Determination of drought tolerance using root activities in Robinia pseudoacacia ''Idaho'' transformed with mtl-D gene

Idaho locust (Robinia pseudoacacia 'Idaho') is an exotic multi-purpose tree used in landscaping, soil and water conservation, fodder sources and others. To improve its drought tolerance for reclaiming arid land, five lines of transformed mtl-D gene, as osmotic regulator in plant cells, have been selected and managed to determine their drought tolerance under experimental conditions.Qualitative and quantitative variables of transformed plants were studied. The critical value of drought tolerance was determined by detecting the 2,3,5-triphenyl tetrazolium chloride (TTC) reductants in roots and soil water content (SWC). The critical value for drought tolerance was SWC 6% while for the control plants the critical SWC was 8%; a moderate level of SWC is 13% and the highest SWC for plant endurance was 18%. The method proved to be reliable and sensitive in the evaluation of drought tolerance for forest trees.     

Determination of drought tolerance using root activities in Robinia pseudoacacia ‘Idaho’ transformed with mtl-D gene

Idaho locust (Robinia pseudoacacia ‘Idaho’) is an exotic multi-purpose tree used in landscaping, soil and water conservation, fodder sources and others. To improve its drought tolerance for reclaiming arid land, five lines of transformed mtl-D gene, as osmotic regulator in plant cells, have been selected and managed to determine their drought tolerance under experimental conditions. Qualitative and quantitative variables of transformed plants were studied. The critical value of drought tolerance was determined by detecting the 2,3,5-triphenyl tetrazolium chloride (TTC) reductants in roots and soil water content (SWC). The critical value for drought tolerance was SWC 6% while for the control plants the critical SWC was 8%; a moderate level of SWC is 13% and the highest SWC for plant endurance was 18%. The method proved to be reliable and sensitive in the evaluation of drought tolerance for forest trees.     

Growth CO2 concentration modifies the transpiration response of Populus deltoides to drought and vapor pressure deficit

Cottonwood (Populus deltoides Bartr. ex Marsh.) trees grown for 9 months in elevated carbon dioxide concentration ([CO2]) showed significant increases in height, leaf area and basal diameter relative to trees in a near-ambient [CO2] control treatment. Sample trees in the CO2 treatments were subjected to high and low atmospheric vapor pressure deficits (VPD) over a 5-week period at both high and low soil water contents (SWC). During these periods, transpiration rates at both the leaf and canopy levels were calculated based on sap flow measurements and leaf-to-sapwood area ratios. Leaf-level transpiration rates were approximately equivalent across [CO2] treatments when soil water was not limiting. In contrast, during drought stress, canopy-level transpiration rates were approximately equivalent across [CO2] treatments, indicating that leaf-level fluxes during drought stress were reduced in elevated [CO2] by a factor equal to the leaf area ratio of the two canopies. The shift from equivalent leaf-level transpiration to equivalent canopy-level transpiration with increasing drought stress suggests maximum water use rates were controlled primarily by atmospheric demand at high SWC and by soil water availability at low SWC. Changes in VPD had less effect on transpiration than changes in SWC for trees in both CO2 treatments. Transpiration rates of trees in both CO2 treatments reached maximum values at a VPD of about 2.0 kPa at high SWC, but leveled off and decreased slightly in both canopies as VPD increased above this value. At low SWC, increasing VPD from approximately 1.4 to 2.5 kPa caused transpiration rates to decline slightly in the canopies of trees in both treatments, with significant (P = 0.004) decreases occurring in trees in the near-ambient [CO2] treatment. The transpiration responses at high VPD in the presence of high SWC and throughout the low SWC treatment suggest some hydraulic limitations to water use occurred. Comparisons of midday leaf water potentials of trees in both CO2 treatments support this conclusion.     

