because fertiliser application increased the leaf area index. The relationship between S and basal area was strong and paralleled that of foliar nitrogen concentration and basal area growth. Therefore, nitrogen application increased growth rates of trees by improving the nutrient status of trees and lowering the water stress on trees in summer.Families showed markedly different responses of basal area growth to nitrogen, ranging from an increase of 9.4% over three years for the least responsive family to 99.0% for the most responsive. There was no nitrogen × family interaction on or S suggesting that the large genetic variation in the growth response to nitrogen is mediated by factors other than water relations. These results have implications for managing highly productive plantations grown in an environment where rainfall is low compared to potential evapotranspiration.     

Growth rate, plant development and water relations of the ABA-deficient tomato mutant sitiens

Given the close relationship between a plant's growth rate and its pattern of biomass allocation and the effects of abscisic acid (ABA) on biomass allocation, we studied the influence of ABA on biomass allocation and growth rate of wildtype tomato ( Lycopersicon esculentum Mill. cv. Moneymaker) plants and their strongly ABA-deficient mutant sitiens. The relative growth rate of sitiens was 22% lower than that of the wildtype, as the result of a decreased specific leaf area. The net assimilation rate and the leaf weight ratio were not affected. The mutant showed a much higher transpiration rate and lower hydraulic conductance of the roots. These two factors resulted in sitiens having a significantly lower leaf water potential and turgor. resulting in reduced leaf expansion and, consequently, a lower specific leaf area relative to the wildtype. Addition of ABA to the sitiens roots resulted in phenotypic reversion to the wildtype. We conclude that the influence of ABA-deficiency on biomass allocation and relative growth rate is the result of altered water relations in the plants, rather than of a direct effect on sink strength of different plant organs.     

Influence of different soil temperatures on water use,growth and internal water status of soybean

Studies on the effect of soil temperature on internal water relations of well watered soybean (Glycine max L.) at constant air temperature under controlled conditions were carried out. A specially designed thermogradient tank was used for obtaining a range of soil temperatures. Data on shoot height, shoot weight, root length, root weight, leaf area and leaf water potential were obtained at 41 days after sowing and the highest values of these parameters were recorded at 28.6°C. The air temperature during the course of these investigations was 25±1°C and it may be concluded that slightly warmer soil temperatures than air temperatures were optimal for soybean with regard to the above measured parameters.     

Soil water dynamics,transpiration, and water losses in a crested wheatgrass and native shortgrass ecosystem

The status of water in soil and vegetation was monitored in a stand of crested wheatgrass (Agropyron cristatum) and a nearby shortgrass steppe during a growing season. This was done to determine if water use and losses were similar among two very different communities in a similar climate. Precipitation was similar throughout the study period for both the crested wheatgrass and native shortgrass communities. However, the native shortgrass community with greater root biomass had consistently greater soil water depletion in the deeper soil horizons than was found in the crested wheatgrass community. Greater depletion of soil water by native shortgrass species suggests that they might be more competitive than crested wheatgrass in a water-limited environment.Crested wheatgrass maintained high leaf water potential early in the season, but lower water potential during the latter part of the growing season as compared with the major species of the shortgrass steppe, blue grama (Bouteloua gracilis) and western wheatgrass (Agropyron smithii). Leaf conductance was lower for crested wheatgrass than for the native grasses during the later part of the growing season. Consequently, seasonal transpiration for crested wheatgrass was lower when compared with blue grama or western wheatgrass. Lower conductance allowed crested wheatgrass to maintain relatively high internal water potential and may have accounted for less soil water use at deeper soil depths during the latter part of the growing season.Water loss through transpiration was less for western wheatgrass than for either blue grama or crested wheatgrass because western wheatgrass had less leaf area. However, western wheatgrass was as efficient as the other species in its use of water. Crested wheatgrass transpired more water than blue grama early in the growing season, but less than either native species for the remainder of the growing season. Estimated seasonal transpiration loss was greater in the shortgrass ecosystem than in the established crested wheatgrass stand.     

