Populus Tomentosa Research Articles

Endoplasmic reticulum\u2013localized UBC34 interaction with lignin repressors MYB221 and MYB156 regulates the transactivity of the transcription factors in Populus tomentosa

BackgroundRegulation of lignin biosynthesis is known to occur at the level of transcription factors (TFs), of which R2R3-MYB family members have been proposed to play a central role via the AC cis-elements. Despite the important roles of TFs in lignin biosynthesis, the post-translational regulation of these TFs, particularly their ubiquitination regulation, has not been thoroughly explored.ResultsWe describe the discovery of a Populus tomentosa E2 ubiquitin-conjugating enzyme 34 (PtoUBC34), which is involved in the post-translational regulation of transactivation activity of lignin-associated transcriptional repressors PtoMYB221 and PtoMYB156. PtoUBC34 is localized at the endoplasmic reticulum (ER) membrane where it interacts with transcriptional repressors PtoMYB221 and PtoMYB156. This specific interaction allows for the translocation of TFs PtoMYB221 and PtoMYB156 to the ER and reduces their repression activity in a PtoUBC34 abundance-dependent manner. By taking a molecular biology approach with quantitative real-time polymerase chain reaction (qRT-PCR) analysis, we found that PtoUBC34 is expressed in all aboveground tissues of trees in P. tomentosa, and in particular, it is ubiquitous in all distinct differentiation stages across wood formation, including phloem differentiation, cambium maintaining, early and developing xylem differentiation, secondary cell wall thickening, and programmed cell death. Additionally, we discovered that PtoUBC34 is induced by treatment with sodium chloride and heat shock.ConclusionsOur data suggest a possible mechanism by which lignin biosynthesis is regulated by ER-localized PtoUBC34 in poplar, probably through the ER-associated degradation (ERAD) of lignin-associated repressors PtoMYB221 and PtoMYB156.

Heterologous Expression of the DREB Transcription Factor AhDREB in Populus tomentosa Carrière Confers Tolerance to Salt without Growth Reduction under Greenhouse Conditions

The DREB transcription factors regulate multiple stress response genes, and are therefore useful for molecular plant breeding. AhDREB, a stress-inducible gene, was isolated from Atriplex hortensis L. and introduced into Populus tomentosa Carrière under the control of the CaMV35S promoter. Under salt stress, the chlorophyll content and net photosynthetic rate were higher in transgenic lines than in the wild type (WT). Moreover, the rate of electrolyte penetration (REC) was lower in the transgenic lines. Additional analyses revealed that the AhDREB transgenic plants generally displayed lower malondialdehyde (MDA) activity but higher superoxide dismutase (SOD) and peroxidase (POD) activities and proline content than the WT under salt stress. RNA sequencing indicated that AhDREB could enhance tolerance to salt by activating various downstream genes in the transgenic plants. Furthermore, no growth inhibition was detected in transgenic plants expressing AhDREB driven by the constitutive CaMV35S promoter. The transcriptome showed 165 and 52 differentially expressed genes in transgenic plants under stress and non-stress conditions, respectively, among which no significant metabolic pathway was enriched and no unintended effects have yet been identified. Together, these results suggest that AhDREB may be a good candidate gene for increasing salt tolerance in transgenic poplar breeding.

Over-expression of PttEXPA8 gene showed various resistances to diverse stresses.

Expansins play a pivotal role in plant adaptation to environmental stress via cell wall loosening. To evaluate the roles of expansin in response to different environmental stress conditions, the expansin gene PttEXPA8 from Populus tomentosa was transformed into tobacco. Analysis of physiological indices demonstrated the transgenic plants with improved resistance to heat, drought, salt, cold, and cadmium stress but to different extents. In mature plants, PttEXPA8 exerted the greatest effect on heat stress, with a response index value of 137.46%, followed by drought, cadmium, cold, and salt stress with response index values of 101.04%, 70.61%, 69.95%, and 54.68%, respectively. Over-expression of PttEXPA8 resulted in differential responses in physiological indices to the stresses. Soluble sugar content showed the highest response to the stresses, with an average response index value of 29.29%, whereas the absolute response index value for malondialdehyde content, relative electrolyte leakage, chlorophyll content, and superoxide dismutase activity ranged from 11.01% to 19.21%. The present results provide insight into the roles of expansin in stress resistance in Populus.

