Leaf hydraulic conductance, measured in situ, declines and recovers daily: leaf hydraulics, water potential and stomatal conductance in four temperate and three tropical tree species

Controls on leaf stomatal conductances imposed by soil water availability and foliage acclimation to long‐term integrated irradiance were studied in a natural mixed deciduous stand composed of shade‐intolerant Populus tremula L. and shade‐tolerant Tilia cordata Mill. Positive relationships between maximum stomatal conductance and seasonal integrated average daily quantum flux density ($$Q_{\mathrm{int}\,}$$, mol m$$^{-2}$$ d$$^{-1}$$) were observed in both species, whereas the slope of this relationship declined with increasing soil water limitations. There were negative correlations between $$Q_{\mathrm{int}\,}$$ and leaf water and osmotic potentials, and stomatal conductances reached in conditions of severe water stress were relatively lower in the upper than in the lower canopy in both species. Thus, even at a constant soil water availability, foliar water stress increased with increasing seasonal average integrated light in the canopy. A number of plastic structural and chemical adjustments improving the apparent tolerance of water deficits were observed in the foliage along the light gradient. Leaf dry mass per unit area and the content of leaf osmotica per unit area increased, and an estimate of symplasmic leaf fraction—leaf water contents per unit leaf dry mass—decreased with increasing $$Q_{\mathrm{int}\,}$$. In addition to stomatal closure, the leaves had a substantial and rapid capacity for osmotic adjustment of leaf water potential in response to water stress, and because of light‐related foliar modifications, this capacity was greatest in the upper canopy leaves. Across the whole set of data, there was a negative correlation between minimum daily leaf water potential and stomatal conductance, because both variables covaried with irradiance. When the covariation with light was accounted for by a multiple linear regression analysis, minimum leaf water potential had no significant effect on stomatal aperture. Instead, stomatal conductance correlated positively with soil water potential in both species. Concentration of xylem sap abscisic acid (CABA) was analyzed to assess its role as a potential messenger of soil water status. Instantaneous CABA was negatively correlated with soil water potential, and with stomatal conductance only in the drought‐stressed leaves. Thus, there was evidence that stomatal sensitivity to abscisic acid (ABA) increased with advancing water stress. Tilia cordata, stomata of which were more sensitive to water limitations, also appeared to be more responsive to abscisic acid. We found a negative correlation between CABA and $$Q_{\mathrm{int}\,}$$, which possibly resulted from greater transpiration rates at greater $$Q_{\mathrm{int}\,}$$. Since stomatal conductances were more responsive to drought in the upper canopy, where ABA concentrations were the lowest, we suggest that stomatal sensitivity to ABA is not constant along the canopy light gradient.

Corylus avellana L. is a species highly susceptible to water stresses caused by vapor pressure deficit and high temperature. Under such conditions, transpiration is strongly constrained even with good soil water availability. This is due to ineffective drought resistance mechanisms and indicates the need to identify early indicators of plant stress that are easy to measure, effective and efficient. This research explored the possibility of using stomatal conductance and leaf water potentials as early indicators of stress. For this purpose, an experiment was set up in a commercial 5-year-old Corylus avellana L. var. 'McDonald' orchard located in Willamette valley. The experimental designed featured irrigated and rainfed trees, and potential stress indicators were monitored at different times of the day in canopy sections aligned to cardinal directions.Results show that hazelnut trees rapidly reduced leaf stomatal conductance when the vapor pressure deficit increased to 2 and 2.5 kPa during the diurnal cycle in both irrigated and rainfed trees, even with good water availability. This suggests leaf stomatal conductance can be an efficient and effective early indicator of stress. In addition, results suggest that stomatal conductance should be measured on leaves on the west and north aspects of the canopy, where they showed lowest and highest values respectively. Leaf and stem water potential values increased during the measurement period and show a strong correlation, but their mean values do not show statistically significant differences between treatments. In Willamette valley conditions, stomatal conductance provided earlier indication of stress than water potential. The results obtained are of methodological importance for the future design of experimental plans.

