Spatial pattern analysis of pre- and post-hurricane forest canopy structure in North Carolina,USA

Existing spatial patterns of a forest are in part a product of its disturbance history. Using laser altimetry and field measures of canopy top height to represent pre- and post-hurricane canopy topography, respectively, we measured changes in spatial patterns of stand structure of a United States southern mixed coniferous-deciduous for est. Autocorrelative and fractal properties were measured in this opportunistic study to quantify changes in canopy architecture along twelve, 190-250 m transects that were subjected to moderate to high levels of wind disturbance. Prior to the hurricane, canopy heights were autocorrelated at scales <40 m with an average fractal dimension of 1.71. After the disturbance, autocorrelation disappeared; the average fractal dimension rose to 1.94. This shift towards spatial randomness illustrates part of the cyclical nature of ecosystem development. It shows how a catastrophic collapse of biomass accumulation corresponds to a decrease in ecosystem organization across a landscape. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combining competition from Lolium perenne and an insect–fungus combination to control Rumex obtusifolius seedlings

Although adult Rumex obtusifolius are problematic weeds, their seedlings are poor competitors against Lolium perenne, particularly in established swards. We investigated the possibility of using this weakness to augment control of R. obtusifolius seedlings with combinations of Gastrophysa viridula (Coleoptera: Chrysomelidae) and the rust fungus Uromyces rumicis. Rumex obtusifolius seedlings were grown in competition with L. perenne sown at different rates and times after R. obtusifolius: they competed successfully with L. perenne when sown 21 days before the grass. Sowing both species at the same time resulted in a dominant grass sward, with R. obtusifolius becoming dominant when sown 42 days prior to L. perenne. Grass sowing rate had no effect on R. obtusifolius growth or biomass. A second experiment investigated how competition from L. perenne sown 21 days after R. obtusifolius combined with damage from G. viridula and/or U. rumicis (applied at either the 3–4‐ or 10–13‐leaf stage, or at both stages) affected the growth and final biomass of R. obtusifolius. Beetle grazing at the latter leaf stage was the only treatment that reduced R. obtusifolius biomass, although rust infection at the earlier application led to an increase in shoot and root weight. The results are discussed in terms of the potential for use of these agents in the field.     

植物寄生线虫效应蛋白调控寄主防卫反应分子机制研究进展

在植物寄生线虫与寄主互作过程中,线虫分泌器官如食道腺细胞分泌的效应蛋白在寄主细胞壁修饰和调控寄主免疫反应以及取食位点形成和维护中发挥着关键作用。解析植物寄生线虫关键效应蛋白的功能及其与寄主互作机制将为探索植物寄生线虫防控新策略提供重要的理论基础。本文从效应蛋白降解寄主细胞壁、调控寄主基础免疫反应、诱导免疫反应机制和介导翻译后修饰调控寄主免疫反应以及植物激素代谢途径的调控机制等方面进行了概述。     

烟碱乙酰胆碱受体及其与新烟碱类相互作用的研究进展

对烟碱乙酰胆碱受体(nAChRs)的结构与功能、配体结合部位、门控机理以及与新烟碱类的相互作用进行了综述,并对nAChRs亚基基因突变和敲除对新烟碱类和多杀菌素敏感性的影响进行了讨论。nAChRs在脊椎动物和昆虫的胆碱能突触的快速神经传递中起着重要作用,其在昆虫中仅存在于中枢神经系统(CNS)中,而在脊椎动物中同时存在于CNS和神经肌肉连接处。nAChRs是新烟碱类杀虫剂、多杀菌素和杀螟丹的作用靶标。肌肉和CNS中的nAChRs是一个由两个α和三个非α(β,γ和δ)亚基组成的异数五聚体,该受体主要有三部分:一个在细胞外发现的区域(胞外区)、一个位于膜内的区域(跨膜区),另一个是位于细胞内的区域(胞质区)。每个亚基(从N-C端)都具有一个包含乙酰胆碱(ACh)结合部位的细胞外结构域;4个跨膜结构域(M1~4),其中M2的大部分氨基酸位于离子通道的内壁;一个胞质噜扑(loop)和一个胞外C端。通道门位于孔道内的疏水区。ACh结合部位位于天然和功能受体的两个亚基的界面,是由一个亚基的3个噜扑(A-C)和另一个亚基的3个噜扑(D-F)构成。每当受体与ACh(或其他激动剂)分子结合时,M2 α螺旋体的构象发生改变,使通道开启,处于阳离子传导状态,直至一个或两个激动剂分子从结合口袋解离,通道才关闭。如果激动剂一直存在,并反复结合,则通道处于脱敏状态。nAChRs与新烟碱类的各种选择性作用取决于新烟碱类的结构以及nAChRs的亚基组成。     

植物-植食性昆虫互作关系中早期信号事件研究进展

诱导防御反应的产生取决于植物对植食性昆虫相关信号迅速和准确地识别。在植物与植食性昆虫互作过程中,早期信号事件是负责植物识别和触发下游信号转导途径的最早反应,它们发生在植物防御相关基因表达和防御相关代谢物产生之前,对植物的防御过程至关重要。本文将植物与植食性昆虫互作的早期事件,包括植物对植食性昆虫的感知、电信号和Ca~(2+)信号的产生和转导,活性氧的迸发以及促细胞分裂原活化蛋白激酶(MAPK)信号级联途径等研究进展进行了综述,并提出今后的研究重点与方向,促进对植物诱导防御反应调控网络的研究,以期为改进农业害虫的治理提供重要的理论和技术支撑。     

