Field response of wheat to arbuscular mycorrhizal fungi and drought stress

Mycorrhizal plants often have greater tolerance to drought than nonmycorrhizal plants. This study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat (Triticum aestivum L.) cultivars grown in the field under well-watered and water-stressed conditions. Wheat seeds were planted in furrows after treatment with or without the AM fungi Glomus mosseae or G. etunicatum. Roots were sampled at four growth stages (leaf, tillering, heading and grain-filling) to quantify AM fungi. There was negligible AM fungi colonization during winter months following seeding (leaf sampling in February), when soil temperature was low. During the spring, AM fungi colonization increased gradually. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi isolates than water-stressed plants. Plants inoculated with G. etunicatum generally had higher colonization than plants colonized with G. mosseae under both soil moisture conditions. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. etunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentrations than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.     

Phosphorus supply and the growth of frequently defoliated white clover (Trifolium repens L.) in dry soil

A previous study found that increased phosphorus (P) supply to frequently defoliated white clover plants, growing in a low-P, dry soil, alleviated water stress symptoms and increased plant recovery on rewatering. In this study we determined how these stresses influence white clover growth. Measurements were made of the leaf canopy, stolon infrastructure and root system of the white clover plants growing in a low-P soil. Treatments included the factorial combination of four levels of P supply, two defoliation frequencies and two soil water treatments. White clover growth declined markedly when P-deficient plants were exposed to frequent defoliation and dry soil conditions. Leaf area was more affected than other parameters, in that the combination of stresses reduced leaf area to 2% of maximum observed for infrequently defoliated plants growing in high-P soil, with adequate water. Increased P supply generally increased the growth of all plant parts. Frequently defoliated plants growing in dry soil produced similar or greater leaf mass and leaf area as plants from similar treatments growing in wet soil, when the P supply increased to 50 mg P kg-1 soil. Higher P rates were able to negate the effect of dry soil on these frequently defoliated plants, as a result of larger water and P uptake. Also, the frequently defoliated plants with restricted root growth did not respond to a small increase in P supply (17 mg P kg-1 soil) for the leaf growth, irrespective of whether they were growing in wet or dry soil. Infrequently defoliated plants with greater root growth, compared to frequently defoliated plants, more than doubled their leaf mass with this P treatment.     

Root halotropism: Salinity effects on Bassia indica root

Abstract

Plant roots are responsible for the acquisition of nutrients and water from the soil and have an important role in plant response to soil stress conditions. The direction of root growth is gravitropic in general. Gravitropic responses have been widely studied; however, studies about other root tropisms are scarce. Soil salinity is a major environmental response factor for plants, sensed by the roots and affecting the whole plant. Our observations on root architecture of Kochia (Bassia indica) indicated that salinity may cue tropism of part of the roots toward increasing salt concentrations. We termed this phenomenon “positive halotropism”. It was observed that Kochia individuals in the field developed horizontal roots, originating from the main tap root, which was growing toward saline regions in the soil. Under controlled conditions in greenhouse experiments, Kochia plants were grown in pots with artificial soil salinity gradients, achieved by irrigation with saline and fresh water. It was shown that plants grown in low‐salt areas developed a major horizontal root toward the higher salt concentration region in the gradient. In regions of high salinity and in the absence of a salinity gradient, roots grew vertically without a major horizontal root. The novel finding of “positive halotropism” is discussed.     

陆生植物自身能否排放甲烷?

