沿干旱梯度小叶锦鸡儿灌丛化对草本植物叶片矿质元素浓度及地上生物量累积的影响

草原灌丛化通过改变物种之间的相互作用深刻影响着群落的结构和功能。然而,当前有关灌木如何影响不同功能群草本植物对矿质元素吸收和累积的研究仍明显不足。在内蒙古草原沿干旱梯度选取了4个研究地点,对比分析了小叶锦鸡儿(Caragana microphylla)灌丛斑块内和斑块外群落中禾草和非禾草功能群植物叶中矿质元素浓度以及地上生物量生产的差异,旨在阐明干旱和灌木对群落草本植物叶元素累积的影响,揭示灌草间相互作用的元素利用特征及其随干旱梯度的变化。结果显示：1)随干旱加剧,灌丛斑块内的非禾草功能群植物地上生物量保持恒定,但叶中的K、Ca、Mg、Fe、Mn和Cu元素浓度显著增加(P<0.05)。该结果表明群落中的非禾草功能群植物通过提高叶中的矿质元素水平来抵御和适应干旱胁迫。2)随干旱加剧,灌丛对非禾草功能群植物地上生物量,叶中Ca、Fe、Cu和Zn,禾草功能群植物叶中的P的累积影响从负(RII<0)或中性(RII=0)转变为正效应(RII>0)。该结果与胁迫梯度假说相符,表明灌木对草本植物的促进效应随干旱胁迫加剧而增加。3)灌丛的“沃岛”效应是驱动灌木对草本植物元素累积正效应...     

冬季郑州市12个常绿树种的光合特性及滞尘能力

为筛选出北方城市冬季生态效益突出的常绿树种,以缓解大气CO2和粉尘颗粒物污染,并为这些树种的园林应用提供科学支持,该文选取郑州市园林绿化应用广泛的12个常绿树种,利用LI-6400便携式光合测定仪和洗脱-质量差值法,并对其光合特性及滞尘能力进行测定,计算出其光合参数[叶片的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度...     

荒漠灌丛土壤动物分布及其生态功能

在干旱、半干旱荒漠生态系统中,灌丛作为一种重要的植被类型,其独特的形态和生理适应特性能够有效促进退化生态系统结构与功能的恢复。土壤动物是荒漠生态系统中不可或缺的重要组成部分,对促进灌丛"肥岛"演变具有重要的生态作用,有利于灌丛生态功能的发挥及退化生态系统的恢复。近年来,国内外学者对荒漠灌丛微生境土壤动物的研究逐步深入,取得大量的研究成果。在此基础上,首先综述荒漠灌丛微生境土壤动物群落分布和生态功能,总结灌丛与土壤动物分布间作用关系的数学模型,针对荒漠灌丛土壤动物研究中存在的问题提出了未来可能的研究方向和建议。     

宁夏东部荒漠草原灌丛引入对土壤水分动态及亏缺的影响

全球气候变化背景下,荒漠草原人工灌丛引入加速其灌丛化进程,对草原土壤水分产生重要影响。为了解宁夏东部荒漠草原灌丛引入过程中土壤水分动态及亏缺现状,选取了封育草地、放牧草地、不同年限(3a、12a、22a)和间距(40 m、6 m、2 m)灌丛柠条(Caragana korshinskii)地进行土壤水分测定,并利用土壤水分相对亏缺指数(compared soil water deficit index,CSWDI)、样地土壤水分相对亏缺指数(plot compared soil water deficit index,PCSWDI)对土壤水分亏缺进行定量分析。结果表明:灌丛引入过程中不同年限、间距灌丛地0—200 cm土层土壤含水量均显著低于封育草地与放牧地(P<0.05);各样地季节动态均表现为春季返潮、夏季消耗、秋季蓄积的季节规律,但不同年限、间距灌丛地表现为春季返潮微弱,土壤含水量仅为7.80%—10.90%,显著低于封育草地和放牧地(11.90%—16.09%);灌丛引入过程中各灌丛地0—100 cm有效储水量(-16.98—18.69 mm)均低于封育草地(34.67 ...     

The effect of fire and ants on the seed-bank of a shrub in a semi-arid grassland

Abstract Invasion of grasslands by woody plants following the introduction of domestic stock is a worldwide phenomenon. Burning is frequently recommended as a remedial measure but for a pastoral enterprise it is costly and the frequency of the fires required is of critical economic importance. The size and longevity of the soil seed-bank is an essential part of the response of shrub populations to prescribed fire regimes. In this study the seed-bank of the semi-arid zone shrub Dodonaea attenuata in Eragrostis eriopoda tussock grassland was examined in relation to harvesting by ants and the burning history of the sites. On unburnt sites, more than 3500 seeds per m2 entered the seed-bank in the summer 1984–85 but sites burnt 5 years previously produced less than one-third of that number. Burnt shrubs did not flower for 5 years and no seeds survived in the soil through to 1985. Burning immediately prior to seed ripening destroyed the seed crop but burning after seed-fall stimulated a greater germination in the following spring than on unburnt treatments. Ants rapidly harvested most of the seeds produced and after 20 months the combined effects of ant harvesting and germination had reduced the seed-bank at unburnt sites to 8–21 seeds per m2 and at sites burnt 7 years previously to less than two seeds per m2. Seeds were initially harvested in summer by Pheidole spp. of ants for their elaiosome and then discarded in middens outside the entrance to the ant nest. During the subsequent cool season the seeds were taken back into the nest and stored at depths ranging from 2 to 30cm. It was concluded that ants provided short-range dispersal (< 10 m) and promoted the contagious distribution of D. attenuata, which is advantageous for a fire-susceptible, arid-zone shrub invading a grassland liable to be burnt: seedlings derived from seeds in ant storage chambers near the soil surface and in sparse grass situations caused by competition from shrubs may obtain some survival advantage. Prescribed fire has potential as a management tool for controlling population density of D. attenuata because, depending upon season and frequency, it reduces seed rain by killing shrubs, suppresses flowering activity and destroys seed crops on the plant. Under the influence of a regime of regular burning, such as prevailed prior to the European pastoral industry, the limited soil seed-bank would have been a major constraint on D. attenuata populations.     

