Changes in respiration and chemical content during autumnal senescence of Populus tremuloides and Quercus rubra leaves

Changes in respiration rate, chemical content and chemical concentration were measured in leaves of field-grown Populus tremuloides Michx. and Quercus rubra L. trees throughout the growing season and autumnal senescence. Chlorophyll, soluble sugar, N, P, K and Mg contents and concentrations all declined during leaf senescence, whereas Ca content and concentration increased. Leaf dry mass per area declined 24 and 35% in P. tremuloides and Q. rubra, respectively, during senescence. In leaves of both species, respiration rates peaked during leaf expansion in the spring and then declined, as a result of reduced cytochrome-mediated respiration, to reach relatively constant rates by midsummer. In senescing P. tremuloides leaves, respiration rates remained relatively constant until mid-October and then declined rapidly. In senescing Q. rubra leaves, respiration rates increased in late September, as a result of the appearance of residual respiration that could not be reduced by respiratory inhibitors, and then declined quickly in early November. No changes in alternative pathway respiratory activity were observed in leaves of either species during senescence until late autumn when rates declined. Because respiration rates were correlated with both leaf sugar and nitrogen content during leaf senescence, we conclude that respiration rates were maintained or increased during leaf senescence to supply energy for degradation and mobilization of chemical constituents.     

毛竹叶片衰老过程碳氮元素及灰分含量的季节动态

于2006年4月—2007年3月,对福建永春毛竹(Phyllostachys pubescens)成熟叶和老叶的C、N元素及灰分含量的季节动态及元素的内吸收率进行研究。结果表明:①毛竹成熟叶和老叶的C、N元素含量存在一定的季节变化,从成熟叶到老叶,C含量保持相对稳定,而N含量呈现下降趋势。②毛竹成熟叶、老叶灰分含量月变化趋势相似,毛竹成熟叶、老叶的灰分含量在秋季(10月)至翌年春季(3月)灰分含量较高,而春夏季相对较低;毛竹成熟叶的灰分含量在7.56%～15.91%之间,老叶的灰分含量在7.46%～16.67%,老叶灰分含量高于成熟叶(P=0.0199)。③毛竹叶片衰老过程N的内吸收率为36.68%。     

Leaf exchange in a Mediterranean shrub: water, nutrient, non-structural carbohydrate and osmolyte dynamics

Leaf exchange is an abrupt phenological event that drastically modifies the morphology and physiology of the aerial portion of the plant. We examined if water and osmolyte differences between old leaves and new organs trigger leaf exchange, and whether the differences are closely linked to the resource resorption process in senescing leaves. We monitored concentrations of osmolyte, water, non-structural carbohydrate, nitrogen and potassium in senescing leaves and in emerging new leaves and inflorescences of a Mediterranean leaf exchanger (Cistus laurifolius L.) growing in NE Spain. Old leaves rehydrated markedly during most of the senescence process, which co-occurred with the extension of new shoots, suggesting the lack of a clear-cut switch in water supply from old to new organs. The accumulation of osmolytes in the early stage of leaf senescence might account for this rehydration. Osmolyte dynamics in old leaves depended largely on the progression of resource resorption from senescing organs but were mostly unrelated to water content during late senescence. We conclude that dehydration of old leaves is not a prerequisite for the triggering of leaf exchange. The finding that most nutrients and carbohydrates accumulated in new organs before senescing leaves massively exported resources, and the absence of relevant differences between the dynamics of old leaves at the base of inflorescences and those at the base of vegetative shoots, indicate that the nutrient and carbohydrate demands of new organs do not trigger leaf exchange.     

