Nitrate reduction in ramets of a clonal plant Eichhornia crassipes responding to nitrate availability during clonal growth stage

Effect of nitrate availability on nitrate reduction was examined in inter-connected ramets of invasive clonal plant Eichhornia crassipes grown with two nitrate supply regimes during different clonal growth stage. Increase of nitrate availability accelerated nitrate reductase activity (NRA) in parent and offspring ramets of E. crassipes, and there was greatly different pattern in inter-connected ramets during clonal growth stage. Leaf NRA was lower in offspring than that in parent ramets in phase 1, while significantly higher leaf NRA in offspring ramets was detected during phase 2. The results indicated NRA in inter-connected ramets of E. crassipes was highly dependent on nitrate availability and growth stage.     

Differential Effects of Ammonium and Nitrate on Growth Performance of <i>Glechoma longituba</i> under Heterogeneous Cd Stress

Water, minerals, nutrients, etc., can be shared by physiological integration among inter-connected ramets of clonal plants. Nitrogen plays an important role in alleviating cadmium (Cd) stress for clonal plants. But how different forms of nitrogen affect growth performance of clonal plants subjected to heterogeneous Cd stress still remains poorly understood. A pot experiment was conducted to investigate the differential effects of ammonium and nitrate on growth performance of Glechoma longituba under heterogeneous Cd stress. In the experiment, parent ramets of Glechoma longituba clonal fragments were respectively supplied with modified Hoagland solution containing 7.5 mM ammonium, 7.5 mM nitrate or the same volume of nutrient solution without nitrogen. Cd solution with different concentrations (0, 0.1 or 2.0 mM) was applied to offspring ramets of the clonal fragments. Compared with control (N-free), nitrogen addition to parent ramets, especially ammonium, significantly improved antioxidant capacity [glutathione (GSH), proline (Pro), peroxidase (POD,) superoxide dismutase (SOD) and catalase (CAT)], PSII activity [maximum quantum yield of PSII (F_v/F_m) and effective quantum yield of PSII (ΦPSII)], chlorophyll content and biomass accumulation of the offspring ramets suffering from Cd stress. In addition, negative effects of nitrate on growth performance of whole clonal fragments were observed under Cd stress with high concentration (2.0 mM). Transportation or sharing of nitrogen, especially ammonium, can improve growth performance of clonal plants under heterogeneous Cd stress. The experiment provides insight into transmission mechanism of nitrogen among ramets of clonal plants suffering from heterogeneous nutrient supply. Physiological integration might be an important ecological strategy for clonal plants adapting to heterogeneous environment stress conditions.     

Clonal integration ameliorates the carbon accumulation capacity of a stoloniferous herb,Glechoma longituba,growing in heterogenous light conditions by facilitating nitrogen assimilation in the rhizosphere

Background and Aims Enhanced availability of photosynthates increases nitrogen (N) mineralization and nitrification in the rhizosphere via rhizodeposition from plant roots. Under heterogeneous light conditions, photosynthates supplied by exposed ramets may promote N assimilation in the rhizosphere of shaded, connected ramets. This study was conducted to test this hypothesis.Methods Clonal fragments of the stoloniferous herb Glechoma longituba with two successive ramets were selected. Mother ramets were subjected to full sunlight and offspring ramets were subjected to 80 % shading, and the stolon between the two successive ramets was either severed or left intact. Measurements were taken of photosynthetic and growth parameters. The turnover of available soil N was determined together with the compostion of the rhizosphere microbial community.Key Results The microbial community composition in the rhizosphere of shaded offspring ramets was significantly altered by clonal integration. Positive effects of clonal integration were observed on NAGase activity, net soil N mineralization rate and net soil N nitrification rate. Increased leaf N and chlorophyll content as well as leaf N allocation to the photosynthetic machinery improved the photosynthetic capability of shaded offspring ramets when the stolon was left intact. Clonal integration improved the growth performance of shaded, connected offspring ramets and whole clonal fragments without any cost to the exposed mother ramets.Conclusions Considerable differences in microbial community composition caused by clonal integration may facilitate N assimilation in the rhizosphere of shaded offspring ramets. Increased N content in the photosynthetic machinery may allow pre-acclimation to high light conditions for shaded offspring ramets, thus promoting opportunistic light capture. In accordance with the theory of the division of labour, it is suggested that clonal integration may ameliorate the carbon assimilation capacity of clonal plants, thus improving their fitness in temporally and spatially heterogeneous habitats.     

