Physiological integration ameliorates effects of serpentine soils in the clonal herb Fragaria vesca

Small-scale heterogeneity in soil characteristics and the facility of clonal systems to spread may lead to situations where parent ramets in favourable microhabitats are connected to offspring in stressful conditions. Clonal plants are physiologically integrated if connections among ramets allow transport of resources. Thus, ramets in favourable habitats may provide support to developing or stressed ramets. We examined effects of integration in Fragaria vesca growing in patches of contrasting quality (potting compost vs serpentine soil). Serpentine soil was used to create unfavourable growing conditions. We assessed whether survival, biomass and photosynthetic efficiency (estimated by fluorescence and reflectance) of parents and offspring were affected by integration and soil quality. Integration increased photochemical efficiencies of parents but more consistently in parents with offspring growing in serpentine soils. We suggest that the assimilate demand from offspring enhanced the photosynthetic efficiency of parents by a mechanism of feedback regulation. This result extends the concept of physiological integration in clonal plants to include photochemical responses. Connected parents also showed significantly higher biomass than disconnected parents. In our system, integration did not entail costs for the whole clone in terms of biomass. Integration also improves the survival, growth and photochemical efficiency of developing ramets, suggesting that integration represents a mechanism for increasing survival in stressful habitats, as the serpentine soils.     

An analysis of the costs and benefits of physiological integration between ramets in the clonal perennial herb Glechoma hederacea

Summary The costs and benefits, measured in terms of dry weight, of physiological integration between clonal ramets, were analysed in two experiments conducted on the clonal herb Glechoma hederacea. Firstly, integration between consecutively-produced ramets was examined in an experiment in which stolons grew from one set of growing conditions (either unshaded or shaded and either nutrient-rich or nutrient-poor) into conditions in which light or nutrient level was altered. Comparisons were made between the dry weight of the parts of the clones produced before and after growing conditions were changed, and the dry weights of the corresponding part of control clones subjected to constant growing conditions. In a second experiment, integration between two distinct parts of G. hederacea clones was investigated. In this experiment clones were grown from two connected parent ramets and the parts of the clone produced by each parent ramet were subjected independently to either nutrient-rich or nutrient-poor conditions. Ramets in resource-rich conditions provided considerable physiological support to those in resource-poor conditions. This was measured as a dry weight gain compared with the weight of the corresponding part of the control clones growing in resource-poor conditions. However, when stolons grew from resource-poor conditions into resource-rich conditions, there was no similar evidence of the resourcepoor ramtes receiving support from resource-rich ramets. Physiological integration did not result in dry weight gains when this would have necessitated basipetal translocation of resources.Because of the predominantly acropedal direction of movement of translocates in G. hederacea, the structure of the clone was important in determining the effectiveness of integration between ramets. Where physiological integration was effective, the cost to the supporting ramets in terms of dry weight was insignificant. Physiological integration allows clones to maintain a presence in less favourable sites with insignificant cost to ramets in favourable sites, thereby reducing the probability of invasion by other plants, and providing the potential for rapid clonal growth if conditions improve. Integrated support of ramets in unfavourable conditions also enables the clone to grow through unfavourable sites, thus increasing the probability of encountering more favourable conditions by wider foraging.     

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.     

Small-scale heterogeneity in soil quality influences photosynthetic efficiency and habitat selection in a clonal plant

