Objective: This study aims to explore the effects of biochar and organic fertilizer on soil quality in a poplar (triploid Populus tomentosa) plantation by using the decomposition of standardized wood stakes from different tree species, together with changes in soil enzyme activity related to soil nutrient cycling. Method: In a split-plot experiment, manure (M: 0, 3, 9 t·hm^?2) and biochar (B: 0, 2.5, 10 t·hm^?2) were respectively used as whole plot and split-plot to treat the sandy loam soil of triploid P. tomentosa plantation (a total of 9 soil treatments, M0B0, M0B2.5, M0B10, M3B0, M3B2.5, M3B10, M9B0, M9B2.5, and M9B10). Wood stakes of three tree species (poplar, P. tomentosa; aspen, Populus tremuloides; pine, Pinus taeda) were installed by both horizontally placing on the soil surface (surface stakes) and vertically inserting into 20 cm of mineral soil (mineral stakes) to serve as decomposition substrates. After two years of soil treatments, acid phosphatase, cellulase, α-glucosidase, β-glucosidase, N-acetyl-β-D-glucosidase, and aryl sulfatase activities in 0?20 cm soil layer were measured; and in 2.5 years after wood stake installation, the decomposition (density loss) and water content of the wood stakes were measured. Result: The M9B10 treatment significantly increased soil water content, especially during the rainy season. As for enzymes, the 9 t·hm^?2 manure significantly increased soil acid phosphatase activity. Compared to the un-treated M0B0, M3B10, M9B0, and M9B2.5 treatments significantly increased soil α-glucosidase activity, M0B10, M3B2.5, and M9B2.5 treatments significantly increased soil β-glucosidase activity, M3B2.5, M9B0, M9B2.5, and M9B10 treatments significantly increased soil N-acetyl-β-D-glucosidase activity, and all soil treatments significantly increased soil aryl sulfatase activity by 62.84%–248.14%. Wood stakes decomposition rates varied dependent on the placement positions (mineral > surface) and tree species (the two Populus > pine). On the soil surface, M3B0 and M9B2.5 treatments significantly increased the decomposition of wood stakes of three species, while M0B10, M3B2.5, and M3B10 treatments accelerated the degradation of the two Populus wood stakes as compared to the M0B0. In the mineral soil, as compared to the un-treated M0B0, M3B0 increased poplar stake decomposition, while all soil treatments except M3B2.5, M3B10, and M9B10 accelerated the decomposition of loblolly pine stakes. Conclusion: Soil biochar and manure amendments increase soil water content and enzyme activities as well as accelerate wood stake decomposition both on the soil surface and in the 20 cm mineral soil layer. They can be used to enhance soil quality in plantations. However, more field studies are necessary to make appropriate soil management policies based on soil conditions and climates.

Objective: This study aims to find the response and sensitivity of multiple tree species in urban forests to drought under diverse habitat conditions and provides a reference basis for rapid screening of adaptive tree species with high drought tolerance and healthy growth. Method: The measurement of annual shoot lengths (ASL) of 24 tree species with different age (early-young, young, and mature) in diverse habitats (closed forest, open forest, and avenue tree) between 2005 and 2020 was conducted, and the calculation of the relative ASL increase (RAI, the ratio of the ASL increase between before and after drought to the non-drought period) was used to indicate trees’ growth sensitivity in response to drought stress. Result: 1) Trees’ ASL was decreasing consistently with age, and the early-young trees growing in the shaded forests and young trees in the open stands showed relatively higher ASL values than the mature trees planted along the avenues. 2) The correlation between the ASLs and the standardized precipitation indices of the present-year and the previous-year was significantly strong (r²=0.687, P<0.01),Fraxinus excelsior and Quercus robur in the shaded forest, as well as F. excelsior and Q. robur in the open forests, were found to be non-sensitive to drought, but the other 14 tree species were drought-sensitive. 3) The mean value and minimum of the leaf water potential at the turgor loss point significantly correlated with each other （r²=0.549, P<0.01）, but did not correlate to growth sensitivity. 4) Xylem structure significantly correlated with RAI （r=0.553, P<0.01）and growth sensitivity（r=0.545, P<0.01）, and the ASL performance of the ring-porous species was better than semi-ring-porous species and diffuse-porous species. Conclusion: Although the responses of tree annual shoot growth to drought were affected by multiply interior and external factors, ASL measurement was recommended to be an easy, fast and effective method to assess tree growth vitality and adaptability in response to their habitats, this method was also helpful to select urban tree species with high tolerance under climate change impacts.

