水淹对三峡库区两种岸生植物秋华柳(Salix variegata Franch.)和野古草(Arundinella anomala Steud.)水下光合的影响

为了阐明水淹对三峡库区岸生植物秋华柳(Salix variegata Franch.)和野古草(Arundinella anomala Steud.)水下光合作用的影响,模拟三峡库区消落带水淹发生情况,考察了在不同水淹处理下秋华柳和野古草的水下光合.实验设置了对照(不进行水淹,常规供水管理)和2m深度水淹(植株置于水中,植株顶部在水面下2 m)2个不同的水淹深度和5、15、20、40 d和60 d等5个不同的水淹时间处理,采用Chlorolab-2液相氧电极(英国Hansatech公司生产)测定了在不同水淹时间和水淹深度处理下秋华柳和野古草的水下光合作用.实验结果表明: (1) 水淹60d后,秋华柳和野古草的存活率均为100%,而典型的陆生植物香樟和马唐分别在水淹40d和15d后全部死亡.(2) 在相同的水淹时间和水淹深度下,秋华柳和野古草的水下光合速率(放氧速率)显著高于典型的陆生植物(香樟(Cinnamomum camphora(L.) Presl.)和马唐(Digitaria sanguinalis (L.)Scop.)) (3) 在长期水淹的条件下,秋华柳和野古草仍具有水下光合的能力.在水淹60 d后,水淹2 m的秋华柳和野古草植株的水下放氧速率显著低于对照植株的水下放氧速率,但仍具有水下光合的能力,其水下光合速率分别为0.202 μmol · m-2 · s-1和0.139 μmol · m-2 · s-1.同时,研究也表明在水淹40 d和60 d后,秋华柳表现出比野古草强的水下光合能力.研究表明,秋华柳和野古草在存活率和水下光合方面对长期水淹表现出良好的适应性,是可以用于三峡库区消落区植被构建的优良植物物种.     

水淹对三峡库区岸生植物秋华柳(Salix variegata Franch.)存活和恢复生长的影响

植物在水淹后的存活和恢复生长状况可以衡量其对水淹的耐受能力,为了解三峡库区岸生植物秋华柳(Salix variegata Franch.)的水淹耐受能力,研究了长期水淹条件下秋华柳植株的存活和恢复生长状况.实验设置了3个水淹深度:对照,水淹根部(植株置于水中,仅地下部分被淹没)和水淹2m(植株置于水中,顶部距水面2m),6个水淹时间:20d,40d,60d,90d,120d和180d.研究结果表明:(1)水淹对秋华柳植株存活率的影响较小.水淹根部处理的植株在水淹180d后,存活率仍为100%,水淹2m处理的植株在水淹120d后,存活率也为100%,直到180d后,存活率才下降为0.(2)水淹后,秋华柳植株仍然可以进行恢复生长,表现出很强的恢复生长能力,但因水淹处理的不同,其恢复生长存在差异.随着水淹时间的延长,秋华柳植株出水后到开始恢复生长之前所需的时间增加,但所有水淹处理的植株在水淹结束后一周内都可以开始恢复生长.在相同水淹时间处理下,水淹处理的秋华柳植株在恢复生长期间的相对生长速率都高于对照植株,水淹40d,60d,90d后,水淹2m的秋华柳植株分别比对照植株高57.8%,143.4%,130.4%.水淹结束时,秋华柳地上部分生物量随水淹深度的不同而不同,水淹根部处理的植株几乎与对照植株无显著差异,水淹2m处理的植株都低于对照植株.水淹结束后,不同处理的秋华柳植株生长2个月后的地上部分生物量与其在水淹结束时不同处理植株地上部分生物量的变化趋势相似.本研究表明,秋华柳在长时间的水淹后具有很高的存活率,并可以进行很好的恢复生长,表现出较强的水淹耐受能力,可以考虑将其应用于三峡库区消落区的植被构建.     