秋水仙素诱导野生杜鹃花变异试验

应用0.5、1.0、2.0、3.0 mg/mL 4种浓度的秋水仙素溶液诱导正在发育的映山红(Rhododendron simsii)、马银花(Rh.ovatum)、满山红(Rh.mariesii)的花芽和叶芽,观察其花粉粒及气孔变异情况.结果表明,3种杜鹃叶芽和花芽表现出的多倍性有一定的变化,映山红花粉粒在3.0 mg/mL的浓度处理时变异最大,增加37.99%;满山红花粉粒在2.0 mg/mL的浓度处理时变异最大,增加21.96%;随着秋水仙素浓度的增加,3种杜鹃的气孔器大小变异增加,在3.0 mg/mL浓度处理时增加最多,出现气孔增长、保卫细胞宽增加、保卫细胞长度增加等多倍体表现;气孔密度变化与多倍性联系规律不明显.     

Determination of lignin,holocellulose, and organic solvent extractives in fresh leaf,litterfall, and organic material on forest floor using near-infrared reflectance spectroscopy

We report the results of a study regarding the near-infrared reflectance spectra of various leaf stages from fresh to senescing, and to decomposing leaf. A broad absorbance feature increased in the region of 1100–1400nm with the advance of the leaf senescence and leaf decomposition. A decrease was seen in the region over 1440nm during the senescence and decomposition process. These differences of spectra showed the changes in constituents of leaf in terms of the degree of the senescence and decomposition. A comparison of multiple linear regression between the near-infrared reflectance spectra and proximate chemical analyses showed that near-infrared reflectance spectroscopy achieved a certain level of useful accuracy. We consider that near-infrared reflectance spectroscopy has the potential to predict the contents of carbon fractions in plant materials, and that this method can replace previous methods due to faster determination of carbon fractions, and its ability to significantly increase the number of samples that can be collected and measured.     

Nutrient changes in potting mix and Eucalyptus nitens leaf tissue under macadamia biochar amendments

The effect of macadamia nut shell biochar on nitrogen,potassium,phosphorus,magnesium,calcium and sodium concentrations in potting mix used to grow Eucalyptus nitens seedlings was investigated in a glasshouse experiment.The treatments combined two fertiliser rates(50 and 100% rate of the commercial mix commonly used in forestry nurseries) with eight biochar rates(0,2,5,10,20,50,80 and 100 t ha~(-1)) arranged in a randomised complete block with three replicates of four sample plants.Nutrients were quantified in the potting mix and seedling leaves at four destructive harvests 135,177,219 and269 days after planting.Biochar significantly increased nitrate-N,Colwell P,Colwell K and exchangeable Na andreduced ammonium-N,Mg and Ca concentrations in the potting mix.Seedling leaf concentrations of P,K and Na were increased by biochar application,while N remained dependent on fertiliser rate only.Mg and Ca leaf concentrations decreased in response to increasing biochar rates.Elevated nitrate-N and decreased ammonium-N concentrations suggest that biochar might have increased nitrification in the potting mix.We presumed that biochar mediated processes that reduced uptake of P and K when high doses of biochar were combined with full fertilisation.Changes in potting mix K,Na,Mg and Ca were consistent with selective adsorption of ions to biochar surfaces.     

Diurnal changes in leaf chemical constituents and (14)C partitioning in cottonwood

Diurnal changes in concentrations of leaf chemical fractions and partitioning of photosynthetically fixed (14)C within the plant and among chemical fractions were studied in rapidly growing cottonwood (Populus deltoides Bartr. ex Marsh.) seedlings. During the light period, leaf weight (mg cm(-2)) increased by about 25% primarily as a result of the accumulation of starch and sucrose, and to a lesser extent because of an increase in the content of amino acids and the chloroform fraction (pigments plus lipids). In contrast, reducing sugars and organic acids decreased in concentration. The partitioning of (14)C within the plant also changed during the light period. Acropetal transport to developing leaves and stem decreased from 81 to 55% of the total (14)C translocated from a source leaf in 4 hours, whereas basipetal transport to stem and roots increased from 13 to 37%. Although assimilation rate ((14)C fixed in 0.5 h) remained constant during the light period, the percentage of fixed (14)C translocated out of the source leaf in 4 h decreased from 27 to 9%. This change in transport rate of recently fixed (14)C was caused by a shift in (14)C partitioning from transport sucrose to storage starch. During the light period, the incorporation ratio ((14)C-sugar/(14)C-starch) decreased from 40 at 0700 h to 2 at 1900 h. The partitioning of carbon to different chemical fractions within the source leaf and the interactions or feedback between different sinks and the source leaf have a major influence on plant growth and development. Control of this carbon partitioning is located in both source and sink leaves.     