Objective: The biomass distribution characteristics and the species-specific allometric equations of the major afforestation tree species in Northeast China were analyzed in this study, to provide model reference for the biomass estimation of forests in this area. Method: This study was based on the biodiversity and ecosystem function experiment plantation in Shulan, Jilin Province. The well-growing trees in the forest plot were selected for whole-plant sampling from July to August 2021, and 15 to 21 individuals of each tree species were selected. The biomass of each tree’s roots, stems, and leaves were measured, respectively. Meanwhile, the aboveground (i.e., leaves + stems) biomass and the total (i.e., leaves + stems + roots) biomass were measured. The species-specific and all-tree species allometric models were established based on the dependent (i.e., tree height and base diameter) and independent variables (i.e., different organs, aboveground, and total biomass) using univariate linear, multivariate linear, and power functions. Coefficient of determination, parametric significance, and the Akaike Information Criterion (AIC) were employed to evaluate the models. Result: 1) The biomass distribution of the 10 tree species exhibited generally the highest proportion in stems (45%) followed by roots (35.5%), and the lowest proportion in leaves (19.5%). With the increase in base diameter, the proportion of stem biomass showed an upward trend, the proportion of leaf biomass showed a downward trend, while the proportion of root biomass did not change significantly. 2) The biomass equations in the form of power functions were demonstrated to be the best-fit equations. Specifically, the form of Y=a(D²H)^b and Y=aD^b were selected as the optimal model for single-tree species, while the form of Y=a(D²H)^b and Y=aD^bH^c were selected as the optimal model all-tree species biomass models. Conclusion: The models in the form of a power function were identified as the optimal models, equations based on single tree species have high accuracy for species-specific biomass estimation, while the equation of whole tree species have wider applicability for regional biomass estimation.

Objective: In this paper, we explored the gender-differential responses of dioecious plants to interspecific competition using Rhamnus schneideri var. manshurica, with a view to providing a theoretical basis for the analysis of life history strategies under competitive stress. Method: A permanent fixed monitoring sample plot of 23.76 hm² was established in Jiaohe City, Jilin Province in July 2009. The diameter at breast height(DBH), tree height, first live branch height, and crown width of woody plants in the sample plots were measured, and their location coordinates were recorded, and retested in July 2014 and July 2019, respectively. A certain number of male and female plants were selected in the sample plots in 2019 flower and fruit period and 2020 fruit period. The new shoot, leaves, flowers and fruits of each Rhamnus schneideri var. manshurica plant were surveyed and sampled, and the biomass of each component was calculated for each plant. Quantifying the intensity of competition from neighboring heterospecific trees by means of the Hegyi index; differences in vegetative growth and reproduction in response to the intensity of interspecific competition between male and female individuals were compared using linear regression; differences in fruit number and fruit biomass of Rhamnus schneideri var. manshurica female trees in 2019 and 2020 were tested by means of ANOVA. Result: The Growth at DBH of female trees was significantly inhibited by interspecific competition (P<0.05), whereas the growth at DBH of male was not significantly correlated with the intensity of competition. Reproduction of both male and female plants was not significantly affected by competition, while new shoot and foliage biomass of female trees was significantly inhibited by interspecific competition during the flower period (P<0.05). Female trees had significantly higher fruit number and fruit biomass in the 2020 fruit period than in the 2019 fruit period (P<0.05), and their vegetative biomass was significantly suppressed by interspecific competition in 2020 (P<0.05), while it was not significantly affected by interspecific competition in 2019. Conclusion: There are no gender differences in the response of reproductive activity to interspecific competition in Rhamnus schneideri var. manshurica, and reproduction of both male and female plants was not affected by the intensity of competition. In contrast, the response of vegetative growth to interspecific competition showed significant gender differences, interspecific competition had more negative effects on the nutritional growth of female trees. The greater the input of female trees to reproduction, the greater their vegetative growth was negatively affected by interspecific competition. This suggests that an increase in reproductive inputs of female trees leads to an increase in the negative effects of interspecific competition on female trees.

