克隆整合对天胡荽分株间有性和克隆繁殖策略的影响

研究了克隆整合特性对天胡荽在异质性土壤养分环境中繁殖策略的影响。结果表明: 克隆整合可显著提高相连分株中处于低资源条件下近端分株的结果数和坐果率、总种子数量, 及其单个克隆分株的平均结籽数, 但对各处理单果重量的无显著影响。克隆整合有利于促进资源缺乏端的有性繁殖; 促进生理顶端分株的克隆繁殖。在低资源条件下, 克隆整合促进近端分株的有性繁殖以及远端分株的克隆繁殖; 相反则促进远端分株的有性繁殖和克隆繁殖。因此, 克隆整合特性是天胡荽对异质性环境的重要适应对策, 它使天胡荽能够扩展到不适合植物生长的低养分斑块中, 从而增加了天胡荽对恶劣环境的繁殖适合度及适应能力。     

高寒草甸放牧扰动与两种植物的反应研究

对不同放牧强度下矮嵩草草甸植物垂穗披碱草和鹅绒委陵菜的生长和繁殖特性进行了5年研究。结果表明,垂穗披碱草株高、分蘖数、地上物量、地下生物量、有性繁殖效力在不放牧或轻度放牧下最大,营养生长效力在重度放牧中最大,而贮藏效力在重度放牧中最小。鹅绒委陵菜叶数、匍匐茎长度、地上生物量、匍匐茎生物量、开花数、生殖生物量、有性繁殖效力及营养繁殖效力在放牧区显著高于不放牧的对照区。说明适当的放牧干扰有利于垂穗披碱草营养生长,但放牧过重会抑制其有性繁殖;由于放牧采食减少了种间竞争影响,从而提高了鹅绒委陵菜营养,生长效力和有性繁殖效力。两物种地下贮藏物的比例随着放牧强度增加显著减少。放牧强度对高寒草甸的群落演替方向有显著影响。     

毛乌素沙地优势克隆半灌木生物量配置对小尺度植被盖度变异的响应

克隆植物根据其构型可以分为游击型和密集型。游击型克隆植物的间隔子长,分株在水平空间的扩展范围大,可以利用更大空间范围内的资源,其通过克隆生理整合作用发生的非局部反应的能力强。由此可以得出的推论之一是,小生境斑块的环境发生变化,生长于其中的密集型克隆植物的反应可能会更灵敏。这种反应可能会体现在生物量以及配置格局的变化上。以毛乌素地区沙生半灌木群落中两种优势克隆植物羊柴(H edy sarum laeve)和油蒿(A rtem isia ord osica)为研究对象,前者是典型的游击型克隆植物,后者是密集型克隆植物。采取野外调查的方式,观测在不同植被盖度的小生境斑块内二者地上生物量分配格局的变化情况,并结合二者的克隆构型和生活史特征试图探讨产生这种格局的原因。结果表明:羊柴的地上各部分生物量对植被盖度变化的响应不如油蒿敏感。这或者是因为羊柴的游击型克隆构型决定其可以跨越小尺度斑块实现克隆生理整合,可以利用不同小生境斑块的资源导致的。油蒿只能利用小生境斑块内的资源,当小生境斑块的条件改变,其生物量以及配置方式也随之发生相应的变化。在繁殖方式上,羊柴的有性繁殖结构以及有性繁殖投资显著小于油蒿。在资源有限的条件下,对一种繁殖方式的投资常常会削弱另一种繁殖方式。羊柴主要依靠克隆繁殖,这或者符合并支持配置理论的观点。     