ABSTRACTDiurnal patterns of hydraulic conductance of the leaf lamina (Kleaf) were monitored in a field‐grown tropical tree species in an attempt to ascertain whether the dynamics of stomatal conductance (gs) and CO2 uptake (Aleaf) were associated with short‐term changes in Kleaf. On days of high evaporative demand mid‐day depression of Kleaf to between 40 and 50% of pre‐dawn values was followed by a rapid recovery after 1500 h. Leaf water potential during the recovery stage was less than −1 MPa implying a refilling mechanism, or that loss of Kleaf was not linked to cavitation. Laboratory measurement of the response of Kleaf to Ψleaf confirmed that leaves in the field were operating at water potentials within the depressed region of the leaf ‘vulnerability curve’. Diurnal courses of Kleaf and Ψleaf predicted from measured transpiration, xylem water potential and the Kleaf vulnerability function, yielded good agreement with observed trends in both leaf parameters. Close correlation between depression of Kleaf, gs and Aleaf suggests that xylem dysfunction in the leaf may lead to mid‐day depression of gas exchange in this species.

Trends in leaf water, osmotic, and turgor potentials of cotton (Gossypium hirsutum L., cv. ‘Dunn 56C’) and sorghum (Sorghum bicolor L. Moench, cv. ‘RS671’) were monitored on both a seasonal and diurnal basis. The effects of differential soil water availability on leaf water potential components were examined in order to ascertain the differences in the water relations of these two species.Decreasing availability of soil water was responsible for decreased morning and afternoon leaf water potentials in sorghum and cotton. The magnitude of degression in leaf water potential was greater in cotton than in sorghum at equivalent soil water potentials. Decreasesin osmotic potentials maintained positive turgor in both species when sufficient soil water was available. However, as water stress increased, turgor potentials became zero due to the failure of osmotic potentials to decrease more than water potentials.Diurnal changes in water potential components were distinctly different for each species. Leaf water potentials of sorghum came into approximate equilibrium with soil water potential in the early morning, whereas leaf water potentials of cotton did not. Concomitant changes in leaf osmotic potentials on a diurnal basis resulted in specific trends of increasing turgor in sorghum, while anomalous fluctuations were evident in cotton leaf turgor potentials.The relationship between leaf water potential and relative water content was determined for each species. The change in relative water content per unit change in leaf water potential was greater in cotton than in sorghum.Drought tolerance of these two species appears to be dependent on species speciIic relationships in leat water potential components.

SummaryFor many field-grown crops, including sugar beet, there is little information on the seasonal changes in leaf water potential and its components as the soil dries. Therefore, seasonal changes in leaf water, osmotic and turgor potentials of sugar beet were measured in two seasons, in crops that experienced differing degrees of soil moisture stress. In 1983 potentials of crops exposed to early and late droughts were compared with those of irrigated crops, and in 1984 measurements were made in a non-irrigated crop. In the irrigated crop the midday leaf water potential changed little during the season, except in response to fluctuating evaporative demand. In the drought and non-irrigated treatments there was a sharp fall in leaf water potential as soon as the soil water potential decreased. The size of the midday leaf water potential was primarily determined by soil dryness. However, the leaf water potential did not decrease below about — 1·5 MPa in either year. The leaf osmotic potential declined at the same time as the leaf water potential, but the extent to which this happened differed in the two years. Only in the 1984 non-irrigated crop did the osmotic potential continue to decrease as the soil dried, suggesting that osmotic adjustment had taken place in 1984 but not in 1983. Thus higher turgor was maintained in the 1984 crop than in the 1983 drought-affected crops. Some turgors were recorded as apparently negative in 1983.Since the leaf water potential declined to a minimum of about — 1·5 MPa, the soil water potential minima were also about — 1·5 MPa. However, deeper soil was not dried to this extent, suggesting that the extra resistance for water uptake from deep soil was limiting or the rooting density was too low.The pattern of recovery of leaf water potential overnight suggested that the rhizosphere resistance to water movement was small, even as the soil dried. However, measurement of stem water potentials in 1984 indicated that a significant resistance to water flow existed within the aerial part of sugar beet plants. This shows that the use of the water potential in leaves as an estimate of that in stems or roots can be misleading.