Objective: Quercus palustris is mainly propagated by seeds, but it is very difficult for seed storage due to its sensitiveness to the desiccation. This study aims to explore the changes of water phases during desiccation of Q. palustris seeds and find out the semi-lethal and lethal water contents, so as to provide a theoretical basis for scientific storage and transportation of seeds, and provide a new technique for the study of other recalcitrant seeds. Method: The newly collected Q. palustris seeds were used as research materials in this study. The natural drying method was used to reduce moisture content of seeds. Nuclear Magnetic Resonance (NMR) technology was used to detect the changes of water phases and content in seeds during the desiccation process. Combined with the germination percentages of seeds under different water contents, the effects of water phases on seed dehydration were analyzed. Result: 1) The moisture content of fresh Q. palustris seeds was 38.0%, and the germination percentage was 96.00%. With the decrease of moisture content, the germination percentage decreased continuously. The seeds died completely when moisture content decreased to 10.0%. According to the fitting curve calculation, the semi-lethal moisture content was 17.39%. 2) The NMR spectrum showed that there was a significant linear relationship between the water content (x) of Q. palustris seeds and the peak area (y) of the NMR relaxation spectrum, and the linear regression equation was: y=21132x+698.05, R²=0.9996. 3) From left to right, the peaks in T₂ relaxation spectrum of transverse relaxation were bound water (T₂₁), immobile water (T₂₂), and free water (T₂₃). 4) The proportion of free water in fresh Q. palustris seeds was the highest, accounting for 66.39%, while bound water and immobile water were 4.28% and 29.07%, respectively. In the process of desiccation, the binding capacity, peak area and peak proportion of water in each phase were in dynamic changes. During the desiccation process, the bound water was stable and hard to be removed. The peak time of immobile water generally shifted to the left, and the binding ability was enhanced. The free water had stronger fluidity, and the peak time shifted to right during the desiccation. When the water content was reduced to 25.0%, the peak area of free water decreased significantly, while the immobile water and bound water increased significantly, and the peak proportion also increased. When water content decreased to 20.0%, the peak area of bound water and its proportion increased, while the peak area of immobile water decreased. Subsequently, the peak area of water in each phase decreased. Conclusion: With the extension of dehydration time, the germination percentage of Q. palustris seeds decreases, and the water content during its storage and transportation should not be lower than the semi-lethal water content of 17.39%. In the process of desiccation, there are three water phases in the seeds, namely bound water, immobile water and free water. Desiccation has a great effect on the quality of Q. palustris seeds. During the desiccation, the water binding ability of seeds becomes stronger to slow down the loss of water and maintain the stability of cell membrane.