氮、硫互作对克隆植物互花米草繁殖和生物量累积与分配的影响

氮、硫均是影响入侵植物互花米草（Spartina alterniflora Loisel.）生长与繁殖的重要营养元素,研究其交互作用可能有助于揭示互花米草成功入侵机制。本文在人工控制条件下,以河沙为栽培基质,研究了氮、硫互作对互花米草繁殖和生物量积累与分配的影响。实验结果表明：中氮和高氮处理下的互花米草分支强度、初级分株数、次级分株数、根状茎数及其总长要显著高于低氮,不同硫水平及氮硫互作对互花米草无性繁殖没有显著影响;互花米草的种子数和种子生物量受硫以及氮硫交互作用的影响显著,在高氮水平下,中硫处理的互花米草种子数和种子生物量要远远高于其他处理。中氮和高氮处理下的互花米草叶、茎、根、根状茎和总生物量显著高于低氮处理;只有在高氮水平下,高硫处理的生物量才显著低于其他处理。在中氮和高氮营养条件下,高硫处理会促使互花米草对地上部分投入更多的生物量。中硫-高氮作用对互花米草有性繁殖的促进,使互花米草能在硫浓度较高的滩地保持高有性繁殖率;虽然过高的硫会抑制互花米草的有性繁殖,但却能促进根状茎数目的增加,从而加速其向外短距离扩张;这些特性均有利于互花米草对滨海盐沼的入侵。     

沙埋对半灌木羊柴幼苗的存活、生长和生物量分配的影响

羊柴 (HedysarumlaeveMaxim .)是中国北方沙地飞播进行植被恢复与重建的主要植物种。在晚春与夏初的出苗期 ,羊柴幼苗经常遭受不同深度的沙埋。研究旨在探明沙埋对羊柴幼苗存活、生长和生物量分配格局的影响。6周的沙埋试验结果显示 :当沙埋深度达到其株高时 ,约有 70 %的幼苗死亡 ;沙埋深度达到其株高的 133%时 ,可使羊柴幼苗全部死亡 ;沙埋深度分别为株高的 33%和 6 7%时 ,羊柴幼苗的整株生物量、叶片生物量、根系生物量以及相对生长率都相应地高于非沙埋的对照 (即 :0 %沙埋 )。与非沙埋的对照相比 ,羊柴幼苗在 33%和 6 7%沙埋条件下并不显著地改变其生物量分配格局 ;并且羊柴幼苗的叶数和株高与对照无明显差异 ,但试验期内的新生叶数是沙埋处理 (即 :33%、6 7%和 10 0 %沙埋 )的幼苗明显地高于非沙埋的对照。     

模拟源株密度对蝴蝶花生长和克隆繁殖的影响

通过不同蝴蝶花(Iris japonica)起始源株密度的控制实验, 探讨源株对克隆植物蝴蝶花克隆繁殖、生长和生物量分配的影响。结果表明: 1)克隆数量特征: 1个起始源株处理(O)蝴蝶花新分株数显著高于2个起始源株(T)及4个起始源株处理(F), 而新分株死亡率显著低于后二者; 随着起始源株数增加(竞争增强), 一级与二级子株数显著降低。随着源株竞争增强, 克隆细根茎与根的长度、表面积、体积与根(茎)长密度逐渐降低。2)叶片特征: 随着源株竞争增强, 母株重度枯萎与总枯萎叶片数显著增加, 子株中度枯萎、重度枯萎与总枯萎叶片数显著增加; 源株竞争增强, 源株叶面积、源株与子株叶片数显著降低, 而源株叶面积比(leaf area ratio, LAR)显著增加。3)生物量及分配: 随着源株竞争增强, 细根茎、粗根茎、克隆繁殖、地上部分、地下部分及总生物量显著降低, 细根茎与地下部分分配降低, 母株粗根茎分配与地上部分分配显著增加。总的看来, 随着蝴蝶花源株竞争增强, 植株叶片生长状况受到更大的影响, 植株生长受限, 克隆繁殖减弱, 而其通过增加LAR, 提高叶片效率与增加母株粗根茎分配, 降低生长强度与消耗, 储备资源, 以待来年的生长与繁殖。     