三峡库区岸生植物野古草(Arundinella anomala Steud.)光合作用对水淹的响应

为了阐明水淹对三峡库区岸生植物野古草光合作用的影响,模拟了三峡库区消落带水淹发生情况,考察了在不同水淹处理下野古草(Arundinella anomalaSteud.)的光合及叶绿素荧光特性。实验设置了对照(不进行水淹,常规供水管理)、半淹(植株置于水中,植株地上部分一半被淹没)、水下0.5m(植株置于水中,植株顶部在水面下0.5m)、水下2m(植株置于水中,植株顶部在水面下2m)4个不同的水淹深度和02、0、40d和60d等4个不同的水淹时间处理,测定了在不同水淹深度和水淹时间处理下野古草的净光合速率、总叶绿素含量、PSⅡ的最大光化学效率、电子传递速率、表观量子效率、叶绿素利用效率与羧化效率。结果发现,在水淹前期,水淹对野古草的光合特性影响较小,直到水淹60d后,才对野古草的光合特性产生明显影响,且影响程度随水淹深度的不同而不同。野古草在水淹20d和水淹40d后,各水淹处理的净光合速率与对照相比无明显降低,其中水淹20d后,半淹处理的野古草叶片净光合速率比对照还高出16.1%。水淹60d后,水下0.5m和水下2m的净光合速率显著低于对照和半淹,其净光合速率分别为7.51μmol.m-2.s-1和9.15μmol.m-2.s-1。结果表明,水淹20d和40d对野古草的电子传递速率、表观量子效率和羧化效率没有影响。水淹处理60d后,与对照植株相比,半淹处理植株的电子传递速率、表观量子效率、叶绿素利用效率和羧化效率没有明显变化,但水下0.5m和水下2m处理植株的电子传递速率、表观量子效率、叶绿素利用效率和羧化效率有明显降低。在整个实验期间,半淹处理植株的净光合速率、电子传递速率、表观量子效率和羧化效率没有受到任何不利影响。尽管在水淹60d后水下0.5m和水下2m处理植株的净光合速率、电子传递速率、表观量子效率、叶绿素利用效率和羧化效率降低,但降低后的数值仍不低于甚至高于一些自然生长的未受水淹的植物物种。研究表明,野古草对水淹具有很好的耐受能力,是一种可以用于三峡库区消落区植被构建的优良植物物种。     

淹水对三峡库区消落带香附子生长及光合特性的影响

为了阐明三峡库区消落带水位变化对香附子实生幼苗的影响,本研究模拟三峡库区消落带水淹环境,设置对照(CK)、根淹(T1)、半淹(T2)、全淹(T3)4个处理组,揭示香附子对库区消落带水位变化引起的不同水淹环境的光合生理响应机制。结果表明:经过45d的水淹后,所有处理香附子植株的基径、茎高和非光化学淬灭都有所增加,说明香附子植株对不同水淹环境都做出了积极的响应;植株叶长、叶宽及地上生物量在不同水淹环境中有不同的响应,与对照相比,半淹处理植株叶长、叶宽及地上生物量有所增加,而根淹、全淹处理植株叶长、叶宽及地上生物量有所下降;随着水淹时间的增加,所有水淹处理植株叶片比叶面积、净光合速率、气孔导度、蒸腾速率、最大光化学效率、电子传递速率以及光化学淬灭都显著低于对照,根淹和半淹植株虽有下降,但仍能保持较高的水平,而全淹植株则下降明显。研究表明,香附子能很好地适应水淹环境(尤其是部分水淹环境),未来可以应用于三峡库区消落带的植被重建,特别是针对长期遭受水位涨落的低海拔区域(145～160m),同时,香附子响应水淹的特性也为未来三峡库区消落带耐淹植物的筛选提供了依据。     

