Twig Water Potential Research Articles

Exploring water relations and phenological traits of Betula utilis (D. Don) in western Himalayan treeline ecotone

Betula utilis exhibits intriguing characteristics and interactions with its environment and has specific adaptations that enable it to thrive in various water conditions. Drought has a prominent role in influencing the growth and development of vegetation, while temperature serves as a crucial determinant of species distribution in high-altitude environments. The investigation was centered on the eco-physiological dimension of B. utilis in areas near the treeline. Across different seasons, sites, and years, the most negative pre-dawn twig water potentials (ΨPD) and mid-day twig water potentials (ΨMD) were − 0.81 and − 1.24 MPa, respectively. The highest seasonal change (ΔΨ) in twig water potential (Ψtwig) was in the post-monsoon season. Osmotic potential at full turgor (Ψπ100) declined by − 0.66 MPa and osmotic potential at zero turgor (Ψπ0) declined by − 1.07 MPa. The highest leaf conductance (gw) of 380.26 mmol m−2 s−1 was measured in the afternoon. During the initiation of flowering, ΨPD of the twig was − 0.72 MPa and gradually rose to − 0.17 MPa by the end of the flowering period. This study provides key insight into the Ψ dynamics, leaf conductance, and phenology of B. utilis, highlighting its adaptation to changing environmental conditions and the need for effective management strategies to ensure the resilience and conservation of this Critically Endangered species.

Twenty years of irrigation acclimation is driven by denser canopies and not by plasticity in twig- and needle-level hydraulics in a Pinus sylvestris forest.

Climate change is predicted to increase atmospheric vapor pressure deficit, exacerbating soil drought, and thus enhancing tree evaporative demand and mortality. Yet, few studies have addressed the longer-term drought acclimation strategy of trees, particularly the importance of morphological versus hydraulic plasticity. Using a long-term (20 years) irrigation experiment in a natural forest, we investigated the acclimation of Scots pine (Pinus sylvestris) morpho-anatomical traits (stomatal anatomy and crown density) and hydraulic traits (leaf water potential, vulnerability to cavitation (Ψ50), specific hydraulic conductivity (Ks), and tree water deficit) to prolonged changes in soil moisture. We found that low water availability reduced twig water potential and increased tree water deficit during the growing season. Still, the trees showed limited adjustments in most branch-level hydraulic traits (Ψ50 and Ks) and needle anatomy. In contrast, trees acclimated to prolonged irrigation by increasing their crown density and hence the canopy water demand. This study demonstrates that despite substantial canopy adjustments, P. sylvestris may be vulnerable to extreme droughts because of limited adjustment potential in its hydraulic system. While sparser canopies reduce water demand, such shifts take decades to occur under chronic water deficits and might not mitigate short-term extreme drought events.

Stomatal, mesophyll and biochemical limitations to photosynthesis and their relationship with leaf structure over an elevation gradient in two conifers.

Photosynthetic responses across complex elevational gradients provides insight into fundamental processes driving responses of plant growth and net primary production to environmental change. Gas exchange of needles and twig water potential were measured in two widespread coniferous tree species, Pinus contorta and Picea engelmannii, over an 800-m elevation gradient in southeastern Wyoming, USA. We hypothesized that limitations to photosynthesis imposed by mesophyll conductance (gm) would be greatest at the highest elevation sites due to higher leaf mass per area (LMA) and that estimations of maximum rate of carboxylation (Vcmax) without including gm would obscure elevational patterns of photosynthetic capacity. We found that gm decreased with elevation for P. contorta and remained constant for P. engelmannii, but in general, limitation to photosynthesis by gm was small. Indeed, estimations of Vcmax when including gm were equivalent to those estimated without including gm and no correlation was found between gm and LMA nor between gm and leaf N. Stomatal conductance (gs) and biochemical demand for CO2 were by far the most limiting processes to photosynthesis at all sites along the elevation gradient. Photosynthetic capacity (A) and gs were influenced strongly by differences in soil water availability across the elevation transect, while gm was less responsive to water availability. Based on our analysis, variation in gm plays only a minor role in driving patterns of photosynthesis in P. contorta and P. engelmannii across complex elevational gradients in dry, continental environments of the Rocky Mountains and accurate modeling of photosynthesis, growth and net primary production in these forests may not require detailed estimation of this trait value.

