外源脱落酸对干旱胁迫下滇润楠幼苗生长及生理特性的影响

以滇润楠一年生实生苗为试验材料,研究在良好水分条件(土壤含水量为70%～75%田间持水量)、轻度干旱胁迫及重度干旱胁迫处理下(50%～55%和30%～35%田间持水量)进行外源脱落酸(ABA)喷施对其生长及生理特性的影响。结果表明: 干旱胁迫使得滇润楠幼苗叶片的相对含水量、株高和生物量显著下降,净光合速率及叶绿素荧光参数(PSⅡ最大光化学效率,F_v/F_m)有不同程度的下降,而根冠比、膜脂过氧化产物丙二醛(MDA)含量显著增加。外源ABA的喷施可提高干旱胁迫下滇润楠幼苗的适应性,尤其是重度干旱下,外源ABA显著提高了叶片相对含水量21.0%,同时增加了植株株高和生物量的累积,提高了根冠比,为良好水分条件的2.1倍;减少了干旱下膜脂过氧化产物MDA的累积,提高了抗氧化酶过氧化氢酶、超氧化物岐化酶的活性,显著增加了脯氨酸的含量,为良好水分条件的7.7倍。外源ABA的喷施显著缓解了干旱胁迫对植株光合器官的不利影响,减少干旱引起的叶片净光合速率及气孔导度的下降,并且减轻了PSⅡ受到干旱的伤害程度,重度干旱下喷施ABA的植株的F_v/F_m显著高于未喷施ABA的植株。外源ABA的喷施可以减轻干旱对滇润楠植株的伤害,提高其抗旱性。     

Arbuscular Mycorrhizal Fungi Alter Fractal Dimension Characteristics of Robinia pseudoacacia L. Seedlings Through Regulating Plant Growth,Leaf Water Status,Photosynthesis, and Nutrient Concentration Under Drought Stress

The influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Rhizophagus intraradices, on plant growth, leaf water status, chlorophyll concentration, photosynthesis, nutrient concentration, and fractal dimension (FD) characteristics of black locust (Robinia pseudoacacia L.) seedlings was studied in pot culture under well-watered, moderate drought stress, and severe drought stress treatments. Mycorrhizal seedlings had higher dry biomass, leaf relative water content (RWC), and water use efficiency (WUE) compared with non-mycorrhizal seedlings. Under all treatments, AMF colonization notably enhanced net photosynthetic rate, stomatal conductance, and transpiration rate, but decreased intercellular CO₂ concentration. Leaf chlorophyll a and total chlorophyll concentrations were higher in AM seedlings than those in non-AM seedlings although there was no significant difference between AMF species. AMF colonization improved leaf C, N, and P concentrations, but decreased C:N, C:P, and N:P ratios. Mycorrhizal seedlings had a larger FD value than non-mycorrhizal seedlings. The FD value was positively and significantly correlated to the plant growth parameters, photosynthesis, RWC, WUE, and nutrient concentration but negatively correlated to leaf/stem ratio, C:N and C:P ratios, and intercellular CO₂ concentration. We conclude that AMF lead to an improvement of growth performance of black locust seedlings under all growth conditions, including drought stress via improving leaf water status, chlorophyll concentration, photosynthesis, and nutrient uptake. Moreover, FD technology proved to be a powerful non-destructive method to characterize the effect of AMF on the physiology of host plants during drought stress.     

Drought tolerance in three hybrid poplar clones submitted to different watering regimes

Aims Poplars grown in North China may experience water-deficient periods in their life cycle. The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine which clone among the three is the best adapted to drought conditions.Methods Three hybrid poplar clones (clone DN-34, R-247 and OP-367) were used in the present experiment. The seedlings of the three clones were grown under four watering regimes: control (well watered, 100% field water capacity (FC)) and three drought treatments (drought stress I, 50% FC; drought stress II, 40% FC; drought stress III, 30% FC). Changes in morphological, physical and biochemical indicators of the three hybrid poplar clones were investigated.Important findings Drought treatment (50%, 40% and 30% FC) decreased net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), shoot height, total biomass and chlorophyll (Chl) content in all the three clones and it increased activities of antioxidant enzymes and free proline content. The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30% FC, followed by clone DN-34 and R-247. Relative leaf water content (RWC) and stem diameter (sd) markedly declined in clone R-247 and DN-34 under drought stress I, II and III, whereas RWC and sd declined in clone OP-367 only under drought stress II and III. Clone OP-367 had more RWC and sd than DN-34 and R-247. Only the 30% FC induced an increase in the root-to-shoot ratio (rs) and water use efficiency (WUE) in all the three clones. OP-367 was the most efficient clone in water absorption and use, for plants of the clone had the highest values of rs and WUE. Our data demonstrate that among the three clones, OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.     

