Salicylic Acid Alleviates the Adverse Effects of Salt Stress in Torreya grandis cv. Merrillii Seedlings by Activating Photosynthesis and Enhancing Antioxidant Systems

Background

Salt stress is a major factor limiting plant growth and productivity. Salicylic acid (SA) has been shown to ameliorate the adverse effects of environmental stress on plants. To investigate the protective role of SA in ameliorating salt stress on Torreya grandis (T. grandis) trees, a pot experiment was conducted to analyze the biomass, relative water content (RWC), chlorophyll content, net photosynthesis (Pn), gas exchange parameters, relative leakage conductivity (REC), malondialdehyde (MDA) content, and activities of superoxide dismutase (SOD) and peroxidase (POD) of T. grandis under 0.2% and 0.4% NaCl conditions with and without SA.

Methodology/Principal Findings

The exposure of T. grandis seedlings to salt conditions resulted in reduced growth rates, which were associated with decreases in RWC and Pn and increases in REC and MDA content. The foliar application of SA effectively increased the chlorophyll (chl (a+b)) content, RWC, net CO₂ assimilation rates (Pn), and proline content, enhanced the activities of SOD, CAT and POD, and minimized the increases in the REC and MDA content. These changes increased the capacity of T. grandis in acclimating to salt stress and thus increased the shoot and root dry matter. However, when the plants were under 0% and 0.2% NaCl stress, the dry mass of the shoots and roots did not differ significantly between SA-treated plants and control plants.

Conclusions

SA induced the salt tolerance and increased the biomass of T. grandis cv. by enhancing the chlorophyll content and activity of antioxidative enzymes, activating the photosynthetic process, and alleviating membrane injury. A better understanding about the effect of salt stress in T. grandis is vital, in order gain knowledge over expanding the plantations to various regions and also for the recovery of T. grandis species in the future.     

Spatial Heterogeneity of Selected Soil Nutrients Related to <i>Torreya grandis</i> cv. <i>Merrillii</i> Plantation in Southeastern China

Chinese Torreya grandis (Torreya grandis cv. Merrillii) is a unique economic tree species in China. Intensive management related to application of chemical fertilizer and herbicides caused serious soil quality degradation of Chinese Torreya grandis plantations. Totally, 120 soil samples were collected from the main disbtributed areas of Chinese Torreya grandis in Southeastern China. In this area, soil pH values varied from 3.68 to 6.78, with a median value of 4.91, implying a trend of acidification. The average concentrations of organic matter, available nitrogen, available phosphorus and available potassium were 27.52 g kg⁻¹, 135.77 mg kg⁻¹, 15.12 mg kg⁻¹, and 153.43 mg kg⁻¹, respectively. The results of spatial analysis revealed that target variables had clear spatial patterns. The soil fertility was relevantly high in most of the study area, with soil nutrient imbalances existing. The stand age had a large effect on soil properties, which were also mainly influenced by human activities. Therefore, it is necessary to change the fertilization method for a sustainable management of Torreya grandis plantation.     

亚热带典型树种对模拟酸雨胁迫的高光谱响应

对亚热带地区6种典型树种幼苗在不同模拟酸雨梯度下的光谱响应特征进行了研究。结果表明,针叶树种和阔叶树种对酸雨敏感性具有明显差异。针叶树种马尾松、杉木和香榧对酸雨敏感性高于阔叶树种刨花楠、香樟和杨梅。针叶树种内部,马尾松和杉木叶绿素含量随酸雨浓度变化的幅度明显高于香榧;而阔叶树种内部,刨花楠、香樟和杨梅三者之间无显著差别。马尾松、香樟和香榧不能承受长时间高浓度酸雨胁迫,叶绿素含量呈先增加后减少趋势,杉木则先减少后增加,杨梅能承受长时间高浓度酸雨胁迫,pH值2.5处理下叶绿素含量高于pH值5.6处理。刨花楠4期试验中叶绿素含量变化无明显规律。各受试植物光谱反射率红边位置与其叶绿素含量变化规律基本一致。针叶树种马尾松和香榧主要表现为"蓝移",杉木则先"蓝移"后"红移",表现出对高浓度酸雨长时间的抗性;阔叶树种香樟先"红移"后"蓝移",对高浓度模拟酸雨表现出先促进后抑制现象,杨梅光谱反射率一阶导数曲线比较平缓,无明显"红移"和"蓝移"现象,刨花楠则"红移"和"蓝移"交替出现,与其叶绿素含量变化相一致,对酸雨敏感性不明显。     

Salicylic acid induces physiological and biochemical changes in Torreya grandis cv. Merrillii seedlings under drought stress

Key message

SA treatment effectively ameliorated the negative effect of moderate drought stress on T. grandis Seedlings through increasing the water content, Pn, proline content, antioxidant enzymes activity and reducing MDA.

