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.     

Effects of salinity and clonal integration on growth and sexual reproduction of the invasive grass Spartina alterniflora

The purpose of this study was to explore clonal integration of Spartina alterniflora under gradually changing substrate salinity conditions. We hypothesized that there might be a trade-off between growth and sexual reproduction influenced by soil salinity and, that clonal integration would change this trade-off. The experiment consisted of three levels of substrate salinity (5‰, 20‰ and 35‰), two clonal integration treatments (rhizomes severed or not), and three growth stages of daughter ramets (21, 40 and 60 cm tall). Both growth and sexual reproduction of S. alterniflora greatly decreased with increasing salinity. Clonal integration enhanced the survival, growth and sexual reproduction of daughter ramets experiencing salt stress, especially for young ramets, whereas the performance of mother ramets was reduced by clonal integration. Therefore, clonal integration did not affect performance of the whole clones. Contrary to expectations, there was no evidence for a trade-off between growth and sexual reproduction associated with salinity. In addition, clonal integration did not change the effect of salinity on the growth and sexual reproduction of mother and daughter ramets nor of the whole clones.     

Does clonal integration improve competitive ability? A test using aspen (Populus tremuloides [Salicaceae]) invasion into prairie

Many clonal plants consist of many connected individual ramets, allowing them to share water and nutrients via physiological integration. Integration among ramets may also improve the ability of clonal plants to tolerate abiotic stress or improve the competitive ability of individual ramets. Here I use a field experiment to determine whether clonal integration improves ramet performance for a widespread clonal tree species invading into native prairie. Aspen (Populus tremuloides) dominates the southern treeline in western Canada, has long-lived belowground connections between mother and daughter ramets, and reproduces vegetatively via resprouting rhizomes after disturbance. I applied two competition treatments (neighbors present or absent) and two clonal integration treatments (belowground rhizomes between mother and daughter ramets either severed or left intact) to 12 replicate Populus daughter ramets at each of three sites. Neighbors improved the survivorship of Populus ramets by 25-35% after 2 yr, but decreased growth by ～20%. Clonal integration tended to improve ramet survival and growth, but these trends were often not significant. Clonal integration did not alter the effects of competition from neighboring vegetation, suggesting that connections between ramets do not necessarily improve the competitive ability of Populus invading into native prairie.     

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。     

The effects of clonal integration on morphological plasticity and placement of daughter ramets in black locust (Robinia pseudoacacia)

We studied the field response of Robinia pseudoacacia L. to light, total soil nitrogen, available soil phosphorus and soil pH. Results indicated that there was very strong clonal integration between mother and daughter ramets. Mother ramets can provide nitrogen and phosphorus to daughter ramets sufficient for their continued growth through strong clonal integration, but cannot provide enough photosynthate. With clonal integration, soil nitrogen and phosphorus availability had no effect on biomass allocation to roots, number of ramets and length of connection roots. Biomass allocation to roots increased markedly and responded to nitrogen and phosphorus availability, when the connections were severed. Light had a significant effect on the percent of biomass allocation to leaves and number of ramets, but no effect on the length of connection roots. Daughter ramets allocated more resources to leaves, and clones placed more daughter ramets in high light patches than in low light patches. Soil pH had a significant effect on ramet number and connection root length. Clones concentrated in alkaline patches and escaped from acid patches through selective placement of daughter ramets and changing the length of connection roots. We suggest that the clonal integration may be very strong and provide sufficient soil resources to daughter ramets, then affect the daughter ramets’ morphology and placement, if the size of a specific ramet is significantly larger than the other ramets in an arbor clone.     

Effects of inoculation with native arbuscular mycorrhizal fungi on clonal growth of Potentilla reptans and Fragaria moschata (Rosaceae)

Many clonal plants live in symbiosis with ubiquitous arbuscular mycorrhizal (AM) fungi, however, little is known about their interaction with respect to clonal reproduction and resource acquisition. The effects of arbuscular mycorrhiza on the growth and intraclonal integration between ramets of two stoloniferous species were studied experimentally in a nutritionally homogenous soil environment. Two species coexisting at the same field site, Potentilla reptans and Fragaria moschata, were selected as model plants for the study. Pairs of their ramets were grown in neighbouring pots with each ramet rooted separately. Four inoculation treatments were established: (1) both mother and daughter ramets remained non-inoculated, (2) both ramets were inoculated with a mixture of three native AM fungi from the site of plant origin, (3) only mother or (4) daughter ramet was inoculated. The stolons connecting the ramets were either left intact or were disrupted. Despite the consistent increase in phosphorus concentrations in inoculated plants, a negative growth response of both plant species to inoculation with AM fungi was observed and inoculated ramets produced fewer stolons and fewer offspring ramets and had lower total shoot dry weights as compared to non-inoculated ones. A difference in the extent of the negative mycorrhizal growth response was recorded between mother and daughter ramets of P. reptans, with daughter ramets being more susceptible. Due to AM effect on ramet performance, and thereby on the source-sink relationship, inoculation also significantly influenced biomass allocation within clonal fragments. Physiological integration between mother and daughter ramets was observed when their root systems were heterogeneous in terms of AM colonization. These results hence indicate the potential of mycorrhizal fungi to impact clonal growth traits of stoloniferous plant species, with possible consequences for their population dynamics.     

