盐胁迫下氮素形态对油菜和水稻幼苗离子运输和分布的影响

【目的】土壤盐碱化是制约农作物产量的主要因素之一,盐胁迫影响养分运输和分布,造成植物营养失衡,导致作物发育迟缓,植株矮小,严重威胁着我国的粮食生产。在必需营养元素中,氮素是需求量最大的元素,NO-3和NH+4是植物吸收氮素的两种离子形态。植物对盐胁迫的响应受到不同形态氮素的调控,研究不同形态氮素营养下植物的耐盐机制对提高植物耐盐性及产量具有重要的意义。【方法】本文以喜硝植物油菜(Brassica napus L.)和喜铵植物水稻(Oryza sativa L.)为试验材料,采用室内营养液培养方法,研究了NO-3和NH+4对Na Cl胁迫下油菜及水稻苗期生长状况、对Na+运输和积累的影响,以对照与盐胁迫植株生物量之差与Na+积累量之差的比值,评估Na+对植株的伤害程度。【结果】1)在非盐胁迫条件下,硝态氮营养显著促进油菜和水稻根系的生长;盐胁迫条件下,油菜和水稻生物量均显著受到抑制,Na Cl对供应铵态氮营养植株的抑制更为显著。2)盐胁迫条件下,两种供氮形态下,油菜和水稻植株Na+含量均显著增加,硝态氮营养油菜叶柄Na+显著高于铵态氮营养,叶柄Na+含量/叶片Na+含量大于铵营养油菜,硝态氮营养水稻根系Na+含量显著低于铵营养,地上部则相反。3)铵营养油菜和水稻Na+伤害度显著高于硝营养植株。4)盐胁迫条件下,硝态氮营养油菜地上部和水稻根系K+含量均显著高于铵态氮营养。5)盐胁迫条件下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株。【结论】与铵营养相比,硝营养油菜和水稻具有更好的耐盐性。硝态氮处理油菜叶柄Na+显著高于铵态氮处理,能够截留Na+向叶片运输。同时,供应硝态氮营养更有利于油菜和水稻吸收K+,有助于维持植物体内离子平衡。盐胁迫下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株,表明硝态氮营养油菜和水稻木质部-韧皮部对离子有较好的调控能力,是其耐盐性高于铵营养的原因之一。     

铵态氮和硝态氮调节盐胁迫豌豆幼苗生长和根系呼吸的作用

【目的】 土壤盐渍化在干旱和半干旱灌溉区是制约农业生产的非生物因素之一,合理的调控措施可以减轻盐渍化对植物的危害,本文探讨了氮源调节豆科植物盐胁迫的生理生态机制。 【方法】 采用砂培试验,以3个豌豆品种 (银豌1号、S5001-1和Ha) 为供试材料,设定三个盐分浓度(0、50、100 mmol/L),分别供应铵态氮和硝态氮4 mmol/L,每个品种均设六个处理。培养29天后对豌豆幼苗生物量、根系生长参数、根系呼吸及植株盐分离子含量进行测定。 【结果】 1) 三个盐分浓度相比,50 mmol/L NaCl处理下的3个豌豆品种幼苗的地上生物量和根系生长指标(根干重、根长和根表面积)显著高于0和100 mmol/L NaCl处理,且硝态氮处理显著高于铵态氮;2) 与无NaCl处理相比,3个豌豆品种植株含水量在100 mmol/L NaCl处理下明显降低,且硝态氮处理的显著低于铵态氮处理;3)豌豆根系呼吸速率均随着盐分浓度的增加和培养时间的延长总体呈降低趋势。3个豌豆品种根系呼吸速率对硝态氮和铵态氮的反应不同,相同盐分水平下,银豌1号铵态氮处理的高于硝态氮,Ha品种则相反,而S5001-1品种在两种氮源间差异不大。在50 mmol/L NaCl胁迫下,豌豆品种S5001-1与Ha硝态氮处理的根系呼吸累积量明显高于铵态氮,而银豌1号则相反;100 mmol/L NaCl胁迫下,豌豆品种Ha硝态氮处理的根系呼吸累积量显著高于铵态氮,其他两个品种在不同氮源处理间无差异。相同盐分胁迫水平下,银碗1号铵态氮处理的根系呼吸累积量明显高于品种S5001-1和Ha,而硝态氮处理下,品种Ha的根系呼吸累积量最高。4) 3个豌豆品种幼苗地上部Na+和Cl–含量均随盐浓度的增加而增加,而不同氮源对Na+在豌豆体内累积的影响因豌豆品种而异。 【结论】 在中度盐分胁迫下,施氮肥可缓解盐分胁迫对豌豆幼苗生长的影响,硝态氮缓解能力高于铵态氮,但在重度盐分胁迫下,盐胁迫是影响植物生长和离子吸收的主导因子,氮源调节作用变弱。尽管不同豌豆品种的根系呼吸对NH₄+-N与NO₃–-N的反应不同,但NO₃–-N缓解盐胁迫的效果总体上好于NH₄+-N。      

