Altitudinal differences in the leaf fitness of juvenile and mature alpine spruce trees (Picea crassifolia)

In many plant species, leaf morphology varies with altitude, an effect that has been attributed to temperature. It remains uncertain whether such a trend applies equally to juvenile and mature trees across altitudinal gradients in semi-arid mountain regions. We examined altitude-related differences in a variety of needle characteristics of juvenile (2-m tall) and mature (5-m tall) alpine spruce (Picea crassifolia Kom.) trees growing at altitudes between 2501 and 3450 m in the Qilian Mountains of northwest China. We found that stable carbon isotope composition (delta C-13), area- and mass-based leaf nitrogen concentration (N-a, N-m), number of stomata per gram of nitrogen (St/N), number of stomata per unit leaf mass (St/LM), projected leaf area per 100 needles (LA) and leaf mass per unit area (LMA) varied nonlinearly with altitude for both juvenile and mature trees, with a relationship reversal point at about 3 100 m. Stomatal density (SD) of juvenile trees remained unchanged with altitude, whereas SD and stomatal number per unit length (SNL) of mature spruce initially increased with altitude, but subsequently decreased. Although several measured indices were generally found to be higher in mature trees than in juvenile trees, N-m, leaf carbon concentration (C.), leaf water concentration. (LWC), St/N, LA and St/LM showed inconsistent differences between trees of different ages along the altitudinal gradient. In both juvenile and mature trees, VC correlated significantly with LMA, N-m, N-a, SNL, St/LM and St/N. Stomatal density, LWC and LA were only significantly correlated with delta C-13 in mature trees. These findings suggest that there are distinct ecophysiological differences between the needles of juvenile and mature trees that determine their response to changes in altitude in semi-arid mountainous regions. Variations in the fitness of forests of different ages may have important implications for modeling forest responses to changes in environmental conditions, such as predicted future temperature increases in high attitude areas associated with climate change.

Mitochondrial and chloroplast phylogeography of Picea crassifolia Kom. (Pinaceae) in the Qinghai-Tibetan Plateau and adjacent highlands

The disjunct distribution of forests in the Qinghai-Tibetan Plateau (QTP) and adjacent Helan Shan and Daqing Shan highlands provides an excellent model to examine vegetation shifts, glacial refugia and gene flow of key species in this complex landscape region in response to past climatic oscillations and human disturbance. In this study, we examined maternally inherited mitochondrial DNA (nad1 intron b/c and nad5 intron 1) and paternally inherited chloroplast DNA (trnC-trnD) sequence variation within a dominant forest species, Picea crassifolia Kom. We recovered nine mitotypes and two chlorotypes in a survey of 442 individuals from 32 populations sampled throughout the species' range. Significant mitochondrial DNA population subdivision was detected (G(ST) = 0.512; N-ST = 0.679), suggesting low levels of recurrent gene flow through seeds among populations and significant phylogeographical structure (N-ST > GST, P < 0.05). Plateau haplotypes differed in sequence from those in the adjacent highlands, suggesting a long period of allopatric fragmentation between the species in the two regions and the presence of independent refugia in each region during Quaternary glaciations. On the QTP platform, all but one of the disjunct populations surveyed were fixed for the same mitotype, while most populations at the plateau edge contained more than one haplotype with the mitotype that was fixed in plateau platform populations always present at high frequency. This distribution pattern suggests that present-day disjunct populations on the QTP platform experienced a common recolonization history. The same phylogeographical pattern, however, was not detected for paternally inherited chloroplast DNA haplotypes. Two chlorotypes were distributed throughout the range of the species with little geographical population differentiation (G(ST) = N-ST = 0.093). This provides evidence for highly efficient pollen-mediated gene flow among isolated forest patches, both within and between the QTP and adjacent highland populations. A lack of isolation to pollen-mediated gene flow between forests on the QTP and adjacent highlands is surprising given that the Tengger Desert has been a geographical barrier between these two regions for approximately the last 1.8 million years.

