Plant Recruitment and Soil Microbial Characteristics of Rehabilitation Seedings Following Wildfire in Northern Utah

One goal of post‐fire native species seeding is to increase plant community resistance to exotic weed invasions, yet few studies address the impacts of seeding on exotic annual establishment and persistence. In 2010 and 2011, we investigated the influence of seedings on exotic annuals and the underlying microbial communities. The wildfire site in northern Utah was formerly dominated by Artemisia tridentata ssp. wyomingensis, but burned in September 2008. Experimental seeding treatments were installed in November 2008 to examine strategies for establishing native species using two drills, hand broadcasts and different timing of seed applications (resulting in 13 seeding treatments). We collected aboveground biomass of invasive annuals (Halogeton glomeratus, Salsola kali, and Bromus tectorum), other volunteer plants from the extant seed bank, and seeded species from all treatments in the second and third years after fire. We sampled soils within microsites beneath native perennial bunchgrass and exotic annuals to characterize underlying soil microbial communities. High precipitation following seeding led to strong seedling establishment and we found few differences between seeding treatments established with either drill. All seeded treatments reduced exotic biomass by at least 90% relative to unseeded controls. Soil microbial communities (phospholipid fatty acid analysis), beneath B. tectorum, Poa secunda, and Pseudoroegneria spicata microsites differed little 3 years after fire. However, microbial abundance beneath P. spicata increased from June to July, suggesting that microbial communities beneath successful seedings can vary greatly within a single growing season.     

Population variation and natural selection on leaf traits in cork oak throughout its distribution range

A central issue in evolutionary biology is the exploration of functional trait variation among populations and the extent to which this variation has adaptive value. It was recently proposed that specific leaf area (SLA), leaf nitrogen concentration per mass (N_mass) and water use efficiency in cork oak play an important role in adaptation to water availability in the environment. In order to investigate this hypothesis, we explored, first, whether there was population-level variation in cork oak (Quercus suber) for these functional traits throughout its distribution range; if this were the case, it would be consistent with the hypothesis that different rainfall patterns have led to ecotypic differentiation in this species. Second, we studied whether the population-level variation matched short-term selection on these traits under different water availability conditions using two fitness components: survival and growth. We found high population-level differentiation in SLA and N_mass, with populations from dry places exhibiting the lowest values for SLA and N_mass. Likewise, reduced SLA had fitness benefits in terms of growth for plants under dry conditions. However, contrary to our expectations, we did not find any pattern of association between functional traits and survival in nine-year-old saplings despite considerable drought during one year of the study period. These results together with findings from the literature suggest that early stages of development are the most critical period for this species. Most importantly, these findings suggest that cork oak saplings have a considerable potential to cope with dry conditions. This capacity to withstand aridity has important implications for conservation of cork oak woodlands under the ongoing climate change.     

Substantial reorganization of China's tropical and subtropical forests: based on the permanent plots

There is evidence that climate change induced tree mortalities in boreal and temperate forests and increased forest turnover rates (both mortality and recruitment rates) in Amazon forests. However, no study has examined China's tropical and subtropical evergreen broadleaved forests (TEBF) that cover >26% of China's terrestrial land. The sustainability of this biome is vital to the maintenance of local ecosystem services (e.g., carbon sequestration, biodiversity conservation, climatic regulation), many of which may influence patterns of atmospheric circulation and composition at regional to global scales. Here, we analyze time‐series data collected from thirteen permanent plots within China's unmanaged TEBF to study whether and how this biome has changed over recent decades. We find that the numbers of individuals and species for shrub and small tree have increased since 1978, whereas the numbers of individuals and species for tree have decreased over this same time period. The shift in species composition is accompanied by a decrease in the mean diameter at breast height (DBH) for all individuals combined. China's TEBF may thereby be transitioning from cohorts of fewer and larger individuals to ones of more and smaller individuals, which shows a unique change pattern differing from the documented. Regional‐scale drying is likely responsible for the biome's reorganization. This biome‐wide reconstitution would deeply impact the regimes of carbon sequestration and biodiversity conservation and have implications for the sustainability of economic development in the area.     

Locking the Active Conformation of c-Src Kinase through the Phosphorylation of the Activation Loop

Molecular dynamics umbrella sampling simulations are used to compare the relative stability of the active conformation of the catalytic domain of c-Src kinase while the tyrosine 416 in the activation loop (A-loop) is either unphosphorylated or phosphorylated. When the A-loop is unphosphorylated, there is considerable flexibility of the kinase. While the active conformation of the kinase is not forbidden and can be visited transiently, it is not the predominant state. This is consistent with the view that c-Src displays some catalytic activity even when the A-loop is unphosphorylated. In contrast, phosphorylation of the A-loop contributes to stabilize several structural features that are critical for catalysis, such as the hydrophobic regulatory spine, the HRD motif, and the electrostatic switch. In summary, the free-energy landscape calculations demonstrate that phosphorylation of tyrosine 416 in the A-loop essentially “locks” the kinase into its catalytically competent conformation.     