一般认为自然来源的甲烷是在厌氧环境下形成的,而最近研究却发现在有氧环境下植物自身也能释放甲烷,这将对全球甲烷收支产生重大影响。但这一发现目前还存在很大争议,一些研究证实植物在有氧环境下能排放甲烷,果胶、聚半乳糖醛酸等含甲氧基官能团的组分是植物产生甲烷的主要来源物质,甚至纤维素、木质素等植物结构组分也能排放甲烷;而另一些研究却发现植物并不能排放甲烷或者排放速率极小,而观测到的植物甲烷排放可能来自于土壤中,即溶解有甲烷的土壤水分被被植物吸收并通过蒸腾或蒸发作用而排放到大气中。有氧环境下植物排放甲烷的机制仍不清楚,光照、温度、紫外辐射、机械损伤等环境胁迫可能是导致植物排放甲烷的重要原因,但这些因素的影响作用仍存在很大的不确定性。即使如此,一些研究仍对全球或区域植物甲烷排放的通量进行了估算,估计全球植物甲烷排放通量为10-236Tg.a-1。未来研究应在更多地区针对不同生境的各种植物是否排放甲烷进行独立检验,并在此基础上探讨植物排放甲烷的机制。     

Growth conditions impact 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE) accumulation by Cucurbita pepo

Laboratory experiments were conducted to study the effects of soil moisture content, planting density, plant age, and the growth of multiple generations on the bioconcentration of weathered p,p'-DDE by the plant Cucurbita pepo. As soil moisture content increased from 7.4% to 29.9% (by weight), rates of contaminant accumulation by plant roots were increased by more than a factor of 2. Higher planting density also led to higher uptake, as the root bioconcentration factor (BCF, dry-weight ratio of contaminant concentration in the tissue to that in the soil) increased by 15-fold as the number of plants per pot was raised from 1 to 3. Concentrations of the compound in plant roots were inversely related to plant age, with root BCF declining by approximately a factor of 3 as plants aged from 14 to 28 d. Finally, no change in the bioavailability of the compound was observed in successive generations of plants grown in the same contaminated soil. The results suggest that phytoremediation is influenced by a number of factors and that the cleanup of contaminated soil can be enhanced by an understanding of environmental and other conditions affecting plant growth and bioconcentration.     

Proline as a biochemical marker in relation to the ecology of two halophytic Juncus species

Aims Osmolytes, used for maintaining osmotic balance and as 'osmoprotectants', are synthesized in plants as a general, conserved response to abiotic stress, although their contribution to stress-tolerance mechanisms remains unclear. Proline, the most common osmolyte, accumulates in many plant species in parallel with increased external salinity and is considered a reliable biochemical marker of salt stress. We have measured proline levels in two halophytic, closely related Juncus species under laboratory and field conditions to assess the possible relevance of proline biosynthesis for salt tolerance and therefore for the ecology of these two taxa.Methods Proline was quantified in plants treated with increasing NaCl concentrations and in plants sampled in two salt marshes located in the provinces of Valencia and Alicante, respectively, in southeast Spain. Electrical conductivity, pH, Na + and Cl ? concentrations were measured in soil samples collected in parallel with the plant material.Important findings Treatment with NaCl inhibited growth of J. acutus plants in a concentration-dependent manner, but only under high salt conditions for J. maritimus. Salt treatments led to proline accumulation in both species, especially in the more salt-tolerant J. maritimus. The results, obtained under laboratory conditions, were confirmed in plants sampled in the field. In all the samplings, proline contents were significantly lower in J. acutus than in the more tolerant J. maritimus growing in the same area. No direct correlation between soil salinity and proline levels could be established, but seasonal variations were detected, with increased proline contents under accentuated water deficit conditions. Our results suggest that proline biosynthesis is not only an induced, general response to salt stress but also an important contributing factor in the physiological mechanisms of salt tolerance in Juncus, and that it therefore correlates with the ecology of both species.     

Early growth of Brazilian pine (Araucaria angustifolia[Bertol.] Kuntze) in response to soil compaction and drought