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.     

Effects of the loss of clonal integration on four sedges that differ in ramet aggregation

Although clonal growth is a dominant mode of plant growth in wetlands, the importance of clonal integration, resource sharing among ramets, to individual ramet generations (mother and daughter) and entire clones of coexisting species has not been well investigated. This study evaluated the significance of clonal integration in four sedge species of varying ramet aggregations, from clump-forming species (Clumpers –Carex sterilis, Eleocharis rostellata), with tightly aggregated ramets (rhizomes<1cm), to runner species (Runners –Schoenoplectus acutus, Cladium mariscoides), with loosely aggregated ramets. We manipulated clonal integration by either severing connections between target mother and daughter ramets or leaving connections intact, and then planted them in an intact neighborhood of a fen in Michigan, USA. We measured growth parameters of original and newly produced ramets over two growing seasons and conducted a final biomass harvest, to address four hypotheses. First, we expected integrated clones to accumulate more biomass than severed clones. However, final clone-level biomass and ramet production were the same for both treatments in all species although severing initially stimulated ramet production by Schoenoplectus and produced a more compact ramet aggregation in Cladium. Second, we hypothesized that mother ramets would experience a cost of integration, through reduced ramet or biomass production, while daughters would experience a benefit, through increased resource availability from mothers. Mother ramets of Cladium suffered a cost from integration, while Schoenoplectus mothers suffered a slight cost and Carex daughters saw a slight benefit. Finally, we hypothesized that integration would be more active in runner species than in clumper species. Indeed, we documented more active integration in runners than clumpers, but none of the study species were dependent upon integration for growth or survival once daughter ramets were established with their own roots and shoots. This study demonstrates that integration between established ramets may not be the most important advantage to clonal growth in this wetland field site. The loss of integration elicited varied responses among coexisting species in their natural habitat, somewhat but not completely related to their growth form, suggesting that a combination of plant life history traits contributes to the dependence upon clonal integration among established ramets of clonal species.     

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。     

Clonal integration in Ranunculus reptans: by‐product or adaptation?

We studied fitness consequences of clonal integration in 27 genotypes of the stoloniferous herb Ranunculus reptans in a spatially heterogeneous light environment. We grew 216 pairs of connected ramets (eight per genotype) with mother ramets in light and daughter ramets in shade. In half of the pairs we severed the stolon connection between the two ramets at the beginning of the experiment. During the experiment, 52.7% of the ramet pairs with originally intact connection physically disintegrated. We detected significant variation among genotypes in this regard. Survival of planted ramets was 13.3% higher for originally connected pairs. Moreover, there was significant variation among genotypes in survival, in the difference in survival between plant parts developing from mother and daughter ramets, and in the effect of integration on this difference. In surviving plants connection between ramets decreased size differences between mother and daughter parts. Variation among genotypes was significant in growth and reproduction and marginally significant in the effect of physiological integration on growth and reproduction. Connected daughter ramets had longer leaves and internodes than daughters in severed pairs indicating that integration stimulated plant foraging in both the vertical and the horizontal plane. Observed effects of integration on fitness components in combination with genetic variation in maintenance and effects of connection indicate that clonal integration in R. reptans has the capability to evolve, and therefore suggest that clonal integration is adaptive. If genetic variation in integration is common, future studies on clonal integration should always use defined genetic material and many clones to allow extrapolation of results to population and wider levels.     

Partial mechanical stimulation facilitates the growth of the rhizomatous plant Leymus secalinus: modulation by clonal integration

Background and Aims

Mechanical stimulation (MS) often induces plants to undergo thigmomorphogenesis and to synthesize an array of signalling substances. In clonal plants, connected ramets often share resources and hormones. However, little is known about whether and how clonal integration influences the ability of clonal plants to withstand MS. We hypothesized that the effects of MS may be modulated by clonal integration.

