Lipid concentration and composition in xylem sap of woody angiosperms from a tropical savanna and a seasonal rainforest

Lipids may play an important role in preventing gas embolisms by coating nanobubbles in xylem sap.Few studies on xylem sap lipids have been reported for temperate plants,and it remain unclear whether sap lipids have adaptational significance in tropical plants.In this study,we quantify the lipid composition of xylem sap for angiosperm species from a tropical savanna(seven species)and a seasonal rainforest(five species)using mass spectrometry.We found that all twelve species studied contained lipids in their xylem sap,including galactolipids,phospholipids and triacylglycerol,with a total lipid concentration ranging from 0.09 to 0.26 nmol/L.There was no difference in lipid concentration or composition between plants from the two sites,and the lipid concentration was negatively related to species’open vessel volume.Furthermore,savanna species showed little variation in lipid composition between the dry and the rainy season.These results support the hypothesis that xylem sap lipids are derived from the cytoplasm of individual conduit cells,remain trapped inside individual conduits,and undergo few changes in composition over consecutive seasons.A xylem sap lipidomic data set,which includes 12 tropical tree species from this study and 11 temperate tree species from literature,revealed no phylogenetic signals in lipid composition for these species.This study fills a knowledge gap in the lipid content of xylem sap in tropical trees and provides additional support for their common distribution in xylem sap of woody angiosperms.It appears that xylem sap lipids have no adaptive significance.

Monitoring Xylem Transport in the Stem of Lilium lancifolium Using Fluorescent Dye 5(6)-Carboxyfluorescein Diacetate

The xylem undergoes physiological changes in response to various environmental conditions during the process of plant growth.To understand these physiological changes,it is extremely important to observe the transport of xylem.In this study,the distribution and structure of vascular bundle in Lilium lancifolium were observed using the method of semithin section.Methods for introducing a fluorescent tracer into the xylem of the stems were evaluated.Then,the transport rule of 5(6)-Carboxyfluorescein diacetate(CFDA)in the xylem of the stem of L.lancifolium was studied by fluorescence dye in live cells tracer technology.The results showed that the vascular bundles of L.lancifolium were scattered in the basic tissue,the peripheral vascular bundles were smaller and densely distributed,and the closer to the center,the larger the volume of vascular bundles and the more sparsely distributed.The vascular bundles of L.lancifolium are limited external tenacity vascular bundles,which are composed of phloem and xylem.The most suitable method for CFDA labeling the xylem of isolated stem segments of L.lancifolium was solution soaking for 24 h.The running speed of CF in the isolated stem was 0.3 cm/h,which was consistent with the running speed of the material in the field.CF could be transported between the xylem and parenchyma cells,indicating that the material transport in the xylem could be through the symplastic pathway.The above results laid a foundation for the study of the xylem transport mechanism and the xylem pathogen disease of lily.

Xylem中国公司正式成立

11月4日．全球领先的水技术专业公司Xylem（塞莱默1公司（下称Xylem）在京举行公司启动仪式暨新品牌发布会，宣布Xylem中国公司正式成立。Xylem拥有上百年水务经验，专注于水输送、水处理和水测试，借助旗下众多知名产品、专业经验和创新实力．帮助市政、住宅和商业建筑业、工业及农业等行业实现高效水技术应用。

On the Function of Wall Sculpturing in Xylem Conduits

The water-conducting network of capillaries in vascular plants has evolved over hundreds of millions of years in order to be able to cope with bubble clogging,a problem which also affects modern microfluidic devices.Decades of anatomical studies have revealed that plants growing in habitats in which the formation of bubbles,or emboli,is likely to be a frequent occurrence often have various forms of geometrical sculpturing on the internal surfaces of the xylem conduits.The possible function of such wall sculpturing has long been the subject of speculation.We have investigated the hypothesis that wall sculpturing is a functional adaptation designed to increase the wettability of the walls of xylem conduits,an effect which could be described as the inverse of the well-known lotus-effect.Our results show that wall sculpturing does enhance wettability.Importantly,theoretical calculations reveal that the geometric parameters of various types of wall sculpturing are such that the resulting surfaces are sufficiently rough to enhance wettability,but not significantly rougher.The results provide an appealing answer to the long-standing debate on the function of wall sculpturing in xylem conduits,and may provide biomimetic clues for new approaches to the removal of bubbles in microfluidic channels.

