异质水分环境下野牛草相连分株间光合同化物的生理整合及其调控

异质环境下,克隆植物通过生理整合机制使资源在分株间实现共享,提高了其对异质性环境的适应能力,具有重要的生态进化意义,研究生理整合机制及其调控机理可为进一步发掘克隆植物应用潜力提供理论依据。以野牛草3个相连分株为材料,对其中一个分株用30%聚乙二醇6000(PEG-6000)模拟水分胁迫,通过Hoagland营养液培养试验,研究了异质水分环境下光合同化物在野牛草相连分株间的生理整合及分株叶片与根系内源激素ABA与IAA含量的变化规律。结果表明,14C-光合同化物在克隆片断内存在双向运输,但以向顶运输为主,异质水分环境下,受胁迫分株光合同化物的输出率明显降低,而与其相邻分株合成的光合同化物向受胁迫分株方向运输率明显增加;异质水分环境下,各分株ABA含量均明显增加,但以受胁迫的分株叶片及根系ABA的含量增加幅度最大,各分株IAA含量较对照均显著下降(P0.05),且以受胁迫分株IAA含量下降幅度最大;各分株叶片与根系ABA/IAA均显著提高(P0.05),相邻分株ABA/IAA增加幅度低于受胁迫分株。异质水分环境影响野牛草克隆分株间光合同化物的生理整合,且ABA与IAA在分株间光合同化物运输与分配过程中具有重要的调节作用。     

疏叶骆驼刺母株与子株间的水分整合

在未灌溉的土地上, 疏叶骆驼刺(Alhagi sparsifolia)通常不能进行有性繁殖, 克隆繁殖是其种群维持和延续的唯一方式。因此, 克隆性及其相关克隆性状(如水分整合)在疏叶骆驼刺自然种群的维持过程中可能扮演了极其重要的角色。该文通过疏叶骆驼刺母株和子株之间的间隔子切断和给母株补充水分的方法, 研究了母株和子株在各处理下的水势、叶形态和植株生长变化情况。结果表明: (1)间隔子切断后, 疏叶骆驼刺母株和子株正午水势均明显增大(p < 0.01), 说明间隔子切断使得母株和子株水分亏缺值都增大。(2)给母株补水后, 间隔子切断组和间隔子相连组中的母株水势均有明显增加, 同时间隔子相连组的子株水势明显增加(p < 0.01), 而间隔子切断组子株水势没有明显变化(p > 0.05)。(3)间隔子切断组的子株叶片含水率明显低于间隔子相连组子株, 而其株高、冠幅、分枝数和基径的增长量都明显小于间隔子相连组的子株(p < 0.01)。疏叶骆驼刺母株和子株间存在水分整合, 母株会通过根系向子株传输水分。研究成果对塔克拉玛干沙漠南缘的植被恢复以及水资源的合理利用有着重要的意义。     

毛乌素沙地根茎灌木羊柴的基株特征和不同生境中的分株种群特征

通过对毛乌素沙地常见的豆科根茎灌木羊柴的基株的分株种群的调查研究,揭示植物的克隆生长的生态适应意义。研究表明：１）根茎灌木羊柴具有合轴型分枝类型和游击型基株构型。多年生根茎在沙基质中形成多层密集网络结构。２）固定沙丘的羊柴分株种群与半固定沙丘比具有较大的密度和较长的根状茎节间,较小的平均株距,但两种生境中的分株高度是相似的。固定沙丘的种群生物量和对根茎与花果生物量的投资也高于半固定沙丘上的种群。本     

