Taxodin A, a Cytotoxic C30 Terpenoid from Taxodium mucronatum with a Unique Skeleton.

Taxodin A (1), a unique C30 terpenoid featuring an unprecedented skeleton composed of an abietane-type diterpene and a menthane-type monoterpene, was obtained from the leaves and branches of Taxodium mucronatum. The structure and absolute configuration of compound 1 was unequivocally established by the combination of extensive spectroscopic analyses and X-ray single-crystal diffraction analysis. Compound 1 exhibited potent cytotoxic activities against A549, SMMC-7721, MDA-MB-231, and SW480 cell lines with IC50 values of 15.35±0.73, 8.49±0.35, 17.53±0.79, 18.93±0.60 µM, respectively.

Molecular Mechanism of Different Rooting Capacity between Two Clones of Taxodium hybrid 'Zhongshanshan'.

The conifer Taxodium hybrid 'Zhongshanshan' (T. hybrid 'Zhongshanshan') is characterized by rapid growth, strong stress resistance, and high ornamental value and has significant potential for use in afforestation, landscaping, and wood production. The main method of propagating T. hybrid 'Zhongshanshan' is tender branch cutting, but the cutting rooting abilities of different T. hybrid 'Zhongshanshan' clones differ significantly. To explore the causes of rooting ability differences at a molecular level, we analyzed the transcriptome data of cutting base and root tissues of T. hybrid 'Zhongshanshan 149' with a rooting rate of less than 5% and T. hybrid 'Zhongshanshan 118' with rooting rate greater than 60%, at the developmental time points in this study. The results indicated that differentially expressed genes between the two clones were mainly associated with copper ion binding, peroxidase, and oxidoreductase activity, response to oxidative stress, phenylpropanoid and flavonoid biosynthesis, and plant hormone signal transduction, among others. The expression pattern of ThAP2 was different throughout the development of the adventitive roots of the two clone cuttings. Therefore, this gene was selected for further study. It was shown that ThAP2 was a nuclear-localized transcription factor and demonstrated a positive feedback effect on rooting in transgenic Nicotiana benthamiana cuttings. Thus, the results of this study explain the molecular mechanism of cutting rooting and provide candidate gene resources for developing genetic breeding strategies for optimizing superior clones of T. hybrid 'Zhongshanshan'.

Physiological and transcriptional regulation in Taxodium hybrid 'Zhongshanshan' leaves in acclimation to prolonged partial submergence.

MAIN CONCLUSION: Taxodium 703 leaves activate fermentation, amino acids metabolism and ROS detoxification, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress. Taxodium hybrid 'Zhongshanshan 703' (T. mucronatum × T. distichum; Taxodium 703) is a highly flooding-tolerant woody plant. To investigate the physiological and transcriptional regulatory mechanisms underlying its leaves in acclimation to long-term flooding, we exposed cuttings of Taxodium 703 to either non-flooding (control) or partial submergence for 2 months. The leaf tissues above (AL) and below (BL) flooding-water were separately harvested. Partial submergence decreased concentrations of chlorophyll (a + b) and dehydroascorbate (DHA) and lactate dehydrogenase (LDH) activity in AL, and reduced biomass, concentrations of succinic acid, fumaric acid and malic acid, and transcript levels of genes involved in tricarboxylic acid (TCA) cycle in BL. Under partial submergence, concentrations of starch, malondialdehyde and abscisic acid (ABA) decreased, and also mRNA levels of nine-cis-epoxycarotenoid dioxygenases that are involved in ABA biosynthesis in AL and BL of Taxodium 703. Partial submergence increased O2- content in AL, and improved concentrations of pyruvate and soluble sugars and activities of LDH and peroxidase in BL. In addition, partial submergence increased concentrations of ethanol, lactate, alanine, γ-aminobutyric acid, total amino acids and ascorbic acid (ASA), and ASA/DHA, activities of alcohol dehydrogenases (ADH) and ascorbate peroxidase, as well as transcript levels of ADH1A, ADH1B and genes involved in alanine biosynthesis and starch degradation in AL and BL of Taxodium 703. Overall, these results suggest that Taxodium 703 leaves activate fermentation, amino acids metabolism and reactive oxygen species detoxification, and maintain a steady supply of sugars, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress.