Abstract

Water availability is one of the most critical factors that limits the growth and development of plants. Salicylic acid (SA) is an important signal molecule that modulates plant responses to abiotic stress. To elucidate the regulating mechanism of exogenous SA on Torreya grandis cv. Merrillii under different water stresses, a pot experiment was conducted in a greenhouse. Exposure of T. grandis seedlings to drought conditions resulted in reduced growth rate that was associated with a decline in water content and CO₂ assimilation. Foliar application of SA effectively increased the water content, net CO₂ assimilation rate, proline content and antioxidant enzymes activity in the plants, which helped T. grandis to acclimate to moderate drought stress and increase the shoot dry matter. However, when the plants were under severe drought stress, the relative water content and CO₂ assimilation in the SA-treated plants were significantly lower than those in the control plants. Therefore, our results indicated that SA can effectively ameliorate the negative effect of moderate drought stress on T. grandis seedling growth.     

Characterization of Arbuscular Mycorrhizal Fungus Communities of Aquilaria crassna and Tectona grandis Roots and Soils in Thailand Plantations

Aquilaria crassna Pierre ex Lec. and Tectona grandis Linn.f. are sources of resin-suffused agarwood and teak timber, respectively. This study investigated arbuscular mycorrhizal (AM) fungus community structure in roots and rhizosphere soils of A. crassna and T. grandis from plantations in Thailand to understand whether AM fungal communities present in roots and rhizosphere soils vary with host plant species and study sites. Terminal restriction fragment length polymorphism complemented with clone libraries revealed that AM fungal community composition in A. crassna and T. grandis were similar. A total of 38 distinct terminal restriction fragments (TRFs) were found, 31 of which were shared between A. crassna and T. grandis. AM fungal communities in T. grandis samples from different sites were similar, as were those in A. crassna. The estimated average minimum numbers of AM fungal taxa per sample in roots and soils of T. grandis were at least 1.89 vs. 2.55, respectively, and those of A. crassna were 2.85 vs. 2.33 respectively. The TRFs were attributed to Claroideoglomeraceae, Diversisporaceae, Gigasporaceae and Glomeraceae. The Glomeraceae were found to be common in all study sites. Specific AM taxa in roots and soils of T. grandis and A. crassna were not affected by host plant species and sample source (root vs. soil) but affected by collecting site. Future inoculum production and utilization efforts can be directed toward the identified symbiotic associates of these valuable tree species to enhance reforestation efforts.     

不同树龄香榧土壤有机碳特征及其与土壤养分的关系

该研究以浙江省诸暨市的香榧国家森林公园5个树龄段(0~50、50~100、100~300、300~500和500a以上)的香榧(Torreyagrandis)为研究对象,通过野外采集土壤样品,分析其0~20、20~40、40~60cm土层土壤总有机碳(TOC)、易氧化碳(ROC)、轻组有机质(LFOM)及土壤养分含量,探讨不同树龄香榧土壤有机碳变化规律,为香榧林的土壤质量评价与持续利用,以及香榧古树的保护提供理论依据。结果表明:(1)不同树龄香榧土壤的总有机碳、易氧化碳和轻组有机质含量均随香榧树龄的增加呈先增大后减小的趋势,且300~500a生的数值最大,但易氧化碳与轻组有机质含量在各树龄间的差异不明显。(2)不同树龄香榧土壤中易氧化碳占总有机碳的比例总体表现为:50~100a0~50a100~300a300~500a500a以上(0~20cm土层除外)。(3)各树龄段香榧土壤易氧化碳和轻组有机质含量与土壤总有机碳之间的相关性均达到极显著水平;不同树龄段香榧土壤总有机碳、各活性有机碳组分与全氮(TN)、水解性氮(AN)、有效磷(AP)之间的相关性较好(0~50a生除外),与速效钾(AK)、交换性钙(Ca)和交换性镁(Mg)之间的相关性较差(500a以上除外);500a以上香榧土壤总有机碳、各活性有机碳组分与土壤养分的相关性均达到极显著水平。     