Leaf gas exchange, water potential, and specific leaf area of two tropical semi-deciduous tree species, Brosimum lactescens S. Moore and Tovomita schomburgkii Planch & Triana, were quantified to establish how these properties were affected by seasonal variations in rainfall and leaf canopy position. The study was conducted at a site near Sinop Mato Grosso, Brazil, which is located within the ecotone of savanna and tropical rain forest. Both species exhibited significant declines in leaf water potential (ΨL), specific leaf area, area- and mass-based light saturated photosynthesis and dark respiration, and maximum stomatal conductance during the dry-season, suggesting that leaf structural properties and gas exchange are significantly altered by drought that develops during the 4-month dry season. Internal leaf CO2 concentrations (Ci) were consistently lower during the dry season suggesting that the decline in maximum photosynthesis was due in part to a decline in stomatal conductance. However, seasonal variations in leaf gas exchange were larger for upper-canopy leaves, indicating an important interaction between drought stress and canopy position. The seasonal variation in leaf gas exchange and morphology was presumably due to a combination of drought stress and leaf lifespan. The results of this study suggest that drought has important implications for the leaf physiology and morphology of semi-deciduous Amazonian forest trees.

Hydraulic characteristics and water relations of net house-grown bell pepper as affected by irrigation regimes in a Mediterranean climate

PDF HTML阅读 XML下载 导出引用 引用提醒 平潭岛典型海岸草丛沙堆植物群落水势日变化特征及其影响因素 DOI: 10.5846/stxb201411172277 作者: 作者单位: 中山大学地理科学与规划学院,中山大学地理科学与规划学院,中山大学地理科学与规划学院,中山大学地理科学与规划学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41101011,41371030);中央高校基本科研业务费专项资金(121gpy15) Diurnal variations of water potential and its influencing factors in typical plant communities on coppice dunes of pingtan island Author: Affiliation: School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:水势是反映植物受到环境胁迫的重要指标之一,可用来确定其受胁迫的程度和适应能力大小。以福建省平潭岛海岸典型沙生植物老鼠艻(Spinifex littoreus)形成的草丛沙堆为研究对象,选取晴朗无云的天气,采用PSYPRO水势测量系统对其植物叶、茎水势及其所形成的沙堆土壤水势进行测定,同时采用HUMIPORT10手持式温湿度计对当日的气象要素进行同步观测。结果表明:(1)老鼠艻的叶水势呈现出与早晚高午间低相反的反梯度现象,叶、茎水势的日变化均表现为"M"型变化趋势,除18:00后,其它时间均表现为叶片水势下降、茎干水势上升,并且发现叶、茎水势的变化趋势存在位相后移现象;(2)老鼠艻的叶、茎水势在10:00时差异达到最大的0.65MPa,且茎水势高于叶水势,在14:00左右,植物茎水势出现低于叶水势的反常现象,在18:00时叶、茎水势趋于相同;(3)除表层30cm外,其它层土壤水势日变化特征总体表现为从早晨开始下降,14:00达到最低,但总体变化不明显;(4)随着深度增加,草丛沙堆土壤水势呈现为依次增加的趋势,但80cm以下土壤水势变化不显著(P > 0.1);(5)叶水势与大气水势具有较好的相关性,且变化显著(P < 0.1),与茎水势及浅层土壤水势有一定相关性,但变化不显著(P > 0.1),与50cm以下土壤水势均无相关性。 Abstract:Water potential is one of the most important factors that reflect environmental stress on plants, and can be used to identify the level of stress a plant experiences and its adaptation ability. This study focused on the coppice dunes formed by the psammophyte Spinifex littoreus on Pingtan Island, Fujian province. The PSYPRO Water Potential System was used to determine the water potential of the leaves, stems, and soil, and a HUMIPORT10 hand-held hygrometer was used to simultaneously measure the meteorological variables on cloudless, sunny days. Spinifex littoreus showed an opposite pattern of leaf water potential, which is in contrast to the normal phenomenon of increased leaf water potential in the morning and evening compared to that at midday. The diurnal variations of leaf and stem water potential all demonstrated an 'M’ curve pattern, indicating a decrease of leaf water potential and increase of stem water potential in daytime, until 18:00. Furthermore, we found that the changes of leaf water potential occurred later than those of stem water potential. The biggest discrepancy between stem and leaf water potential, reaching 0.65MPa, appeared at 10:00, when stem water potential was higher than leaf water potential. At about 14:00, an abnormal phenomenon appeared, in which leaf water potential was higher than stem water potential, but at about 18:00, leaf and stem water potential tended to be the same. With the exception of soil water potential at 30cm, the diurnal variation of soil water potential showed a decrease starting in the morning, which reached the minimum at 14:00; however, this tendency was not statistically significant(P > 0.1). With increasing depth, the soil water potential showed a tendency to increase, but this trend disappeared below a depth of 80cm. Strong correlations and significant changes (P < 0.1) in water potential were observed between the atmosphere water potential and leaf. Leaf, stem, and 30-cm-deep soil water potential showed some correlations, but the variations were not statistically significant (P > 0.1). Leaf water potential was not correlated with the water potential of soil at other depths. 参考文献 相似文献 引证文献

