亚热带天然次生常绿阔叶林与杉木人工林土壤动物群落特征比较

调查了中亚热带会同林区毗邻的天然次生常绿阔叶林、一代杉木纯林和二代杉木纯林土壤动物群落特征．结果表明,采伐天然林,接着栽植杉木人工林后,土壤动物的多度和多样性均出现明显下降,而土壤动物的生物量和生产力却没有明显差别．杉木连栽对土壤动物的多度、多样性、生物量影响甚少,特别是杉木一、二代土壤动物的生产力接近相等．此项研究结果支持植被是影响土壤动物演替的一个主要原因,也暗示杉木长期连作对土壤动物群落的影响是一个非常缓慢的过程．     

浙江天童常绿阔叶林栲树种子雨的时空格局

在浙江天童常绿阔叶林中选择5株栲树,通过种子筐和地表取样,分析了栲树种子雨的时空格局特征.结果表明,栲树种子雨从11月3日到12月16日,持续45d,存在散落的高峰期(11月18日～27日);散落在地表的种子雨主要集中在离母株树干1.5～5.5m区段内,占总数的85.6%,最远不超过8m,空间格局符合二次分布;整个种子雨期间,单株平均落果数为112.8个·m^-2(70个·m^-2～239.5个·m^-2),东南向较多(135.6个·m^-2)、西北向较少(86.8个·m^-2),但无显著差异;种子雨中有活力的坚果占总数的27.3%、未成熟的占25.7%,昆虫幼虫侵害的占42%,松鼠啃食的占5%.     

澳门路环岛灌丛群落的特征

初步分析了澳门路环岛灌丛群落的种类组成及种群的多度、频度、重要值及外貌,结果表明:群落植物种类丰富,种属组成分散,具有典型的南亚热带区系特点。广东蒲桃、豺皮樟、亮叶柃、桃金娘等在群落中占明显优势,但本区灌丛群落均匀性偏低。具有较高丰富度的种类仅占很少部分,可能与乔木缺乏和种群竞争有关。群落的外貌主要是由小型和中型落叶草质及常绿革质、全缘单叶的高位芽植物所决定的。在分析灌丛群落特征的基础上,对其生态保护提出了建议。     

Spectral feature differences between shrub and grass communities and shrub coverage retri- eval in shrub-encroached grassland in Xianghuang Banner,Nei Mongol,China

Aims Shrub-encroached grassland has become an important vegetation type in China’s arid and semi-arid region. Our study objective is to explore the spectral features of shrub and grass communities, as well as their empirical relationships with shrub coverage. The quantitative estimation of shrub cover based on medium-resolution Landsat satellite imagery provides the practical basis for long term retrieval of large areas of shrub expansion in the grassland region. Methods Linear models and Multiple Endmember Spectral Analysis Model (MESMA) based on medium resolution Landsat satellite imagery were developed to quantify the shrub coverage in a shrub-encroached grassland region in Xianghuang Banner, Nei Mongol using the spectral features and their seasonal differences between the shrub and grass communities. Important findings Compared to Leymus chinensis and Stipa krylovii dominated grass communities, Caragana microphylla community had a higher normalized difference vegetation index (NDVI), modified red edge normalized difference vegetation index (mNDVI₇₀₅), and red edge slope. The red edge position of C. microphylla community shifted to longer wavelengths. The average and the maximum shrub coverage was 13% and 25%, respectively, in the shrub-encroached grassland based on both models. The correlation coefficient of determination (R²) and root mean square error (RMSE) of the linear model was 0.31 and 0.05, respectively. We found that the linear model based on seasonal differences of shrub and grass community was more suitable for retrieving shrub coverage in the study area from medium resolution imagery than the MESMA model that is based on mid-summer images.     

Patterns of shrub expansion in Alaskan arctic river corridors suggest phase transition

Recent increases in deciduous shrub cover are a primary focus of terrestrial Arctic research. This study examined the historic spatial patterns of shrub expansion on the North Slope of Alaska to determine the potential for a phase transition from tundra to shrubland. We examined the historic variability of landscape‐scale tall shrub expansion patterns on nine sites within river valleys in the Brooks Range and North Slope uplands (BRNS) between the 1950s and circa 2010 by calculating percent cover (PCTCOV), patch density (PADENS), patch size variability (CVSIZE), mean nearest neighbor distance (MEDIST) and the multi‐scale information fractal dimension (d_I) to assess spatial homogeneity for shrub cover. We also devised conceptual models for trends in these metrics before, during, and after a phase transition, and compared these to our results. By developing a regression equation between PCTCOV and d_I and using universal critical d_I values, we derived the PCTCOV required for a phase transition to occur. All nine sites exhibited increases in PCTCOV. Five of the nine sites exhibited an increase in PADENS, seven exhibited an increase in CVSIZE, and five exhibited a decrease in MEDIST. The d_I values for each site exceeded the requirements necessary for a phase transition. Although fine‐scale heterogeneity is still present, landscape‐scale patterns suggest our study areas are either currently in a state of phase transition from tundra to shrubland or are progressing towards spatial homogeneity for shrubland. Our results indicate that the shrub tundra in the river valleys of the north slope of Alaska has reached a tipping point. If climate trends observed in recent decades continue, the shrub tundra will continue towards homogeneity with regard to the cover of tall shrubs.     

