新疆准噶尔盆地不同径级梭梭和白梭梭的水分来源

在干旱区,水是植物生长发育的主要限制性因子。运用稳定氧同位素技术探究了准东地区生长在相邻地段不同径级的梭梭(Haloxylon ammodendron)和白梭梭(Haloxylon persicum)的水分来源。通过测定不同径级梭梭和白梭梭的小枝木质部水、不同土层的土壤水以及地下水的δ~(18)O同位素值,运用MixSIAR模型、平均吸水深度模型和直观图法分析不同径级梭梭和白梭梭对各潜在水源的利用比例和主要吸水层位。结果表明:生长在丘间低地的四个径级梭梭主要水源是土壤水,随着径级的增长,梭梭水分利用方式更加灵活,趋向于利用稍浅层的土壤水。生长在沙丘顶部的四个径级白梭梭主要水源是土壤水,随着径级的增长,白梭梭更趋向于利用深层土壤水。梭梭和白梭梭通过不同的水分利用策略合理的利用干旱区有限的水源。     

新疆艾比湖湿地自然保护区荒漠优势种体内的水分来源

植物体内各水分来源的比例反映植物的适应特征,在水分作为限制因子的荒漠区,其更是物种间生态位分化、荒漠多样性维持的重要机理之一。通过检测艾比湖湿地自然保护区内4个生境(荒漠、河岸林、盐沼地和沙丘)的8科14种优势种的木质部,以及当地河水、地下水、4层不同深度(0—40,40—70,70—100 cm和100—150 cm)土壤水的稳定氧同位素值(δ~(18)O),估算各物种和各科植物体内各种水分来源的比例,随后依据根系的空间位置再将14种植物分成13个中深根系和1个浅根系物种,进一步利用δ~(18)O值分析深浅根系植物间的水分差别,以及各水源间的补给关系。结果表明:(1)艾比湖湿地自然保护区内,不同物种体内水分来源存在差别。将所有优势物种按科属归类后,类似物种水平,不同科属植物体内的水分来源也存在差别;(2)地下水是大部分植物的主要补给水源,多数植物很少利用0—40 cm表层土壤水;(3)深浅根系植物的水分来源不同,深根系植物主要利用地下水和河水,而浅根系植物主要利用土壤水;(4)艾比湖湿地自然保护区内,地下水补给河水,随后两者共同从土壤深层至浅层依次补给土壤水。综上可知:干旱荒漠内,水源可利用性的多样化,导致不同区域植物体内各水分来源的比例存在差别。在离河岸距离、地下水位高低、土壤表层盐渍化程度等因素的综合影响下,多年生和盐渍环境生长的植物,趋向于吸收地下水、河水和深层土壤水,相反,一年生或短命植物趋向于利用其能触及到的各种水源。     

元阳梯田水源区旱冬瓜水分来源

旱冬瓜(Alnus nepalensis)是元阳梯田水源区的优势树种之一,其作为一种速生树种被发展为当地居民重要的薪炭林和经济林,树种的生长发育和地理分布受到水分制约,其吸收水分和水分利用的变化将会直接影响森林生态系统的水循环。该研究于2014年5－11月间进行,研究时段内累计降雨1262 mm,地下水δD 值在－71‰~－53‰范围,δ18 O 在－10.6‰~－7.0‰范围,受环境因子的影响很小,基本上保持常年稳定。土壤水是可供树种直接吸收利用的水源,基于氢氧稳定同位素技术,对比元阳梯田水源区旱冬瓜树种茎干水δD 和其林地不同深度土壤水δD 的同位素组成情况,结合不同深度土壤含水量,定性分析判断旱冬瓜对土壤水的利用,结果表明旱冬瓜旱季利用的土壤水主要分布在40 cm 土层附近,而雨季利用的土壤水范围较广,分布在0~60 cm 的土层。利用多元线性混合模型 IsoSource 软件定量分析旱冬瓜对土壤水和地下水的利用,结果表明：旱冬瓜水分来源分布较广,各土层土壤水和地下水均有贡献,雨季旱冬瓜主要利用0~60 cm 深土壤水,其中雨后旱冬瓜绝大部分水分来源于0~10 cm 的土壤水分,利用比例为66％~73％;其它时间主要利用40~60 cm 的土壤水,贡献率高达73％;旱季旱冬瓜的绝大部分水分来源于地下水,对地下水的利用比例为18％~68％,同时,40~60 cm 的土壤水也是其重要的水源。从不同时间尺度考察旱冬瓜对土壤水和浅层地下水的需求,更加准确地认识元阳梯田水源区不同森林类型优势树种的水分来源,为梯田森林生态系统经营与维护以及梯田的可持续发展提供了理论依据。     