Objective: In this study, the number and opening angle adjustment of Torreya grandis cv. Merrillii skeleton branches were performed in order to explore their effects on the formation of mixed bud and fruit setting, so as to provide a scientific basis for tree cultivation of T. grandis cv. Merrillii young forest and to promote early fruiting and high yield. Method: Single factor and interactive experiments with the number and opening angle of skeleton branches were conducted to investigate the development of flowers and fruits, proportion of mixed buds, and fruit setting rate. Light intensity, endogenous hormone content, photosynthetic carbon assimilate content, carbon nitrogen ratio and other indicators were determined. Result: The number adjustment of skeleton branches had a great effect on the light transmission ability, and 3 skeleton branches (N3) and 4 skeleton branches (N4) significantly increased the light intensity in the central and lower layers of T. grandis cv. Merrillii canopy, which was conducive to improving the utilization of light energy and promoting flowering and fruit setting. Treatment with an opening angle of 60° (A60°) significantly reduced the contents of auxin (IAA), gibberellin (GA₁ and GA₃) in mixed buds, increased the ratio of ABA/IAA, ABA/GA₁₊₃, CTKs/IAA and CTKs/GA₁₊₃, and significantly increased the contents of sucrose and starch, and C/N ratio in mixed buds. The proportion of mixed buds in a tree significantly increased. The interactive treatment with the number and opening angle of skeleton branches effectively improved the light intensity and the net photosynthetic rate. Under the treatments of N3-A60° and N4-A60°, the light intensity of the central layer reached 25 000–27 000 lux, and that of the lower layer reached 11 000–14 000 lux, and the net photosynthetic rate reached 9.07 and 9.70 μmol CO₂·m^?2 s^?1, respectively. In addition, N3-A60° and N4-A60° also significantly increased the contents of GAs and some cytokinins in young fruits, significantly promoted the accumulation of sucrose and total soluble sugars in fruits, and improved the fruit setting rate. Conclusion: Both the number and opening angle of skeleton branches can promote the flowering and fruit setting of T. grandis cv. Merrillii young forest, and the interaction between 3 and 4 skeleton branches with opening angle of 60° has the best promotion effect.

Objective: Auxin plays an important regulatory role in plant growth and development via its signal transduction. Auxin receptor is one of the most critical components in auxin signaling pathway. Therefore, it is of great significance to study the roles of auxin receptor family gene (FBL) in the growth and development of poplar to reveal the mechanism of auxin in the secondary growth of woody plants. In this study, the sequence structure, tissue specific expression and subcellular localization of PagFBL3 in poplar ‘84K’ (Populus alba × P. glandulosa) were investigated to exlore the effects of PagFBL3 on stem secondary growth by creating transgenic poplar overexpressing PagFBL3, so as to provide support in further elucidating the mechanism of action of auxin receptors in secondary stem growth. Method: The bioinformatics methods and related software were used to analyze the phylogenetic relationship, sequence similarity and biochemical characteristics. PagFBL3 gene was cloned and identified from 84K poplar, and its expression levels in roots, young leaves, mature leaves, young stems, vascular cambium, xylem and phloem were detected by real-time quantitative PCR. The fusion expression vector 35S::PagFBL3-GFP was constructed using the Gateway technique, and the subcellular localization of PagFBL3 was analyzed by transient transformation of tobacco leaf epidermal cells. At the same time, the coding region of PagFBL3 was recombined into the PMDC32 vector to construct the plant overexpression vector 35S::PagFBL3. The transgenic poplar was created by Agrobacterium-mediated transformation method. The effects of overexpressing PagFBL3 gene on growth and development of transgenic poplar stem were analyzed by phenotype and tissue sections assays. Result: PagFBL3 gene was able to encode 571 amino acid residues and its encoded protein was localized in the nucleus. PagFBL3 gene was expressed in roots, stems and leaves, and was highly expressed in mature leaves and secondary stems. Based on resistance screening and molecular identification, 11 transgenic poplar lines overexpressing PagFBL3 were generated, and two transgenic lines with high expression levels were selected for further functional analysis. Compared with non-transgenic 84K poplar plants, overexpression of PagFBL3 gene promoted xylem development, significantly increased xylem width of transgenic poplars, and improved stem radial growth. The two transgenic lines showed 6.7% and 8.5% increase in ground diameter, and 17.3% and 19.9% increase in the xylem width of the fifteen internodes, respectively. In addition, overexpression of PagFBL3 gene promoted plant height of transgenic poplar. The two transgenic lines showed 6.3% and 6.9% increase in stem height, respectively. Conclusion: PagFBL3 gene is mainly expressed in mature leaves and secondary stems and plays a role in regulating the radial growth of poplar by affecting xylem development and improving xylem width. This study provides a reference for further revealing the molecular mechanism of PagFBL3 gene involved in the stem growth and development of poplars.

