转基因抗虫棉根系分泌物对棉花黄萎病菌生长的影响

转基因抗虫棉的抗病性下降已成为制约我国棉花生产的重要因素之一.以转基因抗虫棉及其亲本非转基因棉花对照为材料,研究转基因抗虫棉根系分泌物对棉花黄萎病菌孢子萌发和菌丝生长的影响,并对其根系分泌物中氨基酸及糖类的组成和含量进行了测定.结果表明：与亲本非转基因棉相比,2种转基因抗虫棉对棉花黄萎病菌的抗性下降,转基因抗虫棉的根系分泌物对黄萎病菌孢子萌发和菌丝生长均具有促进作用.与亲本常规棉中23相比,转基因双价抗虫棉中41根系分泌物中多了甲硫氨酸和赖氨酸,并且天冬氨酸、谷氨酸、丝氨酸、丙氨酸、缬氨酸、亮氨酸、酪氨酸的含量显著升高.泗棉三号与单价抗虫棉GK12的根系分泌物中虽然含有相同的氨基酸组分,但GK12的根系分泌物中酪氨酸、缬氨酸、亮氨酸的含量显著下降.中41根系分泌物中检测出4种糖类,而中23中仅检测出葡萄糖.抗虫棉GK12和泗棉三号根系分泌物中都检测出4种糖类,但其含量差异明显.     

Responses of biomass allocation across two vegetation types to climate fluctuations in the northern Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau (QTP) is particularly sensitive to global climate change, especially to elevated temperatures, when compared with other ecosystems. However, few studies use long‐term field measurements to explore the interannual variations in plant biomass under climate fluctuations. Here, we examine the interannual variations of plant biomass within two vegetation types (alpine meadow and alpine shrub) during 2008–2017 and their relationships with climate variables. The following results were obtained. The aboveground biomass (AGB) and belowground biomass (BGB) response differently to climate fluctuations, the AGB in KPM was dominated by mean annual precipitation (MAP), whereas the AGB in PFS was controlled by mean annual air temperature (MAT). However, the BGB of both KPM and PFS was only weakly affected by climate variables, suggesting that the BGB in alpine ecosystems may remain as a stable carbon stock even under future global climate change. Furthermore, the AGB in PFS was significantly higher than KPM, while the BGB and R/S in KPM were significantly higher than PFS, reflecting the KPM be more likely to allocate more photosynthates to roots. Interestingly, the proportion of 0–10 cm root biomass increased in KPM and PFS, whereas the other proportions both decreased, reflecting a shift in biomass toward the surface layer. Our results could provide a new sight for the prediction how alpine ecosystem response to future climate change.     

Use of plants by Myzus persicae in agroecosystems: Potential applications in conservation biological control

Myzus persicae (Sulzer) is a highly polyphagous aphid species that attacks several economically important crop plants. Here, trophic webs involving M. persicae, its host plants and its parasitoids were described and quantified in wheat, oat and alfalfa agroecosystems from central Argentina, with special emphasis on the sub-habitats where interactions occur: crops and adjacent field margins. Three fields cultivated with each crop species and their margins were sampled during three years; aphid abundance and mummification percentage were compared among crop plants and the diverse natural vegetation in the borders. Interactions were described using a quantitative food web approach, and abundance and mummification percentage e data were analysed using a generalized linear model. Four plant species present in the borders (Capsella bursa-pastori, Rapistrum sp., Melilotus sp. and Trifolium repens) hosted M. persicae and its parasitoids. The alfalfa agroecosystem produced a significantly higher number of aphids than oat and wheat; however, in all cases, crops and borders sustained similar aphid abundance. A total of six Aphidiinae species attacked M. persicae, with no significant differences in the richness of parasitoid species between the borders and the crops, but with significant differences in parasitoid abundance, being higher in the crops. Mummification percentage were higher in crops than in the borders, with Lysiphlebus testaceipes, Aphidius colemani and A. ervi being the most abundant species. Almost 70% of M. persicae individuals were collected from fields borders, which highlights the importance of including these sites in studies of trophic interactions in crop fields.     