三峡库区岸生植物野古草(Arundinella anomala Steud.)光合作用对水淹的响应

为了阐明水淹对三峡库区岸生植物野古草光合作用的影响,模拟了三峡库区消落带水淹发生情况,考察了在不同水淹处理下野古草(Arundinella anomala Steud.)的光合及叶绿素荧光特性。实验设置了对照 (不进行水淹,常规供水管理)、半淹 (植株置于水中,植株地上部分一半被淹没)、水下0.5m (植株置于水中,植株顶部在水面下0.5m)、水下2m (植株置于水中,植株顶部在水面下2m) 4个不同的水淹深度和0、20、40d和60d等 4个不同的水淹时间处理,测定了在不同水淹深度和水淹时间处理下野古草的净光合速率、总叶绿素含量、PSⅡ的最大光化学效率、电子传递速率、表观量子效率、叶绿素利用效率与羧化效率。结果发现,在水淹前期,水淹对野古草的光合特性影响较小,直到水淹60d后,才对野古草的光合特性产生明显影响,且影响程度随水淹深度的不同而不同。野古草在水淹20d和水淹40d后,各水淹处理的净光合速率与对照相比无明显降低,其中水淹20d后,半淹处理的野古草叶片净光合速率比对照还高出16.1%。水淹60d后,水下0.5m和水下2m的净光合速率显著低于对照和半淹,其净光合速率分别为7.51μmol•m－2•s－1和9.15μmol•m－2•s－1。结果表明,水淹20d和40d对野古草的电子传递速率、表观量子效率和羧化效率没有影响。水淹处理60d后,与对照植株相比,半淹处理植株的电子传递速率、表观量子效率、叶绿素利用效率和羧化效率没有明显变化,但水下0.5m和水下2m处理植株的电子传递速率、表观量子效率、叶绿素利用效率和羧化效率有明显降低。 在整个实验期间,半淹处理植株的净光合速率、电子传递速率、表观量子效率和羧化效率没有受到任何不利影响。尽管在水淹60d后水下0.5m和水下2m处理植株的净光合速率、电子传递速率、表观量子效率、叶绿素利用效率和羧化效率降低,但降低后的数值仍不低于甚至高于一些自然生长的未受水淹的植物物种。研究表明,野古草对水淹具有很好的耐受能力,是一种可以用于三峡库区消落区植被构建的优良植物物种。     

长期水淹条件下香根草(Vetiveria zizanioides)、菖蒲(Acorus calamus)和空心莲子草(Alternanthera philoxeroides)的存活及生长响应

人工构建三峡库区消落区植被是控制消落区水土流失、保护消落区生态环境的重要措施,选择能够耐受长时间完全水淹的植物物种是该措施实施的关键.为了验证香根草、菖蒲、空心莲子草能否用于消落区植被的构建,实验模拟消落区的长期完全水淹条件,设置30d、60d、90d、120d、150d和180d等6个完全水淹时间水平,研究了3种植物在完全水淹条件下生长、生物量积累及存活状况.结果发现:(1)3种植物在经受长时间的完全水淹后有较高的存活率,180d全淹处理后,香根草、菖蒲和空心莲子草的存活率分别为87.5%、100%和50%.(2)这3种植物有不同的水下生长能力.全淹条件下,香根草生长缓慢,几乎没有产生新的叶片,总叶长也没有显著变化;菖蒲能够持续产生较对照植株更为细长的叶片,空心莲子草只在水淹初期(30d内)能够快速伸长地上部分的枝条,并迅速产生新叶片,但随水淹时间的延长,总枝条长及总叶片数没有再显著增加.(3)与对照植株相比,全淹处理抑制了3种植物总生物量的增加,但对3种植物的地上、地下部分生物量抑制程度不同.全淹条件下,香根草的地上部分和地下部分生物量与水淹0d水平(水淹处理开始前一天,下同)相比无显著变化,根冠比高于对照植株;菖蒲的地上部分生物量随水淹时间延长而降低,但却高于对照植株,地下部分生物量始终低于水淹0d水平,根冠比低于对照植株;空心莲子草的地上部分生物量与水淹0d水平相比无显著差异,但地下部分生物量与水淹0d水平相比大幅降低,根冠比低于对照植株.结果表明,这3种植物都有很强的水淹耐受能力,可应用于三峡库区消落区植被的构建.同时,发现植物对长期完全水淹的耐受能力很大程度上与植株在水下的生长情况及植株的营养储备水平相关,剧烈的水下生长会消耗大量的营养储备,进而造成植株存活率降低.植株在全淹条件下有限的生长能力及丰富的营养储备可能是耐淹物种的重要特征.     

