实验室条件下两种生物土壤结皮对荒漠植物种子萌发的影响

生物土壤结皮广泛分布在干旱、半干旱区,深刻影响着土壤表层特性,进而对植物种子散布、萌发和定居产生极大的影响。到目前为止,生物土壤结皮与植物关系的研究很少见到,并且这些有限的研究所得出的结论存在着争议。研究了不同年龄的两种生物土壤结皮（苔藓结皮和藻类结皮）对油蒿（Artemisia ordosica）和雾冰藜（Bassia dasyphylla）种子萌发的影响,同时也研究了这两种结皮在失去活性前后对油蒿、雾冰藜和小画眉草（Eragrostis poaeoides）种子萌发的影响。苔藓和藻类结皮的出现对油蒿和雾冰藜种子的萌发均有显著的促进作用,而结皮年龄对植物种子的萌发没有显著的差异。对于不同的植物种,结皮类型和活性对种子的萌发具有不同的作用。雾冰藜在两种结皮上的萌发有显著的差异而油蒿和小画眉草在两种结皮上的萌发没有显著差异。活藻类显著地增加了三种植物的种子萌发,活苔藓仅增加了油蒿和雾冰藜种子萌发量而对小画眉草种子的萌发没有作用,研究表明,生物土壤结皮对一些植物种子萌发具有明显的促进作用。     

陕北黄土丘陵沟壑区14种植物的萌发特性

在实验室条件下观测了陕北黄土丘陵沟壑区14种植物的萌发特性,结果发现：萌发率在80%以上的植物有杠柳、铁杆蒿和茭蒿;在60%～80%之间的物种有白羊草、紫丁香、阿尔泰狗娃花、大针茅、沙棘和猪毛蒿;长芒草为37.3%;小于20%的植物有达乌里胡枝子、刺槐、虎榛子和狼牙刺。14种植物的萌发时滞最短的为2 d,最长的为8 d;几乎所有植物种子达到T50的时间都在其萌发开始后的7 d以内,且大部分物种在萌发开始后的15 d完成总萌发量的90%;萌发持续时间最短的为6 d,有刺槐、狼牙刺、虎榛子、沙棘4种,最长的为猪毛蒿,达32 d。这些植物种子的萌发特性及生态适宜性决定了它们在陕北黄土丘陵沟壑区植被演替中的角色与地位。     

科尔沁沙地69种植物种子重量比较研究

 研究了科尔沁沙地69种植物的繁殖体（30种为种子,39种为果实）重量。结果表明：1）传播体为果实的植物可分为4个组别（即果实单粒重<0.1 mg、0.1～0.999 9 mg、1～9.999 9 mg、10～99.999 9 mg）;黄蒿（Artemisia scoparia）果实(0.051 7 mg)和小香蒲（Typha minima）果实(0.068 2 mg)最轻,苍耳（Xanthium sibiricum）单个果实（77.894 3 mg）最重;2）传播体为种子的植物可分为3个组别（即种子单粒重0.1～0.999 9 mg、1～9.999 9 mg、10～99.999 9 mg）;马齿苋（Portulaca oleracea）种子（0.151 4 mg）最轻,苦参（Sophora flavescens）种子(46.781 6 mg)最重;3）黄蒿、马齿苋、轮叶沙参（Adenophora tetraphylla）、碱地肤（Kochia sieversiana）、狼尾花（Lysimachia barystachys）、灰绿藜（Chenopodium glaucum）、刺沙蓬（Salsola ruthenica）、菟丝子（Cuscuta chinensis）、大籽蒿（Artemisia sieversiana）、狗尾草（Setaria viridis）、野古草（Arundinella hirta）等植物所以广泛分布可能是因为它们繁殖体轻（<1 mg）且具有持久土壤种子库;4）流沙上的先锋植物或沙生演替系列前期植物沙蓬（Agriphyllum squarrosum）、差巴嘎蒿（Artemisia halodendron）、乌丹蒿（Artemisia wudanica）、狗尾草、雾冰藜（Bassia dasyphylla）的繁殖体要么重量居中或偏大,要么有降低位移的其它机制。     

