旱生和湿生生境对蒲公英体内抗氧化物质的影响

选择旱生和湿生生境中生长的蒲公英(Taraxacum mongolicum Hand.-Mazz)分根、叶、花序分别测定抗氧化成分及总抗氧化能力,并比较了SOD同工酶谱的变化情况。结果表明不同生境选取的蒲公英叶片中抗氧化物质以SOD、POD、CAT等抗氧化酶和Vc等小分子为主,花序中可溶性糖、类黄酮和绿原酸含量最高;湿生蒲公英各器官尤其是根中的SOD、CAT、POD活性高于旱生蒲公英对应器官中的酶活性,旱生蒲公英各器官尤其是花序中的可溶性糖、类黄酮和绿原酸含量高于湿生蒲公英对应器官中的含量;旱生和湿生生境未诱导出新的SOD同工酶带;旱生和湿生蒲公英对应器官的总抗氧化能力接近。     

储藏方式和时间对三峡水库消落区一年生植物种子萌发的影响

为了明确不同储藏方式和储藏时间对三峡水库消落区4种1年生植物稗(Echinochloa crusgalli)、苍耳(Xanthium sibiricum)、合萌(Aeschynomene indica)和水蓼(Polygonum hydropiper)种子萌发能力的影响,筛选出有利于其萌发的最佳储藏方式及时间,采取5种储藏方式(室温、冷藏、冷冻、干沙、湿沙)、8个储藏时间段(30、60、90、120、150、180、210、240d)对种子进行储藏实验。在光照培养箱昼25℃/夜20℃和周期性光照(昼12h/夜12h,光强100μmol·m-·2s-1)条件下进行种子萌发,每次萌发持续时间为30d。结果显示:(1)稗、苍耳和水蓼的种子在湿沙储藏条件下萌发起始时间缩短,种子萌发率、萌发指数高于其它储藏方式;湿沙储藏条件下,稗的种子储藏90-180d萌发率达到80%以上,苍耳的种子储藏180d萌发率达(64±2)%,水蓼的种子储藏30-240d萌发率均超过90%。(2)冷冻储藏能有效地解除合萌种子休眠,显著提高其种子萌发率和发芽指数;冷冻储藏90-180d合萌的种子萌发率均超过80%,之间没有显著差异。(3)果皮是限制苍耳种子萌发的主要因素之一,而去除果皮对合萌种子萌发没有显著影响。研究结果建议:采用种子来进行消落区植被恢复和重建时,稗、苍耳和水蓼的最佳储藏方式是湿沙储藏,合萌的最佳储藏方式是冷冻储藏。结合三峡水库水位调度原则,在适宜的储藏方式下,本实验中储藏120-180d的种子能够应用于消落区实地播种中。     

苍耳形态解剖学研究

现蕾期苍耳茎的解剖结构以初生结构为主。维管形成层已经形成,但次生结构尚不发达。茎表皮由普通表皮区和色斑区组成。叶的主脉维管组织与茎中维管组织排列方式类似,而不同于大多数双子叶植物。     

Nitrogen retranslocation in plants of maize,lupin and cocklebur

Summary In a split root experiment translocation of N from shoot to root was studied using¹⁵NO ₃ ^– . The three plant species selected for this experiment differed significantly with respect to root NRA. For lupin, maize and cocklebur about 80, 50 and 6% of all absorbed NO ₃ ^– was assmilated in the roots, respectively.Although NO ₃ ^– was reduced in the roots of lupin and maize plants to a greater extent than required for the roots' demand for organic N, a significant phloem flow of N from shoot to roots was found in these plants. Unexpectedly, for cocklebur, the plant with the very low root NRA, the fraction of total N present in the root that has been imported from the shoot was only half that as found for lupin and maize.     

Reversal of ethylene action on cocklebur seed germination in relation to duration of pre-treatment soaking and temperature

Abstract At 23°C, both C₂H₄ and CO₂ stimulated the germination of freshly imbibed upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds, but C₂H₄, unlike CO₂, changed to an inhibitor of germination under some soaking conditions. However, when seeds were pre-soaked for more than several hours at 23 °C prior to treatment, C₂H₄ strongly inhibited their germination at 33 °C, the degree of inhibition increasing with the duration of pre-soaking. Maximum inhibition occurred at 1–3 cm³ m^?3 C₂H₄ when seeds were pre-soaked for 1 week; further increases of C₂H₄ concentration and pre-soaking period decreased the inhibitory effect. C₂H₄ was synergistic with CO₂ when C₂H₄ promoted germination, whereas it was antagonistic when inhibitory. Such a transition of the C₂H₄ action occurred at ca. 27 °C. Also 1-andnocyclopropane-1-carboxylic acid, a C₂H₄ precursor, inhibited the germination of pre-soaked seeds at 33 °C, although it promoted the germination at 23 °C. When pre-soaked seeds were prepared for germination by chilling at 8 °C for 3 d, the inhibitory effect of C₂H₄ on the subsequent germination was manifested even at 23 °C. The reversal of the C₂H₄ action from promotion to inhibition in cocklebur seed germination is discussed in relation to the engagement of two respiratory pathways in the imbibed seeds.     