Drought-Induced Changes in Xylem Sap pH, ABA and Stomatal Conductance

Upstream signals potentially regulating evaporation and stomatal conductance wereinvestigated using 6-8-leaf-old maize (Zea may L.) seedlings which were grown in agreenhouse. Pressure chamber was used to measure leaf water potential and to collectxylem sap. The pH of xylem sap in stems was higher than that in root, and the abscisicacid (ABA) concentration in stems was the highest in well-watered seedlings. The ABAconcentration and pH of xylem sap in roots, stems and leaves increased, and the ABAconcentration in leaves reached the maximum during drought stress. The treatment ofroots with exogenous ABA solution (100molL-1) increased xylem sap ABA concentration inall organs measured, and induced stomatal closure, but did not change ABA distributionamong organs of maize seedlings. The combined effects of external pH buffer on pH, ABAof xylem sap and stomatal behavior indicated that pH, as a root-source signal to leavesunder drought stress, regulated stomatal closure through accumulating ABA in leaves orguard cells.

Anatomical and FTIR analyses of phloem and xylem of Tetracentron sinense

The fast growth of Tetracentron sinense is a potential valuable timber resource, but whether its anatomy and chemical components are suitable for timber is unknown. We used light microscopy and SEM to examine the anatomical structure and FITR to measure the chemical components of the phloem and xylem of this tree. Radial variations in growth ring width and tracheid dimensions were also evaluated. The sieve tube, phloem parenchyma cell and sclereids clusters were the main cells in phloem, and the tracheid was the fundamental cell in xylem. An unusual tracheid type, fiber-tracheids or vessel-liked elements was visible. Wood rays nonstoried, uniseriate and multiseriate, including heterogeneous II, occasionally I, and usually 3-6 cells wide. The mean growth-ring width was 2.53 +/- 0.46 mm, and the percentage of late wood was over 60%. For radial variation, growth-ring width increased at an early growth stage, and reached the largest increment during years 11-15, then decreased. The maximum growth-ring width was 5.313 mm. During late growth (60-85 years), trees also maintained a high radial growth increment. Radial variation in the percentage of late wood was uniform, about 50-70%, throughout the growth years. Growth patterns in the length and width of early and late wood were similar as the trees aged. From the FTIR results, the chemical components differed significantly between xylem and phloem, hemicellulose in particular was higher in the xylem than in the phloem, where it was apparently absent. All of these suggest that the composition of phloem in T. sinense is very similar to that of hardwood, and it has higher growth ratio and uniform wood properties.

Safety-efficiency trade-offs in the cotton xylem：acclimatization to different soil textures

The acclimatization of plant xylem to altered environmental conditions has attracted considerable attention from researchers over several decades. Plants growing in natural environments must seek a balance between water uptake and the water loss of leaves from evaporation. Thus, the adaptation of xylem to different soil textures is important in maintaining plant water balance. In this study, we investigated the xylem changes of cotton（Gossypium herbaceum L.） xylem in sandy, clay and mixed soils. Results showed that soil texture had a significant effect on xylem vessel diameter and length of stems and roots. Compared with G. herbaceum growing in the clay soil, those plants growing in the sandy soil developed narrower and shorter xylem vessels in their roots, and had a higher percentage of narrow vessels in their stems. These changes resulted in a safer（i.e. less vulnerable to cavitation）, but less-efficient water transport system when soil water availability was low, supporting the hydraulic safety versus efficiency trade-off hypothesis. Furthermore, in sandy and mixed soils, the root： shoot ratio of G. herbaceum increased twofold, which ensures the same efficiency of leaves. In summary, our finding indicates that the morphological plasticity of xylem structure in G. herbaceum has a major role in the acclimatization of this plant species to different soil textures.