榧属分类学研究

本文对榧属的研究历史作了回顾, 以形态性状为依据, 结合其他学科的研究成果, 对榧属的分类进行了研究, 该属共6种2变种和11个栽培变种, 其中有1新变种(九龙山榧)、1改级新组合(云南榧)和6个新栽培变种。支持根据种子胚乳深皱与微皱建立两个组和榧属为红豆杉科进化类群的观点。     

First record of the insect pathogenic alga Helicosporidium sp. (Chlorophyta: Trebouxiophyceae) infection in larvae and pupae of Rhizophagusgrandis Gyll. (Coleoptera, Rhizophaginae) from Turkey

The predator beetle Rhizophagus grandis Gyll. (Coleoptera, Rhizophaginae) is one of the most important biological control agents, mass-bred and used to suppress populations of an important pest: the great spruce bark beetle, Dendroctonus micans. The achlorophyllous alga Helicosporidium sp. was first discovered in the pest. Later it was also found in the predator, but only in the adults. In this study, the pathogenic alga Helicosporidium sp. was discovered in larvae and early pupae of R. grandis for the first time. The morphological characteristics of the pathogenic alga were revealed by light and electron microscopy. Infection rates of Helicosporidium sp. in the larvae and pupae of R. grandis were 23.5% and 6.25%, respectively.     

18-Oxoferruginol from the leaf of Torreya nucifera

From the leaf of the conifer Torreya nucifera, a new diterpenoid has been isolated and shown to be 18-oxoferruginold (12-hydroxy-8,11,13-abietatrien-18-al) on the basis of its spectroscopic properties and its chemical conversion to the known 18-hydroxyferruginol (8,11,13-abietatriene-12,18-diol).     

New observations on some poorly known protasterid ophiuroids from the Lower Devonian Hunsrück Slate of Germany

Four genera and species of protasterid ophiuroids have been reported from the Lower Devonian Hunsrück Slate:Bundenbachia beneckei, Palaeophiomyxa grandis, Mastigophiura grandis, andPalaeophiura simplex. In addition, the speciesMiospondylus rhenanus has traditionally been recognized as a member of the Lapworthuridae, a group of ophiuroids with paired but unfused ambulacrals. This ambulacral arrangement would make it unique among Hunsrück Slate ophiuroids.Palaeophiura simplex andM. rhenanus were originally based on Single, poorly preserved specimens, and their morphology has remained poorly understood. A restudy of the type material offP. simplex andM. rhenanus and a detailed comparison to other Hunsrück ophiuroids warrants reassignment of these taxa toBundenbachia beneckei.Palaeophiura simplex is a juvenile example of this species andM. rhenanus is a peculiarly preserved adult. A newly prepared, well-preserved specimen ofBundenbachia beneckei expands our knowledge of the morphology of its mouthframe. In addition,Mastigophiura grandis is revised and redescribed based on newly recognized fossil material.     

Description and Phylogeny of Urostyla grandis wiackowskii subsp. nov. (Ciliophora,Hypotricha) from an Estuarine Mangrove in Brazil

Interphase specimens, aspects of physiological reorganization and divisional morphogenesis were investigated in a strain of a hypotrichous ciliate highly similar to Urostyla grandis Ehrenberg, 1830 (type species of Urostyla), collected from a mangrove area in the estuary of the Paraíba do Sul river (Rio de Janeiro, Brazil). The results revealed that albeit interphase specimens match with the known morphologic variability in U. grandis, morphogenetic processes have conspicuous differences. Parental adoral zone is entirely renewed during morphogenesis, and marginal cirri exhibit a unique combination of developmental modes, in which left marginal rows originate from multiple anlagen arising from innermost left marginal cirral row, whereas right marginal ciliature originates from individual within‐row anlagen. Based on such characteristics, a new subspecies, namely U. grandis wiackowskii subsp. nov. is proposed, and consequently, U. grandis grandis Ehrenberg, 1830 stat. nov. is established. Bayesian and maximum‐likelihood analyses of the 18S rDNA unambiguously placed U. grandis wiackowskii as adelphotaxon of a cluster formed by other U. grandis sequences. The implications of such findings to the systematics of Urostyla are discussed.     