毛乌素沙地游击型克隆半灌木羊柴对局部沙埋的反应

 不同程度的沙埋是生长在干旱和半干旱区内陆沙丘的植物经常遭遇的事件,沙埋可以改变植物所处的生物和非生物环境条件。已有研究表明不同程度的沙埋对于植物的影响不同 。轻微程度的沙埋可以增加植物高度、促进生物量的积累和新生分株的产生。如果沙埋强度不断增加,对植物的影响由正效应逐渐转变为负效应。即超过一定沙埋阈值后,沙埋会削弱植物的生长,甚至影响植物的存活。干旱和半干旱区内陆沙丘中常常生长着许多克隆植物, 克隆整合常常可以缓解克隆植物分株所遭受的局部环境胁迫。根茎型克隆植物羊柴（Hedysarum laeve）是毛乌素沙地的优势半灌木之一,也是当地重要的固沙植物。为了探讨克隆整合的作用是否可以提高沙埋阈值,并有助于羊柴忍受高强度的沙埋,以其为研究对象开展了野外实验。结果表明：轻微程度的沙埋（例如沙埋深度是原始羊柴分株高的10%～20%）可以加速羊柴分株的高生长,提高叶片生物量、茎生物量以及整个地上部分的生物量。高强度的沙埋（例如沙埋深度是原始羊柴分株高的80%～100%）会削弱羊柴分株的存活和生长。在与不遭受沙埋分株相连的情况下,羊柴分株遭受沙埋的阈值高于没有分株相连的,而且在高强度的沙埋下,前者（有分株相连的遭受沙埋的分株）比后者（没有分株相连的遭受沙埋的分株）在株高增量、茎生物量、叶片生物量以及地上分株生物量上都要显著高。这暗示着克隆整合提高了羊柴遭受沙埋的阈值并有助于羊柴分株忍受高强度的沙埋。     

Effects of nitrogen addition on clonal integration between mother and daughter ramets of Moso bamboo: a 13C-CO2 pulse labeling study

用¹³C-CO₂脉冲标记法研究氮添加对毛竹母子分株克隆整合的影响 相连分株间的资源共享(即克隆整合)是克隆植物的显著特征。克隆整合使毛竹(Phyllostachys pubescens)对多种环境条件具有较强的适应性。但毛竹通过克隆整合获得性能提升的机制尚不明确。本 研究区分并分析了毛竹光合碳的顶向整合和基向整合,以探究毛竹克隆片段如何在土壤氮异质性条件下 提高整体收益。本研究以由两株不同年龄毛竹分株组成 的克隆片段为研究对象,分株间通过根状茎连接。 每个分株设置氮添加或无氮添加两种处理,并通过单株母株或子株的¹³C-CO₂脉冲标记对光合碳的顶向整合和基向整合进行区分。研究结果表明,子株氮添加显著促进了光合碳由母株向子株的顶向整合,无论母株是否有氮添加,均向氮添加子株转运更多的光合碳。转运自无氮添加母株的光合碳主要分配至氮添加子株的 叶片,而转运自氮添加母株的光合碳则主要分配至根系。与无氮添加处理的子株相比,氮 添 加子株转运更多的光合碳至母株,且该过程不受母株氮添加的影响。转运自氮添加子株的光合碳主要 分配至无氮添加母株的根系和氮添加母株的叶片。这些结果说明,母株优先将更多的资源投入到具有高 养分可利用性的子株,随后子株作为更高效的资源采集点,根据母株的养分状况针对富集资源进行获取。通过这种方式,克隆植物可以降低资源获取成本并提高资源获取效率,最大限度地提升其整体表现。     

