Effects of parental light environment on growth and morphological responses of clonal offspring

• Environments experienced by parent ramets of clonal plants can potentially influence fitness of clonal offspring ramets. Such clonal parental effects may result from heritable epigenetic changes, such as DNA methylation, which can be removed by application of DNA de‐methylation agents such as 5‐azacytidine.
• To test whether parental shading effects occur via clonal generation and whether DNA methylation plays a role in such effects, parent plants of the clonal herb Alternanthera philoxeroides were first subjected to two levels of light intensity (high versus low) crossed with two levels of DNA de‐methylation (no or with de‐methylation by application of 5‐azacytidine), and then clonal offspring taken from each of these four types of parent plant were subjected to the same two light levels.
• Parental shading effects transmitted via clonal generation decreased growth and modified morphology of clonal offspring. Offspring responses were also influenced by DNA methylation level of parent plants. For clonal offspring growing under low light, parental shading effects on growth and morphology were always negative, irrespective of the parental de‐methylation treatment. For clonal offspring growing under high light, parental shading effects on offspring growth and morphology were negative when the parents were not treated with 5‐azacytidine, but neutral when they were treated with 5‐azacytidine.
• Overall, parental shading effects on clonal offspring performance of A. philoxeroides were found, and DNA methylation is likely to be involved in such effects. However, parental shading effects contributed little to the tolerance of clonal offspring to shading.

     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

Nutrient addition does not increase the benefits of clonal integration in an invasive plant spreading from open patches into plant communities

• One benefit of clonal integration is that resource translocation between connected ramets enhances the growth of the ramets grown under stressful conditions, but whether such resource translocation reduces the performance of the ramets grown under favourable conditions has not produced consistent results. In this study, we tested the hypothesis that resource translocation to recipient ramets may reduce the performance of donor ramets when resources are limiting but not when resources are abundant.
• We grew Mikania micrantha stolon fragments (each consisting of two ramets, either connected or not connected) under spatially heterogeneous competition conditions such that the developmentally younger, distal ramets were grown in competition with a plant community and the developmentally older, proximal ramets were grown without competition. For half of the stolon fragments, slow‐release fertiliser pellets were applied to both the distal and proximal ramets.
• Under both the low and increased soil nutrient conditions, the biomass, leaf number and stolon length of the distal ramets were higher, and those of the proximal ramets were lower when the stolon internode was intact than when it was severed. For the whole clone, the biomass, leaf number and stolon length did not differ between the two connection treatments. Connection did not change the biomass of the plant communities competing with distal ramets of M. micrantha.
• Although clonal integration may promote the invasion of M. micrantha into plant communities, resource translocation to recipient ramets of M. micrantha will induce a cost to the donor ramets, even when resources are relatively abundant.

     

Sheltered from the storm? Population viability analysis of a rare endemic under periodic catastrophe regimes

Rare species are important targets for biodiversity conservation efforts because rarity often equates to small populations and increased endangerment. Rare species are prone to stochastic extinction events and may be particularly susceptible to catastrophes. Therefore, understanding how rare species respond to disturbances is critical for evaluating extinction risk and guiding conservation managers. Population viability analyses (PVAs) are essential for assessing rare species' status yet they seldom consider catastrophic events. Accordingly, we present a PVA of a rare tropical epiphyte, Lepanthes caritensis (Orchidaceae), under simulated disturbance regimes to evaluate its demographics and extinction risk. We aimed to test how demographic models incorporating catastrophes affect population viability estimates. Our goal was to better guide management of these orchids and other rare plants. Results revealed L. caritensis numbers have declined recently, but projected growth rates indicated that most subpopulations should increase in size if undisturbed. Still, projection models show that moderate catastrophes reduce growth rates, increase stochasticity in subpopulation sizes, and elevate extinction risk. Severe catastrophes had a more pronounced effect in simulations; growth rates fell below replacement level, there was greater variation in projected population sizes, and extinction risk was significantly higher. PVAs incorporating periodic catastrophes indicate that rare species may have greater extinction probabilities than standard models suggest. Thus, precautionary conservation measures should be taken in disturbance prone settings and we encourage careful monitoring after environmental catastrophes. Future rare plant PVAs should incorporate catastrophes and aim to determine if rescue and reintroduction efforts are necessary after disturbances to insure long-term population viability.     