青海省东部农业区植被覆盖时空演变遥感监测与分析

基于象元二分模型,利用MODIS植被指数产品定量估算研究区2000—2009年生长季(4—9月)植被覆盖度,采用相关系数法和有序聚类分析方法对植被覆盖度时空变化趋势及突变进行了分析,并结合DEM分析其对地形因子的响应。结果显示:1)研究区2000—2009年整体植被覆盖度在波动中呈不显著增加趋势,其中2001年是显著突变年份,表明研究区植被覆盖度发生比较显著的变化;2)通过对地形因子的响应分析,植被覆盖度在高程2500m和4100m,坡度4°和26°发生突变;对各高程带、坡度带植被覆盖度年际变化趋势及突变年份进行分析,获得了各带的变化趋势及其突变年份。对研究获得的结果进行讨论,结果表明:研究区降水量的变化及退耕还林措施是植被覆盖度变化的重要影响因素,其中退耕还林措施对植被覆盖度变化的影响较大。     

粤港澳大湾区不同恢复模式植物群落结构与生态系统健康的动态变化

基于长期定位监测数据,量化揭示了红锥纯林（Castanopsis hystrix）、10种与30种乡土树种混交林等3种乡土人工林植物群落的生物量、物种多样性、生物热力学健康水平（eco-exergy）和土壤理化性状在种植后13年内的发展动态,并与尾叶桉（Eucalyptus urophylla）纯林,以及自然恢复系统（灌草坡）进行了比较。结果表明：（1）研究期间,5种恢复模式的植物群落生物量均呈现波动上升趋势,但在发展节率上有所差异。13龄时的尾叶桉纯林与两种乡土树种混交林生物量显著高于其各自1龄时的水平,且显著高于自然恢复灌草坡;相较于其他人工林,红锥纯林生物量增长缓慢,但快于灌草坡;（2）5种恢复模式植物群落的物种多样性（物种丰富度、Shannon-Wiener指数、Pielou均匀度指数）在6至13龄间均呈下降趋势,且30种乡土树种混交林下降趋势最为显著。13龄时,两种混交林Shannon-Wiener指数略高于两种纯林,显著高于灌草坡;10种乡土树种混交林的Pielou均匀度指数略高于红锥纯林与30种乡土树种混交林,显著高于尾叶桉纯林与灌草坡。（3）4种人工林的植物群落生物热力学健康水平皆在6至13龄间显著增加;13龄时两种乡土混交林群落生态显著高于两种纯林,两种纯林显著高于灌草坡,且该差异主要源自于乔木层生态的差异。（4）不同植被恢复模式中,10种乡土树种混交林土壤养分的累积效果最佳,13龄时其土壤总氮含量显著高于红锥纯林和自然恢复灌草坡,但与30种乡土树种混交林和尾叶桉纯林无显著差异。（5）冗余分析结果显示,研究期间植被与土壤间的相关关系逐步建立,土壤理化性状对地上植被结构变化的解释度由1龄时的73.3%逐步上升至13龄时的82.0%,但只有土壤有机碳含量在13龄时与地上植被结构的相关性达到显著水平。上述结果表明,乡土种人工林与外来种人工纯林群落结构、生物热力学健康水平、及植被与土壤间关系的发展规律相似,且相对而言,混交林优于纯林,纯林优于自然恢复灌草坡。植被恢复的起始物种丰富度并不是越高越好;发展到13龄时,10种乡土树种混交林在植被结构与土壤改良方面均优于30种乡土树种混交林。植被与土壤间相关关系的建立是一个长期的过程,不同植被恢复模式对土壤理化性状的差异性影响难以在短期内有所显现。     

Restoration of Northwest Florida Sandhills Through Harvest of Invasive Pinus clausa