不同林龄樟子松叶片养分含量及其再吸收效率

树木叶片的养分再吸收效率能够反映树木对养分保存、利用以及对养分贫瘠环境的适应能力。以科尔沁沙地东南缘章古台地区樟子松人工林为研究对象,分析了11、20、29、45年生树木叶片的基本特征、养分含量及其再吸收效率。结果表明:叶片衰老后其质量和面积明显减少;叶片凋落前的平均养分含量没有表现出随樟子松年龄增加而出现有规律的变化;凋落叶片中的N、P、K、Mg含量表现出随年龄增加而增加的趋势,而Ca的趋势与之相反;11年生和20年生的樟子松叶片N、P、K的再吸收效率相似,都显著高于29年生和45年生樟子松(P<0.05),而樟子松叶片对Mg的再吸收效率表现出随年龄增大而显著降低,Ca随叶片的衰老而不断累积,再吸收效率表现为负值,20年生的樟子松叶片Ca再吸收效率最大,11年生和45年生最低。樟子松叶片的N、P、K、Mg养分再吸收效率随年龄增加而降低的趋势表明,随年龄增加樟子松对贫瘠养分生境的适应能力逐渐降低,反映了樟子松养分保存方面的衰退特征。     

Nutrient changes in potting mix and <Emphasis Type="Italic">Eucalyptus nitens</Emphasis> leaf tissue under macadamia biochar amendments

The effect of macadamia nut shell biochar on nitrogen, potassium, phosphorus, magnesium, calcium and sodium concentrations in potting mix used to grow Eucalyptus nitens seedlings was investigated in a glasshouse experiment. The treatments combined two fertiliser rates (50 and 100% rate of the commercial mix commonly used in forestry nurseries) with eight biochar rates (0, 2, 5, 10, 20, 50, 80 and 100 t ha^?1) arranged in a randomised complete block with three replicates of four sample plants. Nutrients were quantified in the potting mix and seedling leaves at four destructive harvests 135, 177, 219 and 269 days after planting. Biochar significantly increased nitrate-N, Colwell P, Colwell K and exchangeable Na and reduced ammonium-N, Mg and Ca concentrations in the potting mix. Seedling leaf concentrations of P, K and Na were increased by biochar application, while N remained dependent on fertiliser rate only. Mg and Ca leaf concentrations decreased in response to increasing biochar rates. Elevated nitrate-N and decreased ammonium-N concentrations suggest that biochar might have increased nitrification in the potting mix. We presumed that biochar mediated processes that reduced uptake of P and K when high doses of biochar were combined with full fertilisation. Changes in potting mix K, Na, Mg and Ca were consistent with selective adsorption of ions to biochar surfaces.     

不同土壤水分含量下落羽杉根、茎、叶营养水平的差异

应用温室盆栽试验方法,采用完全随机试验设计,研究了土壤水分含量对1年生落羽杉实生苗的营养吸收及分配的影响。试验共有5种处理,即W1(淹水,水深为土壤表面以上5cm)、W2(渍水,水面与土面保持水平)、W3、W4、W5(土壤含水量分别为土壤田间持水量的75%、50%和25%),处理时间为130d。研究结果表明:(1)随着土壤水分含量的减少,落羽杉根、茎和叶中全N质量浓度均逐渐升高,根、茎、叶中全P质量浓度则又先升高后下降的趋势,以W3水分处理最高,根、茎和叶中全Ca、全K、全Na、全Mg、全Fe质量浓度则有不同的变化趋势;(2)所有处理根、茎、叶中全Fe、全N、全P、全Mg、全Na、全Ca、全K质量浓度大小的顺序为叶>根>茎;(3)随着土壤水分含量的减少,落羽杉对各种营养元素的吸收累积量减少,分配到根和茎中的比例增加,分配到叶中的比例逐渐减少。     