Ultrasonic Acoustic Emissions from Leaf Xylem of Potted Wheat Subject to a Soil Drought and Rewatering Cycle

Ultrasonic acoustic emissions （AEs） from leaf xylem of both water stressed and well watered potted winter wheat （Triticum aestivum L.） plants during drought and rewatering cycle were investigated with a ‘PCI-2 Based AE System＇ （Physical Acoustics Corp. New Jersey, USA） for estimation of leaf xylem cavitation and embolism. Very few AEs occurred in xylem of wheat leaves in well-watered plant, and also in plant subject to mild and moderate soil water stress conditions over the first 4 d of the drought cycle. Great amounts of AEs have occurred since d 5 of the drought cycle as plant showed obvious leaf curling, indicating significant cavitation in leaf xylem on plant exposed to severe soil water deficit. At this point, relative soil water content （RSWC） and leaf xylem pressure （ψ1） dropped to 24.0-26.5% and -1.92 MPa, respectively, with reductions in leaf stomatal conductance （gs）, leaf transpiration （Tr） and leaf CO2 assimilation rate （A） of as much as 69.8, 60.7 and 46.5%, respectively. The effect of soil water deficit was in the order gs 〉 Tr 〉 A 〉 AE. Waveform physical property parameters such as amplitude, counts, rise time, duration, absolute energy and signal strength were analyzed. These parameters varied within very broad ranges, with frequency distribution of most parameters being well fitted by the exponential function y = yo- A exp （-x/t）. The proportion of stronger AE signals rose as soil dehydrated. While AEs occurrence in water stressed plant remained higher than in well-watered control at the following day after rewatering, waveform signal strength and related physical property parameters dropped immediately to that of control. Difference in AEs occurrence characterization between field-grown and potted wheat leaves was discussed.

Contrast in vulnerability to freezing-induced xylem embolism contributes to divergence in spring phenology between diffuse-and ring-porous temperate trees

Background:The spring phenology and growth strategy of temperate tree species can be strongly linked to their sensitivity to frosts,which deserve more profound investigations under the background of climate warming particularly considering the advancement of spring phenology as well as the increase in frequency and intensity of spring cold waves.Methods:Spring phenologies,stem radial growth characteristics,frost sensitivity of leaves and stem hydraulic systems were studied in five diffuse-porous and five ring-porous temperate tree species under a common garden condition.Results:The results showed that the spring leaf phenology of the diffuse-porous species was one to two weeks earlier than that of the ring-porous species.The ring-porous species had significantly higher stem hydraulic conductivity than the diffuse-porous species(1.81 and 0.95 kg·m^(-1)·s^(-1)·MPa^(-1),P<0.05)but were more vulnerable to freeze-thaw induced xylem embolism than the latter.After a simulated freeze-thaw event,the average percentage loss of hydraulic conductivity in the current year shoots increased from 26.0%(native embolism)to 86.7%in the ring-porous species,while it only increased from 21.3%to 38.3%in the diffuse-porous species.The spring phenology was clearly correlated with vulnerability to freeze-thaw induced embolism,with the more vulnerable ring-porous species exhibited substantially delayed phenology to reduce risks of catastrophic hydraulic dysfunction during spring frosts.Nevertheless,ring-porous species can offset the postponed onset of growth and gained even higher annual growth due to significantly higher hydraulic efficiency and leaf gas exchange rates.Conclusions:Contrasts between ring-porous and diffuse-porous species in resistance to freeze-thaw induced embolism suggest that they face different selective pressures from early spring frosts,which may at least be partially responsible for their divergence in spring phenology and growth strategy and can potentially lead to different responses to climate regime shifts.

Relating Xylem Cavitation to Gas Exchange in Cotton

Acoustic emissions (AEs) from xylem cavitation events are characteristic of transpiration processes. Though a body of work exists describing AEs and limited stem hydraulic conductivity under water stress, there is limited information about the effects of AEs on stomatal aperture and limitation on carbon assimilation. The objective of this work was to relate AEs to drought stress in cotton. Cotton was grown in mini-lysimeters in the greenhouse and instrumented with a portable photosynthesis system and ultrasonic transducers connected to a digital signal-processing unit. Whole plant transpiration, leaf level gas exchange and ultrasonic AEs were measured. Xylem cavitation events temporally associated with the onset of drought stress. The results are consistent with stomatal closure in response to reduced hydraulic conductance from xylem cavitation events. Clear direct empirical evidence of a reduction in carbon assimilation associated with xylem cavitation resulting from water stress is presented.