BACKGROUND AND AIMS: In clonal plants, internode connections allow translocation of photosynthates, water, nutrients and other substances among ramets. Clonal plants form large systems that are likely to experience small-scale spatial heterogeneity. Physiological and morphological responses of Fragaria vesca to small-scale heterogeneity in soil quality were investigated, together with how such heterogeneity influences the placement of ramets. As a result of their own activities plants may modify the suitability of their habitats over time. However, most experiments on habitat selection by clonal plants have not generally considered time as an important variable. In the present study, how the foraging behaviour of clonal plants may change over time was also investigated. METHODS: In a complex of environments with different heterogeneity, plant performance was determined in terms of biomass, ramet production and photosynthetic activity. To identify habitat selection, the number of ramets produced and patch where they rooted were monitored. KEY RESULTS: Parent ramets in heterogeneous environments showed significantly higher maximum and effective quantum yields of photosystem II than parents in homogeneous environments. Parents in heterogeneous environments also showed significantly higher investment in photosynthetic biomass and stolon/total biomass, produced longer stolons, and had higher mean leaf size than parents in homogeneous environments. Total biomass and number of offspring ramets were similar in both environments. However, plants in homogeneous environments showed random allocation of offspring ramets to surrounding patches, whereas plants in heterogeneous environments showed preferential allocation of offspring to higher-quality patches. CONCLUSIONS: The results suggest that F. vesca employs physiological and morphological strategies to enable efficient resource foraging in heterogeneous environments and demonstrate the benefits of physiological integration in terms of photosynthetic efficiency. The findings indicate that short-term responses cannot be directly extrapolated to the longer term principally because preferential colonization of high-quality patches means that these patches eventually show reduced quality. This highlights the importance of considering the time factor in experiments examining responses of clonal plants to heterogeneity.     

Physiological integration modifies δ15N in the clonal plant Fragaria vesca,suggesting preferential transport of nitrogen to water-stressed offspring

Background and Aims

One of the most striking attributes of clonal plants is their capacity for physiological integration, which enables movement of essential resources between connected ramets. This study investigated the capacity of physiological integration to buffer differences in resource availability experienced by ramets of the clonal wild strawberry plant, Fragaria vesca. Specifically, a study was made of the responses of connected and severed offspring ramets growing in environments with different water availability conditions (well watered or water stressed) and nitrogen forms (nitrate or ammonium).

Methods

The experimental design consisted of three factors, ‘integration’ (connected, severed) ‘water status’ (well watered, water stressed) and ‘nitrogen form’ (nitrate, ammonium), applied in a pot experiment. The effects of physiological integration were studied by analysing photochemical efficiency, leaf spectral reflectance, photosynthesis and carbon and nitrogen isotope discrimination, the last of which has been neglected in previous studies.

Key Results

Physiological integration buffered the stress caused by water deprivation. As a consequence, survival was improved in water-stressed offspring ramets that remained connected to their parent plants. The nitrogen isotope composition (δ¹⁵N) values in the connected water-stressed ramets were similar to those in ramets in the ammonium treatment; however, δ¹⁵N values in connected well-watered ramets were similar to those in the nitrate treatment. The results also demonstrated the benefit of integration for offspring ramets in terms of photochemical activity and photosynthesis.

Conclusions

This is the first study in which carbon and nitrogen isotopic discrimination has been used to detect physiological integration in clonal plants. The results for nitrogen isotope composition represent the first evidence of preferential transport of a specific form of nitrogen to compensate for stressful conditions experienced by a member clone. Water consumption was lower in plants supplied with ammonium than in plants supplied with nitrate, and therefore preferential transport of ammonium from parents to water-stressed offspring could potentially optimize the water use of the whole clone.     

Morphological responses to local light conditions in clonal herbs from contrasting habitats,and their modification due to physiological integration

Morphological responses to light and effects of physiological integration on local morphological responses are examined for Hydrocotyle vulgaris and Lamiastrum galeobdolon, stoloniferous herbs from open fenlands and forest understoreys, respectively. An assessment was made of whether these clonal herbs of similar morphology but from contrasting habitats show different foraging behaviour for light. In a garden experiment, the plants wer subjected to four levels of light availability, and to a split treatment in which the primary stolons grew along the border of patches of the two intermediate light levels. In this treatment the plant parts on opposite sides of the primary stolons were in contrasting light environments. Petiole extension was more responsive to light conditions in Hydrocotyle than in Lamiastrum, while the opposite was true for leaf area. Both species showed similar responses in stolon internode length and specific leaf area (SLA). Integration did not significantly modify local responses in stolon internode length in either species. Local responses in petiole length, leaf area and SLA of Hydrocotyle ramets were not significantly affected by physiological integration, except for the SLA of ramets in high light which was evened out by integration. In contrast, in Lamiastrum, local responses in petiole length, leaf area and SLA of many ramets in the shaded and/or light patch were significantly evened out by integration. As a result, interconnected ramets in patches of different light supply developed very different morphologies in Hydrocotyle, but not in Lamiastrum. The results indicate that the species differed in ramet morphological responses to light intensity as well as in effects of integration on local morphological responses, and suggest that species from different habitats show different foraging behaviour for light.     