Investigating seed dormancy in cotton (Gossypium hirsutum L.): understanding the physiological changes in embryo during after‐ripening and germination

• The dormancy of seeds of upland cotton can be broken during dry after‐ripening, but the mechanism of its dormancy release remains unclear.
• Freshly harvested cotton seeds were subjected to after‐ripening for 180 days. Cotton seeds from different days of after‐ripening (DAR) were sampled for dynamic physiological determination and germination tests. The intact seeds and isolated embryos were germinated to assess effects of the seed coat on embryo germination. Content of H₂O₂ and phytohormones and activities of antioxidant enzymes and glucose‐6‐phosphate dehydrogenase were measured during after‐ripening and germination.
• Germination of intact seeds increased from 7% upon harvest to 96% at 30 DAR, while embryo germination improved from an initial rate of 82% to 100% after 14 DAR. Based on T₅₀ (time when 50% of seeds germinate) and germination index, the intact seed and isolated embryo needed 30 and 21 DAR, respectively, to acquire relatively stable germination. The content of H₂O₂ increased during after‐ripening and continued to increase within the first few hours of imbibition, along with a decrease in abscisic acid (ABA) content. A noticeable increase was observed in gibberellic acid content during germination when ABA content decreased to a lower level. Coat removal treatment accelerated embryo absorption of water, which further improved the accumulation of H₂O₂ and changed peroxidase content during germination.
• For cotton seed, the alleviation of coat‐imposed dormancy required 30 days of after‐ripening, accompanied by rapid dormancy release (within 21 DAR) in naked embryos. H₂O₂ acted as a core link between the response to environmental changes and induction of other physiological changes for breaking seed dormancy.

     

福建省主要入侵植物空间分异及其影响因素

在实地调查数据的基础上,本研究结合GIS空间分析技术和地理探测器模型,分析福建省入侵植物空间分布情况,以及地理与社会环境因子及其交互作用对入侵植物分布的影响.结果表明:福建省共记录入侵植物82种,其中,优势科为菊科,小蓬草、藿香蓟和空心莲子草出现频次最高.沿海区域的入侵植物物种数量多于内陆区域,福州和厦门为福建省外来入侵植物的两大热点地区.入侵植物在不同海拔均有分布,但入侵植物的种类随着海拔的升高总体呈下降趋势.地理探测器分析显示,自然环境因子中降水和社会经济因子中路网密度、人口密度是入侵植物空间分布的主要影响因子.各因子的空间交互作用会正向影响入侵植物的空间分布,这反映出入侵植物空间分布影响要素的复杂性.综上,将地理探测器应用到入侵植物研究领域是可行的,筛选出的环境指示因子可用于监测福建省入侵植物的适生区,从而为采取有效的防控措施提供科学依据.     

不同钙浓度对宽叶雀稗幼苗的生长和抗性生理的影响

研究不同钙浓度对宽叶雀稗(Paspalum wettsteinii)幼苗生长和生理的影响, 对于揭示宽叶雀稗对不同钙浓度环境的适应机理至关重要。该研究采用盆栽砂培试验, 研究不同钙浓度(0、5、25、50、100和200 mmol·L^-1 CaCl₂)和不同处理时间(7、14、21和28天)对宽叶雀稗幼苗生长、渗透调节物质含量、抗氧化酶活性、叶绿素含量和光合参数的影响。结果表明, 随着CaCl₂浓度的增加和处理时间的延长, 宽叶雀稗幼苗株高等形态指标、生物量、渗透调节物质含量、抗氧化酶活性、叶绿素含量和光合参数呈先增后减的趋势, 低钙浓度(5-50 mmol·L^-1)环境下, 株高、叶长、叶宽、根长和生物量与对照(0 mmol·L^-1)相比均升高, 脯氨酸、可溶性蛋白和可溶性糖含量、过氧化物酶、过氧化氢酶和超氧化物歧化酶活性提高, 丙二醛含量和胞间CO₂浓度降低、叶绿素含量增加以及净光合速率、蒸腾速率和气孔导度增强; 高钙浓度(200 mmol·L^-1)环境下, 脯氨酸、可溶性蛋白和可溶性糖含量、过氧化物酶、过氧化氢酶和超氧化物歧化酶活性降低, 丙二醛含量和胞间CO₂浓度增加, 叶绿素含量减少以及净光合速率、蒸腾速率和气孔导度减弱。结合隶属函数分析, 低钙盐浓度(5-50 mmol·L^-1)处理对宽叶雀稗幼苗无抑制作用, 说明宽叶雀稗对低钙浓度具有一定的耐受性; 而在高钙浓度(200 mmol·L^-1)下, 宽叶雀稗幼苗通过提高自身有机渗透调节物质含量、增强酶活性、增加叶绿素含量以及增强光合作用等方式来快速调节植物生理代谢功能, 进而适应高钙浓度环境条件。     