准噶尔盆地东南缘多枝柽柳、白刺和红砂水分来源的异同

荒漠生态系统中, 水是植物生长最主要的限制因子。为了比较同一生境下不同荒漠植物的水分来源特征, 选取了同一生境下的多枝柽柳(Tamarix ramosissima)、白刺(Nitraria sibirica)和红砂(Reaumuria soongorica), 测定了这3种植物茎水和各潜在水源(降水、土壤水和地下水)的氢、氧稳定同位素比率(δD和δ¹⁸O)值, 并利用IsoSource软件计算了3种植物对潜在水源的利用比例。结果表明: 红砂和白刺的茎水δD和δ¹⁸O值及其水分来源有明显的季节波动特征。其中, 红砂为浅根系植物, 春季(3-5月)以表层土壤水为主要水源, 夏秋季节(6-10月)表层土壤含水量显著降低, 其主要的水分来源逐渐偏向于较深层的土壤水; 白刺的根系分布范围介于红砂和多枝柽柳之间, 在春季能够较多地利用表层土壤水, 而到了夏秋季节, 所利用的水分更多地来源于深层土壤水或地下水; 多枝柽柳为深根系植物, 其90%以上的水分来源于深层土壤水和地下水, 而且茎水δD和δ¹⁸O值及其水分来源没有季节波动特征。3种植物水分来源特征的差异与其水分利用策略密切相关, 同时, 也说明荒漠灌木可以通过自身调节向着最优(最有利)表现型发展, 从而最大限度地获取水分。     

Water use strategy of Ammopiptanthus mongolicus community in a drought year on the Mongolian Plateau

在荒漠生态系统中,水分是植物生长和植被动态的一个限制因子。来自深层土壤或地下水相对稳定的水分对于干旱条件下植物的生存至关重要。在荒漠生态系统中,保护和恢复濒危植物的根本在于理解它们的水分利用策略,例如蒙古高原的沙冬青(Ammopiptanthus mongolicus)。本 论文通过稳定氢、氧同位素技术研究了沙冬青和与其伴生的两种灌木黑沙蒿(Artemisiaordosica)和旱蒿(Artemisiaxerophytica)的 主要水分来源;利用IsoSource模型计算了不同水分来源对每个物种的贡献,并通过比较3种灌木叶片δ ¹³C值和和其根系分布探讨了3种 灌木的长期水分利用策略。结果表明,沙冬青依赖地下水和150–200 cm 深层土壤水,前者几乎贡献其水源的一半。黑沙蒿主要利用150–200 cm 深 层土壤水,但是夏季和秋季也利用100 cm以内的浅层土壤水。旱蒿主要利用150–200 cm深层土壤水和地下水,后者对其总水源的贡献率 大约为30%–60%。3种灌木具有双型根系或深根系,这些根系特征与其水分来源一致。常绿植物沙冬青的叶片δ ¹³C值高于两种落叶蒿属灌木,这可能使其在适应荒漠生态系统中具有优势。因此,地下水是干旱年份蒙古高原濒危灌木沙冬青的一个主要水源,而且沙冬青和两种蒿属灌木竞争深层土壤水和地下水。     