Biomechanical properties of plant root systems and their ability to stabilize slopes in geohazard-prone regions

Vegetation is widely used for reinforcing slopes, and thus controlling shallow landslides, because plant root systems can increase soil shear strength by anchoring soil layers and modifying hydrological characteristics. However, limited information is available regarding the vertical variation of soil reinforcement by roots at the slope scale, and how slope stability is influenced, especially in plantation areas. In this paper we examine the biomechanical effects on slope stability of the roots of Populus tomentosa, Robinia pseudoacacia and Olea europaea in a geohazard-prone region in China. Root density, variation in root area ratio (RAR) with depth, root tensile strength and root peak tensile force are measured, along with calculating the contribution of root cohesion to the factor of safety. The Wu-Waldron model and fiber bundle model are used to estimate static stress and dynamic stress adherence of plant roots to soil during debris flows and landslides, and a two-dimensional finite element model is used to calculate the increase in the factor of safety caused by additional root cohesion. The results show that RAR is higher for P. tomentosa than for R. pseudoacacia and O. europaea. The vertical soil profile of R. pseudoacacia roots has the highest soil water content (7.06%). The additional cohesion provided by R. pseudoacacia roots (10.35–15.12 kPa) is greater than that provided by P. tomentosa roots (6.19–10.26 kPa) and O. europaea roots (2.31–5.06 kPa). The stable area is also larger on a slope planted with R. pseudoacacia compared with the other two species. Young growth roots (8 years) are shown to affect the distribution of soil water and are limited by soil water in the semi-humid region. R. pseudoacacia roots provide significant additional cohesion by both static and dynamic stress for slope stability. This study aims to increase current understanding of the biomechanical properties of plantation species roots and their efficacy in soil reinforcement.

Identification and Analysis of microRNAs in the SAM and Leaves of Populus tomentosa

The shoot apical meristem (SAM) is a crucial tissue located at the tops of plants which can continually grow and differentiate to develop into all aboveground parts. SAM development is controlled by a series of complicated molecular regulation networks, among which microRNAs (miRNAs) and their target genes play key roles. However, little is known about these miRNAs in woody plants. In this study, we used small RNA (sRNA) sequencing to build four libraries derived from shoot tips and mature leaf tissues of Populus tomentosa, and identified 99 known miRNA families. In addition, 193 known miRNAs, including phytohormone-, developmental-, and cellular process-related miRNAs, showed significant differential expression. Interestingly, quantitative real-time reverse transcription polymerase chain reaction (PCR) analysis of miR172, miR164, and miR393 expression showed marked changes in expression patterns during the development of shoot tips. The target genes of these miRNAs were involved in the regulation of hormone responses and stem cell function. In particular, the miR172 target APETALA2 (AP2), involved in the maintenance of stem cells in the shoot apex, was expressed specifically during the initial active stage of development. These findings provide new insights into the regulatory mechanisms of miRNAs involved in SAM development and differentiation in tree species.

Auxin-mediated Aux/IAA-ARF-HB signaling cascade regulates secondary xylem development in Populus.

Wood development is strictly regulated by various phytohormones and auxin plays a central regulatory role in this process. However, how the auxin signaling is transducted in developing secondary xylem during wood formation in tree species remains unclear. Here, we identified an Aux/INDOLE-3-ACETIC ACID 9 (IAA9)-AUXIN RESPONSE FACTOR 5 (ARF5) module in Populus tomentosa as a key mediator of auxin signaling to control early developing xylem development. PtoIAA9, a canonical Aux/IAA gene, is predominantly expressed in vascular cambium and developing secondary xylem and induced by exogenous auxin. Overexpression of PtoIAA9m encoding a stabilized IAA9 protein significantly represses secondary xylem development in transgenic poplar. We further showed that PtoIAA9 interacts with PtoARF5 homologs via the C-terminal III/IV domains. The truncated PtoARF5.1 protein without the III/IV domains rescued defective phenotypes caused by PtoIAA9m. Expression analysis showed that the PtoIAA9-PtoARF5 module regulated the expression of genes associated with secondary vascular development in PtoIAA9m- and PtoARF5.1-overexpressing plants. Furthermore, PtoARF5.1 could bind to the promoters of two Class III homeodomain-leucine zipper (HD-ZIP III) genes, PtoHB7 and PtoHB8, to modulate secondary xylem formation. Taken together, our results suggest that the Aux/IAA9-ARF5 module is required for auxin signaling to regulate wood formation via orchestrating the expression of HD-ZIP III transcription factors in poplar.