大鹅观草与蛇河披碱草属间杂种的细胞遗传学研究

为探讨大鹅观草(Roegneria grandis,2n=4x=28)的染色体组组成,为其正确的分类处理提供细胞学依据。该研究通过人工远缘杂交,成功获得3株大鹅观草与蛇河披碱草(Elymus wawawaiensis,2n=4x=28)属间杂种F1植株。杂种植株形态介于两亲本之间,不育。亲本及杂种经I2-IK溶液染色后进行花粉育性检测,结果显示Roegneria grandis和Elymus wawawaiensis的花粉可育,育性高达94.6%和90.5%;杂种F1不育。花粉母细胞减数分裂中期I染色体配对结果显示,亲本花粉母细胞配对正常,均形成14个二价体,以环状二价体为主,Roegneria grandis有频率很低(0.04/细胞)的单价体出现;杂种F1平均每个花粉母细胞形成6.46个二价体,变化范围为5~8;在观察的83个花粉母细胞中,有35.2%的花粉母细胞形成了7个二价体,形成6个二价体的细胞占42.59%,较少细胞形成8个二价体;平均每个细胞形成14.66个单价体,变化范围为10~18;平均每细胞观察到0.14个三价体;杂种花粉母细胞染色体构型为14.66 I+6.46 II+0.14 III;平均每细胞交叉数为9.83,C值为0.35。结果表明:(1)R.grandis与Elymus wawawaiensis有一组染色体组同源的St染色体组,另外一组染色体组不是St或者H染色体组,Roegneria grandis的染色体组组成不是St Stg;(2)较低频率的三价体(平均0.14个/细胞),可能是由于R.grandis的St和Y染色体组间具有一定的同源性,也可能是染色体易位等原因导致,对于Y染色体组的起源还需深入地研究;(3)在不同地理来源的披碱草属和鹅观草属物种中St染色体组同源性不同,R.grandis与来自于北美的Elymus lanceolatus与E.wawawaiensis的St染色体组较与分布于亚洲的E.sibiricus和E.caninus的St染色体组同源性反而更高,其原因还需要进一步地研究。     

巨桉根系分解对菊苣生长及光合特性的影响

巨桉是我国退耕还林过程中采用的重要速生树种之一,被广泛用于人工造林。采用盆栽试验,研究了巨桉根系分解初期对菊苣幼苗生长和光合生理特性的影响。试验设置A1(50 g/盆)、A2(100 g/盆)和对照(CK)3个根系水平,将各处理的根系分别与10 kg土壤混合后装盆,播种菊苣。待A2处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标。结果表明:在巨桉根系分解初期,明显抑制了菊苣高生长、根生长、生物量积累、叶面积扩展及光合色素的合成,且随着根系添加量的增加抑制作用加大;菊苣叶片胞间CO2浓度(Ci)增加,而净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著低于对照;随土壤中根系含量的增加,除CO2补偿点(CCP)呈增加趋势外,其他光响应和CO2响应的特征参数均呈明显的下降趋势,并与对照差异显著;各生长指标除与胞间CO2浓度呈现出负相关外,与其它光合特征参数、光合色素以及相应的响应曲线参数之间均呈现出显著或极显著的正相关关系;通过GC-MS检测表明,巨桉根系中含有2,6-二叔丁基对甲酚、N-甲基苯乙胺等多种具有化感潜力化学物质,在其分解过程中,这些化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长。     

抗风桐(Pisonia grandis)的生态生物学特征

对收集于广西桂林的17份野生毛葡萄种质和24份栽培葡萄种质,分别使用12条ISSR和12条SCoT引物进行了遗传多样性和亲缘关系检测。结果表明：两种分子标记均能产生较丰富的多态性片段,可有效应用于葡萄的遗传多样性检测,但在聚类分析结果上表现出一定的差异性,SCoT分子标记能更好地区分野生种质和栽培品种,说明SCoT分子标记在葡萄遗传多样性检测和系统进化研究上可能更有优势。从SCoT聚类结果上看,广西植物研究所收集的3个野生毛葡萄种质zws1、zws2和zws3相对其它野生种质而言,更偏向于与栽培种质聚为一类,说明这一类野生毛葡萄可能是这些栽培品种的原始亲本来源之一。不同的野生种质聚为多个类群,并表现出明显的地域特性,但遗传距离相对较远,说明桂林野生毛葡萄资源具有丰富的遗传变异。栽培品种没有明显的聚类特点,可能因为所选用的栽培品种的地域代表性并不是很强,也可能是因为栽培品种在不断的人工杂交选育过程中,遗传背景趋向一致,遗传多样性降低。该研究证明SCoT分子标记在葡萄遗传多样性研究上具有一定的优势。该研究结果为桂林毛葡萄资源的保护、利用和品种选育提供了理论依据,也为葡萄的系统进化研究提供了参考。     