檫木叶片秋季衰老时叶色、色素和营养元素的关系

【目的】从叶片衰老角度研究檫木叶片叶色、色素和营养元素的变化规律,为秋色叶观赏树种檫木的选育以及栽培提供理论依据。【方法】以栽植于同一环境条件下的3年生檫木为试验材料,从檫木叶片停止生长到脱落,分5个时期对叶片的叶色值、色素含量和营养元素含量进行观测和分析。【结果】观测前期与观测后期,檫木叶片叶色值、色素含量和营养元素含量存在极显著差异;叶片进入衰老阶段后,叶绿素含量和类胡萝卜素含量呈下降趋势,而花色素苷含量逐渐上升;N、P、K含量在叶片衰老阶段逐渐下降。由典型相关分析可知,叶色a*值与叶绿素含量具有显著负相关,与花色素苷含量呈显著正相关;花色素苷含量与N含量成反比,类胡萝卜素含量与P含量成正比;N元素再利用效率的载荷值符号与N含量载荷值的符号相反,而P元素再利用效率的载荷值符号与P含量载荷值的符号相同;檫木叶片衰老分为3个阶段,第1阶段从9月中下旬到10月上旬,为叶片衰老准备期;第2阶段从10月中下旬到11月上旬,为叶片缓慢衰老期;第3阶段从11月中下旬到叶片脱落,为叶片衰老末期。【结论】檫木叶色最佳观赏期是从10月中下旬到11月上旬的叶片缓慢衰老期;从叶片衰老准备期到叶片衰老末期,叶绿素和类胡萝卜素被分解,花色素苷合成;N、P、K 3种营养元素逐渐被转移,其中N含量越高,N元素再利用效率就越低;与之相反,P含量越高,P元素再利用效率就越高。     

Nutrient retranslocation within the foliage of Pinus sylvestris

During the period 1983-1987, retranslocation of N, P, K, Ca, Mg, Mn, Zn, Fe, B and Al within the foliage of Scots pine (Pinus sylvestris L.) was studied in sapling, pole-stage and mature stands in eastern Finland. Needle concentrations of the mobile nutrients N, P, and K varied seasonally because of retranslocation. In unfertilized plots, needle contents of N, P and K decreased 62-92% during senescence and needle dry weight decreased 19-51%. In some years, needle contents of Ca, Mn, Zn, Fe, B and Al increased during senescence. Retranslocation was more efficient from needles with greater dry weight. In the fertilized, pole-stage stand, needle dry weight did not decrease at senescence four years after fertilization and nutrient content decreased less than in the other years. In the mature stand, there were no clear differences in needle dry weight and nutrient changes during senescence between years or between unfertilized and fertilized plots.     

Nutrient accessions to the forest floor in karri (Eucalyptus diversicolor F. Muell.) forests of varying age

Nutrient accessions to the forest floor in rainfall, throughfall and stemflow from the understorey and tree strata were measured in karri (Eucalyptus diversicolor F. Muell.) forest of south-west Western Australia. These data, for stands aged 2, 6, 9, and 40 years and for mature forest, were compared with annual accessions of nutrients in litterfall.

With increasing age of the stands, the concentration and amounts of Ca, K, Mg, Na and Cl in throughfall increased. The amounts of Mg, Na and Cl in stemflow from the overstorey were also greatest in the older stands. Although concentrations of nutrients in stemflow from the tree stratum were higher than from the understorey, the quantities of nutrients transported to the forest floor in stemflow from the understorey were greater because of its greater volume.