黄土丘陵沟壑区主要物种植冠种子库动态及其生态策略

植冠种子库是植物适应环境并应对外界干扰的种子生态策略之一,研究了黄土丘陵沟壑区12种主要植物植冠种子库动态,结果表明:杠柳不具有植冠种子库,其他11种植物均具有植冠种子库;除了黄刺玫种子在翌年5月达到脱落高峰,其他植物大部分种子在冬季脱落,其中杠柳、达乌里胡枝子、茭蒿、黄柏刺和水栒子的大部分种子脱落集中偏早,铁杆蒿和土庄绣线菊的大部分种子脱落集中偏晚;植冠宿存对大部分植物种子的萌发特性表现为促进作用;但不同植物种子的萌发时滞对植冠宿存响应差异较大;9种植物种子在植冠上宿存至翌年2月底,其种子活力仍能维持达60%以上;该区植物表现出不同的植冠种子库策略,通过不同的方式来减少干扰的威胁,提高成功萌发与更新的几率,它们或具有较大规模的宿存量、或调控种子萌发特性、或提高种子维持活力的百分比。此外,全面了解该区植物形成植冠种子库的机理及对应的生态策略还有待于全面、深入的研究。     

植冠与土壤种子库储存种子的萌发特性及策略

为明确黄土丘陵沟壑区植物种子库如何调控种子萌发来提高个体适合度,选择研究区7种具有种子库的主要物种为研究对象,以刚成熟和室内储存种子为对照,比较植冠宿存(5个宿存期)和土壤埋藏(5a埋藏期)对植物种子萌发特性的影响,探讨植冠种子库与土壤种子库储存下的种子萌发策略。结果表明:7种植物种子经过不同种子库储存后萌发特性表现出明显的种间差异,黄刺玫(Rosa xanthina)和水栒子(Cotoneaster multiflorus)种子萌发力表现为植冠宿存不变型、土壤储存增强型,土壤储存明显提高水栒子种子萌发速率;达乌里胡枝子(Lespedeza davurica)和狼牙刺(Sophora davidii)种子萌发力表现为植冠宿存增强型、土壤储存减弱型,种子萌发历时表现为植冠宿存延长型,土壤种子库储存还可加快达乌里胡枝子萌发速率、缩短萌发历时;茭蒿(Artemisia giralaii)和铁杆蒿(Artemisia gmelinii),种子萌发率随植冠宿存时间先升高后降低,随土壤储存时间先降低后升高,土壤储存可推迟其萌发,铁杆蒿种子萌发速率在植冠与土壤储存后均加快;紫丁香(Syringa oblata)种子萌发率随植冠宿存先升高后降低,土壤储存明显加快其种子启动萌发与速率。在黄土丘陵沟壑区,植物种子经过植冠或土壤种子库储存,或增加、加快、提早萌发充分利用有利条件提高占据性,或减少、减缓、推迟萌发分摊不利条件的风险;而且该区植物植冠与土壤储存后种子萌发特性间的关系,体现各自适应环境与应对干扰的分工与协作策略,主要表现为:单一主导型和相辅相成型。     

黄土丘陵区退耕还草植被恢复阶段优势种铁杆蒿的化感效应

为揭示黄土丘陵区退耕还草植被恢复阶段植被群落结构的形成与植物化感作用之间的关系,阐明退耕还草植被恢复阶段铁杆蒿群落形成的原因,采用种子萌发实验,对黄土丘陵区退耕还草中后期群落优势种铁杆蒿(恢复10 a、15 a、20 a、30 a)浸提液(水浸提液和甲醇浸提液)对其伴生种达乌里胡枝子(Lespedeza davurica,LD)、狗尾草(Setaria viridis,SV)、茵陈蒿(Artemisia capillaries,AC)以及铁杆蒿(Artemisia sacrorum,AS)自身化感作用进行研究。结果表明:铁杆蒿浸提液对3种伴生种以及自身种子萌发的化感作用差异显著(P0.05),总体表现出低促高抑"浓度效应",且根受到的抑制作用要强于芽。茎叶浸提液的浓度为0.1 g/mL时,对茵陈蒿种子萌发和幼苗生长的化感指数RI为-1.00,达到完全抑制。铁杆蒿不同器官的化感作用差异显著(P0.05),茎叶及根系浸提液不同程度的抑制LD、AC种子的萌发和幼苗生长,且在同一浓度下抑制作用随着恢复时间的增长逐渐增强。根际土浸提液促进了伴生植物及铁杆蒿自身种子的萌发,抑制了LD和AC幼苗的生长。铁杆蒿种群的化感作用可能是导致铁杆蒿在退耕还草中后期成为优势种的原因之一。     

