Morphological and Physiological Acclimation Responses to Contrasting Light and Water Regimes in <Emphasis Type="Italic">Primula sieboldii</Emphasis>

The effects of the availability of light (high, medium and low) and soil water (wet and dry) on morphological and physiological traits responsible for whole plant carbon gain and ramet biomass accumulation were examined in a splitter-type clonal herbaceous species Primula sieboldii, a spring plant inhabiting broad range of light environments including open grassland and oak forest understory. Growth experiments were conducted for three genets originated from natural microhabitats differing in light and soil water availability. Ramets of a genet from high light and wet microhabitat, which were grown in low light (relative photon flux density: R-PPFD of 5%) showed 41% less light-saturated photosynthetic rate, 50% less dark respiration rate and earlier defoliation than the ramets in high light (R-PPFD of 61%). The estimation of daily photosynthesis revealed that the light acclimation response in leaf gas exchange contributes to efficient carbon gain of whole plants, irrespective of experimental light conditions. Water stress increased root weight ratio, decreased ramet leaf area, petiole length and photosynthetic capacity. These morphological effects of water stress were larger in high and medium light regimes than in low light regime. The consequence of the above responses was recognized in the relative growth rate of the ramets. The relative growth rate of the ramets in high light with wet regime was four-fold of that in low light plus wet regime, and was 1.5-fold of that in high light plus dry regime. However, even in low light and/or dry regimes, ramets kept positive relative growth rates and produced gemma successfully. We could not detect significant variation in growth responses among genets. The high photosynthetic plasticity revealed in the present study should enable Primula sieboldii to inhabit in a broad range of light and soil water availability.     

The interaction between water and nitrogen translocation in a rhizomatous sedge (Carex flacca)

In order to examine whether the translocation of water and nitrogen in clonal plants is interdependent, interramet translocation of these two resources was investigated in the greenhouse. Two-ramet systems of Carex flacca were imposed to different spatial patterns of water and nitrogen supply. The experimental design allowed to examine the effects of water heterogeneity on nitrogen sharing, and, vice versa, the effects of nitrogen heterogeneity on water sharing. Interramet translocation of both water and nitrogen was quantified by stable isotope labelling. If one of the ramets was deprived of water, nitrogen or both resources (parallel resource heterogeneity), resource translocation towards this ramet was markedly enhanced compared to a control treatment in which both ramets received ample water and ample nitrogen. Under these conditions, the amount of water or nitrogen translocated was not significantly affected by the pattern of heterogeneity of the other resource imposed on the two-ramet system. If one of the interconnected ramets was rooted in dry but nitrogen-rich soil and the other ramet was placed in nitrogen-deficient but well-watered soil (reciprocal resource heterogeneity), a significant amount of water was translocated towards the ramet in dry soil, while the low-N ramet hardly received any nitrogen. These results show that little nitrogen is translocated between ramets in a direction opposite to the transpiration stream within the rhizome. However, nitrogen may be translocated independently from water if both are transported in a similar direction within the clonal system. The effects of translocation on ramet performance (in terms of transpiration, nitrogen accumulation, and biomass) were assessed by comparing interconnected ramets with isolated (severed) ramets that were treated identically. Integration enhanced the performance of ramets deficient of one or both of the resources. In case of water translocation, the transpiration and growth of the water exporting (donor) ramets was similar to the transpiration and growth of their isolated counterparts. When nitrogen was heterogeneously supplied, however, nitrogen accumulation and growth of the donor ramet was reduced to the same extent as the performance of the nitrogen-deficient ramet was increased. Water translocation thus enhanced the performance of the whole plant, while nitrogen only reduced the differences in ramet performance within the plant. In the case of the reciprocal heterogeneity treatment, the benefits of translocation were strongly unidirectional towards the ramet in dry soil. The data for this treatment suggested that total nitrogen accumulation was enhanced by the acquisition of nitrogen from the dry pot as a result of “hydraulic lift” and water exudation in the dry soil. We conclude that nitrogen translocation in clonal plants, and the associated benefits in terms of resource utilization and growth, may strongly depend on the pattern of interramet water transport. The implications are discussed for studies of physiological integration in clonal plants and the patterns of interramet resource sharing in the field. Received: 2 November 1997 / Accepted: 9 April 1998     