Where to monitor the soil-water potential for scheduling drip irrigation in Populus tomentosa plantations located on the North China Plain?

Determining the optimal tensiometer placement is crucial for scheduling irrigation based on soil water potential (SWP) in poplar plantations. However, such work has never been done. The stand-age effect on the tensiometer placement is still unknown, hindering the development of a dynamic irrigation regime. In a surface drip irrigated Populus tomentosa, short-rotation plantation on sandy loam soil, the variation of SWP at different positions [hereafter expressed in spatial coordinates (distance from dripper in cm, depth in cm)] within the soil wetting volume (WV), and the daily tree growth rates were continuously monitored in one growing season. Whereas, the transpiration and fine root distribution were measured in two growing seasons. The HYDRUS model was calibrated using soil water and transpiration data from one growing season and validated using data in another growing season. Then the model was applied to simulate sixty scenarios, which were combinations of different SWP measurement positions (ten scenarios), root distribution patterns (three scenarios; mainly using rooting depth as a proxy for trees at different ages), and irrigation thresholds (two scenarios). Based on the simulation results, we estimated the ratio of actual to potential transpiration (Ta/Tp) and irrigation efficiency (IE; calculated as (Ta/Tp)/irrigation amount) for each scenario. The absolute value of the mean relative difference of SWP was smaller at (15, 10) than at any other positions within the WV. The proportion of variation in growth (R2 = 0.294) and transpiration rates (R2 = 0.247) explained by root water-uptake was also highest at (15, 10). Fine roots concentrated on both sides of dripper as the trees grew bigger, with the maximal root density finally occurring at about (15, 10) and (−15, 10). Under the (−15, 10), (0, 10), (15, 10) and (0, 30) position scenarios, the Ta/Tp was at a high level relative to other scenarios, while the IE were at a middle level. As rooting depth increased, the ranks of different tensiometer positions in Ta/Tp and IE changed only a little, and Ta/Tp decreased slightly, implying the optimal placement should not vary with stand age. Therefore, tensiometer was recommended to place at 10 cm depth and about 15 cm distance from the dripper to schedule drip irrigation in different-aged P. tomentosa plantations on sandy loam soil. This will bring benefits to minimizing the use of irrigation water and maximizing production. Besides, the comprehensive approach used in this study can be adopted, when determining the optimal soil water measurement positions for scheduling irrigation for other plant species growing on other soil types.

Effects of pressurized superheated-steam heat treatment on set recovery and mechanical properties of surface-compressed wood

The recovery behavior and selected mechanical properties were studied for Populus tomentosa wood subjected to surface compression followed by heat treatment. The surface compression of wood was carried out in an open hot-pressing system at 180 °C with compressed thickness of 2 to 18 mm. The surface-compressed wood was treated by atmospheric heat treatment or 0.30 MPa pressurized superheated-steam heat treatment at 180 °C for 2 h. The results showed that the set recovery of compressed wood decreased with increasing compressed thickness before post-treatment. Atmospheric and pressurized heat treatment reduced the average set recovery of compressed wood significantly from 12.9% to 4.1% and 1.5% respectively, after conditioning at 40 °C and 90% relative humidity. Moreover, mechanical properties including the modulus of elasticity (MOE), modulus of rupture (MOR), hardness, and surface hardness increased with elevating compressed thickness. Both atmospheric and pressurized heat treatment reduced the MOR, hardness, and surface hardness of compressed wood. Analysis of variance showed that the effects of heat treatment on mechanical properties was not significant, except pressurized heat treatment decreased hardness significantly. With a compressed thickness of 10 mm, MOE, MOR, hardness and surface hardness were increased by 52.6%, 36.4%, 122.0% and 129.6%, respectively, compared with untreated wood.

Effect of hot pressing temperature on the density profile of compressed solid wood

To expand the applications of low-density wood, solid white poplar (Populus tomentosa) wood with a moisture content of 10.6% was compressed 5 mm radially at 90 °C, 120 °C, 150 °C, 180 °C, and 210 °C, and the density profile characteristics were analyzed. It was found that compressed wood with a non-uniform density profile contributed to the peak density and average density of the compressed layer, where the highest values were 0.87 g/cm3 and 0.72 g/cm3, respectively. The density peak and compressed layer were formed at various distances from the wood surface according to the pressing temperatures tested. It was concluded that the pressing temperature had a great effect on the density profile of the compressed wood and the pressing temperature effectively controlled the shape of the density profile.