Methods

We conducted an experiment in which ramet pairs of Leymus secalinus were subjected to three treatments: (1) connected ramet pairs under a homogeneous condition [i.e. the proximal (relatively old) and distal (relatively young) ramets were not mechanically stressed]; (2) connected ramet pairs under a heterogeneous condition (i.e. the proximal ramet was mechanically stressed but the distal ramet was not); and (3) disconnected ramet pairs under the same condition as in treatment 2. At the end of the experiment, we harvested all plants and determined their biomass and allocation.

Key Results

Clonal integration had no significant influence on measured traits of distal L. secalinus ramets without MS. However, under MS, plants with distal ramets that were connected to a mother ramet produced more total plant biomass, below-ground biomass, ramets and total rhizome length than those that were not connected. Partial MS exerted local effects on stimulated ramets and remote effects on connected unstimulated ramets. Partial MS increased total biomass, root/shoot ratio, number of ramets and total rhizome length of stimulated proximal ramets, and increased total biomass, root weight ratio, number of ramets and total rhizome length of connected unstimulated ramets due to clonal integration.

Conclusions

These findings suggest that thigmomorphogenesis may protect plants from the stresses caused by high winds or trampling and that thigmomorphogenesis can be strongly modulated by the degree of clonal integration.     

Effects of soil heterogeneity and clonal integration on Alternanthera philoxeroides populations with a radial ramet aggregation

Some clonal plants can spread their ramet populations radially, and soil heterogeneity and clonal integration may greatly affect the establishment of these types of populations. We constructed Alternanthera philoxeroides populations with a radial ramet aggregation, allowing old ramets of clonal fragments to concentrate in central pots and younger ramets to root in peripheral pots. The peripheral pots were supplemented either with three different levels (high, medium and low) of soil nutrients to simulate a heterogeneous soil environment, or only one medium level of soil nutrients to simulate a homogeneous environment. Stolon connections between the central older ramets and the peripheral younger ramets were left intact or severed to test the effect of clonal integration. The maintenance of stolon connection could induce the division of labor between different‐aged ramets, by increasing the root investment in central ramets and the above‐ground growth in peripheral ramets. The maintenance of stolon connection could improve the growth of the central and peripheral ramets, clonal fragments and even the whole population. However, the positive consequence in peripheral ramets and whole fragments was only detected in the high‐nutrient patch of heterogeneous treatment. In sum, in the population with the radial ramet aggregation, clonal integration can play a key role in the rapid recruitment of young ramets of A. philoxeroides fragments, as well as the expansion of the whole population. The magnitude of clonal integration also became more obvious in the peripheral young ramets and whole fragments that experienced high‐nutrient patches.     

Clonal integration improves compensatory growth in heavily grazed ramet populations of two inland-dune grasses

Herbaceous species possess several mechanisms to compensate for tissue loss. For clonal herbaceous species, clonal integration may be an additional mechanism. This may especially hold true when tissue loss is very high, because other compensatory mechanisms may be insufficient. On inland dunes in northern China, we subjected Bromus ircutensis and Psammochloa villosa ramets within 0.5 m×0.5 m plots to three clipping treatments, i.e., no clipping, moderate (50% shoot removal) and heavy clipping (90% shoot removal), and kept rhizomes at the plot edges connected or disconnected. Moderate clipping did not reduce ramet, leaf or biomass density of either species. Under moderate clipping, rhizome connection significantly improved the performance of Psammochloa, but not that of Bromus. Heavy clipping reduced ramet, leaf and biomass density in the disconnected plots of both species, but such negative effects were negated or greatly ameliorated when the rhizomes were connected. Therefore, clonal integration contributed greatly to the compensatory growth of both species. The results suggest that clonal integration is an additional compensatory mechanism for clonal plants and may be important for their long-term persistence in the heavily grazed regions in northern China.     

Response of physiological integration in Trifolium repens to heterogeneity of UV-B radiation