Responses of sugar beet (Beta vulgaris L.) to drought and nutrient deficiency stress

The responses of two sugar beet genotypes, 24367 (putative droughttolerant) and N6 (putative drought intolerant), to drought and nutrientdeficiency stress were investigated in an attempt to identify reliable andsensitive indicators of stress tolerance. In glasshouse-grown plants of bothgenotypes, relative water content (RWC) of the leaves decreased and leaftemperature increased in response to drought stress. Genotype differences inresponse to drought included leaf RWC, glycine betaine accumulation, alterationof shoot/root ratio and production of fibrous roots. Thus, in comparison to N6,genotype 24367 lost less water from leaves, produced more fibrous roots,produced more glycine betaine in shoots and tap roots and had a much reducedshoot/root ratio in response to withholding water for up to 215 h.The hydraulic conductance and sap flow of sugar beet seedlings grown innutrientculture decreased when subjected to nitrogen deficiency stress. Under nitrogensufficient conditions sap flow was greater in 24367 than in N6. The resultsindicate that genotype 24367 is more tolerant to stresses induced by water andnitrogen deficiency and that increased fibrous root development may be a majorfactor in increasing sap flow via a concomitant enhancement of aquaporinactivity.     

Ecophysiological responses of Abies fabri seedlings to drought stress and nitrogen supply

Abies fabri (Mast.) Craib. (A. fabri) is an endemic and dominant species in typical subalpine dark coniferous forests distributed in mountainous regions of Western Sichuan, China. We investigated the ecophysiological responses of A. fabri seedlings to short‐term experimental drought, nitrogen supply and their interaction. Drought stress was created by excluding natural precipitation with automatically controlled plastic roof that covered the seedlings. Nitrogen fertilization was applied weekly by spraying over seedlings ammonium nitrate solution (50 kg N ha^?1 year^?1) during the growing season of 2009. The results showed that drought stress decreased leaf relative water content (RWC), whereas it caused marked increases in root mass ratio (RMR) and root/shoot mass ratio by 6.19 and 10.39%, respectively, as compared with the control. Drought stress increased malondialdehyde (MDA) content, electrolyte leakage, proline content, soluble sugars content and the activities of antioxidant enzymes, whereas nitrogen supply decreased MDA content, but enhanced activities of some antioxidant enzymes [especially peroxidase (POD)]. In the drought stressed plots, nitrogen supply increased RWC and decreased the content of MDA. The combination of drought stress and nitrogen supply also decreased the activities of antioxidant enzymes. These results indicated that the negative effects of drought stress on A. fabri seedlings might be alleviated by nitrogen supply.     

干旱胁迫对不同施氮水平麻疯树幼苗光合特性及生长的影响

采用盆栽控水的方法,研究了干旱胁迫（连续干旱0 d,5 d,10 d,…,45 d）对不同施氮水平(对照 0 kg N·hm^-2、低氮 96 kg N·hm^-2、中氮 288 kg N·hm^-2、高氮 480 kg N·hm^-2)麻疯树幼苗光合特性及其生长的影响.结果表明: 随干旱胁迫强度的增加,各施氮水平麻疯树幼苗叶片相对含水量、苗高生长量、地径生长量、叶面积、净光合速率、蒸腾速率和气孔导度均降低,且各水分处理间差异极显著(P<0.01);随干旱时间的延长,叶绿素含量和水分利用效率表现出先升高后降低的趋势,而胞间CO₂浓度呈先降低后升高的趋势.正常供水时,施氮处理均不同程度提高了麻疯树幼苗的光合能力,促进了麻疯树幼苗的生长,且施氮量越高效果越好;干旱条件下,氮素营养对植株光合能力和生长的影响与干旱程度和施氮水平有关.轻度干旱时,提高施氮水平对植株光合能力和生长具有明显的促进作用;中度干旱时,中氮的促进作用明显高于其他施氮水平;严重干旱时,低氮的促进效果最好,高氮的促进作用减弱并逐渐转向抑制.     

