高阶混合中立型差分方程的振动性质

研究了一类高阶混合中立型差分方程的振动性质,得到了这类差分方程的振动判据.     

中国成熟天然林土壤有机碳垂直分异特征

以分布在中国不同气候区的131个成熟天然林土壤为研究对象,测定不同土层(0～10、10～20、20～30、30～50和50～100 cm)土壤有机碳(SOC)密度,分析其与气象因子、土壤性质的关系,研究天然林SOC垂直分布特征及其影响机理。结果表明: 温带针叶林、温带落叶阔叶林、亚热带落叶阔叶林和亚热带常绿阔叶林0～30 cm土层SOC密度均随土壤深度增加而降低。在0～100 cm土层,SOC密度地带性分异明显,温带针叶林SOC密度显著高于温带落叶阔叶林,亚热带常绿阔叶林SOC密度显著高于亚热带落叶阔叶林。SOC密度与土壤黏粒、年降水量以及地上净初级生产力呈显著正相关,与土壤pH和年均温呈显著负相关。年降水量与年均温调节天然林SOC输入与输出,土壤pH与黏粒影响天然林SOC积累,对成熟的天然针叶林与常绿阔叶林进行有效保护,有利于增加我国森林土壤碳库。     

果实大小对油茶象幼虫生长的影响

为了明确小果油茶果实大小对油茶象幼虫生长发育的限制作用,采用Logistic方程对油茶象老熟幼虫体质量与其寄主果实体积大小的关系进行了拟合.结果表明: 油茶象幼虫体质量随果实体积增大而增长,符合Logistic模型;油茶象幼虫体质量增长符合边际效应递减原则,可分为快速增长阶段(<3.216 cm³,每果1头;<4.747 cm³,每果2头)和渐进增长阶段(>3.216 cm³,每果1头;>4.747 cm³,每果2头);油茶象寄生的最小果实阈值为1.500 cm³(每果1头)或2.539 cm³(每果2头).明确了落果中油茶象老熟幼虫逃逸的时间格局,果实收集后幼虫逃逸数量逐天递减,逃逸高峰期集中在6:00—10:00,占43.9%,尤以7:00—8:00为甚,占21.1%;幼虫体质量越大,逃逸越早.寄主果实大小对油茶象幼虫生长发育具有限制作用,亲代雌虫选择大果实产卵是增加后代适合度的一种行为适应策略.
     

小麦株高构成指数与茎秆抗弯能力模型

为了提高小麦的抗弯能力,本文建立了小麦茎干抗弯能力的多元参数平衡方程,其中参数为株高构成指数.通过非线性优化分析,得到了最优参数样本,优化后的小麦所能承受的最大水平力比试验样本提高了14.49%,并得到基部第二节间的株高构成指数对小麦抗弯能力影响最大的结论.最后,本文从遗传学、栽培学、耕作学以及化学调控等方面分析了优化小麦茎秆株高构成指数的可行性,对于生产实践具有一定的指导意义.     

Effects of 2＇-O-methyl nucleotide on ligation capability of T4 DNA ligase

To further understand the ligation mechanism, effects of 2＇-O-methyl nucleotide （2＇-OMeN） on the T4 DNA ligation efficiency were investigated. Fluorescence resonance energy transfer assay was used to monitor the nick-joining process by T4 DNA ligase. Results showed that substitutions at 5＇- and 3＇-ends of the nick decreased the ligation efficiency by 48.7% ± 6.7% and 70.6% ±4.0%, respectively. Substitutions at both 5＇- and 3＇-ends decreased the ligation efficiency by 76.6%±1.3%. Corresponding kinetic para- meters, Vmax, Kin, and kcat, have been determined in each case by using the Michaelis-Menten equation. The kinetic data showed that the 2＇-OMeN substitutions reduced the maximal initial velocity and increased the Michaelis constant of T4 DNA ligase. Mismatches at 5＇- and 3＇-ends of the nick have also shown different influences on the ligation. Results here showed that the sugar pucker conformation at 3＇-end impairs the ligation efficiency more profoundly than that at 5＇-end. Different concentrations of Mg2＋, Ca2＋, K＋, Na＋, and ATP were also demonstrated to affect the T4 DNA ligase activ- ity. These results enriched our knowledge about the effects of 2＇-OMEN substitutions on the T4 DNA ligase.     

Community characteristics and spatial distribution of dominant tree species in a deciduous broad-leaved forest of Muzhaling,Henan, China

Aims The objective of this paper is to quantify the species composition and spatial distribution pattern in a deciduous broad-leaved forest in temperate to subtropical ecological transition zone.
Methods In this study, a 3-hm² forest was selected in the temperate to subtropical ecological transition zone to analyze the community species composition, structure of diameter at breast height, community classification and spatial distribution pattern of dominant tree species.
Important findings Our results showed that in the plot there were 85 species, 52 genera and 31 families, mainly composed of Betulaceae, Celastraceae, Caprifoliaceae, Salicaceae and Aceraceae. Quercus aliena var. acuteserrata and Pinus armandii are dominant species of the community tree layer. The rare species and occasional species accounted for 20.0% and 28.24% of total species respectively. Size distribution of all species showed an invert J-shape, which indicates that the community is in a stable and normal growth status. Using multiple regression trees, the community in this plot can be divided into four categories: 1) Quercus aliena var. acuteserrata + Pinus armandii + Litsea tsinlingensis + Cerasus clarofolia + Lindera obtusiloba; 2) Quercus aliena var. acuteserrata + Salix chaenomeloides + Sorbus hupehensis; 3) Quercus aliena var. acuteserrata + Ailanthus altissima + Cerasus clarofolia + Litsea tsinlingensis; 4) Quercus aliena var. acuteserrata + Fraxinus chinensis + Litsea tsinlingensis + Philadelphus incanus. Under the completely random distribution model, the main species in the plot display clustered distributions, with the different species occurring in different habitat types, showing obvious terrain habitat preferences. However, under the heterogeneous Poisson distribution model, these species at different scales are distributed randomly or regularly. This study helps to understand the plant community species composition of the Muzhaling World Geopark, community structure and community distribution. The results show that the terrain habitat heterogeneity is an important factor influencing the spatial distribution of the species. The present work improves the understanding of plant community in Muzhaling World Geopark, and provides technical reference for biodiversity conservation and forest management of this area.     