Objective: This study aims to investigate the growth and physiological characteristics of Eucalyptus grandis in response to Funneliformis mosseae and Ralstonia solanacearum, so as to provide some theoretical support for application mycorrhizal technology to prevent and control Eucalyptus bacterial wilt disease. Method: E. grandis seedlings were used to study the effects of F. mosseae mycorrhizal during the infection course of R. solanacearumon the host plant growth and defense-related enzyme activities. Result: 1) F. mosseae was well symbiotic with the root of E. grandis. The plant height, ground diameter, dry weight and root-shoot ratio of mycorrhizal Eucalyptus were 2.30, 4.38, 2.75 and 1.71 times higher than those of non-mycorrhizal Eucalyptus, respectively. Compared with non-mycorrhizal E. grandis seedlings, the root length, root diameter, root surface area, root volume, root-shoot ratio, and nitrogen, phosphorus and potassium content in roots and leaves of mycorrhizal E. grandis seedlings were significantly increased (P<0.05). 2) With the increase ofR. solanacearum infection time, activities of defense-related enzymes in mycorrhizal Eucalyptus leaves were significantly higher than those in the corresponding non-mycorrhizal Eucalyptus leaves. Peroxidase (POD), polyphenol oxidase (PPO) and β-1,3-glucanase activity increased firstly and then decreased in tissues of mycorrhizal Eucalyptus, reaching the peak at 48, 24 and 144 hpi, respectively. In leaves of mycorrhizal Eucalyptus, activities of superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL) and chitinase were first increased then declined, reaching the peak after 96 hpi of R. solanacearum infection. 3) The control effect of inoculating F. mosseae on bacterial wilt of Eucalyptus was 81.67%. Conclusion: Inoculation with F. mosseae significantly promotes the growth of Eucalyptus seedlings. After infection with R. solanacearum, activities of defense-related enzymes rapidly and greatly increase in the mycorrhizal Eucalyptus seedlings, enhancing the host defense ability against R. solanacearum.

Objective: The shrinkage model of wood control volume is established, the wood profile density measured by X-ray method is used to calculate the moisture content distribution, which provides a new method for the calculation of wood moisture content distribution. Method: The wood before oven drying is divided into control volume along the thickness direction, the oven-dry shrinkage parameter is introduced, the thickness of the wood control volume after oven drying is calculated according to the wood shrinkage principle, the density of the control volume is calculated by the wood profile density, and the calculation model for computing the moisture content of the wood control volume before oven drying is constructed. In the calculation model, the moisture content of the wood control volume before oven drying and the thickness and density of the wood control volume after oven drying are highly coupled. Therefore, the results of the above variables are computed by developing an iterative algorithm and compiling a calculation program in Matlab software. The algorithm takes the actual thickness of the wood after oven drying as the constraint condition to continuously correct the oven-dry shrinkage parameter of the wood, it can effectively avoid the calculation error caused by the deviation between the introduced value of oven-dry shrinkage and the real value. At the same time, this study carried out Populus tomentosa in the convective drying test of wood, the calculation method of this study is used to calculate the moisture content distribution of wood in different drying stages, and compared with the actual average moisture content of wood (weighing method) and the moisture content distribution calculated by method of assuming uniform shrinkage in the thickness direction of wood. Result: The average moisture content of wood measured by the calculation method in this study is very close to that measured by the weighing method, and the correlation coefficient square (R²) is more than 0.999 2. Compared with uniform shrinkage method the distribution of wood moisture content calculated by the two calculation methods is consistent above FSP (fiber saturation point); Below FSP, the moisture content calculated by the calculation method in this study is relatively low in the wood surface layer, relatively high in the wood core layer, and large moisture content gradient in the wood core and surface layer. When the wood is dried for 45 h, 69 h and 134 h respectively, the moisture content differences of core and surface wood calculated by the calculation method of this study are 22.61%, 15.65% and 5.58% respectively. The moisture content differences of core and surface wood calculated by existing uniform shrinkage method are 18.06%, 11.51% and 4.27% respectively. The absolute deviations of the two calculation methods are 4.55%, 4.14% and 1.34% respectively. Compared to the uniform drying method, the accuracy of the moisture content distribution of wood measured by the calculation method in this study was improved by 3.80%, 6.00% and 4.04% at 45 h, 69 h and 134 h respectively. Conclusion: The control volume shrinkage model constructed in this study fully considers the non-uniform shrinkage caused by moisture content distribution, which can make up for the deficiency of assuming uniform shrinkage of wood in existing uniform shrinkage method so as to improve the calculation accuracy of wood moisture content distribution and provide an effective technical means for the dynamic detection of wood moisture content distribution.