A bimodal germination response to temperature in cocklebur seeds. I. Cyanide-sensitive and cyanide-resistant respirations

Abstract. Pre-imbibed cocklebur ( Xanthium penn-sylvanicum Wallr.) seeds displayed bimodal germination-temperature responses with two optima at 8 and 33° C. Such germination responses occurred subsequent to bimodal respiration-temperature upsurges at lower and higher temperature regions. At lower temperatures, cocklebur seeds respired predominantly through a cyanide-sensitive cytochrome pathway. A rise in temperature resulted in a marked increase in flux via an alternative pathway, a propyl gallate- (PG) or benzohydroxamic-acid- (BHAM) sensitive pathway, thus resulting in an increase in the ratio of this pathway relative to the cytochrome pathway. Both an increased capacity for the alternative pathway and an increase in the ratio of this pathway to the cytochrome pathway were obtained when pre-imbibed seeds were exposed to either 8 or 33°C for a short period. The effects of low temperature were reduced as the exposure time was prolonged beyond 3d, resulting in a reduction in germination. Neither PG nor BHAM had an inhibitory effect on the chilling-induced germination, but the germination-stimulating effect of high temperatures was less pronounced in the presence of PG or BHAM. At high temperatures, on the other hand, KCN and NaN₃ were ineffective or, rather, slightly inhibited germination. It was thus concluded that low and high temperatures exert their germination-stimulating effects by an essentially similar manner which increases fluxes both via the cytochrome pathway and, especially, via the alternative pathway and, as a result, raises the ratio of the latter to the former.     

Predicting phenology shifts of herbaceous plants on the Qinghai-Xizang Plateau under climate warming with the space-for-time method

气候变暖背景下的植物物候变化广受关注, 然而常用的植物物候变化预测模型未充分考虑植物对环境的适应性, 给预测结果带来了较大的不确定性。该文基于2002-2011年青藏高原10个站点的地面物候观测资料以及年平均气温数据, 对空间换时间模型预测车前(Plantago asiatica)和蒲公英(Taraxacum mongolicum)各主要物候事件(展叶始期、开花始期和黄枯普遍期)变化的可行性及其在升温背景下的变化规律进行了分析。首先利用不同海拔高度的气温和物候事件分别与地理因子(经度、纬度和海拔)建立多元线性回归模型, 然后在此基础上剔除经度和纬度的影响, 单独考察海拔变化所引起的气温与植物物候变化, 最后以海拔高度作为桥梁来考察物候变化与温度变化的关系。结果表明, 采用各站点对应的海拔高度来模拟年平均气温空间差异的R²均大于0.89, 表明海拔梯度可以用来反映时间尺度下的年际温度变化; 车前和蒲公英各物候事件发生日期拟合值均与海拔高度变化关系显著, R²均大于0.70, 表明海拔变化是影响它们各物候事件变化的主要地理因子; 在物候事件发生日期拟合值和年平均气温拟合值的回归方程中, R²均大于0.93, 说明基于不同海拔高度模拟得到的年平均气温变化可以对时间尺度上车前和蒲公英的物候事件变化进行预测。空间换时间预测表明, 温度每升高1 ℃, 车前展叶始期和开花始期分别提前5.1和5.4 d, 而黄枯普遍期推迟4.8 d; 蒲公英展叶始期和开花始期分别提前6.5和7.8 d, 而黄枯普遍期推迟6.7 d。     

Assessing the contributions of multiple interacting traits to plant reproductive success: environmental dependence

The reproductive success of sibling cocklebur plants (Compositae: Xanthium strumarium) was monitored after growth at different levels of availability of water and nutrient resources. Variation in reproductive success among individual plants was related to physiological, structural, and phenological characteristics. Reproductive success increased with increased availability of resources, but the relative contribution of particular traits to reproductive success varied with resource availability. Allocation of biomass to different vegetative tissues, time to seedling emergence, degree of branching, transpiration rates, water use efficiency, the rate of decline in height growth after seedling emergence and final plant size all varied significantly with resource availability. However, the changes in each of these phenotypic traits across three garden environments did not always correlate with reproductive success. The shifts across environments in the apparent importance of somatic traits for reproductive success were attributed to plastic changes in the traits but also to changes in the phenotypic correlations of the traits with reproductive success.     

Epizoochorous dispersal by ungulates depends on fur,grooming and social interactions

The transport phase of the animal‐mediated plant dispersal process is critical to dispersal effectiveness as it determines the spatial distribution of the diaspores released and their chance for further recruitment. Assessing this specific phase of the dispersal process generally requires combining diaspore retention times with the associated distances covered. Here, we specifically tested the effect of grooming behavior, interindividual contacts and ungulate fur on diaspore retention times and associated dispersal distances for the hooked diaspores of Xanthium strumarium L. experimentally attached to tamed individuals of three ungulate species. We used a comparative approach based on differing fur quality on different body zones of these three ungulates. During 6‐hr sessions, we monitored for grooming and social interactions that may induce intended or inadvertent diaspore detachment. Additionally, we proposed innovative approaches to directly assessing diaspore dispersal distances by red deer in situ. Fat‐tailed functions fitted diaspore retention time, highlighting the potential for long‐distance dispersal events. The longer the hair, the higher the retention capacity of diaspores in the animal's fur. As predicted, donkey retained diaspores longer than red deer and dwarf goat; and we also confirmed that diaspores attached to the short hair of the head fell off more quickly than did those on the other body zones. Dwarf goat groomed more often than both red deer and donkey, but also when it carried diaspores. Up to 14% of the diaspores detached from animal fur after specific grooming behavior. We observed, in controlled conditions, for the first time and for each ungulate species, interindividual transfers of diaspores, representing 5% of the diaspores attached to animals’ fur. Our results militate for incorporating animal behavior into plant dispersal modeling approaches.