The complete chloroplast genome of Populus tomentosa narrow crown, native to Northern China

Populus tomentosa narrow crown [P. tomentosa (NC)], natural distributes in northern China, is an economically important ecotype of P. tomentosa. In this study, we assembled its complete chloroplast (cp) genome. The total genome size of P. tomentosa (NC) is 156,368 bp in length, containing a large single copy region of 84,623 bp, a small single copy region of 16,533 bp, and a pair of inverted repeat regions of 27,606 bp. We annotated 130 genes in the genome, including 85 protein-coding genes, 37 tRNA genes, and 8 rRNA genes, 12 genes of which have 1 intron and 3 genes contain 2 introns. The overall GC content of the whole genome is 36.8%. Phylogenetic analysis using 24 complete cp genome of Salicaceae suggested that P. tomentosa (NC) is most closely related to P. alba. var. pyramidalis.

Colchicine did not affect the viability of induced 2n pollen in <i>Populus tomentosa</i>

Colchicine is widely used as a mutagen to induce production of diploid gametes in plants. However, whether colchicine affects induced pollen viability remains unclear. To clarify whether colchicine affected the viability of induced pollen, we induced production of diploid pollen by colchicine, followed by pollen germination and crossing induced pollen with normal gametes to produce triploid in Carrière. The results showed that the predominant meiotic stages and the number of colchicine injections had significant effects on the occurrence rates of induced 2n pollen. When the colchicine injection was given at diakinesis, a significant decrease in the pollen production per bud was observed ( < 0.001). The morphology of the colchicine-induced 2n pollen was similar to that of the natural 2n pollen in its ectexine structure. The pollen germination experiments revealed that there was also no significant difference in germination rates between the induced diploid pollen and natural 2n pollen grains, and 68 triploids were created by crossing colchicine-induced pollen. Our findings revealed that colchicine injection could induce to produce 2n pollen and will not lead to dysfunction of induced diploid pollen.in vitroPopulus tomentosapP. tomentosa

