Morphological and physiological variation in western redcedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) populations under contrasting soil water conditions

Adaptation to precipitation conditions may induce genetic diversity that changes morphological and physiological traits. This hypothesis was investigated in the seedlings of seven western redcedar (Thuja plicata Donn ex D. Don) populations, which were collected along a precipitation transect from the Pacific coast to the southern interior of British Columbia, Canada. The experimental seedlings were either well-watered or soil-droughted and measured for growth, gas exchange rates, transpiration efficiency, and carbon isotope discrimination during or at the end of the third growing season. Significant variation was found in most of these morphological and physiological traits among the populations. Much of this variation occurred under well-watered, but not so much under droughted conditions. Mean height increments and transpiration efficiency showed a significant linear relationship, but biomass increments exhibited a quadratic relationship with precipitation on the origin site of these populations. Measurements of water use efficiency obtained from instantaneous gas exchange measurements, carbon isotope discrimination, and transpiration efficiency were intercorrelated in the seedlings. However, neither did any of these measurements consistently rank the populations, nor were they indicative of adaptation to climatic precipitation conditions in these western redcedar populations.     

不同灌溉方式对水稻生物学特性与水分利用效率的影响

以杂交水稻两优培九为试验材料,利用测坑栽培条件,比较了4种灌溉方式下的水稻生物学特性与水分利用效率.结果表明,与淹水灌溉相比,间歇灌溉叶面积指数大,叶片光合速率高,蒸腾速率较低,叶片水分利用效率高;半干旱栽培叶片水分利用效率相对较高;干旱栽培叶面积指数小,叶片净光合速率和水分利用效率降低,且后期叶片早衰.间歇灌溉、半干旱栽培和干旱栽培比淹水灌溉分别节水8.75%、17.96%和29.69%;产量分别增产24.02%、减产5.07%和减产38.93%;水分利用效率以间歇灌溉最高,半干旱栽培次之,淹水灌溉和干旱栽培较低.间歇灌溉下稻粒的整精米率、精米率、粒长均高于其它处理,但垩白粒率和垩白度低于其它处理;随着稻田耗水量的减少,水稻的直链淀粉含量降低,而胶稠度和蛋白质含量提高.试验结果表明间歇灌溉为南方稻区较适宜的灌溉方式.     

Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation,carbon isotope discrimination and leaf water potential

Leaf gas exchange rates, predawn _wp and daily minimum _wm leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination () was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The values were 2.7 higher in the pioneer species than in the late stage species. The calculated time integratedC _i values derived from the values averaged 281 mol mol^–1 in the pioneers and 240 mol mol^–1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO₂ assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol^–1 in the pioneers and the values were 64 and 74 mmol mol^–1 for the two late stage species. The high values were associated—at least inJ. copaia—with high maximumg values and with high plant intrinsinc specific hydraulic conductance [Cg/(_wm–_wp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of for distinguishing ecophysiological functional types among rainforest trees.     

Evaluation of physiological traits for improving drought tolerance in faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.)

Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ¹³C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ¹³C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ¹³C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ¹³C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ¹³C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.     

田间不同条件下玉米叶片的气孔阻力及与光合、蒸腾作用的关系

以玉米17个自交系和10个杂交种为试材,在田间条件下研究了不同光强、不同叶位、不同生育期、不同源库比例和株间差异状态下的气孔阻力及其与光合(PH)、蒸腾(TR)和叶片水分利用效率(WUE)的关系,结果表明,不同自交系之间RS具有显著的差异,相差最大可达2.3倍以上;光照条件变弱、穗叶位差增加、生育期推延和源/库比例改变等均可引起RS值的增加;在各种情况下导致RS变化的同时也引起TR和PH产生相应的变化,RS与TR、PH表现出显著或极显著的负相关,且相关系数r_RS-TR>r_RS-PH;RS与WUE的相关关系在不同的条件下表现出不稳定性.     