黄顶菊在中国的潜在适生区

菊科黄菊属植物黄顶菊近年出现在我国华北地区天津市和河北省的衡水、廊坊等地,其入侵范围有不断扩大的趋势.黄顶菊是一种入侵性极高的一年生杂草,对农牧业生态系统有极大的破坏性.为指导黄顶菊的防除和制定相关的控制政策,本研究根据黄顶菊在其原产地南美洲及扩散入侵地的分布资料,采用CLIMEX生态位模型对其在中国的潜在适生分布区域进行预测.结果表明,黄顶菊在中国的潜在适生区域集中分布于东南部的广东、广西、云南、海南、福建、台湾、江西、湖南、贵州、四川、重庆、湖北、安徽、江苏、上海15个省（市、自治区）,其中高风险区域包括广东、广西、台湾、海南、福建、云南、四川、贵州、重庆和西藏局部地区.     

利用红边面积形状参数估测水稻叶层氮浓度

研究红边面积参数与叶层氮素状况的定量关系, 有助于水稻(Oryza sativa)生长信息的实时无损获取及精确追氮管理。该研究基于多年不同施氮水平和不同水稻品种的冠层高光谱数据, 系统分析了水稻的红边区域光谱、面积形状特征及其与叶层氮浓度的定量关系。结果表明, 水稻冠层红边区域微分光谱随不同氮素水平变化出现“三峰”现象, 峰值分别出现在700、720和730 nm附近, 且3个波段的峰值高低发生交替变化; 同时, 以3个峰值波段为中心与x坐标轴组成的微分光谱面积和形状相应发生变化。发现基于两两峰值波段划分所得红边子面积所构成的比值(双峰对称度)、归一化差值(归一化对称度)参数与叶层氮浓度具有密切的定量关系, 可作为估测水稻叶层氮浓度的红边面积形状参数。经曲线拟合和模型检验的结果显示, 双峰对称度DPS (A_675-700, A_675-755), 即由675~700 nm区域面积与675~755 nm区域面积的比值, 和DPS (A_730-755,A_675-700) (由730~755 nm区域面积和675~700 nm区域面积的比值)对水稻叶层氮浓度的估测效果最好, 可用于不同水稻品种和生长条件下的叶层氮浓度估测。     

枣粮间作系统节肢动物群落组成与时序动态

为揭示枣粮间作系统中枣园和农田两个亚系统节肢动物群落的关系,将枣粮间作系统区分为枣园亚系统和农田亚系统进行节肢动物生态调查并分析时序动态.调查共发现节肢动物14 936头,分属3纲、14目、96科,其中枣园亚系统个体5 992头,分属3纲、14目、82科,农田亚系统个体8 971头,分属3纲、14目、80科,且枣园、农田两个亚系统节肢动物群落的结构存在一定差异.对系统进行时间序列的最优分割可将其划分为4个不同的时期,即麦田亚系统衰落期、系统物种增长期、系统发展稳定期、系统动荡衰落期.系统主要天敌物种在4个阶段中表现出相互迁移的特性,且两个亚系统寄生性天敌物种对另一系统的害虫存在着制约作用.枣粮间作系统中枣园和农田两个亚系统节肢动物群落间的物种迁移和相互作用对提高系统的稳定性和控害能力有积极意义.     

东北山地灌木沼泽植物铜、锌分布特征及季节动态

研究了东北山地灌木沼泽主要植物--细叶沼柳、五蕊柳、丛苔草和修氏苔草中Cu、Zn分布、积累及其季节动态.结果表明:Cu含量变动范围为6～12 mg·kg-1,细叶沼柳和五蕊柳各器官Cu含量为根》枝》叶;丛苔草和修氏苔草为茎》叶》根,Cu主要积累在灌木的根系和苔草的茎叶中,灌木和苔草中Cu含量相差较小.Zn含量变动在30～250 mg·kg-1之间,细叶沼柳和五蕊柳各器官Zn含量为叶》枝》根,尤其是叶和枝中都在150 mg·kg-1以上;丛苔草和修氏苔草各器官Zn含量为根》茎》叶.Zn多积累在灌木的叶和苔草的根中,且灌木各器官Zn含量明显高于苔草.细叶沼柳和五蕊柳各器官对Zn的富集系数均大于1.45,显示出较强的Zn富集能力.4种供试植物在生长初期地上部分Cu、Zn含量较高,且随着季节变化呈波动式降低趋势,而根中则表现出生长初期和末期Cu、Zn含量较高的特点.     

景观格局对洞庭湖区鼠害的影响

景观空间格局与生态学过程的关系是景观生态学研究中的一个核心问题.不论物种保护还是生物灾害的防治,均与生物生存环境的景观格局息息相关.选择洞庭湖区为研究区域,分析了典型样区的景观格局特征,并对耕地和房舍中的鼠类捕获率与反映景观格局特征的景观指数进行相关分析.结果表明:耕地中鼠类的捕获率与景观聚集度、连接度以及斑块形状显著相关;房舍中鼠害的捕获率与建设用地的斑块形状显著相关.从景观格局角度提出了降低耕地和房舍中鼠害捕获率的方法.