沙埋对半灌木羊柴幼苗的存活、生长和生物量分配的影响

羊柴(Hedysarum laeve Maxim.)是中国北方沙地飞播进行植被恢复与重建的主要植物种.在晚春与夏初的出苗期 ,羊柴幼苗经常遭受不同深度的沙埋.研究旨在探明沙埋对羊柴幼苗存活、生长和生物量分配格局的影响.6周的沙埋试验结果显示:当沙埋深度达到其株高时,约有70%的幼苗死亡 ;沙埋深度达到其株高的133%时,可使羊柴幼苗全部死亡;沙埋深度分别为株高的33%和67% 时,羊柴幼苗的整株生物量、叶片生物量、根系生物量以及相对生长率都相应地高于非沙埋的对照(即:0%沙埋).与非沙埋的对照相比,羊柴幼苗在33%和67%沙埋条件下并不显著地改变其生物量分配格局;并且羊柴幼苗的叶数和株高与对照无明显差异,但试验期内的新生叶数是沙埋处理(即:33%、67%和100%沙埋)的幼苗明显地高于非沙埋的对照.     

刈割干扰下内蒙古草原两种丛生禾草繁殖策略的适应性调节

刈割是内蒙古草原的主要利用方式之一。当植物面对刈割干扰时, 可以通过繁殖策略的调节适应变化的环境。研究刈割干扰下植物繁殖策略的调节对于揭示植物的适应与进化机制具有重要意义。为此, 选择内蒙古典型草原的大针茅(Stipa grandis)和糙隐子草(Cleistogenes squarrosa), 在1979年围封的羊草(Leymus chinensis)样地(对照)和毗邻的长期刈割区对其繁殖策略进行了研究。结果显示: 1)长期刈割干扰下, 大针茅的种群生物量与对照区无显著差异, 由于其株丛生物量显著降低, 大针茅种群生物量的维持得益于种群密度的显著增加。糙隐子草的种群生物量比对照区显著提高, 由于其株丛生物量与对照区无显著差异, 糙隐子草种群生物量的增加也是因为密度的显著提高。因此, 密度调节是两种植物应对长期刈割干扰的重要的调节机制。2)长期刈割干扰下, 两种植物在无性繁殖和有性繁殖过程所采取的密度调节策略并不相同。大针茅种群生殖株丛的密度无显著变化, 非生殖株丛的密度显著提高, 导致其非生殖株丛的相对密度显著增加, 而生殖株丛的相对密度显著降低。因此刈割干扰下大针茅种群在密度调节上采取了保持有性繁殖株丛密度, 增加无性繁殖株丛密度的策略。糙隐子草种群非生殖株丛的密度显著增加, 但生殖株丛的密度增加幅度更大, 导致其非生殖株丛的相对密度显著降低, 而生殖株丛的相对密度显著提高。因此刈割干扰下糙隐子草种群在密度调节上采取了增加无性繁殖株丛密度的同时, 更大幅度地增加有性繁殖株丛密度的策略。3)长期刈割干扰下, 两种植物对生物量生殖分配的调节采取了不同的策略。大针茅株丛生物量向生殖枝分配的比例无显著变化, 通过降低生殖枝向穗的生物量分配比例, 降低了对有性生殖过程的生物量分配的投入; 而糙隐子草则通过增加株丛生物量向生殖枝分配的比例, 维持生殖枝向穗的生物量分配比例, 从而增加了对有性繁殖过程生物量分配的投入。4)长期刈割干扰下, 大针茅的株丛面积和株丛分蘖数与对照区无显著差异。糙隐子草株丛面积降低, 但是株丛分蘖数无显著变化。本实验说明, 植物种群有性繁殖和无性繁殖之间的密度调节和资源分配调节是草原植物应对刈割干扰下的重要调节机制, 不同的响应策略影响着植物种群的消长动态。     

