Contribution of aboveground litter to soil respiration in Populus davidiana Dode plantations at different stand ages

Soil respiration from decomposing aboveground litter is a major component of the terrestrial carbon cycle. However, variations in the contribution of aboveground litter to the total soil respiration for stands of varying ages are poorly understood. To assess soil respiration induced by aboveground litter, treatments of litter and no litter were applied to 5-, l0-, and 20-year-old stands of Populus davidiana Dode in the sandstorm source area of Beijing-Tianjin, equations were applied to China. Optimal nonlinear model the combined effects of soil temperature and soil water content on soil respiration. Results showed that the monthly average contribution of aboveground litter to total soil respiration were 18.46% ± 4.63%, 16.64% ± 9.31%, and 22.37% ± 8.17% for 5-, 10-, and ao-year-old stands, respectively. The relatively high contribution in 5- and 20-year-old stands could be attributed to easily decomposition products and high accumulated litter, resoectivelv. Also. it fluctuated monthly for all stand ages due to substrate availability caused by phenology and environmental factors. Litter removal significantly decreased soil respiration and soil water content for all stand ages （P 〈 0.05） but not soil temperature （P 〉 0.05）. Variations of soil respiration could be explained by soil temperature at 5-cm depth using an exponential equation and by soil water content at lo-cm depth using a quadratic equation, whereas soil respiration was better modeled using the combined parameters of soil temperature and soil water content than with either soil temperature or soil water content alone. Temperature sensitivity （Q10） increased with stand age in both the litter and the no litter treatments. Considering the effects of aboveground litter, this study provides insights for predicting future soil carbon fluxes and for accurately assessing soil carbon budgets.

Improved salt tolerance of Populus davidiana × P. bolleana overexpressed LEA from Tamarix androssowii

Development of transgenic plants with tolerance to environ- mental stress is an important goal of plant biotechnology. （LEA） proteins accumulate in seeds dur- ing late embryogenesis, where they protect cellular membranes and macromolecules against drought. In this work, we transferred the Tamarix androssowii LEA gene into hybrids of Populus davidiana xp. bolleana. We compared relative rates of height growth, chlorophyll fluo- rescence kinetic parameters, and leaf Na＋ levels of six TaLEA-containing lines with non-transferred plants （NT）, all grown under 0.8% NaC1 stress condition. Survival percentages of transgenic lines were all higher than for NT controls after rehydration and the sur- vival percentage of SL2 was five-fold higher than for NT controls. Seed- ling height increased 48.7% in SL2 （from the onset of induced stress to the end of the growing season）, 31% more than for the NT controls. Chlorophyll fluorescence kinetic parameters showed a marked increase in photosynthetic capacity in SL2 and SL5. Na＋ levels in young leaves of transgenic lines were lower than in control NT leaves, but higher in yel- low and withered leaves, indicating improved salt tolerance in transgenic lines.

Propagation techniques on root turion sprout browse of Populus davidiana Dode

The root segments selected from dominant trees of Populus davidiana Dode were taken as reproductive material and were buried in different depths to carry out the reproduction of root turion sprout. The affecting factors of germination rate, survival rate, and height growth for cutting wood of root sprout were comparatively analyzed. The results showed that the best suitable substrate for burying root is pearlite, with a germination rate of 15.16%. 3-4-cm root segments has the highest rate of germination (12.4%). The mixture of sand and soil (2:1) is the best cutting substrate, with a survival rate of 81.3%, while as to height growth of cutting wood, the mixture of turfy and soil (1:1) is the best. The cutting woods selected from different positions of stem show difference in height growth. The cutting wood from top stem is higher obviously than those from middle or low stem.

Effects of Water State of Soil on Ecological Boundary of Leaf Surface of Populus davidiana

The effect of water state of soil on eco-boundary over leaf surface was disscussed by takingPopulus davidiana as experimental material. The results show that to change soil water state by some methods was to adjust and control the forming quality of eco-boundary in fact. The plant in good water condition must be accompanied by thinner eco-boundary. This eco-boundary is beneficial to exchange and flow of the substances between plant and environment.

A new diterpenoid from the stem bark of Populus davidiana

A new diterpenoid, named populusol A （1）, was isolated from the methanolic extraction of the stem bark of Populus davidiana. The structure was elucidated on the basis of extensive 1D and 2D NMR as well as HRFAB-MS spectroscopic analysis.

A new salicin derivative from the stem bark of Populus davidiana

Phytochemical study on the BuOH-soluble fraction of the stem bark of Populus davidiana resulted in the isolation of a new salicin derivative （1）, named davidianoside. The structure was elucidated on the basis of extensive physicochemical and spectroscopic analyses.

FRACTAL DIMENSION OF POPULUS DAVIDIANA LEAF SURFACE ROUGH EXTENT

The rough extent of leaf surface may be described by protruding of waxes which like as wart and of stomatal aperture and of width of the cuticular ledge around guard cells. Because the morphology of the leaf surface has obviously similar itseIf, so one can use the theory of the fractal dimension to deal with the problems of leaf surface rough. The paper studied the rough extent and the result showed: with the leaf growing up, the waxes accumulate more and more, the leaf surface is more rough and the dimension is larger. The dimension D which indicates the rough extent of warts protruding is about 2. 10-2.20 on the above epidermis; On the beneath epidermis the dimension D of stomatal opening protruding is about 2.00-2.24, Maximum width L of cuticular ledge is about 1.0-7.4μm.

Promotion of biomass, photosynthesis, and root growth of seedling biomass, photosynthesis, and root growth of Populus davidiana × P. bolleana by two species of ectomycorrhizal fungi

The addition of ectomycorrhizal fungi(ECMF),beneficial rhizosphere microorganisms,to the soil can pro-mote plant growth and resistance.Here,Populus davidi-ana×Populus bolleana tissue culture seedlings were grown for 3 months in soils inoculated with one of the species,then seedlings were assessed for mycorrhizal colonization rate and growth,physiological and root traits.Suillus luteus and Populus involutus each formed ectomycorrhizal associa-tions with the seedlings.Seedling height,ground diameter,biomass,and leaf area were significantly greater after treat-ment with ECMF than in the non-inoculated controls.Treat-ment improved all physiological and root variables assessed(chlorophylls and carotenoids,cellulose,and soluble sugars and proteins;root length,surface area,projected area,mean diameter,volume,number of root tips).Seedlings inocu-lated with S.luteus outperformed those inoculated with P.involutus.

冀北山地山杨次生林优化经营策略

根据冀北山地山杨(Populus davidiana)林的立地条件、群落结构特征,划分为毛榛-山杨林、沟谷山杨林、绣线菊-山杨林和胡枝子-山杨林4种林型,分析了其生长发育特点和存在的主要问题。根据林型、立地和林分特征,针对不同林龄期和生长发育阶段的山杨次生林的生长规律及演替特点提出了混交造林、轻度抚育、疏伐更新和补植造林4项优化经营策略。