海拔高度对中国沙棘水碳代谢和生长的影响——以关帝山区为例

PDF HTML阅读 XML下载 导出引用 引用提醒 海拔高度对中国沙棘水碳代谢和生长的影响——以关帝山区为例 DOI: 10.5846/stxb202111193260 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 山西省重点研发计划项目（201903D221051）；山西省自然科学基金项目（2019D211360）；北方功能油料树种培育与研发山西省重点实验室（201805D111010） Effects of altitude on water and carbon metabolism and growth of hippophae rhamnoides in Guandi Mountain Author: Affiliation: 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:海拔是影响中国沙棘自然分布和生长的的重要环境因子，水分代谢和碳代谢的平衡是植物存活和生长的基础，研究海拔对中国沙棘的水碳代谢和生长的影响有利于全面了解中国沙棘对海拔高度的适应性及其生理机制。以山西西部关帝山地区野生中国沙棘为研究对象，测定了海拔1100-2100 m的中国沙棘雌株在6月和8月的小枝正午水势、枝条导水损失率、枝条导管直径和导管密度、光合作用、不同部位非结构性碳水化合物（NSC）浓度，同时测定了不同海拔沙棘的株高和冠幅。结果表明：随着海拔的升高，6月和8月的土壤含水量均呈增加趋势；小枝正午水势先升高后降低；枝条导水损失率在6月先降低后升高；随着海拔的升高沙棘的导管直径没有显著性变化，但导管密度、枝条最大比导水率、叶面积呈现先升高后降低的趋势。随着海拔的升高6月和8月光合速率均呈增加趋势；根和叶NSC含量没有较大幅度变化；随着海拔高度的增加中国沙棘树高和冠幅均呈现先增加后降低的趋势。以上结果表明：低海拔（1100-1300 m）和高海拔（1900-2100 m）中国沙棘生长均受到一定程度的抑制，在低海拔主要受干旱胁迫的影响，高海拔对中国沙棘的生长的抑制作用体现在低温引起的水分状况变差、生长季缩短和低温抑制树木的生长。 Abstract:Altitude is an important environmental factor that affects Chinese seabuckthorn (Hippophae rhamnoides L. subsp. sinensis Rousi) distribution and growth. The balance of water metabolism and carbon metabolism is the basis of plant survival and growth. Studies about the effect of altitude on water-carbon metabolism and growth of Chinese seabuckthorn will contribute to fully understanding its adaptability and physiological mechanism to altitude. In this study, wild Chinese seabuckthorn growing in Guandi Mountain area of western Shanxi Province was used as the study object. Twig water potential, branch percentage loss of conductivity (PLC), photosynthesis and nonstructural carbohydrate (NSC) concentration of female seabuckthorn plants at elevation1100 m to 2100 m were measured in June and August, and plant height and crown width were also measured at different elevations. The results showed that with the elevation increasing, the soil water content increased in both June and August, and the midday twig water potential increased first and then decreased. The branch PLC decreased first and then increased in June.With the increase of altitude, the branch vessel diameter did not change significantly, but the vessel density, branch maximum specific water conductivity and leaf area increased first and then decreased. And the net photosynthetic rate increased in June and August. There was no significant change of NSC content in both roots and leaves. With the increase of altitude, both tree height and crown width increased first and then decreased. The above results suggested that the growth of seabuckthorn was inhibited to some extent at both low altitude (1100-1300 m) and high altitude (1900-2100 m). Seabuckthorn at low altitude was mainly affected by drought stress. And the growth inhibition at high altitude was reflected in the poor water status resulting from low temperature, shortened growing season and the inhibition of low temperature on tree growth. 参考文献 相似文献 引证文献

Effects of Water Deficits on Prosopis tamarugo Growth, Water Status and Stomata Functioning.