局部根系水分胁迫下氮形态对玉米幼苗光合特性的影响

本文通过测定玉米幼苗光合特性的变化来研究局部根系水分胁迫下氮形态对植物生长的影响及其机理。试验采用分根装置,聚乙二醇(PEG6000)只向一侧根室加入以模拟局部根系水分胁迫。设置3种形态氮(铵态氮;硝态氮;含铵态氮、硝态氮各为50%的混合氮),两侧根室均匀供应。水分胁迫后第4、5、7天测定玉米幼苗光合与叶绿素荧光参数、生物量等的变化。结果发现在局部根系水分胁迫时,相对于另外2种氮形态,在胁迫初期铵态氮供应的植株光合速率(Pn)、实际光化学量子产量(Yield)、电子传递速率(ETR)、光化学淬灭系数(qP)较高,玉米幼苗生长较快;而在水分胁迫第7天,铵态氮供应的植株光合速率、Yield、ETR、qP较低,叶绿素含量下降,植株生长滞缓,而硝态氮以及混合氮处理的植株生长相对加快。     

不同氮素形态对茅苍术光合特性和光合氮素利用效率的影响

研究不同氮素形态对茅苍术光合特性和氮素吸收的影响,为其栽培氮肥高效利用提供理论依据。以一年生茅苍术为材料,研究不施氮肥、施用硝态氮、铵态氮和酰胺态氮对茅苍术叶片光响应曲线和光合氮素利用效率的影响。结果表明,施用氮肥可不同程度改善叶片光合特性,其中硝态氮处理的叶绿素含量、表观光量子效率、最大净光合速率,光饱和点、净光合速率、气孔导度、蒸腾速率均最高,但其光补偿点和胞间二氧化碳浓度显著低于铵态氮和酰胺态氮处理。同时,硝态氮处理能显著增大叶面积、降低比叶重,促进植株生长,使得其整株生物量比铵态氮和酰胺态氮处理提高6.89%和17.05%。此外,硝态氮处理还增加叶片氮素含量,提高光合氮素利用效率,分别比铵态氮和酰胺态氮处理提高2.43%和6.76%。可见,茅苍术光合特性对硝态氮更敏感,施用硝态氮肥能改善光能特性,促进氮素高效利用。     

淹涝胁迫和氮形态对苗期玉米糖、氮代谢底物量的影响

采用砂培培养方法,比较研究淹水和不同氮形态(铵态氮、硝态氮以及铵态氮︰硝态氮为1︰1)对苗期玉米根、茎鞘和叶的糖、氮代谢底物——可溶性糖、还原糖、硝态氮和游离氨基酸等物质含量的影响。结果表明,当淹涝胁迫持续7 d时,在非淹涝胁迫条件下,铵态氮处理的根、茎鞘和叶的可溶性糖和游离氨基酸含量均显著高于硝态氮处理(P<0.05);在淹涝胁迫条件下,硝态氮处理的根、茎鞘和叶的生物量干重显著低于铵态氮处理(P<0.05),其根和叶的生物量干重也显著低于铵态氮、硝态氮混合处理(P<0.05)。与非淹涝条件相比,在淹涝胁迫条件下,硝态氮处理的根系和叶的硝态氮含量显著降低(P<0.05),降低幅度分别高达62.6%和30.0%;此外,与非淹涝条件相比,在淹涝胁迫条件下,铵态氮处理的根的可溶性糖、还原糖以及游离氨基酸含量,茎鞘的可溶性糖和还原糖含量以及叶的可溶性糖和游离氨基酸含量均显著升高(P<0.05),而硝态氮处理仅根、茎鞘和叶的还原糖含量以及叶的游离氨基酸含量显著升高(P<0.05)。因此,在本试验条件下,由于糖、氮代谢底物含量充足,铵态氮处理的苗期玉米具有相对较强的耐淹涝胁迫能力。     