Comparative chloroplast genomics of the genus Taxodium.

BACKGROUND: Chloroplast (cp) genome information would facilitate the development and utilization of Taxodium resources. However, cp genome characteristics of Taxodium were poorly understood. RESULTS: We determined the complete cp genome sequences of T. distichum, T. mucronatum, and T. ascendens. The cp genomes are 131,947 bp to 132,613 bp in length, encode 120 genes with the same order, and lack typical inverted repeat (IR) regions. The longest small IR, a 282 bp trnQ-containing IR, were involved in the formation of isomers. Comparative analysis of the 3 cp genomes showed that 91.57% of the indels resulted in the periodic variation of tandem repeat (TR) motifs and 72.46% single nucleotide polymorphisms (SNPs) located closely to TRs, suggesting a relationship between TRs and mutational dynamics. Eleven hypervariable regions were identified as candidates for DNA barcode development. Hypothetical cp open reading frame 1(Ycf1) was the only one gene that has an indel in coding DNA sequence, and the indel is composed of a long TR. When extended to cupressophytes, ycf1 genes have undergone a universal insertion of TRs accompanied by extreme length expansion. Meanwhile, ycf1 also located in rearrangement endpoints of cupressophyte cp genomes. All these characteristics highlight the important role of repeats in the evolution of cp genomes. CONCLUSIONS: This study added new evidence for the role of repeats in the dynamics mechanism of cp genome mutation and rearrangement. Moreover, the information of TRs and hypervariable regions would provide reliable molecular resources for future research focusing on the infrageneric taxa identification, phylogenetic resolution, population structure and biodiversity for the genus Taxodium and Cupressophytes.

An Integrated Transcriptome and Proteome Analysis Reveals Putative Regulators of Adventitious Root Formation in Taxodium 'Zhongshanshan'.

Adventitious root (AR) formation from cuttings is the primary manner for the commercial vegetative propagation of trees. Cuttings is also the main method for the vegetative reproduction of Taxodium 'Zhongshanshan', while knowledge of the molecular mechanisms regulating the processes is limited. Here, we used mRNA sequencing and an isobaric tag for relative and absolute quantitation-based quantitative proteomic (iTRAQ) analysis to measure changes in gene and protein expression levels during AR formation in Taxodium 'Zhongshanshan'. Three comparison groups were established to represent the three developmental stages in the AR formation process. At the transcript level, 4743 genes showed an expression difference in the comparison groups as detected by RNA sequencing. At the protein level, 4005 proteins differed in their relative abundance levels, as indicated by the quantitative proteomic analysis. A comparison of the transcriptome and proteome data revealed regulatory aspects of metabolism during AR formation and development. In summary, hormonal signal transduction is different at different developmental stages during AR formation. Other factors related to carbohydrate and energy metabolism and protein degradation and some transcription factor activity levels, were also correlated with AR formation. Studying the identified genes and proteins will provide further insights into the molecular mechanisms controlling AR formation.

Terpenoids of the Swamp Cypress Subfamily (Taxodioideae), Cupressaceae, an Overview by GC-MS.

The resins bled from stems and in seed cones and leaves of Cryptomeria japonica, Glyptostrobus pensilis, Taxodium distichum, and T. mucronatum were characterized to provide an overview of their major natural product compositions. The total solvent extract solutions were analyzed as the free and derivatized products by gas chromatography-mass spectrometry to identify the compounds, which comprised minor mono- and sesquiterpenoids, and dominant di- and triterpenoids, plus aliphatic lipids (e.g., n-nonacosan-10-ol). Ferruginol, 7α-p-cymenylferruginol, and chamaecydin were the major characteristic markers for the Taxodioideae conifer subfamily. The mass spectrometric data can aid polar compound elucidation in environmental, geological, archeological, forensic and pharmaceutical studies.

High-density genetic map construction and quantitative trait loci identification for growth traits in (Taxodium distichum var. distichum × T. mucronatum) × T. mucronatum.