三峡库区9种植物种子萌发特性及其在植被恢复中的意义

三峡大坝蓄水后形成的库区消涨带面临植被消亡、生态退化等问题。为了筛选出适用于库区消涨带植被恢复的植物, 将9种1年生植物种子放置在库区消涨带不同海拔进行水淹(W 165-8 m, 121 d;W 155-18 m, 230 d;W 147-26 m, 271 d), 然后在实验室条件下进行萌发, 研究在消涨带淹水胁迫下这些种子的萌发特性。结果表明: (1) 除马唐(Digitaria sanguinalis)、小蓬草(Conyza canadensis)、金色狗尾草(Setaria glauca)种子在各条件下萌发率都较低外, 不同水淹条件对萌发率影响不同: 与新鲜种子相比, W 165水淹后, 旱稗(Echinochloa hispidula)和婆婆针(Bidens bipinnata)种子萌发率显著上升, 其余种子萌发率均显著下降; W 155水淹后, 所有种子的萌发率都显著下降且只有鱧肠(Eclipta prostrate)、黄花蒿(Artemisia annua)、合萌(Aeschynomene indica)3个物种有萌发, 萌发率分别为11.0%、7.3%和2.7%; W 147水淹后, 旱稗和婆婆针种子萌发率显著上升, 鱧肠种子无显著差异, 其余种子萌发率显著下降。(2) 鱧肠、黄花蒿、婆婆针和旱稗种子比其它物种更耐水淹。W 165水淹后, 鱧肠、黄花蒿、婆婆针、旱稗种子萌发率分别为44.7%、42%、20.7%和4.3%, W 147水淹后分别为76.3%、23%、15%和26.3%, 高于其他物种。(3) 水淹后种子萌发时间格局也受到影响, 大部分种子起始萌发时间推迟、萌发速度变慢。鱧肠、黄花蒿、婆婆针和旱稗的种子对三峡库区消涨带的水淹胁迫具有一定的适应能力, 可根据它们对水淹条件适应能力的差异在消涨带不同海拔高度进行植被恢复。     

The “Trojan horse” strategy: Seed fungal endophyte symbiosis helps to explain the invasion success of the grass,Poa annua,in Maritime Antarctica

Aim

Poa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P. annua, and its competitiveness with the native Antarctic hairgrass Deschampsia antarctica, is influenced by symbioses formed with seed fungal endophytes, and whether plants derived from seeds from four global regions differ in their performance.

Locations

Four regions (Maritime Antarctica, sub-Antarctica, South America and Europe).

Methods

Endophyte frequency was measured in P. annua seeds collected from the four regions. The germination, survival, biomass accumulation, flowering and competitiveness with D. antarctica of P. annua plants grown from endophyte-uncolonised and uncolonised seeds was determined in the laboratory. The effects of endophytes on P. annua seed germination and survival and seedling osmoprotection were also assessed in the Maritime Antarctic natural environment using locally-sourced seeds.

Results

Endophytes were at least twice as frequent in seeds from Maritime Antarctica than in those from other regions. A higher proportion of endophyte-colonized seeds germinated and survived than did uncolonised seeds, but only when they originated from Maritime Antarctica. Seed endophytes increased the competitiveness of P. annua with D. antarctica, but only for plants grown from Maritime Antarctic seeds. In the field, endophyte-colonized seeds from Maritime Antarctica germinated and survived more frequently than uncolonised seeds, and osmoprotection was higher in seedlings grown from colonized seed.

Main Conclusions

The findings indicate beneficial effects of seed endophytes on invasion-related traits of P. annua, such as survival, germination success and flowering. Together with vegetative and reproductive traits facilitating the colonization process, the seed-fungal endophyte symbiosis can be invoked as an important factor explaining the invasiveness of P. annua in Maritime Antarctica.     

