11-year-old Betula alnoides plantations for density trial with five planting spacing treatments were investigated through stem analysis at Pingxiang City, Guangxi, to assess the effects of initial density on tree growth process. The results showed that the initial density had no remarkable effects on tree height growth and stem shape index, while there were significant differences in diameter at breast height (DBH), individual tree volume and stand volume among treatments of initial density, and the stand volume of treatment of 2 m×3 m was significantly higher than that of other treatments. The fast growing period of DBH trended to increase with the decrease of initial density, the DBH growth commenced to decrease since the sixth year after planted under the 1.5 m×2 m treatment, while it decreased mostly since the eighth year under other treatments, indicating that thinning should be conducted at the sixth year for 1.5 m×2 m treatment, and at the eighth year for 2 m×3 m and 3 m×3 m treatments, while for other treatments, it was delayed with the decrease of density. All the current and mean annual increment curves of tree height crossed when 5-6 years old, and did not reach quantity mature until 11 years old for all density treatments, while remarkable differences of the current annual increment of individual tree volume were seen among treatments. Taking factors such as growth performance, stand volume, and use efficiency of forest land, etc. into consideration, 2 m×3 m was determined as the most optimum planting density in the present study.

Betula alnoides Buch.-Ham. Ex D.Don is a fast-growing and precious tree species in tropical and warm subtropical regions. The wood borer damage has recently been one of key factors limiting the large-scale expansion of B. alnoides plantations. A trial including 26 provenances and 322 families were established at Shaoguan State-owned Forest Farm in northern Guangdong Province, which were suffered from heavy damage of wood borers within two years after planted. The growth performance and resistances to wood borers of B. alnoides were investigated for the purpose of early selection of germplasm. The results showed that there were significant differences among provenances in height and base diameter (PB. alnoides. Anoplophora chinensis (Förster) was the principal species of wood borer, which damaged trunk within the height of 20 cm above stem base. 1-5 larva of this species were found on each tree attacked, and the attack rate by A. chinensis was significantly and positively related to the diameter growth (P＜0.05). The attack rate showed no significant difference among provenances (P＞0.05), and the mean attack rates for one-year-old and two-year-old B. alnoides trees were 48.21% and 36.27%, respectively. Early selection of B. alnoides provenance was carried out based on its growth performance and the attack rate by the wood borers. These findings could be contributive to understand the occurrence of A. chinensis, protect from its damage, and provide evidences to select germplsm of B. alnoides with good growth performance and strong resistance to A. chinensis in northern Guangdong and surrounding areas with similar environment.

应用各种浓度蔗糖、蔗糖+硼酸培养基于系列温度下开展西南桦花粉萌发对比试验,研究了蔗糖、硼酸浓度对西南桦花粉离体萌发的影响,筛选出适合西南桦花粉萌发培养基的适宜组分和适宜培养温度,并应用4个单株的花粉对其萌发特征进行了初步研究。结果表明:蔗糖基本培养基上添加硼酸能够显著促进西南桦花粉萌发;西南桦花粉离体萌发的合适培养基为15%蔗糖+ 200 mg·kg-1硼酸,适宜培养温度为30 ℃;在此条件下培养3 h后花粉萌发率基本稳定,培养7 h后花粉管长度也趋于稳定。

从花序、单株、林分水平上对广西靖西县的一个土石山生态交错区内不同立地条件下西南桦的开花物候进行了观察和比较。结果表明:西南桦雌、雄花序开花持续时间为2 3 d,同一植株相同部位的雌花序较雄花序晚开花约14 d;其单株开花持续时间为4 28 d,开花同步性指数为0.160 0.259,绝大多数植株的冠层开花顺序依次为下层、中层和上层,土山和石山立地间单株开花持续时间和开花同步性均差异不显著 (P＞0.05);在林分水平上,西南桦开花持续时间为40 58 d,两种立地间差异不显著。