不同高程短尖苔草对水位变化的生长及繁殖响应

在淡水湿地生态系统中,水位通常是制约植被生长和繁殖动态的关键因素,进而对物种组成、群落演替和植被分布格局产生决定性影响。无性繁殖是洞庭湖湿地克隆植物适应环境胁迫的重要策略之一,以洞庭湖湿地典型克隆植物-短尖苔草(Carex brevicuspis C.B.Clarke)为对象,研究了不同分布高程(23.7 m和25.8 m)的植物对水位变化(0 cm,-15 cm,-30 cm)的生长和繁殖特征响应。结果表明:水位变化对不同分布高程分布短尖苔草的生长和克隆繁殖特征均产生显著影响(P0.05)。对高程区的短尖苔草而言,克隆繁殖特征如分株数、分株总生物量、芽数和芽生物量随水位的降低而增加,而对生长特征(株高及总生物量)无显著影响(P0.05),表明适当干旱有利于高程区苔草的克隆繁殖。对于低程区分布短尖苔草而言,水位变化对其生长特征有显著影响(P0.05),如株高和总生物量随着水位的降低而增加;分株数和总芽生物量等克隆繁殖特征则随水位的降低而减少,而水位对低程区短尖苔草的分株总生物量和总芽数影响不显著(P0.05)。因此,短尖苔草的克隆繁殖特征除受到水位的影响外,还受其分布高程的影响。可见,同一种短尖苔草因长期适应于不同生境而对相同的环境胁迫表现出了不同的生长繁殖策略,     

水分供应对毛乌素沙地油蒿和羊柴种间关系的影响

油蒿和羊柴为毛乌素沙地的共生优势物种, 然而关于土壤水分对其种间关系的研究相对较少。设置低水(200mL)、中水(300 mL)和高水(400 mL)三个水分处理水平及单独和混合生长两种种植方式, 通过油蒿和羊柴的生长响应,来研究不同水分供应条件下两物种种间关系的变化。结果表明: 水分处理显著提高了油蒿的株高和基径以及羊柴的基径, 竞争存在与否对两物种的形态生长指标均没有显著影响。在生物量积累方面, 水分处理对于油蒿总干重的影响表现为先增加后降低, 且主要是在混合生长条件下; 水分显著降低单独生长油蒿的根冠比。竞争对油蒿总干重的促进作用主要是在中水条件下, 对其根冠比的抑制作用是在低水条件下。对于羊柴, 水分处理显著提高其总干重而降低其根冠比, 竞争仅对其总干重有显著的降低作用且是在中水条件下。通过对相对竞争系数的进一步研究发现, 油蒿和羊柴的种间关系表现为在低水、高水下竞争, 在中水条件下共存, 并且两物种的相对竞争能力随处理的时间而变化。上述实验结果表明, 中等水分供应条件对两物种的共存是有利的, 这可为毛乌素优势群落的管理提供一定的理论参考。     

Clonal plasticity in response to rhizome severing and heterogeneous resource supply in the rhizomatous grass Psammochloa villosa in an Inner Mongolian dune, China

In a field experiment, Psammochloa villosa plants were subjected to rhizome severing. Severing rhizomes reduced growth in the young, detached rhizome segments compared to the controls in terms of all measured clonal growth-related characters, i.e. number of rhizomes and shoots, total rhizome length and total number of rhizome nodes. In a container experiment, the control ramets received uniform water and nutrient supply but in heterogeneous treatments high and low levels of water and nutrient supply, respectively were established. The number of ramets, total rhizome length, dry weight per ramet and biomass allocation to the rhizome had higher values at high water and nutrient supply, while spacer length (length of rhizome between shoots) and rhizome internode length were not affected. The local response of ramets given low water supply was enhanced due to connection to a well watered parent ramet in terms of number of ramets, total rhizome length and dry weight per ramet. A remote effect was not observed in the other treatments or in the other measured characters.     