硝态氮抑制尖孢镰刀菌侵染促进黄瓜生长的内在生理机制

  【目的】  连作障碍严重影响设施农业的发展。不同形态氮素可影响黄瓜土传枯萎病的发生，然而其内在生理机制尚不明确。通过氮素营养调控植物–微生物互作关系，为防控土传病害的发生提供理论依据。  【方法】  以黄瓜品种津春2号和尖孢镰刀菌黄瓜专化型菌 (FOC) 为试材，进行温室营养液培养试验。设营养液中添加铵态氮不接菌 (A)、硝态氮不接菌 (N)、铵态氮接菌 (AI) 和硝态氮接菌 (NI) 共4个处理。尖孢镰刀菌侵染8天后进行植株样品的采集及测定，包括株高、根长、生物量、病情指数、叶绿素含量、光合特性、叶片温度，并进行了叶肉细胞超微结构的观察，测定了植物全氮、可溶性蛋白及可溶性糖含量。  【结果】  与铵态氮相比，硝态氮营养显著抑制了黄瓜植株枯萎病的发病率，并显著促进了植株的生长以及植株生物量的增加。未接菌条件下，供应铵态氮的植株光合速率、气孔导度、蒸腾速率、羧化效率及表观量子效率均显著高于供应硝态氮的植株；尖孢镰刀菌的侵染导致供应铵态氮的植株叶绿体结构受损，显著降低了其光合速率、气孔导度、蒸腾速率、细胞间隙CO₂浓度、羧化效率及表观量子效率，而病原菌侵染对供应硝态氮的植株叶片光合特性无显著影响。未接菌条件下，供应铵态氮的植株叶片温度及水分利用效率显著低于供应硝态氮的植株；尖孢镰刀菌侵染后，供应铵态氮的植株叶片温度及水分利用率显著增加，而病原菌侵染对供应硝态氮的植株无显著影响。叶片温度与蒸腾速率呈显著负相关关系，而与水分利用率呈显著正相关关系。供应铵态氮的植株根系全氮、可溶性蛋白及可溶性糖含量均显著高于供应硝态氮的植株，从而促进病原菌对供应铵态氮的植株的侵染。尖孢镰刀菌侵染后，供应铵态氮的植株根系可溶性蛋白含量显著增加，可溶性糖含量降低，而尖孢镰刀菌侵染对供应硝态氮的植株可溶性蛋白及可溶性糖含量无显著影响。  【结论】  硝态氮能够有效地抑制黄瓜枯萎病的发生，维持叶绿体结构的完整性，保持黄瓜植株正常的光合作用及生长，并减少碳水化合物向根系的运输，从而抑制病原菌的侵染及病害的发生。在黄瓜的设施栽培中，可适当增加硝态氮肥的施用而减少铵态氮肥的投入，以抑制土传枯萎病发生。     

分根交替灌溉下氮形态对番茄苗期光合日进程的影响

本试验以番茄为材料,研究分根区交替灌溉下氮形态对番茄苗期叶片光合日变化规律的影响。试验设置灌溉方式(正常灌溉、交替根区灌溉)以及氮素形态(铵态氮、硝态氮),且交替根区灌溉设置两种灌溉下限(60%或40%田间持水量,θf)。水分处理30d后测定番茄苗叶片光合日进程与叶绿素含量、生物量等的变化。结果表明:(1)与硝态氮处理相比,铵态氮处理有利于苗期番茄生长发育;(2)与正常灌溉相比,交替灌溉处理下植株叶片光合速率、蒸腾速率、气孔导度、叶绿素含量及生物量随灌溉下限不同而有差异,只要交替灌溉水分下限控制适当(60%θf),在节约水分的同时对番茄光合作用与生长的影响不大,但过分的水分胁迫对番茄的生长发育产生不利的影响并最终导致生物量降低。     