The effect of water deficit on growth, water status and stomatal functioning of Prosopis tamarugo was investigated under controlled water conditions. The study was done at the Antumapu Experiment Station of the University of Chile. Three levels of water stress were tested: (i) well-watered (WW), (ii) medium stress intensity (low-watered (LW)) and (iii) intense stress (non-watered (NW)), with 10 replicates each level. All growth parameters evaluated, such as twig growth, specific leaf area and apical dominance index, were significantly decreased under water deficit. Tamarugo twig growth decreased along with twig water potential. The stomatal conductance and CO2 assimilation decreased significantly under the water deficit condition. Tamarugo maintained a high stomatal conductance at low leaf water potential. In addition, tamarugo reduced its leaf area as a strategy to diminish the water demand. These results suggest that, despite a significant decrease in water status, tamarugo can maintain its growth at low leaf water potential and can tolerate intense water deficit due to a partial stomatal closing strategy that allows the sustaining of CO2 assimilation in the condition of reduced water availability.

A field experiment to determine the effect of dry-season irrigation on vegetative and reproductive traits in the wet-deciduous tree Bonellia nervosa

AbstractSeasonally dry tropical forests (SDTFs) stand out by the diversity of phenological patterns used by plants to deal with dry periods. Although the predominant phenological pattern is dry deciduousness, in Mesoamerican SDTFs the heliophilous tree species Bonellia (formerly Jacquinia) nervosa displays an unusual inverted leaf phenology, producing and holding leaves through the dry season while becoming deciduous in the rainy season. Applying a dry season irrigation field experiment (no water, low watering, high watering), we studied the consequences of contrasting water availability from a phenological plasticity response perspective. Contrary to our expectations, our results show no effect of irrigation treatment on leaf phenology. In addition, mid-day twig water potential showed no significant differences across treatments, but reproductive phenological responses varied among treatments: canopy flowering per cent decreased gradually until the beginning of the wet season in all treatments; meanwhile canopy fruit per cent showed a significant decline under low irrigation. Finally, non-structural carbohydrate concentration (starch) was significantly higher in the high irrigation treatment. Our results showed that inverted leaf phenology remains unaffected regardless of supplemental water availability, and suggest a reallocation of non-structural carbohydrates to fruits and seeds in high-irrigation treatments. Given the current and expected increase in extreme drought events, investigations on the responses of trees of different phenologies, including those of inverted leafing such as Bonellia nervosa, are warranted.

Influence of tree water potential in inducing flowering in Rhododendron arboreum in the central Himalayan region

Rise in temperature has been reported as the principal cause of variation in flowering phenology in several tree species around the globe. In this study, we hypothesized that not only temperature but also rainfall periodicity, soil moisture and the related changes of twig water potential (ψ) in winter and early spring are important drivers of bud expansion and flowering in Rhododendron arboreum in central Himalayas. To this purpose, phenological and physiological variables (flowering time, flower bud size and twig water potential) were monitored over two years in a wild population of R. arboreum (Uttarakhand, India) and related with environmental variables (rainfall, soil moisture and temperature). Results showed that a rise in twig ψ to -0.7MPa, one week after moderate winter precipitation resulted in flower bud enlargement. In both years flowering was triggered after twig ψ reached the threshold of -0.5 Mpa, though the starting date differed between years. Floral bud size was correlated positively with twig ψ (r = 0.43, df =162, p < 0.001) and soil moisture (r = 0.61, df = 71, p < 0.001), while temperature did not influence flower bud size, soil moisture and twig ψ. Flower bud size increment was related with increase in twig ψ and soil moisture. Based on our results, we concluded that water availability plays an important role in inducing flowering in R. arboreum.