额济纳三角洲胡杨和多枝柽柳水分来源解析

为研究黑河下游额济纳三角洲典型河岸带植物胡杨(Populus euphratica)和多枝柽柳(Tamarix ramosissima)的水分来源及其时空变化特征,于2015–2016年植物生长期在额济纳东、西河沿岸选取8处样点,分别采集胡杨和多枝柽柳木质部、土壤以及降水、河水、地下水样品,分析测试获取各样品的氧稳定同位素比率(δ18O),并利用氧同位素直接对比法确定植物主要吸水层位,利用Iso Source线性混合模型确定胡杨和多枝柽柳水分来源构成及比例。研究表明:河水和地下水为胡杨和多枝柽柳的主要补给水源,降水补给因雨水少且入渗浅可忽略不计;胡杨和多枝柽柳吸收土壤水的层位因地下水位波动、土壤物理特性、河水对土壤水的侧向补给及漫溢补给等存在较大的空间差异,但其利用河水和地下水的比例未见明显空间差异;胡杨更多地利用河水(68%),而多枝柽柳更多地利用地下水(65%);植物水分来源对生态输水工程响应敏感,河水贡献率在输水期增大至84%和48%,非输水期下降至63%和30%,地下水贡献率在输水期下降至16%和52%,非输水期增大至37%和70%。值得指出的是,河岸带地下水与河水交互作用强烈,导致地下水与河水的δ18O较为接近,使得源分解析定量具有不确定性。     

基于氢氧稳定同位素的黄河兰州段河岸植物水分来源

多枝柽柳和旱柳是北方地区河岸生态修复的良好树种,具有护河防洪、调节区域气候的作用和营造河岸地带植被景观的功能。本研究选取黄河兰州段沿岸2处样点,采集了多枝柽柳和旱柳木质部以及各潜在水源的样品,利用氧同位素直接对比法、贝叶斯混合模型MixSIAR和相似性比例指数(PS指数),分析了多枝柽柳和旱柳对各潜在水源的利用率以及两者之间的水分利用关系。结果表明: 在整个生长季,浅层土壤水(0～30 cm)是多枝柽柳和旱柳的主要水分来源,利用率分别为28.3%和24.4%,多枝柽柳对河水的利用率最小(16.6%),旱柳对地下水的利用率最小(17.9%);在土壤含水量较低的月份,植物会增加对河水和地下水的利用比例,样点S₁和S₂的PS指数分别为91.0%和87.7%,两个样点均在5月的PS指数最大,不同月份的水分利用关系存在一定的差异;处于河漫滩这一特殊地理位置,多枝柽柳和旱柳对各潜在水源的利用比较平均,最大程度地获取各潜在水源的水分,是一种最优的吸水模式。本研究可为开展黄河兰州段河岸休闲旅游活动和黄河流域生态环境保护中植物水分管理提供一定的理论基础。     

降雨对高寒沙地不同林龄中间锦鸡儿水分利用特征的影响

为明确不同林龄中间锦鸡儿水分来源对降雨的响应,利用稳定同位素技术测定青海共和盆地不同林龄的中间锦鸡儿(4 a、9 a、17 a和31 a)在降雨前后土壤水、木质部水、地下水和雨水的δ²H、δ¹⁸O组成,运用Iso-Source模型计算植物对各潜在水源的利用比例。结果表明: 各林龄中间锦鸡儿的浅层(0～40 cm)土壤水δ²H、δ¹⁸O组成对降雨的响应最明显;降雨前后各林龄中间锦鸡儿的木质部水、土壤水分和地下水同位素值均位于当地大气降水线(LMWL)的右下侧,其截距和斜率均小于LMWL和全球大气降水线(GMWL),且降雨后中间锦鸡儿的木质部水和土壤水的同位素组成更趋近LMWL;降雨前,4 a和9 a中间锦鸡儿主要利用浅层土壤水,17 a中间锦鸡儿主要利用中层(40～90 cm)土壤水,31 a中间锦鸡儿主要利用深层土壤水;降雨后,各林龄中间锦鸡儿的吸水层位均为降雨补充的浅层土壤水;各林龄对地下水的利用率仅有1.8%～11.9%。说明不同林龄中间锦鸡儿的水分来源对降雨的响应方式相同,均优先利用降雨补充的浅层土壤水,对地下水的利用减少。     