水淹对秋华柳幼苗生理生态特征的影响

秋华柳广泛分布于三峡库区河谷与溪流坡岸,对水土保持及稳固堤岸具有重要作用.通过模拟水淹试验,研究了秋华柳幼苗对水淹的适应能力及机理.结果表明：所有处理秋华柳植株全部存活.水淹对秋华柳幼苗的最大光合速率、蒸腾强度、气孔导度和水分利用效率都有显著影响.水淹初期(20 d),植株的各项生理指标值变化较小,其中最大光合速率和蒸腾强度分别比对照下降18.5%和2.2%;30 d后,分别下降53.4%和23.7%,随后又趋于稳定.植株叶绿素和类胡萝卜素含量及其比值均随水淹时间的增加而逐渐降低,其中叶绿素/类胡萝卜素比值在4.873～6.883,而叶绿素a/b比值则在2.855～3.912之间变动.水淹还诱导秋华柳幼苗产生不定根,有利于植株氧气的补给.说明秋华柳幼苗对水淹的适应能力较强,可作为库区水位消落带植被恢复与重建的先锋物种.     

EFFECTS OF LONG-TERM SUBMERGENCE ON SURVIVAL AND RECOVERY GROWTH OF FOUR RIPARIAN PLANT SPECIES IN THREE GORGES RESERVOIR REGION, CHINA

 地瓜藤(Ficus tikoua)、荻(Triarrhena sacchariflora)、牛鞭草(Hemarthria altissima)和狗牙根(Cynodon dactylon)是三峡库区常见的岸生植物, 自然分布于河岸带不同垂直高程的地段。为了明确它们在成库后“三峡库区消落区”长期完全水淹条件下的存活和生长情况, 实验设置对照(不进行水淹, 常规供水管理)和完全水淹两个处理, 30、60、90、120、150和180 d 6个水淹时间水平, 研究了4种植物在完全水淹条件下的存活、生物量变化和恢复生长。结果发现: 1) 4种植物在完全水淹条件下的存活率与其在河岸带上的垂直分布高程密切相关。分布于距江面高程较高的河岸段的地瓜藤植株, 在全淹30 d后就全部死亡; 分布在中高程河岸段的荻在全淹150和180 d后全部死亡; 可以分布于低高程河岸段的牛鞭草和狗牙根, 淹没180 d后存活率分别为90%和100%。2)全淹抑制了荻、牛鞭草和狗牙根的生长, 总生物量增量显著低于对照植株。与水淹0 d相比, 全淹处理植株的地上部分生物量显著降低, 荻在全淹60和120 d后, 地下部分生物量显著降低, 但牛鞭草和狗牙根的地下部分生物量与水淹0 d水平相比无显著差异。3)水淹处理结束后, 存活的荻、牛鞭草和狗牙根植株都能很好地恢复生长。在恢复生长过程中, 全淹30、60和90 d后, 荻、牛鞭草和狗牙根植株的总分枝长相对生长速率与对照植株无显著差异, 全淹120、150和180 d后, 牛鞭草和狗牙根植株的总分枝长相对生长速率显著高于对照植株。全淹处理的荻、牛鞭草和狗牙根植株的总叶片数相对生长速率始终显著高于对照植株。遭受长期完全水淹后, 植株在有限的营养储备条件下, 快速产生叶片以迅速积聚光合产物可能是植物更为优化的恢复生长方式。     