木通科植物分类学研究

本文对木通科植物进行全面分类学修订，确认8属35种（包括16亚种）。这8个属是：猫儿屎属(Decaisnea，1种)，串果藤属(Sinofranchetia，1种)，牛藤果属(parvatia，2种)，野木瓜属(Stauntonia，24种)，长萼木通属(Archakebia，1种)，木通属（Akebia，4种），拉氏藤属（Lardizabala，1种）和勃奎拉属（Boquila，1种）。我们建立了1个新属(长萼木通属Archakebia)、4个新种（短蕊八月瓜Stauntonia brachyandra，厚叶八月瓜S．crassifolia，离丝野木瓜S．libera和墨脱八月瓜S．medogensis）和5个新亚种（长萼三叶木通Akebia trifolialassp. longisepala，线叶五风藤Stauntonia angustifolia ssp. linearifolia，三叶五风藤S．a．ssp, trifoliata，海南野木瓜S．chinensis ssp. hainaensis和纸叶八月瓜S．latifolia ssp. chartacea)，重新组合了8个名称(Parvatia brunoniana ssp. elliptica，Stauntonia angustifolia，S． chapaensis，S．coriacea，S．grandiflora，S．latifolia，S．obovatifoliola .ssp. urophylla和S．pterocaulis)和归并了32个类群（种及种下等级）。 我们对1989年系统进行了补充，在拉氏藤族(tribe Lardizabaleae)中建立两个亚族，并对野木瓜属(Stauntonia)提出一个详尽的属下分类系统，包括两个亚属4个组。本修订主要根据作者对近七千余份腊叶标本的研究和野外考察结果撰写而成。在前一部分中，我们全面阐述木通科形态性状特征及其演化意义，并应用于科下种上分类群的划分及其亲缘关系讨论。在此基~础上，我们进一步确认串果藤族(Sinofranchetieae)和猫儿屎族(Decaisneeae)均为木通科植物早期演化的分支，也是系统位置比较孤立的类群;拉氏藤族(Lardizabaleae)与亚洲类群分开的历史很长，其内部分化也很显著;木通族(Akebineae)是木通科植物演化的主干，也是较晚近时期发生的类群，它正处在强烈分化之中，存在有各种演化式样，是木通科植物分类实践的难点。 作者仍然认为木通科植物是毛茛类与木兰类之间联系的扭带，它可能在白垩纪初期就已经在联合古陆上起源，并在古陆分裂之前就发生了东亚及南美两群植物的隔离事件。 我们在本文后一部分（即分类处理）中，描述了每个种（共35种）的性状特征、物候期、生态习性及其与近缘种的关系，并作出种分布图和形态线描图。最后列出所研究标本的索引（中英对照）。

中国特有针叶树种对气候变化的敏感性研究

About 214 trees in 9 sampling sites, representing 5 endemic conifer species, were collected from the western Sichuan Province and eastern Qinghai Province, China. In this study, structure we try to investigate tree-ring sensitivity to climate in order to obtain primary information of reconstructing past climate from the trees in this region. All the 5 species present distinct ring boundaries ^ few ABS(absent rings) and available for cross-dating,which are all past the test by program COFECHA. Statistics for all the 8 tree-ring width residual chronologies present significant inter-correlation between series and high values of mean sensitivity. As well as the maximum latewood density of Picea crassifolia Kom and Pinus densata Mast. These results indicate usefulness of these chronologies for dendrochronological studies. Pearson correlation analyses were applied to provide a basic estimate of the causal relationships between tree-ring width and climate factors. We found some significant relationships between tree-ring width> maximum density and temperature as well as precipitation. Especially, there is high correlation between the maximum density of the Picea crassifolia Kom and the index of moisture, the ratio of precipitation and temperature, which can indicate well the climate; however the higher correlation can be see between the maximum density of Pinus densata Mast and the total temperature from June to September. Regardless of tree species, chronologies in our study region presented accordant variations of which may reveal strong common climate signal. Thus these chronologies are shown to be dependable for building tree-ring network in the nearly future. However, there are limitations in this study, only monthly mean of temperature and precipitation were available. Also, for this typical subtropical mountain system, meteorological stations are usually located in valley and biased to represent moisture conditions on the slopes. Thus the estimation of precipitation both in temporal and spatial domain was rather restricted. Further study, such as wood anatomy, physiology and densitometry, are needed for better understanding the environmental and climatic history in this area.