资源异质性环境中三种匍匐茎草本植物克隆内资源共享和分株功能特化

研究了3种来自中国北方林下、草地和碱化草甸匍匐茎型克隆草本植物绢毛匍匐委陵菜 (Potentilla reptans L. var. sericophylla Franch.)、鹅绒委陵菜 (P. anserina L.) 和金戴戴 (Halerpestes ruthenica (Jacq.) Qvcz.) 对由高光照低养分斑块和低光照高养分斑块组成的资源交互斑块性生境的适应性对策.当生长于高光照低养分条件下分株 (HL分株) 与生长于低光照高养分条件下分株 (LH分株) 之间的匍匐茎连接时, 3种克隆植物HL分株、LH分株以及整个分株对系统 (HL分株 + LH分株) 的生物量均得到显著提高.同时, LH分株根冠比显著增加, 而HL分株根冠比显著下降.这表明, 当互连分株置于由低光照高养分斑块和高光照低养分斑块组成的异质性环境中时, 3种植物克隆分株均发生了环境诱导的功能特化.克隆内资源共享以及克隆内不同分株的功能特化有利于整个分株系统对局部丰富资源的获取, 从而能够缓解资源交互斑块性生境对克隆植物的不利影响.     

Integration in the clonal plant <Emphasis Type="Italic">Eriophorum angustifolium</Emphasis>: an experiment with a three-member-clonal system in a patchy environment

A clonal plant in heterogeneous environments is usually expected to profit from resource exchange via a clonal network where ramets placed in contrasting environments can specialise so to acquire the most abundant resources. An experiment was designed using the three member clonal system of Eriophorum angustifolium, which consisted of one parent ramet growing in a resource poor environment and two offspring: one was limited in growth by nutrients while the other was light limited; the contrast in availability of limited resources between the offspring ramets was high, medium or none, with the system either connected or severed. The total resource availability was the same in all treatments. We proposed four possible scenarios for the system: offspring ramets will share resources via the deficient parent ramet, and the whole clone will profit from the contrasting environment (scenario 1); offspring ramets will support exclusively the parent ramet, and the whole clone will profit from a homogeneous environment (scenario 2); offspring ramets will stop the export of the limiting resource to the parent ramet, with split and connected treatments not differing (scenario 3); and offspring ramets will exhaust the carbon stored in the biomass of the parental ramet; offspring ramet will profit from connection (scenario 4). In the experiment, the limiting resources were sent to the strongest sink (scenario 2). The parent ramet growing in a deficient environment received the highest support in the treatment where both offspring ramets were growing in the same conditions (no-contrast treatment). Production of new shoots, but not biomass of whole clone, was supported in a homogenous environment. The experiment revealed that multiple stresses might prohibit free exchange of limiting resources via the clonal network and supports the idea that experimental studies on more complex clones are essential for understanding the costs and benefits of clonal growth.     

资源异质性环境中三种匍匐茎草本植物克隆内资源共享和分株功能特化(英文)

研究了 3种来自中国北方林下、草地和碱化草甸匍匐茎型克隆草本植物绢毛匍匐委陵菜 (PotentillareptansL .var.sericophyllaFranch .)、鹅绒委陵菜 (P .anserinaL .)和金戴戴 (Halerpestesruthenica (Jacq .)Qvcz .)对由高光照低养分斑块和低光照高养分斑块组成的资源交互斑块性生境的适应性对策。当生长于高光照低养分条件下分株(HL分株 )与生长于低光照高养分条件下分株 (LH分株 )之间的匍匐茎连接时 ,3种克隆植物HL分株、LH分株以及整个分株对系统 (HL分株 LH分株 )的生物量均得到显著提高。同时 ,LH分株根冠比显著增加 ,而HL分株根冠比显著下降。这表明 ,当互连分株置于由低光照高养分斑块和高光照低养分斑块组成的异质性环境中时 ,3种植物克隆分株均发生了环境诱导的功能特化。克隆内资源共享以及克隆内不同分株的功能特化有利于整个分株系统对局部丰富资源的获取 ,从而能够缓解资源交互斑块性生境对克隆植物的不利影响     

Effects of clonal integration on plant plasticity in Fragaria chiloensis

The ability of clonal plants to transport substances between ramets located in different microsites also allows them to modify the plastic responses of individual ramets to local environmental conditions. By equalising concentrations of substances between ramets, physiological integration might decrease responses to local conditions. However, integration has also been observed to increase plasticity and induce novel plastic responses in ramets. To ask how integration modifies plant plasticity in the clonal herb, Fragaria chiloensis, ramets were given either low light and high nitrogen or high light and low nitrogen, simulating a pattern of resource patchiness in their native habitat. Ramets in contrasting light/nitrogen treatments were either connected or single. Effects of light/nitrogen and connection were measured at three levels of morphological organisation, the organ, the ramet, and the clonal fragment. Connection between ramets reduced or had no effect on plastic responses in leaf size at the level of the plant organ. This suggested that integration dampened certain plastic responses. Connection induced a new plastic response at the level of the clonal fragment, an increase in allocation to vegetative reproduction in patches of low light and high nitrogen. It is concluded that clonal integration can have different effects on plant plasticity at different levels of plant organisation. It appears that, at least in this species, integration can increase plasticity at the level of the clonal fragment and concentrate vegetative reproduction in particular microsite types.     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

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.     