冬季水淹对秋华柳的开花物候及繁殖分配的影响

开花物候及繁殖分配是植物适应环境的重要因素,为了解长期冬季水淹对三峡库区耐淹物种秋华柳(Salix variegata Franch.)繁殖的影响,研究了长期冬季水淹条件下秋华柳的开花物候和繁殖分配情况。实验在2006年11月份设置了如下处理:对照,完全水淹(植株置于水中,顶部距水面2m)30,60,90,120d和150d。结果表明:(1)对照及各水淹处理的秋华柳花期都较长,在7-11月份持续开花,个体开花进程(开花振幅曲线)呈单峰曲线。(2)冬季水淹对秋华柳群体及个体的开花物候有显著影响。水淹时间越长,始花期越晚,花期持续时间越短(P0.05)。(3)长期冬季水淹下,秋华柳显著降低了繁殖分配比例和全株生物量及单株花序数(P0.05)。(4)开花物候指数与繁殖分配的相关分析表明:始花时间越晚的个体,花期持续时间越短。花期持续时间越短的个体花序数越少,致使繁殖分配越小。总的来说,冬季水淹下,秋华柳通过推迟开花日期、缩短花期持续时间使繁殖分配比例降低,将更多的资源分配到生存力上,是秋华柳对长期冬季水淹的一种适应。同时,在长期冬季水淹后,秋华柳仍保持一定的开花繁殖能力,是其在应用于三峡水库消落区植被构建后产生后代延续种群的前提条件。     

水淹对狗牙根营养繁殖植株的生理生态学效应

通过控制实验,测定了经过水淹处理的狗牙根营养繁殖体在恢复阶段的光合作用及其相关的生理生化指标的变化。结果显示,水淹时间对恢复阶段营养繁殖体的蒸腾作用和叶片温度的影响达到显著水平,水淹深度对该时期营养繁殖体的光合作用、气孔导度、胞间二氧化碳浓度和叶片温度有显著影响。水淹还导致了恢复期间植株叶片光合色素含量的显著变化。经过水淹的植株的各类光合色素含量以及色素总含量都显著高于对照植株,其中全淹处理的植株显著高于半淹处理的植株,叶绿素a与叶绿素b的比例也是全淹处理的植株显著高于半淹处理的植株。结果表明狗牙根营养繁殖体具有较强的恢复生长和生理活动的能力,是一种适宜于水电工程库区消落带生态恢复的物种。     

三峡库区两种耐水淹植物的存活率和碳水化合物储备关系

野古草和秋花柳是三峡库区消落带两种强水淹耐受能力的植物物种。以往研究显示植物的水淹耐受性和体内碳水化合物储备有关。为了探明野古草和秋花柳水淹下的高存活率是否和碳水化合物储备有关, 研究了在室外6个月的模拟水淹条件下两个物种在不同水淹时间(40、90、120和180d)和不同水淹深度下(不水淹、根部水淹和完全淹没)的生物量积累、存活率和碳水化合物含量和分布。结果表明: (1)野古草和秋花柳对长期水淹具有很高的耐受性, 根部水淹植物6个月处理后完全存活; 而完全淹没条件下, 野古草仅在4个月, 秋花柳仅在6个月处理后才开始死亡; (2)碳水化合物主要储备在野古草的茎和秋花柳的茎与主根中, 野古草的根和秋华柳的细根中碳水化合物含量很低; (3)水淹深度和水淹时间对植物生物量积累和碳水化合物含量影响显著(P 0.05):与未水淹植株相比, 根部水淹仅略微降低了生物量积累以及可溶性糖和淀粉含量 (P 0.05), 且保持基本稳定或增加的趋势, 而完全淹没的植株生物量随水淹时间逐渐降低, 碳水化合物含量在前90天快速下降 (P 0.05), 之后缓慢下降或保持不变。研究结果表明, 野古草和秋花柳强的水淹耐受性是和它们高的碳水化合物储备以及水淹条件下对碳水化合物的动用能力有关, 后期的死亡率增加与碳水化合物储备消耗殆尽有关, 野古草和秋花柳对碳水化合物储备对水淹的响应的差异可能和它们的碳水化合物储备在不同组织中的分配模式有关。       