TRANSPORT OF CARBON AMONG CONNECTED RAMETS OF EICHHORNIA CRASSIPES (PONTEDERIACEAE) AT NORMAL AND HIGH LEVELS OF CO2

The floating, stoloniferous plant, Eichhornia crassipes, has high rates of productivity and rapidly invades new sites. Because the transport of carbon among connected ramets is known to increase the growth of clonal plants, we asked whether there is intraclonal carbon transport in E. crassipes. Because net photosynthesis of E. crassipes is significantly higher at high levels of atmospheric CO₂, we also asked if high CO₂ can change patterns of carbon transport in ways that might modify clonal growth. We exposed individual ramets within groups of connected ramets to ¹⁴CO₂ for 15–45 min and measured the distribution of ¹⁴C in the group after 4 days of growth at 350, 700, 1,400, or 2,800 μ1 1^−-1 CO₂. At 350 μ1 1^−-1 CO₂, a parent ramet exported approximately 10% of the ¹⁴C that it assimilated to its first rooted offspring ramet. The offspring exported a similar percentage of the ^l4C it assimilated toward the parent; two-thirds of this ¹⁴C was retained by the parent, and one-third moved into new offspring of the parent. In all ramets, imported carbon moved into leaves as well as roots. At the higher levels of CO₂, the percentage of assimilated carbon exported from a parent ramet to the leaf blades of its first offspring was lower by half. High CO₂ had little other effect on carbon transport. E. crassipes maintains bidirectional transport of carbon between ramets even under uniform and favorable environmental conditions and when external CO₂ levels are very high.     

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.     

Effects of clonal fragmentation on intraspecific competition of a stoloniferous floating plant

Disturbance is common and can fragment clones of plants. Clonal fragmentation may affect the density and growth of ramets so that it could alter intraspecific competition. To test this hypothesis, we grew one (low density), five (medium density) or nine (high density) parent ramets of the floating invasive plant Pistia stratiotes in buckets, and newly produced offspring ramets were either severed (with fragmentation) or remained connected to parent ramets (no fragmentation). Increasing density reduced biomass of the whole clone (i.e. parent ramet plus its offspring ramets), showing intense intraspecific competition. Fragmentation decreased biomass of offspring ramets, but increased biomass of parent ramets and the whole clone, suggesting significant resource translocation from parent to offspring ramets when clones were not fragmented. There was no interaction effect of density x fragmentation on biomass of the whole clone, and fragmentation did not affect competition intensity index. We conclude that clonal fragmentation does not alter intraspecific competition between clones of P. stratiotes, but increases biomass production of the whole clone. Thus, fragmentation may contribute to its interspecific competitive ability and invasiveness, and intentional fragmentation should not be recommended as a measure to stop the rapid growth of this invasive species.     

Exploitation of patchy soil water resources by the clonal vine <Emphasis Type="Italic">Ficus tikoua</Emphasis> in karst habitats of southwestern China

The karst habitats of southwestern China are characterized by a highly heterogeneous distribution of water resources. We hypothesized that the clonal integration between connected ramets of the clonal vine Ficus tikoua was an important adaptive strategy to the patchy distribution of water resources in these habitats. We grew ramet pairs (each consisting of a parent and an offspring ramet) in both homogeneously and heterogeneously watered conditions. The offspring ramets were well-watered, whereas their connected parent ramets were randomly assigned to four water treatments: well-watered, mild water stress, moderate water stress, and severe water stress. Increasing water stress decreased leaf water potential, relative water content, net assimilation rate, maximum quantum yield of PSII (F _v/F _m), and biomass of the parent ramets. Subjecting the parents to water stress significantly increased root biomass and root mass ratio (RMR) of their offspring ramets. Exploitation of plentiful water resources through the increased adventitious roots connected to another soil patch permitted the complete restoration of water relations and photosynthetic capacity of offspring ramets after an initial depression. Water relations and gas exchange of the parents were not affected by the water supply to their connected offspring ramets, suggesting that offspring ramets hardly exported water to the stressed parents. However, net assimilation rate and proline content of the offspring ramets increased when they were connected to water-stressed parents. The compensatory photosynthetic responses of offspring ramets connected to stressed parents revealed an increasing trend as the experiment progressed. Morphological and physiological plasticity of F. tikoua in response to heterogeneous water resources allow them to adapt to karst habitats and be suitable candidates for vegetation restoration projects.     