Soil compaction leads to changes in soil physical properties such as density, penetration resistance and porosity, and, by consequence, affects root and plant growth. The initial growth of Brazilian pine is considered as being more affected by soil physical than chemical conditions, and the presence of a well-developed tap root system has been associated with this fact. A greenhouse experiment was conducted in order to evaluate the impact of soil compaction on the growth of Brazilian pine seedlings and on their susceptibility to a simulated drought period. In the first phase of the experiment, the effects of three levels of soil compaction on root morphology and plant growth were examined. Soil cylinders were artificially compacted in PVC tubes. Pre-germinated seeds were planted, and 147 days later 10 plants from each treatment were harvested for analysis. Higher values of soil density were associated with a shorter and thicker tap root. Growth of lateral roots and shoots remained unaffected at this stage. In the second phase, half of the plants (12) in each compaction treatment were drought-stressed by withholding water for a period of 77 days. Increased soil compaction again resulted in reduced length and increased diameter of the main tap root. This time, the effects were also extended to the lateral roots. Shoot extension growth and overall plant mass, however, increased with soil compaction. This greater mass accumulation in plants growing under increased soil compaction may be attributed to a more intimate contact between roots and soil particles. Drought stress reduced both root and shoot growth, but root mass was more negatively affected by drought stress in plants growing under high levels of soil compaction. Future investigations on the effects of soil compaction on the initial growth of Brazilian pine should include a wider range of compaction levels to better establish the relationship between soil physical parameters and plant growth.     

A hydraulic signal in root-to-shoot signalling of water shortage

Photosynthesis and biomass production of plants are controlled by the water status of the soil. Upon soil drying, plants can reduce water consumption by minimizing transpiration through stomata, the closable pores of the leaf. The phytohormone abscisic acid (ABA) mediates stomatal closure, and is the assigned signal for communicating water deficit from the root to the shoot. However, our study does not support ABA as the proposed long-distance signal. The shoot response to limited soil water supply is not affected by the capacity to generate ABA in the root; however, the response does require ABA biosynthesis and signalling in the shoot. Soil water stress elicits a hydraulic response in the shoot, which precedes ABA signalling and stomatal closure. Attenuation of the hydraulic response in various plants prevented long-distance signalling of water stress, consistent with root-to-shoot communication by a hydraulic signal.     

蕾期土壤盐度降低后棉花叶片的生理功能恢复

试验于2011—2012年在江苏南京江苏省农业科学院经济作物研究所试验田进行,采用盆栽方法,以鲁棉研37号和苏棉22号为供试材料,设置土壤盐度降低试验(初始土壤含盐量为0.2%,棉花进入二叶期后每7d加入混合盐1次,每次增加0.1%,使土壤含盐量逐渐达到0.5%,蕾期进行盐度降低处理,使土壤含盐量降低到0.2%左右),研究蕾期土壤盐度降低后棉花叶片的生理代谢动态特征。结果表明:土壤盐度降低后,棉花叶片叶绿素(Chl)、类胡萝卜素(Car)含量和Chl/Car升高;净光合速率和气孔导度升高,且分别在土壤盐度降低后第14天和7天接近于低盐对照;土壤盐度降低后棉花叶片超氧化物歧化酶(SOD)和过氧化物酶(POD)活性升高,过氧化氢酶(CAT)活性和丙二醛(MDA)含量降低,MDA含量在土壤盐度降低后第14天接近于低盐对照;土壤盐度降低后棉花叶片中可溶性糖、游离氨基酸和脯氨酸含量降低,且接近于低盐对照。上述结果表明土壤盐度降低后,棉花叶片生理功能逐渐恢复,进而实现棉花生长发育的恢复补偿。棉花叶片生理功能在土壤盐度降低后的恢复能力存在品种间差异,鲁棉研37号较苏棉22号叶片生理功能表现出更强的恢复能力。     

Benefit, cost and water-use efficiency of arbuscular mycorrhizal durum wheat grown under drought stress