Effects of Waterlogging on the Gibberellin Content and Growth of Tomato Plants

Flooding of tomato roots results in decreased stem growth. Wehave shown that flooding will reduce levels of gibberellins(GA) in the roots, shoots, and bleeding sap of tomato plants.The adventitious roots that appear on the third day of waterloggingmay be responsible for the production of GA that accumulatein the shoot after 3 to 4 days of flooding. The endogenous GAof tomato will stimulate stem growth of tomato plants. Initially,application of gibberellic acid (GA₃) will stimulate the growthof flooded plants to a greater extent than that of nonwaterloggedplants. It is suggested that one of the first effects of floodingis to reduce GA levels and so inhibit stem elongation. At alater stage of waterlogging GA₃ is less effective and otherfactors appear to inhibit shoot growth.     

Occupational strategy of <Emphasis Type="Italic">Persicaria thunbergii</Emphasis> in riparian area: Rapid recovery after harsh flooding disturbance

Persicaria thunbergii is a representative annual herb in Korean wetlands, widely inhabits not only in lentic wetlands, but also in unstable riparian wetlands. To better understand the occupational strategy of this plant, we investigated environment, growth characteristics before and after harsh flooding disturbance in FDA (flooding disturbed area) and NDA (non-disturbed area). Water level, fresh soil moisture and organic matter of NDA were significantly higher than FDA. Before flooding disturbance, plant height, individual length, number of node, individual biomass and biomass per 1 m² were significantly higher in FDA than in NDA. After flooding disturbance, plant height, biomass per 1 m², coverage and relative coverage were significantly lower in FDA than in NDA, yet individual length, number of node, individual biomass and aerial seed production were not different. In FDA, creeping stems survive despite a flooding disturbance because they are parallel with the water flow and are firmly fixed to the ground through numerous adventitious roots. Surviving creeping stems make new shoots rapidly and P. thunbergii recovers its biomass during less than a month. Every regenerated shoots make reproductive organs. Thus, P. thunbergii can reproduce and successfully survive the next generation in the riparian habitat despite the harsh flooding disturbance every year.     

Responses of Melaleuca quinquenervia seedlings to flooding

Abstract Studies were conducted on effects of flooding for 15, 30, 60, and 90 days on morphological changes, stomatal aperture, water potential, and growth of seedlings of Melaleuca quinquenervia, a species often planted for reclamation of swamps. Flooding rapidly induced formation of many hair-like adventitious roots as well as a few thick adventitious roots that originated on the original root system. Some adventitious roots also formed on submerged portions of the stem. Melaleuca seedlings were very tolerant of flooding as shown by only slight reduction in dry weight increment of shoots after 30 days of flooding in stagnant water. Although flooding for 60 or 90 days significantly reduced dry weight increment of leaves, dry weight increment of roots was not inhibited by any flooding treatment, reflecting both degeneration of some of the original roots and compensatory growth of adventitious roots. On certain days flooding induced stomatal closure on both adaxial and abaxial leaf surfaces. Extensive production of adventitious roots and some stomatal reopening after a critical period of flooding appeared to be important factors in the flooding tolerance of Melaleuca and are consistent with its aggressiveness and vigorous growth on wet sites.     