Rainfall is the major source of Na (64–91%) and Cl (51–79%) and it also contributes significantly to Mg (19–50%) accessions. Of the nutrient pathways between canopy and forest floor, litterfall accounts for the largest proportion of N (89–93%), Ca (80–87%) and P (67–79%) recycled in the karri forest. About equal amounts of K are transferred in litterfall, throughfall and stemflow with approximately 80% of stemflow K originating from the understorey strata.     

Nutrient contents and concentrations in relation to growth of Picea abies and Fagus sylvatica along a European transect

Mineral nutrition of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) was investigated along a transect extending from northern Sweden to central Italy. Nitrogen (N) concentrations of needles and leaves in stands growing on acid soils did not differ significantly between central Italy and southern Sweden (1.0 +/- 0.1 mmol N g(-1) for needles and 1.9 +/- 0.14 mmol N g(-1) for leaves). In both species, foliar N concentrations were highest in Germany (1.2 mmol N g(-1) for needles and 2.0 mmol N g(-1) for leaves) and decreased by 50% toward northern Sweden (0.5 mmol N g(-1)). Both species showed constant S/N and P/N ratios along the transect. Calcium, K and Mg concentrations generally reflected local soil conditions; however, Mg concentrations reached deficiency values in Germany. Leaf area per unit dry weight varied significantly along the transect with lowest values for Norway spruce recorded in northern Sweden and Italy (3.4 m(2) kg(-1)) and a maximum in central Europe (4.7 m(2) kg(-1)). A similar pattern was observed for beech. Despite the low variation in foliar N concentrations on the large geographic scale, local and regional variations in N concentrations equalled or exceeded the variation along the entire continental transect. Furthermore, nutrient contents (i.e., nutrient concentration x dry weight per needle or leaf) showed a greater variation than nutrient concentrations along the transect. Nitrogen contents of Norway spruce needles reached minimum values in northern Sweden (2.4 micro mol N needle(-1)) and maximum values in Denmark (5.0 micro mol N needle(-1)). The N content of beech leaves was highest in Denmark (242 micro mol N leaf(-1)). At the German site, foliar N content rather than N concentration reflected the seasonal dynamics of foliar growth and N storage of the two species. During foliage expansion, there was an initial rapid increase in N content and a decrease in N concentration. This pattern lasted for about 2 weeks after bud break and was followed by 6 weeks during which dry weight and N content of the foliage increased, resulting in a further decrease in N concentration. During summer, dry weight and N content of mature needles of Norway spruce increased further to reach a maximum in autumn, whereas N concentration remained constant. In spring, reallocation of N from 1- and 2-year-old needles was 1.5 and 1.0 micro mol N needle(-1), respectively. This remobilized N was a major source of N for the development of new needles, which had an N content of 1.5 micro mol N needle(-1) after bud break. The seasonal remobilization of N from old foliage decreased with increasing needle age. Needle N content and dry weight decreased progressively with age (1 micro mol N needle(-1) between age classes 2 and 5), whereas N concentrations remained constant. For Norway spruce, annual stemwood production was correlated with needle N content but not with foliar N concentration or with the total amount of N in the canopy. Interspecific and geographical differences in plant nutrition are discussed on the basis of competitive demands for C and N between growth of foliage and wood.     

叶面喷施多效唑对盆栽风信子生长与开花的影响

以风信子品种‘蓝夹克’为供试材料研究了叶面喷施不同浓度的多效唑(PP333)对风信子生长和开花的影响,研究结果表明叶面喷施100 mg/L的PP333延缓‘蓝夹克’的生长,使植株适量矮化、叶面积适度减小,植株更紧凑;与对照相比,叶片厚度增加了5.8%,小花直径增加了2.8%,种球质量增加了5.3%。同时提高了植株叶片的叶绿素含量,将现蕾时间推迟4天,并使花期延长4天,总体上提高了‘蓝夹克’的观赏价值。叶面喷施300 mg/L的PP333因浓度较高,表现出一定的抑制作用。     

