Seasonality of cavitation and frost fatigue in Acer mono Maxim.

Although cavitation is common in plants, it is unknown whether the cavitation resistance of xylem is seasonally constant or variable. We tested the changes in cavitation resistance of Acer mono before and after a controlled cavitation–refilling and freeze–thaw cycles for a whole year. Cavitation resistance was determined from ‘vulnerability curves’ showing the percent loss of conductivity versus xylem tension. Cavitation fatigue was defined as a reduction of cavitation resistance following a cavitation–refilling cycle, whereas frost fatigue was caused by a freeze–thaw cycle. A. mono developed seasonal changes in native embolisms; values were relatively high during winter but relatively low and constant throughout the growing season. Cavitation fatigue occurred and changed seasonally during the 12‐month cycle; the greatest fatigue response occurred during summer and the weakest during winter, and the transitions occurred during spring and autumn. A. mono was highly resistant to frost damage during the relatively mild winter months; however, a quite different situation occurred during the growing season, as the seasonal trend of frost fatigue was strikingly similar to that of cavitation fatigue. Seasonality changes in cavitation resistance may be caused by seasonal changes in the mechanical properties of the pit membranes.     

PERMANENT GENETIC RESOURCES: Development of polymorphic microsatellite markers in Acer mono Maxim

Thirteen polymorphic microsatellite markers were developed for Acer mono Maxim., one of the major components of deciduous forests in Japan. An average of 13.8 alleles were found, with expected heterozygosity ranging from 0.140 to 0.945 in 34 A. mono individuals from the Ogawa Forest Reserve in Ibaraki Prefecture, Japan. This set of microsatellite markers can be used to analyse mating patterns and gene flow in A. mono populations.     

Evolutionary history of a widespread tree species Acer mono in East Asia

East Asia has the most diverse temperate flora in the world primarily due to the lack of Pleistocene glaciation and the geographic heterogeneity. Although increasing phylogeography studies in this region provided more proofs in this issue, discrepancies and uncertainty still exist, especially in northern temperate deciduous broad‐leaved and coniferous mixed forest region (II). And a widespread plant species could reduce the complexity to infer the relationship between diversity and physiographical pattern. Hence, we studied the evolution history of a widespread temperate tree, Acer mono, populations in region II and the influence of physiographic patterns on intraspecific genetic diversity. Analyses of chloroplast sequences and nuclear microsatellites indicated high levels of genetic diversity. The diversity distribution was spatially heterogeneous and a latitudinal cline existed in both markers. The spatial distribution pattern between genetic diversity within A. mono and the diversity at species level was generally consistent. Western subtropical evergreen broad‐leaved forest subregion (IVb) had a unique ancient chloroplast clade (CP3) and a nuclear gene pool (GP5) with dominance indicating the critical role of this area in species diversification. Genetic data and ecological niche model results both suggested that populations in region II disappeared during the last glacial maximum (LGM) and recovered from south of Changbai Mt. and the Korean Peninsula. Two distribution centers were likely during the LGM, one in the north edge of warm temperate deciduous broad‐leaved forest region (III) and another in the south edge of region III. This was reflected by the genetic pattern with two spatially independent genetic groups. This study highlights the key role of region III in sustaining genetic diversity in the northern range and connecting diversity between southern and northern range. We elucidated the diversity relationship between vegetation regions which could facilitate the understanding of biodiversity origin and maintenance in East Asia.     

转基因烟草在PEG6000模拟干旱胁迫条件下的生理响应

该研究以转高山离子芥的CbPLDα、CbPLDβ基因烟草为材料,研究了渗透调节物质和保护酶系对PEG6000溶液模拟干旱胁迫的响应机制.结果表明:渗透调节物质脯氨酸、可溶性糖、可溶性蛋白分别以各自不同的响应方式在干旱胁迫下增强转基因烟草的抗旱性,且在所有浓度PEG6000模拟的干旱胁迫下,转基因烟草的脯氨酸、可溶性糖、可溶性蛋白的含量始终显著高于野生型烟草(P<0.05).说明干旱胁迫下两种转基因烟草的渗透调节能力要强于野生型烟草.保护酶系中,超氧化物歧化酶(SOD)和过氧化物酶(POD)在减轻干旱胁迫下转基因烟草膜脂过氧化伤害中起到协同互补作用,而过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)在干旱胁迫下转基因烟草清除过氧化氢机制中发挥主要作用,说明保护酶系在抵制干旱胁迫和保护转基因烟草免受干旱伤害方面具有重要的生物学功能,这从生理角度揭示了高山离子芥CbPLDα、CbPLDβ响应干旱的生理生态机理.综上,高山离子芥CbPLDα、CbPLDβ基因参与了干旱胁迫下烟草的膜稳定性调节、渗透调节物质的积累和抗氧化酶系的调控.该研究结果为提高植物抗旱性研究及应用提供了新的基因资源,对于加强PLD功能研究、补充植物抗干旱理论及抗低温干旱育种种质资源的开发利用具有重要意义.     