不同氮素形态对干旱胁迫杉木幼苗养分吸收及分配的影响

【目的】干旱胁迫是限制植物生长的重要非生物因素之一,而适宜的氮素营养可以提高植物的抗旱性。本文探讨了供应不同形态氮源对干旱条件下杉木[Cunninghamia lanceolata (Lamb.) Hook]幼苗养分吸收及分配的影响。【方法】采用水培试验,供试杉木材料为2个无性系幼苗(7–14号和8–8号),在营养液中添加10%(w/v)PEG-6000进行干旱胁迫。营养液中的氮源处理包括硝态氮、铵态氮、硝铵混合氮,氮素浓度均为4.571mmol/L,每个品种均设6个处理。培养20天后,测定了杉木幼苗根、茎、叶的养分含量及生物量。【结果】与正常水分供应相比较,干旱胁迫条件下供应铵态氮可促进叶片N、K以及茎叶P、K的吸收,供应混合氮可促进根部K的吸收;供应铵态氮可促进根、茎对Ca的吸收,对叶片Ca无明显作用。干旱胁迫对根部Fe、Mn、Cu、Zn吸收量影响显著,氮素供应不同程度地降低了干旱胁迫下各器官Mg、Fe、Mn和Cu吸收量,表现为抑制吸收,但添加铵态氮比硝态氮的降低幅度小。3个氮源处理均降低了干旱条件下根部Zn吸收量,但没有降低甚至增加了茎、叶中Zn的吸收量,说明氮营养可调节Zn在各器官间的分配,缓解干旱导致的缺锌现象。不同器官之间各养分吸收量差异显著,3个氮源处理中,N和P吸收量表现为叶>根>茎,K和Ca为叶>茎>根,Fe、Cu为根>叶>茎,Mg、Mn和Zn在各器官之间的分配规律不一。铵态氮吸收量均表现为叶>根>茎,且各器官铵态氮吸收量显著高于硝态氮,说明杉木具有明显的喜铵特性。【结论】在干旱胁迫下,氮素供应形态显著影响杉木幼苗对养分的吸收及在各器官中的分配,作用效果因家系品种和元素种类而异。总体来讲,铵态氮提高干旱胁迫下杉木幼苗养分吸收的效果好于硝态氮,杉木可以认为是喜铵植物。     

外源K~+、Ca~(2+)和Mg~(2+)对3个玉米自交系萌发期和幼苗期耐盐性的影响

为了研究盐胁迫条件下营养元素K+、Ca2+和Mg2+对不同自交系玉米耐盐性影响的差异,探讨玉米耐盐胁迫的生理机制,以玉米耐盐自交系81162和8723及盐敏感自交系P138为材料,在盐胁迫条件下(180mmol/L NaCl),提高溶液中Ca2+和Mg2+的含量,比较营养元素K+、Ca2+和Mg2+浓度的变化对不同基因型玉米萌发期和幼苗期耐盐性的影响。结果表明,盐胁迫条件下提高溶液中Ca2+和Mg2+的含量,可显著降低萌发期和幼苗期植株体内Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+比,各项萌发指标、生长和生理生化指标都得到明显改善,明显减轻盐胁迫的危害,增强玉米耐盐胁迫能力,且Ca2+处理的效果优于Mg2+处理;提高溶液中K+含量的效果远远小于Ca2+和Mg2+处理,K+对玉米耐盐性的影响相对不明显,不能显著降低植株体内Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+比,这也是K+处理对玉米耐盐性影响相对不明显的内在原因。盐胁迫条件下,耐盐自交系(81162和8723)与盐敏感自交系(P138)相比,植株体内有较低的Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+比,有较高的K+含量,这些都是耐盐自交系耐盐胁迫能力高于盐敏感自交系的内在原因。因此,K+、Ca2+和Mg2+在植株体内的含量及其与Na+的比值变化都会影响玉米萌发期和幼苗期耐盐性;适当提高玉米生长环境的Ca2+和Mg2+浓度可以明显增强植株耐盐胁迫能力,营养元素Ca2+的效果比Mg2+明显;而K+对玉米耐盐性的影响相对不明显。     