 Arbuscular mycorrhizal fungi (AMF) living symbiotically with host plants enhance plant growth by improving the acquisition of mineral nutrients and water relations. This study determined the effects of AMF inoculation on growth, benefit/cost and water-use efficiency (grams dry matter produced per kilogram water evapotranspired) in two durum wheat genotypes (drought sensitive and drought tolerant) under water-stressed and well-watered conditions. Plants were grown in a low-P silty clay (Typic Xerochrept) soil mix in a greenhouse. Shoot and root dry matter (DM) and root AMF colonization were higher for well-watered than for water-stressed plants. The mycorrhizal plants were more water-use efficient than nonmycorrhizal plants. Shoot DM differences between mycorrhizal and nonmycorrhizal plants represent the benefit derived by plants from AMF-root associations. Shoot DM differences between mycorrhizal and nonmycorrhizal plants under similar conditions of water treatment represent the cost to the plant of AMF-root associations. Values of benefit/cost for AMF-root associations were highest when plants were water-stressed and decreased under well-watered conditions. Genotypic differences in calculated costs and benefits were pronounced. Benefit/cost analysis may be helpful in evaluating host plant genotypes in order to optimize efficiencies of AMF symbiosis under different environmental conditions. Accepted: 4 April 1998     

Expression of an Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) in cotton improves drought‐ and salt tolerance and increases fibre yield in the field conditions

The Arabidopsis gene AVP1 encodes a vacuolar pyrophosphatase that functions as a proton pump on the vacuolar membrane. Overexpression of AVP1 in Arabidopsis, tomato and rice enhances plant performance under salt and drought stress conditions, because up‐regulation of the type I H⁺‐PPase from Arabidopsis may result in a higher proton electrochemical gradient, which facilitates enhanced sequestering of ions and sugars into the vacuole, reducing water potential and resulting in increased drought‐ and salt tolerance when compared to wild‐type plants. Furthermore, overexpression of AVP1 stimulates auxin transport in the root system and leads to larger root systems, which helps transgenic plants absorb water more efficiently under drought conditions. Using the same approach, AVP1‐expressing cotton plants were created and tested for their performance under high‐salt and reduced irrigation conditions. The AVP1‐expressing cotton plants showed more vigorous growth than wild‐type plants in the presence of 200 mm NaCl under hydroponic growth conditions. The soil‐grown AVP1‐expressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in greenhouse conditions. Furthermore, the fibre yield of AVP1‐expressing cotton plants is at least 20% higher than that of wild‐type plants under dry‐land conditions in the field. This research indicates that AVP1 has the potential to be used for improving crop’s drought‐ and salt tolerance in areas where water and salinity are limiting factors for agricultural productivity.     

Effects of soil salt levels on the growth and water use efficiency of Atriplex canescens (Chenopodiaceae) varieties in drying soil

The effect of salt stress on the growth and water use efficiency of the xerohalophyte Atriplex canescens (Pursh.) Nutt. in drying soil was determined by growing plants to the wilting point in soils receiving a one-time irrigation of nutrient solution containing low, medium, and high levels of NaCl. The experiment compared three varieties of A. canescens that differed in salt tolerance and capacity for Na and K uptake in previous research. Contrary to expectations, we did not find that water and salt stress were strictly additive in reducing plant performance. Soil salts enhanced the growth performance of the plants in drying soil by increasing their days to wilting, ability to extract water from the soil, organic matter production, and water use efficiency. The variety with the highest salt tolerance also had the highest growth rates and water use efficiency on drying soils. We conclude that tolerances to water and salt stress are linked through a common mechanism of Na uptake for osmotic adjustment in this species.     

Sedum cools soil and can improve neighboring plant performance during water deficit on a green roof

Green roofs have the potential to function as islands of biodiversity within urban and suburban environments. However, plant diversity is constrained by the harsh environment of a green roof, especially summertime water deficit and heat stress. We hypothesized that Sedum species, which are highly tolerant of the roof-top environment, would reduce peak soil temperature and increase performance of neighboring plants during summer water deficit. To test these hypotheses, we grew focal plant species with and without Sedum on a green roof. We then monitored growth during wet periods and drought tolerance during dry periods. During a three-year experiment, S. album reduced maximum growth of neighbor plants, Agastache rupestris and Asclepias verticillata, during favorable growth conditions, but increased performance of neighbors during summer water deficit. In a second experiment, four species of Sedum were each found to decrease peak soil temperature by 5-7 °C. All species decreased total growth of neighboring Agastache ‘Black Adder’ during favorable growth conditions, but again increased performance during summer water deficit. These results suggest that the palette of green roof plants can be expanded by using Sedum species as nurse plants.     