Nitrogen addition decreases seed germination in a temperate steppe

Seed germination and seedling establishment play an important role in driving the responses of plant community structure and function to global change. Nitrogen (N) deposition is one of the driving factors of global change, which often leads to a loss in species richness in grassland ecosystems. However, how seed germination responds to N addition remains unclear. A pot incubation test was conducted in a semi‐arid grassland in the Mongolian Plateau, Northern China, to investigate the effect of N addition (0, 5, 10, 20, 40, and 80 g N/m²) on seed germination from May to October 2016. Twenty species germinated under all treatments; however, the responses of the 20 species to N addition were different. The densities of Stipa krylovii, Leymus chinensis, and Artemisia frigida, which are the dominant species in this temperate steppe, decreased significantly as the amount of N addition. Moreover, N addition significantly suppressed seedling densities of the community, perennial forbs, perennial grasses, and annuals and biennials. Furthermore, species richness of the community, perennial forbs, and annuals and biennials decreased sharply with increasing N addition level, but perennial grass species richness did not change. The Shannon–Wiener diversity index also decreased as the amount of N addition increased. Our results suggest that N enrichment plays an important role in the seed germination stage and decreases supplements of seedlings to adult plants. These findings may help explain the causes of species loss by atmospheric N deposition in grassland ecosystems.     

The Dynamics of Seed Bank on Shapotou Artificially Stabilized Dunes

There were 46 species belonging to 17 families in the soil seed bank on Shapotou artificially stabilized dunes. Compositae was the family with most species '(11 species) and the others were Chenopodiaceae (7 species), Gramineae (7 species), Leguminosae (4 species), etc. 33.3 % of the species lived in the community also had seeds in soil. The seed production of Artemisia ordosica, Hedysarum scoparium, Caragana korshinskii was 545.57 ± 676.73 grains/m2. 6.67 ±13.74 grains/m2. 0. 032±0. 024 grains/m2, respectively. The seeds of A. ordosica were not destroyed by pests, but 31.9%, 83.29% of the seeds of H. scopariurn. C. korshinskii respectively were destroyed by pests. Under the most suitable burying depth, the cumulative seed germination rate of A. ordosica, H. scoparium, C. korshinskii were 78. 3%, 66.7%. 85.0%, respectively. The rate of germination was in the order of: A. ordosica>H, scoparium>C, korshinskii. The vegetation succession would tend towards community mainly consisted of A. ordosica, Bassia dasyphylla, Eragrostis poaeoides, etc.     

Comparing methods of weed seed exposure to predators

Several methods of seed exposure are used in seed predation studies, but how these methods influence the results remains poorly studied. In this article, two commonly used methods of seed exposure – seed cards and plasticine trays – were compared in the field and in the laboratory using three species of weed seeds. In the field, cards or trays with seeds were exposed either with or without cages to keep vertebrates out and either with or without impermeable roofs to provide protection from the weather. The overall seed retrieval from the control stands varied significantly between the methods of seed exposure, roof treatment and the species of seeds, and the scatter in the seed retrieval increased or decreased monotonically with the temperature or precipitation for some species of seeds. This indicates that the controls were more or less relevant depending on the weather conditions and species. The seed removal from cards varied between the species of seeds. The effect of exclosure cages indicated that invertebrates were the dominant seed predators of Capsella bursa‐pastoris, while in Poa annua and Stellaria media both vertebrates and invertebrates were important. Higher seed removal from plasticine trays compared to seed cards was found for all three species of seeds, and placing roofs over the seeds affected seed removal in C. bursa‐pastoris and P. annua. In the laboratory, seed consumption varied with the method of exposure in 10 out of 12 combinations of seed species and predator (two species of carabids and two species of isopods). The overall tendency was the opposite of the field observations: seed consumption was higher for seeds on filter paper and cards compared to seeds on tin trays. We conclude that seed cards are more convenient for short term studies in the field, while tin trays are useful in laboratory multi‐choice experiments. To measure the realistic consumption of invertebrate predators in the laboratory, filter paper seems to be the best option as it does not present an obstacle to predators eating the seed. Using roofs introduced further bias regarding the estimates of seed removal in the field and thus should be avoided.     