风对黄花蒿水力学性状和生长的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 风对黄花蒿水力学性状和生长的影响 DOI: 10.5846/stxb201410071963 作者: 作者单位: 山西农业大学林学院,中国林业科学研究院林业新技术所,山西农业大学林学院,山西农业大学林学院,中国林业科学研究院林业新技术所,中国林业科学研究院林业新技术所 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级公益科研院所基本业务专项资金(CAFINT2010K09);山西农业大学博士启动基金(2013YJ19) Effects of wind on hydraulic properties and growth of Artemisia annua Linn Author: Affiliation: College of Forestry, Shanxi Agricultural University,,,,,Chinese Academy of Forestry, Institute of New Forestry Technology 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:吹风会影响到植物的水力学结构、光合作用、生物量分配以及植物的力学性状,研究风对植物的综合影响有助于深入了解植物应对风胁迫的响应机制。以黄花蒿为研究对象,每天吹风4h,风速为5m/s,吹风处理60d,测定了风吹条件下黄花蒿的水力学特征、光合作用、生物量分配和茎干力学特性。结果表明:在风吹条件下,黄花蒿正午水势显著低于对照,茎干导水损失率(PLC)增加了16%,最大光合速率仅为对照的62%,气孔导度为对照的55%。在试验结束时风吹植株株高仅为对照的68%,但基茎显著高于对照,同时风吹显著降低了黄花蒿的总生物量,但根冠比显著高于对照,风吹显著减小了茎导管直径和导管密度,风吹植物导管直径和导管密度分别为对照的77%和55%,同时,风吹植物茎干导水率显著低于对照,但茎干的抗弯刚度显著高于对照。以上结果表明风吹抑制了植物的水分输导能力,导致叶片水分匮缺,限制了植物的光合作用。风吹增加了茎干的力学稳定性,但同时降低了茎干的水分输导能力,这是植物茎在力学性状和水分输导之间的权衡。这种改变有利于在有风条件下维持植物的力学稳定性,但同时降低了水分输导能力。 Abstract:Wind is one of the most ubiquitous ecological factors affecting hydraulic properties, photosynthesis, mechanical properties and biomass distribution. In spite of more than two centuries of research, the response mechanism of plants to wind remains poorly understood. A major difficulty with understanding the effects of wind is that it affects both water balance by blowing the air and mechanical properties by wind drag. Yet it is uncertain that what patterns wind blowing influences stem hydraulic structure of plants. The relation between stem hydraulic structure and mechanical properties imposed by wind is rarely studied. Thus, study on comprehensive effects of wind on plants can contribute to understanding plant response mechanism under wind stress. In this study, Artemisia annua was used as material to evaluate the impacts of wind on plants. The wind-treated plants were blowed four hours everyday with wind speed of 5m/s for 60 days. We comparatively measured hydraulic properties, photosynthesis, mechanical properties of stem and biomass distribution of A. annua between wind blowing treatment and no wind control. The results showed that wind blowing significantly reduced midday twig water potential, and wind blowing significantly increased stem percent loss in conductivity (PLC), with PLC being 60.6% and 44.3% for wind blowing treatment and control respectively. The maximum net photosynthetic rate and stomatal conductance of plants subjected to the wind were also reduced, which was only 62% and 55% of the control respectively. The height of A. annua subjected to wind blowing was only 68% of the control at the end of the experiment, while the stem taper of wind blowing treatment was markedly higher than that of control. Total biomass was significantly decreased by the wind, with total biomass being (44.0±6.03) g and (32.8±7.01) g for control and wind blowing treatment respectively, while root/shoot ratio was significantly increased. However, flexural stiffness (EI) of treated plants was considerably higher compared to the control. Meanwhile, wind blowing reduced both stem vessel diameter and vessel density, with stem vessel diameter and vessel density being 77% and 55% as much as that of control respectively. Those results indicated that wind blowing limited the ability of plant hydraulic conductivity, leading to leaf water deficits through increasing cavitation embolism and decreasing the abality of hydraulic conductivity of stem, which limited plant photosynthesis, resulting in the reduction of total biomass. Wind blowing increased the mechanical stability of the stem through increasing thickness of stem and supporting tissue proportion, but decreased the hydraulic conductivity, which was a trade-off between mechanical properties and water transport in stem. These changes were beneficial to maintaining mechanical stability for plants subjected to the wind, but the ability of water transport was lowed at the same time. 参考文献 相似文献 引证文献