Interactive effects of temperature and precipitation on soil respiration in a temperate maritime pine forest

Soil respiration (SR) was monitored periodically throughout 2001 in a Scots pine (Pinus sylvestris L.) stand located in the Belgian Campine region. As expected for a temperate maritime forest, temperature was the dominant control over SR during most of the year. However, during late spring and summer, when soil water content (SWC) was limiting, SR was insensitive to temperature (Q(10) = 1.24). We observed that during prolonged rain-free periods, when SWC was less than 15% (v/v), SR decreased dramatically (up to 50%) and SWC took over control of SR. During such drought periods, however, rain events sometimes stimulated SR and restored temperature control over SR, even though SWC in the mineral soil was low. We hypothesize that restoration of temperature control occurred only when rain events adequately rewetted the uppermost soil layers, where most of the respiratory activity occurred. To quantify the rewetting capacity of rain events, an index (I(w)) was designed that incorporated rainfall intensity, time elapsed since the last rain event, and atmospheric vapor pressure deficit (a proxy for evaporative water losses). To simulate SR fluxes, a model was developed that included the effects of soil temperature and, under drought and non-rewetting conditions (I(w) and SWC < threshold), an SWC response function. The model explained 95% of the temporal variability in SR observed during summer, whereas the temperature function alone explained only 73% of this variability. Our results revealed that, in addition to temperature and SWC, rain plays a role in determining the total amount of carbon released from soils, even in a maritime climate.     

Drought tolerance of Acacia karroo, a native tree species to South Africa, in Beijing

Acacia karroo is an indigenous, strong drought-tolerant and widely planted tree in South Africa. In order to match the plant with its adaptation to forest sites in China, it is important to know the drought-tolerance of this species under Chinese forest site conditions. Our study was carried out in cinnamon soils in Beijing and with Platycladus orientalis, the most drought-tolerant tree in Beijing, as control. Physiological parameters of young plants of the trees were measured and divided into three groups in response to soil drying. The first group included root activity, ABA content in roots and peroxidase (POD) activity in leaves. Their values changed similarly to those of P. orientalis and dramatically increased to maximum values when the soil water content (SWC) decreased from its normal level of 20% to 7.6% where the three indices decreased dramatically when SWC was reduced further from 7.6%. The second group of parameters included the contents of proline, soluble protein and malondialdehyde (MDA). Their values showed greater variation than those of P. orientalis and significantly increased when SWC decreased from 20% in response to soil drying. However, the proline and soluble protein contents fluctuated in A. karroo at a lower level than those in P. orientalis. In contrast, the content of MDA in A. karroo was much higher than that in P. orientalis which almost did not increase in the drying soil. The third group of parameters consisted of soluble sugar, superoxide dismutase (SOD) and catalase (CAT). These parameters showed greater diversity and fluctuations among the three varieties of A. karroo compared with the control in response to soil drying. These results suggest that A. karroo is characterized as a strong, drought tolerant species in most of physiological parameters but weaker than P. orientalis in membrane lipid antioxidation.     

Revisiting the use of soil water budget assessment to predict site productivity of sessile oak (<Emphasis Type="Italic">Quercus petraea</Emphasis> Liebl.) in the perspective of climate change

Climate change is expected to increase the frequency and severity of drought events over the next few decades in Western Europe. Consequently, there is a crucial need for an efficient tool for field water budget diagnosis to enable forest managers to estimate tree survival and productivity. Robust estimates of water budget using soil and topography were compared for their ability to predict site yield of Quercus petraea (Matt.) Liebl. Site yield was estimated using site index at 100 years. Ninety-nine even-aged high-forest stands located in northern France were investigated. Water budget was estimated by topographic position and soil water capacity (SWC) calculated for different soil depths down to a maximum 2.0 m. (1) Site index predictions improved when calculating SWC for increasing depths until 1.0 m. (2) Site index predictions did not improve when calculating SWC at depths below 1.0 m, thus confirming that the water contained in deep soil layers is not used for tree growth but probably contributes to tree fitness or survival by maintaining a not too negative in-tree water potential. (3) Topographic position was also a predictor of site index in addition to SWC. Practical recommendations for estimating extractable soil water content are given.     