毛乌素沙地根茎禾草拂子茅对异质性水分供应的表型可塑性

拂子茅(Calamagrostis epigejos（L.)Roth)为根茎型多年生禾草,具细长根茎。为了探讨拂子茅在异质性水分环境中的表型差异,在内蒙古鄂尔多斯高原的毛乌素沙地对拂子茅由母株、子株组成的分株对给予了高水、低水两种不同的异质性土壤水分处理。实验结果表明：土壤水分状况显著地影响着拂子茅分株的生长表型。在高土壤水分条件下,拂子茅的分株产生的根茎、新生后代分株较多,并使生物量主要分配于地上部分,地上生物量积累多;在低土壤水分条件下,拂子茅分株产生较少的根茎与新生后代分株,并且分配到根系的生物量明显增大。在具有一定对比度的异质性土壤水分环境中,拂子茅分株并不因相连的其他分株所处的土壤水分状况而在根茎生长、新生后代分株的产生和生物量分配等特征上,与同质环境中的具有相同土壤水分状况的分株相比,有明显差异。这些结果揭示：拂子茅仅以分株的形式对异质性水分供应发生表型反应;相连的克隆分株在向顶向和向基向这两个基本方向上,不能对另一分株的土壤水分状况在生K表型上发生反应,它们在水分关系上可能是相互相对独立的。分株的相对独立可能有利于在气候干旱、扰动强烈的沙地环境中实现风险分摊,提高基株的存活几率。     

内蒙古锡林河流域不同生境中羊草的克隆构型和分株种群特征

 克隆植物的形态可塑性在基株和种群水平上分别表现为克隆构型和分株种群特征的变化。研究对象为内蒙古锡林河流域草地、林地、沙地3种生境下的羊草(Leymus chinensis)种群,通过对羊草根茎节间长度、间隔子长度、分枝强度、分枝角度、株高和分株密度等指标的测定和分析,对这3种不同生境中羊草的克隆构型及分株种群特征进行了研究。结果表明羊草克隆构型相关特征,如,根茎节间长度,根茎节间长度频次分布格局、间隔子长度、间隔子长度频次分布格局,在不同生境差异较大。同时,羊草的分枝角度在不同生境间差异显著。而每间隔子所     

毛乌素沙地根茎禾草拂子茅对异质性水分供应的表型可塑性

拂子茅(Calamagrostis epigejos(L.)Roth.)为根茎型多年生禾草,具细长根茎.为了探讨拂子茅在异质性水分环境中的表型差异,在内蒙古鄂尔多斯高原的毛乌素沙地对拂子茅由母株、子株组成的分株对给予了高水、低水两种不同的异质性土壤水分处理.实验结果表明:土壤水分状况显著地影响着拂子茅分株的生长表型.在高土壤水分条件下,拂子茅的分株产生的根茎、新生后代分株较多,并使生物量主要分配于地上部分,地上生物量积累多;在低土壤水分条件下,拂子茅分株产生较少的根茎与新生后代分株,并且分配到根系的生物量明显增大.在具有一定对比度的异质性土壤水分环境中,拂子茅分株并不因相连的其他分株所处的土壤水分状况而在根茎生长、新生后代分株的产生和生物量分配等特征上,与同质环境中的具有相同土壤水分状况的分株相比,有明显差异.这些结果揭示:拂子茅仅以分株的形式对异质性水分供应发生表型反应;相连的克隆分株在向顶向和向基向这两个基本方向上,不能对另一分株的土壤水分状况在生长表型上发生反应,它们在水分关系上可能是相互相对独立的.分株的相对独立可能有利于在气候干旱、扰动强烈的沙地环境中实现风险分摊,提高基株的存活几率.     

克隆水分整合有助胡杨无性系幼株在极端干旱生境下保持更高生存优势

以塔里木河下游的胡杨为对象,研究胡杨母株与其克隆幼株间的克隆水分整合特征及对克隆幼株生理机能的影响.结果表明: 胡杨母株与其克隆幼株间存在明显的以顶向传输为特征的水分整合,母株对克隆幼株的日平均水分整合流量为同区域长势相近的实生幼株通过自身根系日平均获取水量的3倍,克隆幼株因水分整合而能够获取与母株相似且较实生幼株水分来源相对较深层的土壤水,拥有更好的水分获取能力.这使胡杨克隆幼株较实生幼株保持显著更高的叶片水分含量,且黎明前和正午叶水势分别显著增加10.0%和29.7%.更好的水分生理状态使克隆幼株的光合电子传递速率与光适应下实际光化学效率显著高出实生幼株23.4%和11.5%,并能够保持显著更低的光系统Ⅱ过剩激能比例和光抑制风险.这可能让胡杨克隆幼株在极端干旱生境中较实生幼株保持更高的生存优势.     

