不同时间和空间尺度上台湾水青冈群落谱系结构动态变化

群落谱系结构是了解群落聚群过程的一个基础研究内容。但是现有大部分研究内容集中在群落组成和结构的时空差异,对谱系结构的动态变化研究较少。以浙江省清凉峰国家级自然保护区的国家二级保护植物台湾水青冈(Fagus hayatae)林为研究对象,利用2006年、2011年、2016年3次群落动态调查数据,从10、20、50m的3个空间尺度上研究该群落在10a间的谱系结构动态变化,分析时空尺度对台湾水青冈群落谱系结构的影响,探究调控台湾水青冈群落动态变化的主要因子,为后期台湾水青冈林的保护提供理论基础。研究发现(1)在10a森林动态变化过程中,群落的MPD指数下降,MNTD指数增加。NRI和NTI指数在大尺度上随时间显著增加,但在小尺度上无显著变化。(2)随着空间尺度的增加,上述指数的动态变化趋势均不断增强。以上结果表明,2006—2016年间台湾水青冈群落总体谱系结构表现出不断聚集的趋势,而近缘种的谱系关系则不断疏远;群落谱系结构的聚集趋势随空间尺度的增加而增强。大尺度上的环境过滤和小尺度上的随机过程和种间竞争作用可能是导致该地区台湾水青冈群落谱系结构动态变化的主要生态学过程。     

环境筛选和扩散限制在地表和地下螨群落物种共存中的调控作用

识别扩散限制和环境筛选在群落物种共存中的相对作用,是土壤动物群落物种共存机制研究的重要内容,然而少有针对地表和地下土壤动物群落的探讨。在三江平原农田生态系统,设置一个50 m×50 m的空间尺度,探讨环境筛选和扩散限制对地表和地下土壤螨群落物种共存的调控作用。基于Moran特征向量图(MEMs)和变差分解的方法来区分环境筛选和扩散限制的调控作用;采用偏Mantel检验进一步分析环境距离和空间距离的相对贡献;使用RDA分析环境因子对螨群落物种组成的解释能力。变差分解结果表明,空间变量对地表、地下和地表-地下土壤螨群落具有较大的显著方差解释量,而环境变量和空间环境结构的解释量相对较小且不显著;偏Mantel检验没有发现环境距离或空间距离的显著贡献;RDA分析表明土壤p H值、大豆株高和土壤含水量对土壤螨群落具有显著的解释能力,说明环境变量对螨群落物种组成的重要作用。研究表明,在三江平原农田生态系统,地表和地下土壤螨群落物种共存主要受到扩散限制的调控作用,同时环境筛选的调控作用也不容忽视。     

Environmental filtering rather than dispersal limitation dominated plant community assembly in the Zoige Plateau

Identifying the mechanisms that underlie the assembly of plant communities is critical to the conservation of terrestrial biodiversity. However, it is seldom measured or quantified how much deterministic versus stochastic processes contribute to community assembly in alpine meadows. Here, we measured the decay in community similarity with spatial and environmental distance in the Zoige Plateau. Furthermore, we used redundancy analysis (RDA) to divide the variations in the relative abundance of plant families into four components to assess the effects of environmental and spatial. Species assemblage similarity liner declined with geographical distance (p < .001, R ² = .6388), and it decreased significantly with increasing distance of total phosphorus (TP), alkali‐hydrolyzable nitrogen (AN), available potassium (AK), nitrate nitrogen (NO₃ ⁺–N), and ammonia nitrogen (NH₄ ⁺–N). Environmental and spatial variables jointly explained a large proportion (55.2%) of the variation in the relative abundance of plant families. Environmental variables accounted for 13.1% of the total variation, whereas spatial variables accounted for 11.4%, perhaps due to the pronounced abiotic gradients in the alpine areas. Our study highlights the mechanism of plant community assembly in the alpine ecosystem, where environmental filtering plays a more important role than dispersal limitation. In addition, a reasonably controlled abundance of Compositae (the family with the highest niche breadth and large niche overlap value with Gramineae and Cyperaceae) was expected to maintain sustainable development in pastoral production. These results suggest that management measures should be developed with the goal of improving or maintaining suitable local environmental conditions.     

Suction volume and filtering efficiency of silver carp (Hypophthalmichthys molitrix Val.) and bighead carp (Aristichthys nobilis Rich.)

Experiments were conducted to measure the suction volume of silver carp and bighead carp of age 1 + with respiratory chamber, and to calculate the suction volume and the filtering efficiency with respect to changes in concentrations of food particles. Suction volume (B. ml/mouth) and filtering efficiency (E. %) were calculated using the following formula: C ₁=C₀(1-BE/v)ⁿ where C₀ and C₁ were the concentrations of specific food particles at the beginning and at the end of experiment, respectively, V was the volume (ml) of experimental water, and n was the total number of observation of suction made during the experimental period. The relationships between suction volume (ml/mouth) of age I+ silver carp (B_h) and bighead carp (B_a) and their standard lengths (L, cm) were: B _h=0.561L-8.94, B_a= 0.627L-7.48 while those of the fingerlings were: B _h= O.l70L-0.837, B_a= 0.157L-0.418. The suction volume of the fingerlings was mainly affected by fish size, the function of temperature between 15 and 25° C being negligible. However, temperature affected filtering rate (filtered volume per unit time) through its effect on filtering frequency. The filtering efficiency of the fishes for rotifers (Brachionus caliciflorus) was 100 per cent. The relationships between filtering efficiency and sizes of food particles smaller than or equal to that of a rotifer were: E _h=25.1 ln e.s.d. -13.6, E_a=22.2 In e.s.d. -33.1 where E_h and E_a were filtering efficiency of silver carp and bighead carp, respectively, and e.s.d. was the equivalent spherical diameter (μm) of food particles.     

