虫害叶损失造成的树木非结构性碳减少与树木生长、死亡的关系研究进展

大规模虫害爆发可造成区域森林死亡, 近年的气候变化进一步增加了虫害的频度和危害程度。森林和林地植物死亡会导致植被生产力降低, 改变生态系统结构和功能, 使森林由一个净的碳汇转变为一个碳源。因此, 加深虫害对树木危害机制的认识有重要意义。虫害造成的叶损失(虫害叶损失)降低树木光合作用能力, 增加非结构性碳(NSC)消耗, 使得树木体内碳储备降低, NSC降低到一定程度会导致树木因碳饥饿而死亡。外部环境和树木自身的补偿性机制也会对这个过程产生正或负的影响。在近年气候变化背景下, 树木死亡在全球尺度上增多, 重新激起了人们对碳饥饿的重视, 碳饥饿被视为解释树木死亡的主要生理机制之一。该文介绍了碳饥饿的定义, 综述了虫害叶损失减少树木NSC储备与树木生长、死亡的关系, 以及树木虫害和叶损失与气候变化之间的关系, 并对今后的研究进行了展望。     

长白山次生针阔混交林乔木幼苗存活的影响因素分析

基于长白山次生针阔混交林样地, 以520个1 m × 1 m幼苗样方中胸径小于1 cm的乔木幼苗为研究对象, 选取2013年和2014年的幼苗调查数据, 运用广义线性混合模型(GLMM)分析了生物邻体和生境异质性对幼苗存活的影响, 探讨了次生针阔混交林幼苗存活影响因素及物种共存机制。结果表明: (1)适宜大树生长的局域生境同样也适宜幼苗的存活, 幼苗存活率与土壤含水量和有效氮等土壤养分显著正相关。(2)幼苗个体之间存在明显的竞争, 较多的幼苗邻体显著降低幼苗的存活率。同种大树邻体和同种幼苗邻体与幼苗存活显著负相关, 表明存在负密度制约效应。(3)随着幼苗年龄的增加, 生境异质性对幼苗存活的影响逐渐增大。该研究证实了密度制约效应和生境异质性对幼苗存活有着重要影响, 其相对重要性随着幼苗年龄级、功能群以及物种种类而变化。     

夜间增温对亚高山针叶林主要树种无机氮吸收的影响

吸收营养物质是植物根系的主要生理功能。氮素吸收是植物体内氮代谢的第一步, 也是最关键的一步。为了全面地认识亚高山针叶林在全球气候变化背景下对两种主要无机氮(NH₄⁺和NO₃^-)吸收特点的变化, 该研究以川西亚高山针叶林优势树种——云杉(Picea asperata)和岷江冷杉(Abies fargesii var. faxoniana)为材料, 通过红外辐射加热器模拟增温, 利用非损伤微测技术(non-invasive micromeasurement technology)研究了这两个树种吸收NH₄⁺和NO₃^-特点的变化, 同时还探究了NH₄⁺和NO₃^- 之间的相互作用对植物吸收这两种离子的影响。研究结果显示: 在云杉根系中, NH₄⁺和NO₃^-的最大吸收速率分别发生在距离根尖最顶端17-18 mm区域和17 mm处, 而岷江冷杉对这两种离子的最大吸收速率分别发生在距离根尖顶端11 mm和11.5 mm处。增温对云杉和岷江冷杉根系吸收NH₄⁺和NO₃^-有促进作用。在增温条件下, NO₃^-能够促进云杉根系对NH₄⁺的吸收, 而NH₄⁺则抑制了其对NO₃^-的吸收。无论是否增温, 岷江冷杉对NH₄⁺的吸收都不受NO₃^-的影响, 而在增温条件下, NH₄⁺会抑制岷江冷杉对NO₃^-的吸收。     

Estimating tree and stand sapwood area in spatially heterogeneous southeastern Australian forests