The mating system of the tropical understory shrub Ardisia escallonioides (Myrsinaceae)

Electrophoretic analysis of progeny arrays was used to determine whether Ardisia escallonioides (Myrsinaceae). a self-compatible tropical understory shrub in south Florida, exhibits a mixed-mating system. Ten seedlings from seven to 16 maternal plants from four populations were analyzed using five polymorphic enzyme systems. Multilocus population out-crossing rates ranged from 0.39 to > 1, with three populations showing high levels of selfing. Both single and multilocus inbreeding coefficients (F) indicated excess homozygosity in seedlings but not adults for three of the four populations. Population outcrossing rate was not positively correlated with increased numbers of flowering plants. The importance of annual variation in population outcrossing rates is discussed with regard to the high temporal variability in seedling recruitment in this species.     

中国亚热带常绿阔叶林优势种常见种分布与气候的相关分析

 广泛收集植物的分布资料,包括杨梅科、胡桃科、壳斗科、木兰科、樟科、山茶科、金缕梅科、交让木科、杜英科、五加科、安息香科、冬青科、杜鹃花科、山矾科的优势种和常见种112个,利用目前在国际上被认为是较好的几种研究植被—气候相互关系的指标和方法,包括：Kira方法;Penman公式;Thornthwaite方法与分类;Holdridge生命地带分类系统指标与方法,分析中国亚热带常绿阔叶林优势种及常见种分布与气候的生态关系,找出它们的地理分布特征和气候指标特征,建立现代植被与气候的关系。(1)利用Kira的温暖指数(WI)和寒冷指数(CI)及徐文铎的湿润指数(HI),计算了中国亚热带常绿阔叶林112个优势种及常见种的水热指标值,分析了树种分布与气候的关系,并将优势种及常见种划分为5个Kira水热指标分布类群。(2)计算了112个优势种及常见种的Penman可能蒸散(PET)和干燥度(A)值,划分了5个优势种及常见种的Penman水热指标分布类群。(3)计算了树种的Thornthwaite潜在可能蒸散(APE)及湿润指数(IH)、干旱指数(IA)和水分指数(IM),划分了优势种及常见种的Thornthwaite水热指标分布类群。(4)计算了树种的Holdridge生物温度(BT)、可能蒸散(PE)、降水量(P)及可能蒸散率(PER),划分了优势种及常见种的Holdridge水热指标分布类群。     

Carbon dioxide concentrations within forest canopies—variation with time, stand structure, and vegetation type

Vertical CO₂ profiles (between 0.02 and 14.0 m) were studied in forest canopies of Pinus contorta, Populus tremuloides, and in a riparian forest with Acer negundo and Acer grandidentatum during two consecutive growing seasons. Profiles, measured continuously during 1- to 13-day periods in four to five stands differing in overstorey canopy area index (CAI < 4.5; including leaves, branches and stems), were well stratified, with highest [CO₂] just above the forest floor. Canopy [CO₂] profiles were influenced by stand structure (CAI, presence of understorey vegetation), and were highly dependent on vegetation type (deciduous and evergreen). A doubling of CAI in Acer spp. and P. tremuloides stands did not show an effect on upper canopy [CO₂], when turbulent mixing was high. However, increasing understorey biomass in Acer spp. stands had a profound effect on lower canopy [CO₂]. In open stands with a vigorous understorey layer, higher soil respiration rates were offset by increased understorey gas exchange, resulting in [CO₂] below those of the convective boundary layer (CBL). Midday depletions up to 20 ppmv below CBL values could be frequently observed in deciduous canopies. In evergreen canopies, [CO₂] stayed generally above the CBL background values, [CO₂] profiles were more uniform, and gradients were smaller than in deciduous stands with similar CAI. Seasonal changes of canopy [CO₂] reflected changes in soil respiration rates as well as plant phenology and gas exchange of both dominant tree and understorey vegetation. Seasonal patterns were less pronounced in evergreen than in deciduous forests.     

Species diversity of Chinese beech forests in relation to warmth and climatic disturbances

The trends in the occurrence of climatic disturbances in the ChineseFagus range are described, and the relationship between woody species diversity and climatic factors in eight old-growth Chinese beech forests is characterized. In the ChineseFagus range that lies in the humid mountains of southern China, wind storms and heavy rain frequency increase towards the eastern coast. Thunderstorm frequency increases southwards. Snowfall frequency increases northwards. Glaze storm frequency peaks in the center near Lake Dongtian, but much higher in the east than in the west. Hailstorm frequency also peaks in the center. The forests sampled in this study are widely separated. Their canopies consist of either deciduous broad-leaved trees or a mixture of evergreen and deciduous broad-leaved trees. Their species diversity increases towards warmer sites and towards the east. The importance of the evergreen trees in relation to warmth and minimum temperature increases southwards. Our analysis suggests that wind storms and heavy rains enhance the species diversity of Chinese beech forests. Cold disturbances such as glaze and snow diminish the diversity and canopy dominance of evergreen broad-leaved trees but favor deciduous broad-leaved trees, especially beech. The annual precipitation received by the forests in this study varies from 1400–2550 mm. This is not correlated with diversity, however, probably because all of these forests grow in humid conditions with sufficient water being supplied by precipitation throughout the year.