盐胁迫对黄瓜幼苗根系生长和水分利用的影响

采用营养液水培法,研究了NaCl胁迫对两个耐盐性不同的黄瓜品种幼苗根系生长、活力、质膜透性和叶片生长、蒸腾速率（T_r）、相对含水量（RWC）及水分利用率（WUE）的影响.结果表明,盐胁迫下黄瓜植株根系吸收面积下降,质膜透性升高,叶片数减少,叶片T_r和RWC在盐胁迫2 d后明显下降,根系活力和叶片WUE均先升后降,50、75和100 mmol·L^-1NaCl胁迫9 d时,耐盐性较弱的津春2号根系活力降低幅度分别比耐盐性较强的长春密刺高18.01%、12.17%和10.95%,胁迫8 d时WUE下降幅度分别比长春密刺高2.74%、5.27%和0.23%.短期盐胁迫下,黄瓜植株通过提高根系吸收能力来补偿根系吸收面积的下降,通过降低叶片T_r和提高WUE来减少水分散失,在一定程度上有利于缓解水分失衡,提高植株耐盐性;盐胁迫5 d后,根系活力和WUE的下降导致水分失衡加剧,表明根系吸收能力的下降是导致水分失衡的重要原因,叶片WUE的下降是水分失衡的反应,两者均与品种的耐盐性关系密切.     

Effects of water stress and nitrogen supply on leaf gas exchange and fluorescence parameters of <Emphasis Type="Italic">Sophora davidii</Emphasis> seedlings

Two-month-old seedlings of Sophora davidii were subjected to a randomized complete block design with three water (80, 40, and 20 % of water field capacity, i.e. FC₈₀, FC₄₀, and FC₂₀) and three N supply [N0: 0, Nl: 92 and Nh: 184 mg(N) kg⁻¹(soil)] regimes. Water stress produced decreased leaf area (LA) and photosynthetic pigment contents, inhibited photosynthetic efficiency, and induced photodamage in photosystem 2 (PS2), but increased specific leaf area (SLA). The decreased net photosynthetic rate (P _N) under medium water stress (FC₄₀) compared to control (FC₈₀) might result from stomatal limitations, but the decreased P _N under severe water deficit (FC₂₀) might be attributed to non-stomatal limitations. On the other hand, N supply could improve photosynthetic capacity by increasing LA and photosynthetic pigment contents, and enhancing photosynthetic efficiency under water deficit. Moreover, N supply did a little in alleviating photodamages to PS2 caused by water stress. Hence water stress was the primary limitation in photosynthetic processes of S. davidii seedlings, while the photosynthetic characters of seedlings exhibited positive responses to N supply. Appropriate N supply is recommended to improve photosynthetic efficiency and alleviate photodamage under water stress.     

Drought stress induced changes in some organic substances in nodules and other plant parts of two potential legumes differing in salt tolerance

A greenhouse experiment was conducted to assess the effect of water stress on growth and metabolic changes in nodules and other plant parts of two leguminous species, Phaseolus vulgaris and Sesbania aculeata, with the major objective that nodules play a vital role in drought tolerance. Imposition of water deficit conditions for 45 days to 15-day-old plants of P. vulgaris and S. aculeata reduced shoot mass and nodule mass of both species, but the reduction was more pronounced in P. vulgaris than in S. aculeata. Nitrate reductase (NR) activity was reduced more in the leaves and nodules of P. vulgaris than in S. aculeata. Soluble proteins in the nodules of S. aculeata were more decreased as compared to that in P. vulgaris. Free amino acids increased in all parts of both species due to water deficit, but a higher increase was observed in leaf and nodules of P. vulgaris than in S. aculeata. Osmoprotectants such as proline and glycine betaine increased more in the nodules and other parts of S. aculeata under drought stress. In conclusion, S. aculeata (salt tolerant) showed a higher degree of drought tolerance than P. vulgaris (salt sensitive). Drought tolerance of S. aculeata was found to be associated with a smaller reduction in number and mass of root nodules, a high activity of nitrate reductase in leaves and nodules, high accumulation of free proline in roots and nodules, and high glycine betaine content in nodules.     