Aims Natural and anthropogenic changes in forests can have important influences on transpiration and water production. Understanding the effects of increasing disturbances, due for example to climate change and forest harvesting, requires detailed information on how forest density and structural attributes relate to transpiration. Mean annual transpiration of eucalypt forest communities is often strongly correlated with total cross-sectional sapwood area. Our aim was to test an efficient method for estimating sapwood area at 1.3 m height (SA 1.3) in a large number of trees to understand the spatial heterogeneity of tree and stand sapwood area within and between forest communities, and develop allometric relationships that predict SA 1.3 with forest inventory data. We also apply tree competition models to determine the degree to which the relationship between SA 1.3 and tree basal area at 1.3 m height (BA 1.3) is influenced by competition.Methods We visited 25 recently harvested southeastern Australian forest sites consisting of 1379 trees and 5 Eucalyptus species to evaluate a new efficient data collection method for estimating SA 1.3 with tree taper and stump dimensions data using mixed effects models. The locations of 784 stumps within one 5-ha site were accurately mapped using an unmanned aerial vehicle (UAV), and four distance-dependent tree competition models were applied across the site to explain within-stand variation in the ratio of SA 1.3 to BA 1.3. Data from 24 additional sites, consisting of ten 15 m radial plots per site, were used to analyse within-site variation in R Ha (the ratio of stand sapwood area SA Ha to stand basal area BA Ha). The radial plots were merged within each site to evaluate between-site variations in R Ha across the landscape. For predicting SA Ha with forest inventory data, we computed the relationship between SA Ha and a new index of total stem perimeter per hectare, defined as ? B A H a N T, where N T is tree stocking density.Important findings Our 1379 measured stems represent the most comprehensive measure of sapwood area, surpassing the 757 measured stems in native eucalypt forests published in literature. The species-specific R Ha varied considerably across sites and therefore extrapolating SA Ha with spatially distributed BA Ha maps and a generalized R Ha would introduce local uncertainty. We found that the species-specific stem perimeter index was more effective at capturing variability in SA Ha across the landscape using forest composition, structure and density data (R 2 : 0.72–0.77). The strong correlation between tree SA 1.3 and BA 1.3 improved slightly using tree competition models (R 2 increased from 0.86 to 0.88). Relating SA Ha to routinely measured forest inventory attributes within permanent plots and Light Detection and Ranging (LiDAR) data may provide opportunities to map forest water use in time and space across large areas disturbed by wildfire and logging.     

Reproductive biology of Magnolia sinica (Magnoliaecea), a threatened species with extremely small populations in Yunnan,China

Magnolia sinica is one of the most threatened trees endemic to Southeast Yunnan. Based on our investigations, only 52 individuals and eight populations are found in the wild. M. sinica has been categorized as Critically Endangered on the IUCN Red List and identified as a “Plant Species with Extremely Small Populations (PSESP)”. Its fruit/seed set is very low and seedlings are rarely found in the wild. It is hypothesized that it may encounter obstacles to reproductive success. This study, therefore, focuses on its reproductive biology, knowledge of which is essential for effective conservation. Flowers of this species are protogynous and nocturnal, and possess a two-day rhythm of sexual presentation. For the first night of anthesis, the flowers are in the pistillate stage during which tepals open at dusk and close approx. 1 h later (except for the open outer ones). They remain closed until the next afternoon, when flowers, now in the staminate stage, re-open and remain so until the tepals drop. Nocturnal beetles enter into the flowers and remain trapped throughout the night as the flower closes, during which time they feed on tepals. Pollen-gathering bees are found to visit the re-opened flowers and the beetles are released during this stage. Two species of Pleocomidae and Curculionidae beetles appear to be effective pollinators.M. sinica is a self-compatible, pollinator-dependent species, and its fruit/seed set can be significantly increased by hand-pollination. No functional seed dispersers have been found in its extant natural habitats. These findings suggest that it may face both pollination and seed disperser insufficiencies in its current fragmented habitats, which may account for its low regeneration. Here we propose conservation strategies based on our findings.     

层次分析法在粤北高速公路沿线绿化树种选择中的运用

以广东省仁化至博罗高速公路(仁化至新丰段路)为例,通过对该路段沿线乡土植物调查,运用层次分析法(AHP)对388种乡土植物的环境适应性、培植特性、功能特性和经济效应进行评价和综合分析。结果表明,在一级指标中,环境适应性权重最大(0.5476);其次是功能特性(0.2051)。在选取的14个二级指标中, 耐贫瘠权重最大(0.1642),耐旱能力和耐寒性的权重相对也比较大,分别为0.1533、0.0916。根据AHP模型,对所调查的388种乡土植物进行评价,其中评分80分以上适宜高速公路绿化的有64种。结合观赏性、耐寒性评价和市场苗木供应情况最终筛选出20种乡土植物作为仁新高速沿线绿化的建议树种。     