Across much of the southeastern U.S.A., sandhills have become dominated by hardwoods or invasive pine species following logging of Pinus palustris (longleaf pine) and fire suppression. At Eglin Air Force Base where this study was conducted, Pinus clausa (sand pine) has densely colonized most southeastern sandhill sites, suppressing groundcover vegetation. The objectives of this study were: to determine if suppressed groundcover vegetation recovers following the removal of P. clausa; to compare species composition and abundance in removal plots with that in reference, high quality sandhills; to test the assumption that recolonization by P. clausa seedlings decreases with proximity to the centers of removal plots; and to measure the survival of containerized P. palustris seedlings that were planted on P. clausa removal plots. One year post‐removal (1995), the number of plant species decreased by 50%, but then increased by 100% from 1995 to 1997, followed by a small reduction in 1998. The number of plant species was greater in reference plots than in removal plots prior to 1997. Eighty‐five percent of the original species were recorded 4 years post‐harvest in removal plots. Shrubs and large trees remained at low density after harvest. Densities of graminoids, legumes, other forbs, woody vines, and small trees increased after harvest. Plant densities of all life forms, except woody vines, were greater in reference plots than in removal plots. The density of recolonizing P. clausa seedlings 2–4 years post‐harvest significantly decreased with increasing proximity to the centers of removal plots. On average, 80% of planted P. palustris seedlings survived their first 2 years. Harvest of P. clausa followed by fire and the planting of P. palustris is a reasonably effective restoration approach in invaded sandhills. However, supplementary plantings of some herbaceous species may be necessary for full restoration.     

Can vegetation be discretely classified in species‐poor environments? Testing plant community concepts for vegetation monitoring on sub‐Antarctic Marion Island

The updating and rethinking of vegetation classifications is important for ecosystem monitoring in a rapidly changing world, where the distribution of vegetation is changing. The general assumption that discrete and persistent plant communities exist that can be monitored efficiently, is rarely tested before undertaking a classification. Marion Island (MI) is comprised of species‐poor vegetation undergoing rapid environmental change. It presents a unique opportunity to test the ability to discretely classify species‐poor vegetation with recently developed objective classification techniques and relate it to previous classifications. We classified vascular species data of 476 plots sampled across MI, using Ward hierarchical clustering, divisive analysis clustering, non‐hierarchical kmeans and partitioning around medoids. Internal cluster validation was performed using silhouette widths, Dunn index, connectivity of clusters and gap statistic. Indicator species analyses were also conducted on the best performing clustering methods. We evaluated the outputs against previously classified units. Ward clustering performed the best, with the highest average silhouette width and Dunn index, as well as the lowest connectivity. The number of clusters differed amongst the clustering methods, but most validation measures, including for Ward clustering, indicated that two and three clusters are the best fit for the data. However, all classification methods produced weakly separated, highly connected clusters with low compactness and low fidelity and specificity to clusters. There was no particularly robust and effective classification outcome that could group plots into previously suggested vegetation units based on species composition alone. The relatively recent age (c. 450,000 years B.P.), glaciation history (last glacial maximum 34,500 years B.P.) and isolation of the sub‐Antarctic islands may have hindered the development of strong vascular plant species assemblages with discrete boundaries. Discrete classification at the community‐level using species composition may not be suitable in such species‐poor environments. Species‐level, rather than community‐level, monitoring may thus be more appropriate in species‐poor environments, aligning with continuum theory rather than community theory.     

黑龙江省大兴安岭林区火烧迹地森林更新及其影响因子

林火干扰是大兴安岭森林更新的影响因子之一,研究火烧迹地森林更新的影响因子(立地条件、火前植被、火干扰特征)对理解生态系统的结构、功能和火后演替轨迹具有重要意义。选取呼中及新林林业局55个代表性火烧样地,利用增强回归树分析法分析了火烧迹地森林更新的影响因素。结果表明:(1)立地条件是影响针、阔叶树更新苗密度的主要因素;海拔对针叶树更新苗密度的影响最大;坡度对阔叶树更新苗密度影响最大;(2)距上次火烧时间对针叶树更新苗比重影响最大,其次是林型;(3)中度林火干扰后森林更新状况好于轻度和重度火烧迹地。根据火烧迹地森林更新调查分析可知:林型影响火后演替模式,火前为针叶树或阔叶树纯林,火后易发生自我更新(火后树种更新组成与火前林型相同),而针阔混交林在火干扰影响下易于发生序列演替(火后初期以早期演替树种更新为主)。