Response of stem sap flow and leaf photosynthesis in <Emphasis Type="Italic">Tamarix chinensis</Emphasis> to soil moisture in the Yellow River Delta,China

Soil moisture is the main limiting factor for vegetation growth at shell ridges in the Yellow River Delta of China. The objective of this study was to explore the soil moisture response of photosynthetic parameters and transpiration in Tamarix chinensis Lour., a dominant species of shell ridges. Leaf photosynthetic light-response parameters and sap flow were measured across a gradient of relative soil water content (RWC), from drought (23%) to waterlogging (92%) conditions. Leaf photosynthetic efficiency and stem sap flow of T. chinensis showed a clear threshold response to soil moisture changes. Leaf net photosynthetic rate, water-use efficiency (WUE), light-saturation point, apparent quantum yield, maximum net photosynthetic rate, and dark respiration rate peaked at moderately high RWC, decreasing towards high and low values of RWC. However, peak or bottom RWC values substantially differed for various parameters. Excessively high or low RWC caused a significant reduction in the leaf photosynthetic capacity and WUE, while the high photosynthetic capacity and high WUE was obtained at RWC of 73%. With increasing waterlogging or drought stress, T. chinensis delayed the starting time for stem sap flow in the early morning and ended sap flow activity earlier during the day time in order to shorten a daily transpiration period and reduce the daily water consumption. The leaf photosynthetic capacity and WUE of T. chinensis were higher under drought stress than under waterlogging stress. Nevertheless, drought stress caused a larger reduction of daily water consumption compared to waterlogging, which was consistent with a higher drought tolerance and a poor tolerance to waterlogging in this species. This species was characterized by the low photosynthetic capacity and low WUE in the range of RWC between 44 and 92%. The RWC of 49–63% was the appropriate range of soil moisture for plant growth and efficient physiological water use of T. chinensis seedlings.     

土壤干旱条件下氮素营养对玉米内源激素含量影响

在田间持水量分别保持于35％、55％和75％±5％的土壤水分条件下,利用盆栽实验研究了土壤干旱和氮素营养对玉米内源激素和气孔导度的影响．结果表明,土壤干旱下氮素营养明显降低了玉米根系木质部汁液ABA浓度,而正常供水下施氮处理间则无显著差异(施氮处理仍较低),同时测定的叶片ABA浓度则呈相反的变化趋势,表现为干旱下施氮处理要高于不施氮处理;施氮处理木质部汁液中ZRs浓度应低于相应的不施氮处理,在调控气孔行为方面并未表现拮抗ABA作用;3种土壤水分条件下,施氮玉米叶片的气孔导度均高于不施氮处理,与木质部汁液ABA浓度呈负相关,说明施氮处理较低的根源ABA浓度是导致其气孔导度较大的主要原因．     

干旱复水对柑橘幼苗叶片光合、叶绿素荧光和根系构型的影响

干旱严重影响柑橘的生长和发育.为探索柑橘对干旱胁迫的响应机制,本试验以抗旱性不同的三湖红橘和三湖化红为材料,通过盆栽控水进行干旱胁迫和复水处理,研究处理后植株叶片光合、叶绿素荧光和根系构型的变化.结果表明: 干旱显著降低了两种柑橘幼苗的净光合作用速率、气孔导度、蒸腾速率和胞间CO₂浓度,而三湖红橘的下降幅度更小;复水后,光合参数均有所恢复,但仍低于对照.三湖红橘水分利用率在干旱15 d后开始显著高于对照,而三湖化红除干旱15 d外的其他处理时间均低于对照.干旱提高了两种幼苗的PSII最大光合效率,但抑制了三湖化红的PSII实际光合效率.干旱到一定程度后,两种幼苗的PSII电子传递速率和光化学淬灭均下降,干旱和复水后非光化学淬灭在三湖红橘中下降,但在三湖化红中上升.根系构型分析表明,干旱导致两种幼苗的根表面积和根体积下降,同时抑制了三湖化红的总根长,但能够提高三湖红橘的总根长和总根尖数.进一步分析不同直径的侧根长度发现,三湖红橘的一类侧根长度在干旱胁迫10 d后开始增加,而三湖化红的一类侧根长度在干旱前期没有变化,干旱20 d时显著下降;除三湖红橘的三类侧根外,两种幼苗其余直径等级侧根的生长均受干旱抑制.除总根尖数外,复水后根系生长各参数均没有恢复.干旱对三湖红橘光合性能的影响小于三湖化红,并且前者能够维持更高的水分和光能利用率.干旱后三湖红橘根尖数和细根长度增加,可能有助于提高其对水分的吸收能力.     