Growth response of Douglas-fir seedlings to nitrogen fertilization: importance of Rubisco activation state and respiration rates

High foliar nitrogen concentration ([N]) is associated with high rates of photosynthesis and thus high tree productivity; however, at excessive [N], tree productivity is reduced. Reports of excessive [N] in the Douglas-fir forests of the Oregon Coast Range prompted this investigation of growth and needle physiological responses to increasing foliar N concentrations in 1-year-old Douglas-fir seedlings. After 1 year of N fertilization, total seedling biomass increased with each successive increase in N fertilizer concentration, except in the highest N fertilization treatment. Of the many physiological responses that were analyzed, only photosynthetic capacity (i.e., Vcmax), respiration rates and leaf specific conductance (KL) differed significantly between N treatments. Photosynthetic capacity showed a curvilinear relationship with foliar [N], reaching an apparent maximum rate when needle N concentrations exceeded about 12 mg g(-1). In vitro measurements of ribulose-1,5-bisphosphate carboxylase (Rubisco) activity suggested that photosynthetic capacity was best related to activated, not total, Rubisco content. Rubisco activation state declined as foliar [N] increased, and based on its significant correlation (r2= 0.63) with foliar Mn:Mg ratios, it may be related to Mn inactivation of Rubisco. Respiration rates increased linearly as foliar N concentration increased (r2= 0.84). The value of K(L) also increased as foliar [N] increased, reaching a maximum when foliar [N] exceeded about 10 mg g(-1). Changes in K(L) were unrelated to changes in leaf area or sapwood area because leaf area to sapwood area ratios remained constant. Cumulative effects of the observed physiological responses to N fertilization were analyzed by modeling annual net CO2 assimilation (Anet) based on treatment specific values of Vcmax, dark respiration (Rdark) and KL. Estimates of Anet were highly correlated with measured total seedling biomass (r2= 0.992), suggesting that long-term, cumulative effects of maximum Rubisco carboxylation, Rdark and KL responses to N fertilization may limit seedling production when foliar N exceeds about 13 mg g(-1) or is reduced to less than about 11 mg g(-1).     

西南桦和尾巨桉凋落叶分解及其与土壤性质的相关性

[目的]探讨南亚热带西南桦和尾巨桉人工纯林的凋落叶分解动态及其与土壤化学性质之间的相关关系.[方法]采用原位分解袋法研究凋落叶的分解过程.[结果]表明:西南桦、尾巨桉人工林凋落叶分解系数分别为0.96 a^-1和0.88 a^-1.在为期12个月的分解试验中,2种凋落叶有机C含量在整个分解过程中呈逐渐下降趋势;全K含量和C/N比在分解前期迅速下降,之后趋于平缓;全N含量和全P含量在整个分解过程中呈逐渐上升趋势;2种凋落叶N/P比则呈先升高后下降的趋势.无论是分解前期还是分解后期,凋落叶质量损失与N含量均呈显著正相关(前期R=0.877;后期R=0.855),与C/N均呈显著负相关(前期R=-0.735;后期R=-0.697).与尾巨桉林地土壤性质相比,西南桦凋落叶分解提高了林地0~10、10~20 cm土壤的有机C、全N、全P、全K、N/P,对2030 cm土壤有机C、全K、pH值、C/N、N/P则未产生显著影响.相关分析表明:凋落叶初始有机C含量与土壤有机C、全N、全P、全K、N/P显著相关;凋落叶初始全N含量与土壤全N、pH值、C/N显著相关.[结论]凋落叶的养分含量与土壤养分的关系紧密;与尾巨桉相比,西南桦凋落叶的养分含量明显较高,分解速率更快,释放到土壤中的养分也更多.     