Disturbances in European beech water relation during an extreme drought

In the context of a probable increase in intensity and frequency of extreme summer drought events, a better understanding of the key processes involved in water relations is needed to improve the theoretical foundations of predictive process-based models. This paper aims to analyse how temperate deciduous trees cope with water shortage. The exceptional summer drought of 2003 in Europe provided an opportunity to monitor stomatal conductance and twig water potential in European beech (Fagus sylvatica L.) at predawn and midday and to analyse variations with respect to leaf height within the canopy. By comparing our field measurements of twig water potential to values found in the literature, we confirmed the strong impact of soil water shortage on crown water relations. This paper shows that (1) the vertical gradient of stomatal conductance within the crown disappeared under extreme soil water depletion; (2) at maximum drought intensity, predawn twig water potential (ψ pd) reached −2.3 MPa at a height of 14 m in the crown and −2.0 MPa at a height of 10 m. The significant differences in ψ pd between the two measurement heights in the canopy may be due to night transpiration; (3) there was a close relationship between predawn twig water potential and relative extractable soil water; (4) as drought conditions intensified, there was a close relationship between canopy radiation interception and predawn water potential, as estimated daily from relative extractable soil water.

Oak restoration in water-limited pine plantations: interactive effects of overstory light interception and water availability on understory oak performance

Oak regeneration within pine monocultures is an opportunity to diversify forest structure. We examined the relationships between overstory (Pinus brutia) light interception and understory oak (Quercus ithaburensis) performance in water-limited forests. The study was performed in a mature pine plantation in Mediterranean Israel. Twenty-year-old oaks differing in location with respect to pine overstory and representing a gradient of light availability, such as open space (irradiance 100 %), interface (17–77 %), and understory (14–23 %), were monitored. Photosynthetic photon flux density (PPFD), leaf gas exchange, and twig water potential (TWP) were measured during the growth season under increasing drought stress. Predawn TWP decreased sharply from early to late spring and was positively related to irradiance during mid-spring only. Predawn to midday TWP gradient was positively related to irradiance mostly so during mid-spring. Daily averages of stomatal conductance (gs), net carbon assimilation rate (A), and transpiration rate (E) were highest in early spring and decreased gradually toward late spring. They were positively related to irradiance though this relationship became less pronounced from early to late spring. Oak height and stem basal area were positively related to irradiance. A/gs ratio was positively related to irradiance throughout the entire growth season. It increased from early to mid-spring but decreased toward late spring. A/PPFD ratio decreased from early to late spring showing a negative relationship with irradiance. We concluded that light availability was mainly responsible for spatial variation in oak performance and proposed that small-scale overstory gaps aiming for direct sunlight exposure during early spring should achieve maximum understory oak performance with minimal pine removal.

Effects of soil thickness on dry-season water relations and growth in Robinia pseudoacacia

Aims Our main purposes were to explore effects of soil thickness on the soil water carrying capacity of black locust (Robinia pseudoacacia) forests and to investigate the role of soil moisture in causing decline of black locust forests in regions of northern China in recent years. Methods We measured soil moisture, pre-dawn twig water potential and gas exchange of black locust in the dry season and wet season. We also measured stable carbon isotope ratio (δ13C) of leaf, leaf morphology and growth of black locust. Combined with the differential response in the dry season and wet season, we analyzed the relationship between water status of black locust and the soil thickness. Important findings In the dry season, the twig pre-dawn water potential and soil moisture significantly declined with decreased soil thickness, and the net photosynthetic rate and stomatal conductance of black locust also decreased. But there were no significant differences in these indexes in the wet season. Average soil moisture in the dry season was only 60% that in the wet season. With decrease in soil thickness, δ13C increased, area of leaf decreased and leaf mass per area increased. As a result, tree height and diameter at breast height significantly decreased with decrease in soil thickness. Results revealed that the water status of black locust in the different seasons strongly reflected water supply capacity of the soil, and that thin soil thickness was the main cause for the decline of black locust forests due to low carrying capacity of vegetation caused by inadequate water storage in the dry season.