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.     

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.     

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.     

Habitat selection in spatially heterogeneous environments: a test of foraging behaviour in the clonal submerged macrophyte Vallisneria spiralis

1. To test whether clonal macrophytes can select favourable habitats in heterogeneous environments, clonal fragments of the stoloniferous submerged macrophyte Vallisneria spiralis were subjected to conditions in which light intensity and substratum nutrients were patchily distributed. The allocation of biomass accumulation and ramet production of clones to the different patches was examined. 2. The proportion of both biomass and ramet number of clones allocated to rich patches was significantly higher than in poor patches. The greatest values of both clone and leaf biomass were produced in the heterogeneous light treatment, in which clones originally grew from light‐rich to light‐poor patches, while clones produced the most offspring ramets in the treatments with heterogeneous substratum nutrients. Similarly, root biomass had the highest values in nutrient‐rich patches when clones grew from nutrient‐rich to nutrient‐poor patches. 3. The quality of patches in which parent ramets established significantly influenced the foraging pattern. When previously established in rich patches, a higher proportion of biomass was allocated to rich patches, whereas a higher proportion of ramet number was allocated to rich patches when previously established in poor patches. 4. Results demonstrate that the clonal macrophyte V. spiralis can exhibit foraging in submerged heterogeneous environments: when established under resource‐rich conditions V. spiralis remained in favourable patches, whereas if established in adverse conditions it could escape by allocating more ramets to favourable patches.     

Do Physiological Integration and Soil Heterogeneity Influence the Clonal Growth and Foraging of <Emphasis Type="Italic">Schoenoplectus pungens</Emphasis>?

Physiological integration and foraging behavior have both been proposed as advantages for clonal growth in heterogeneous environments. We tested three predictions concerning their short- and long-term effects on the growth of the clonal perennial sedge Schoenoplectus pungens (Pers.) Volk. ex Schinz and R. Keller: (1) growth would be greatest for clones with connected rhizomes and on heterogeneous soil, (2) clones would preferentially place biomass in the nutrient-rich patches of a spatially heterogeneous environment, and (3) physiological integration would decrease a clone’s ability to forage. We tested our predictions by growing S. pungens clones for 2 years in an experimental garden with two severing treatments (connected and severed rhizomes) crossed with two soil treatments (homogeneous and heterogeneous nutrient distribution). Severing treatments were only carried out in the first year. As predicted, severing significantly decreased total biomass and per capita growth rate in year one and individual ramet biomass both in year one and the year after severing stopped. This reduction in growth was most likely caused by severing damage, because the total biomass and growth rate in severed treatments did not vary with soil heterogeneity. Contrary to our prediction, total biomass and number of ramets were highest on homogeneous soil at the end of year two, regardless of severing treatment, possibly because ramets in heterogeneous treatments were initially planted in a nutrient-poor patch. Finally, as predicted, S. pungens concentrated ramets in the nutrient-rich patches of the heterogeneous soil treatment. This foraging behavior seemed enhanced by physiological integration in the first year, but any possible enhancement disappeared the year after severing stopped. It seems that over time, individual ramets become independent, and parent ramets respond independently to the conditions of their local microsite when producing offspring, a life-history pattern that may be the rule for clonal species with the spreading “guerrilla” growth form.     

The ideal free distribution of clonal plant's ramets among patches in a heterogeneous environment

The plastic response of clonal plant to different patch quality is not always the same and the degree is different too. So the result of this kind of foraging behaviour is different. In order to make clear whether the ramtes stay in favourable patches and get the quantitative relationship between the ramets distribution among patches and the available resource amount in heterogeneous environment, we develop a theoretical work under ideal free distribution (IFD) theory framework by neglecting some morphological plasticity of the spacer in this article. The results of our general model show that the ramet distribution should obey input matching rule at equilibrium. That means the ratio of ramet number in different patches should be equal to the ratio of available resource amount in these patches. We also use the simulation to predict the distribution pattern under history mattering. The results show that the initial ramets number has significant influence on the final distribution: over matching and under matching both can occur. More initial ramets in favourable patch result in over matching and more initial ramets in unfavourable patch result in under matching. The degree of the deviation from input matching rule is great when the difference of patches is small. These results prove that ideal free distribution theory works the same with animals. The ramets can stay in favourable patches sometimes in spite of the plasticity of the spacer, and the distribution depends on both patch quality and the history factors. But these results are true only when the functional response is type II.     