不同土壤水分条件下中国沙棘雌雄株光合作用、蒸腾作用及水分利用效率特征

采用LI-6400便携式光合系统对野外不同生境(沟底、坡面)和田间不同土壤水分条件下中国沙棘雌雄株的净光合速率和蒸腾速率及水分利用效率特征进行了观测,结果表明,中国沙棘雌雄株在水分条件较好的生境中均表现较强的生活力,净光合速率和蒸腾速率主要受光照强度和大气温度的影响,雄株表现出更高的光合、蒸腾、水分利用效率;在水分条件较差的生境中,雌雄株均通过降低蒸腾和提高水分利用效率来适应逆境,净光合速率和蒸腾速率的影响因子增多,雄株的光合速率大幅度下降,雌株仍保持较高的光合速率,雌株的水分利用效率高于雄株.可见,在反映植物瞬时生理变化的性状方面,雌株对土壤水分减少表现出了更强的适应性,雄株对土壤水分变化表现出了更大的敏感性.     

Symbiotic nitrogen fixation of Rhizobium (Galega) in acid soils,and its survival in soil under acid and cold stress

Summary Goat's rue (Galega orientalis) is a potential perennial forage legume for northern temperate acid soils. Greenhouse experiments were performed to compare symbiotically nitrogen fixing goat's rue with plants receiving mineral nitrogen in five different acid soils. Soil acidity had the same effect on yields of symbiotically grown plants as on plants receiving mineral nitrogen, suggesting that the acid sensitivity of the symbiosis was not limiting plant growth, even under very acidic conditions. The survival of an antibiotic resistant Rhizobium (Galega) strain in acid soil and freezing conditions was also studied. The survival of the bacteria was not affected at 15°C, when the pH of the soil (measured in 0.01M CaCl₂) was 5.2 or 4.9. In pH 3.4, and after freezing to –5°C, the population density decreased from 3×10⁸ to 1×10⁵/g in a few weeks. It is concluded that goat's rue, its symbiotic nitrogen fixation and R. (Galega) are tolerant of moderately acid agricultural soils, but that harsh winters may reduce bacterial numbers in the soil.     

Water relations of Fino lemon plants on two rootstocks under flooded conditions

Potted two-year-old Fino lemon plants (Citrus limon (L.) Burm. fil.) grafted on two different rootstocks: sour orange (C. aurantium) (SO), and C. macrophylla (CM) were submitted to two different treatments: non-flooded (control) and flooded for 8 days, under field conditions. Lemon/CM plants had lower plant plus soil resistance to water flow (R_(p+s)) values for both treatments. The decrease in leaf water potential (Ψ_l) and leaf turgor potential (Ψ_p) values, observed in the last part of the flooding period, in both flooded scion/rootstock combinations, can be related to the increase in the resistance to water flow. The maintenance in Ψ_l and Ψ_p values in flooded plants at values similar to those of the control plants, at the beginning of the flooding period and during the recovery period, can be ascribed to the stomatal control observed (decrease in leaf conductance (g₁) values). The later g₁ recovery in lemon/CM than in lemon/SO flooded plants, could explain the lower vegetative growth of lemon/CM plants by flooding effect. The observed g₁ response to soil flooding suggested that porometry is a reliable indicator of the altered behaviour caused by flooding in lemon plant.     

Soybean cultivar variability for nodule formation and growth under drought

Both nodulation and nitrogen fixation in soybean [Glycine max (L.) Merr.] are sensitive to soil drying, which can have important negative effects on yield. An exception to this general response has been the identification of the cultivar Jackson as being drought tolerant for N₂ fixation. The objectives of this research were to examine nodule formation and growth in Jackson among other soybean cultivars in response to soil drying under field conditions. Two field experiments were conducted to examine the genetic variation in the sensitivity of nodule numbers and dry weights to soil drying. Substantial variation among soybean lines was found, and the drought-tolerance trait was demonstrated again in Jackson. Greenhouse experiments were conducted to further analyze the variation of nodulation response to soil water content. The differences among cultivars observed in the field were confirmed in the greenhouse. Importantly, the relative drought insensitivity of N₂ fixation in cultivar Jackson was associated with high individual nodule dry weight under drought conditions, relative to well-watered plants. It was concluded that large variation in nodulation sensitivity to water deficit exists among soybean cultivars and that the response of N₂ fixation rates to drought is related in part to nodule formation and growth.     