Morphological and biomass characteristic acclimation of trident maple (Acer buergerianum Miq.) in response to light and water stress

Acer buergerianum Miq. (Trident maple) is a native species of China with a large distribution, but exist in small population. Water and light are two important factors limiting plant growth and are crucial in the framework of forest regeneration. However, there is no consensus on how shade interacts with drought. Four hypotheses in the recent literature variously predict that shade will have a stronger, weaker or equal impact on seedlings under drought stress. This study investigated the interactive responses of A. buergerianum to light and water focusing on seedling growth, leaf morphology and biomass partitioning by performing a growth experiment in pots with different water supply regimes [15, 35, 55, 75, 95 % of field capacity (FC)] combined with two light regimes (10 and 66 % of full sunlight). After 123 days treatment, the results showed that shade greatly reduced growth and biomass, in contrast enhancing the amount of chlorophyll, the amount of water in the leaves, and the specific leaf area. Drought reduced growth, biomass, and the bulk of the leaves. Most leaf traits and biomass characteristics had strong interactions in their responses to light and water treatments. Allometric analysis revealed that water and light had no effects on root to shoot ratios, main root to lateral root ratios, and root mass ratios. Shade alleviated the negative impact of drought. A. buergerianum successfully adapted to the various light and water conditions. We recommend a water supply above 15 % FC to keep the seedlings vigorous, under both sunlight conditions.     

Responses of Nouelia insignis Franch (Asteraceae) and Terminalia franchetii Gagnep. (Combretaceae) seedlings to long-term water stress

The responses in terms of seedling growth, biomass allocation and photosynthesis of Nouelia insignis Franch. and Terminalia franchetii Gagnep. to long-term water stress were studied in a greenhouse experiment. Three-month-old seedlings were subjected to the following water supplies for about 79 days: 80, 60, 40 and 20% of field water capacity (FC). The results showed that, as water stress was increased, seedling height, leaf number, root length, specific leaf area (SLA), biomass production and stomatal limitation value (L_s) of both seedlings decreased, and water use efficiency (WUE) increased, and biomass allocation, the diurnal gas exchange and P_n-PAR response curves also altered. Water supply <40% FC was the threshold of drought-initiated negative effects on these parameters of both seedlings. Most growth and biomass parameters of T. franchetii seedlings were much higher than those of N. insignis seedlings. However, T. franchetii seedlings were more vulnerable to long-term water stress than N. insignis seedlings. Simultaneously, N. insignis seedlings had a higher ability to use strong light and a lower ability to use weak light than T. franchetii seedlings. Although water stress had a great impact on their growth, biomass allocation and photosynthesis, both of N. insignis and T. franchetii seedlings displayed considerable water stress resistance, and they tolerated even the most severe water stress (20% FC), and no seedlings died. However, the field conditions were worse; most of them might be hard to get though the long dry season.     

多效唑和干旱胁迫对毛竹实生苗活力、光合能力及非结构性碳水化合物的影响

以1年生毛竹实生苗为研究对象,研究多效唑对不同水分条件下毛竹实生苗的叶绿素含量、光合参数、非结构性碳水化合物(NSC)含量、碳氮比、根系活力的影响。设置3个水分梯度:W1(75%相对田间持水量,CK)、W2(50%相对田间持水量,中度干旱)和W3(35%相对田间持水量,重度干旱),以及2个多效唑浓度:P1(0mg/L)、P2(40mg/L)。结果表明:随干旱强度增加,P1W1、P1W2、P1W3处理叶色逐渐变淡。与对照P1W1相比,P1W2和P1W3处理下叶绿素a、叶绿素b、类胡萝卜素、叶绿素a/b和叶绿素总含量显著下降(P0.05),Pn、Tr、WUE显著下降(P0.05),Ls显著上升(P0.05),毛竹叶片及根系中非结构性碳水化合物(NSC)含量显著上升(P0.05),毛竹根系活力显著下降。多效唑处理后,P2W2和P2W3的叶片色素含量相对于P2W1显著提高,但P2W2与P2W3无显著差异。同时,施加多效唑使Pn显著提高,P2W3较P1W3增加了146.9%。此外,P2W3处理使可溶性糖大量积累,达最大值3.41mg/g;毛竹叶片及根系淀粉含量显著上升,根系活力显著提高。试验揭示了多效唑通过提高干旱水平下毛竹实生苗的根系活力、光合速率,增加光合色素、非结构性碳水化合物含量,并将养分从地上转移到地下部分,进而抵御干旱胁迫带来的伤害。     