Carbon isotopes and water use efficiency: sense and sensitivity

We revisit the relationship between plant water use efficiency and carbon isotope signatures (δ¹³C) of plant material. Based on the definitions of intrinsic, instantaneous and integrated water use efficiency, we discuss the implications for interpreting δ¹³C data from leaf to landscape levels, and across diurnal to decadal timescales. Previous studies have often applied a simplified, linear relationship between δ¹³C, ratios of intercellular to ambient CO₂ mole fraction (C _i/C _a), and water use efficiency. In contrast, photosynthetic ¹³C discrimination (Δ) is sensitive to the ratio of the chloroplast to ambient CO₂ mole fraction, C _c/C _a (rather than C _i/C _a) and, consequently, to mesophyll conductance. Because mesophyll conductance may differ between species and over time, it is not possible to determine C _c/C _a from the same gas exchange measurements as C _i/C _a. On the other hand, water use efficiency at the leaf level depends on evaporative demand, which does not directly affect Δ. Water use efficiency and Δ can thus vary independently, making it difficult to obtain trends in water use efficiency from δ¹³C data. As an alternative approach, we offer a model available at to explore how water use efficiency and ¹³C discrimination are related across leaf and canopy scales. The model provides a tool to investigate whether trends in Δ indicate changes in leaf functional traits and/or environmental conditions during leaf growth, and how they are associated with trends in plant water use efficiency. The model can be used, for example, to examine whether trends in δ¹³C signatures obtained from tree rings imply changes in tree water use efficiency in response to atmospheric CO₂ increase. This is crucial for predicting how plants may respond to future climate change. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Leaf functional traits of Neotropical savanna trees in relation to seasonal water deficit

The seasonal savannas (cerrados) of Central Brazil are characterized by a large diversity of evergreen and deciduous trees, which do not show a clear differentiation in terms of active rooting depth. Irrespective of the depth of the root system, expansion of new foliage in deciduous species occurs at the end of the dry season. In this study, we examined a suite of leaf traits related to C assimilation, water and nutrients (N, P) in five deciduous and six evergreen trees that were among the dominant families of cerrado vegetation. Maximum CO₂ assimilation on a mass basis (A_mass) was significantly correlated with leaf N and P, and specific leaf area (SLA; leaf area per unit of leaf mass). The highest leaf concentrations of both nutrients were measured in the newly mature leaves of deciduous species at the end of the dry period. The differences in terms of leaf N and P between evergreen and deciduous species decreased during the wet season. Deciduous species also invested less in the production of non-photosynthetic leaf tissues and produced leaves with higher SLA and maintained higher water use efficiency. Thus, deciduous species compensated for their shorter leaf payback period by maintaining higher potential payback capacity (higher values of A_mass) and lower leaf construction costs (higher SLA). Their short leafless period and the capacity to flush by the end of the dry season may also contribute to offset the longer payback period of evergreen species, although it may involve the higher cost of maintaining a deep-root system or a tight control of plant water balance in the shallow-rooted ones.     

Δ13C and tree-ring width reflect different drought responses in Quercus ilex and Pinus halepensis

Holm oak (Quercus ilex L.) and Aleppo pine (Pinus halepensis Mill) are representative of two different functional types of trees extensively found in the Mediterranean: evergreen sclerophyllous and drought-adapted conifers. The former is considered a partially drought-tolerant species, whereas the latter is a typically drought-avoiding, water-saving species. We postulated that contrasting strategies in response to water deficits in Q. ilex and P. halepensis would lead to a differential sensitivity to changes in water availability. To test this hypothesis, we compared the response of both species in growth rate (measured as radial increments) and intrinsic water use efficiency [WUE_i, as inferred from carbon isotope discrimination (¹³C) in wood samples] among sites from different provenance regions in NE Spain. We found significant differences in ¹³C and growth among provenance regions, partly explained by contrasting water availability. Wood ¹³C was positively related with precipitation and the ratio between precipitation and potential evapotranspiration (P / E). However, these relationships were stronger in P. halepensis (for P / E, r ²=0.67, P <0.001) than in Q. ilex (r ²=0.42, P <0.01). In addition, radial growth was positively related with precipitation and ¹³C in P. halepensis (r ²=0.32 and r ²=0.35, respectively, P <0.01), but not in Q. ilex. We concluded that P. halepensis was more sensitive than Q. ilex to water availability, showing faster increase in WUE_i in response to water stress. We also found that the effect of north/south aspect on ¹³C and growth was site-specific, and unrelated to climatic variables.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