Riparian plant community responses to increased flooding: a meta‐analysis

A future higher risk of severe flooding of streams and rivers has been projected to change riparian plant community composition and species richness, but the extent and direction of the expected change remain uncertain. We conducted a meta‐analysis to synthesize globally available experimental evidence and assess the effects of increased flooding on (1) riparian adult plant and seedling survival, (2) riparian plant biomass and (3) riparian plant species composition and richness. We evaluated which plant traits are of key importance for the response of riparian plant species to flooding. We identified and analysed 53 papers from ISI Web of Knowledge which presented quantitative experimental results on flooding treatments and corresponding control situations. Our meta‐analysis demonstrated how longer duration of flooding, greater depth of flooding and, particularly, their combination reduce seedling survival of most riparian species. Plant height above water level, ability to elongate shoots and plasticity in root porosity were decisive for adult plant survival and growth during longer periods of flooding. Both ‘quiescence’ and ‘escape’ proved to be successful strategies promoting riparian plant survival, which was reflected in the wide variation in survival (full range between 0 and 100%) under fully submerged conditions, while plants that protrude above the water level (>20 cm) almost all survive. Our survey confirmed that the projected increase in the duration and depth of flooding periods is sufficient to result in species shifts. These shifts may lead to increased or decreased riparian species richness depending on the nutrient, climatic and hydrological status of the catchment. Species richness was generally reduced at flooded sites in nutrient‐rich catchments and sites that previously experienced relatively stable hydrographs (e.g. rain‐fed lowland streams). Species richness usually increased at sites in desert and semi‐arid climate regions (e.g. intermittent streams).     

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara

Background and Aims Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages.Methods Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments.Key Results Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding.Conclusions The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant’s life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants.     

Morphological and photosynthetic responses of riparian plant Distylium chinense seedlings to simulated Autumn and Winter flooding in Three Gorges Reservoir Region of the Yangtze River, China

To evaluate the tolerance of riparian plant Distylium chinense in Three Gorges Reservoir Region to anti-season flooding, a simulation flooding experiment was conducted during Autumn and Winter, and morphology and photosynthesis of D. chinense seedlings and their recovery growth after soil drainage were analyzed in different duration of flooding and flooding depth. The seedlings were submitted to four treatments: (1) 40 seedlings unflooded and watered daily as control (Unflooded, CK); (2) 120 seedlings flooded at 1 cm above the ground level (F-1 cm); (3) 120 seedlings flooded at 12 cm above the ground level (F-12 cm) and (4) 120 seedlings completely submerged with 2 m water depth (F-2 m, top of plants at 2 m below water surface). The flooding survival, plant height, stem diameter, adventitious roots, stem lenticels, epicormic shoots, chlorophyll content and photosynthesis parameters were determined at 0, 15, 30, 90 days in flooding stress and 15, 60 days after soil drainage. The results showed that the survival of the seedlings subjected to flooding was 100% for all repeated measurements in all treatments. Adventitious roots, hypertrophied lenticels and stem hypertrophy were observed in the seedlings flooded for more than 15 d, and increased with the prolonged flooding duration, while disappeared after the soil was drained. Flooding duration and flooding depth showed significant individual and interactive effects on leaf chlorophyll a (Chl a), chlorophyll b (Chl b), and their ratio, chlorophyll (a + b), the net photosynthesis rate (P_n), transpiration rate (T_r), stomatal conductance (C_s), and inter-cellular CO₂ concentration (C_i) of D. chinense seedlings (P < 0.01). After 15 days of flooding, there was no significant decrease in P_n of the flooded seedlings as compared with that of the control seedlings. P_n of the flooded seedlings was significantly lower than that of the control seedlings after 30 days of flooding (P < 0.05), whereas P_n showed no significant difference among seedlings from three flooding depths. After 90 days of flooding, P_n of the F-2 m flooded seedlings was significantly lower than that of the controls, F-1 cm and F-12 cm flooded seedlings (P < 0.05), but still maintained high photosynthetic capacity. P_n of the F-1 cm and F-12 cm flooded seedlings rose gradually after soil drainage, while, it was significantly lower than that of the control seedlings after 15 days of recovery (P < 0.05). After 60 days of recovery, P_n of all seedlings flooded with different depths showed no significant difference as compared with that of the control seedlings and new leaves grew out in the F-2 m flooded seedlings. The effect of all flooding treatments on Gs, T_r, Chl a, Chl b, Chl a/Chl b and chl (a + b) was basically the same as their effect on P_n, while the effect of all flooding treatments on C_i was quite the contrary. Correlation analysis showed that P_n was positively relative with Gs, T_r, Chl a, Chl b and chl (a + b) (P < 0.05) and significantly negative with C_i (P < 0.05). Therefore, the present study demonstrates that D. chinense has high survival and good recovery growth after long-term flooding in anti-season flooding and could be taken as an excellent candidate species in the re-vegetation of water-level-fluctuation areas in Three Gorges Reservoir Region.     