杉木和木荷种子萌发及幼苗生长对光梯度的响应

光是影响种子萌发和幼苗生长的关键因素.为理解不同树种种子萌发及幼苗生长对光梯度变化的响应机制,本文研究了不同光照强度(分别为自然光强的100%、60%、40%、15%和5%)对杉木和木荷种子萌发及幼苗生长的影响,探讨了两树种种子萌发和幼苗生长对光照响应的差异性.结果表明: 光照强度对两树种的种子萌发和幼苗生长均具有显著影响. 随着光照强度的减弱, 杉木种子萌发率增大,萌发指数增大,木荷种子萌发率和萌发指数则先增大后减小,在40%光照强度下达到最大值.两树种幼苗存活率在全光照(100%光照)下均为0,在5%～60%光照处理下则随着光照强度的减弱而显著降低.两树种幼苗根长、地径和株高对光梯度变化的响应趋势一致,随着光照强度的减弱,根长显著减小,地径和株高则先增大后减小,在5%光照强度下达到最小.随着光照强度的减弱,杉木幼苗根、茎、叶及总生物量降低,木荷幼苗生物量积累在15%～60%光照强度下较高, 5%光照强度下最小,且相同光照强度下,木荷幼苗各部分生物量均大于杉木.两树种幼苗应对低光环境时,表现出较大的茎和叶的生物量分配比,而根生物量比和根冠比降低.表明杉木苗期生长不耐阴,需要相对较强的光照,而木荷苗期具有较强的耐阴性,对弱光环境的适应性更强,能够在郁闭的林冠下定植和正常生长.     

AM真菌摩西管柄囊霉对干旱胁迫下枳抗氧化酶基因表达的影响

测定分析了接种丛枝菌根（AM）真菌摩西管柄囊霉Funneliformis mosseae对正常供水与干旱处理的盆栽枳Poncirus trifoliata实生苗生长、活性氧代谢及抗氧化酶基因表达量的影响。结果表明,7周干旱处理显著降低了根系菌根侵染率。接种摩西管柄囊霉显著促进了干旱处理的枳植株生长,增加了根系体积和叶片相对含水量,显著降低了叶片脯氨酸含量,同时也上调了干旱处理的枳叶片精氨酸脱羧酶基因（PtADC1和PtADC2）和超氧化物歧化酶基因（PtFe-SOD和PtMn-SOD）、过氧化物酶基因（PtPOD）和过氧化氢酶基因（PtCAT1）的表达,因而维持了一个相对更低的活性氧水平（如过氧化氢）,有利于增强植株的抗旱性。     

Morphological and physiological responses of <Emphasis Type="Italic">Vitex negundo</Emphasis> L. var. <Emphasis Type="Italic">heterophylla</Emphasis> (Franch.) Rehd. to drought stress

Water is a main factor limiting plant growth. Integrative responses of leaf traits and whole plant growth to drought will provide implications to vegetation restoration. This study investigated the drought responses of Vitex negundo L. var. heterophylla (Franch.) Rehd. with a focus on leaf morphology and physiology, seedling growth and biomass partitioning. Potted 1-year-old seedlings were subjected to four water supply regimes [75, 55, 35 and 15% field capacity (FC)], served as control, mild water stress, moderate water stress and severe water stress. Leaf morphological traits varied to reduce the distance of water transfer under water stress and leaflets were dispersed with drought. Net photosynthetic rate decreased significantly under water stress: stomatal closure was the dominant limitation at mild and moderate drought, while metabolic impairment was dominant at severe drought. The physiological impairment at severe drought could also be detected from the relative lower water use efficiency and non-photochemical quenching to moderate water stress. Total biomass of well-watered plants was more than twice that at moderate water deficit and nearly ten times that at severe water deficit. In summary, V. negundo var. heterophylla had adaptation mechanism to water deficit even in the most serious condition, but different strategies were adopted. Seedlings invested more photosynthate to roots at mild and moderate drought while more photosynthate to leaves at severe drought. A nearly stagnant seedling growth and a sharp decline of total biomass were the survival strategy at severe water stress, which was not favorable to vegetation restoration. Water supply above 15% FC is recommended for the seedlings to vegetation restoration.     