Effect of alkaline and saline substrates on ABA contents,distribution and transport in plant roots

The distribution of the phytohormone abscisic acid (ABA) between plant and soil and within plants growing on an alkaline substrate has been studied in order to separate the true effect of high soil pH from any effects that might be a result of the high salinity normally observed in alkaline soils. Leaves of a range of plants grown in an alkaline and saline solid substrate (municipal solid waste incinerator bottom slag) exhibited higher ABA levels than leaves of control plants. In contrast, roots of most plants grown on alkaline and saline substrates, particularly those without an exodermis (various species of Fabaceae), had slightly lower than or comparable ABA contents to control roots. However, in corn roots (Zea maysL. cv. Garant FAO 240) which possess a well-developed exodermis, alkaline and saline conditions in the rhizosphere did not reduce the endogenous ABA concentration, because the leaching of ABA from corn roots into the rhizosphere was lower than that from Vicia faba (variety Dreifache Weisse) roots. ABA efflux from corn and Vicia roots into the soil solution was observed only during the first days of the experiments and thereafter became substantially decreased. Because the leaching of ABA from Vicia faba roots into the rhizosphere was higher than that from corn roots, the leaves of Vicia plants grown in alkaline soil at low salinity no longer exhibited an elevated ABA concentration. However, whilst the roots of corn plants grown on desalted slag retained ABA levels that were higher than those of the control, the ABA content of leaves was not significant higher than the controls. For this reason, root ABA retention must be enough to induce tolerance to alkalinity in corn plants and there is no need to implicate changes in ABA concentrations in the aerial parts of the plant as having a role in this tolerance. In alkaline soil substrates, considerable portions of the ABA synthesised in the roots leached out into the soil solution of the rhizosphere according to the anion trap concept. An exodermis substantially reduces this leakage. The transient nature of ABA efflux into the rhizosphere was a result of the fact that the salt stress itself was only a transient phenomenon due to a washout of salt by irrigation. The results match predictions of mathematical models describing the effect of alkaline pH on the distribution of abscisic acid within plants and between roots and the rhizosphere. Species that can retain root ABA in the face of its tendency to leach into the more alkaline compartment are able to tolerate these normally harmful sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

NaCl胁迫下AM真菌对棉花生长和叶片保护酶系统的影响

利用盆栽实验研究了 Na Cl胁迫条件下 AM真菌对棉花生长和叶片保护酶系统的影响。结果表明 :在土壤中加入 0、0 .1%、0 .2 %、0 .3%浓度 Na Cl条件下 ,Na Cl胁迫对 AM真菌的接种效果有显著影响。接种 AM真菌提高了棉花根系菌根侵染率 ,增加了棉株的生物产量 ,以 0～ 0 .2 % Na Cl浓度时 AM真菌接种效果最好。 AM真菌对棉株生理参数和保护酶活性的影响因生育期和 Na Cl浓度不同而异 ,现蕾期和低盐浓度 (0～ 0 .1% )下叶片叶绿素含量明显增加 ;中高盐水平 (0 .2 %～ 0 .3% )和生育后期叶片可溶性蛋白质含量和 SOD、POD、CAT等保护酶活性显著提高 ,MDA含量明显降低 ;棉株 K、Ca、Mg含量因植株部位和盐浓度不同而变化。 AM真菌增强宿主植物的耐盐性可能源于促进宿主根系对土壤矿质元素吸收的直接作用和改善植物体内离子平衡和生理代谢活动、提高保护酶活性的间接作用