Morphological and photosynthetic responses of riparian plant Distylium chinense seedlings to simulated Autumn and Winter flooding in Three Gorges Reservoir Region of the Yangtze River, China

To evaluate the tolerance of riparian plant Distylium chinense in Three Gorges Reservoir Region to anti-season flooding, a simulation flooding experiment was conducted during Autumn and Winter, and morphology and photosynthesis of D. chinense seedlings and their recovery growth after soil drainage were analyzed in different duration of flooding and flooding depth. The seedlings were submitted to four treatments: (1) 40 seedlings unflooded and watered daily as control (Unflooded, CK); (2) 120 seedlings flooded at 1 cm above the ground level (F-1 cm); (3) 120 seedlings flooded at 12 cm above the ground level (F-12 cm) and (4) 120 seedlings completely submerged with 2 m water depth (F-2 m, top of plants at 2 m below water surface). The flooding survival, plant height, stem diameter, adventitious roots, stem lenticels, epicormic shoots, chlorophyll content and photosynthesis parameters were determined at 0, 15, 30, 90 days in flooding stress and 15, 60 days after soil drainage. The results showed that the survival of the seedlings subjected to flooding was 100% for all repeated measurements in all treatments. Adventitious roots, hypertrophied lenticels and stem hypertrophy were observed in the seedlings flooded for more than 15 d, and increased with the prolonged flooding duration, while disappeared after the soil was drained. Flooding duration and flooding depth showed significant individual and interactive effects on leaf chlorophyll a (Chl a), chlorophyll b (Chl b), and their ratio, chlorophyll (a + b), the net photosynthesis rate (P_n), transpiration rate (T_r), stomatal conductance (C_s), and inter-cellular CO₂ concentration (C_i) of D. chinense seedlings (P < 0.01). After 15 days of flooding, there was no significant decrease in P_n of the flooded seedlings as compared with that of the control seedlings. P_n of the flooded seedlings was significantly lower than that of the control seedlings after 30 days of flooding (P < 0.05), whereas P_n showed no significant difference among seedlings from three flooding depths. After 90 days of flooding, P_n of the F-2 m flooded seedlings was significantly lower than that of the controls, F-1 cm and F-12 cm flooded seedlings (P < 0.05), but still maintained high photosynthetic capacity. P_n of the F-1 cm and F-12 cm flooded seedlings rose gradually after soil drainage, while, it was significantly lower than that of the control seedlings after 15 days of recovery (P < 0.05). After 60 days of recovery, P_n of all seedlings flooded with different depths showed no significant difference as compared with that of the control seedlings and new leaves grew out in the F-2 m flooded seedlings. The effect of all flooding treatments on Gs, T_r, Chl a, Chl b, Chl a/Chl b and chl (a + b) was basically the same as their effect on P_n, while the effect of all flooding treatments on C_i was quite the contrary. Correlation analysis showed that P_n was positively relative with Gs, T_r, Chl a, Chl b and chl (a + b) (P < 0.05) and significantly negative with C_i (P < 0.05). Therefore, the present study demonstrates that D. chinense has high survival and good recovery growth after long-term flooding in anti-season flooding and could be taken as an excellent candidate species in the re-vegetation of water-level-fluctuation areas in Three Gorges Reservoir Region.