BACKGROUND: 'Zhongshanshan' is the general designation for the superior interspecific hybrid clones of Taxodium species, which is widely grown for economic and ecological purposes in southern China. Growth is the priority objective in 'Zhongshanshan' tree improvement. A high-density linkage map is vital to efficiently identify key quantitative trait loci (QTLs) that affect growth. RESULTS: In total, 403.16 Gb of data, containing 2016,336 paired-end reads, was obtained after preprocessing. The average sequencing depth was 28.49 in T. distichum var. distichum, 25.18 in T. mucronatum, and 11.12 in each progeny. In total, 524,662 high-quality SLAFs were detected, of which 249,619 were polymorphic, and 6166 of the polymorphic markers met the requirements for use in constructing a genetic map. The final map harbored 6156 SLAF markers on 11 linkage groups, and was 1137.86 cM in length, with an average distance of 0.18 cM between adjacent markers. Separate QTL analyses of traits in different years by CIM detected 7 QTLs. While combining multiple-year data, 13 QTLs were detected by ICIM. 5 QTLs were repeatedly detected by the two methods, and among them, 3 significant QTLs (q6-2, q4-2 and q2-1) were detected in at least two traits. Bioinformatic analysis discoveried a gene annotated as a leucine-rich repeat receptor-like kinase gene within q4-2. CONCLUSIONS: This map is the most saturated one constructed in a Taxodiaceae species to date, and would provide useful information for future comparative mapping, genome assembly, and marker-assisted selection.

Effects of cadmium stress on the antioxidant system and chlorophyll fluorescence characteristics of two Taxodium clones.

KEY MESSAGE: The T.118 and T.406 seedlings showed strong adaptability under Cd concentrations ≤ 50 µM. The mechanisms of photoprotection in T.118 and T.406 differed in high-Cd concentrations. To explore the physiological response characteristics of Taxodium hybrids to cadmium (Cd) stress and provide basis for screening of Cd-tolerant species, the hydroponic cultivation of T.118 and T.406 seedlings was conducted to demonstrate the effects of Cd stress on seedling growth, antioxidant system, and chlorophyll fluorescence parameters. After 35 days of Cd stress at a concentration ≤ 50 µM, the dry weight biomass of the two clones did not significantly differ from that of the control. T.406 exhibited a significant increase in POD activity compared to T.118 and maintained high SOD activity after exposure to high concentrations of Cd, whereas MDA levels showed little changes. Under low-Cd stress, chlorophyll content and fluorescence parameters remained stable, especially for T.406. Under high-Cd concentration stress, the above parameters were lower than the control, with a more significant decrease in T.118 than in T.406. The non-photochemical quenching coefficient (NPQ) of both clones increased with increasing Cd concentration. T.118 showed a greater increase than T.406, particularly under high-Cd concentration stress. The T.118 and T.406 seedlings adapted to low-Cd concentration stress by enhancing their antioxidant enzyme activity to maintain the balance of reactive oxygen metabolism and reduce cellular damage. The photochemical activity of mesophyll cells remained high to maintain photosynthetic capacity and normal seedling growth. T.406 showed stronger resistance to Cd than T.118. T.406 prevented photodamage by promoting the photochemical utilization of the excitation energy and maintaining a strong antioxidant stress ability. Enhancement of heat dissipation capability may be the main photoprotection mechanism of T.118.

Inferences of population structure and demographic history for Taxodium distichum, a coniferous tree in North America, based on amplicon sequencing analysis.

PREMISE OF THE STUDY: Studies of natural genetic variation can elucidate the genetic basis of phenotypic variation and the past population structure of species. Our study species, Taxodium distichum, is a unique conifer that inhabits the flood plains and swamps of North America. Morphological and ecological differences in two varieties, T. distichum var. distichum (bald cypress) and T. distichum var. imbricarium (pond cypress), are well known, but little is known about the level of genetic differentiation between the varieties and the demographic history of local populations. METHODS: We analyzed nucleotide polymorphisms at 47 nuclear loci from 96 individuals collected from the Mississippi River Alluvial Valley (MRAV), and Gulf Coastal populations in Texas, Louisiana, and Florida using high-throughput DNA sequencing. Standard population genetic statistics were calculated, and demographic parameters were estimated using a composite-likelihood approach. KEY RESULTS: Taxodium distichum in North America can be divided into at least three genetic groups, bald cypress in the MRAV and Texas, bald cypress in Florida, and pond cypress in Florida. The levels of genetic differentiation among the groups were low but significant. Several loci showed the signatures of positive selection, which might be responsible for local adaptation or varietal differentiation. CONCLUSIONS: Bald cypress was genetically differentiated into two geographical groups, and the boundary was located between the MRAV and Florida. This differentiation could be explained by population expansion from east to west. Despite the overlap of the two varieties' ranges, they were genetically differentiated in Florida. The estimated demographic parameters suggested that pond cypress split from bald cypress during the late Miocene.