香榧主产区林地土壤养分空间异质性及其肥力评价

选取浙江省香榧(Torreya grandis cv.Merrillii)主产区为研究对象,系统采集表层土壤(0—20 cm)样品121个,基于地统计学及Moran′s I等空间分析方法揭示土壤养分的空间异质性,估算了香榧林地土壤综合肥力并分析其影响因素。结果表明:研究区土壤pH较低,有机质、碱解氮、有效磷和速效钾含量较高,平均含量分别为4.91、30.60 g/kg、136.77 mg/kg、15.02 mg/kg、153.42 mg/kg;基于半方差函数分析得出,土壤pH和养分要素属于中等空间相关性,其中pH的变程最小为3.29 km,有机质、碱解氮、有效磷和速效钾的变程分别为8.52、5.84、8.82、6.49 km;克里格空间插值和局部Moran′s I指数结果揭示土壤pH、有机质、碱解氮、有效磷和速效钾均存在明显的空间分布格局和局部空间聚集现象,土壤有机质、碱解氮、有效磷和速效钾低值区主要分布在诸暨市和东阳市,高值区主要分布在柯桥区和嵊州市,而pH的空间分布格局与之相反;诸暨市和东阳市部分地区土壤综合肥力指数较低,而其他区域的土壤肥力水平较高。总体上,浙江省香榧主产区土壤酸化以及养分失衡现象较为严重,尤其是速效钾含量过高。从相关性分析结果来看,环境变量对香榧林地土壤养分的影响较小,而林龄对土壤pH和养分的影响较大。可见,研究区土壤养分受人为活动影响明显。因此,需根据实际情况,改善林农的施肥管理方式,调整施肥数量和结构并开展土壤酸性改良,因地制宜制定区域施肥规划。     

Ecological Effects of the Invasive Giant Madagascar Day Gecko on Endemic Mauritian Geckos: Applications of Binomial-Mixture and Species Distribution Models

The invasion of the giant Madagascar day gecko Phelsuma grandis has increased the threats to the four endemic Mauritian day geckos (Phelsuma spp.) that have survived on mainland Mauritius. We had two main aims: (i) to predict the spatial distribution and overlap of P. grandis and the endemic geckos at a landscape level; and (ii) to investigate the effects of P. grandis on the abundance and risks of extinction of the endemic geckos at a local scale. An ensemble forecasting approach was used to predict the spatial distribution and overlap of P. grandis and the endemic geckos. We used hierarchical binomial mixture models and repeated visual estimate surveys to calculate the abundance of the endemic geckos in sites with and without P. grandis. The predicted range of each species varied from 85 km² to 376 km². Sixty percent of the predicted range of P. grandis overlapped with the combined predicted ranges of the four endemic geckos; 15% of the combined predicted ranges of the four endemic geckos overlapped with P. grandis. Levin''s niche breadth varied from 0.140 to 0.652 between P. grandis and the four endemic geckos. The abundance of endemic geckos was 89% lower in sites with P. grandis compared to sites without P. grandis, and the endemic geckos had been extirpated at four of ten sites we surveyed with P. grandis. Species Distribution Modelling, together with the breadth metrics, predicted that P. grandis can partly share the equivalent niche with endemic species and survive in a range of environmental conditions. We provide strong evidence that smaller endemic geckos are unlikely to survive in sympatry with P. grandis. This is a cause of concern in both Mauritius and other countries with endemic species of Phelsuma.     

Edaphic factors do not govern the ectomycorrhizal specificity of Pisonia grandis (Nyctaginaceae)

Pisonia grandis (Nyctaginaceae), a widespread tree of Pacific coral atolls and islands, displays one of the more restrictive ranges of ectomycorrhizal (ECM) fungus associates among autotrophic plants. Only five ECM fungi are currently known associates; our study adds one. In many habitats, P. grandis is restricted to large seabird colonies where nitrogen and phosphorus inputs in the form of guano are substantial. It has been suggested that the ECM specificity displayed by P. grandis is the result of the unusual nutrient-rich habitat in which P. grandis grows. On Rota, Commonwealth of the Northern Mariana Islands, P. grandis grows in habitats heavily influenced by guano additions and also in upland forests where seabirds do not roost or nest. To test the hypothesis that the ECM specificity displayed by P. grandis is the result of nutrient-related or toxicity-related factors associated with guano inputs, we sampled P. grandis growing in both guano-rich and guano-poor habitats on Rota, Commonwealth of the Northern Mariana Islands. We identified ECM symbionts of P. grandis from both habitats as well as two symbionts of Intsia bijuga (Fabaceae) from nutrient-rich habitats. We identified three ECM symbionts of P. grandis from Rota; all three were found in both guano-rich and guano-poor habitats. No differences in community diversity were detected between guano-rich and guano-poor habitats. We also detected two ECM fungal species associating with I. bijuga but not associating with P. grandis inside guano-rich habitats. From these results, we infer that edaphic factors are not responsible for limiting the ECM community associating with P. grandis to its observed level of specificity.     