Buffalograss decreases ramet propagation in infertile patches to enhance interconnected ramet proliferation in fertile patches

Buffalograss (Buchloë dactyloides) is known for its low-nutrient tolerance. However, in natural habitats, nutrients are usually patchily distributed. For clonal plants like buffalograss, physiological integration is an important strategy to cope with adverse environmental conditions. In order to examine how integration helps buffalograss to survive in patchy conditions, a greenhouse experiment was conducted for 91 days. Interconnected ramet pairs of stoloniferous buffalograss were planted in two partitioned same-sized containers, and subjected to identical or contrasting nutrient supply. In contrast to normally perceived resource-sharing concepts, results showed that buffalograss genets reduced production of new ramets in nutrient-poor patches promoting at the same time propagation of interconnected ramets in nutrient-rich patches. Ramets in nutrient-rich patches gained significant benefit from heterogeneous treatments, whereas nutrient-poor ramets performed even worse than in uniform low-nutrient treatment. Younger ramets developed more biomass than elder ramets with the same amounts of nutrient supply under homogeneous treatment, while elder ramets were more tolerant when nutrients were scarce. Heterogeneity had a particular strong effect on stolons and new ramet production in nutrient-rich patches. Rooted ramets in nutrient-poor patches suffered from a by-pass of nutrients to interconnected ramets on nutrient-rich substrate that probably resulted from different transpiration rates. We conclude that this resource-sharing strategy is advantageous for buffalograss to concentrate more ramets in fertile patches, and facilitate the survivorship of more buffalograss ramets in adverse environments with uneven nutrient supply.     

Clonal Integration of Fragaria orientalis in Reciprocal and Coincident Patchiness Resources: Cost-Benefit Analysis

Clonal growth allows plants to spread horizontally and to experience different levels of resources. If ramets remain physiologically integrated, clonal plants can reciprocally translocate resources between ramets in heterogeneous environments. But little is known about the interaction between benefits of clonal integration and patterns of resource heterogeneity in different patches, i.e., coincident patchiness or reciprocal patchiness. We hypothesized that clonal integration will show different effects on ramets in different patches and more benefit to ramets under reciprocal patchiness than to those under coincident patchiness, as well as that the benefit from clonal integration is affected by the position of proximal and distal ramets under reciprocal or coincident patchiness. A pot experiment was conducted with clonal fragments consisting of two interconnected ramets (proximal and distal ramet) of Fragaria orientalis. In the experiment, proximal and distal ramets were grown in high or low availability of resources, i.e., light and water. Resource limitation was applied either simultaneously to both ramets of a clonal fragment (coincident resource limitation) or separately to different ramets of the same clonal fragment (reciprocal resource limitation). Half of the clonal fragments were connected while the other half were severed. From the experiment, clonal fragments growing under coincident resource limitation accumulated more biomass than those under reciprocal resource limitation. Based on a cost-benefit analysis, the support from proximal ramets to distal ramets was stronger than that from distal ramets to proximal ramets. Through division of labour, clonal fragments of F. orientalis benefited more in reciprocal patchiness than in coincident patchiness. While considering biomass accumulation and ramets production, coincident patchiness were more favourable to clonal plant F. orientalis.     