Antileishmanial and Cytotoxic Activity of Some Highly Oxidized Abietane Diterpenoids from the Bald Cypress, Taxodium distichum.

Two new compounds, namely, a para-benzoquinone ring-containing abietane (1) and a para-benzoquinone ring-containing 7,8-seco-abietane (2), and 14 other known highly oxidized abietane diterpenoids (3-16) were isolated from an extract prepared from the cones of Taxodium distichum, collected in central Ohio. The active subfraction from which all compounds isolated in this study were purified was tested in vivo using Leishmania donovani-infected mice and was found to dose-dependently reduce the parasite burden in the murine livers after iv administration of this crude mixture at 5.6 and 11.1 mg/kg. The structures of 1 and 2 were established by detailed 1D- and 2D-NMR experiments, HRESIMS data, and electronic circular dichroism studies. Compounds 3 and 4 were each fully characterized spectroscopically and also isolated from a natural source for the first time. Compounds 2-16 were tested in vitro against L. donovani promastigotes and L. amazonensis intracellular amastigotes. Compound 2 was the most active against L. amazonensis amastigotes (IC50 = 1.4 µM), and 10 was the most potent against L. donovani promastigotes (IC50 = 1.6 µM). These compounds may be suggested for further studies such as in vivo experimentation either alone or in combination with other Taxodium isolates.

Increase in platinum group elements in Mexico City as revealed from growth rings of Taxodium mucronatum ten.

Tree rings may be used as indicators of contamination events providing information on the chronology and the elemental composition of the contamination. In this framework, we report PGEs enrichment in growth rings of Taxodium mucronatum ten for trees growing in the central area of Mexico City as compared to trees growing in a non-urban environment. Concentrations of PGE were determined by ICP-MS analysis on microwave-digested tree rings. The element found in higher concentrations was Pd (1.13-87.98 µg kg(-1)), followed by Rh (0.28-36.81 µg kg(-1)) and Pt (0.106-7.21 µg kg(-1)). The concentration trends of PGEs in the tree-ring sequences from the urban area presented significant correlation values when comparing between trees (r between 0.618 and 0.98, P < 0.025) and between elements within individual trees (r between 0.76 and 0.994, P < 0.01). Furthermore, a clear increase was observed for rings after 1997, with enrichment of up to 60 times the mean concentration found for the sequence from the non-urban area and up to 40 times the mean concentration for the pre-1991 period in the urban trees. These results also demonstrate the feasibility of applying T. mucronatum ten to be used as a bioindicator of the increase in PGE in urban environments.

Direct identification of diverse alicyclic terpenoids in Suwannee River Fulvic Acid.

The chemical complexity of dissolved organic matter (DOM) obstructs our ability to definitively recover source compounds from within DOM, an objective which has the capacity to alter our understanding of carbon sequestration on a global scale. To advance compositional studies of DOM we have applied a previously published reduction method to an environmental standard, Suwannee River Fulvic Acid (SRFA). The reduction products, comprising 12% of the prereduced carbon, were then separated by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS). Results indicate that the majority of observed reduced compounds corresponded to alicyclic hydrocarbons in the size range C10 to C17. Cyclic terpenoids are the only biomolecule class with contiguous, alicyclic carbon backbones of this size. These terpenoid reduction products contain series offset by CH2 and exhibit great isomeric diversity, features previously inferred from ultrahigh resolution mass spectrometry and NMR studies of unreduced SRFA. Reduction of Taxodium leaf litter as a source material to SRFA confirmed the prevalence of terpenoids in SRFA and provided insight into the parent compounds that must be diagenetically modified on relatively short time scales. These data corroborate several recent studies that suggest alicyclic hydrocarbons to be important components of longer-lived DOM.

De novo sequencing, assembly, and analysis of the Taxodium 'Zhongshansa' roots and shoots transcriptome in response to short-term waterlogging.