Objective: In order to provide guidance and reference for the pyrolysis and utilization of bamboo to become high-quality gas fuel and carbon materials, the pyrolysis properties of the cellulose, hemicellulose and lignin extracted from bamboo fiber and parenchyma under different pyrolysis conditions were explored. The effects of pyrolysis process on solid residues and volatiles composition were analyzed to provide technical guidance for the development of clean and efficient gradient carbonization and physical activation processes. Method: The pyrolysis characteristics and relative gas content of 3-year-old moso bamboo powder, bamboo fiber and parenchyma separated by water separation and three main components extracted by chemical method were analyzed semi quantitatively by TG-FTIR at heating rates of 10, 20 and 30 ℃·min^?1. Result: Under 10 ℃·min^?1 and N₂ atmosphere, the main pyrolysis stage of bamboo powder, bamboo fiber and parenchyma were 180-400 ℃, and the final solid residues were 19.8%, 21.3% and 17.5%. The main pyrolysis stages of cellulose, hemicelluloses and lignin in bamboo fiber and parenchyma occurred at 250-400 ℃, 190-365 ℃ and 100-500 ℃ respectively. The solid residues of cellulose, hemicelluloses and lignin in the two cells were 9.9% and 6.3%, 20.2% and 18.3%, 30.4% and 25.8%. TG-FTIR analysis showed that the gases produced by pyrolysis of all samples were mainly composed of CO₂, CO and CH₄. The highest relative content of functional group compounds such as C=O and C—O—C in cellulose pyrolysis products was 65.8%. The highest relative content of CO₂ in hemicelluloses was 42.7%. The content of combustible gas (CH₄, CO) in the gas products of lignin was the highest, which was 27.3%. With the increase of heating rate, the relative content of functional group compounds such as C=O and C—O—C in cellulose pyrolysis products and syngas in lignin decreased by about 5%, and the content of CO₂ in hemicellulose increased by nearly 10%. Conclusion: 1) Bamboo powder, different types of cells and their three components had different pyrolysis characteristics. The solid residue of parenchyma-cellulose was the lowest and that of fiber-lignin was the highest. 2) The pyrolysis gas composition types of bamboo powder, bamboo fiber and parenchya and three main components were basically the same, but the relative contents were obviously different. The main gas products of the cellulose pyrolysis were compounds containing C=O and C—O—C functional groups, the main products of hemicellulose pyrolysis were CO₂ and compounds containing C=O functional groups, and the main products of lignin pyrolysis were CO₂ and compounds containing C—O—C functional groups. 3) With the increase of heating rate, the TG/DTG curves of bamboo powder, different types of cells and three main components moved to the high temperature side as a whole. The FTIR absorption peak intensity of pyrolysis gas products increased, in which the relative content of CO and compounds containing C=O functional groups decreased gradually.