目的 研究西南桦天然林物种组成和多样性特征，为西南桦天然林生物多样性保护及西南桦人工林近自然经营提供科学依据。 方法 在云南省德宏州瑞丽派罗山1958年皆伐后形成的天然次生林(PLS)和芒市桦桃岭刀耕火种1967年丢荒地形成的天然次生林(HTL)内分别设置总面积为10 000 m² 和5 000 m²的样地开展物种多样性调查。运用Simpson优势度指数、Shannon-Wiener多样性指数和Pielou均匀度指数，分析乔木层、灌木层和草本层物种组成和多样性，并对林分整体及重要值 > 5.00%的乔木层主要树种绘制径级分布图。 结果 PLS林分内无绝对优势种，树种润楠的重要值最大（14.76%），其次为西南桦（9.55%）；HTL林分，树种西南桦的重要值最大 (26.47%)，在林分内占据绝对优势。PLS林分各林层物种丰富度 (草本层除外)、Simpson优势度指数、Shannon-Wiener多样性指数和Pielou均匀度指数均高于HTL，但物种优势度低于HTL，物种分布更均匀。不同林层间Simpson优势度指数、Shannon-Wiener多样性指数和Pielou均匀度指数均以灌木层最高，而物种丰富度则乔木层最高。2种林分的径级结构均呈倒J形分布，重要值 > 5.00%的主要树种除西南桦分布在中大径级外，均集中分布在中小径级。 结论 PLS林分较HTL更接近演替后期，二者均属于稳定的群落类型。研究结果为西南桦天然林保护以及人工纯林近自然化改造和经营提供理论依据和技术参考。

目的 探究西南桦间接器官发生过程的愈伤组织诱导、不定芽分化、生根诱导等各阶段的适宜培养基配方，建立西南桦高频再生体系，为其遗传转化和良种繁育提供理论依据和技术支持。 方法 以西南桦TC2号无性系的节间茎段为外植体开展愈伤组织诱导、不定芽分化以及生根培养基筛选试验，并优化了预培养条件，揭示了愈伤组织诱导阶段基本培养基、激素浓度、暗培养时间，愈伤组织分化阶段激素组合，以及预培养条件等因素对不定芽分化的影响。 结果 (1) 预培养的适宜条件为：弱光培养 (1 000 lx) 15 d后转至暗培养7 d，再正常光照 (2 000 lx) 培养8 d，该条件下可获得适度黄化的植株，其平均株高和节间长度分别为6.6 cm和3.1 cm； (2) 适合西南桦节间茎段愈伤组织诱导的培养基为WPB5 + 1.0 mg·L⁻¹ TDZ + 0.2 mg·L⁻¹ NAA + 20 g·L⁻¹蔗糖 + 5.8 g·L⁻¹琼脂 (pH5.8)，适宜暗培养时间为15 d；(3) 适合愈伤组织分化的培养基为WPM + 0.8 mg·L⁻¹ 6-BA + 0.5 mg·L⁻¹ GA₃ + 30 g·L⁻¹蔗糖 + 5.8 g·L⁻¹琼脂 (pH5.8)；(4) 采用上述最优方案，其茎段诱导的愈伤组织分化率和净增殖系数为88.9%和6.2以上，平均每个预培养植株可产生56.8个不定芽；(5) 适宜生根培养基为WPM + 0.1 mg·L⁻¹ NAA + 20 g·L⁻¹蔗糖 + 5.8 g·L⁻¹琼脂 (pH5.8)，培养30 d后生根率可达100%。 结论 本研究完整构建了高效稳定、重复性好的西南桦节间茎段高频再生体系，该体系不仅愈伤组织分化率和增殖系数较高，还可提升节间茎段取材的效率，为今后开展西南桦组培快繁以及利用基因工程进行其遗传性状改良奠定了基础。

目的 开展西南桦无性系早期生长变异及生长节律研究，揭示其生长规律及适应性，为西南桦无性系选育及速生丰产林营建提供参考。 方法 以滇西地区20个无性系参试的3年生西南桦无性系测定林为研究对象，每月定期测定其树高、胸径，探讨各无性系的生长变异，应用聚类分析划分生长类型，运用有序聚类分析进一步揭示各类型无性系的生长节律特征，通过相关性分析探明影响生长节律的主要气象因子。 结果 20个西南桦无性系间树高和胸径差异极显著（P < 0.01），根据生长表现，可将其划分为速生、中等和慢生3种类型，其中，B3、A10、Q3、Q4、Q2无性系属于速生型，其树高、胸径年均生长量大多超过2 m和2 cm；与中等和慢生型无性系相比，速生型无性系的生长优势并非完全表现在速生期，其在缓生期和滞生期的生长优势更大；各类型西南桦无性系的生长节律基本一致，其树高生长高峰在7—9月，低谷为4月和12月；其胸径生长高峰为5、10月，8月和12月为低谷，尤以8月生长最慢，这与该月的日照时数低有关。 结论 在滇西地区，B3、A10、Q3、Q4、Q2等5个无性系生长最迅速，颇具发展潜力。从经营措施看，宜在树高、胸径生长高峰之前，即5月和9月加强幼林抚育施肥，促进林木生长。