养分异质条件下结缕草克隆分株生长及光合作用的生理整合

通过对连接和断开的分株进行不同养分处理,研究养分异质条件下结缕草克隆分株生长及光合作用的变化.结果表明:在养分异质条件下,处于中、高养分水平的母株可以提高与其相连子株的叶长、叶宽、根质量、叶质量、光合速率、气孔导度、蒸腾速率和水分利用效率,高养分条件下分别提高16.0%、8.3%、24.4%、58.1%、30.3%、54.0%、9.2%和21.9%,降低根冠比和胞间CO2浓度,在高养分下分别降低21.6%和31.5%;处于中、高养分水平的子株对与其相连母株的生长及光合特性没有显著影响.在养分异质条件下,结缕草母株对子株存在生理整合,养分梯度越大,整合强度越强.结缕草克隆子株可以从母株获益,但母株不能从子株获益,子株是生理整合单向获益者.     

Clonal integration and its ecological significance in Hedysarum laeve,a rhizomatous shrub in Mu Us Sandland

Hedysarum laeve, a rhizomatous clonal half-shrub, commonly dominates in inland dunes in semiarid areas of northern China. This species propagates vegetatively by the extension of horizontal rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, (14)C labeling and experimental defoliation were employed to test the photosynthate translocation within the interconnected parent-daughter ramet pairs. A proportion of (14)C-photosynthates was transported from the parent ramet into the daughter ramet, the roots of the daughter ramet, and the rhizome; these three components showed more than 70% sink activity after 24-h translocation. On the other hand, the basipetal translocation (from daughter ramet into parent ramet) was relatively small with sink activity of less than 5%, but sink activity of the rhizome exceeded 10%. Defoliation had an influence on the photosynthate translocation between parent and daughter ramets. The intact parent ramets significantly increased their (14)C-photosynthate translocation into defoliated daughter ramets when compared to intact daughter ramets. The daughter ramets transported significantly more (14)C-photosynthates to the defoliated parent ramets than to the intact parent ramets. A portion of (14)C-photosynthates was transported into the rhizome from both parent and daughter ramets, indicating that the rhizome is supported by both ramets for photosynthates. The clonal integration between ramets of the species through rhizome connection may confer benefit both to the ramets and the genet in adverse environments.     

Clonal integration and its ecological significance in Hedysarum laeve, a rhizomatous shrub in Mu Us Sandland

Hedysarum laeve, a rhizomatous clonal half-shrub, commonly dominates in inland dunes in semiarid areas of northern China. This species propagates vegetatively by the extension of horizontal rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, ¹⁴C labeling and experimental defoliation were employed to test the photosynthate translocation within the interconnected parent–daughter ramet pairs. A proportion of ¹⁴C-photosynthates was transported from the parent ramet into the daughter ramet, the roots of the daughter ramet, and the rhizome; these three components showed more than 70% sink activity after 24-h translocation. On the other hand, the basipetal translocation (from daughter ramet into parent ramet) was relatively small with sink activity of less than 5%, but sink activity of the rhizome exceeded 10%. Defoliation had an influence on the photosynthate translocation between parent and daughter ramets. The intact parent ramets significantly increased their ¹⁴C-photosynthate translocation into defoliated daughter ramets when compared to intact daughter ramets. The daughter ramets transported significantly more ¹⁴C-photosynthates to the defoliated parent ramets than to the intact parent ramets. A portion of ¹⁴C-photosynthates was transported into the rhizome from both parent and daughter ramets, indicating that the rhizome is supported by both ramets for photosynthates. The clonal integration between ramets of the species through rhizome connection may confer benefit both to the ramets and the genet in adverse environments. Received: April 12, 2001 / Accepted: November 26, 2001     

The significance of rhizome connection of semi-shrub Hedysarum laeve in an Inner Mongolian dune,China