Evaluation of weed eradication programs: the delimitation of extent

Eradication is a management strategy that can provide substantial ecological and economic benefits by eliminating incursions of pest organisms. In contrast to eradication efforts that target other pests, weed eradication programs can be very protracted owing to the presence of persistent seed banks and difficulties in detecting the target. Hence there is a need to develop criteria to assist in the evaluation of progress towards eradication. Knowledge of the extent of a weed incursion (the ‘delimitation’ criterion) is considered fundamental for eradication success, as an incursion will progress from any infestations that remain undetected and thus uncontrolled. This criterion is examined with regard to eradication programs targeting Bassia scoparia L. A.J. Scott [= Kochia scoparia L. Schrader], Chondrilla juncea L. (both in Western Australia) and Orobanche ramosa L. in South Australia. The B. scoparia incursion, which has been eradicated, was largely delimited within 12 months of the inception of its eradication program. In contrast, the Western Australian C. juncea incursion has never been delimited, owing to insufficient investment in surveillance during an eradication program spanning 30 years. An exponential decrease in the detection ratio (infested area detected/area searched) over time suggests that delimitation has been approached within 6 years of the inception of the eradication program for O. ramosa. An effective surveillance program is essential for achieving delimitation of a weed incursion.     

气候变化背景下青藏高原东部猪毛蒿物候的变化规律和影响因素

近几十年来青藏高原正经历着广泛而深远的气候变化,这种变化对当地物种的物候及分布格局产生了显著影响。猪毛蒿作为干旱半干旱地区的优势物种和影响群落稳定性的关键物种,青藏高原东缘是其重要的分布区域之一,然而其物候将如何应对气候变化目前我们尚不清楚。为此,基于青海省东部连续20年的气象数据和原位物候观测实验,探讨猪毛蒿物候的变化规律及量化不同气候因子的相对贡献率。结果表明：1)过去20年间年均温和年均每日日照时长分别呈现出显著的上升和下降趋势,而年降水和年均每日最大风速没有显著的变化;2)20年间猪毛蒿返青-开花的时间间隔和开花-结果的时间间隔并未表现出显著的变化趋势,结果-枯黄的时间间隔显著缩短;3)所有气候因子均对猪毛蒿不同物候的时间间隔有显著影响,其中最大风速是影响猪毛蒿物候时间间隔最重要的气候因子。这一研究发现可以为气候变化情景下青藏高原高寒植物的保护和利用提供理论依据。     

陕北黄土丘陵区撂荒群落共存种活性氧清除指标对水分胁迫的响应

群落共存种对环境变化的生理生态响应差异是群落演替的重要因素,其中活性氧清除是生理生态响应的重要方面。该研究以黄土丘陵区10个常见撂荒群落共存种(阿尔泰狗娃花、猪毛蒿、铁杆蒿、茭蒿、小花棘豆、达乌里胡枝子、白羊草、冰草、中华隐子草和无芒隐子草)为研究对象,测定了不同水分处理条件下(适宜水分、中度胁迫及重度胁迫)生长季中3个月份(8、9和10月)个体和种群的生长表现(个体株高、生物量和种群存活率),及主要活性氧清除指标［类胡萝卜素含量、超氧化物歧化酶(SOD)活性和谷胱甘肽(GSH)含量］,分析群落共存种的生态适合度和活性氧清除指标对水分处理的响应差异及其相互关系,以明确演替生态位置上各指标的变化趋势。结果表明：(1)随水分胁迫程度的增加,演替前期种——猪毛蒿的的适合度有所下降,后期种——白羊草有所上升。(2)GSH和类胡萝卜素含量均随水分胁迫程度增强显著升高。(3)类胡萝卜素含量、SOD活性和GSH含量存在显著的种间差异,其中达乌里胡枝子的类胡萝卜素含量、小花棘豆的SOD活性、中华隐子草的SOD活性和GSH含量、无芒隐子草的类胡萝卜素含量和GSH含量均相对较高,且这3个指标的生长季变化也较为明显,8月份类胡萝卜素含量和GSH含量相对较高,而10月份GSH含量和SOD活性相对较高。(4)演替生态位置上,10个共存种在演替序列上以前期种的适合度和类胡萝卜素含量相对较低,而演替后期种相对较高,表明演替后期的植物较为耐旱。     