Analysis of Cavitation Processes in Xylem

Cavitation in plants is caused by development of air bubbles, which is related to their equilibrium and development. There is a univariate cubic equation for bubble balance. New root formula of this kind of equation was proposed by Shenjin Fan, which is simpler than the Caldan’s. Using Shenjin formulas and taking water pressure P1 as an independent variable, this paper gives the exact solution of the equation under certain conditions. The stability of the equilibrium of an air bubble in its different radius ranges is obtained by the way different from the previous. This kind of cavitation includes two types: First type may be caused by the growth of pre-existent air bubbles;Second type is air seeding, here defined as the sucking of air bubbles from already gas-filled conduits. For air seeding three ways of cavitation have been proposed. For the first type this paper puts forward that two ways of cavitation can occur, which are the same with the first two ways of air seeding except of air reservoirs. Moreover, for the first way of the first type, the range of water pressures is the same with that of the first way of air seeding. For the second way of the first type the range of water pressures is much wider, or the pressure range equals the pressure sum of the second and third ways of air seeding. Through the specific data the relationship between the two types is given.

Xylem中国公司宣布成立

2011年11月4日，全球领先的水技术专业公司Xylem（塞莱默）公司（下称“Xylem”）在北京举办了隆重的公司启动仪式暨新品牌发布会，宣布Xylem中国公司正式成立。

Transport of Nitrogen Assimilation in Xylem Vessels of Green Tea Plants Fed with NH_4-N and NO_3-N

在 15N-NO3 和 15N-NH4 被喂到茶(山茶 sinensis L.) 的根以后，一个实验被执行由在木部树液监视 N 混合物的动态作文从茶根学习氮(N) 吸收的运输过程。结果证明主要氨基酸是夫酸安， theanine，精氨酸， asparic 酸和 glutamic，分别地，它在木部树液全部的氨基酸占了 49% ， 17% ， 8% ， 7% ，和 4% 。在茶为 48 h 用 15N-NO3 和 15N-NH4 被喂以后，在木部树液的全部的氨基酸的数量显著地增加了，有 15N-NH4 的那些美联储与 15N-NO3 比那些有更高的增长。二个小时在 15N- NO3 和 15N-NH4 被喂以后，在夫酸安，天门冬素， glutamic，丙氨酸，和精氨酸的 15N 丰富随着时间的过去快速被检测并且增加。这显示让 NO3-N 和 NH4-N 被茶根吸收拿了不到 2 h，合并了到上述氨基酸并且搬运了到木部树液。在有 15N-NO3 的茶美联储的木部树液的 15N-NO3 的快速的增加显示那硝酸盐能直接被搬运到木部树液。夫酸安， theanine，和丙氨酸是与 15N-NO3 和 15N-NH4 在茶美联储的木部树液搬运的主要氨基酸。

Quantitative Changes in Main Parameters of Secondary Xylem during Aging Process in Pinus bugeana

ＱｕａｎｔｉｔａｔｉｖｅＣｈａｎｇｅｓｉｎＭａｉｎＰａｒａｍｅｔｅｒｓｏｆＳｅｃｏｎｄａｒｙＸｙｌｅｍｄｕｒｉｎｇＡｇｉｎｇＰｒｏｃｅｓｓｉｎＰｉｎｕｓｂｕｇｅａｎａＬＩＮＪｉｎ－ｘｉｎｇ；（林金星），ＬＩＮＹｕｅ－ｈｕｉ；（林月惠），ＷＥＩＬｉｎ－...