BACKGROUND: Taxodium is renowned for its strong tolerance to waterlogging stress, thus it has great ecological and economic potential. However, the scant genomic resources in genus Taxodium have greatly hindered further exploration of its underlying flood-tolerance mechanism. Taxodium 'Zhongshansa' is an interspecies hybrid of T. distichum and T. mucronatum, and has been widely planted in southeastern China. To understand the genetic basis of its flood tolerance, we analyzed the transcriptomes of Taxodium 'Zhongshansa' roots and shoots in response to short-term waterlogging. RESULTS: RNA-seq was used to analyze genome-wide transcriptome changes of Taxodium 'Zhongshansa 406' clone root and shoot treated with 1 h of soil-waterlogging stress. After de novo assembly, 108,692 unigenes were achieved, and 70,260 (64.64%) of them were annotated. There were 2090 differentially expressed genes (DEGs) found in roots and 394 in shoots, with 174 shared by both of them, indicating that the aerial parts were also affected. Under waterlogging stress, the primary reaction of hypoxic-treated root was to activate the antioxidative defense system to prevent cells experiencing reactive oxygen species (ROS) poisoning. As respiration was inhibited and ATP decreased, another quick coping mechanism was repressing the energy-consuming biosynthetic processes through the whole plant. The glycolysis and fermentation pathway was activated to maintain ATP production in the hypoxic root. Constantly, the demand for carbohydrates increased, and carbohydrate metabolism were accumulated in the root as well as the shoot, possibly indicating that systemic communications between waterlogged and non-waterlogged tissues facilated survival. Amino acid metabolism was also greatly influenced, with down-regulation of genes involvedin serine degradation and up-regulation of aspartic acid degradation. Additionally, a non-symbiotic hemoglobin class 1 gene was up-regulated, which may also help the ATP production. Moreover, the gene expression pattern of 5 unigenes involving in the glycolysis pathway revealed by qRT-PCR confirmed the RNA-Seq data. CONCLUSIONS: We conclude that ROS detoxification and energy maintenance were the primary coping mechanisms of 'Zhongshansa' in surviving oxygen deficiency, which may be responsible for its remarkable waterlogging tolerance. Our study not only provided the first large-scale assessment of genomic resources of Taxodium but also guidelines for probing the molecular mechanism underlying 'Zhongshansa' waterlogging tolerance.

Phytomonitoring of chlorinated ethenes in trees: a four-year study of seasonal chemodynamics in planta.

Long-term monitoring (LTM) of groundwater remedial projects is costly and time-consuming, particularly when using phytoremediation, a long-term remedial approach. The use of trees as sensors of groundwater contamination (i.e., phytoscreening) has been widely described, although the use of trees to provide long-term monitoring of such plumes (phytomonitoring) has been more limited due to unexplained variability of contaminant concentrations in trees. To assess this variability, we developed an in planta sampling method to obtain high-frequency measurements of chlorinated ethenes in oak (Quercus rubra) and baldcypress (Taxodium distichum) trees growing above a contaminated plume during a 4-year trial. The data set revealed that contaminant concentrations increased rapidly with transpiration in the spring and decreased in the fall, resulting in perchloroethene (PCE) and trichloroethene (TCE) sapwood concentrations an order of magnitude higher in late summer as compared to winter. Heartwood PCE and TCE concentrations were more buffered against seasonal effects. Rainfall events caused negligible dilution of contaminant concentrations in trees after precipitation events. Modeling evapotranspiration potential from meteorological data and comparing the modeled uptake and transport with the 4 years of high frequency data provides a foundation to advance the implementation of phytomonitoring and improved understanding of plant contaminant interactions.

Integrated small RNA, transcriptome and physiological approaches provide insight into Taxodium hybrid 'Zhongshanshan' roots in acclimation to prolonged flooding.