毛白杨树干呼吸及其温度敏感性季节变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 毛白杨树干呼吸及其温度敏感性季节变化特征 DOI: 10.5846/stxb201806151336 作者: 作者单位: 河北工程大学水利水电学院;,河北工程大学水利水电学院,河北工程大学水利水电学院,中国科学院沈阳应用生态研究所/中国科学院森林生态与管理重点实验室,河北雄安新区生态环境局,中国农业大学水利与土木工程学院,中国水利水电科学研究院 水利研究所,河北工程大学水利水电学院,河北工程大学水利水电学院,河北工程大学水利水电学院,河北工程大学水利水电学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31570402）；河北省自然科学基金面上项目（C2016402088）；河北省高等学校青年拔尖人才计划项（BJ2016012）；河北省引进留学人员资助项目（CN201702） Seasonal variations in stem respiration and temperature sensitivity of Populus tomentosa Author: Affiliation: School of Water Conservancy and Hydropower,Hebei University of Engineering;China;,School of Water Conservancy and Hydropower,Hebei University of Engineering,School of Water Conservancy and Hydropower,Hebei University of Engineering,Key Laboratory of Forest Ecology and management,Institute of Applied Ecology,Chinese Academy of Sciences,Ecology and Environment Bureau of Hebei Xiong-An New District,School of Water Resources and Civil Engineering,China Agricultural University,Beijing,Department of Irrigation and Drainage,China Institute of Water Resources and Hydropower Research,Beijing,School of Water Conservancy and Hydropower,Hebei University of Engineering,School of Water Conservancy and Hydropower,Hebei University of Engineering,School of Water Conservancy and Hydropower,Hebei University of Engineering,School of Water Conservancy and Hydropower,Hebei University of Engineering Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:树干呼吸（Es）是森林生态系统碳循环过程的重要组成部分，深入理解树干呼吸过程对未来气候变暖的响应及反馈机制有助于更加精确地估算森林生态系统碳储量。为揭示毛白杨树干呼吸及其温度敏感性的昼夜变化和季节动态规律，利用Li-Cor6400便携式光合作用测定系统及其配套使用的土壤呼吸测量气室（LI-6400-09）对冀南平原区毛白杨的树干呼吸和树干温度实施为期1年的连续监测。结果表明：（1）在生长季，毛白杨树干呼吸与树干温度之间在晚上呈现正相关的关系（R2=0.88）；相反，两者在白天为负相关的关系（R2=0.96）。（2）整个观测期内，毛白杨树干呼吸和树干温度均呈现"钟形"的变化曲线，树干呼吸与树干温度之间存在着较好的指数函数关系（R2=0.93），且树干呼吸的温度敏感性系数（Q10）为2.62；不同季节毛白杨树干呼吸的Q10存在差异，生长季的Q10（1.95）明显低于非生长季（3.00），表明生长呼吸和维持呼吸对温度的响应也并不相同。（3）温度矫正后的毛白杨树干呼吸（R15）在昼夜和季节尺度上均存在明显的变异，即夜晚的R15显著高于白天（P < 0.01），生长季的R15明显高于非生长季（P < 0.05）；树干可溶性糖含量与生长季的R15存在较好的相关性（R2=0.52），而非生长季的R15却主要受到树干淀粉含量的影响。研究结果表明，在生长季，毛白杨树干呼吸的在日变化主要受到温度的影响，而在季节尺度上Q10的变异则与树干呼吸中维持呼吸所占比例及树干中非结构性碳水化合物（可溶性糖和淀粉）的含量及类型紧密相关。 Abstract:Stem respiration plays a pivotal role in forest ecosystem carbon cycling, and understanding further its response to future climate warming has important significance for accurately estimating the carbon storage of forest ecosystems. To examine the seasonal variations of stem respiration of Chinese white poplar (Populus tomentosa), we measured stem respiration rate and stem temperature using the horizontally oriented soil chamber technique, from January 2016 to January 2017. We also conducted a 24 h measurement to examine the diurnal variation of stem respiration in May 2016. We found that (1) the stem respiration rate was positively related to stem temperature at night time (R2=0.88), whereas the relationship between stem respiration rate and stem temperature featured a negative linear curve during day time (R2=0.96); (2) the seasonal dynamics of the stem respiration rate followed the change of the stem temperature with a bell-shaped curve, and stem temperature explained 93% of the seasonal variation of stem respiration rate, with the temperature sensitivity (Q10) of 2.62 over the entire observation period. The Q10 was obviously different among seasons, with a lower value found in the non-growing season (3.00), and a higher value in the growing season (1.95), indicating that the growth and maintenance respiration had different temperature responses; (3) the temperature-normalised stem respiration (R15) also featured obviously diurnal and seasonal variations, where the R15 at night time and during the growing season were significantly higher than those of the daytime (P < 0.01), and non-growing season (P < 0.05). The principal factor responsible for the seasonal variation of R15 was the soluble sugar content in the growing season, and the starch content in the non-growing season. These results suggested that the stem respiration rate of Chinese white poplar was mainly disturbed by temperature at the diurnal scale, and closely related to the content and types of non-structural carbohydrates (soluble sugar and starch) and respiration component at seasonal scales, besides temperature. 参考文献 相似文献 引证文献

A greener approach to byproducts from the production of heat-treated poplar wood: Analysis of volatile organic compound emissions and antimicrobial activities of its condensate

Although many properties of plantation wood are greatly enhanced by heat treatment, large quantities of volatile organic compounds (VOCs) are released from this process, resulting in potential problems for the environment and human health. Volatile byproducts were collected from Populus tomentosa wood that was treated at 160, 180, 200, and 220 °C for 2 h. The VOC gases were partly collected at the heating, holding, and cooling stages of the process and were then analyzed by gas chromatography-mass spectrometry and thermogravimetry. The results show that over 90% of the volatiles from the first and third stages were alkane compounds. The mass losses in the heating and holding stages were almost at the same level, and the liquid byproduct contained approximately 48% phenolic products at 160 °C. The volatiles at 180 °C were mainly alkanes, terpenes, and aromatic compounds, and the absolute amount of VOCs released in the holding stage was much higher than that in the heating stage. The concentrations of phenols and ketones in the liquid byproducts decreased when the treatment temperature was increased, and more complex chemicals such as N-containing compounds emerged. Ester and aromatic compounds increased with the treatment temperature. The condensate collected at 160 °C exhibited considerable biological activity in the bacterial and mildew resistance tests. These results suggest that thermally treated byproducts can be turned into wood preservatives, which would also make the wood heat treatment cleaner.