乌桕对南方根结线虫与地上不同食性昆虫互作的光合生理响应

本文通过比较乌桕对两种地上不同食性昆虫(专食性癞皮夜蛾、广食性斜纹夜蛾)与南方根结线虫互作的光合生理响应,分析不同空间植食性生物间的互作关系及植物的响应机制。结果表明:无南方根结线虫胁迫下,2种地上不同食性昆虫对乌桕的净光合速率(P_n)、气孔导度(G_s)及胞间CO_2浓度(C_i)的影响与对照组无显著差异;而南方根结线虫胁迫下,2种地上昆虫显著降低了乌桕G_s及C_i。其中,与对照组及癞皮夜蛾处理组相比,南方根结线虫与斜纹夜蛾的共同胁迫显著降低了乌桕P_n、G_s及C_i。此外,斜纹夜蛾为害增加了乌桕叶绿素含量,南方根结线虫胁迫降低了叶绿素含量。因此,南方根结线虫与斜纹夜蛾间形成一种加性效应,并对乌桕光合生理产生了拮抗效应,而这种效应在南方根结线虫与癞皮夜蛾间并不显著。由此可见,乌桕对地上-地下植食性生物胁迫形成不足补偿机制,且具体的响应机制与植食性生物的食性相关。     

Response of snails and slugs to fragmentation of lowland forests in NW Germany

Habitat fragmentation is a major cause for species loss, but its effect on invertebrates with low active dispersal power, like terrestrial gastropods, has rarely been studied. Such species can not cross a hostile habitat matrix, for which the predictions of island theory, such as positive relations between species richness and patch size, should apply. In order to test this prediction, we studied gastropod species diversity by assessing gastropod assemblage characteristics from 35 sites in 19 fragments of deciduous old-growth forests in the Lower Rhine Embayment, Germany. Assemblages differed between larger (≥700 ha) and smaller forests (<400 ha), those of large forests held a higher percentage of forest species. Although α-diversity was similar between the two forest size classes, small forests often comprised matrix species, resulting in a higher β-diversity. Edge effects on the species richness of matrix species were noticeable up to 250 m into the forest. Hierarchical partitioning revealed that distance to disturbances (external edge, internal edges like roads) explained most assemblage variables, whereas forest size and woodland cover within a 1 km radius from the sites explained only a few assemblage variables. Densities of two forest-associated species, Discus rotundatus and Arion fuscus, decreased with forest size. Yet, forest size was positively correlated with richness of typical forest species and densities of Limax cinereoniger. The latter species seems to need forests of >1,000 ha, i.e., well above the size of most fragments. In conclusion, the prediction is valid only for forest species. The response to fragmentation is species specific and seems to depend on habitat specialization and macroclimatic conditions. Jean-Pierre Maelfait: Deceased.     

生态系统服务多样性与景观多功能性——从科学理念到综合评估

生态系统和景观是构成地球表层系统的基本功能单元.从对人类生存和发展支撑作用以及人类对环境合理利用和保护的角度,逐渐形成了生态系统服务和多功能景观的科学概念,相关的理论和应用研究也很快成为学术热点.但是从国内外主要进展上看,生态系统服务和景观多功能性的定量化研究都还比较薄弱.生态系统与景观具有等级关联性,前者是构成后者的基本要素,生态系统服务和景观功能具有同源性.因此,将生态系统服务与景观多功能性研究紧密结合既有现实基础又能够深化彼此研究的定量化水平,并进一步提出了生态系统服务与景观多功能性综合定量研究的整体性框架.从当前国内外研究文献看,该框架具有可行性,可以作为进一步深化生态系统服务和景观多功能性研究的现实途径.     

Impact of soil engineering by two contrasting species of earthworms on their dispersal rates

By burrowing galleries and producing casts, earthworms are constantly changing the structure and properties of the soils in which they are living. These changes modify the costs and benefits for earthworms to stay in the environment they modify. In this paper, we measured experimentally how dispersal behaviour of endogeic and anecic earthworms responds to the cumulative changes they made in soil characteristics. The influence of earthworm activities on dispersal was studied in standardised mesocosms by comparing the influence of soils modified or not modified by earthworm activities on earthworm dispersal rates.The cumulative use of the soil by the earthworms strongly modified soil physical properties. The height of the soil decreased over time and the amount of aggregates smaller than 2 mm decreased in contrast to aggregates larger than 5 mm that increased. We found that: (i) earthworm activities significantly modified soil physical properties (such as bulk density, soil strength and soil aggregation) and decreased significantly the dispersal rates of the endogeic species, whatever the species that modified the soil; (ii) the decreasing in the dispersal proportion of the endogeic species suggests that the cost of engineering activities may be higher than the one of dispersal; (iii) the dispersal of the anecic species appeared to be not influenced by its own activities (intra-specific influences) or by the activities of the endogeic species (inter-specific influences). Overall these results suggest that the endogeic species is involved in a process of niche construction, which evolved jointly with its dispersal strategy.