短周期尾巨桉能源林生物量与能量特征研究

为开发和利用尾巨桉能源林,通过测量1~4年生植株的叶片、树枝、树根、树干和树皮的热值和生物量,对短周期尾巨桉能源林的生物量和能量特征进行了研究。结果表明,尾巨桉叶片、树枝、树干、树根、树皮和林分生物量均随林龄增加而增加,叶片、树枝、树皮生物量占单株总生物量的比例逐年减小,而树干则呈逐年升高趋势。1~4年生尾巨桉单株和林分的生物量分别为4.32~66.29 kg和10.68~153.33 t hm-2。生物量的结构特征表明,尾巨桉林分在第4年开始郁闭,生长以增加树干的生物量为主。尾巨桉各组分的平均干质量热值为17.23~20.56 kJ g-1,且差异极显著(P<0.01),以叶片的值最高、树皮的最低;同一组分不同林龄的热值差异不显著(P>0.05)。1~4年生尾巨桉的单株和林分能量现存量为81.61~1255.22 MJ和201.83~2903.32 GJ hm-2,其变化趋势及大小排列顺序与生物量相同。因此,对尾巨桉能源林可以4年短周期进行经营。     

Pyrones from the bark of Garcinia conrauana: Conrauanalactone,a novel C20 derived α-pyrone

Conrauanalactone has been isolated from the bark of Garcinia conrauana Engl. (Guttiferae) and identified, on the basis of spectral and chemical evidence, as 4-hydroxy-6-pentadecyl- 2-pyrone. Minor constituents of the bark have been identified as 5,7-dihydroxychromone and eriodictyol.     

速生树种尾巨桉和竹柳幼苗耗水特性和水分利用效率

速生树种尾巨桉和竹柳因其水分消耗和利用问题引起了一些争议,因而受到了广泛的关注,由于尚缺乏科学的观测数据,而其中许多指责或支持也尚无定论,因此必须深入研究此2种树种耗水性能和水分利用效率,以期科学评价其水分消耗和利用性能。采用盆栽苗木称重法和Li-6400光合系统测定方法分别测定尾巨桉(Eucalyptus urophylla×Eucalyptus grandis)和竹柳(Salix sp.)苗木在不同土壤水分条件下耗水量、耗水速率和苗木不同生长期叶片净光合速率(Pn)、蒸腾速率(Tr)和水分利用效率(WUE),研究表明:(1)正常水分条件下,尾巨桉和竹柳日总耗水量和最大耗水速率分别为(182.05±12.74)g/d、(100.48±10.95)g/d和(66.31±9.91)g·m-2·h-1、(89.50±13.54)g·m-2·h-1,土壤水分条件下降时,2种苗木耗水量和耗水速率均呈显著下降趋势,严重干旱胁迫时尾巨桉降幅更大。(2)正常水分条件和轻度水分胁迫下2种苗木耗水速率日变化趋势均为明显"单峰"曲线,且峰值均出现在12:00—14:00,中度干旱胁迫时则其变化趋势呈"双峰"曲线,峰值分别在10:00—12:00和14:00—16:00出现,严重干旱胁迫时日变化规律不明显。(3)正常水分条件和轻度水分胁迫下2种苗木耗水速率与环境温度显著正相关,与相对湿度显著负相关,随着干旱胁迫的发展,环境因子对耗水速率的影响有所减弱。(4)叶片水平来看,与尾巨桉相比,竹柳具有高光合、低蒸腾、高水分利用效率的特点,2种苗木由生长初期进入生长旺期时,净光合速率和蒸腾速率均发生相同幅度增加,而水分利用效率基本保持不变。(5)从单株耗水量和耗水速率以及叶片水分利用效率综合来看,竹柳属节水性能较好速生树种,而尾巨桉虽然存在叶片水平高蒸腾和低水分利用效率的情况,但从单株苗木水平上来讲,其耗水速率甚至低于竹柳,特别在土壤水分严重亏缺情况下其白天平均耗水速率仅为(4.02±0.60)g·m-2·h-1,也表现出了一定的抗旱节水能力。