茉莉酸甲酯喷施和光肩星天牛（Anoplophora glabripennis(Motschulsky)咬食后五角枫释放的挥发物

茉莉酸甲酯喷施和光肩星天牛(Anoplophora glabripennis(Motschulsky)咬食后五角枫(Acer mono Maxim.)植株均诱导产生了乙酸丁酯、2-壬醇、乙酸己酯、3-甲基-2-丁醇、1-辛烯、里那醇、3-蒈烯、1-丁醇、(Z)-2-己烯醛9种正常植株中没有检测到的挥发物。两种处理均诱导或促进了萜烯类、醇类和醛类挥发物的大量释放,且乙酸-3-己烯酯、乙酸乙酯、己醇、反-2-己烯醇、乙基己醇、1-辛烯、石竹烯、法尼烯等挥发物的时序变化趋势也非常相似。因而推测光肩星天牛咬食五角枫后在植物体内诱导产生了茉莉酸信号传导途径。     

二重雌雄异型异熟物种色木槭3种表型花的细胞形态学研究

二重雌雄异型异熟,即雌雄功能按雄-雌-雄顺序分别表达,是有花植物中较为少见的异熟机制.槭属(Acer)大部分物种具有二重雌雄异型异熟的开花物候,且第一期雄花与第二期在形态上差别较大.为深入探讨花发育模式对花形态和开花物候的影响,本文应用石蜡切片技术和光镜技术,对色木槭(Acer mono)各个发育时期的3种类型花(雄花...     

暖温带落叶阔叶林辽东栎和五角枫生长和光合生理生态特征对模拟氮沉降的响应

暖温带落叶阔叶林在维护区域生态系统功能和平衡中起着重要的作用, 研究其在氮添加下的生长和生理生态响应, 有助于深入理解暖温带落叶阔叶林在全球氮沉降背景下的生长和变化规律。该研究通过在北京东灵山落叶阔叶林的模拟氮沉降控制实验, 以优势种辽东栎(Quercus wutaishanica)和伴生种五角枫(Acer pictum subsp. mono)为研究对象, 设置对照和氮添加2种处理, 每种处理4个重复, 对照样地不做处理; 氮添加样地施加尿素(CO(NH₂)₂), 总的氮添加量为100 kg·hm ^-2·a ^-1, 测定氮添加对其生长和光合生理生态特征的影响。结果显示: 氮添加显著提高了两个树种的净光合速率、蒸腾速率、叶绿素含量, 同时扩大了叶片光系统II反应中心电子传递体库, 增加了基于光合电子流驱动的初级受体醌(Q_A)被还原的周转次数。氮添加也增加了两个树种当年生枝条的长度和生物量, 同时在一定程度上提高了辽东栎种子的质量。辽东栎光合作用氮利用效率、枝条生物量对氮添加的响应程度明显超过五角枫。在未来氮沉降加剧的情景下, 东灵山暖温带落叶阔叶林优势种辽东栎的优势地位会进一步加强。     

Solar tracking response to drought in a desert annual

Summary The responses to drought of the solar tracking winter annualLupinus arizonicus (Wats.) were examined under field and laboratory growth regimes. Under drought conditions tracking movements were maintained until the plant reached the wilting point. The leaves and leaflets were observed to cup in response to decreases in the xylem water potential. This resulted in a negative, but linear relationship between the cosine of the angle of incidence of the direct solar beam upon the leaf and water potential. Leaf conductance was also significantly related to xylem water potential in natural populations. Leaf and leaflet cupping seem to be responding directly to changing plant water status, resulting in reduced solar radiation load to drought stressed plants. It is hypothesized that this property may have adaptive consequences in relation to the water relations, energy budget, and carbon balance of the plant.     