贵州喀斯特区C4植物物种组成与水分生态型划分

该研究通过查阅文献、核对贵州大学林学院标本库及现场群落调查与标本采集,并运用碳同位素比值法研究典型C_4植物水分利用特性,探索C_4植物在喀斯特植被恢复中的地位,进而揭示贵州喀斯特地区C_4植物资源的基本特征。结果表明:贵州喀斯特区共有C_4植物141种,隶属于74属15科,分别占全国科属种的62.50%、46.25%、24.48%,以禾本科(Gramineae)和莎草科(Cyperaceae)为主;区内C_4植物种均为一年生或多年生草本,多年生植物种略多于一年生植物种;水分生态型整体偏旱生,旱生和中生植物分别占总数的24.82%和31.21%;喀斯特区C_4植物具有高水分利用效率,但不同水分生态型间差异不显著;贵州喀斯特区C_4植物资源具有资源丰富、利用途径广泛、能长期利用、竞争力强、能大面积分布、偏旱生且水分利用幅度广的基本特征,适合喀斯特区生境,自然状态下多为恢复早期物种,有利于喀斯特区生态恢复。在贵州喀斯特恶劣生态环境下C_4植物有较好的生态适应性,并表现出较高的药用、食用、饲用、景观应用等价值,对其开发利用对贵州经济、社会发展及生态恢复有重要意义。     

西藏虎头兰高效植株再生体系的研究

为建立西藏虎头兰(Cymbidium tracyanum)的高效快速繁殖体系,该研究以野生西藏虎头兰种子为外植体,通过分析不同基本培养基和植物激素配比对原球茎诱导、增殖和分化的影响,以及光照时间和培养温度对试管苗生长的影响,筛选出适宜西藏虎头兰植株高效再生的条件。结果表明:适宜西藏虎头兰生长的基本培养基为1/2 MS;种子萌发和原球茎诱导的最适培养基为1/2 MS+1.0 mg·L~(-1)6-BA+0. 5 mg·L~(-1)NAA,培养50 d后,有95.00%的种子发育成原球茎;原球茎增殖的最适培养基为1/2 MS+2.0 mg·L~(-1)NAA,培养30 d,增殖倍数为4.25;原球茎的最适分化培养基为1/2 MS+2.0 mg·L~(-1)NAA+60 g·L~(-1)土豆泥+0.5g·L~(-1)活性炭,培养10 d,不定芽发生率为98.33%,培养40 d,幼苗生根率为94.67%;试管苗在温度20℃、光照时间12 h·d~(-1)、光照强度2 000 lx的条件下培养,苗长势好,叶片生理性焦尖发生率仅为3.33%;以腐殖土作为栽培基质,试管苗的移栽成活率为97.78%。该研究结果为保护西藏虎头兰野生资源和工厂化育苗提供了科学依据和技术支持。     

苦豆子表型性状多样性分析及综合评价

该研究以自然分布的内蒙、宁夏、甘肃、新疆、陕西等23个不同地理来源(种源)的野生苦豆子种子及其播种于内蒙古鄂托克前旗同质园内的当年生植株为材料,采用方差分析、主成分分析、聚类分析等方法对种子长、宽、千粒重以及植株的叶长、叶宽、叶面积、叶形指数、苗高、地径及生物量等10个表型性状的多样性进行了研究。结果表明:各个表型性状种源间均呈极显著差异,其中种子表型性状的变异系数为5.24%,植株表型性状的变异系数为18.34%,表明种子性状的稳定性高于植株性状。同时,10个性状的表型分化系数均高于70%,说明苦豆子表型多样性主要来源于种源间的表型变异;各种源苦豆子种子性状的表型分化系数均值高达97.55%,且种长、千粒重分别与采集地经度、纬度和海拔等环境因子呈极显著相关性,说明种子表型性状受环境因素的影响较大;相关性分析显示,苦豆子植株性状叶长(LL)、叶面积(LA)分别与种子性状千粒重(TW)、种长(SL)和种宽(SW)有显著相关性,暗示表型性状中的可遗传变异影响;利用主成分和聚类分析对23个种源苦豆子进行综合评价,筛选出生物量较大、苗高较高、千粒重较重、叶面积较大等综合表现较好的6个种源,共分为两类,分别是DK、JY、WY、WH、ETK和YN,这为苦豆子种质资源定向开发以及选育和栽培提供了一定的理论支撑和基础材料。