Physiological integration has been documented in many clonal plants growing under resource heterogeneity. Little is still known about the response of physiological integration to heterogeneous ultraviolet-B radiation. In this paper, the changes in intensity of physiological integration and of physiological parameters under homogeneous and heterogeneous ultraviolet-B radiation (280-315 nm) were measured in order to test the hypothesis that in addition to resource integration a defensive integration in Trifolium repens might exist as well. For this purpose, homogeneous and heterogeneous ultraviolet-B radiation was applied to pairs of connected and severed ramets of the stoloniferous herb Trifolium repens. Changes in intensity of water and nutrient integration were followed with acid fuchsin dye and ¹⁵N-isotope labeling of the xylem water transport. In order to assess the patterns of physiological integration contents of chlorophyll, ultraviolet-B absorbing compounds, soluble sugar and protein were determined and activities of superoxide dismutase (SOD) and peroxidase (POD) measured. When ramets were connected and exposed to heterogeneous UV-B radiation, the velocity of water transportation from the UV-B treated ramet to its connected sister ramet was markedly lower and the percentage of ¹⁵N left in labelled ramets that suffered from enhanced UV-B radiation was higher and their transfer to unlabelled ramets lower. In comparison with clones under homogeneous ultraviolet-B radiation, the content of chlorophyll, ultraviolet-B absorbing compounds, soluble sugar and activities of SOD and POD increased notably if ultraviolet-B stressed ramets were connected to untreated ramets. Chlorophyll and UV-B absorbing compounds were shared between connected ramets under heterogeneous UV-B radiation. This indicated that physiological connection improved the performance of whole clonal plants under heterogeneous ultraviolet-B radiation. The intensity of physiological integration of T. repens for resources decreased under heterogeneous ultraviolet-B radiation in favor of the stressed ramets. Ultraviolet-B stressed ramets benefited from unstressed ramets by physiological integration, supporting the hypothesis that clonal plants are able to optimize the efficiency of their resistance maintaining their presence also in less favorable sites. The results could be helpful for further understanding of the function of heterogeneous UV-B radiation on growth regulation and microevolution in clonal plants.     

Combined effects of resource heterogeneity and simulated herbivory on plasticity of clonal integration in a rhizomatous perennial herb

Previous lines of investigation assuming potential advantage of clonal integration generally have neglected its plasticity in complex heterogeneous environments. Clonal plants adaptively respond to abiotic heterogeneity (patchy resource distribution) and herbivory‐induced heterogeneity (within‐clone heterogeneity in ramet performance), but to date little is known about how resource heterogeneity and simulated herbivory jointly affect the overall performance of clones. Partial damage within a clone caused by herbivory might create herbivory‐induced heterogeneity in a resource‐homogeneous environment, and might also decrease or increase the extent of heterogeneity under resource‐heterogeneous conditions. We conducted a greenhouse experiment in which target‐ramets of Leymus chinensis segments within homogeneous or heterogeneous nutrient treatments were subject to clipping (0% or 75% shoot removal). In homogeneous environments with high (9:9) nutrient availability, ramet biomass of L. chinensis with intact or severed rhizomes is 0.70 or 0.69 g. Conversely, target‐ramet biomass with intact rhizomes is obviously lower than that of the severed target‐ramets in the homogeneous environments with medium (5:5) and low (1:1) nutrient availability. High resource availability and the presence of herbivory can alleviate negative effects of rhizome connection under homogeneous conditions, by providing copious resource or creating herbivory‐induced heterogeneity respectively. Herbivory tolerance of clonal fragments with connected rhizomes was higher than that of fragments with severed rhizomes under heterogeneous conditions. These findings confirmed the unconditional advantage of clonal integration on reproduction under the combined influence of resource heterogeneity and simulated herbivory. Moreover, our results made clear the synergistically interactive effects of resource heterogeneity and simulated herbivory on costs and benefits of clonal integration. This will undoubtedly advance our understanding on the plasticity of clonal integration under complex environmental conditions.     

水分胁迫条件下草莓克隆分株间水分调控及其对光合功能的影响

以盆栽草莓(Fragaria×ananassa)为材料研究了水分胁迫下克隆植物草莓母株和子株间的水分调控机制及其与碳同化、光系统Ⅱ激发能分配的关系.实验材料分为匍匐茎连接和剪断两个大组,进行两步实验.第1步实验,对连接组和剪断组的所有母株控水,子株充分供水;4d后进入第2步实验,把连接组分为两小组,对其中一组充分供水子株开始控水,另一组保持不变.结果表明,土壤干旱引起母株叶片失水,并使其净光合速率和气孔导度显著降低.但是连接组中供水良好的子株能有效缓解缺水母株的水分胁迫.当供水良好的子株也开始受到干旱处理的时候,则会加剧与之相连母株的水分胁迫.受胁迫母株可以通过加强渗透调节能力和降低水势从相连子株获取水分.虽然土壤干旱会造成受胁迫母株叶片脱落酸(abscisic acid, ABA)含量的大幅度增加,但是与之相连子株的叶片ABA含量并没有增加;并且气孔导度与ABA变化趋势一致.(1)草莓母株和子株间的水分运输是由二者的水势差驱动的;(2)ABA不会通过匍匐茎在母株和子株间传递并影响相邻子株气孔导度;(3)在水分异质性较大情况下,生理整合可明显提高克隆系统的碳同化能力和光系统Ⅱ激发能利用效率.     

