岷江干旱河谷优势灌丛对土壤微生物群落组成的影响

通过调查岷江干旱河谷两河口、飞虹、撮箕和牟托4个样地优势灌丛及其灌丛间空地的表土土壤物理化学性质和微生物群落组成,探讨植物灌丛群落对土壤微生物群落组成的影响。研究发现不同灌丛种类对土壤微生物群落组成以及土壤物理化学性质并没有显著影响,而同一样地灌丛与空地间的差异却较为显著。灌丛下比空地土壤中具有更高的有机质、养分含量,更高的土壤含水量和更低的容重,而灌丛下相对富集的养分资源是造成灌丛与空地间微生物群落组成差异的主要原因。不同样地影响微生物群落的主要因子存在一定差异,但与氮相关的因子(总氮、有效氮、碳/氮比)对土壤微生物群落着非常重要的影响,特别是对土壤微生物群落总生物量和细菌类群(革兰氏阳性菌、革兰氏阴性菌、细菌等)。虽然不同灌丛和空地下土壤中细菌群落都没有显著地变化,但真菌和菌根真菌却明显的在灌丛下富集。在飞虹和牟托样地,总磷和碳/磷比与真菌类群,主要指真菌和菌根真菌,表现出显著正相关性,这或许反映了真菌类群对于该区域磷循环的重要作用。研究结果揭示了灌丛植被在干旱河谷地区地下生态系统中的重要作用,以及氮、磷这两种养分元素对土壤微生物群落的重要影响。同时,未来对于干旱河谷地区植物-土壤关系的研究应该关注真菌和菌根真菌类群的作用。     

贵州山区3种木本植物无机碳利用特性的比较

以生长在喀斯特高原地区玉舍国家森林公园内的成熟银鹊树(Tapiscia sinensis)、白栎(Quercus fabri)和亮叶桦(Betula luminifera)为实验材料,通过对光合作用、叶绿素含量、叶绿素荧光参数、羧化效率(CE)、呼吸速率(Resp)、碳酸酐酶活性(WA)以及稳定碳同位素组成(δ13 C)等指标的测定,分析3种植物不同的无机碳利用特性,为该区生态环境修复选择合适的建群植物种提供依据。结果显示:(1)银鹊树、白栎和亮叶桦分布都较为广泛,银鹊树生长的最佳土壤pH是4.5~5.5,而白栎更倾向于中性到弱酸性土壤,肥沃的酸性土壤则更有益亮叶桦生长;白栎和亮叶桦都能忍受干旱和贫瘠,但是银鹊树不能忍受干旱和高温。(2)银鹊树叶片的Pn、Tr和Gs显著大于白栎和亮叶桦,亮叶桦和白栎的Pn、Tr和Gs分别是银鹊树的69.5%、48.2%、66.7%和28.6%、21.7%、22.2%;亮叶桦叶绿素含量均为银鹊树和白栎的2倍,但3种植物间的WUE则无显著差异。(3)3个树种叶片净光合速率均随着CO2浓度升高呈持续上升的趋势,但它们之间的CO2补偿点和饱和点明显不同。其中,银鹊树和亮叶桦的CO2补偿点均低于50μmol·mol-1,而白栎的则在250~300μmol·mol-1之间;银鹊树的CO2饱和点在1 200μmol·mol-1左右,亮叶桦则在2 300μmol·mol-1左右,而白栎的CO2饱和点明显高于2 300μmol·mol-1。(4)3个树种的CE、Resp和WA均为银鹊树>亮叶桦>白栎;而δ13 C值则以银鹊树最低,亮叶桦和白栎较高。其中,白栎和亮叶桦的CE、Resp、WA分别为银鹊树的5.1%、25.7%、4.0%和45.3%、54.6%、6.8%,且树种间差异显著;白栎和亮叶桦的δ13 C值显著高于银鹊树。研究表明,银鹊树能够吸收大气中的CO2或者在高活性碳酸酐酶作用下转化利用细胞内的HCO3-,它拥有较高的CO2利用能力及无机碳同化效率,因而能够拥有较高的产能;亮叶桦只能获取大气中的CO2作为无机碳源,但它对CO2的利用能力也较高,其产能仅次于银鹊树;白栎同样只能获取大气中的CO2作为无机碳源,同时它对大气中CO2的捕获、利用能力均低于银鹊树和亮叶桦,因而白栎生长非常缓慢,造成其本身对无机碳的需求也最低,所以其产能最低。     