Although Taxodium hybrid 'Zhongshanshan' 406 (Taxodium mucronatum Tenore × Taxodium distichum; Taxodium 406) is an extremely flooding-tolerant woody plant, the physiological and molecular mechanisms underlying acclimation of its roots to long-term flooding remain largely unknown. Thus, we exposed saplings of Taxodium 406 to either non-flooding (control) or flooding for 2 months. Flooding resulted in reduced root biomass, which is in line with lower concentrations of citrate, α-ketoglutaric acid, fumaric acid, malic acid and adenosine triphosphate (ATP) in Taxodium 406 roots. Flooding led to elevated activities of pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, which is consistent with higher lactate concentration in the roots of Taxodium 406. Flooding brought about stimulated activities of superoxide dismutase and catalase and elevated reduced glutathione (GSH) concentration and GSH/oxidized glutathione, which is in agreement with reduced concentrations of O2- and H2O2 in Taxodium 406 roots. The levels of starch, soluble protein, indole-3-acetic acid, gibberellin A4 and jasmonate were decreased, whereas the concentrations of glucose, total non-structural carbohydrates, most amino acids and 1-aminocyclopropane-1-carboxylate (ACC) were improved in the roots of flooding-treated Taxodium 406. Underlying these changes in growth and physiological characteristics, 12,420 mRNAs and 42 miRNAs were significantly differentially expressed, and 886 miRNA-mRNA pairs were identified in the roots of flooding-exposed Taxodium 406. For instance, 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8) was a target of Th-miR162-3p and 1-aminocyclopropane-1-carboxylate oxidase 4 (ACO4) was a target of Th-miR166i, and the downregulation of Th-miR162-3p and Th-miR166i results in the upregulation of ACS8 and ACO4, probably bringing about higher ACC content in flooding-treated roots. Overall, these results indicate that differentially expressed mRNA and miRNAs are involved in regulating tricarboxylic acid cycle, ATP production, fermentation, and metabolism of carbohydrates, amino acids and phytohormones, as well as reactive oxygen species detoxification of Taxodium 406 roots. These processes play pivotal roles in acclimation to flooding stress. These results will improve our understanding of the molecular and physiological bases underlying woody plant flooding acclimation and provide valuable insights into breeding-flooding tolerant trees.

[Structural Diversity and Its Temporal Variation in the Soil Bacterial Community Under Plantations of Taxodium distichum in the Riparian Zone of the Three Gorges Reservoir Area].

The riparian zone supports important ecological functions and acts as an ecotone connecting terrestrial and aquatic areas. Soil microbes under the revegetation of woody species are crucial to the biogeochemical cycle of nutrients. Here, soil samples were collected to examine the soil microbes during different emergence phases in 2019 (May:T1, July:T2, and September:T3) in the riparian zone of the Three Gorges Reservoir, China. The variations in the bacterial community were evaluated using high-throughput sequencing. The results showed that:during the emergence phases, soil properties such as pH value (pH), ammonium nitrogen (NH4+-N), and nitrate-nitrogen (NO3--N) and soil enzymes changed significantly(P<0.05), and soil bacterial α diversity also changed with time. Except for the Chao1 index, the richness of rhizosphere soil bacteria showed T1>T2>T3, whereas the α diversity of non-rhizosphere soil bacteria showed T3>T1>T2. The redundancy analysis (RDA) test implied that soil urease, NH4+-N, pH, and NO3--N were the key factors structuring the microbial community. Proteobacteria and Acidobacteria were the two dominant components among the 60 phyla that were detected in the soil. Based on phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) prediction, metabolism was the basic function of soil bacterial communities of Taxodium distichum; in the secondary functional layer, the metabolic pathways related to carbon, nitrogen, and phosphorus mainly included amino acid metabolism, carbohydrate metabolism, lipid compound metabolism, and energy metabolism, and the relative abundance of each metabolic function had a certain time difference in different periods. These findings could help us better understand how soil microbes change after restoring vegetation in the Three Gorges Reservoir area.

How Biochar Derived from Pond Cypress (Taxodium Ascendens) Evolved with Pyrolysis Temperature and Time and Their End Efficacy Evaluation.