Sandwich compression of wood: effects of preheating time and moisture distribution on the formation of compressed layer(s)

Wood sandwich compression technology can on the one hand effectively improve the physical and mechanical properties of low-density fast-growing wood, on the other hand it saves at least 25 vol% of raw materials (compared to the traditional wood compression technology) by controlling the position of compressed layer(s). In this study, white poplar (Populus tomentosa) lumbers were firstly soaked in water for 2 h, then preheated at 180 °C for 0–600 s. After the preheating process, radial compression was applied to obtain sandwich-compressed wood, and the compression was fixed by superheated steam treatment. Moisture distribution along the wood thickness and density distribution in the compressed wood were characterized. Furthermore, effects of preheating time on moisture distribution, position and thickness of the compressed layer(s) were investigated. Results indicated that the position of the compressed layer(s) moved from the wood surface to the center as a result of preheating time extension. The initial moving speed of the compressed layer(s) was 0.040 mm/s, which was sharply reduced to 0.014 mm/s with the extension of preheating time to 120 s. Further extension of preheating time above 120 s did not extensively reduce the compressed layer(s) moving speed. When the preheating time was 480 s, two compressed layers in the compressed wood converged to one at the center along the thickness in the compressed wood. More importantly, it was found that the positions of the compressed layer(s) highly matched up with high moisture content (MC) regions in the preheating process. A significant linear correlation between positions of the MC peak in high MC region of the preheated lumbers and density peak in the compressed layer(s) was built. In addition, moisture distribution along the thickness of wood can be controlled by adjusting the preheating time to eventually control the position and thickness of the compressed layer(s) in the sandwich-compressed wood. Superheated steam treatment after wood sandwich compression contributed to the reduced set recovery percentage of 1.58% after conditioning at 40 °C and relative humidity of 90%.

Isomeric Phenolic Glycosides from from Populus tomentosa

Isomeric Phenolic Glycosides from from Populus tomentosa

How Does Leaf Surface Micromorphology of Different Trees Impact Their Ability to Capture Particulate Matter?

Particulate matter (PM), including PM10 and PM2.5, has a major impact on air quality and public health. It has been shown that trees can capture PM and improve air quality. In this study, we used two-way ANOVA to investigate the significance of micro-morphological leaf surface characteristics of green trees in capturing PM at different parks in Beijing. The results show that leaf structure significantly impacts the ability of plants to capture PM. Pinus tabuliformis Carr. and Pinus bungeana Zucc. were mainly impacted by the density of stomata, waxy cuticle, and epidermis, while the major contributor to PM retention in other test trees, including Acer truncatum Bunge, Salix matsudana Koid., Populus tomentosa Carr. and Ginkgo biloba Linn. was leaf roughness. There were significant variations in leaf-droplet contact angle (representative of leaf wettability) and the ability of trees to capture PM (p &lt; 0.05): the bigger the contact angle, the less able the plant was to capture particulate matter.

Modeling soil evaporation and the response of the crop coefficient to leaf area index in mature Populus tomentosa plantations growing under different soil water availabilities

In order to improve water management in Populus tomentosa plantations, the variation in the FAO-56 parameters of the basal crop coefficient (Kcb) and soil evaporation (Es) in mature P. tomentosa plantations under different soil water availability treatments were investigated over two growing seasons. Empirical models for predicting Es in well-watered drip irrigated stands were constructed and validated. Changes in the relationship between Kcb and leaf area index (LAI) during the growing seasons and differing soil water availabilities, were also studied. The Kcb in all treatments increased rapidly to its maximum in about mid-May, and then decreased and remained relatively constant until late August or September. The Kcb increased sharply with increasing LAI, but plateaued when the LAI reached a critical value. With increasing stand age, the limit of Kcb of all treatments increased, while the critical values of the LAI declined markedly. In contrast, these two values declined with decreasing soil water availability, but the difference in Kcb limit could disappear with increasing stand age. Distinct spatial heterogeneity in Es appeared only from April to June, during which the Es from the wet soil zone accounted for 66% of the total Es on average. Among the five empirical models, the L-ww (constructed model based on LAI data during the “well-watered” period) and LT-ww (constructed model based on data of LAI multiplied by soil temperature at 20 cm depth during the “well-watered” period) models had the lowest Es prediction errors (RMSE of 0.25 and 0.20 mm d−1), and the highest modelling efficiency (0.49 and 0.63) and index of agreement (0.84 and 0.88) for the “whole year” and “well-watered” periods, respectively. In conclusion, for predicting stand transpiration more accurately using a crop coefficient model, the quantitative relationship between LAI and Kcb needs to be adjusted for stand age and soil water availability. Spatial heterogeneity in Es should be considered when estimating Es in drip irrigated plantations of P. tomentosa and other tree species.