基于同位素技术分析不同生长季节杨树水分利用

本文利用碳、氢、氧同位素示踪技术,将直接判断法、多元线性混合模型相结合,分析正蓝旗地区杨树不同季节的吸水来源和水分利用效率。结果表明:杨树吸水来源具有明显季节性规律,生长前期和末期(4、5、10月),主要利用0~50 cm浅层土壤水和150 cm以下的深层土壤水或地下水;生长中期(6、7、8、9月)主要利用0~150 cm土壤中的降水水源。该地区杨树的水分利用效率较高,5—9月水分利用效率为208.68、133.90、62.01、61.92、257.55 mmol C·mol-1H2O。当雨季浅层土壤水无法满足杨树的需水量时,杨树吸收较深层的土壤水,并逐渐提高水分利用效率;有降水时,杨树开始从最上层的土壤水中吸收降雨水源并逐渐降低水分利用效率。以上结果表明,半干旱地区杨树具有较高的水分利用效率,同时可以调节自身吸水来源和用水效率,朝着最有利于生长发展的方向最大程度上利用水分。     

Dynamics of water usage in Haloxylon ammodendron in the southern edge of the Gurbantünggüt Desert

植物的水分来源是荒漠地区植物水分关系研究的重要方面, 有助于理解荒漠植物对干旱环境的适应。为了研究古尔班通古特沙漠主要建群种梭梭(Haloxylon ammodendron)生长季的水分利用动态, 以及其对发生在不同时期相似量级降水脉冲的响应, 利用稳定性同位素技术测量了梭梭小枝木质部水、降水、0-300 cm不同土层的土壤水和地下水的δ ¹⁸O值。水源依据深度划分为4个: 浅层土壤水(0-40 cm), 中层土壤水(40-100 cm), 深层土壤水(100-300 cm)和地下水。然后, 应用IsoSource模型计算了梭梭对潜在水源的利用比例。结果表明: 4月份, 梭梭主要利用浅层土壤水, 利用比例为62%-95%; 5-9月份梭梭主要利用地下水, 利用比例为68%-100%。梭梭对不同时期发生的两场相似量级的降水具有不同程度的响应。5月22日, 6.7 mm降水后第1天, 梭梭对土壤水的吸收达到最大值, 由降水前的9.8%增长为降水后的40.4%, 同时降低了对地下水的吸收, 由降水前的83%-98%下降为42%-81%。8月31日7 mm降水后, 梭梭对土壤水的吸收没有增加, 仍然保持对地下水的高比例利用, 达71%-98%。低的土壤含水量可能抑制了表层根系的活性, 导致梭梭对降水不敏感。由冬季融雪和春季降水补给的浅层土壤水和地下水是梭梭种群可利用的两个重要水源。梭梭的水分利用动态反映了其对干旱环境的适应。     

Water sources of dominant species in three alpine ecosystems on the Tibetan Plateau, China

Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope （δD and δ^18O） values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species （Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum） in three typical ecosystems （forest, shrub and desert） were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. δ^18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future.     

Comparisons in water relations of plants between newly formed riparian and non-riparian habitats along the bank of Three Gorges Reservoir,China

The water table in the Three Gorges Reservoir (TGR) rose significantly since the construction of the Three Gorges Dam across the Yangtze River. Little is known about how such a change in local hydrological condition will affect the ecophysiology of plants along the bank of the world’s largest reservoir. In this study, water relations of the dominant plants were investigated over an entire year period by comparing stable isotope compositions of xylem water, leaf water potentials and foliar carbon isotope ratios at a newly-formed riparian site near the river bank and two non-riparian sites at higher elevations. The isotopic compositions of xylem water indicated that the plants in the newly-formed riparian zone acquired water mainly from the soil previously infiltrated by local rain rather than the Yangtze River water. Predawn and midday water potentials of the riparian trees were also similar to those at the non-riparian sites. Leaf δ¹³C values of plants across the three sites also showed no difference, even though there was a significant difference among species. Our results indicate that plants at the newly formed transient riparian area along the bank of TGR do not depend on the Yangtze River water for their water sources and that rising water levels in this reservoir may not lead to immediate changes in water relations of the plants along the bank. Communicated by K. Winter.     