Clonal integration and heavy-metal stress: responses of plants with contrasting evolutionary backgrounds

Physiological integration between ramets can ameliorate the growth and survival of clonal plants in spatially-heterogeneous environments, as ramets from favourable patches can provide support to those found in stressful patches. However, the advantage conferred by clonal integration might also depend on the evolutionary history of plants with regards to the presented stress. Here, we compared the benefit of clonal integration in response to the distribution of a heavy metal as a stress factor, and asked if this benefit would differ between ecotypes that have either undergone selection to tolerate heavy metals or not. In a greenhouse experiment, we grew pairs of connected and severed ramets of the metal hyperaccumulator Arabidopsis halleri, which originated from populations of either metalliferous or non-metalliferous soils. The ramets were grown in paired pots, which were contaminated with cadmium (Cd) either heterogeneously (100 or 0 ppm Cd per pot) or homogenously (50 ppm Cd per each pot). A. halleri ecotypes that originated from non-metalliferous soils performed better when ramets were connected and the distribution of Cd was heterogeneous. However, clonal integration had no effect on the performance of genotypes from metalliferous soils, regardless of the distribution of Cd. These results support the hypothesis that clonal integration is beneficial in stressful environments as long as the stress is patchily distributed, and particularly for plants that did not undergo selection to withstand it.     

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.     

Ecological benefits of integration of Calamagrostis epigejos ramets under field conditions

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

Effects of stolon severing on the expansion of Alternanthera philoxeroides from terrestrial to contaminated aquatic habitats

Few studies have examined the effects of clonal integration (translocation of resources between interconnected ramets) during the expansion of amphibious clonal plants from terrestrial to aquatic habitats. We conducted a greenhouse experiment to simulate the expansion of plants from terrestrial to contaminated aquatic habitats in the amphibious stoloniferous herb Alternanthera philoxeroides (alligator weed). The proximal ramets (i.e. relatively old) of clonal fragments grown in uncontaminated soils were connected to (allowing clonal integration) or disconnected from (preventing clonal integration) distal ramets (i.e. relatively young) grown either in uncontaminated water (control, no CuSO₄) or in four copper‐contaminated water treatments containing 31.25, 62.5, 125 and 250 mg/L CuSO₄, respectively. When a stolon connection was severed, all distal ramets grown in the contaminated water died. When the stolon connection was intact, however, the survival rate of the distal ramets was 85–100% when they were grown at the three lower levels of contamination and 43.75% at the highest level. Moreover, the survival rate and growth of the distal ramets grown in the three lower levels of contamination treatments did not differ from those in the control (uncontaminated water). These results suggest that clonal integration could greatly improve the survival and growth of alligator weed subjected to moderate levels of copper stress. Although clonal integration could also increase the survival rate of the connected distal ramets subjected to the highest level of copper stress (250 mg/L CuSO₄) compared with that of disconnected distal ramets, the survival rate and growth measures were still significantly lower than those in the control. This suggests that clonal integration plays a limited role in the survival and growth of alligator weed when it is subjected to severe stress by high levels of copper contamination.     

The effects of physiological integration on biomass partitioning in plant modules: an experimental study with the stoloniferous herb Glechoma hederacea

Morphological and physiological plasticity are crucial attributes enabling plants to acquire resources from heterogeneous habitats. Although physiological integration can modify biomass partitioning in modules, especially when connected modules experience different conditions, its ecological importance has been largely overlooked. This experiment examined its effects on above- and belowground biomass partitioning by modules in the stoloniferous herb Glechoma hederacea. We studied how biomass allocation to roots by younger ramets was affected by connection to older ramets, and by nutrient conditions. A lower proportion of biomass was allocated to roots by younger ramets growing under low nutrient (LN) conditions when connected to older ramets in high nutrient (HN) conditions than when they were isolated, demonstrating localised modification of biomass partitioning due to physiological integration. The proportion of biomass allocated to roots by younger ramets was also lower when connected to older ramets in HN conditions than when connected to older ramets in LN conditions. Thus, the effect of integration on biomass partitioning depended on the nutrient conditions experienced by connected ramets. Such changes in biomass partitioning would result in more extensive stolon growth, and greater lateral displacement of new ramets. Understanding the ecological implications of phenotypic plasticity in plants will require further examination of the effects of physiological integration when connected modules experience contrasting growing conditions. This study demonstrates that such integration affects the biomass allocation strategy of connected ramets, enhancing resource acquisition in heterogeneous habitats. The widespread success of clonality in many communities is likely to be strongly promoted by this characteristic.     

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。