Adsorption/desorption characteristics and enrichment of quercetin, luteolin and apigenin from Flos populi using macroporous resin

In this study, the adsorption/desorption characteristics of quercetin, luteolin and apigenin from Flos populi extract (Populus tomentosa Carrière, Salicaceae) on twelve macroporous resins (NKA-9, HPD-600, HPD-826, HPD-750, HPD-400, DM-130, AB-8, SP-825, X-5, D-101, HPD-100, HPD-200) were evaluated. Both high adsorption and desorption capacities of quercetin, luteolin and apigenin from Flos populi extract on SP-825 resin indicated that SP-825 resin was appropriate and its data were well fitted to the Langmuir and Freundlich isotherms. To get the optimal separation process, the influences of factors such as flow rates, loading sample volumes, concentrations of desorption solution were further investigated. Column packed with SP-825 resin was used to perform dynamic adsorption and desorption experiments. After one round of treatment, the contents of quercetin, luteolin and apigenin in the final products were 3.75-fold, 3.67-fold and 3.54-fold increased with recovery yields of 87.25, 85.19 and 82.22%, respectively. The results showed that the preparative enrichment of quercetin, luteolin and apigenin was available via adsorption and desorption on SP-825 resin. This method is a promising basis for the large-scale preparation of quercetin, luteolin and apigenin from Flos populi.

Leaf Phenology Variation within the Canopy and Its Relationship with the Transpiration of Populus tomentosa under Plantation Conditions

To provide a theoretical basis for developing intensive cultivation practices for Populus tomentosa plantations, the leaf phenology variation within the canopy and its relationship with transpiration of well-watered P. tomentosa tree in a dense plantation were investigated. The variation in canopy light interception, indicated by the ratio between net radiation under (Rn-u) and above (Rn-a) canopy, with leaf development was also studied. During the growing season, the achievement of maximum leaf number tended to be later in higher parts of the canopy. In the lower and middle canopy, the leaf number maximized earlier in the east-facing side than in the west-facing side, but this difference disappeared in the upper canopy. The Rn-u/Rn-a was stable in May, but declined and then varied steadily until late August. Generally, in May, the crop coefficient (Kcb) of the tree reached its highest level and was not correlated with leaf area (LA) in all layers (p &gt; 0.05). However, it increased linearly (p &lt; 0.001) with LA in the layers above a canopy height of 3 m from June to late August, and most of its variation was explained by LA in the 5–7 m layer. After late August, Kcb decreased linearly with decreasing LA in all layers (p &lt; 0.001). Consequently, a temporal ecological strategy seems to be adopted by P. tomentosa leaves in different layers and azimuthal sides for efficient light acquisition. The contribution of the different canopy layers to tree transpiration can vary, with the leaves in the upper and all layers mainly controlling transpiration in summer and in spring and autumn, respectively.

Preparation and Antifungal Activities of Microcapsules of Neem Extract Used in Populus tomentosa Deteriorated by Three Mold Fungi

Microcapsules of neem extract (MNE) were observed using an optical microscope (OM) and scanning electron microscope (SEM). The antifungal activity of the extract was evaluated by an agar diffusion assay. The MNE were induced into the wood material by a full-cell process. The diameters of the microcapsules were measured by OM, and the distribution of microcapsules in wood was observed by SEM. Wood blocks of Populus tomentosa were treated with the MNE, neem extract (NE), and an acid mixture of melamine formaldehyde resin (MF) and sodium dodecyl sulfate (AMS); their antifungal properties against Penicillium citrinum, Trichoderma virens, and Aspergillus niger were visually assessed. The microcapsules prepared by MF, 1% sodium dodecyl sulfate (SDS), and 10% NH4Cl showed regular shape and good dispersion. The agar diffusion assay showed that the neem extract had significant inhibition against all tested fungi, and the optimum concentration of NE was 10%. The diameters of the microcapsules were normally distributed in a range of 0.4 μm to 4 μm, and the microcapsules were unevenly distributed in the vessels and surface of Populus tomentosa. Wood specimens treated with MNE observed complete inhibition to all studied fungi, and the mark grades of specimens treated with MNE against three fungi all reached 5 (no growth of fungi).