天山林区4种主要灌木夏季水分来源差异

天山林区群落结构相对简单、木本植物种类较少,但天山林区灌木群落中主要木本植物间的水分竞争模式尚不明确,水分利用动态缺乏定量分析。运用稳定同位素技术,对天山林区灌木群落4种主要灌木的茎杆水分及各潜在水源的氢氧稳定同位素组成进行测定,运用IsoSource模型定量分析4种灌木在夏季对各潜在水源的相对利用比例,探讨天山林区灌木群落主要灌木树种水分来源差异及动态变化。结果发现:7月,当浅层土壤含水量充足时,密刺蔷薇、黑果栒子和金丝桃叶绣线菊均大幅度吸收利用浅层土壤水,相对利用比例高于89.3%,异果小檗则相反,即吸收利用各潜在水源(浅层土壤水30.7%、中层土壤水29.4%、深层土壤水25.7%、溪水14.2%,下同);8月,当浅层土壤含水量降低时,密刺蔷薇转移至60-100 cm深层土壤水和溪水,相对利用比例分别为64.8%和27%,黑果栒子和金丝桃叶绣线菊以相似比例吸收利用各潜在水源(33.8%和36.8%、30.9%和29.7%、23.5%和22.3%、11.8%和11.2%),异果小檗则表现出可能吸收利用80-100 cm以下更稳定的深层土壤水;9月,当浅层土壤含水量升高时,4种灌木均大量吸收利用浅层土壤水,相对利用比例高于72.2%。这表明,天山林区灌木群落主要树种可通过可塑性转换水分来源来应对环境水分变异,在时间和空间上有效分割灌丛水源从而减缓对水分资源的竞争压力,从而通过在水分资源利用上的生态位分化促进物种间的共存。     

Seasonal water use patterns of woody species growing on the continuous dolostone outcrops and nearby thin soils in subtropical China

In karst regions, forests often grow on bedrock outcrops, however the water sources used by the forest vegetation are not known. This study aimed at investigating whether there were seasonal shifts (dry/wet season) of water sources for plants growing on the continuous dolostone outcrops, and comparing their differences with those growing on nearby thin soils in karst areas of southwest China. Rainwater, soil water within 0–30 cm depths, spring water (as a reflection of local deep water sources) and plant xylem water were sampled in March (late dry season) and July (mid rainy season) 2009, respectively. A direct inference approach and the IsoSource mixing model were used to estimate the contributions of different sources to the plant xylem water. On the outcrops, the deciduous tree species Radermachera sinica mainly used deep water sources during the dry season and a mixture of rainwater and deep water sources during the wet season. By contrast, the deciduous small shrub Alchornea trewioides largely relied on recent rainwater during both dry and wet seasons. Three non-deciduous species (Sterculia euosma, Schefflera octophylla and Ficus orthoneura) appear to rely on deep water sources during the wet seasons. In nearby thin soils, R. sinica mainly utilized deep water in the dry season and a mixture of soil water and deep water in the wet season. A. trewioides relied on the same water sources (rainwater-derived soil water) in the different seasons. The above results indicate that inter-specific differences in rooting patterns and leaf phenologies may lead to the differences in the sources of water used by coexisting plant species in karst regions.     