干热河谷几种典型造林树种的水分利用效率研究

干热河谷地区造林成活率低一直是困扰国内学者的难题之一,其中影响其成活的关键因子之一就是土壤水分。进行科学合理的节水灌溉就显得十分必要。相思适宜的土壤含水率（SWC）范围为12％～24％;合欢适宜的土壤含水率（SWC）范围为12％～28％;车桑子适宜的土壤含水率（SWC）范围为10％～26％。在此范围内,水分利用效率较高,光合速率水平也不低,林木能进行正常的生长及结实,不影响产量。植物的抗旱性与水分利用效率没有相关关系。植物的抗旱性强弱与其本身的形态、抗性生理生态特性有关。就本文中所涉及的几个指标来说,得出植物的抗旱性强弱顺序为：新银合欢（Leucaena sp．）〈车桑子（Dodonaea viscose）〈赤桉（Eucalyptus camaldulensis）〈台湾相思（Acacia confusa）;而水分利用效率的顺序则是：相思〈车桑子=桉树〈合欢。     

Responses of Prunus ferganensis,Prunus persica and two interspecific hybrids to moderate drought stress

Prunus ferganensis (Kost. & Riab) Kov. & Kost, a close relative of cultivated peach (Prunus persica (L.) Batsch.), is native to arid regions of central Asia. A distinguishing feature of P. ferganensis is its prominent, elongated, unbranched pattern of leaf venation. To determine whether the long-vein trait could be used as a marker in breeding for drought tolerance, we investigated the association between this trait and the leaf morphological and physiological parameters related to drought response in P. ferganensis, P. persica and two interspecific hybrids, one with the long-vein trait (BY94P7585) and one without (BY94P7589). The four genotypes were grafted onto "Guardian" peach rootstock and half of the plants were assigned to a drought treatment in which irrigation was limited to 25-50% of the evapotranspiration (ET) rate measured in the remaining well-watered plants, which were irrigated to runoff daily. The drought treatment reduced photosynthesis and leaf conductance by 49-83% and reduced total leaf area per plant by 17-24%, but generally did not affect mid-morning leaf water potential. Leaf gas exchange did not differ among genotypes in either treatment. Sorbitol accumulated in mature leaves in response to drought, but neither its amount nor its metabolism varied systematically with climatic adaptation among genotypes. Accumulation of transport sugars was highest in P. ferganensis, indicating that growth reduction may represent an important strategy for coping with drought in this species. Prunus ferganensis and the hybrids had higher ET than P. persica, and seemed to use water opportunistically, maintaining high gas exchange rates and consequently high ET when water was available, and avoiding low water potentials through stomatal closure as soil water declined. Leaf size (cm(2) leaf(-1)) and specific leaf area (cm(2) g(-1) dry mass) were lower in P. ferganensis and the hybrids than in P. persica. We conclude that the long-vein trait is not a reliable marker for drought tolerance, but leaf traits of P. ferganensis such as size and specific leaf area may be useful in P. persica breeding programs targeting drought tolerance.     

Effects of arbuscular mycorrhizal fungi on leaf solutes and root absorption areas of trifoliate orange seedlings under water stress conditions

The effects of the arbuscular mycorrhizal (AM) fungus Glomus mosseae on plant growth, leaf solutes and root absorption area of trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings were studied in potted culture under water stress conditions. Inoculation with G. mosseae increased plant height, stem diameter, leaf area, shoot dry weight, root dry weight and plant dry weight, when the soil water content was 20%, 16% and 12%. AM inoculation also promoted the active and total absorption area of root system and absorption of phosphorus from the rhizosphere, enhanced the content of soluble sugar in leaves and roots, and reduced proline content in leaves. AM seedings had higher plant water use efficiency and higher drought tolerance than non-AM seedlings. Effects of G. mosseae inoculation on trifoliate orange seedlings under 20% and 16% soil water content were more significant than under 12% soil water content. AM infection was severely restrained by 12% soil water content. Thus, effects of AM fungi on plants were probably positively related to the extent of root colonization by AM fungi. The mechanism of AM fungi in enhancing drought resistance of host plants ascribed to greater osmotic adjustment and greater absorption area of root system by AM colonization. __________ Translated from Journal of Plant Physiology and Molecular Biology, 2005, 30(5): 583–588 [译自: 植物生理与分子生物学报, 2005, 30(5): 583–588]     