尾巨桉树干木质部液流密度径向变化特征

目前尾巨桉(Eucalyptus urophylla×Eucalyptus grandis)在中国南部大面积种植,尤其是在广西。其水分利用效率对森林的可持续发展以及水资源管理越来越受到关注。在不了解树干液流径向变化的前提下,将最外层边材液流测定值推广到整树或者林分尺度会产生很大的误差。为了准确测定整树耗水,采用热消散探针法(TDP)研究了南宁七坡林场4年生尾巨桉树干液流的径向变化特征。结果表明:各个深度有相似的日变化规律,0~20 mm深液流占有很大比例,随季节有所变化,20~40 mm深液流保持相对稳定;通过对0~20 mm和20~40 mm两个边材深度的日平均液流密度进行曲线回归分析,两者存在显著的幂指数相关关系(R20.90,P=0.00);同时分析了不同深度的径向分布格局,发现尾巨桉属于4大液流径向分布格局之一的递减型,且递减程度比较陡峭;白天和夜间的径向变化规律不一样,白天液流密度径向变化较明显,夜间则表现稳定。本文的发现有助于通过更精确地计算季节性液流密度来准确估算混种桉树的水分利用效率,对土地管理有重要的意义。     

Genomics in a changing arctic: critical questions await the molecular ecologist

Molecular ecology is poised to tackle a host of interesting questions in the coming years. The Arctic provides a unique and rapidly changing environment with a suite of emerging research needs that can be addressed through genetics and genomics. Here we highlight recent research on boreal and tundra ecosystems and put forth a series of questions related to plant and microbial responses to climate change that can benefit from technologies and analytical approaches contained within the molecular ecologist's toolbox. These questions include understanding (i) the mechanisms of plant acquisition and uptake of N in cold soils, (ii) how these processes are mediated by root traits, (iii) the role played by the plant microbiome in cycling C and nutrients within high‐latitude ecosystems and (iv) plant adaptation to extreme Arctic climates. We highlight how contributions can be made in these areas through studies that target model and nonmodel organisms and emphasize that the sequencing of the Populus and Salix genomes provides a valuable resource for scientific discoveries related to the plant microbiome and plant adaptation in the Arctic. Moreover, there exists an exciting role to play in model development, including incorporating genetic and evolutionary knowledge into ecosystem and Earth System Models. In this regard, the molecular ecologist provides a valuable perspective on plant genetics as a driver for community biodiversity, and how ecological and evolutionary forces govern community dynamics in a rapidly changing climate.     

Substantial variation in leaf senescence times among 1360 temperate woody plant species: implications for phenology and ecosystem processes

Background and Aims Autumn leaf senescence marks the end of the growing season in temperate ecosystems. Its timing influences a number of ecosystem processes, including carbon, water and nutrient cycling. Climate change is altering leaf senescence phenology and, as those changes continue, it will affect individual woody plants, species and ecosystems. In contrast to spring leaf out times, however, leaf senescence times remain relatively understudied. Variation in the phenology of leaf senescence among species and locations is still poorly understood.Methods Leaf senescence phenology of 1360 deciduous plant species at six temperate botanical gardens in Asia, North America and Europe was recorded in 2012 and 2013. This large data set was used to explore ecological and phylogenetic factors associated with variation in leaf senescence.Key Results Leaf senescence dates among species varied by 3 months on average across the six locations. Plant species tended to undergo leaf senescence in the same order in the autumns of both years at each location, but the order of senescence was only weakly correlated across sites. Leaf senescence times were not related to spring leaf out times, were not evolutionarily conserved and were only minimally influenced by growth habit, wood anatomy and percentage colour change or leaf drop. These weak patterns of leaf senescence timing contrast with much stronger leaf out patterns from a previous study.Conclusions The results suggest that, in contrast to the broader temperature effects that determine leaf out times, leaf senescence times are probably determined by a larger or different suite of local environmental effects, including temperature, soil moisture, frost and wind. Determining the importance of these factors for a wide range of species represents the next challenge for understanding how climate change is affecting the end of the growing season and associated ecosystem processes.     