宁夏盐池不同坡位旱地紫苜蓿水分来源

紫苜蓿(Medicago sativa)是一种经济和生态价值较高的优良牧草, 但其耗水量大, 在西北半干旱地区仅靠天然降水难以满足紫苜蓿的正常生长发育。宁夏盐池北部地处毛乌素沙地南缘, 地下水埋深较浅, 地下水有可能成为紫苜蓿的潜在水源, 弥补天然降水的不足。本试验在地势平坦的缓坡丘陵梁地和丘间低地, 选择8年生旱地紫苜蓿试验地作为研究对象, 采用稳定同位素技术, 研究了不同海拔的4个坡位(海拔自低到高分别为: 坡1、坡2、坡3和坡4)紫苜蓿的水分来源及其生长生理表现。结果表明: 坡位对0-300 cm土壤剖面含水量有显著影响, 海拔最低的坡1土壤含水量最高。土壤水和植物茎秆水δ ¹⁸O-δD坐标点大部分位于中国西北地区地方大气降水线(LMWL)的右侧, 说明植物利用的水源氢氧同位素组成受到蒸发的影响而发生了富集作用。0-450 cm土壤剖面水δ ¹⁸O值随着海拔高度的增加而增大。同一坡位土壤水δ ¹⁸O值随着土壤深度的增加逐渐下降。深层土壤水δ ¹⁸O值与地下水δ ¹⁸O相近, 说明地下水通过土壤毛细管上升而补充其上层土壤水分。0-40 cm土壤水δ ¹⁸O值随季节波动较大, 270 cm以下土壤水δ ¹⁸O值较为稳定。4、7、8月份坡1紫苜蓿茎秆水δ ¹⁸O值显著低于其他3个坡位(p < 0.001)。在4、6、7三个月, 坡位1紫苜蓿对深层土壤水(270 cm以下)的利用率最高。而在8月份, 坡1、坡3、坡4紫苜蓿主要利用150-270 cm、270-450 cm土层土壤水以及地下水, 坡2对表层(0-20 cm)土壤水利用率最高。坡1紫苜蓿的产量、整株Δ ¹³C值及气孔导度显著高于其他3个坡位。本研究表明: 在平均年降水量只有280 mm的西北半干旱地区种植旱地紫苜蓿要尽量选择地势较低的滩地, 使其能够利用到埋深较浅地下水, 以满足植物生长发育的需要并取得较好的生态和经济效益。     

Water sources of Populus euphratica and Tamarix ramosissima in Ejina Delta,the lower reaches of the Heihe River,China

Aims We aim to evaluate the water sources of typical riparian arbor species (Populus euphratica) and shrub species (Tamarix ramosissima), and analyze the spatial and temporal dynamics of plant water source in Ejina Delta, the lower reaches of the Heihe River, China.Methods Eight sampling sites were selected in the riparian zones along the East River and West River in Ejina. The plant xylem water, soil moisture, rainwater, stream water and groundwater were taken and pretreated during the growing season in 2015-2016, and the stable oxygen isotope ratio (δ¹⁸O) for each water sample was measured. The δ¹⁸O of plant xylem water and soil moisture were compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” were applied to determine plant water sources and quantify their proportions.Important findings This study indicated that the main recharge sources for P. euphratica and T. ramosissima were stream water and groundwater. The contributions of rain water to them was negligible due to the limited amount and the shallow infiltration depth of local rainfall. As affected by groundwater level fluctuation, soil physical properties, as well as lateral and vertical recharge of stream water on soil moisture, the dominant depth of root water uptake spatially varied. However, the relative contributions of stream water or groundwater to plant water sources did not change significantly across space. Populus euphratica used more stream water (68%), while T. ramosissima used more groundwater (65%). Plant water sources were sensitive to environmental flow controls. The contributions of stream water to the water sources of the two species went up to 84% and 48% for P. euphratica and T. ramosissima respectively during the discharge period, but dropped to 63% and 30% during the non-discharge period. On the other hand, the contributions of groundwater decreased to 16% and 52% during the discharge period, but increased to 37% and 70% during non-discharge period. It is noteworthy that the high similarity of δ¹⁸O between stream water and groundwater due to extensive water exchange in the riparian zone made increase the uncertain in quantifying plant water sources.     