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

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

     

Clonal integration facilitates spread of Paspalum paspaloides from terrestrial to cadmium‐contaminated aquatic habitats

• Cadmium (Cd) is a hazardous environmental pollutant with high toxicity to plants, which has been detected in many wetlands. Clonal integration (resource translocation) between connected ramets of clonal plants can increase their tolerance to stress. We hypothesised that clonal integration facilitates spread of amphibious clonal plants from terrestrial to Cd‐contaminated aquatic habitats.
• The spread of an amphibious grass Paspalum paspaloides was simulated by growing basal older ramets in uncontaminated soil connected (allowing integration) or not connected (preventing integration) to apical younger ramets of the same fragments in Cd‐contaminated water.
• Cd contamination of apical ramets of P. paspaloides markedly decreased growth and photosynthetic capacity of the apical ramets without connection to the basal ramets, but did not decrease these properties with connection. Cd contamination did not affect growth of the basal ramets without connection to the apical ramets, but Cd contamination of 4 and 12 mg·l^?1 significantly increased growth with connection. Consequently, clonal integration increased growth of the apical ramets, basal ramets and whole clones when the apical ramets were grown in Cd‐contaminated water of 4 and 12 mg·l^?1. Cd was detected in the basal ramets with connection to the apical ramets, suggesting Cd could be translocated due to clonal integration. Clonal integration, most likely through translocation of photosynthates, can support P. paspaloides to spread from terrestrial to Cd‐contaminated aquatic habitats.
• Amphibious clonal plants with a high ability for clonal integration are particularly useful for re‐vegetation of degraded aquatic habitats caused by Cd contamination.

     

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

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

     

Clonal Transgenerational Effects Transmit for Multiple Generations in a Floating Plant

Environmental conditions of a parent plant can influence the performance of their clonal offspring, and such clonal transgenerational effects may help offspring adapt to different environments. However, it is still unclear how many vegetative generations clonal transgenerational effects can transmit for and whether it depends on the environmental conditions of the offspring. We grew the ancestor ramets of the floating clonal plant Spirodela polyrhiza under a high and a low nutrient level and obtained the so-called 1^st-generation offspring ramets of two types (from these two environments). Then we grew the 1^st-generation offspring ramets of each type under the high and the low nutrient level and obtained the so-called 2^nd-generation offspring ramets of four types. We repeated this procedure for another five times and analyzed clonal transgenerational effects on growth, morphology and biomass allocation of the 1^st- to the 6^th-generation offspring ramets. We found positive, negative or neutral (no) transgenerational effects of the ancestor nutrient condition on the offspring of S. polyrhiza, depending on the number of vegetative generations, the nutrient condition of the offspring environment and the traits considered. We observed significant clonal transgenerational effects on the 6^th-generation offspring; such effects occurred for all three types of traits (growth, morphology and allocation), but varied depending on the nutrient condition of the offspring environment and the traits considered. Our results suggest that clonal transgenerational effects can transmit for multiple vegetative generations and such impacts can vary depending on the environmental conditions of offspring.     

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 in Fragaria vesca growing in metal-polluted soils: parents face penalties for establishing their offspring in unsuitable environments

Clonal plants often establish descendent ramets in sites with contrasting presence of favourable and unfavourable factors. Connections between ramets allow translocation of essential resources from established ramets to developing ramets and, as consequence, integration confers net benefits to ramets growing under unfavourable conditions. Therefore, integrated ramets may survive in habitat patches that would be lethal to independent ramets or non-clonal plants. This experiment aimed to investigate the physiological and morphological responses of the clonal plant Fragaria vesca growing in heterogeneous substrate with patches of contrasting quality (i.e. uncontaminated or heavy-metal-contaminated). We observed that parents reduced their photosynthetic efficiencies and growth as consequence of maintaining their offspring. This cost did not affect survival of the parents. Physiological integration brings about benefits to offspring ramets growing both at uncontaminated and heavy-metal-contaminated soils. The benefits of integration were detected in both physiological and morphological traits, enhancing the survivorship of offspring ramets in the Cu-polluted soils. We conclude that integration improves the performance of developing ramets of F. vesca growing in heavy-metal-contaminated habitats, allowing clone systems to overcome the establishment risks and maintain their presence in these less favourable sites.     