不同沟灌模式对沙漠绿洲区葡萄生长和水分利用的效应

在甘肃河西荒漠绿洲区研究了覆膜与不覆膜条件下隔沟交替灌溉、常规沟灌对葡萄生长和水分利用的影响.结果表明,隔沟交替灌溉可以保证作物一部分根区处于比较湿润状态,另一部分根区处于相对干燥状态,湿润与干燥区域的交替出现可诱导葡萄的补偿生长效应.隔沟交替灌溉条件下葡萄叶片气孔开度减小,光合速率略有降低或下降不显著,而蒸腾速率明显下降,水分利用效率增大.光合作用日变化也表现出类似规律.隔沟交替灌溉与地膜覆盖技术相结合能显著提高水分利用效率,为在田间实施气孔最优化调控提供了一种有效途径.     

田间不同条件下玉米叶片的气孔阻力及与光合,蒸腾作用的关系

以玉米 1 7个自交系和 1 0个杂交种为试材 ,在田间条件下研究了不同光强、不同叶位、不同生育期、不同源库比例和株间差异状态下的气孔阻力及其与光合 (PH)、蒸腾(TR)和叶片水分利用效率 (WUE)的关系 ,结果表明 ,不同自交系之间RS具有显著的差异 ,相差最大可达 2 .3倍以上 ;光照条件变弱、穗叶位差增加、生育期推延和源 /库比例改变等均可引起RS值的增加 ;在各种情况下导致RS变化的同时也引起TR和PH产生相应的变化 ,RS与TR、PH表现出显著或极显著的负相关 ,且相关系数rRS TR>rRS PH;RS与WUE的相关关系在不同的条件下表现出不稳定性     

Ecological and ecophysiological patterns in a pre-altiplano shrubland of the Andean Cordillera in northern Chile

We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (Δ) of 3.7–7.5‰ through C₃ species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of c _i :c _a ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities. This revised version was published online in June 2006 with corrections to the Cover Date.     

水分和氮磷水平对小麦碳同位素分辨率和水分利用效率的影响

 依据盆栽试验数据,利用植物稳定性碳同位素分辨率的理论模型,研究了水分和氮磷营养对小麦叶片碳同位素分辨率(Carbon-isotope discrimination △)的影响。结果表明：水分差异引起碳同位素分辨率较大变异,碳同位素分辨率随土壤相对含水量(Soil relative water content)的提高而提高,在土壤相对含水量为60％～70％条件下碳同位素分辨率最高。缺水时磷水平提高,碳同位素分辨率提高。水分利用效率(Water use efficiency)与碳同位素分辨率关系受土壤水分和养分水平的影响。缺水条件下水分利用效率与碳同位素分辨率之间为负相关,充分供水下为正相关;在低氮水平下的关系不明显,施氮150kg·hm-2时相关性显著。     

Zinc fertilization and water stress affects plant water relations, stomatal conductance and osmotic adjustment in chickpea (Cicer arientinum L.)