Root growth dynamics of Aleppo pine (Pinus halepensis Mill.) seedlings in relation to shoot elongation, plant size and tissue nitrogen concentration

Large and high nitrogen (N) concentration seedlings frequently have higher survival and growth in Mediterranean forest plantations than seedlings with the opposite traits, which has been linked to the production of deeper and larger root systems in the former type of seedlings. This study assessed the influence of seedling size and N concentration on root growth dynamics and its relation to shoot elongation in Aleppo pine (Pinus halepensis Mill.) seedlings. We cultivated seedlings that differed in size and tissue N concentration that were subsequently transplanted into transparent methacrylate tubes in the field. The number of roots, root depth, and the root and shoot elongation rate (length increase per unit time) were periodically measured for 10 weeks. At the end of the study, we also measured the twig water potential (ψ) and the mass of plant organs. New root mass at the end of the study increased with seedling size, which was linked to the production of a greater number of new roots of lower specific length rather than to higher elongation rate of individual roots. Neither plant size nor N concentration affected root depth. New root mass per leaf mass unit, shoot elongation rate, and pre-dawn ψ were reduced with reduction in seedling size, while mid-day ψ and the root relative growth rate were not affected by seedling size. N concentration had an additive effect on plant size on root growth but its overall effect was less important than seedling size. Shoot and roots had an antagonistic elongation pattern through time in small seedlings, indicating that the growth of both organs depressed each other and that they competed for the same resources. Antagonism between shoot and root elongation decreased with plant size, disappearing in large and medium seedlings, and it was independent of seedling N concentration. We conclude that root and shoot growth but not rooting depth increased with plant size and tissue N concentration in Aleppo pine seedlings. Since production of new roots is critical for the establishment of planted seedlings, higher absolute root growth in large seedlings may increase their transplanting performance relative to small seedlings. The lack of antagonism between root and shoot growth in large seedlings suggests that these plants can provide resources to sustain simultaneous growth of both organs.

When do nurse plants stop nursing? Temporal changes in water stress levels in Austrocedrus chilensis growing within and outside shrubs

AbstractQuestion: Does the proximity of shrubs affect seasonal water stress of young Austrocedrus chilensis trees (a native conifer of the Austral Temperate Forest of South America) in xeric sites?Location: A. chilensis xeric forest in northwest Patagonia, Argentina.Methods: We examined the dependence of predawn twig water potential on tree development (seedling to adult) and proximity to nurse shrubs during spring and summer. We analysed spatial associations of seedlings, saplings and adult trees with nurse shrubs, and also evaluated if trees affected shrub canopy vitality.Results: Water stress in Austrocedrus trees was affected by shrub presence. Small trees (i.e.&lt;0.5 m in height) growing in the open were most stressed, particularly in summer. Small trees growing within a shrub canopy had low water stress and little change between spring and summer. The opposite trend, however, was true for the medium‐height category (i.e. 0.5‐1.5 m in height); trees in this size category were more stressed when growing within the shrub canopy than in the open. Larger Austrocedrus trees (i.e.&gt;2 m in height) were not affected by shrub presence. Austrocedrus trees were spatially associated with shrubs in all height classes; however, the percentage of living shrub canopy decreased with tree height.Conclusions: In xeric areas of northwest Patagonia, the strength and direction of interactions between A. chilensis and shrubs, in terms of tree water stress, are dynamic and modulated by tree size and environmental conditions. Overall, positive effects of shrubs on early developmental stages appear to be more important than subsequent negative interactions, since nursing effects could generate a spatial association of shrubs and Austrocedrus trees that persists through later successional stages. These findings shed light on mechanisms behind successional changes, and have important conservation and management implications.

Maximum height in a conifer is associated with conflicting requirements for xylem design