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.     

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 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.     

Environmentally-induced functional specialization for locally abundant resources in the stoloniferous herb Duchesnea indica

Reciprocally patchy environments, where the availability of two resources are patchily distributed and negatively correlated in each patch, are common in many ecosystems. Interconnected ramets of clonal plants can specialize in the uptake of locally abundant resources. Ramet pairs of the stoloniferous herb Duchesnea indica were grown in reciprocally patchy environments i.e., one ramet of a pair was grown in the high light but low water patch (high light patch) and the other in the low light but high water patch (high water patch). Biomass allocation pattern (root-shoot ratio), morphological traits (leaf area and root length) and physiological traits (photosynthetic rate and chlorophyll content) were altered in a way that potentially enables ramets to enhance the capture of the locally abundant resource (i.e., increase the capture of light resource in the high light patch and of water in the high water patch). As a result,biomass and number of ramets in the connected ramet pairs were greatly improved. Functional specialization of ramets, modified by clonal integration, may have contributed greatly to the growth increase of D. indica in the reciprocally patchy environment.     

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。     

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.     

光强对比度对大米草克隆整合作用的影响

通过温室控制试验,分析不同光强及光强对比度处理下克隆植物大米草生长性状的差异,研究同质异质光强条件下克隆整合对大米草响应遮阴能力的修饰作用.结果表明： 在同质条件下,大米草在无遮阴(高光强：温室内自然光照强度)条件下的生物量显著大于中度遮阴(中光强：光照强度为高光强的70%)和深度遮阴(低光强：光照强度为高光强的30%).在低对比度异质性光强条件下(分株对的一个分株不遮阴,另一个分株中度遮阴),大米草遮阴分株的叶片数、根长和生物量均显著高于同质中度遮阴处理,而无遮阴分株各生长指标与同质无遮阴处理相比均无显著差异.因此,在低对比度异质性光强下,大米草受体(遮阴)分株通过克隆整合显著受益;同时,对供体(非遮阴)分株没有显著的耗损.然而,在高对比度处理下(分株对的一个分株不遮阴,另一个分株深度遮阴),克隆整合对受体(遮阴)分株的效应不显著.大米草的克隆整合并不随着光强对比度的增加而增加.在自然生境中度遮阴情况下,克隆整合可以提高大米草的生长和克隆繁殖能力,但在深度遮阴情况下,克隆整合对大米草适应性的作用可能很小.     

Ramet dynamics in a centrifugally expanding clonal sedge: a matrix analysis

Carex humilis is a clonal sedge that can form distinct rings of densely aggregated ramets. We hypothesize that rings form because both production of new ramets and ramet dispersal are positively correlated to ramet size. This would lead to an overrepresentation of fast-moving and large ramets with high ramet production at the periphery, whereas slow-moving and small ramets with low ramet production would mainly be found in the interior of rings. We use matrix models to analyse how ramet populations both at the periphery and in the interior develop in the absence of ramet dispersal. We found that the stable size class distributions of ramets predicted by the models were not different from the distributions found in the field. Also, the asymptotic ramet population growth rates (λ₁) were the same. Hence, we conclude that rings would form even in the absence of a link between ramet dispersal and ramet production. Further analysis of the matrix models showed that the ramet population increases at the periphery but decreases in the interior of rings because medium and large ramets produce fewer large ramets in the interior than at the periphery. We also found that the temporal variance in λ₁ and transitions rates during the four study years was much higher at the periphery than in the interior. Our results suggest that rings may form because C. humilis ramets use below-ground resources from a much larger area than the one covered by the shoots. As the clone grows larger, the soil volume available to the ramets in the interior decreases because their access to soil outside the ring is cut-off by the ramets at the periphery. Ramet density in the interior is therefore decreasing.     

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.     