Chickpea (Cicer arietinum) is an important dryland pulse crop in many parts of the world. Productivity is often limited by periods of water deficit and in a number of regions zinc deficiency occurs, but the interaction between zinc nutrition and water stress has not been studied extensively. This interaction was examined in two glasshouse experiments. Chickpea was grown under deficient (no applied Zn) or adequate (2.5 μg Zn/g soil) levels of zinc in pots for either 53 days (Experiment 1) or 40 days (Experiment 2) before being exposed to a single period of water stress that lasted for 12 days (Experiment 1) or 23 days (Experiment 2). In one experiment four genotypes (Tyson, ICC-4958, T-1587 and NIFA-88) differing in their sensitivity to zinc deficiency were compared during a single drying cycle, and in the second experiment a single cultivar (Tyson) was compared under well-watered and water stress conditions. Water stress was induced by allowing the soil to dry gradually and the responses in shoot biomass, water use, plant water relations and carbon isotope discrimination (Δ, ‰) were measured. Shoot biomass, water use and water use efficiency were reduced by zinc deficiency. Stomatal conductance was lower in zinc-deficient plants as well. Zinc deficiency reduced Δ by about 1‰ and there were significant differences in Δ between genotypes which were independent of the level of zinc nutrition. At an adequate level of zinc there was a significant negative correlation between Δ and shoot biomass and between Δ and water use efficiency among the four chickpea genotypes, but these correlations were not significant under zinc deficiency. Osmotic potential was lower and turgor higher in the leaves of zinc-deficient plants, but the ability to adjust osmotically was reduced by zinc deficiency as stress developed. In conclusion, zinc-deficiency reduced the efficiency with which the water was used for biomass production and compromised the plant’s capacity to respond to water stress by osmotic adjustment.     

Photosynthesis on individual leaves of sugar beet (Beta vulgaris) during the ontogeny at variable water regimes

It is well known that the extent of yield reduction depends not only on the severity of water stress but also on the stage of plant development. Assessing photosynthetic response of individual leaves to water deficit during the ontogeny may, therefore, offer a clue to better understand the whole plant behaviour. This research aimed at investigating the influence of early and late water stress on net photosynthesis (P_n), carbon‐isotope discrimination and other related traits on individual leaves during ontogeny. Sugar beet plants were grown in rain‐sheltered soil columns of relevant volume (300 L), subdivided into well‐watered (WW); early (S1) and late (S2) stress. In general, water stress significantly reduced leaf lifespan and P_n. Relieving the stress at about one‐third and two‐thirds of potential leaf life substantially restored P_n at the levels of WW. Stressing a previously WW leaf brought about a comparatively heavier loss than stressing a leaf since the beginning. As for leaves at different phenological times, the early leaves had higher initial photosynthetic peaks but steeper falls during their lives. An insight into the relationships between P_n and substomatal CO₂ concentration (C_i) shows that in mature leaves the photosynthetic restoration following stress relief did not entail a full recovery of the electron transport rate, the parameter most severely affected by the stress. The partial reversibility of the effects of water deficiency, associated to the anticipated leaf senescence and to the natural slow‐down of net assimilation during leaf life, may be seen as a key factor in predicting to what extent the plant can tolerate drought and the damages caused by water stress.     

Assessing the effects of nitrogen deposition and climate on carbon isotope discrimination and intrinsic water‐use efficiency of angiosperm and conifer trees under rising CO2 conditions

The objective of this study is to globally assess the effects of atmospheric nitrogen deposition and climate, associated with rising levels of atmospheric CO₂, on the variability of carbon isotope discrimination (Δ¹³C), and intrinsic water‐use efficiency (iWUE) of angiosperm and conifer tree species. Eighty‐nine long‐term isotope tree‐ring chronologies, representing 23 conifer and 13 angiosperm species for 53 sites worldwide, were extracted from the literature, and used to obtain long‐term time series of Δ¹³C and iWUE. Δ¹³C and iWUE were related to the increasing concentration of atmospheric CO₂ over the industrial period (1850–2000) and to the variation of simulated atmospheric nitrogen deposition and climatic variables over the period 1950–2000. We applied generalized additive models and linear mixed‐effects models to predict the effects of climatic variables and nitrogen deposition on Δ¹³C and iWUE. Results showed a declining Δ¹³C trend in the angiosperm and conifer species over the industrial period and a 16.1% increase of iWUE between 1850 and 2000, with no evidence that the increased rate was reduced at higher ambient CO₂ values. The temporal variation in Δ¹³C supported the hypothesis of an active plant mechanism that maintains a constant ratio between intercellular and ambient CO₂ concentrations. We defined linear mixed‐effects models that were effective to describe the variation of Δ¹³C and iWUE as a function of a set of environmental predictors, alternatively including annual rate (N_rate) and long‐term cumulative (N_cum) nitrogen deposition. No single climatic or atmospheric variable had a clearly predominant effect, however, Δ¹³C and iWUE showed complex dependent interactions between different covariates. A significant association of N_rate with iWUE and Δ¹³C was observed in conifers and in the angiosperms, and N_cum was the only independent term with a significant positive association with iWUE, although a multi‐factorial control was evident in conifers.     