克隆整合对异质性光照环境下紫竹根际土壤氮素有效性的影响

以根状茎克隆植物紫竹为对象,研究克隆整合对遭受异质性光照胁迫分株根际土壤有机碳(SOC)、总氮(TN)、溶解性有机碳(DOC)、溶解性有机氮(DON)、氨氮(NH_4~+-N)、硝态氮(NO_3~--N)以及微生物群落组成的影响。所取紫竹克隆片段由一个母本分株和一个子代分株组成,母本分株置于全光照下,而子代分株置于80%遮阴环境中,同时母本分株与子代分株间的根茎保持连接或割断处理。结果表明:与切断处理相比,紫竹遮荫子代分株根际土壤的SOC、TN、DOC、NH_4~+-N在保持根状茎连接时显著更高,这表明异质性光照环境下克隆整合可能改善紫竹连接遮荫子代分株根际土壤的氮素有效性。克隆整合提高了连接遮阴状态下紫竹子代分株根际土壤中的放线菌、真菌和革阴细菌的PLFAs浓度。通过对遮阴子代分株根际土壤微生物群落PLFAs主成分分析得出克隆整合导致遮阴子代分株根际土壤微生物群落结构发生显著变化。该研究结果暗示了紫竹可能通过克隆整合作用降低土壤中某些对氮利用有效性影响较低的细菌数量,而增加对土壤氮利用起重要作用的放线菌和真菌的数量,进而改善紫竹对土壤中氮利用的有效性,这有利于增强克隆植物对时空异质性生境的适应能力。     

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.     

Patterns of Solidago altissima ramet growth and mortality: the role of below-ground ramet connections

Summary For the rhizomatous perennial, Solidago altissima, I identified clonal fragments in the field, mapped ramet spatial locations, and documented patterns of ramet recruitment, growth, and mortality. Parent ramet size influenced the size and number of daughter ramets produced, and small ramets had lower survivorship and fecundity than large ramets. Similarly, small rhizomes tended to develop into small ramets, and ramets that survived to produce daughter ramets had longer parent-daughter rhizome connections than ramets that did not survive. In addition, most ramets that died during the growing season were connected to (genetically identical) ramets that persisted. There were large size inequalities among rhizomes, ramets, and clonal fragments. Inequalities in the size of ramets increased during the early part of the growing season, then decreased at the end of the season; similar patterns were observed for the growth of clonal fragments. In both instances, the decrease in size inequality could be attributed to the mortality of small individuals (ramets or clonal fragments). I found little evidence that ramet size hierarchies were structured by intraspecific competition. For example, path analyses and randomization tests indicated that size variation among S. altissima ramets was influenced little by the size of their near neighbors (but was influenced by parent size and rhizome size). In addition, within-season variation for the relative size and growth rate of individual ramets led to poor correlations between early and final ramet size; this result suggests that there was no stable hierarchy of dominant and suppressed ramets. I discuss implications of my results for contrasting interpretations of clonal plant population dynamics.     

To share or not to share: clonal integration in a submerged macrophyte in response to light stress

The ability of clonal plant species to share resources has been studied in many experiments. The submerged macrophyte Potamogeton perfoliatus produces interconnected ramets within short time intervals and hence may or may not share resources with ramets growing in less favourable microhabitats. From a genet point of view, sharing with ramets growing under less favourable conditions might not be an optimal strategy when photosynthates could be used to establish other ramets growing under more favourable conditions. To analyse the plasticity in clonal integration of P. perfoliatus, we set up a factorial aquaria experiment with unshaded or shaded recipient ramets (offspring), which were connected to or separated from donor ramets (parents). Increased biomass production of offspring in parent–offspring systems compared with severed offspring in both light and shade showed that ramets share resources through clonal integration. The relative translocation to the first- and second-offspring generation was influenced by habitat quality: If first-offspring ramets grew in a shaded microhabitat, second-offspring ramets clearly profited. This may be at least partially because of the fact that resources are shifted from first-offspring to second-offspring ramets, indicating controlled senescence of the first-offspring. This complex sharing behaviour might be relevant when plants produce ramets within a dense patch of macrophytes, where support of a shaded ramet might not pay off.     