PagERF81 regulates lignin biosynthesis and xylem cell differentiation in poplar

Lignin is a major component of plant cell walls and is essential for plant growth and development. Lignin biosynthesis is controlled by a hierarchical regulatory network involving multiple transcription factors. In this study, we showed that the gene encoding an APETALA 2/ethylene-responsive element binding factor(AP2/ERF) transcription factor, PagERF81,from poplar 84 K(Populus alba × P. glandulosa) is highly expressed in expanding secondary xylem cells. Two independent homozygous Pagerf81 mutant lines created by gene editing, produced significantly more but smaller vessel cells and longer fiber cells with more lignin in cell walls, while PagERF81 overexpression lines had less lignin,compared to non-transgenic controls. Transcriptome and reverse transcription quantitative PCR data revealed that multiple lignin biosynthesis genes including Cinnamoyl CoA reductase 1(PagCCR1),Cinnamyl alcohol dehydrogenase 6(PagCAD6), and 4-Coumarate-CoA ligase-like 9(Pag4CLL9) were upregulated in Pagerf81 mutants, but down-regulated in PagERF81 overexpression lines. In addition, a transient transactivation assay revealed that PagERF81 repressed the transcription of these three genes.Furthermore, yeast one hybrid and electrophoretic mobility shift assays showed that PagERF81 directly bound to a GCC sequence in the PagCCR1 promoter. No known vessel or fiber cell differentiation related genes were differentially expressed, so the smaller vessel cells and longer fiber cells observed in the Pagerf81 lines might be caused by abnormal lignin deposition in the secondary cell walls. This study provides insight into the regulation of lignin biosynthesis, and a molecular tool to engineer wood with high lignin content, which would contribute to the lignin-related chemical industry and carbon sequestration.

Evidence of advancing spring xylem phenology in Chinese forests under global warming

Phenological responses of vegetation to the ongoing warming trend impact current and future primary productivity.However,few studies focus on wood phenology because its observed data are much scarcer,which hinders the estimation and prediction of forest carbon budgets over large regions.Here,we use a physiological process-based tree-ring growth model(Vaganov-Shashkin model)to investigate the spatial and temporal variations of spring xylem phenology(start of the growing season of xylem,SOS_(x))in tree-ring sites of China during 1962-2016 CE.The model is calibrated on measured tree-ring width chronologies(70 tree-ring chronologies)and successfully validated with field observations of xylogenesis.We found that spring xylem phenology significantly advances during 1962-2016 CE period under global warming,with the rate of advance quickly increasing after the 1990s to an average of 0.25 days per year.The preseason daily mean temperature is the main climatic driver for spring xylem phenology as indicated by its significant correlations with SOS_(x)at most sites(71%).Warmer preseason allows heat requirements for tree growth to be reached more quickly,with increase of 1℃in temperature of preseason anticipates SOS_(x)by 6 to 7 days,which will benefit the radial growth of trees in the relatively cold-humid environments.In addition,the significant positive correlation between the simulated spring xylem phenology and remote sensing derived phenology highlights the primary and secondary growth may be governed by the same variable(temperature)and change in the same direction with global warming.This study provides the long-term perspective on the spring xylem phenology variations covering most of China.

大小龄红松木质部解剖特征的年龄效应及其对气候变化的响应差异

树龄是影响树木生长的最重要因素之一。在气候变暖背景下,利用树干木质部解剖特征,分析不同树龄生长-气候关系,对准确评估树木对气候变化的响应和适应策略、预测气候变化下的森林动态至关重要。利用木材解剖学方法,比较了小兴安岭溪水地区针阔混交林内大、小龄红松(Pinus koraiensis)木质部解剖特征及其对气候变化的响应异同。结果表明:大龄红松主要管胞特征值随年龄增加而呈上升趋势,但小龄红松的变化趋势并不明显,两者均在1840—1890年和1980—2010年间出现剧烈的波动。大、小年龄红松部分管胞特征与气候因子的关系具有一致性,管胞数量和理论导水率分别与月最高温度负相关和正相关;总管胞面积(负相关)、理论导水率(正相关)、平均水力直径(正相关)与月最低温度的关系一致;理论导水率与月总降水正相关;管胞占比、平均管胞面积、理论导水率、平均水力直径均与平均相对湿度正相关,且大龄红松相关性更强。大、小年龄红松管胞特征与气候因子的关系的不一致表现在,大龄红松管胞占比、平均管胞面积、总管胞面积和平均水力直径与月最高温度正相关,而这些关系在小龄红松则表现为负相关。大龄红松管胞数量与7—9月最低温度正相关,而在小龄红松表现为显著负相关;大、小龄红松除理论导水率外其他管胞特征与降水关系基本相反,其中管胞数量的相关性更强;大龄红松与7月、9月、年总降水量显著正相关,而小龄红松与6月和年总降水显著负相关;与月平均相对湿度的相关关系大龄红松表现为正相关或不显著,而小龄红松呈负相关关系。温度是限制大、小龄红松管胞特征生长的主要气候因子,降水的影响相对较弱,平均相对湿度对大小龄红松的影响差异不大。近几十年,小兴安岭地区气候暖干化趋势逐渐增强,这种暖干化会造成大、小龄红松生长的响应差异。若气候持续变暖或加剧,小龄红松会出现严重生长衰退。