Water relations and stomatal characteristics of Mediterranean plants with different growth forms and leaf habits: responses to water stress and recovery

The aim of this study was to extent the range of knowledge about water relations and stomatal responses to water stress to ten Mediterranean plants with different growth forms and leaf habits. Plants were subjected to different levels of water stress and a treatment of recovery. Stomatal attributes (stomatal density, StoD), stomatal conductance (g _s), stomatal responsiveness to water stress (SR), leaf water relations (pre-dawn and midday leaf water potential and relative water content), soil to leaf apparent hydraulic conductance (K _L) and bulk modulus of elasticity (ε) were determined. The observed wide range of water relations and stomatal characteristics was found to be partially depended on the growth form. Maximum g _s was related to StoD and the stomatal area index (SAI), while g _s evolution after water stress and recovery was highly correlated with K _L. Relationships between SR to water deficit and other morphological leaf traits, such as StoD, LMA or ε, provided no general correlations when including all species. It is concluded that a high variability is present among Mediterranean plants reflecting a continuum of leaf water relations and stomatal behaviour in response to water stress.     

Plant water relations and the effects of elevated CO2: a review and suggestions for future research

Increased ambient carbon dioxide (CO₂) has been found to ameliorate water stress in the majority of species studied. The results of many studies indicate that lower evaporative flux density is associated with high CO₂-induced stomatal closure. As a result of decreases in evaporative flux density and increases in net photosynthesis, also found to occur in high CO₂ environments, plants have often been shown to maintain higher water use efficiencies when grown at high CO₂ than when grown in normal, ambient air. Plants grown at high CO₂ have also been found to maintain higher total water potentials, to increase biomass production, have larger root-to-shoot ratios, and to be generally more drought resistant (through avoidance mechanisms) than those grown at ambient CO₂ levels. High CO₂-induced changes in plant structure (i.e., vessel or tracheid anatomy, leaf specific conductivity) may be associated with changes in vulnerability to xylem cavitation or in environmental conditions in which runaway embolism is likely to occur. Further study is needed to resolve these important issues. Methodology and other CO₂ effects on plant water relations are discussed.Abbreviations A net photosynthesis - C_a ambient [CO₂] - C_i internal [CO₂] - E evaporative flux density - g₁ leaf conductance - g_s stomatal conductance - LSC leaf specific conductivity - IRGA infrared gas analyzer - LAI leaf area index - PAR photosynthetically active radiation - total plant water potential - _soil soil water potential - _s solute potential - _pt turgor pressure potential - _px xylem pressure potential - RH relative humidity - R : S root to shoot ratio - RWC relative water content - SLA specific leaf area - SLW specific leaf weight - SPAC soil-plant-atmosphere-continuum - SWC soil water content - VPD vapor pressure deficit - WUE water use efficiency     

Water use efficiency and carbon isotope composition of plants in a cold desert environment

Summary The effects of the availabilities of water and nitrogen on water use efficiency (WUE) of plants were investigated in a sagebrush steppe. The four species studied wereArtemisia tridentata (shrub),Ceratoides lanata (suffrutescent shrub),Elymus lanceolatus (rhizomatous grass), andElymus elymoides (tussock grass). Water and nitrogen levels were manipulated in a two-by-two factorial design resulting in four treatments: control (no additions), added water, added nitrogen, and added water and nitrogen. One instantaneous and two long-term indicators of WUE were used to testa priori predictions of the ranking of WUE among treatments. The short-term indicator was the instantaneous ratio of assimilation to transpiration (A/E). The long-term measures were 1) the slope of the relationship between conductance to water vapor and maximum assimilation and 2) the carbon isotope composition (¹³C) of plant material. Additional water decreased WUE, whereas additional nitrogen increased WUE. For both A/E and ¹³C, the mean for added nitrogen alone was significantly greater than the mean for added water alone, and means for the control and added water and nitrogen fell in between. This ranking of WUE supported the hypothesis that both water and nitrogen limit plant gas exchange in this semiarid environment. The short- and long-term indicators were in agreement, providing evidence in support of theoretical models concerning the water cost of carbon assimilation.     

