高寒森林倒木在不同分解阶段的质量变化

倒木是高寒森林生态系统重要的碳(C)库和养分库, 其不同分解阶段的质量变化, 是认识倒木分解过程中C和养分释放的重要基础。以一个分解序列的岷江冷杉(Abies faxoniana)倒木为研究对象, 研究了心材、边材和树皮在5个分解阶段的C:N:P化学计量特征, 以及木质素和纤维素含量动态。结果显示: I至III分解阶段, 随着分解程度加深, 树皮C含量升高, 而心材和边材C含量降低, 从IV分解阶段开始倒木各组分C含量均开始显著降低。除III分解阶段的心材外, 倒木各组分N含量总体表现为随着分解程度加深而增加的趋势, 除边材N含量在V分解阶段时显著升高外, 其余组分均未达到显著性水平。心材和树皮P含量表现为先降后升的变化趋势, 最小值分别出现在III和II分解阶段; 边材P含量表现为随着分解程度加深而增加。在同一分解阶段, 树皮相对于边材和心材均具有最低的C:N:P化学计量比, 易分解比例F_m也表明树皮更易于分解。边材在I和II分解阶段的C:N:P化学计量比最高, 心材在III到V分解阶段C:N:P化学计量比最高。心材C:P、树皮和边材的C:N和C:P临界值与N和P的初始值成反比。纤维素含量随着倒木分解而降低, 不同分解阶段的纤维素含量表现为: 心材>边材>树皮; 但木质素含量随着分解程度加深而增加, 表现为: 树皮>边材>心材; 倒木3个组分纤维素含量下降均快于木质素, 此外, IV和V分解阶段的树皮木质素与纤维素比值显著增高, 且一直处于较高水平。统计分析结果表明: 倒木N含量显著影响不同分解阶段木质素和纤维素分解。由生态化学计量学理论推测: 树皮分解前期易受N限制, 整个分解阶段均易受P限制, 心材和边材在整个分解阶段均易受N和P限制。     

宿主虫龄对斜纹夜蛾核型多角体病毒病流行的影响

通过对田间感病幼虫跟踪观察,研究了对斜纹夜蛾不同龄期幼虫喷施斜纹夜蛾核型多角体病毒后,病毒病在当代种群中的田间流行动态．结果表明,随虫龄的增大,幼虫对病毒的敏感性下降,宿主幼虫病死率降低,病死速率减慢,病死持续时间延长,幼虫病亡和疾病现患始期、高峰期推迟．对不同龄期幼虫喷施病毒后,幼虫每日病死时间分布可用互补重对数模型较好地拟合(Hosmer-Lemoshow统计量检验不显著),模型中各项系数经t检验达极显著水平;疾病现息时间分布可用Holliday模型拟合,模型经F检验显著,方程中各项系数达到或接近显著水平;幼虫逐日病死时间分布可用’Weibull模型、Gompertz模型及Lo—gistic模型较好地拟合,通过用剩余平方和Q比较各模型的拟合程度,表明Gompertz模型拟合效果最好．     

Graphics for relatedness research

Studies of relatedness have been crucial in molecular ecology over the last decades. Good evidence of this is the fact that studies of population structure, evolution of social behaviours, genetic diversity and quantitative genetics all involve relatedness research. The main aim of this article was to review the most common graphical methods used in allele sharing studies for detecting and identifying family relationships. Both IBS‐ and IBD‐based allele sharing studies are considered. Furthermore, we propose two additional graphical methods from the field of compositional data analysis: the ternary diagram and scatterplots of isometric log‐ratios of IBS and IBD probabilities. We illustrate all graphical tools with genetic data from the HGDP‐CEPH diversity panel, using mainly 377 microsatellites genotyped for 25 individuals from the Maya population of this panel. We enhance all graphics with convex hulls obtained by simulation and use these to confirm the documented relationships. The proposed compositional graphics are shown to be useful in relatedness research, as they also single out the most prominent related pairs. The ternary diagram is advocated for its ability to display all three allele sharing probabilities simultaneously. The log‐ratio plots are advocated as an attempt to overcome the problems with the Euclidean distance interpretation in the classical graphics.     

Plant–plant interactions change during succession on nurse logs in a northern temperate rainforest

Plant–plant interactions change through succession from facilitative to competitive. At early stages of succession, early‐colonizing plants can increase the survival and reproductive output of other plants by ameliorating disturbance and stressful conditions. At later stages of succession, plant interactions are more competitive as plants put more energy toward growth and reproduction. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) and bryophyte succession. How bryophyte‐tree seedling interactions vary through log succession remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 1.0 m² plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA, to test the hypothesis that bryophyte‐tree seedling interactions change from facilitative to competitive as the log decays. Tree seedling density was highest on young logs with early‐colonizing bryophyte species (e.g., Rhizomnium glabrescens) and lowest on decayed logs with Hylocomium splendens, a long‐lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6× higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by forest floor plants, such as H. splendens. Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs enable both tree seedlings and smaller bryophyte species to avoid competition with forest floor plants, including the dominant bryophyte, H. splendens. H. splendens is likely a widespread driver of plant community structure given its dominance in northern temperate forests. Our findings indicate that plant–plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.     