Objective: The study explored agarwood formation process of Aquilaria sinensis and physiological reaction by trunk-filling high-pressure carbon dioxide gas, with the aim to find available solution to induce agarwood formation by carbon dioxide and to understand the physiological mechanisms. Method: A randomized block design was used to deal with eleven-year-old trees. The inflating CO₂ was conducted at every 7 days (T1) and 15 days (T2) interval for three months. POD (peroxidase), SOD (superoxide dismutase) and CAT (catalase) activity and MDA (malonaldehyde) content were detected on the 30th, 60th, 90th, 120th,150th day after first inflating. The content of alcohol soluble extraction and agarotetrol, and the discoloration range of stem wood were determined in seven months and ten months after treatment. Result: 1) It was found that the stem-inflated CO₂ could speed up the transformation of starch granules in ray parenchyma cells and vessels. With the increase of induction time, the tylosis accumulated could completely blocked the ray cells and vessels in 10 months after T1 treatment. 2) Compared to CK1 and CK2, the discoloration ranges of stem xylem with CO₂ treatments was more longer. T1 treatment produced the maximal discoloration ranges of the longitudinal length of 26.45 cm, the horizontal width of 4.17 cm, and the radial length of 9.87 cm.3） The content of alcohol soluble extraction and agarotetrol gradually increased with T1 and T2 treatments, which were significantly higher than that of CK1 and CK2. 4) After 60 days under the T1 treatment, POD and CAT activity reached the peak value and then decreased slowly. However, POD activity was still higher than that of CK2. while the CAT activity had no significant difference with CK2 on the 150th days. SOD activity decreased in the first 90 days and then slowly increased. The content of MDA decreased firstly and dropped to the lowest value that dramatically lower than CK2 on the 90th day. On the 150th days, SOD activity and the content of MDA of T1 had no obvious difference compared with CK2. Conclusion: 1）Exogenous CO₂ could significantly promote conversion of starch in the xylem ray cell, which lead to more blockage with tylosis accumulating in vessel and ray parenchyma cell. 2) Exogenous CO₂ could induce the xylem discoloration, and the lengths in longitudinal, transverse and radial direction were all longer than the control. 3) Exogenous CO₂ could induce A. sinensis trees to form blocky agarwood with exquisite texture. The alcohol-soluble substances and agarotetrol contents was respectively 21.27% and 0.29% in the 10 months after the optimal treatment of T1, and was 1.42 and 2.11 times of that of CK1. 4) Exogenous CO₂ could activate the defense reaction of A. sinensis trees.

Objective: In order to screen suitable wood raw materials for the production of low odor wooden household materials, and to provide the treatment object and basis, the volatile organic compounds(VOCs) composition and odor substance characteristics of main plantation wood in China were studied and determined in this paper. Method: The VOCs compositions of bark/heart wood/sapwood of five main plantations in China, including Populus cathayana, Eucalyptus sp., Cunninghamia lanceolata, Pinus massoniana and Cinnamomum camphora, were analyzed qualitatively and quantitatively by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). At the same time, the odor types and odor intensity of main odor substances in each part of wood were characterized according to the combined sniffing instrument Result: The VOCs components of Populus cathayana, Eucalyptus sp., Cunninghamia lanceolata, Pinus massoniana and Cinnamomum camphora include terpenes, alcohols, ketones, acids, aldehydes, esters, phenols and furan heterocyclic compounds. VOCs are mainly distributed in the heart wood/sapwood of Cinnamomum camphora, Pinus massoniana, and in the heart wood of Cunninghamia lanceolata and Eucalyptus sp. Linalool and safrole are the specific and rich components in Cinnamomum camphora. α-pinene riched in pine heart wood/sapwood also exists in a small amount in Cinnamomum camphora. α-cedrene and β-cadinene are the two largest components in heart wood of Cunninghamia lanceolata. Correspondingly, δ-cadinene and α-muurolene are the two largest components in heart wood of Eucalyptus sp. In addition to a small amount of salicylaldehyde, benzaldehyde and furan components in the bark, the VOCs content in the heart wood/sapwood of Populus cathayana is very small. Wood odor mainly comes from terpenes, alcohols, ketones, aldehydes and esters in wood VOCs. Linalool, safrole, eugenol and β-caryophyllene are the main odor characteristic substance of Cinnamomum camphora. In Pinus massoniana, α-pinene is rich and had the typical aroma of rosin and turpentine. However, the odour intensity of β-caryophyllene, with lower mass concentration, is equal to that of α-pinene. The odor substances in cunninghamia lanceolata and Eucalyptus sp. are concentrated in their heart wood, and the odor intensity of α-muurolene is the highest. Furthermore, the same VOC component shows different odor characteristic when its content is different. And different people have different senses when smelling the same wood, including Eucalyptus sp., Cunninghamia lanceolata, Pinus massoniana and Cinnamomum camphora. Conclusion: The sapwood of Eucalyptus sp., Cunninghamia lanceolata, and the heart wood/sapwood of Populus cathayana are the best choice for the preparation of low total volatile organic compounds (TVOC) and low odor wooden household products.