施磷和杀真菌剂对黄顶菊生长及生理代谢的影响

以黄顶菊为供试植物,通过盆栽试验研究土壤真菌在其入侵过程中的作用,揭示黄顶菊入侵的土壤微生物学机制.试验设置5个施磷( KH2PO4)水平(50 mg·kg-1CaSO4,缺磷处理,P0;空白,不加磷处理,P1;20 mg· kg-1,P2;40 mg·kg-1,P3;80 mg· kg-1,P4),并通过施用杀真菌剂苯菌灵控制土壤真菌,研究二者对黄顶菊入侵性的影响.杀真菌剂处理显著降低了黄顶菊的菌根侵染率,抑制了植株光合作用,降低了植株生物量、可溶性糖的积累及抗氧化保护酶系统(SOD、POD和CAT)活性,在较高施磷水平时(P3、P4)增加植株全P含量,而对植株叶绿素、可溶性蛋白、全N含量等无显著影响.施用磷肥引起的植物磷营养状况的改变,对土壤真菌具有一定的调控作用,真菌效应的发挥因施磷量不同而发生变化,在缺磷和低磷处理(P0～P2)时,真菌对N、P吸收贡献率表现为正效应;而当施磷量较高(P3、P4)时,贡献率表现为负效应.土壤真菌和养分状况对黄顶菊的生长和生理代谢均有重要影响.     

太行山北段地区荆条灌丛和三裂绣线菊灌丛群落谱系结构

灌丛是太行山地区最重要的生态系统类型之一, 灌丛群落生物多样性的维持及其生态系统服务功能对京津冀地区的生态安全具有重要作用。本研究选择太行山最具代表性的两种灌木群落——荆条(Vitex negundo var. heterophylla)灌丛和三裂绣线菊(Spiraea trilobata)灌丛为研究对象, 利用净亲缘关系指数(net relatedness index, NRI)和多元回归等方法探究了两种灌丛群落构建机制的异同及主要的环境影响因子, 同时还利用谱系结构主坐标分析(principal coordinates of phylogenetic structure, PCPS)对决定群落谱系结构的关键系统发育节点进行了探究。结果表明: 两种灌丛群落内灌木植物的物种多样性没有显著差异, 但谱系结构差异显著。三裂绣线菊群落表现出显著的谱系发散趋势, 而荆条群落谱系聚集程度高于三裂绣线菊群落, 但未表现出显著的谱系结构。三裂绣线菊灌丛群落构建的驱动机制是生态位分化, 荆条灌丛中生境过滤作用有所增加, 与生态位分化共同驱动其群落构建过程。与干旱胁迫相关的生境过滤因素增加是荆条灌丛群落谱系聚集程度增加的重要原因。PCPS二维排序结果表明: 荆条灌丛群落谱系趋向聚集与其群落内缺乏蔷薇目、壳斗目等亲缘关系较远的类群有关, 而三裂绣线菊灌丛群落内物种则包含较多的演化分支。总体而言, 环境过滤不是决定太行山地区灌丛群落构建的主要驱动因素, 但水分条件仍然是影响区域群落谱系结构的重要因素。     

Systematic Evaluation of Protein Sequence Filtering Algorithms for Proteoform Identification Using Top‐Down Mass Spectrometry

Complex proteoforms contain various primary structural alterations resulting from variations in genes, RNA, and proteins. Top‐down mass spectrometry is commonly used for analyzing complex proteoforms because it provides whole sequence information of the proteoforms. Proteoform identification by top‐down mass spectral database search is a challenging computational problem because the types and/or locations of some alterations in target proteoforms are in general unknown. Although spectral alignment and mass graph alignment algorithms have been proposed for identifying proteoforms with unknown alterations, they are extremely slow to align millions of spectra against tens of thousands of protein sequences in high throughput proteome level analyses. Many software tools in this area combine efficient protein sequence filtering algorithms and spectral alignment algorithms to speed up database search. As a result, the performance of these tools heavily relies on the sensitivity and efficiency of their filtering algorithms. Here, we propose two efficient approximate spectrum‐based filtering algorithms for proteoform identification. We evaluated the performances of the proposed algorithms and four existing ones on simulated and real top‐down mass spectrometry data sets. Experiments showed that the proposed algorithms outperformed the existing ones for complex proteoform identification. In addition, combining the proposed filtering algorithms and mass graph alignment algorithms identified many proteoforms missed by ProSightPC in proteome‐level proteoform analyses.