Surface properties of Vibrio vulnificus

AIMS: Vibrio vulnificus adheres to a diverse range of surfaces, ranging from the chitinous exoskeleton of mollusks to human tissue. To determine whether environmental and human clinical isolates exhibit different adhesion traits, we studied the ability of 10 environmental isolates and 10 clinical isolates to adhere to human epithelial cells and hydrocarbons with log P values ranging from 3.1 to 8.2. METHODS AND RESULTS: All isolates adhered to varying levels to epithelial cells, and were inhibited to various extents from adherence by mannose and fructose. There was a lack of correlation between adherence to either hydrocarbons or cells and colony opacity. Adherence to hydrocarbons was optimal for solvents with a log P < 8.2. CONCLUSIONS: Vibrio vulnificus clinical and environmental isolates exhibit differential adherence to epithelial cells and hydrocarbons. SIGNIFICANCE AND IMPACT OF THE STUDY: The differential adherence of organisms to hydrocarbons based on log P may have utility in drug design and enhancement of food safety.     

Confidence intervals of effect size for paired studies

To construct a confidence interval of effect size in paired studies, we propose four approximate methods--Wald method, variance-stabilizing transformation method, and signed and modified signed log-likelihood ratio methods. We compare these methods using simulation to determine those that have good performance in terms of coverage probability. In particular, simulations show that the modified signed log-likelihood ratio method produces a confidence interval with a nearly exact coverage probability and highly accurate and symmetric error probabilities even for very small samples. We apply the methods to data from an iron deficiency anemia study.     

Analysis of quantitative trait loci affecting chlorophyll content of rice leaves in a double haploid population and two backcross populations

Chlorophyll content, one of the most important physiological parameters related to plant photosynthesis, is usually used to predict yield potential. To map the quantitative trait loci (QTLs) underlying the chlorophyll content of rice leaves, a double haploid (DH) population was developed from an indica/japonica (Zhenshan 97/Wuyujing 2) crossing and two backcross populations were established subsequently by backcrossing DH lines with each of their parents. The contents of chlorophyll a and chlorophyll b were determined by using a spectrophotometer to directly measure the leaf chlorophyll extracts. To determine the leaf chlorophyll retention along with maturation, all measurements were performed on the day of heading and were repeated 30 days later. A total of 60 QTLs were resolved for all the traits using these three populations. These QTLs were distributed on 10 rice chromosomes, except chromosomes 5 and 10; the closer the traits, the more clustering of the QTLs residing on common rice chromosomal regions. In general, the majority of QTLs that specify chlorophyll a content also play a role in determining chlorophyll b content. Strangely, chlorophyll content in this study was found mostly to be lacking or to have a negative correlation with yield. In both backcross F₁ populations, overdominant (or underdominant) loci were more important than complete or partially dominant loci for main-effect QTLs and epistatic QTLs, thereby supporting previous findings that overdominant effects are the primary genetic basis for depression in inbreeding and heterosis in rice.     

The derivation of log‐transformed abundance data for the quantitative analysis of macroinvertebrate traits – an addendum to ‘A macroecological perspective of trait patterns in stream communities’ by Heino et al. ()

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Stand Structural Dynamics of North American Boreal Forests

Stand structure, the arrangement and interrelationships of live and dead trees, has been linked to forest regeneration, nutrient cycling, wildlife habitat, and climate regulation. The objective of this review was to synthesize literature on stand structural dynamics of North American boreal forests, addressing both live tree and coarse woody debris (CWD) characteristics under different disturbance mechanisms (fire, clearcut, wind, and spruce budworm), while identifying regional differences based on climate and surficial deposit variability. In fire origin stands, both live tree and CWD attributes are influenced initially largely by the characteristics of the stand replacing fire and later increasingly by autogenic processes. Differences in stand structure have also been observed between various stand cover types. Blowdown and insect outbreaks are two significant non-stand replacing disturbances that can alter forest stand structure through removing canopy trees, freeing up available growing space, and creating microsites for new trees to establish. Climate and surficial deposits are highly variable in the boreal forest due to its extensive geographic range, influencing stand and landscape structure by affecting tree colonization, stand composition, successional trajectories, CWD dynamics, and disturbance regimes including regional fire cycles. Further, predicted climate change scenarios are likely to cause regional-specific alterations in stand and landscape structure, with the implications on ecosystem components including wildlife, biodiversity, and carbon balance still unclear. Some stand structural attributes are found to be similar between clearcut and fire origin stands, but others appear to be quite different. Future research shall focus on examining structural variability under both disturbance regimes and management alternatives emulating both stand replacing and non-stand replacing natural disturbances.