保水缓释肥对盐胁迫下水稻矿质元素分配的调控

研究了施加盐碱地保水缓释肥(ZL 2012 1 0400570.0)对盐胁迫水稻幼苗叶长、叶温、氮磷钾(NPK)及钠(Na)的吸收和转运的影响。结果表明:盐胁迫下,水稻植株最大叶长随基质肥配比(1%、2%和4%)的增加而增加,且随处理时间延长,其增加效应愈明显,而其叶温逐渐降低;随高盐(4.68 g kg~(-1)盐分)处理的进行,植株逐渐枯萎死亡。盐胁迫下,该肥料施用明显提高植株的NPK含量,降低Na含量。低盐(2.68 g kg~(-1)盐分)胁迫下,播种40 d,施肥显著增加N和K向植株地上部转运,但显著降低其P转运系数(P-TF)和Na转运系数(Na-TF),显著提高植株K~+、Na~+的选择性比率(S_(K,Na));而播种80 d,施肥导致植株N、P、Na转运下降,而K转运和S_(K,Na)显著上升。高盐胁迫下,施肥对植株氮转运系数(N-TF)无显著影响,而P和Na转运上升,钾转运系数(K-TF)和S_(K,Na)随肥施量增加而显著下降。综上所述,低盐胁迫下,施该颗粒状盐碱地保水缓释肥,可明显提高水稻幼苗植株的NPK吸收,降低植株Na的积累,显著提高了水稻幼苗植株对K的选择性运输,维持体内的离子稳态,从而显著提高水稻植株的耐盐性。高盐胁迫下,该肥短期内亦可明显促进植株矿质营养在体内的积累,降低植株Na含量,从而一定程度上缓解植株盐害。     

Differences in Physiological Traits Among Salt‐Stressed Barley Genotypes

Abstract

The effect of salinity on some physiological parameters in 16 barley genotypes with different salt tolerance was investigated. The results showed 50 mM NaCl treatment increased Na⁺/K⁺ ratio, malondialdehyde (MDA) and proline contents, and decreased cell membrane stability index (CMSI) and fresh shoot biomass (FSB) of all tested genotypes. Salt stress also resulted in a decreased chlorophyll (Chl) content and net photosynthesis (Pn) for most genotypes. Under higher salt stress (300 mM NaCl), the marked increase for Na⁺/K⁺, MDA, and proline content, and decrease for other parameters were found for all genotypes. The affected extent of these parameters by salt stress varied with genotypes. Proline accumulation in barley was associated with injured extent under salt stress, indicating it is not a defensive reaction to the stress. K⁺ uptake was less affected, whereas Na⁺ accumulation in plants was enhanced under high salt stress. The correlation analysis showed that MDA and proline content, Na⁺ concentration and Na⁺/K⁺ were negatively correlated with FSB, whereas other parameters examined in the study were positively correlated with FSB.     

Comparative Effect of Nitrogen Forms on Nitrogen Uptake and Cotton Growth Under Salinity Stress

The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na⁺), ammonium (NH₄⁺), and nitrate (NO₃^?) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO₃-N were greater than those treated with NH₄-N with or without salinity stress. Under salinity stress, the Na⁺ content of seedlings treated with NO₃-N was lower than that in seedlings treated with NH₄-N owing to higher root Na⁺ efflux. A lower net NO₃^? efflux was observed in roots of nitrate-fed plants relative to the net NH₄⁺ efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in different tissues, especially in leaves, thereby enhancing photosynthesis in nitrate-fed plants under salinity stress. Nitrate-N is superior to ammonium-N based on nitrogen uptake and cotton growth under salinity stress.     