盐分和水分胁迫对落羽杉幼苗的生长量及营养元素含量的影响

采用温室盆栽试验方法 ,研究了不同土壤水分下盐胁迫对 1年生落羽杉实生苗的生长及营养吸收的影响。试验共 12种处理 ,3种水分水平 (W1 ,淹水 ;W2 、W3,土壤含水量分别为田间持水量的 75 %和 2 5 % ) ,每种水分下设 4种盐分处理 (NaCl含量为土壤干重的 0、0 15 %、0 3%和 0 4 5 % ) ,处理时间为 130d。结果表明 :土壤盐分胁迫下落羽杉幼苗的生长及对营养的吸收发生了显著的变化 ,这种变化又因土壤含水量的不同而不同。落羽杉相对高生长、相对地径生长和生物量增量随着土壤盐分浓度的增加和土壤水分含量的减少而减少。在淹水条件下 ,随着土壤盐分浓度的增加 ,落羽杉幼苗根、茎、叶中全N、全P、全Na,以及叶片中的全Ca、全Fe的含量均随着升高 ,而根、茎中的全Fe、全Ca、全Mg含量差异较小。在W2 水分条件下 ,各种盐分处理都在不同程度上增加了根、茎、叶中全N、全Na、全Ca和全Fe含量 ,茎和叶中全P、全K和全Mg含量 ,而根系中的全P、全K和全Mg含量在盐分浓度较高时有所下降。在W3水分条件下 ,各种土壤盐分不同程度地增加了叶片全N、全P和全K含量 ,茎和叶中全Mg和全Ca含量 ,以及根、茎、叶中全Na含量 ,而茎和根中全N、全P和全K含量 ,根、茎和叶中全Fe含量均随着土壤盐分浓度的增加而下降。     

Overexpression of AtNHX5 improves tolerance to both salt and drought stress in Broussonetia papyrifera (L.) Vent

Paper mulberry (Broussonetia papyrifera L. Vent) is well known for its bark fibers, which are used for making paper, cloth, rope, etc. It was found that, in addition to its well-documented role in the enhancement of plant salt tolerance, overexpression of the Na+/H+ antiporter (AtNHX5) gene in paper mulberry plants showed high drought tolerance. After exposure to water deficiency and salt stress, the wild-type (WT) plants all died, while the AtNHX5-overexpressing plants remained alive under high salt stress, and had a higher survival rate (>66%) under drought stress. Measurements of ion levels indicated that Na+ and K+ contents were all higher in AtNHX5-overexpressing leaves than in WT leaves in high saline conditions. The AtNHX5 plants had higher leaf water content and leaf chlorophyll contents, accumulated more proline and soluble sugars, and had less membrane damage than the WT plants under water deficiency and high saline conditions. Taken together, the results indicate that the AtNHX5 gene could enhance the tolerance of paper mulberry plants to multiple environmental stresses by promoting the accumulation of more effective osmolytes (ions, soluble sugars, proline) to counter the osmotic stress caused by abiotic factors.     

Evaluation of subtropical ornamental trees for reclaiming salinity affected lands

This study was conducted to evaluate the tolerance of 1-year-old seedlings of ten subtropical ornamental tree species against a range of salinity levels of Na Cl from May 2015 to October 2015. The levels were further enhanced from November to April 2017 as 100% survival was observed in the initial concentrations for all species.The seedlings were grown during the first week of April2015 in 1000 earthen pots containing soil: farmyard manure(2:1), irrigated with tap water for 1 month followed by saline irrigation in May by maintaining electrical conductivity at 0.75, 1.00, 1.25, 1.50, 2.25, and 3.00 d S/m for 30,40, 50, 60, 90, and 120 m M Na Cl. Every 3 months,heights, relative leaf water content, and percent survival were determined;total soluble sugars of the upper leaves of each tree were quantified. All species exhibited consistent early growth and survival when supplied with 30, 40, 50 and 60 m M of Na Cl. Koelreutaria paniculata, Ficus benjamina, Putranjiva roxburghii, Bauhinia purpurea and Millettia ovalifolia were sensitive to elevated salinity levels and did not survive at the highest salt concentrations of 90 and 120 m M.