Drought and salt stress is the major constrains to crop productivity. However, resistant genotypes improve their physiological mechanisms to cope with these stresses. In this study, we have investigated the influences of drought and salt stress on dry weight, leaf osmotic potential, leaf water potential, leaf temperature and stomatal conductance in sensitive and resistant melon genotypes. Four melon genotypes (sensitive, CU 40 and CU 252; resistant CU 196 and CU 159) were grown in a mixture of peat:perlite of 2:1 ratio in growth chamber. Salt and drought stresses were observed in 30 days old melon plants. In order to perform salinity stress, 200 mM NaCI was used. The drought stress was achieved by decreasing irrigation water gradually and finally irrigation was completely stopped. The plants were subjected to the salt and drought stresses for 12 days. At the end of the experiment; shoot dry weight, osmotic potential, leaf water potential and stomatal conductance were lower in salt and drought-sensitive genotypes (CU 40 and CU 252) than the resistant ones (CU 159 and CU 196). The leaf temperature was increased under stress conditions in melon genotypes. The results showed that resistant melon genotypes have more efficient stress protection mechanisms to survive under salinity and drought conditions.

The influence of drought on stomatal conductance and water potential of peach trees growing in the field

A 3-D functional-structural grapevine model that couples the dynamics of water transport with leaf gas exchange.

A reduction in leaf stomatal conductance (g) with increasing leaf-to-air difference in water vapour pressure (D) is nearly ubiquitous. Ecological comparisons of sensitivity have led to the hypothesis that the reduction in g with increasing D serves to maintain leaf water potentials above those that would cause loss of hydraulic conductance. A reduction in leaf water potential is commonly hypothesized to cause stomatal closure at high D. The importance of these particular hydraulic factors was tested by exposing Abutilon theophrasti, Glycine max, Gossypium hirsutum and Xanthium strumarium to D high enough to reduce g and then decreasing ambient carbon dioxide concentration ([CO2]), and observing the resulting changes in g, transpiration rate and leaf water potential, and their reversibility. Reducing the [CO2] at high D increased g and transpiration rate and lowered leaf water potential. The abnormally high transpiration rates did not result in reductions in hydraulic conductance. Results indicate that low water potential effects on g at high D could be overcome by low [CO2], and that even lower leaf water potentials did not cause a reduction in hydraulic conductance in these well-watered plants. Reduced g at high D in these species resulted primarily from increased stomatal sensitivity to [CO2] at high D, and this increased sensitivity may mediate stomatal responses to leaf hydraulics at high D.