Seed weight and germination behavior of the submerged plant Potamogeton pectinatus in the arid zone of northwest China

Variation in seed weight is common within and among plant species, but few studies have attempted to document the pattern of seed weight and germination attributes for aquatic macrophytes at a large scale. This study examined within‐species variation in seed weight and germination attributes and the effects of environmental factors on seed traits of the submerged plant Potamogeton pectinatus in the arid zone of northwest China. Our results showed that the average seed weight was 0.24 g per 100 seeds with a coefficient of variation (CV) of 28.4% among the eight P. pectinatus populations. The total germination fraction of seeds of P. pectinatus was relatively poor, less than 35% in seven P. pectinatus populations, and the lowest germination percentage found was only 2%. There were significant differences in seed weight, time to onset of germination, and total germination fraction among the eight different populations. Hierarchical partitioning analysis showed a strongly positive correlation between seed weight and water temperature and pH. Seed weight and the maternal environmental factors significantly affected both time to initiation of germination and total germination fraction. Our results suggest that (1) seed weight variation in P. pectinatus primarily is the result of temperature variation during fruit development; (2) relatively poor germination fraction suggests that seeds are relatively unimportant in the short‐term survival of populations and that it may be another adaptive trait allowing plants to take place in the right place and at the right time, especially in harsh environment; and (3) variation in seed germination traits should be determined by local environmental and intrinsic factors that interact in a complex fashion.     

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

基于功能性状的毛乌素沙地不同演替阶段适生植物筛选

沙地生态系统修复是恢复生态学研究的热点问题,适生植物筛选是修复的关键。植物功能性状反映了植物在不同环境中的生存策略,探究沙地植物功能性状及其与环境之间的关系,有助于筛选用于植被恢复的物种,为保护沙地生态系统提供理论依据。以毛乌素沙地为研究区,分析了1983-2015年间沙地典型飞播样地群落演替特征及其对环境因子的响应,建立基于10个植物功能性状的毛乌素沙地潜在种库,进一步筛选飞播恢复下沙地不同演替阶段的适生植物。研究表明:(1)飞播恢复下的毛乌素沙地植物群落分为三个演替阶段:固沙先锋物种群落、沙生植物为主的杂类草群落、中生植物为主的杂类草群落。(2)土壤因子是群落演替的主要驱动力,其中土壤全氮、土壤总有机碳、土壤硝态氮是影响群落演替的关键因素。(3)基于功能性状筛选出29种适生物种用于植被恢复,演替第一阶段可用雾冰藜、猪毛菜等,演替第二阶段可用拂子茅、无芒隐子草等,演替第三阶段可用草地风毛菊、猪毛蒿等。通过物种功能性状特征可以快速选择适合沙地退化生态系统修复的候选物种,为植被恢复提供了一定的理论支持。     

干旱胁迫对黄土高原4种蒿属植物叶形态解剖学特征的影响

以黄土高原演替初期阶段的猪毛蒿(Artemisia scoparia Waldst.et Kit.)、茭蒿(Artemisia giraldii Pamp.)、铁杆蒿(Artemisia gmelinii Web.ex Stechm.)3种优势种和1种常见种黄花蒿(Artemisia annua Linn.)为供试材料,采用盆栽试验与称重控水法,将土壤含水量分别控制在田间最大持水量的75%(适宜水分对照)、55%(中度干旱)和35%(重度干旱),研究干旱胁迫对菊科蒿属植物叶片形态解剖学的影响,揭示植物叶片生态适应机制,为生态恢复过程中植被演替的规律提供理论依据。于植物营养生长末期选取代表性的叶片,分别采用电子扫描显微镜、电子透射显微镜和光学显微镜对叶表皮特征、亚细胞显微特征和组织结构进行观察。结果表明:干旱胁迫下,这4种植物表现为不同程度的叶片增厚、栅栏组织厚度、叶片紧实度和角质层厚度增加;3种旱生型植物猪毛蒿、茭蒿和铁杆蒿的叶片下表皮具有浓密的表皮毛,有利于防止水分过度蒸腾,而中生型黄花蒿叶片无此功能;铁杆蒿和黄花蒿上表皮毛稀少,不利于保水和防止强光照,干旱胁迫下依靠降低上表皮气孔密度和叶细胞叶绿体数目来适应环境;茭蒿和猪毛蒿叶绿体形态相似,具有较厚的基粒和浓密的基粒片层,强光下容易引起氧化损伤,猪毛蒿通过浓密的上表皮毛而茭蒿通过较强的抗氧化机制防止光能过剩,两者在重度干旱下均产生大量脂质体。4种蒿属植物中黄花蒿的叶片解剖学特征受到干旱的影响变化最大,铁杆蒿和猪毛蒿次之,茭蒿最弱,3种优势种的干旱适应性显著强于黄花蒿,干旱下叶片解剖学的结论与干旱耐受性指标结果一致。     