From observations to experiments in phenology research: investigating climate change impacts on trees and shrubs using dormant twigs

Background and Aims Climate change is advancing the leaf-out times of many plant species and mostly extending the growing season in temperate ecosystems. Laboratory experiments using twig cuttings from woody plant species present an affordable, easily replicated approach to investigate the relative importance of factors such as winter chilling, photoperiod, spring warming and frost tolerance on the leafing-out times of plant communities. This Viewpoint article demonstrates how the results of these experiments deepen our understanding beyond what is possible via analyses of remote sensing and field observation data, and can be used to improve climate change forecasts of shifts in phenology, ecosystem processes and ecological interactions.Scope The twig method involves cutting dormant twigs from trees, shrubs and vines on a single date or at intervals over the course of the winter and early spring, placing them in containers of water in controlled environments, and regularly recording leaf-out, flowering or other phenomena. Prior to or following leaf-out or flowering, twigs may be assigned to treatment groups for experiments involving temperature, photoperiod, frost, humidity and more. Recent studies using these methods have shown that winter chilling requirements and spring warming strongly affect leaf-out and flowering times of temperate trees and shrubs, whereas photoperiod requirements are less important than previously thought for most species. Invasive plant species have weaker winter chilling requirements than native species in temperate ecosystems, and species that leaf-out early in the season have greater frost tolerance than later leafing species.Conclusions This methodology could be extended to investigate additional drivers of leaf-out phenology, leaf senescence in the autumn, and other phenomena, and could be a useful tool for education and outreach. Additional ecosystems, such as boreal, southern hemisphere and sub-tropical forests, could also be investigated using dormant twigs to determine the drivers of leaf-out times and how these ecosystems will be affected by climate change.     

Long‐term livestock exclusion facilitates native woody plant encroachment in a sandy semiarid rangeland

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The ecological impact of bush encroachment on the yield of grasses in Borana rangeland ecosystem

The ecological impact of woody encroachment and the responses of herbage yield to encroachment were assessed at three locations in Borana rangeland at the end of the growing season. The study was carried out in two communal grazing areas (Medhecho and Dubluk) and one Government ranch (Dida‐Tuyura) in bush and/or shrub encroached and non‐encroached sites. In each area, three altitude ranges were distinguished and in each altitude range one transect, covering both encroached and non‐encroached rangeland, was selected. The assessment was based on the yield and botanical composition of the herbaceous layer. The grasses Cenchrus ciliaris, Chrysopogon aucheri and Panicum coloratum were common or dominant in both encroached and non‐encroached sites. Pennisetum mezianum and Pennise‐tum stramineum were typically found in encroached vegetation. The relative yield increased with non‐encroached sites and varied at different altitude ranges from about 106% to about 150%, thus increases ranged from 75% in Medhecho to 350% in Dubluk as determined from the lower values of the ranges. The encroached vegetation had a significantly lower score for herbage yield than the non‐encroached vegetation for most of the sites, although the differences were small. Differences based on altitude range were also significant for Eragrostis papposa and Pennisetum stramineum, while the three areas showed a significant difference for the mean yield of Aristida adscensionis, Cenchrus ciliaris and Eragrostis papposa.     

Changes in bird communities in Swaziland savannas between 1998 and 2008 owing to shrub encroachment

Aim This study investigates changes in bird communities between 1998 and 2008 in four savanna sites in Swaziland and the extent to which shrub encroachment is responsible for these changes. Location Swaziland, southern Africa. Methods Generalized estimated equations were used to estimate changes in bird species occurrence between 1998 and 2008. Remote sensing of aerial photographs/satellite images was used to assess vegetation changes during the same period. We assessed the role of shrub encroachment for bird communities by testing the relationship between change in species occurrence and species habitat using a general linear model. We also estimated species richness, colonization and extinction and used general linear models to test the effects of vegetation changes on these parameters. Results More than half of the bird species showed a significant change in occurrence between 1998 and 2008: 32 species increased and 29 decreased. Change in species occurrence was significantly explained by species habitat. Species significantly increasing were mainly associated with wooded savanna, whereas species significantly decreasing were mainly associated with open savanna. Species richness decreased significantly, and this decrease was significantly explained by shrub cover increase at the plot scale (from 24% to 44% on average). Extinction at the plot scale was significantly influenced by the loss of grass cover, while colonization at the plot scale was influenced by tree cover increase. Main conclusions This study represents the first evidence of temporal changes in bird communities owing to shrub encroachment in southern Africa. Despite its short time frame (10 years), this study shows dramatic changes in both vegetation structure and bird community composition. This confirms the general concern for southern African bird species associated with open savanna if current trends continue.