Soil–water content and air-filled porosity affect height growth of Scots pine in afforested arable land in Finland

We examined the soil–water content (SWC) and air-filled porosity (AFP) of afforested arable land in situ and related them with tree growth, which was expressed as the total length of 5-year-height growth above 2.5 m stem height. A total of 34 randomly selected sites in western Finland afforested with Scots pine (Pinus sylvestris L.) were sampled and SWC was measured using time domain reflectometry (TDR). Increasing AFP up to 30% and correspondingly decreasing SWC significantly increased tree growth while concentrations of foliar nutrients and contents of soil nutrients had no effect. Increasing organic matter content (OMC) and decreasing bulk density (BD) were accompanied by increasing SWC and decreasing AFP in the 0–10 cm soil layer. SWC values above 70% indicated critical AFP below 10%. It was found that 44% of the studied sites had mean AFP lower than 10%. The results obtained indicate that the afforested Finnish arable land with high soil OMC is commonly characterized by high SWC and low soil aeration, which can limit tree growth.     

Effects of drought and canopy ozone exposure on antioxidants in fine roots of mature European beech (Fagus sylvatica)

We quantified ascorbate, glutathione and alpha-tocopherol in fine roots of mature Fagus sylvatica L. under free-air canopy ozone (O(3)) exposure (twice ambient O(3) concentration, 2x[O(3)]) during two growing seasons that differed in the extent of summer drought (exceptional drought year 2003, average year 2004). This design allowed us to test whether O(3) exposure or drought, or both, affected root antioxidants during the growing season. In both years, root ascorbate and alpha-tocopherol showed a similar relationship with volumetric soil water content (SWC): ascorbate concentrations on a root dry mass basis increased from about 6 to 12 micromol g(-1) when SWC dropped from 25 to 20%, and a-tocopherol increased from 100 to 150 nmol g(-1) at SWC values below 20%. Root glutathione showed no relationship with SWC or differences between the dry and the average year, but it was significantly and consistently diminished by 2x[O(3)]. Our results were inconclusive as to whether shoot-root translocation of glutathione or glutathione production in the roots was diminished. Phloem glutathione concentrations in the canopy remained constant, but reduced transport velocity in the phloem and, as a consequence, reduced mass flow of glutathione cannot be ruled out.     

Perspectives in dryland restoration: approaches for climate change adaptation

Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.     

Water stress responses of seedlings of four Mediterranean oak species

Effects of water stress on phenology, growth, stomatal activity and water status were assessed from April to November 1996 in 2-year-old seedlings of Quercus frainetto Ten. (Quercus conferta Kit.), Quercus pubescens Willd., Quercus macrolepis Kotschy (Quercus aegilops auct.) and Quercus ilex L. growing in containers in northern Greece. All four species developed more than 50% of their total leaf area before the beginning of June--an adaptation to arid climates. Well-irrigated plants tended to develop greater individual leaf area, number of leaves per plant, total plant leaf area, height and root:shoot ratios than water-stressed plants, but the difference between treatments was not significant for any parameter in any species. Quercus macrolepis appeared to be the most drought-tolerant of the four species. It maintained the highest number of leaves of the smallest size and increased the proportion of fine roots during drought. In all species, drought caused significant decreases in stomatal conductance and predawn and midday water potentials from mid-July until the end of August, when the lowest soil water content and highest mean daily air temperatures and midday leaf temperatures occurred; however, the responses were species-specific. Among the four species, Quercus macrolepis sustained the highest stomatal conductance despite very low water potentials, thus overcoming drought by means of desiccation tolerance. Quercus ilex decreased stomatal conductance even before severe water stress occurred, thereby avoiding desication during drought. Quercus pubescens had the highest water potential despite a high stomatal conductance, indicating that its leaf water status was independent of stomatal activity. Quercus frainetto was the least drought-resistant of the four species. During drought it developed very low water potentials despite markedly reduced stomatal aperture.     