Arbuscular mycorrhizal fungi reduce effects of physiological integration in Trifolium repens

Background and Aims

One of the special properties of clonal plants is the capacity for physiological integration, which can increase plant performance through mechanisms such as resource sharing and co-ordinated phenotypic plasticity when plants grow in microsites with contrasting resource availabilities. However, many clonal plants are colonized by arbuscular mycorrhizal fungi (AMF). Since AMF are likely to reduce contrasts in effective resource levels, they could also reduce these effects of clonal integration on plasticity and performance in heterogeneous environments.

Methods

To test this hypothesis, pairs of connected and disconnected ramets of the stoloniferous herb Trifolium repens were grown. One ramet in a pair was given high light and low nutrients while the other ramet was given high nutrients and low light. The pairs were inoculated with zero, one or five species of AMF.

Key Results

Pairs of ramets grown without AMF developed division of labour and benefited from resource sharing, as indicated by effects of connection on allocation to roots, accumulation of mass, and ramet production. Inoculation with five species of AMF significantly reduced these effects of connection, both by inhibiting them in ramets given high nutrients and inducing them in ramets given high light. Inoculation with one species of AMF also reduced some effects of connection, but generally to a lesser degree.

Conclusions

The results show that AMF can significantly modify the effects of clonal integration on the plasticity and performance of clonal plants in heterogeneous environments. In particular, AMF may partly replace the effects and benefits of clonal integration in low-nutrient habitats, possibly more so where species richness of AMF is high. This provides the first test of interaction between colonization by AMF and physiological integration in a clonal plant, and a new example of how biotic and abiotic factors could interact to determine the ecological importance of clonal growth.Key words: Arbuscular mycorrhizal fungi, biomass allocation, clonal plant, division of labour, environmental heterogeneity, light availability, nutrients, white clover     

Clonal integration affects allocation in the perennial herb <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> in N-limited homogeneous environments

Most work on clonal growth in plants has focused on the advantages of clonality in heterogeneous habitats. We hypothesized (1) that physiological integration of connected ramets within a clone can also increase plant performance in homogeneous environments, (2) that this effect depends on whether ramets differ in ability to take up resources, and (3) that only ramets with relatively low uptake ability benefit. We tested these hypotheses using the perennial amphibious herb Alternanthera philoxeroides. We grew clonal fragments and varied numbers of rooted versus unrooted ramets, connection between the apical and basal parts of fragments, and availability of nitrogen. Patterns of final size and mass of fragments did not support these hypotheses. By some measures, severance did reduce the growth of more apical ramets and increase the growth of less apical ones, consistent with net apical transfer of resources. Rooting of individual ramets strongly influenced their growth: second and third most apical ramets each grew most when they were the most apical rooted ramet, and this pattern was more pronounced under higher nitrogen levels. This adds to the evidence that signalling between ramets is an important aspect of clonal integration. Overall, the results indicate that physiological integration between ramets within clones in homogeneous environments can alter the allocation of resources between connected ramets even when it does not affect the total growth of clonal fragments.     

PATCHY CONTRAST OF HABITAT AFFECTS INTRACLONAL DIVISION OF LABOR OF POTENTILLA ANSERINA

 相互连接的克隆植物分株分别处于资源互补性的不同斑块时, 将可能发生形态结构的特化, 以更有效地吸收利用所处斑块中丰富的资源, 形成分株的功能分化, 即克隆内分工。生境的斑块对比度, 作为资源或环境异质性的主要素, 在一定程度上决定克隆内分工的发生状况。该文以鹅绒委陵菜(Potentilla anserina)为材料, 在自然条件下将多组分株对置于不同的斑块对比度处理下, 比较了它们克隆内分工的发生状态, 试图发现分工与斑块对比度的关系, 同时考察在克隆分工过程中分株的可塑性变化及其与分工的关系。该实验的理论假设是: 分株发生分工的程度与分株所处斑块的资源对比度成正相关。研究结果表明, 鹅绒委陵菜分株的高度和叶面积对局部光照环境产生强烈的可塑性反应, 反应的结果是增加了对匮乏的光资源的获取。从分株根冠比和我们提出的分工指数来看, 分工的程度在一定的斑块对比度范围内随斑块对比度的增强而增强, 但到达一个最大值后又迅速降低。鹅绒委陵菜分株之间的分工和结构特化往往滞后于分株对所处局部环境的适应性可塑性变化, 而后者往往在分株之间具有独立性和局部特征。克隆内分工主要依赖于生物量分配的调节而实现, 其发生状态都是分株系统在分工收益、分工代价与分工风险之间权衡的结果, 而这种结果在很大程度上取决于分株所处的斑块对比度。