Effect of nitrogen nutrition on salt tolerance of Pisum sativum during vegetative growth

The influence of different nitrogen (N) forms on salt tolerance of Pisum sativum L. was investigated. Plants of the pea cultivar “Resal” were subjected to 0 (control) or 90 mM NaCl and one of the following nitrogen forms: 5 mM mineral N supplied as either NO , NH , or NH₄NO₃ or N supplied by biological N₂ fixation (inoculated with Rhizobium leguminosarum bv. viciae). Root and shoot biomass were determined 15, 30, 45, and 60 d after emergence, and Na⁺, K⁺, and Cl^– concentrations were determined by capillary electrophoresis. Nitrogen sources induced significant differences in plant growth and in ion accumulation and distribution and in differentially affected salt tolerance. In the absence of salt, the largest biomass accumulation was obtained with NH₄NO₃. In the presence of NaCl, NO ‐fed plants experienced less salt toxicity than plants supplied with other N sources, as indicated by lower Na⁺ and Cl^– and higher K⁺ concentrations in the shoot. The results also suggest that it is possible to establish an effective symbiosis under saline conditions, provided that a salt‐tolerant Rhizobium isolate with good N₂‐fixing ability is used. The use of the appropriate N‐fertilizer source can enhance the growth of Pisum sativum. Hence, NH₄NO₃ may be preferably used under non‐saline and NO under moderately saline conditions.     

Effect of grafting on the growth and ion concentrations of cucumber seedlings under NaCl stress

Abstract

To assess whether grafting raised the salt tolerance of cucumber seedlings by limiting transport of Na⁺ to the leaf and to test whether the salt tolerance of grafted plants was affected by the shoot genotype, two cucumber cultivars (“Jinchun No. 2”, a relatively salt-sensitive cultivar, and “Zaoduojia”, a relative salt-tolerant cultivar) were grafted onto rootstock pumpkin (Cucurbita moschata Duch. cv. “Chaojiquanwang”, a salt-tolerant cultivar). Ungrafted plants were used as controls. The effects of grafting on plant growth and ion concentrations were investigated under NaCl stress. Reductions in the shoot and root dry weights, leaf area and stem diameter of grafted plants were lower and concentrations of K⁺ and Cl^? in the leaves were higher than those of ungrafted plants under the same NaCl stress. The Na⁺ concentration and Na⁺/K⁺ ratio in scion leaves and in the stems of grafted plants were lower, whereas those in rootstock stems and roots were higher than in ungrafted plants under the same NaCl stress. Shoot and root dry weight, leaf area and stem diameter were negatively correlated with leaf Na⁺ concentrations and Na⁺/K⁺ ratio, but were positively correlated with leaf K⁺ concentrations. The Na⁺ concentrations and Na⁺/K⁺ ratio were lower, whereas the K⁺ concentrations in the leaves of grafted “Zaoduojia” plants were higher than those in grafted “Jinchun No. 2” plants under the same NaCl stress. The reductions in leaf area and stem diameter of grafted “Jinchun No. 2” plants were more severe than those of grafted “Zaoduojia” plants. These results indicate that: (1) the higher salt tolerance of grafted cucumber seedlings is associated with lower Na⁺ concentrations and Na⁺/K⁺ ratio and higher K⁺ concentrations in the leaves, (2) grafting improved the salt tolerance of cucumber seedlings by limiting the transport of Na⁺ to the leaves, (3) the salt tolerance of grafted cucumber seedlings is related to the shoot genotype.     

SOME DELETERIOUS EFFECTS OF LONG-TERM SALT STRESS ON GROWTH,NUTRITION, AND PHYSIOLOGY OF GERBERA (GERBERA JAMESONII L.) AND POTENTIAL INDICATORS OF ITS SALT TOLERANCE

Tolerance of gerbera (Gerbera jamesonii L.) to long-term sodium chloride (NaCl) salt stress was evaluated by subjecting plants to 0, 10, 20, 30 and 40 mM NaCl levels for ten weeks. Increased NaCl led to a significant decrease in leaf and stem biomass. Salt stress significantly affected sodium (Na⁺), potassium (K⁺) concentrations in leaves, stems and roots leading to sharp declines in K⁺/Na⁺ ratios. Magnesium concentrations in stems and roots also showed significant declines. Adverse effect of salt stress on chlorophyll content was also significant. Proline seemed less effective in osmotic adjustment under long-term high salt stress. Switching from vegetative to reproductive growth phase was crucial for certain physiological functions. Leaf Na⁺ concentration showed significant correlation with important traits. These data suggest that NaCl threshold level in irrigation water for gerbera is around 10 mM. Leaf fresh weight, chlorophyll content and leaf K⁺/Na⁺ ratio are promising indicators of salt-sensitivity of gerbera.     