Soil organic matter quantity and quality shape microbial community compositions of subtropical broadleaved forests

As two major forest types in the subtropics, broadleaved evergreen and broadleaved deciduous forests have long interested ecologists. However, little is known about their belowground ecosystems despite their ecological importance in driving biogeochemical cycling. Here, we used Illumina MiSeq sequencing targeting 16S rRNA gene and a microarray named GeoChip targeting functional genes to analyse microbial communities in broadleaved evergreen and deciduous forest soils of Shennongjia Mountain of Central China, a region known as ‘The Oriental Botanic Garden’ for its extraordinarily rich biodiversity. We observed higher plant diversity and relatively richer nutrients in the broadleaved evergreen forest than the deciduous forest. In odds to our expectation that plant communities shaped soil microbial communities, we found that soil organic matter quantity and quality, but not plant community parameters, were the best predictors of microbial communities. Actinobacteria, a copiotrophic phylum, was more abundant in the broadleaved evergreen forest, while Verrucomicrobia, an oligotrophic phylum, was more abundant in the broadleaved deciduous forest. The density of the correlation network of microbial OTUs was higher in the broadleaved deciduous forest but its modularity was smaller, reflecting lower resistance to environment changes. In addition, keystone OTUs of the broadleaved deciduous forest were mainly oligotrophic. Microbial functional genes associated with recalcitrant carbon degradation were also more abundant in the broadleaved deciduous forests, resulting in low accumulation of organic matters. Collectively, these findings revealed the important role of soil organic matter in shaping microbial taxonomic and functional traits.     

玉米根分布模拟方法比较

根分布是陆面过程模型中模拟根系吸水过程的重要参数,对其准确表达将可改善水热通量的模拟。利用已有研究中玉米不同发育期根生物量实测资料,对常用于现有主流陆面过程模型中分别由Schenk、Zeng和Jackson建立的3种根分布参数化方案(被定义为M1、M2、M3)的模拟精度进行比较。结果表明:M2和M3模拟精度基本一致,仅在玉米吐丝期以后模拟精度较高,而M1能够对玉米不同发育期根分布进行较高精度的模拟,是3方案中的最优方案;通过对M1方案中玉米不同发育期d50和d95(累积根比例分别为50%和95%的土层深度)2个参数拟合值分析发现,d95值随玉米生育进程逐渐增大,变异性在拔节和成熟期最大,在吐丝期最小;d50值在大喇叭口期以前随生育进程增大,在吐丝期以后趋于稳定;d50和d95值在大喇叭口期以前与现有模型设定值差异最大,可引起陆面过程模拟的误差。     

燕麦幼苗对盐胁迫的响应及过氧化氢对响应的调节

为了探讨‘定莜6号’燕麦对盐胁迫的生理生化响应及H2O2的调节作用,采用水培方法,研究外源H2O2对盐胁迫下燕麦活性氧代谢、渗透溶质积累和Na+、K+平衡的影响。结果表明:小于100 mmol·L-1Na Cl未对‘定莜6号’幼苗的生长造成明显影响,150 mmol·L-1及以上浓度Na Cl使幼苗干重和叶片K+/Na+显著降低,O2-·产生速率、H2O2、丙二醛(MDA)、可溶性蛋白质和脯氨酸含量及过氧化氢酶(CAT)、质膜H+-ATP酶活性明显提高,但抗坏血酸(ASA)和谷胱甘肽(GSH)含量变化不大;外施5μmol·L-1H2O2可显著缓解150 mmol·L-1Na Cl胁迫对燕麦幼苗生长的抑制作用,使燕麦叶片超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和CAT活性及H2O2、GSH含量明显提高,O2-·产生速率和MDA含量显著降低;5μmol·L-1H2O2还提高了150 mmol·L-1Na Cl胁迫下燕麦叶片可溶性蛋白质、可溶性糖、有机酸和脯氨酸含量及质膜H+-ATP酶活性和K+/Na+,降低了游离氨基酸含量;表明外源H2O2可调控燕麦幼苗活性氧代谢和渗透溶质积累,维持K+、Na+平衡,从而增强耐盐性。     

Post‐fire regeneration in alpine heathland: Does fire severity matter?

Fire severity is thought to be an important determinant of landscape patterns of post‐fire regeneration, yet there have been few studies of the effects of variation in fire severity at landscape scales on floristic diversity and composition, and none within alpine vegetation. Understanding how fire severity affects alpine vegetation is important because fire is relatively infrequent in alpine environments. Globally, alpine ecosystems are at risk from climate change, which, in addition to warming, is likely to increase the severity and frequency of fire in south‐eastern Australia. Here we examine the effects of variation in fire severity on plant diversity and vegetation composition, 5 years after the widespread fires of 2003. We used floristic data from two wide‐spread vegetation types on the Bogong High Plains: open heathland and closed heathland. Three alternative models were tested relating variation in plant community attributes (e.g. diversity, ground cover of dominant species, amount of bare ground) to variation in fire severity. The models were (i) ‘linear’, attributes vary linearly with fire severity; (ii) ‘intermediate disturbance’, attributes are highest at intermediate fire severity and lowest at both low‐ and high‐severity; and (iii) ‘null’, attributes are unaffected by fire severity. In both heathlands, there were few differences in floristic diversity, cover of dominant species and community composition, across the strong fire severity gradient. The null model was most supported in the vast majority of cases, with only limited support for either the linear and intermediate disturbance models. Our data indicate that in both heathlands, vegetation attributes in burnt vegetation were converging towards that of the unburnt state. We conclude that fire severity had little impact on post‐fire regeneration, and that both closed and open alpine heathlands are resilient to variation in fire severity during landscape scale fires.