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991.
对河北、河南、山东、甘肃的4块毛白杨无性系测定林中约100个无性系进行了木材基本密度的测定,对木材基本密度在地点和无性系间的遗传变异进行了研究.结果表明:毛白杨无性系的木材基本密度平均值为0.4363g/cm3,木材基本密度在地点和无性系间均存在极显著差异.木材基本密度的无性系重复力为0.82~0.91,属于受遗传控制较强的材性性状.对生长和材性的相关研究表明,木材基本密度与生长性状(包括胸径、树高和材积)一般存在显著的负相关,但不同地点上表现为不同的正或负的相关关系 相似文献
992.
993.
P. S. Shanmugam R. Balagurunathan N. Sathiah N. G. V. Rao 《Journal of pest science》2007,80(3):175-181
Cotton bollworm, Helicoverpa armigera Hubner selected for five generations with Bacillus thuringiensis insecticidal crystal protein Cry1Ac in the laboratory developed 12.98-fold resistance. Resistance and susceptible populations
were mass crossed to study the dominance of resistance. The Cry1Ac—selected (BCR) population showed 5.8-fold resistance to
Cry1Aa and 5.04-fold resistance to Cry1Ab. The degree of dominance (D) was 0.34 and 0.40 for the R × S and S × R hybrids, respectively, which indicates incomplete recessive character of Cry1Ac resistance in the population. The estimated
realized heritability (h
2) and response quotient (Q) of resistance for Cry1Ac were 0.52 and 0.15, respectively. This indicated the lower phenotypic variation in the selected
population. The resistance risk assessment based on h
2 indicated that the resistance would increased tenfold after <9 generations for Cry1Ac in the resistant population. The results
show the ability of H. armigera to develop resistance against Cry1Ac and cross-resistance to Cry1Aa and Cry1Ab. 相似文献
994.
995.
996.
Annualized diameter and height growth equations for Pacific Northwest plantation-grown Douglas-fir, western hemlock, and red alder 总被引:2,自引:0,他引:2
Aaron R. Weiskittel Sean M. Garber Gregory P. Johnson Douglas A. Maguire Robert A. Monserud 《Forest Ecology and Management》2007,250(3):266-278
Simulating the influence of intensive management and annual weather fluctuations on tree growth requires a shorter time step than currently employed by most regional growth models. High-quality data sets are available for several plantation species in the Pacific Northwest region of the United States, but the growth periods ranged from 2 to 12 years in length. Measurement periods of varying length complicate efforts to fit growth models because observed growth rates must be interpolated to a common length growth period or those growth periods longer or shorter than the desired model time step must be discarded. A variation of the iterative technique suggested by Cao [Cao, Q.V., 2000. Prediction of annual diameter growth and survival for individual trees from periodic measurements. Forest Sci. 46, 127–131] was applied to estimate annualized diameter and height growth equations for pure plantations of Douglas-fir, western hemlock, and red alder. Using this technique, fits were significantly improved for all three species by embedding a multi-level nonlinear mixed-effects framework (likelihood ratio test: p < 0.0001). The final models were consistent with expected biological behavior of diameter and height growth over tree, stand, and site variables. The random effects showed some correlation with key physiographic variables such as slope and aspect for Douglas-fir and red alder, but these relationships were not observed for western hemlock. Further, the random effects were more correlated with physiographic variables than actual climate or soils information. Long-term simulations (12–16 years) on an independent dataset using these annualized equations showed that the multi-level mixed effects models were more accurate and precise than those fitted without random effects as mean square error (MSE) was reduced by 13 and 21% for diameter and height growth prediction, respectively. The level of prediction error was also smaller than an existing similar growth model with a longer time step (ORGANON v8) as the annualized equations reduced MSE by 17 and 38% for diameter and height growth prediction, respectively. These models will prove to be quite useful for understanding the interaction of weather and silviculture in the Pacific Northwest and refining the precision of future growth model projections. 相似文献
997.
杏属植物为蔷薇科李亚科杏属木本植物,本文研究的西伯利亚杏(Armeniaca sibirica (L.) Lam.)、东北杏(Armeniaca mandshurica (Maxim.) Skv.)和普通杏的野生类型-野杏(Armeniaca vulgaris Lam. Var.ansu (Maxim.) Yü et Lu),通常为落叶乔木或灌木,原产于大陆性干燥山区,多分布于半干旱、半湿润的风沙平原、山地和丘陵地区[1],喜光、抗寒、耐旱、耐瘠薄、耐风沙、根系发达、萌蘖能力强、容易繁殖、生长快、病虫害少,是固沙保土、涵养水源、改善生态环境的优良乡土树种,并且有较高的经济价值及药用价值[2-6],其中杏仁油可以作为功能性食品保健植物油、高级润滑油、高级化妆品和高级涂料的优质原料[7],也是值得推广种植的木本生物柴油物种[8],杏仁蛋白是一种食用价值极高的植物蛋白[9],杏壳作为优质活性炭的原料也是其重要的副产品[10]. 相似文献
998.
Takahisa Nakai Hiroyuki Yamamoto Masatoshi Hamatake Tetsuya Nakao 《Journal of Wood Science》2006,52(6):539-543
This study investigated the relationship between the initial shape of the stress (σ)-strain (ε) curve of a Chamaecyparis obtusa wood specimen subjected to repeated combined compression and vibration stresses at various angles between the fiber direction
and load direction and the piezoelectric behavior. The main findings of the study are: (1) the σ-ε curve became convex initially, and then the stress was proportional to the strain. The σ-ε curve had almost the same shape during both loading and unloading. (2) The σ-piezoelectric voltage (P) curve was nonlinear, with a maximal point or cusp on the curve, which had almost the same shape during both loading and
unloading, as was also observed for the σ-ε curve. (3) The plot of the first derivative of the stress [dσ/dε (= σ′)] against ε was nonlinear. The σ′-ε and P-ε curves at various angles were fairly similar. (4) The stress at the maximal point (or cusp) of the σ-P curve decreased with an increase in the angle between the fiber direction and load direction. The tendency of the stresses
was very similar to that of Young’s modulus and compression strength calculated from Hook’s law and Hankinson’s law, respectively. 相似文献
999.
1000.
湿地松与马尾松人工林木材物理力学性质的比较研究 总被引:2,自引:0,他引:2
庄奇 《中南林业调查规划》2004,23(2):58-59
通过对湿地松和马尾松人工林木材物理力学性质的测定和比较分析,结果表明:湿地松人工林木材密度、干缩系数和除冲击韧性以外的力学强度均稍大于马尾松人工林木材,而冲击韧性则恰恰相反.经差异显著性t检验表明:湿地松和马尾松木材物理力学性质指标中顺纹抗压强度、抗弯强度、弦面顺纹抗剪强度和冲击韧性差异极显著,气干密度、基本密度、径面顺纹抗剪强度和端面硬度差异显著,除此之外的其余指标差异不显著. 相似文献