Objective: The purpose of this study was to investigate the crack behavior and mechanism of gradient structure in bamboo under grain splitting and radial compression to provide a theoretical basis for the application in engineering materials. Method: The external force of grain splitting and radial compression were applied on bamboo to induce initial crack. Field emission scanning electron microscope (FESEM) was conducted to observe the fracture appearance and crack propagation in vascular bundles, parenchyma and cells along the transverse and longitudinal direction. Micro-mechanical properties of fibers and parenchymal cells wall were measured to further illustrate the fracture mechanism stemming out from the bamboo’s hierarchical configuration. Result: The FESEM results were as follows: grain splitting-induced cracks appeared and grew in the middle lamellae (ML) of fiber and parenchymal cells along the transverse and longitudinal direction, which resulted in the transverse tearing of vascular bundles and parenchyma. Radial compression-induced cracks also appeared and grew in the middle lamellae (ML) of fiber and parenchymal cells along the transverse and longitudinal direction. In the transverse direction, dendritic cracks occurred on the surface of the fibrous sheath and make the vascular bundles disperse into fibrous bundles. In the longitudinal direction, fibers separated and parenchymal cells exfoliated. The nanoindentation results showed that the indentation modulus and hardness of middle lamellae were lower than that of cell wall layer in fiber and parenchymal cells, which was prone to fracture. Conclusion: In this study, by observing the fracture morphology and crack propagation path of vascular bundles and parenchyma under grain splitting and radial compression, it was found that the vascular bundles split into fiber bundles and interlaminar fracture occurred in the parenchyma. It was found that the fiber and parenchymal cells could be separated by the transverse and longitudinal fracture of the middle lamellae (ML) under the grain splitting and radial compression because of the lower mechanical strength.

Tree mortality under drought stress is an important physiological and ecological process that alters the structure and function of forests and influences forest management decisions. Under drought stress conditions, the water and carbon metabolisms in trees have malfunctioned, which leads to tree mortality. However, the exact physiological mechanisms of tree mortality in drought-stressed environments and the physiological-ecological response of various organs in trees during the drought-rewatering process have not yet been elucidated, and this scientific question is currently at the forefront of research worldwide. There are at least three hypotheses for the mechanism of drought mortality in trees: hydraulic failure, carbon starvation and the biological attack hypothesis. The hydraulic failure hypothesis suggests that under drought stress, the xylem of a tree reaches a threshold of embolism and is unable to restore water conduction, thus causing the tree to die of dehydration and desiccation; the carbon starvation hypothesis suggests that under drought stress, stomata are tightened or even closed and the tree cannot photosynthesize to produce organic matter, but the tree is depleted of available carbon in order to maintain its normal growth and metabolism; the biological attack hypothesis suggests that drought stress affects the distribution of biological factors and growth rate, making the tree vulnerable to attack by insects and pathogens, thus causing the tree to die. All hypotheses have been shown to explain a proportion of tree mortality, but are insufficient to explain all tree mortality in drought-stressed environments, and in particular the role of non-structural carbohydrate depletion in the mortality process remains unclear. This paper introduces water relations under drought stress and provides an overall account of the specific physiological processes involved in xylem embolism in the hydraulic failure hypothesis. It then discusses the effects of long-term drought stress on tree growth and development, transpiration, and the resulting changes in non-structural carbohydrate dynamics, explores the physiological mechanisms of individual tree organs during drought mortality, and summarizes the progress of research on physiological and ecological changes in trees during the drought-rehydration process. The current study shows that the hydraulic failure hypothesis remains the dominant hypothesis for tree mortality under drought stress, while the contribution of changes in non-structural organic carbon in trees to tree mortality remains undetermined. Post-drought rehydration can restore plant physiological functions and can compensate to a certain extent for the damage caused by drought, which affects both the morphological and physiological characteristics of trees. This paper also suggests directions for future research on tree mortality, with the aim of providing recommendations for the rational planting and management of trees in the future.