The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψleaf), leaf hydraulic conductance (Kleaf), and stomatal conductance (gs), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (ΨPD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (ΨMD) reduced by 40.71% and 43.20%, Kleaf reduced by 64.80% and 65.61%, and gs reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although gs showed a significant difference between M and L, Ψleaf and Kleaf did not show significant differences between these treatments. The maximum carboxylation rate (Vcmax) and maximum electron transfer rate (Jmax) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P50) under L was not significantly reduced. The gs was positively correlated with ΨMD and Kleaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between gs and Kleaf was observed, with rapid and linear reduction in gs occurring only when Kleaf fell below 8.70 mmol m-2 s-1 MPa-1. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions.

Sap flux density in branches, leaf transpiration, stomatal conductance and leaf water potentials were measured in 16-year-old Quercus suber L. trees growing in a plantation in southern Portugal to understand how evergreen Mediterranean trees regulate water loss during summer drought. Leaf specific hydraulic conductance and leaf gas exchange were monitored during the progressive summer drought to establish how changes along the hydraulic pathway influence shoot responses. As soil water became limiting, leaf water potential, stomatal conductance and leaf transpiration declined significantly. Predawn leaf water potential reflected soil water potential measured at 1-m depth in the rhizospheres of most trees. The lowest predawn leaf water potential recorded during this period was -1.8 MPa. Mean maximum stomatal conductance declined from 300 to 50 mmol m(-2) s(-1), reducing transpiration from 6 to 2 mmol m(-2) s(-1). Changes in leaf gas exchange were attributed to reduced soil water availability, increased resistances along the hydraulic pathway and, hence, reduced leaf water supply. There was a strong coupling between changes in soil water content and stomatal conductance as well as between stomatal conductance and leaf specific hydraulic conductance. Despite significant seasonal differences among trees in predawn leaf water potential, stomatal conductance, leaf transpiration and leaf specific hydraulic conductance, there were no differences in midday leaf water potentials. The strong regulation of changes in leaf water potential in Q. suber both diurnally and seasonally is achieved through stomatal closure, which is sensitive to changes in both liquid and vapor phase conductance. This sensitivity allows for optimization of carbon and water resource use without compromising the root-shoot hydraulic link.

Leaf hydraulics, gas exchange and carbon storage in Pinus edulis and Juniperus monosperma, two tree species on opposite ends of the isohydry-anisohydry spectrum, were analyzed to examine relationships between hydraulic function and carbohydrate dynamics. Leaf hydraulic vulnerability, leaf water potential (Ψl ), leaf hydraulic conductance (Kleaf ), photosynthesis (A), stomatal conductance (gs) and nonstructural carbohydrate (NSC) content were analyzed throughout the growing season. Leaf hydraulic vulnerability was significantly lower in the relatively anisohydric J. monosperma than in the more isohydric P. edulis. In P. edulis, Ψl dropped and stayed below 50% loss of leaf hydraulic conductance (P₅₀) early in the day during May, August and around midday in September, leading to sustained reductions in Kleaf . In J. monosperma, Ψl dropped below P₅₀ only during August, resulting in the maintenance of Kleaf during much of the growing season. Mean A and gs during September were significantly lower in P. edulis than in J. monosperma. Foliar total NSC was two to three times greater in J. monosperma than in P. edulis in June, August and September. Consistently lower levels of total NSC in P. edulis suggest that its isohydric strategy pushes it towards the exhaustion of carbon reserves during much of the growing season.