Coalescent methods for estimating species trees from phylogenomic data

Genome-scale sequence data have become increasingly available in the phylogenetic studies for understanding the evolutionary histories of species. However, it is challenging to develop probabilistic models to account for heterogeneity of phylogenomic data. The multispecies coalescent model describes gene trees as independent random variables generated from a coalescence process occurring along the lineages of the species tree. Since the multispecies coalescent model allows gene trees to vary across genes, coalescent-based methods have been popularly used to account for heterogeneous gene trees in phylogenomic data analysis. In this paper, we summarize and evaluate the performance of coalescent-based methods for estimating species trees from genome-scale sequence data. We investigate the effects of deep coalescence and mutation on the performance of species tree estimation methods. We found that the coalescent-based methods perform well in estimating species trees for a large number of genes, regardless of the degree of deep coalescence and mutation. The performance of the coalescent methods is negatively correlated with the lengths of internal branches of the species tree.     

Ontogenetic transition in leaf traits: a new cost associated with the increase in leaf longevity

Aims Recent work has identified a worldwide 'economics' spectrum of correlated leaf traits that mainly reflects the compromises between maximizing leaf longevity and short-term productivity. However, during the early stages of tree growth different species tend to exhibit a common strategy, because competition for soil water and nutrients forces the maximization of short-term productivity owing to the need for rapid growth during the most vulnerable part of the tree's life cycle. Accordingly, our aim here was to compare the variations that occur during ontogeny in the different leaf traits (morphology and leaf chemical composition) of several coexisting Mediterranean woody species differing in their leaf life spans and to test our hypothesis that tree species with a long leaf life span should exhibit larger shifts in leaf characteristics along ontogeny.Methods Six Mediterranean tree species differing in leaf life span, selected from three plots located in central-western Spain, were studied during three growth stages: seedlings, juveniles and mature trees. Leaf life span, leaf morphology (leaf area, dry weight, thickness and mass per unit area) and chemical composition (N and fibre concentrations) were measured in all six species. The magnitude of the ontogenetic changes in the different traits was estimated and related to the mean leaf longevity of the different species.Important findings Along ontogeny, strong changes were observed in all variables analysed. The early growth stages showed lower leaf thickness, leaf thickness and mass per unit area and N, cellulose and hemicellulose concentrations than mature trees, but a higher lignin content. However, these changes were especially marked in species with a longer leaf life span at maturity. Interspecific differences in leaf life span, leaf morphology and chemical composition were stronger at the mature stage than at the seedling stage. We conclude that greater plasticity and more intense strategy shifts along ontogeny are necessarily associated with long leaf life span. Our results thus provide a new aspect that should be incorporated into the analysis of the costs and benefits associated with the different strategies related to leaf persistence displayed by the different species. Accordingly, the intensity of the alterations in leaf traits among different growth stages should be added to the suite of traits that change along the leaf economics spectrum.     

种子细胞——组织工程连载之三

种子细胞也是组织工程的核心研究内容,获得足够数量和质量的种子细胞是开展体外组织工程的必要基础。用于组织工程的种子细胞必须具有形成新组织结构的能力,主要来源于自体、同种异体或异种,在具体应用时各有利弊。一些成体干细胞由于不存在伦理争议以及发育分化条件相对简单等优势是重要的种子细胞,包括造血干细胞、骨髓干细胞、神经干细胞、脂肪干细胞、皮肤干细胞。人胚胎干细胞及其组织工程要真正在临床医学中得到应用,还有很长的一段路要走。其他一些细胞也可以作为组织工程种子细胞,包括内皮细胞、上皮细胞、成纤维细胞、骨细胞、成骨细胞、角质细胞、前脂肪细胞、脂肪细胞、肌腱细胞等。这些细胞已分化,分裂能力有限,但仍应用于组织工程。理想的种子细胞具有一定标准。     

Characterization of nuclear microsatellite loci in South American Araucariaceae species

The Araucariaceae family has only two species in South America: Araucaria angustifolia and Araucaria araucana. Both species are mainly used for timber and have been overexploited in the past. Currently, they are found as fragmented populations and are classified under the International Union for Conservation of Nature and Natural Resources (IUCN) guidelines as vulnerable species. Population fragmentation may seriously affect the genetic diversity of these two species of Araucariaceae and can consequently lead to decreased survival. To better understand the genetic structure of these South American Araucaria species, eight nuclear microsatellites are reported: six new microsatellites loci developed based on a membrane enrichment procedure and two microsatellites loci transferred from the related species, Araucaria cunninghamii.