Biophysical and morphological leaf adaptations to drought and salinity in salt marsh grasses

Leaf energy budgets were constructed for 13 species of estuarine C₄ grasses (Poaceae) to elucidate the biophysical effects of drought and salinity on the interception and dissipation of solar energy. Spartina alterniflora, S. anglica, S. argentinensis, S. bakeri, S. cynosuroides, S. densiflora, S. foliosa, S. foliosa × S. alterniflora hybrids, S. gracilis, S. patens, S. pectinata, S. spartinae, and Distichlis spicata plants were grown under controlled soil water potential gradients in a greenhouse. Species were grouped into four major ecological functional types, based on elevational zonation ranges: low marsh species, middle marsh species, high marsh species, and freshwater species. Different functional types are adapted to different environmental conditions, and responded differently to reduced water potentials. Latent heat flux decreased similarly across species in response to decreasing water potential. Latent heat loss was found to decrease by as much as 65% under decreasing water potential, leading to an increase in leaf temperature of up to 4 °C. Consequently, radiative and sensible heat losses increased under decreasing water potential. Sensible heat flux increased as much as 336% under decreasing water potential. Latent heat loss appeared to be an important mode of temperature regulation in all species, and sensible heat loss appeared to be more important in high marsh species compared to low marsh species. High marsh species are characterized by narrower leaves than middle and low marsh species, leading to a smaller boundary layer, and providing higher conductance to sensible heat loss. This may be an adaptation for high marsh species to regulate leaf temperature without access to large amounts of water for transpirational cooling. Stomatal conductance decreased with decreasing water potential across species: leaf conductances to water vapor and CO₂ decreased as much as 69% under decreasing water potential. Additionally, oxidative stress appeared to increase in these plants during times of drought or salinity stress. Ascorbate peroxidase activities increased with decreasing soil water potential, indicating increased cellular reactive oxygen species. High marsh species had higher ascorbate peroxidase activities compared to low marsh species, indicating higher tolerance to drought- or salinity-induced stresses. It was concluded that different species of marsh grasses are adapted for growth in different zones of salt marshes. Adaptations include biophysical, biochemical, and morphological traits that optimize heat exchange with the environment.     

干旱胁迫下接种丛枝菌根真菌对七子花非结构性碳水化合物积累及C、N、P化学计量特征的影响

以濒危植物七子花二年生幼苗为研究材料,采用盆栽试验方法,研究干旱胁迫和接种丛枝菌根真菌(AMF)处理对幼苗不同器官C、N、P化学计量关系和非结构性碳水化合物(NSC)含量的影响。试验共设计4个处理:对照(CK)、干旱胁迫(D)、接种AMF(AMF)、干旱胁迫和接种AMF(D+AMF)。结果表明: 在干旱胁迫下七子花根系AMF的侵染率显著下降,但接种AMF处理植株的株高、叶片数显著高于未接种处理。接种AMF显著提高了干旱胁迫下植株根、叶可溶性糖和NSC含量及茎、叶淀粉含量,且茎和叶可溶性糖与淀粉比显著下降。干旱胁迫导致植株C含量在根和叶中显著增加,P含量在茎中显著减少;与干旱胁迫相比,胁迫下接种AMF植株根、茎、叶P含量及叶C含量显著提高,而根C、N含量及茎C含量显著降低。胁迫下接种AMF植株根、茎C∶N、C∶P、N∶P和叶N∶P均显著低于单一胁迫处理。NSC与C∶N∶P计量比的相关性分析表明,根、叶P含量与可溶性糖和NSC含量呈显著正相关,茎P含量与淀粉和NSC含量呈显著正相关,各器官N∶P与NSC含量呈显著负相关。综上,干旱胁迫显著抑制了七子花幼苗的生长,接种AMF通过提高植株根和叶的可溶性糖含量、根的可溶性糖/淀粉,增加地上部分淀粉含量,促进P元素吸收和降低各器官N∶P来增强植株耐旱性,从而提高七子花幼苗在干旱环境中的存活率。