碱性副品红染色法检测木质部导管栓塞技术改进

染色法是测量导管长度、直径、导管分布以及栓塞脆弱性的重要方法。在测量导管栓塞时,染色压力和时间条件将极大地影响实验结果的准确性。为准确利用染色法测定刺槐Robinia pseudoacacia导管栓塞状况,本研究通过使用充气组(人为栓塞100%)以及冲洗组(完全去除栓塞)对碱性副品红染色法进行了压力、时间条件的改良。结果表明,当压力在0.04kpa,染色时间60min时,实验结果最为准确可靠。在此压力下染色过程不会冲开栓塞导管,配合60 min的染色时间可对未栓塞导管进行充分染色。另外,本研究通过诱导组,利用离心机法对枝条诱导不同程度的栓塞与染色法进行了对比验证,结果表明在该染色条件下,可以很好地反映茎段的栓塞状况,保证了实验结果的准确性。在后续试验中,使用碱性副品红染色法研究木质部栓塞时可以沿用此压力及时间条件。

温度和降水对宁夏六盘山自然保护区蒙古栎年内木质部生长的影响

了解我国干旱半干旱地区树木木质部生长动态及其与气候因子之间的关系,对于评估和预测气候变化背景下的森林生产力和固碳潜力十分重要。通过微树芯采样技术,在2个生长季(2019年和2020年)监测了宁夏六盘山自然保护区内4棵蒙古栎(Quercus mongolica)年内木质部生长动态,并采用混合线性模型分别探索温度和降水对其生长速率的影响。研究发现蒙古栎的年内木质部生长动态在2个生长季内无显著差异(P>0.05),均于4月初开始生长,9月中下旬停止生长,生长季长度为(177±17)d(2019年)和(165±24)d(2020年)。混合线性模型结果显示,蒙古栎年内木质部的生长速率与采样前7、10、15天的最高、最低、平均温及总降水量均呈现显著正相关关系(P<0.01)。全球气候变化背景下,宁夏六盘山自然保护区蒙古栎年内木质部生长可能受益于未来增温湿润的气候条件。

宝天曼8种阔叶树木材密度的解剖学决定因素及其与叶性状的协同与权衡

【目的】探究影响木材密度的解剖学机制,揭示茎叶解剖和生理性状的协同与权衡关系,有助于阐明不同树种适应环境的生理生态机制。【方法】选择宝天曼天然林中常见的8种落叶阔叶树,测定木材密度、木质部导管及纤维等解剖性状、叶片压力-容积曲线参数等21个茎叶性状,探究决定木材密度的解剖学性状,分析茎叶性状的协同和权衡关系。【结果】1) 8个树种的木材密度与组成木质部的导管、薄壁组织和纤维组织这3大组织的比例都不相关,更多受到纤维细胞性状的影响。2)对木材密度影响最大的木质部性状是纤维细胞腔占横截面的比例,其次是纤维细胞壁占纤维细胞的比例、纤维细胞壁厚与腔直径比、纤维细胞壁厚度等性状。3)木材密度与叶片单叶面积、失膨压时相对含水量和弹性模量呈负相关。4)失膨压时相对含水量与导管水力直径、最大导管直径、平均导管直径、纤维细胞腔面积、纤维细胞腔直径呈正相关;与导管密度、纤维细胞壁厚与腔直径比、纤维细胞壁占横截面比例呈负相关。【结论】木材密度主要由纤维细胞性状决定,而非导管和薄壁组织性状;高的叶片忍耐失水能力耦合于致密的茎纤维细胞和木材密度。