Despite renewed interest in the nature of limitations on maximum tree height, the mechanisms governing ultimate and species-specific height limits are not yet understood, but they likely involve water transport dynamics. Tall trees experience increased risk of xylem embolism from air-seeding because tension in their water column increases with height because of path-length resistance and gravity. We used morphological measurements to estimate the hydraulic properties of the bordered pits between tracheids in Douglas-fir trees along a height gradient of 85 m. With increasing height, the xylem structural modifications that satisfied hydraulic requirements for avoidance of runaway embolism imposed increasing constraints on water transport efficiency. In the branches and trunks, the pit aperture diameter of tracheids decreases steadily with height, whereas torus diameter remains relatively constant. The resulting increase in the ratio of torus to pit aperture diameter allows the pits to withstand higher tensions before air-seeding but at the cost of reduced pit aperture conductance. Extrapolations of vertical trends for trunks and branches show that water transport across pits will approach zero at a heights of 109 m and 138 m, respectively, which is consistent with historic height records of 100-127 m for this species. Likewise, the twig water potential corresponding to the threshold for runaway embolism would be attained at a height of approximately 107 m. Our results suggest that the maximum height of Douglas-fir trees may be limited in part by the conflicting requirements for water transport and water column safety.

Expression of OePIP2.1 aquaporin gene and water relations of Olea europaea twigs during drought stress and recovery

AbstractTo investigate the effects of drought and recovery on the transcript level of OePIP2.1 (a PIP2 aquaporin gene) in twigs, 2‐year‐old olive trees were subjected to a drought/rewatering treatment (the irrigation was suspended for a period of 4 weeks and restored for the following 4 weeks). Twig water potential, twig hydraulic resistance and incidence of embolisation in the twig were measured in parallel with gene expression under both drought stress and the following recovery. During drought, a decrease in twig water potential, an increase in twig hydraulic resistance and an increase in the extent of xylem vessel embolisation was observed in parallel with a decrease of aquaporin gene expression. Opposite trends were recorded during rewetting. A speculation on a possible contribution of OePIP2.1 aquaporin to modulate shoot embolism during drought and recovery is proposed.

Isolation and functional characterization of three aquaporins from olive (Olea europaea L.)

To study the molecular bases of water transport in olive we characterized cDNAs from Olea europaea cv "Leccino" related to the aquaporin (AQP) gene family. A phylogenetic analysis of the corresponding polypeptides confirmed that they were part of water channel proteins localized in the plasma membrane and in the tonoplast. The full-length sequences were obtained by RACE-PCR and were named OePIP1.1, OePIP2.1 and OeTIP1.1. The OePIP2.1 and OeTIP1.1 encode functional water channel proteins, as indicated by expression assays in Xenopus laevis oocytes. OePIP1.1 and OePIP2.1 expression levels are high in roots and twigs and low in leaves. The highest hybridization signal of OeTIP1.1 was detected in twigs, while in roots and leaves the expression was low. To investigate the effect of abiotic stress on the transcript level of olive AQP genes, olive trees were subjected to drought treatment and the expression levels of the genes were measured by Northern-blot analysis. The transcript levels of each gene diminished strongly in plants submitted to drought stress, when soil moisture, twig water potential and twig hydraulic conductivity progressively decreased. The downregulation of AQP genes may result in reduced membrane water permeability and may limit loss of cellular water during periods of water stress. A possible role for AQPs on shoot embolism repair is discussed.

Measuring and modelling stomatal conductance and photosynthesis in mature birch in Sweden

Stomatal conductance ( g s), net photosynthesis ( A n) and twig water potential ( Ψ t) were measured in mature silver birch ( Betula pendula) during 3 years in southern Sweden. Measurements from 2 years were used to parameterise three different g s models and measurements from a 3rd year were used to validate these models. Two different multiplicative stomatal models were used. In one of these, the g s response function for the water vapour pressure deficit ( D) was fixed, while in the other the g s sensitivity to D increased with the accumulated time after sunrise with D above a certain threshold value. Furthermore, one combined stomatal-photosynthesis model ( L-model) was used. The L-model was run either by using observations of photosynthesis as input data, or by predicting g s and photosynthesis simultaneously from environmental data. The model used to predict photosynthesis was parameterised from measurements of the photosynthetic responses to the photosynthetically active radiation, CO 2 and temperature. The stomatal response functions of the L-model were parameterised using observations of photosynthesis as input data in order to make them independent of the performance of the photosynthesis model. The difference in model performance between the two multiplicative models was relatively small. The multiplicative stomatal models and the L-model were similarly successful in predicting g s when the L-model was driven by observations of photosynthesis. However, the L-model was considerably less successful when photosynthesis was predicted. Photosynthesis was systematically under- and overestimated at high and low Ψ t, respectively, causing errors in the prediction of g s. In most situations, measurements of photosynthesis are not available and g s must be predicted from environmental data. In such cases, we conclude that the two multiplicative models are more successful in predicting g s in mature silver birch than the combined stomatal-photosynthesis model.