Effect of water content and temperature on seed longevity of seven Brassicaceae species after 5 years of storage

Maximising seed longevity is crucial for genetic resource preservation and longevity of orthodox seeds is determined by environmental conditions (water content and temperature). The effect of water content (down to 0.01 g·H₂O·g^?1) on seed viability was studied at different temperatures for a 5‐year storage period in taxonomically related species. Seeds of seven Brassicaceae species (Brassica repanda, Eruca vesicaria, Malcolmia littorea, Moricandia arvensis, Rorippa nasturtium‐aquaticum, Sinapis alba, Sisymbrium runcinatum) were stored at 48 environments comprising a combination of eight water contents, from 0.21 to 0.01 g·H₂O·g^?1 DW and six temperatures (45, 35, 20, 5, ?25, ?170 °C). Survival curves were modelled and P50 calculated for those conditions where germination was reduced over the 5‐year assay period. Critical water content for storage of seeds of six species at 45 °C ranged from 0.02 to 0.03 g·H₂O·g^?1. The effect of extreme desiccation at 45 °C showed variability among species: three species showed damaging effects of drying below the critical water content, while for three species it was neither detrimental nor beneficial to seed longevity. Lipid content could be related to longevity, depending on the storage conditions. A variable seed longevity response to water content among taxonomically related species was found. The relative position of some of the species as long‐ or short‐lived at 45 °C varied depending on the humidity at which storage behaviour was evaluated. Therefore, predictions of survival under desiccated conditions based on results obtained at high humidity might be problematic for some species.     

Seed germination and seedling emergence of three annuals growing on desert sand dunes in China

BACKGROUND AND AIMS: Information on the initial growth characteristics of annuals found in Chinese deserts is very limited. The aim of this study was to investigate seed germination and interactive effects of irrigation and seed burial depth in sand on seedling emergence and seedling survival in three annuals (Agriophyllum squarrosum, Bassia dasyphylla and Aristida adscensionis) commonly growing on sand dunes in these regions. METHODS: Effects of temperature, light and polyethylene glycol-6000 on seed germination were examined by irrigating seeds sown on filter paper in Petri dishes. Seedling emergence was examined for seeds sown on the surface of, or at different depths (5, 10, 20, 30, 40 and 50 mm) in, sand-filled pots, which were irrigated under different regimes. For seeds buried at a depth of 50 mm, seed viability was examined after irrigation of the pots. KEY RESULTS: Seeds of three species germinated at most temperatures recorded between spring and autumn in their native habitats. No seed dormancy was found in any species. For all three species, seedling emergence was most favoured when seeds were buried at a depth of 10 mm. When seeds sown on the sand surface were irrigated, seed germination was considerably suppressed due to water deficiency, but many seeds remained viable. For A. squarrosum and B. dasyphylla, many seeds that were deeply buried and irrigated remained ungerminated but viable, while for A. adscensionis deeply buried seeds germinated, but the seedlings did not emerge due to unfavourable seedling growth in deep sand. CONCLUSIONS: Precipitation is the most crucial factor in determining the seasonal emergence of seedlings of the three tested species in the field. The vertical distribution of seeds in sand determines the proportion of seeds that germinate after precipitation and acts to maintain seed banks over multiple years.