Life history trade-offs in Amphibromus scabrivalvis (Poaceae): allocation to clonal growth,storage, and cleistogamous reproduction

Life history trade-offs among clonal growth, storage, and sexual reproduction were investigated in the perennial grass Amphibromus scabrivalvis in relation to soil nutrients. This species exhibits clonal growth by producing rhizomes and stores reserves in the form of basal corms; seeds are matured in cleistogamous spikelets on panicles enclosed within the leaf sheaths along each culm. Ten seed-derived genotypes (clones) were separated into 72 ramets and planted in the greenhouse. Control ramets received only water while the remainder received fertilizer applied every 2 wk. Twenty-four ramets were harvested per clone at 11, 20, and 26 wk. The dry mass of corms, rhizomes, roots, shoots, and seeds were recorded. Biomass partitioning to rhizomes provided a measure of carbon allocation to clonal growth, partitioning to corms provided a measure of allocation to storage, and partitioning to seeds provided a measure of allocation to sexual reproduction. Allocation to most organs was significantly influenced by clone identity; fertilizer significantly increased allocation to corms and seeds at 20 wk, but never affected rhizome allocation at any age. Corm allocation increased from 2% at 11 wk to 27% at 26 wk; rhizome allocation decreased from 10% at 11 wk to 3% at 26 wk. Significant negative relationships were detected for rhizome vs. seed and corm vs. rhizome allocation in fertilized clones at 20 wk. This suggests an age-dependent physiological life history trade-off between clonality and sexual reproduction and between clonality and storage. In contrast, a significant positive relationship was consistently noted for corm vs. seed allocation in fertilized and unfertilized clones at 20 and 26 wk. The absence of a trade-off between storage and sexual reproduction may indicate that these two processes are not necessarily mutually exclusive components of life history.     

Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration

The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration.     

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。     

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.     

根茎型植物扁秆荆三棱对光照强度和养分水平的生长响应及资源分配策略

自然界中光照和养分因子常存在时空变化,对植物造成选择压力。克隆植物可通过克隆生长和生物量分配的可塑性来适应环境变化。尽管一些研究关注了克隆植物对光照和养分因子的生长响应,但尚未深入全面了解克隆植物对光照和养分资源投资的分配策略。以根茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)为研究对象,在温室实验中,将其独立分株种植于由2种光照强度(光照和遮阴)和4种养分水平(对照、低养分、中养分和高养分)交叉组成的8种处理组合中,研究了光照和养分对其生长繁殖及资源贮存策略的影响。结果表明,扁秆荆三棱的生长、无性繁殖及资源贮存性状均受到光照强度的显著影响,在遮阴条件下各生长繁殖性状指标被抑制。且构件的数目、长度等特征对养分差异的可塑性响应先于其生物量积累特征。在光照条件下,高养分处理的总生物量、叶片数、总根茎分株数、长根茎分株数、总根茎长、芽长度、芽数量等指标大于其他养分处理,而在遮阴条件下,其在不同养分处理间无显著差异,表明光照条件可影响养分对扁秆荆三棱可塑性的作用,且高营养水平不能补偿由于光照不足而导致的生长能力下降。光照强度显著影响了总根茎、总球茎及大、中、小球茎的生物量分配,遮阴条件下,总生物量减少了对地下部分根茎和球茎的分配,并将有限的生物量优先分配给小球茎。总根茎的生物量分配未对养分发生可塑性反应,而随着养分增加,总球茎分配下降,说明在养分受限的环境中球茎的贮存功能可缓冲资源缺乏对植物生长的影响。在相同条件下,根茎生物量对长根茎的分配显著大于短根茎,以保持较高的繁殖能力;而总球茎对有分株球茎的生物量分配小于无分株球茎,表明扁秆荆三棱总球茎对贮存功能的分配优先于繁殖功能。研究为进一步理解根茎型克隆植物对光强及基质养分环境变化的生态适应提供了依据。     

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.     