Combined effects of drought and high temperature on water relations of wheat and sorghum

Drought and high temperature are major factors limiting crop production. The two stresses occur together in many regions, but they usually are investigated separately. This study tested the hypothesis that high temperature interacts with drought to affect water relations, and the effect is greater in heat-sensitive wheat (Triticum aestivum L.) than in sorghum (Sorghum bicolor L. Moench). Wheat and sorghum were grown in soil that was well watered or not watered in controlled chambers at 15/10, 25/20, 35/30 and 40/35 °C day/night. Soil water content (SWC), leaf relative water content (RWC), leaf water potential (), leaf osmotic potential (), leaf turgor potential (P) and osmotic adjustment (OA) were determined at 2-d intervals. All values held nearly constant at all temperatures when soil was well watered but were affected strongly by high temperature when water was withheld. The combined stresses reduced SWC, RWC, Psi and , and unevenly raised P over time, particularly in sorghum. Sorghum also exhibited marked OA at high temperature, which was usually lethal to wheat. High temperature appeared to interact with drought to affect water relations by altering SWC and not by influencing OA. The results demonstrated that crops maintain nearly stable water relations regardless of temperature when moisture is ample, but high temperature strongly affects water relations when water is limiting. Increasing the thermotolerance of wheat might improve its potential to acclimate to both high temperature and drought.     

长期保护性耕作对黄土高原旱地土壤水分及作物叶水势的影响

通过长期定位试验研究了黄土高原西部旱农区,传统耕作方式和5种保护性耕作措施对豌豆-小麦(P→W)和小麦-豌豆(W→P)轮作序列的耕层土壤水分和作物叶水势的影响。结果表明,与传统耕作(T)处理相比,保护性耕作都能不同程度地提高0—30 cm土层土壤含水量,增幅为3.29%—28.67%,其中免耕+秸秆覆盖(NTS)处理的土壤含水量在整个生育期内均为最高。豌豆和春小麦在不同生育期,叶水势的日变化趋势大致相同,均为清晨6:00最高,然后随着时间的推移而下降,大约在12:00—14:00之间达到最低,随后逐渐回升。春小麦各处理在拔节期和抽穗期的叶水势相对较高,孕穗期和开花期次之,灌浆期最低;叶片相对含水量在拔节期和抽穗期最高,开花期次之,灌浆期最低。豌豆各处理的叶水势均在出苗期和孕蕾期达到了最大值,分枝和开花期结荚期次之,灌浆成熟期相对较低;叶片相对含水量均随生育期的进程而呈下降趋势。整个生育期春小麦和豌豆各处理10:00的叶水势与0—30 cm平均土壤含水量之间显著相关,当土壤水分含量较低时,春小麦和豌豆叶水势与耕层土壤含水量的相关性达极显著水平。与传统耕作(T)相比,免耕+秸秆覆盖(NTS)、免耕+地膜覆盖(NTP)、免耕(NT)、传统耕作+秸秆还田(TS)、地膜覆盖(TP)5种保护性耕作措施能不同程度的提高作物叶水势、叶片相对含水量和作物产量,其中免耕+秸秆覆盖(NTS)的优势最明显。     

Rice leaf growth and water potential are resilient to evaporative demand and soil water deficit once the effects of root system are neutralized

Rice is known to be sensitive to soil water deficit and evaporative demand, with a greatest sensitivity of lowland‐adapted genotypes. We have analysed the responses of plant water relations and of leaf elongation rate (LER) to soil water status and evaporative demand in seven rice genotypes belonging to different species, subspecies, either upland‐ or lowland‐adapted. In the considered range of soil water potential (0 to ?0.6 MPa), stomatal conductance was controlled in such a way that the daytime leaf water potential was similar in well‐watered, droughted or flooded conditions (isohydric behaviour). A low sensitivity of LER to evaporative demand was observed in the same three conditions, with small differences between genotypes and lower sensitivity than in maize. The sensitivity of LER to soil water deficit was similar to that of maize. A tendency towards lower sensitivities was observed in upland than lowland genotypes but with smaller differences than expected. We conclude that leaf water status and leaf elongation of rice are not particularly sensitive to water deficit. The main origin of drought sensitivity in rice may be its poor root system, whose effect was alleviated in the study presented here by growing plants in pots whose soil was entirely colonized by roots of all genotypes.     

Effect of increased irradiance on the hormone content,water relations,and leaf elongation in wheat seedlings

In wheat (Triticum durum Desf., cv. Bezenchukskaya 139) seedlings, an increase in irradiance from 20 to 400 μmol/(m² s) PAR enhanced transpiration and increased stomatal conductance by three times on the background of reduced relative water content (RWC). After this treatment, leaves quickly ceased to grow and became even shrunk later. In 40 or 50 min, leaf growth was resumed. At this period, we observed an increase in hydraulic conductivity and RWC and also in leaf extensibility. As soon as 10 min after treatment, some changes in hormone content were noted. In the zones of leaf growth and its mature part, zeatin and zeatin riboside were accumulated, whereas ABA accumulation was observed in the zone of leaf growth and in the roots. The results obtained indicate that leaf expansion at increased irradiance was related to changes in cell-wall extensibility and hydraulic conductivity. The first effect could be due to cytokinin accumulation, whereas the second one, to ABA accumulation.     