Wood diameter indicates diurnal and long-term patterns of xylem water potential in Norway spruce

The stem diameter of adult Norway spruce trees was measured to see whether changes in xylem water potential lead to detectable radial deformation of the wood. The dendrometers used in these experiments measured only the dimensional changes of the woody cylinder (sap- and heartwood). Wood diameter was measured close to the ground and just below the living crown. After correction for thermal expansion of dendrometers and wood, diurnal variation of wood diameter ranged between 50 and 180 µm. Psychrometric measurements showed that xylem water potential varied in parallel to wood diameter. Diameter changes were always more pronounced at the higher stem position and exhibited a clear diurnal pattern. During the day, wood diameter decreased with increasing vapor pressure deficit and transpiration rate and with decreasing twig water potential. At night, the wood re-expanded but did not always reach the dimension of the previous day. Pre-dawn wood diameter decreased during periods of soil drought, a process which rapidly stopped and reversed after rain events. On several days, oscillation in wood diameter was observed during the mid-day hours. The oscillation had a period of approximately 50 min and showed a phase shift between different stem heights. All observed patterns of wood shrinkage and expansion were consistent with the hypothesis that xylem water tension leads to an elastic contraction of xylem conduits. The results demonstrate that xylem diameter is more suitable than whole-stem diameter for monitoring changes in xylem water potential.

European larch and eastern white pine respond similarly during three years of partial defoliation.

To test whether trees with different leaf life spans respond differently to defoliation, eastern white pine (Pinus strobus L.) and European larch (Larix decidua Mill.) trees (9 years old in 1991) were partially defoliated by hand between July 1 and 10 in 1989, 1990 and 1991. At the end of 1991, trees of both species had received either 0, 1, 2 or 3 years of defoliation. Trees that received only 1 year of defoliation were defoliated in 1989. Variables measured included photosynthesis, twig water potential, leaf mass per area and leaf nitrogen concentration. There were few significant responses to defoliation in any of the three years of treatment in either species, and only the current-year defoliation treatments caused significant responses. Both species had reduced photosynthetic rates and less negative twig water potentials in response to defoliation in 1989. In 1990 and 1991, the defoliation treatments had no significant effect on any of the parameters measured in European larch. In 1990, there was a significant reduction in foliar nitrogen concentration in eastern white pine in response to defoliation in 1990. In 1991, eastern white pine had significantly less negative twig water potentials in response to defoliation in 1991. Leaf mass per area was not affected by defoliation in either species. We conclude that, for European larch and eastern white pine, differences in leaf life span have no effect on leaf- and twig-level responses to defoliation.

Diurnal water relations of beech ( Fagus Sylvatica L.) trees in the mountains of Italy

Trees live in oscillating environments. Daytime light and warm periods alternate with night darkness and cooler temperatures. The adaptation of a tree is explained by its accommodation to such diurnal cycles. These diurnal pulses were monitored and simulated on computer. Summer measurements in Abetone (1230 m above sea level) included continuous registration of air temperature, relative humidity, wind speed, solar radiation and precipitation. Soil water contents were approximated from water balance. The response of a beech tree was measured as diurnal cycles of the twig water potential, stomatal conductance and sap water flow reflecting transpiration rate. All these measured output variables were simulated by a soil-plant-atmosphere-continuum (SPAC) model. Additional diurnal responses of the tree were calculated, such as leaf to air temperature difference, Bowen ratio and pool of water content in the tree. The evaluation of the adaptation was related to the recurrent cycles in diurnal loops, as the time-dependent relationship between the twig water potential and the sap water flow. The daily value of transpiration was 1.3 mm at the end of August. Results from simulation indicate that the model behaves correctly and can be used as a research tool for generating new scientific hypotheses.