Hedysarum laeve, a rhizomatous clonal semi-shrub, commonly dominates the inland dunes in semiarid areas of northern China. This species propagates vegetatively by extension of horizontal woody rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, the plants were experimentally manipulated by cutting rhizome connections and ¹⁴C-labelling techniques were employed to investigate the ecological significance of rhizome connections within the H. laeve clone. Severance of rhizome connections had a great effect on the performance of young ramets within a clone. Young ramets severed from their parent ramets experienced a significant reduction both in ramet growth and vegetative propagation, as compared with the intact young ramets. Within clonal fragments, consisting of three interconnected ramets including a mother ramet, a daughter ramet and a granddaughter ramet, ¹⁴C-photosynthates from the fed leaves of mother ramets were acropetally transported to all clonal component parts. The ¹⁴C-photosynthate translocation within the clonal fragment provides evidence that the young ramets were supported by their parent ramets. Our results suggest that the woody rhizome connections among the interconnected ramets are ecologically and strategically important for the species to grow in the sand dune habitat.     

Clonal plant allocation to daughter ramets is a simple function of parent size across species and nutrient levels

The evolution of clonal growth is a widespread phenomenon among plant species, characterized by the production of genetically identical clonal fragments (ramets) via rhizomes or stolons that form an interconnected clonal organism (genet). Clonal plant species are known to differ in their investment into ramet production, and exhibit considerable variation in ramet morphology both within and among species. While patterns of resource allocation are thought to be linked to a number of plant characteristics, many analyses are limited by uncertainty in how clonal plants determine the morphology and resources allocated to new ramets. In this study, we attempted to discern what aspects of parent ramets best predicted resource allocation to new daughter ramets, and the relationship between resource allocation and daughter ramet rhizome morphology. We grew two sedge species, Schoenoplectus tabernaemontani and Eleocharis elliptica, in a greenhouse under two levels of fertilizer addition. By harvesting daughter ramets that had initiated stem production, yet remained aphotosynthetic, we were able to isolate parental investment into non-independent daughter ramets at a point where daughter ramet spacer length became fixed. Our results indicate that parent ramets allocated a non-linear proportion of parent rhizome biomass to the production of daughter ramets. Moreover, this relationship was unaffected by environmental nutrient availability. Daughter ramet biomass, in turn, was strongly correlated with daughter ramet spacer length. These observations shed light on key processes governing clonal growth in plants, and their potential application in unifying allocational and morphological perspectives to explore the fitness implications of variability in clonal growth.     

Carbon allocation during fruiting in Rubus chamaemorus

Background and Aims

Rubus chamaemorus (cloudberry) is a herbaceous clonal peatland plant that produces an extensive underground rhizome system with distant ramets. Most of these ramets are non-floral. The main objectives of this study were to determine: (a) if plant growth was source limited in cloudberry; (b) if the non-floral ramets translocated carbon (C) to the fruit; and (c) if there was competition between fruit, leaves and rhizomes for C during fruit development.

Methods

Floral and non-floral ramet activities were monitored during the period of flower and fruit development using three approaches: gas exchange measurements, ¹⁴CO₂ labelling and dry mass accumulation in the different organs. Source and sink activity were manipulated by eliminating leaves or flowers or by reducing rhizome length.

Key Results

Photosynthetic rates were lower in floral than in deflowered ramets. Autoradiographs and ¹⁴C labelling data clearly indicated that fruit is a very strong sink for the floral ramet, whereas non-floral ramets translocated C toward the rhizome but not toward floral ramets. Nevertheless, rhizomes received some C from the floral ramet throughout the fruiting period. Ramets with shorter rhizomes produced smaller leaves and smaller fruits, and defoliated ramets produced very small fruits.