Effect of potassium on uptake and translocation of sodium and potassium in Chinese cabbage under NaCl stress

To investigate the influence of potassium (K⁺) on the salinity tolerance of Chinese cabbage (Brassica pekinensis Rupr.) seedlings, the plants were cultured at three K⁺ levels (0, 5, or 10?mM), under normal (0?mM NaCl) and high-salt (100?mM NaCl) conditions. The results indicated that the dry weight of Chinese cabbage increased with the application of K⁺ under salt stress. Addition of K⁺ increased K⁺ concentrations and suppressed sodium (Na⁺) concentration, which eventually increased the K⁺/Na⁺ ratios in roots or shoots. Application of K⁺ enhanced the uptake of K⁺ and suppressed the uptake of Na⁺. Moreover, the ratios of shoot-K⁺/root-K⁺ increased considerably, but the ratios of shoot-Na⁺/root-Na⁺ decreased in response to K⁺ application. It was concluded that the application of K⁺ could enhance the salt stress tolerance in Chinese cabbage because more K⁺ than Na⁺ was absorbed and translocated from roots to shoots.     

Molybdenum Affects Photosynthesis and Ionic Homeostasis of Chinese Cabbage under Salinity Stress

A pot trial was conducted to clarify the effects of molybdenum (Mo) on photosynthesis and ionic homeostasis of Chinese cabbage under salinity stress. Mo was applied at three levels (0, 0.15, 0.3 mg kg^?1). Ten days after sowing, 500 ml of 0.8% of NaCl solution was added to half of the plants for each treatment every 10th day for three consecutive times. The results revealed that fresh weight was significantly increased by application of Mo under salt stress; contents of chlorophyll a, chlorophyll b, carotene, and total chlorophyll were all raised by application of Mo; photosynthesis rate was enhanced by nonstomatal factors by application of Mo; and the ratios of potassium/sodium ions (K⁺/Na⁺), calcium/sodium ions (Ca²⁺/Na⁺), and magnesium/sodium ions (Mg²⁺/Na⁺) were all increased by application of Mo under salt stress. The study suggests that the application of Mo enhances salinity stress tolerance in Chinese cabbage by increasing the photosynthesis rate and the ionic homeostasis adjustment.     

Salinity tolerance and sodium localization in mycorrhizal strawberry plants

ABSTRACT

Salinity stress alleviation through arbuscular mycorrhizal fungi (AMF) application and sodium (Na) localization in strawberry plants were investigated. A greenhouse experiment in a completely randomized design with three replications revealed AMF (Gigaspora margarita) association alleviated salinity stress (200 mM NaCl). AMF inoculated plants had greater dry weight, maintained chlorophyll content, and decreased leaves browning compared to the control under salinity stress. The Na⁺ concentration and Na⁺/K⁺ ratio were found lower in the following organs, young and old leaflets and petioles, main roots and lateral roots of mycorrhizal plants than the control. The scanning electron microscope and energy dispersive x-ray spectroscopy (SEM-EDX) analysis of Na in old petiole and main root tissues revealed, excess Na localized in the vascular bundle margin of old petioles and main roots of both the control and mycorrhizal plants. So, suppression of Na absorption through roots might be the mechanism of salt stress alleviation in mycorrhizal plants than to the control Na localization. The higher cellulose and lignin contents in the cell wall of mycorrhizal roots act as the apoplastic barrier which might be suppressing Na influx.     

High K+ supply avoids Na+ toxicity and improves photosynthesis by allowing favorable K+ : Na+ ratios through the inhibition of Na+ uptake and transport to the shoots of Jatropha curcas plants

This study assessed the relationships between external K⁺ supply and K⁺ : Na⁺ ratios associated with Na⁺ toxicity in Jatropha curcas. Plants were exposed to increasing external K⁺ concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K⁺ : Na⁺ ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K⁺ : Na⁺ in xylem and leaves. The transport rates of K⁺ and Na⁺ from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K⁺ : Na⁺ ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K⁺ homeostasis under salinity conditions. The higher K⁺ affinity and selectivity compared with Na⁺ in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K⁺ : Na⁺ ratios at the whole‐plant level. These characteristics, combined with adequate K⁺ concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.