Plant response to drought stress simulated by ABA application: Changes in chemical composition of cuticular waxes

Plant cuticles form the interface between epidermal plant cells and the atmosphere. The cuticle creates an effective barrier against water loss, bacterial and fungal infection and also protects plant tissue from UV radiation. It is composed of the cutin matrix and embedded soluble lipids also called waxes. Chemical composition of cuticular waxes and physiological properties of cuticles are affected by internal regulatory mechanisms and environmental conditions (e.g. drought, light, and humidity). Here, we tested the effect of drought stress simulation by the exogenous application of abscisic acid (ABA) on cuticular wax amount and composition. ABA-treated plants and control plants differed in total aboveground biomass, leaf area, stomatal density and aperture, and carbon isotope composition. They did not differ in total wax amount per area but there were peculiar differences in the abundance of particular components. ABA-treated plants contained significantly higher proportions of aliphatic components characterized by chain length larger than C₂₆, compared to control plants. This trend was consistent both between and within different functional groups of wax components. This can lead to a higher hydrophobicity of the cuticular transpiration barrier and thus decrease cuticular water loss in ABA-treated plants. At both ABA-treated and control plants alcohols with chain length C₂₄ and C₂₆ were predominant. Such a shift towards wax compounds having a higher average chain length under drought conditions can be interpreted as an adaptive response of plants towards drought stress.     

Forest biogeochemistry in response to drought

Trees alter their use and allocation of nutrients in response to drought, and changes in soil nutrient cycling and trace gas flux (N₂O and CH₄) are observed when experimental drought is imposed on forests. In extreme droughts, trees are increasingly susceptible to attack by pests and pathogens, which can lead to major changes in nutrient flux to the soil. Extreme droughts often lead to more common and more intense forest fires, causing dramatic changes in the nutrient storage and loss from forest ecosystems. Changes in the future manifestation of drought will affect carbon uptake and storage in forests, leading to feedbacks to the Earth's climate system. We must improve the recognition of drought in nature, our ability to manage our forests in the face of drought, and the parameterization of drought in earth system models for improved predictions of carbon uptake and storage in the world's forests.     

The functional significance of a stigma color polymorphism in Acer pictum subsp. mono (Aceraceae)

Aims Exploring the characteristics and function of a flower color polymorphism contributes to our understanding of floral evolution in angiosperms. However, little information is available on stigma color polymorphisms in flowering plants despite their important functional role in plant reproduction.Methods We studied a stigma color polymorphism at the individual level in Acer pictum subsp. mono (aka A. mono) by investigating stigma-color morph proportion and comparing stigma performance and components of female fitness (pollen adhesion, pollen germination, fruit set, seed set and fruit weight) between the two morphs (red and greenish-yellow stigma) within natural populations at Dongling Mountain in the north of China. In the flowering period, we conducted hand pollination in natural populations and then made microscopic observations using the aniline blue fluorescence method.Important findings Individuals in the studied populations did not change their stigma color between years, and flowers produced by a single tree were uniform in their stigma color. This strongly suggests that stigma color variation is genetically controlled. The percentage of the red stigma flowers with germinated pollen grains was significantly higher than that of the greenish-yellow stigma flowers when hand pollination was conducted in the early flowering period, but not so in the late flowering period. There was no significant difference in the percentage of flowers with pollen adhesion to the stigma between the two morphs. Fruit set of the red morph was significantly higher than that of the greenish-yellow morph. Our findings suggest that the red morph may be more advantageous for pollen germination and fruit set than the greenish-yellow morph, which may provide a functional explanation for the high incidence of the red stigma morph in the studied populations. Alternative explanations for the stigma color polymorphism are discussed to stimulate further work.     

Zooplankton response to extreme drought in a large subtropical lake

Plankton data from 1997 to 2005 were used to examine impacts of a managed draw-down, subsequent drought and resulting historic low water levels (during 2000 and 2001) on the zooplankton of Lake Okeechobee, Florida. Prior to the drought the lake supported less than 150 ha of submerged vegetation. Following the drought, over 15,000 ha of submerged vegetation developed around the lake shore and conditions favored greater survival of age 0 fish. The zooplankton changed significantly from the pre- to post-drought period, including: (a) a near-complete loss of all dominant species of cladocerans and rotifers; and (b) an abrupt transition to a community with over 80% of total biomass comprised of Arctodiaptomus dorsalis, a calanoid copepod previously described as being resistant to fish predation. These changes persisted over a 5 year post-drought sampling period. In contrast, there were no systematic changes in biomass of bacteria, phytoplankton, inedible cyanobacteria, algal cell size, suspended solids, or any other physical or chemical attributes known to affect zooplankton in shallow lakes. Evidence points towards increased predation by fish, and perhaps invertebrates, as factors responsible for loss of cladocerans and rotifers following the drought, and indicates a need for future research to link changes in water level to shifts in predation pressure in this and other shallow lakes. Handling editor: S.I. Dodson     