Responses of Hedysarum Laeve, a guerrilla clonal semi-shrub in the Mu Us sandland, to local sand burial

In arid and semi-arid inland deserts,one of the environmental stresses for plants is recurrent sand burial,which can influence the physical and biotic microenvironments of the plants and soil.Previous studies have shown that different levels of sand burial have different effects on plants.Slight sand burial could increase the height increment,leaf biomass and the number of new ramets of the plants while heavy sand burial could impair the growth of the plants and even decrease their chances of survival.In other words,below a certain threshold level of burial,the growth of plants is stimulated probably because of multiple factors.However,as the level of burial increases,the positive response starts to decline until it becomes a negative value.Arid and semi-arid inland deserts are frequently colonized and stabilized by many rhizomatous clonal plants.Clonal physiological integration often helps clonal plants buffer local environmental stress encountered by ramets.A rhizomatous clonal semishrub,Hedysarum laeve (H.laeve),is the dominant plant species and important for vegetation restoration in the Mu Us sandland.To investigate whether clonal integration can increase the threshold of sand burial and help rhizomatous H.laeve tolerate heavy sand burial,we conducted a field experiment.The results showed that slight sand burial could accelerate ramet growth and enhance leaf biomass,stem biomass and shoot biomass,while heavy sand burial reducesed the biomass of the plant and impairs survival and growth of the ramets.Clonal integration increased the threshold of sand burial.Under heavy sand burial,ramets connected to other ramets not buried in sand were more in terms of height increment,stem biomass,leaf biomass and shoot biomass compared to the ramets encountering sand burial but disconnected from other ramets.It suggested that clonal physiological integration could help H.laeve ramets tolerate relatively heavy sand burial.We also discussed that clonal integration plays a role in H.laeve presence in the Mu Us sandland.     

Ecological benefits of integration of Calamagrostis epigejos ramets under field conditions

We established two independent experiments to estimate the ecological consequences of artificial severing on ramets of the competitively strong perennial grass Calamagrostis epigejos. We compared the responses of mature ramets of different size growing in different environments. Finally, we tested whether the response of young ramets to the severing depends on the density of surrounding vegetation.Severing decreased biomass and number of rhizomes of young ramets but did not affect their competitive tolerance. It decreased survival of mature ramets (probably due to traumata caused by cutting attached rhizomes) but did not influence total biomass of survived ramets. The response of total biomass of mature ramets to severing changed with size of the ramets. Further, biomass allocation to rhizomes changed differently after ramet severing in the two environments.The results suggest that field grown young ramets of Calamagrostis benefit from physiological integration. In contrast, mature ramets seem to be independent units according to the resource economy. Ecological benefits of integration depended on size of ramet clumps: ramets in clump had larger survival probability than control ramets. They also depended on environmental conditions: severing increased formation of new rhizomes at a sand dune subsrate, but it had a negative effect on plants in the forest experimental site. This intra-specific variation should be taken into account when trying to explain ecological patterns of integration benefits of clonal plants.     

A trade-off between guerrilla and phalanx growth forms in Leymus secalinus under different nutrient supplies

BACKGROUND AND AIMS: A phalanx growth form enables clonal plants to make better use of resource-rich patches, whereas a guerrilla growth form provides them with opportunities to escape from resource-poor sites. Leymus secalinus produces both spreading (guerrilla form) and clumping ramets (phalanx form). Here, the hypothesis that a trade-off between the two growth forms in L. secalinus exists under different resource levels is tested. METHODS: Ramets of L. secalinus were grown under three levels of nutrient supply. KEY RESULTS: With increasing nutrient supply, the proportion of clumping ramets (in total number of ramets) increased, whereas that of spreading ramets decreased. With increasing nutrient supply, the number of buds increased, whereas biomass per bud decreased. A trade-off between bud number and size further supports the above hypothesis because larger buds were more likely to develop into spreading ramets, and smaller buds into clumping ramets. Mean spacer length between spreading ramets was significantly smaller under the high than under the medium nutrient supply. CONCLUSIONS: The results suggest that a trade-off between the two growth forms in L. secalinus exists under different nutrient supplies. Such a trade-off together with plasticity in spacer morphology may enable L. secalinus to make better use of small-scale heterogeneity in resource supply.