Physiological Integration Ameliorates Negative Effects of Drought Stress in the Clonal Herb Fragaria orientalis

Clonal growth allows plants to spread horizontally and to establish ramets in sites of contrasting resource status. If ramets remain physiologically integrated, clones in heterogeneous environments can act as cooperative systems - effects of stress on one ramet can be ameliorated by another connected ramet inhabiting benign conditions. But little is known about the effects of patch contrast on physiological integration of clonal plants and no study has addressed its effects on physiological traits like osmolytes, reactive oxygen intermediates and antioxidant enzymes. We examined the effect of physiological integration on survival, growth and stress indicators such as osmolytes, reactive oxygen intermediates (ROIs) and antioxidant enzymes in a clonal plant, Fragaria orientalis, growing in homogenous and heterogeneous environments differing in patch contrast of water availability (1 homogeneous (no contrast) group; 2 low contrast group; 3 high contrast group). Drought stress markedly reduced the survival and growth of the severed ramets of F. orientalis, especially in high contrast treatments. Support from a ramet growing in benign patch considerably reduced drought stress and enhanced growth of ramets in dry patches. The larger the contrast between water availability, the larger the amount of support the depending ramet received from the supporting one. This support strongly affected the growth of the supporting ramet, but not to an extent to cause increase in stress indicators. We also found indication of costs related to maintenance of physiological connection between ramets. Thus, the net benefit of physiological integration depends on the environment and integration between ramets of F. orientalis could be advantageous only in heterogeneous conditions with a high contrast.     

Clonal integration affects growth and sediment properties of the first ramet generation,but not later ramet generations under severe light stress

克隆整合影响严重光胁迫下第一分株世代的生长和沉积物特征但不影响 后续分株世代的生长和沉积物特征 克隆整合通过缓冲环境压力和提高资源获取效率使克隆植物受益。然而,在一个克隆系统中,受益于克隆整合的连接分株世代的数量很少受到关注。我们进行了一个盆栽实验来评估沉水植物苦草 (Vallisneria natans)克隆系统内的生理整合程度,该克隆系统由一个母株和3个依次连接的后代分株组成。 母株生长在正常光照下,而后代分株被严重遮荫。母株与后代分株间的匍匐茎被切断或保持连接,但3个后代分株之间的连接仍然存在。与遮荫的后代分株连接时,苦草未遮荫的母株的光合能力显著增强,但其生物量积累大大减少。克隆整合显著增加了第一分株世代(相邻分株)的生物量积累和土壤的碳氮可用性、胞外酶活性和微生物生物量,但没有增加后续分株世代的这些特征。我们的结果表明,在严重光胁迫下,来自苦草母株的支持可能仅限于克隆系统中相邻的后代分株,这暗示着一个分株世代的效应。我们的结果有助于更好地理解克隆植物的层次结构和分段化。这些发现表明克隆整合程度在分株种群的生态相互作用中起着至关重要的作用。     

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     

克隆植物沙拐枣的母株和分株对风蚀沙埋的生理生态响应

以中国荒漠区优良的防风固沙克隆灌木沙拐枣为对象,研究了长期风蚀、沙埋环境下沙拐枣母株和克隆分株的同化枝对环境异质性的响应。结果发现:(1)风蚀母株、风蚀分株的叶绿素含量、净光合速率、气孔导度、蒸腾速率、胞间CO2浓度和水分利用效率只有沙埋分株的一半左右,导致同化枝的长度、数量、簇数也仅是沙埋分株的一半,而且风蚀母株的果实宽和果实长也都最小,但浅沙埋有利于沙拐枣的生长和繁殖,表明严峻的风蚀对母株和分株的生长与繁殖都产生了胁迫,但浅沙埋有利于沙拐枣的生长和繁殖。(2)风蚀母株倒伏后同化枝的形态特征是基部优于中部优于顶部,表明严峻风蚀下母株的死亡是从顶部-中部-底部逐渐舍弃的过程。(3)母株的全部根系以及风蚀水平根全部裸露在外但依然能够存活,间接证明沙拐枣克隆整合的方向性——不仅可在分株间进行传递,分株-母株间也可进行传递,否则遭受严峻风蚀胁迫的母株和克隆分株会直接死亡。本研究结果为沙拐枣克隆生长对风沙环境的生态适应机制提供了基础,也是对植物克隆生态学在自然异质环境中研究缺乏的有效补充。