Hydraulic conductance and water potential gradients in squash leaves showing mycorrhiza-induced increases in stomatal conductance

Stomatal conductance (g _s) and transpiration rates vary widely across plant species. Leaf hydraulic conductance (k _leaf) tends to change with g _s, to maintain hydraulic homeostasis and prevent wide and potentially harmful fluctuations in transpiration-induced water potential gradients across the leaf (ΔΨ _leaf). Because arbuscular mycorrhizal (AM) symbiosis often increases g _s in the plant host, we tested whether the symbiosis affects leaf hydraulic homeostasis. Specifically, we tested whether k _leaf changes with g _s to maintain ΔΨ _leaf or whether ΔΨ _leaf differs when g _s differs in AM and non-AM plants. Colonization of squash plants with Glomus intraradices resulted in increased g _s relative to non-AM controls, by an average of 27% under amply watered, unstressed conditions. Stomatal conductance was similar in AM and non-AM plants with exposure to NaCl stress. Across all AM and NaCl treatments, k _leaf did change in synchrony with g _s (positive correlation of g _s and k _leaf), corroborating leaf tendency toward hydraulic homeostasis under varying rates of transpirational water loss. However, k _leaf did not increase in AM plants to compensate for the higher g _s of unstressed AM plants relative to non-AM plants. Consequently, ΔΨ _leaf did tend to be higher in AM leaves. A trend toward slightly higher ΔΨ _leaf has been observed recently in more highly evolved plant taxa having higher productivity. Higher ΔΨ _leaf in leaves of mycorrhizal plants would therefore be consistent with the higher rates of gas exchange that often accompany mycorrhizal symbiosis and that are presumed to be necessary to supply the carbon needs of the fungal symbiont.     

不同施氮量下灌水量对小麦耗水特性和氮素分配的影响

研究了不同施氮量条件下灌水量对高产小麦耗水特性和氮素分配利用的影响。设置4个施氮水平:0kg·hm-2(N0)、120kg·hm-2(N1)、210kg·hm-2(N2)和300kg·hm-2(N3),在每个施氮水平下设置4个灌水量处理:不浇水(W0)、底墒水+拔节水(W1)、底墒水+拔节水+开花水(W2)、底墒水+拔节水+开花水+灌浆水(W3),每次灌水量60mm。结果表明:(1)在N0水平下W0处理日耗水量以拔节至开花期最高,在N1水平下,拔节至开花期日耗水量与开花至成熟期的无显著差异。同一施氮水平下,小麦开花后总耗水量、耗水模系数和日耗水量随灌水量的增加而提高,但产量随灌水量的增加先升高后降低。(2)同一施氮水平下,成熟期W1处理20—140cm各土层土壤含水量低于W2和W3处理,140—200cm土层土壤含水量与W2处理无显著差异;W1处理0—40cm土层土壤硝态氮含量及植株氮素在籽粒中的分配比例高于W2和W3处理,100—140cm土层土壤硝态氮含量及植株氮素在营养器官中的分配量和分配比例低于W2和W3处理。表明灌溉底墒水和拔节水的W1处理,促进了小麦对20—140cm土层土壤水的吸收利用,减少了土壤硝态氮向100cm以下土层的淋溶,而且有利于营养器官中氮素向籽粒的再分配,水分和氮素利用效率较高。(3)在试验条件下,施纯氮210kg·hm-2、灌溉底墒水和拔节水的N2W1处理,籽粒产量最高,水分利用效率和氮素利用效率较高,可供生产中参考。