Timing of disturbance changes the balance between growth and survival of parent and offspring ramets in the clonal forest understory herb Uvularia perfoliata

Preformation of organs involves the initiation of vegetative and generative tissues at least one season before they are actually produced. It is a strategy to deal with environments characterized by predictable seasonality as it enables fast growth of plants at the onset of favorable conditions. However, early preformation also strongly restricts plants in their response to unpredictable environmental changes and disturbance. In this study we investigated the response of the clonal forest understory herb Uvularia perfoliata to disturbance and resource limitation. In U. perfoliata shoot characteristics, as well as vegetative and sexual reproduction are determined at the end of the previous growing season. Plants were grown under two light levels and the rhizome connection between parent and offspring ramets were severed at various times during the growing period. Disturbance did not affect total biomass accumulation but it did affect the relative allocation and survival probability of parents and offspring ramets. Early severing resulted in increased survival chance and future fitness of the parent ramet, while late severing resulted in a higher survival chance and increased fitness of offspring ramets. The response was mediated by plant size and resource availability. These results show that the life history of U. perfoliata includes the possibility to alleviate the effects of disturbance even though the species is characterized by strong developmental canalization through organ preformation.Co-ordinating editor: J. Tuomi     

Carbon Translocation Between Parents and Ramets of a Desert Perennial

Agave deserti, a semelparous, Crassulacean acid metabolism perennialoccurring in the northwestern Sonoran Desert, propagates primarilyvegetatively by ramets produced on rhizomes that extend lessthan 10 cm from the base of a parent plant. Carbon translocationfrom parents to ramets, measured after exposing leaves to ¹⁴CO₂,was essentially complete in 7 d, with parents exporting 3·3%of their assimilated carbon to ramets. Shading ramets belowlight compensation for 6 weeks more than doubled the amountof carbon exported from the parent to shaded ramets, comparedwith unshaded ramets. The total amount of carbon imported bya ramet from its parent was independent of the mass of the ramet.Although the net movement of carbon is expected to be towardsthe ramets, parents also received carbon from labelled ramets,indicating bidirectional translocation. The physiological integrationof parents and ramets allows ramets to draw upon the reservesof the parent for up to 14 years, a longer period than for mostother reported clonal species, thereby facilitating ramet growthand establishment in a resource-limited environment. Agave deserti Engelm., clonal, physiological integration, translocation, ¹⁴CO₂     

Differential influence of clonal integration on morphological and growth responses to light in two invasive herbs

Background and aims

In contrast to seeds, high sensitivity of vegetative fragments to unfavourable environments may limit the expansion of clonal invasive plants. However, clonal integration promotes the establishment of propagules in less suitable habitats and may facilitate the expansion of clonal invaders into intact native communities. Here, we examine the influence of clonal integration on the morphology and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under varying light conditions.

Methods

In a greenhouse experiment, branches, connected ramets and severed ramets of the same mother plant were exposed under full sun and 85% shade and their morphological and growth responses were assessed.

Key results

The influence of clonal integration on the light reaction norm (connection×light interaction) of daughter ramets was species-specific. For A. philoxeroides, clonal integration evened out the light response (total biomass, leaf mass per area, and stem number, diameter and length) displayed in severed ramets, but these connection×light interactions were largely absent for P. canescens. Nevertheless, for both species, clonal integration overwhelmed light effect in promoting the growth of juvenile ramets during early development. Also, vertical growth, as an apparent shade acclimation response, was more prevalent in severed ramets than in connected ramets. Finally, unrooted branches displayed smaller organ size and slower growth than connected ramets, but the pattern of light reaction was similar, suggesting mother plants invest in daughter ramets prior to their own branches.

Conclusions

Clonal integration modifies light reaction norms of morphological and growth traits in a species-specific manner for A. philoxeroides and P. canescens, but it improves the establishment of juvenile ramets of both species in light-limiting environments by promoting their growth during early development. This factor may be partially responsible for their ability to successfully colonize native plant communities.