Electric resistance as a measure of tree water status during seasonal drought in a tropical dry forest in Costa Rica

Variation in electric resistance of stem tissues was used to measure differences and changes in water status among trees in a tropical dry forest in Costa Rica during the dry season. For more than 30 tree species, stem water content (SWC), measured as electric resistance between nails driven 20 mm deep into tree trunks, correlated well with wood density, saturation water content, dehydration, measured with the pressure chamber, and tree development during drought. At dry sites, SWC was lowest in hardwood trees (characterized by high wood density) and highest in stem-succulent lightwood trees (characterized by low wood density). Among hardwood trees, SWC varied with soil water availability. During the dry season, SWC declined before leaf shedding and increased during rehydration preceding bud break. The time course of seasonal changes in SWC apparently constitutes an indirect measure of variation in the relative water content of outer stem tissues, which determines development of dry-forest trees during the dry season.     

Overexpression of AtNHX5 improves tolerance to both salt and drought stress in Broussonetia papyrifera (L.) Vent

Paper mulberry (Broussonetia papyrifera L. Vent) is well known for its bark fibers, which are used for making paper, cloth, rope, etc. It was found that, in addition to its well-documented role in the enhancement of plant salt tolerance, overexpression of the Na+/H+ antiporter (AtNHX5) gene in paper mulberry plants showed high drought tolerance. After exposure to water deficiency and salt stress, the wild-type (WT) plants all died, while the AtNHX5-overexpressing plants remained alive under high salt stress, and had a higher survival rate (>66%) under drought stress. Measurements of ion levels indicated that Na+ and K+ contents were all higher in AtNHX5-overexpressing leaves than in WT leaves in high saline conditions. The AtNHX5 plants had higher leaf water content and leaf chlorophyll contents, accumulated more proline and soluble sugars, and had less membrane damage than the WT plants under water deficiency and high saline conditions. Taken together, the results indicate that the AtNHX5 gene could enhance the tolerance of paper mulberry plants to multiple environmental stresses by promoting the accumulation of more effective osmolytes (ions, soluble sugars, proline) to counter the osmotic stress caused by abiotic factors.     

Verification of the resistance of a LEA gene from Tamarix expression in Saccharomyces cerevisiae to abiotic stresses

The role of late embryogenesis abundant （LEA） proteins in stress tolerance was examined by using a yeast expression system. LEA protein tolerance to the abotic stresses in plants involved in salt, drought and freezing stresses and additional tolerance to heat, NaHCO3 （salt-alkali） and ultraviolet radiation was also investigated. The transgenic yeast harboring the Tamarix LEA gene （DQ663481） was generated under the control of inducible GAL promoter （pYES2 vector）, yeast cells transformed with pYES2 empty vector were also generated as a control. Stress tolerance tests showed that LEA yeast transformants exhibited a higher survival rates than the control transformants under high temperature, NaHCO3, ultraviolet radiation, salt （NaCl）, drought and freezing, indicating that the LEA gene is tolerant to these abiotic stresses. These results suggest that the LEA gene is resistant to a wider repertoire of stresses and may play a common role in plant acclimation to the examined stress conditions.     

金矮生苹果蒸腾速率对光照和水分的响应研究(英文)