Sequential response of whole plant water relations to prolonged soil drying and the involvement of xylem sap ABA in the regulation of stomatal behaviour of sunflower plants

Sunflower plants ( Helianihus animus cv. Tall Single Yellow} were grown in the greenhouse in drain pipes (100 mm inside diameter and 1 m long) rilled with John Innes No. 2 compost. When the fifth leaf had emerged, half of the plants were left unwatered for 6 days, rewatered for 2 days and then not watered for another 12 days. Measurements of water relations and abaxial stomatal conductance were made at each leaf position at regular intervals during the experimental period. Estimates were also made of soil water potentials along the soil profile and of ABA concentrations in xylem sap and leaves.
Soil drying led to some reduction in stomatal conductance alter only 3 days but leaf turgors were not reduced until day 13 (6 days after rewatering). When the water relations of leaves did change, older leases became substantially dehydrated while high turgors were recorded in younger leaves. Leaf ABA content measured on the third youngest leaf hardly changed over the first 13 days of the experiment, despite substantial soil drying, while xylem ABA concentrations changed very significantly and dynamically as soil water status varied, even when there was no effect of soil drying on leaf water relations. We argue that the highest ABA concentrations in the xylem, found as a result of substantial soil drying, arise from synthesis in both the roots and the older leaves, and act to delay the development of water deficit in younger leases.
In other experiments ABA solutions were watered on to the root systems of sunflower plants to increase ABA concentrations in xylem sap. The stomatal response to applied ABA was quantitatively very similar to that to ABA generated as a result of soil drying. There was a log-linear relationship between the reduction of leaf conductance and the increase of ABA concentration m xylem sap.     

基于水分控制的切花百合生长预测模型

光合作用与干物质生产是观赏植物外观品质形成的基础。水分是影响植物光合作用与干物质生产的重要因子。为定量研究水分对切花百合光合作用与干物质生产的影响,以切花百合品种‘索邦’(Lilium‘Sorbonne’)为试验材料,于2009年3月至2010年1月在南京的连栋温室内开展了不同定植期和不同水分处理的栽培试验,以基于光温的温室花卉生长动态预测模型为基础,定量分析了不同定植期和不同水分处理条件下切花百合叶面积指数、光合速率和干物质生产的动态影响,并确定了切花百合正常生长的临界基质水势,建立了基质水势对切花百合光合速率和干物质生产影响的动态预测模型。结果表明,本文所建模型对切花百合叶片最大总光合速率和植株总干质量的预测效果较好,模型对叶面积指数、叶片最大总光合速率和植株干物质量的预测值与实测值之间的决定系数(r2)分别为0.97,0.96,0.94,相对根均方差(rRMSE)分别为7.12%、4.37%、11.14%。该模型能较好地预测水分对切花百合叶片最大总光合速率和植株总干质量的动态影响,可为进一步优化切花百合生产的水分管理提供决策支持。     

Effects of environmental parameters, leaf physiological properties and leaf water relations on leaf water delta18O enrichment in different Eucalyptus species

Stable oxygen isotope ratios (delta18O) have become a valuable tool in the plant and ecosystem sciences. The interpretation of delta18O values in plant material is, however, still complicated owing to the complex interactions among factors that influence leaf water enrichment. This study investigated the interplay among environmental parameters, leaf physiological properties and leaf water relations as drivers of the isotopic enrichment of leaf water across 17 Eucalyptus species growing in a common garden. We observed large differences in maximum daily leaf water delta18O across the 17 species. By fitting different leaf water models to these empirical data, we determined that differences in leaf water delta18O across species are largely explained by variation in the Péclet effect across species. Our analyses also revealed that species-specific differences in transpiration do not explain the observed differences in delta18O while the unconstrained fitting parameter 'effective path length' (L) was highly correlated with delta18O. None of the leaf morphological or leaf water related parameters we quantified in this study correlated with the L values we determined even though L was typically interpreted as a leaf morphological/anatomical property. A sensitivity analysis supported the importance of L for explaining the variability in leaf water delta18O across different species. Our investigation highlighted the importance of future studies to quantify the leaf properties that influence L. Obtaining such information will significantly improve our understanding of what ultimately determines the delta18O values of leaf water across different plant species.