Variations of fine root diameter with root order in Manchurian ash and Dahurian larch plantations

Fine root lifespan and turnover play an important role in carbon allocation and nutrient cycling in forest ecosystems. Fine roots are typically defined as less than 1 or 2 mm in diameter. However, when categorizing roots by this diameter size, the position of an individual root on the complex lateral branching pattern has often been ignored, and our knowledge about relationships between branching order and root function thus remains limited. More recently, studies on root survivals found that longevity was remarkably different in the same branching level due to diameter variations. The objectives of this study were: (1) To examine variations of fine root diameter from the first-to fifth-orders in Fraxinus mandshurica Rupr and Larix gmelinii Rupr roots; and (2) To reveal how the season, soil nutrient, and water availability affect root diameter in different branch order in two species. This study was conducted at Maoershan Forest Research Station (45°21′–45°25′N, 127°30′–127°34′E) owned by Northeast Forestry University in Harbin, northeast China. Both F. mandshurica and L. gmelinii were planted in 1986. In each plantation, fine roots of two species by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0–10 and 10–20 cm) were obtained. The results showed that average diameters of fine roots were significantly different among the five branch orders. The first-order had the thinner roots and the fifth order had the thickest roots, the diameter increasing regularly with the ascending branch orders in both species. If the diameter of fine roots was defined as being smaller than 0.5 mm, the first three orders of F. mandshurica roots and the first two orders of L. gmelinii roots would be included in the fine root population. The diameter ranges of the fine roots from first-order to fifth-order were 0.15–0.58, 0.18–0.70, 0.26–1.05, 0.36–1.43, and 0.71–2.96 mm for F. mandshurica, and 0.17–0.76, 0.23–1.02, 0.26–1.10, 0.38–1.77, and 0.84–2.80 mm for L. gmelinii. The average coefficient of variation in first-order roots was less than 10%, second-and third-order was 10–20%, and fourth-and fifth-order was 20–30%. Thus, variation in root diameter also increased with the ascending root order. These results suggest that “fine roots”, which are traditionally defined as an arbitrary diameter class (i.e., <2 mm in diameter) may be too large a size class when compared with the finest roots. The finest roots have much shorter lifespan than larger diameter roots; however, the larger roots are still considered a component of the fine root system. Differences in the lifespan between root diameter and root order affect estimates of root turnover. Therefore, based on this study, it has been concluded that both diameter and branch order should be considered in the estimation of root lifespan and turnover. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(6): 871–877 [译自: 植物生态学报]     

华山松食用松籽型高产优质无性系初选

在华山松结实性状遗传变异研究的基础上,以各无性系间的单株产籽重、千粒重、出种率等为选择指标,对紫溪山华山松无性系嫁接种子园内78个无性系进行综合选择。结果表明:98,46,42,4和92号等5个无性系综合选择指数(I)值高于1.50,且产量稳定,可选为高产优质无性系。     

巨桉子代测定林与引种改良策略的研究

在福建省华安县建立的巨桉子代测定林，包含代表全分布区的１５０个自由受粉家系。对树高、胸径、枝角和木材基本密度进行研究的结果表明，生长性状在家系间存在着极显著的遗传差异，木材基本密度在种源间和家系间都存在着显著的差异。     

中国银杏种质资源研究进展

作者结合近几年的研究，概述了银杏雌雄株早期鉴定、染色体数目与核型及叶用银杏品种选育等方面的研究进展。     

红松速生丰产林立地选择技术

选择最佳立地是培育红松人工丰产林的基础,也是一种不增加投入,可望取得较大幅度增产的有效途径。为了更好的实现这一目标,经过系列研究与编制红松人工林的立地指数,进行立地质量综合评价,为营造速生丰产林提供科学依据。     

葫芦科植物的遗传转化研究进展

葫芦科植物中包括多种以采收果实为主的蔬菜作物,对其进行品质改良、延迟成熟和抗病虫害的遗传转化研究具有重要的理论和实践意义。目前,在葫芦科植物中已建立了子叶、茎尖、胚轴、茎段、原生质体和子叶节等的再生体系;用于遗传转化的方法有农杆菌介导法、基因枪法、花粉管通道法、DNA浸泡法等;用于转化的目的基因多为抗病毒病基因和延迟成熟的基因;NPTII基因为最常用的筛选标记基因。主要对以上几个方面进行综述,并讨论了葫芦科植物遗传转化过程中的影响因素及存在的问题。     

高阶非线性中立型差分方程组多正解的一个存在定理

利用范数形式的锥拉伸与锥压缩不动点定理,得到了高阶非线性中立型差分方程组Δ^nxi（k）＋pi（k）fi（x1（k-τi1）,…,xm（k-τim））=0,k∈N,i=1,2,…,m多正解的存在性准则.     

叶用型沙棘鲜叶量估算及表型选择初步研究

叶用型沙棘生长适应性和抗逆性相对较强,选育出的优良品种具有枝叶繁茂、生物产量高、棘刺少等特点。本研究对沙棘杂交子代的一系列形态指标进行了调查、统计、分析,并对当年生枝条数、单株鲜叶量进行了估算,然后以当年生枝棘刺密度、鲜叶量作为叶用型沙棘表型选择的指标评选优株。结果表明:杂交子代的表现明显优于其亲本,其中,当年生枝平均棘刺密度比父本低80.75%;鲜叶重均值比母本高193.84%、比父本高8.33%;通过选优排序,选出150、33、188、76、109、171为优良单株,可作为下一步研究的育种材料。     

关于随机故障型单机排序问题的注记

讨论了关于随机故障型单机排序研究领域中工件完工概率问题,具有随机压缩加工时间的二次超前-延误惩罚问题的最优解的存在性问题,以及关于一个随机序的定理的证明的改进.     

政府提供农村公共服务过程中的模式选择

针对当前农村公共服务供给模式存在的弊端和缺陷,基于公共服务及其相关理论,我国政府提供农村公共服务过程中选择的模式应为"多中心治理"的供给模式、"教育优先"的增长模式、"社会性公共服务为主体"的支出模式、"广覆盖、低水平、基本公共服务均等化"的消费模式.