通过对不同光照和水分条件下金矮生苹果 (Maluspumilacv .Goldspur)的蒸腾速率研究表明 ,金矮生苹果蒸腾速率 (Tr)与光照强度 (PAR)和土壤含水率 (SWC)的相关性非常显著 .Tr随着PAR和SWC的改善而增大 .但是 ,当光照和水分任何一种环境胁迫存在时 ,另一条件的改善不会使Tr有较大程度的上升 ,只有当SWC >11%或PAR >4 0 0mol·s-1·m-2 时 ,Tr才能随PAR或SWC的增大有较大幅度的上升 ;但当SWC >15 %或PAR >10 0 0mol·s-1·m-2 后 ,Tr不会随PAR或SWC有较大的变化 .PAR和SWC影响到气孔阻力 (RS)、叶水势 (Ψl)的大小是Tr作出响应的根本原因 .光胁迫降低气孔开启度 ,严重光胁迫时 (PAR <10 0mol·s-1·m-2 ) ,气孔阻力较大 (RS >2 0s·cm-1) ,导致Tr较低 (Tr <5μgH2 O·s-1·cm-2 ) .在严重水分胁迫时 ,导致Tr小于 11μgH2 O·s-1·cm-2 ;当土壤水分充足时 ,Tr将大于 15 μgH2 O·s-1·cm-2 ,基本接近最大值 .11%～ 15 %SWC所对应的RS范围是Tr变化曲线从一种变化趋势向另一变化趋势过渡的“转折区” ,是实行土壤水分控制可考虑的范围 .     

土壤水分和接种VA菌根对构树根系形态和分形特征的影响

石灰岩生态系统是一种脆弱的退化生态系统.由于岩石易水解形成溶蚀地貌,土壤水分难以保存,水土流失现象普遍,尤其原生植被破坏后,生境更加恶化,植被恢复非常困难(谢宗强等,1995).     

Drought effects on water use efficiency, freezing tolerance and survival of Eucalyptus globulus and Eucalyptus globulus × nitens cuttings

Genetic improvement of Eucalyptus genotypes for drought and frost resistance is essential for successful intensive management of commercial plantations. Understanding the physiological mechanisms that relate water use and frost resistance for highly deployed genotypes may allow for better prediction of their future performance, genetic selection and seedling management for site specific purposes. We studied whether instantaneous water use efficiency (WUE _i ) may serve as drought, freezing and photoinhibition tolerance predictor by studying its response on six E. globulus clones (Eg1–Eg6) and four E. globulus × E. nitens hybrid seedlings (Egn1–Egn4) under drought and irrigated (control) treatments. Net photosynthesis (A) and transpiration (E) were studied using a gas exchange system in order to calculate WUE _i (A/E). Simultaneous chlorophyll a fluorescence measurements were performed to assess the non photochemical quenching components. Frost tolerance of plants under control and drought treatments were evaluated by measuring temperatures that exert 50% photoinactivation of photosystem II. Finally, drought tolerance was evaluated by plant survival within each genotype after rehydration. Our results showed significant genotype variability in the rate of soil and xylem water potential decrease during drought. While most of the genotypes reached ?4.0 MPa in about 35 days of drought, genotypes Eg6 and Egn4 required 56 days of drought to reach this xylem water potential. WUE _i exhibited significant differences among genotypes and irrigation treatments. Genotypes Eg5 and Egn4 increased their WUE _i between 70 and 80% after drought. This was associated with a more conservative control of water loss at the stomatal level combined with maintenance of relatively higher rates of net photosynthesis than the other genotypes under drought conditions. Plants exposed to drought were more freezing tolerant than control plants, having in average 3°C lower LT₅₀ than well irrigated ones. There was no a clear correlation between WUE _i and drought tolerance or drought-induced photoinhibition, however WUE _i was inversely correlated with LT₅₀. Our results suggest that WUE _i is not suitable by itself to select drought tolerant genotypes, but may provide evidence for discarding drought sensitive genotypes. In addition, it could provide valuable information to select for freezing tolerance.     

整地措施及苗木类型对麻疯树生长的影响研究

麻疯树耐旱、耐瘠薄,广泛分布于海拔1 500 m以下的干热河谷地区,不仅是干热河谷地区的水土保持树种,也是开发利用前景较好的能源植物。受立地条件及栽培管理措施的影响,双柏县麻疯树座果率低、单株产量小,产量极不稳定。2006～2011年在双柏县大沙坝进行不同整地措施和苗木类型造林试验,结果表明,科学整地、科学选择苗木及合理密植可促进麻疯树速生、丰产和稳产。