黄河三角洲海岸带湿地柽柳在干旱年份的水分利用策略

以黄河三角洲海岸带贝壳堤湿地灌木群落主要建群种柽柳为对象,利用稳定同位素技术测定柽柳木质部和潜在水源δ¹⁸O值的时空变化,采用IsoSource模型计算潜在水源对柽柳的贡献比例,研究海岸带不同生境中柽柳对不同水分条件的适应机制.结果表明: 在降水较少的干旱年份,相对于不稳定的降水,柽柳倾向于利用稳定的土壤水和浅层地下水,但是在不同微地形生境下柽柳的水分利用策略有所差异.滩脊的柽柳72.6%～95.4%水分来源于浅层地下水和含水量相对较高的深层土壤水(40～100 cm);高潮线附近的柽柳有40.7%～97.3%的水分来源于上层土壤水(0～40 cm),以避免海水和浅层地下水的盐分胁迫.柽柳对外界水盐条件变化具有较强的适应性,在海岸带可利用水资源缺乏的恶劣生境中具有更强的种间竞争优势,从而导致柽柳单优灌木群落的形成.     

中国水柏枝属植物的地理分布、濒危状况及其保育策略

水柏枝属(MyricariaDesv.)植物主要分布于中国青藏高原及其邻近地区,为欧亚温带高山植物类群,多为河岸带植物,是分布区湿地生态系统和荒漠生态系统的重要组分。为评价这些特殊生态系统关键植物的分布及受威胁现状,对中国水柏枝属植物的地理分布和濒危状况进行了调查。调查发现,该属中国分布的11个分类群均受到生存胁迫,其中疏花水柏枝即将成为野外灭绝种,宽叶水柏枝已属极危种,心叶水柏枝为濒危种,秀丽水柏枝、泽当水柏枝、小花水柏枝、卧生水柏枝和匍匐水柏枝为渐危种,具鳞水柏枝、三春水柏枝和宽苞水柏枝为受胁种。结果表明,以水利建设为主的人为干扰和土地沙化、气温升高带来的环境改变是导致该属植物生存胁迫的主要原因。最后探讨了水柏枝属这类河岸带湿地和荒漠生境植物的保育策略。     

Determination of the relative uptake of ground vs. surface water by Populus deltoides during phytoremediation

The use of plants to remediate polluted groundwater is becoming an attractive alternative to more expensive traditional techniques. In order to adequately assess the effectiveness of the phytoremediation treatment, a clear understanding of water-use habits by the selected plant species is essential. We examined the relative uptake of surface water (i.e., precipitation) vs. groundwater by mature Populus deltoides by applying irrigation water at a rate equivalent to a 5-cm rain event. We used stable isotopes of hydrogen (D) and oxygen (18O) to identify groundwater and surface water (irrigation water) in the xylem sap water. Pretreatment isotopic ratios of both deuterium and 18O, ranked from heaviest to lightest, were irrigation water > groundwater > xylem sap. The discrepancy in preirrigation isotopic signatures between groundwater and xylem sap suggests that in the absence of a surface source of water (i.e., between rain events) there is an unknown amount of water being extracted from sources other than groundwater (i.e., soil surface water). We examined changes in volumetric soil water content (%), total hourly sapflux rates, and trichloroethene (TCE) concentrations. Following the irrigation treatment, volumetric soil water increased by 86% and sapflux increased by as much as 61%. Isotopic signatures of the xylem sap became substantially heavier following irrigation, suggesting that the applied irrigation water was quickly taken up by the plants. TCE concentrations in the xylem sap were diluted by an average of 21% following irrigation; however, dilution was low relative to the increase in sapflux. Our results show that water use by Populus deltoides is variable. Hence, studies addressing phytoremediation effectiveness must account for the relative proportion of surface vs. groundwater uptake.