Improving the accuracy of indirect methods in estimating leaf area index using three correction schemes in a Larix gmelinii plantation

Aims Woody materials and clumping effects are key error sources in estimating leaf area index (LAI) by optical methods. However, how to correct the error caused by woody materials has not reached consensus. The aims of this study are (1) to evaluate the accuracy of optical methods for estimating effective LAI (L_e) in a deciduous needle leaf forest stand, and (2) to develop a practical correction scheme to improve the accuracy of optical methods in estimating LAI.Methods L_ewas estimated by two indirect methods (i.e., digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer method (LAI-2000 method) in an annual maximum leaf area period in a Larix gmelinii plantation. Then, we developed three correction schemes to improve the accuracy of indirect methods in estimating LAI. Meanwhile, two direct methods (i.e., litter collection and allometry methods) were used to estimate LAI. Taking LAI from litter collection as a reference, we evaluated the effectiveness of three correction schemes and tested the influence of zenith angle ranges on the correction results.Important findings With zenith angle ranges of 0-45° (rings 1-3), 0-60° (rings 1-4), 45°-60° (ring 4) and 0-75° (rings 1-5), L_eobtained from DHP underestimated LAI from both litter collection and allometry by 19%-32% and 18%-29%, respectively. L_efrom LAI-2000 method with four zenith angles also underestimated LAI from both litter collection and allometry by 9%-30% and 8%-28%, respectively. Although the contribution of woody materials to LAI was overestimated in correction scheme A, it was effective in correcting L_efrom DHP with zenith angles of 45º-60º (ring 4), and also effective for L_efrom LAI-2000 method with zenith angles of rings both 1-3 and 1-4. Correction scheme B was all effective in correcting L_efrom DHP with four zenith angle ranges. Generally, correction scheme C was more effective than other two schemes in correcting L_efrom both DHP and LAI-2000 method with four zenith angle ranges. These results indicate that the zenith angle range is a key factor for determining the accuracy of optical methods in estimating LAI besides woody materials and clumping effects.     

低温处理后4个越橘品种部分生理指标的比较及其抗寒性分析

以‘美登’(‘Blomidon ’)、‘北陆’(‘Northland ’)、‘蓝丰’(‘Bluecrop ’)和‘密斯梯’(‘Misty ’)4个越橘( Vaccinium spp.)品种为研究对象,对经-15℃、-20℃、-25℃、-30℃、-35℃和-40℃低温处理后各品种枝条的相对电导率( REC)、丙二醛( MDA)含量、过氧化物酶( POD)和过氧化氢酶( CAT)活性以及各指标的增长量进行比较;在此基础上,建立各品种REC值与温度的Logistic方程并获得各品种的低温半致死温度( LT50),初步确定各品种的抗寒性。结果表明：经不同低温处理后,各品种枝条的REC 值以及 POD 和 CAT 活性总体上极显著(P<0.01)高于对照(10℃),MDA含量极显著或显著(P<0.05)高于对照。随处理温度降低,各品种枝条的REC值和MDA含量逐渐升高,但不同品种间这2个指标的变幅不同;各品种枝条的POD和CAT活性随处理温度降低呈“单峰型”曲线,但不同品种枝条POD和CAT活性的峰值及其达到峰值的处理温度均存在差异,其中,经-25℃低温处理后品种‘密斯梯’枝条的POD和CAT活性最高,而其余3个品种的POD和CAT活性经-30℃低温处理后最高。总体上,品种‘密斯梯’枝条的REC值和MDA含量增长量处于较高水平,POD和CAT活性增长量处于较低水平;而品种‘美登’枝条的REC值和MDA含量增长量则处于较低水平,POD和CAT活性增长量处于较高水平。各品种的Logistic方程拟合度为0.8622~0.9778,且各品种间的拟合度差异均达到极显著或显著水平;REC值与温度的相关性极显著,其相关系数为0.9285~0.9888;品种‘密斯梯’、‘蓝丰’、‘北陆’和‘美登’的LT50值分别为-18.87℃、-26.85℃、-27.52℃和-30.83℃。综合分析结果显示：LT50值、MDA含量变化量、保护酶活性及其变化量均可作为越橘品种抗寒性的评价指标,据此初步确定供试4个越橘品种抗寒性由强至弱依次为‘美登’、‘北陆’、‘蓝丰’、‘密斯梯’。     

种群连续增长模型的学习过程

针对学生提出的问题“种群S型曲线为何在K／2时增长率最大”,通过多种渠道寻求答案,对“K／2”的实际应用提出了自己的见解。     

带有正负系数的一阶震荡中立型微分方程

本文建立了中立型微分方程d/dt[x（t）-R（t）x（t-r）]＋P（t）x（t-r）-Q（t）x（t-δ）=0震荡的一个充分条件．