Biomass type, pyrolysis temperature, and duration can affect biochar properties simultaneously. To further clarify the mechanism of this interaction, the branch and leaf parts of Pond cypress (Taxodium ascendens) were separately pyrolyzed at four peak temperatures (350 °C, 450 °C, 650 °C, and 750 °C) for three different durations (0.5 h, 1 h, and 2 h) in this study. The resulting biochar properties were measured, which included the yield, specific surface area (SSA), pH, EC (electricity conductivity), the bulk and surface elemental composition, and the contents of moisture, ash, fixed carbon, and volatile matter. The results showed that the pyrolysis temperature was more determinant for the modification of all biochar, but the residence time had a significant effect on the yield, pH, and SSA of branch-based biochar (B-biochar) at specific temperatures. However, such a phenomenon only happened on the pH of leaf-based biochar (L-biochar). Results: (1) With the temperature at 350 and 650 °C, the residence time had a significant effect on the yield of B-biochar. (2) The pH of B-biochar and L-biochar varied considerably between durations when the heating temperature hit 650 and 750 °C. (3) The SSA of B-biochar possessed an obvious fluctuation with the time during the pyrolysis from 650 to 750 °C. According to the properties measured above, the principal component and the cluster analysis classified the 24 types of biochar made in this experiment into four groups and revealed that an obvious disparity existed between B-biochar and L-biochar that were pyrolyzed at temperatures ranging from 450 to 750 °C, which suggested that biomass type was the primary factor for biochar-making. All this information can provide valuable references for the optimization of biochar-making in the real world.

Characterization of the genome of bald cypress.

BACKGROUND: Bald cypress (Taxodium distichum var. distichum) is a coniferous tree of tremendous ecological and economic importance. It is a member of the family Cupressaceae which also includes cypresses, redwoods, sequoias, thujas, and junipers. While the bald cypress genome is more than three times the size of the human genome, its 1C DNA content is amongst the smallest of any conifer. To learn more about the genome of bald cypress and gain insight into the evolution of Cupressaceae genomes, we performed a Cot analysis and used Cot filtration to study Taxodium DNA. Additionally, we constructed a 6.7 genome-equivalent BAC library that we screened with known Taxodium genes and select repeats. RESULTS: The bald cypress genome is composed of 90% repetitive DNA with most sequences being found in low to mid copy numbers. The most abundant repeats are found in fewer than 25,000 copies per genome. Approximately 7.4% of the genome is single/low-copy DNA (i.e., sequences found in 1 to 5 copies). Sequencing of highly repetitive Cot clones indicates that most Taxodium repeats are highly diverged from previously characterized plant repeat sequences. The bald cypress BAC library consists of 606,336 clones (average insert size of 113 kb) and collectively provides 6.7-fold genome equivalent coverage of the bald cypress genome. Macroarray screening with known genes produced, on average, about 1.5 positive clones per probe per genome-equivalent. Library screening with Cot-1 DNA revealed that approximately 83% of BAC clones contain repetitive sequences iterated 103 to 104 times per genome. CONCLUSIONS: The BAC library for bald cypress is the first to be generated for a conifer species outside of the family Pinaceae. The Taxodium BAC library was shown to be useful in gene isolation and genome characterization and should be an important tool in gymnosperm comparative genomics, physical mapping, genome sequencing, and gene/polymorphism discovery. The single/low-copy (SL) component of bald cypress is 4.6 times the size of the Arabidopsis genome. As suggested for other gymnosperms, the large amount of SL DNA in Taxodium is likely the result of divergence among ancient repeat copies and gene/pseudogene duplication.

Soil warming alters seed-bank responses across the geographic range of freshwater Taxodium distichum (Cupressaceae) swamps.

PREMISE OF THE STUDY: Climate warming is predicted to have far-reaching effects on the distribution of species, but those effects may depend on the flexibility of regenerating species in responding to climate gradients. We conducted a study to determine whether the variation in the response of seed banks to temperature varied across the latitudinal range of Taxodium distichum swamps in North America. METHODS: The soil was collected in a long-term research network and heated experimentally to three current-day spring normal soil temperatures (average maximum daily spring normal soil temperatures during May in Illinois, Arkansas, and Louisiana, USA, respectively: 22°, 25°, and 29°C). A "normal" is the mean temperature calculated over a 30-yr interval (1971-2000). Seed-bank density and biomass responses were examined in relation to latitude and difference in the soil temperature of the experiment and the spring normal. KEY RESULTS: Using first- and second-order regression analysis, we determined that the variation in total germination density was lowest mid-range and in experimental soil temperatures similar to the spring normal. For some dominant species, the variance in germination density was higher in the northern (Cephalanthus occidentalis) or the southern part of the network (Saururus cernuus and Polygonum pensylvanicum). Overall, the variance of total biomass (root, shoot, whole plant) was higher if the experimental soil temperature was warmer than the spring normal. CONCLUSIONS: Our results suggest that the regeneration of some populations of swamp species may have more flexibility to respond to climate warming than others.