Enzymes and biogeochemical cycling in wetlands during a simulated drought

Possible interactions between soil enzymes and thebiogeochemistry of wetlands were investigated duringa field-based drought simulation. Under control(waterlogged) conditions, correlations were foundbetween the activity of the enzyme B-glucosidase andtwo properties associated with carbon cycling, namelyi) CH₄ release r = 0.79,p lt 0.01) and ii) dissolvedorganic carbon concentration (r= -0.81, p lt 0.01). In contrast,the transition to drought conditions resulted in correlations betweenB-glucosidase activity and certain mineralisationprocesses, namely the release of mg and Ca(r = 0.72, p lt 0.05). Sulphataseactivity correlated with changes in sulphate concentration during the droughtsimulation (r = 0.73, p lt 0.05).Further support for the suggested enzymic involvement in biogeochemicalprocesses was found in laboratory studies. Theseexperiments indicated that increasing the abundance ofB-glucosidase could stimulate trace gas emissions(p lt 0.001) and increase the concentration ofmagnesium and calcium (p lt 0.05). Increasedsulphatase abundance caused a suppression of methane emissions(p = 0.053).     

Microbial response to drought in a Texas highplains shortgrass prairie

The population of the microbial flora of a mixed blue gramma grass (Bouteloua gracilis H. B. K.) and prickly pear (Opuntia polyacantha Haw.) prairie near Amarillo, Texas, was studied during 1971 after a severe drought. Bacteria, fungi, and algae were estimated by plate count and terminal dilution procedures. Rates of grass and paper decomposition were determined. The microbial flora of soil associated with bovine-grazed grass did not differ significantly from the flora associated with ungrazed grass, either qualitatively or quantitatively. During drought, a greater number of fungi were found in soil associated with prickly pear than in that associated with blue gramma grass. The microbial biomass decreased one full log between the surface and a depth of 50 cm, and the percentage of anaerobes increased with depth. The maximum numbers of fungi and algae detected were 8 × 10⁵ and 6 × 10⁴/g respectively. A linear relationship existed between the microbial biomass and soil moisture. The maximum number of aerobic, heterotrophic bacteria detected was 1.5 × 10⁸ viable cells per g of soil.     

Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

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中国北方草原对气候干旱的响应

草原生长动态受气候条件的影响和制约,在很大程度上取决于水分条件.为了较好阐明草原生长与干旱气候关系,利用表征草原生长变化的NDVI(Normalized Difference Vegetation Index)指数和表征干旱的SPI(Standardized Precipitation Index)指数研究了荒漠草原、典型草原、草甸草原与干旱气候的线性关系,表明荒漠草原的生长动态受季节性干旱影响很大,短期、中长期和长期干旱对荒漠草原影响较小.典型草原对季节性干旱响应较强,而对短期、中长期和长期的干旱响应较弱.草甸草原对季节性和长期干旱响应较强.并且草原对降雨量的响应具有时滞效应,水分盈亏对草原的影响是累积效应.利用基于虚拟变量的回归模型和简单回归模型模拟了草原NDVI对SPI指数的响应关系,基于虚拟变量的回归模型显示出对草原NDVI与SPI关系的较优拟合度.表明了草原生长动态对干旱气候响应具有季节性效应.     

Microbial community response to a simulated hydrocarbon spill in mangrove sediments

In this study, we examined the hypothesis that the microbial communities in mangrove sediments with different chemical and historical characteristics respond differently to the disturbance of a hydrocarbon spill. Two different mangrove sediments were sampled, one close to an oil refinery that had suffered a recent oil spill and another that had not been in contact with oil. Based on the sampled sediment, two sets of mesocosms were built, and oil was added to one of them. They were subjected to mimicked mangrove conditions and monitored for 75 days. Archaeal and bacterial communities were evaluated through PCRDGGE. Both communities showed the emergence of small numbers of novel bands in response to oil pollution. 16S rRNA gene clone libraries were constructed from both mesocosms before the addition of oil and at day 75 after oil addition. LIBSHUFF analysis showed that both mangrove-based mesocosms contained similar communities at the start of the experiment and that they were different from the initial one, as well as from each other, after 75 days. These results hint at a role of environmental history that is not obvious from community diversity indicators, but is apparent from the response to the applied stress.