Conclusions

Plant growth appears to be source-limited in cloudberry since a reduction in sink strength did not induce a reduction in photosynthetic activity. Non-floral ramets did not participate directly to fruit development. Developing leaves appear to compete with the developing fruit but the intensity of this competition could vary with the specific timing of the two organs. The rhizome appears to act both as a source but also potentially as a sink during fruit development. Further studies are needed to characterize better the complex role played by the rhizome in fruit C nutrition.Key words: Allocation pattern, ¹⁴C labelling, carbon translocation, carbon reserves, cloudberry, defoliation, fruit production, gas exchange, Rubus chamaemorus, source–sink relationship, flowering     

High levels of inter-ramet water translocation in two rhizomatous Carex species,as quantified by deuterium labelling

We studied water trnaslocation between interconnected mother and daughter ramets in two rhizomatous Carex species, using a newly developed quantitative method based on deuterium tracing. Under homogeneous conditions, in which both ramets were subjected either to wet or dry soil, little water was exchanged between the ramets. When the ramet pair was exposed to a heterogeneous water supply, water translocation became unidirectional and strongly increased to a level at which 30–60% of the water acquired by the wet ramet was exported towards the dry ramet. The quantity of water translocated was unrelated to the difference in water potential between the ramets, but highly correlated to the difference in leaf area. In both species, the transpiration of the entire plant was similar under heterogeneous and homogeneous wet conditions. This was a direct result of an increase in water uptake by the wet ramet in response to the dry conditions experienced by the interconnected ramet. In C. hirta, the costs and benefits of integration in terms of ramet biomass paralleled the responses of water consumption. This species achieved a similar whole-plant biomass in heterogeneous and homogeneous wet treatments, and water translocation was equally effective in the acropetal and basipetal directions. In C. flacca, responses of biomass and water consumption did not match and, under some conditions, water translocation imposed costs rather than benefits to the plants of this species. It is concluded that enhanced resource acquisition by donor ramets may be of critical importance for the net benefits of physiological integration in clonal plants.     

The effect of resource integration on fitness related traits in a clonal dune perennial,Hydrocotyle bonariensis

Summary The costs and benefits of resource integration in Hydrocotyle bonariensis were examined by comparing severed and intact clones grown across multiple resource gradients. Basipetal movement of water, nitrogen and photosynthates was demonstrated to occur between two rhizome branch systems interconnecting hundreds of ramets within a clone. Hydrocotyle clones of this size and larger have been shown to span highly patchy and unpredictable resource conditions in coastal dune environments. The extensive movement of water and nitrogen to portions of a clone deficient in these resources, resulted in a significant net benefit to the clone in terms of fitness-related traits: total biomass, ramet proliferation and seed production. The translocation of photosynthates across light gradients allowed for sexual reproduction and clonal expansion in the shade although this incurred a net cost to the clone in terms of ramet and seed production.     

Inter-ramet water translocation in natural clones of the rhizomatous shrub, <Emphasis Type="Italic">Hedysarum laeve</Emphasis>, in a semi-arid area of China

The patterns of resource translocation among interconnected ramets within a clone may show diversity. In order to understand the pattern of inter-ramet water translocation in natural clones of the rhizomatous shrub Hedysarum laeve (Leguminosae), which frequently dominates inland dunes in semi-arid areas of China, acid fuchsin dye application combined with spectrometric analysis was employed. Dye solutions were fed to the base of plants (near the parent ramet) and to the apical portions (near one of the youngest shoots) and the amount of dye in shoots and rhizomes was measured spectrometrically after 24 h. The total amount of dye translocated from the base in the acropetal direction was approximately four times as high as that of basipetal translocation from cut sections near the apex. Most of the dye was detected in the shoots with very little found in the rhizomes. The average percentage allocation of dye from donor ramet transferred to recipient ramets in the ramet hierarchy closer, due to acropetal and/or basipetal translocation, was significantly greater than those in the ramet hierarchy less close to it. The ramet-hierarchy order had a great influence on dye translocation in either the acropetal or basipetal direction. It is inferred that the donor ramet would transport water towards its recipient ramets in different ramet hierarchies in unequal proportions in this species.