A change from phalanx to guerrilla growth form is an effective strategy to acclimate to sedimentation in a wetland sedge species Carex brevicuspis (Cyperaceae)

The rhizomatous sedge Carex brevicuspis can produce clumping ramets from shortened rhizomes (phalanx) and spreading ramets from elongated rhizomes (guerrilla) to form a combined clonal growth form. In this paper, changes in clonal growth and biomass allocation pattern of C. brevicuspis in response to sedimentation were studied. Four sedimentation depths (0, 3, 6, and 9 cm) were applied to 48 ramets in a randomized block design. Plants were harvested after 20 weeks. With increasing sedimentation depth, the proportion of spreading ramets to total ramets increased from 19.6% in 0 cm to 92.9% in 9 cm sedimentation treatments, whereas that of clumping ramets decreased from 80.4% to 7.1%, indicating a change of clonal growth form from phalanx to guerrilla as a response to sedimentation. With increasing sedimentation depth, biomass allocation to shoots and roots did not change, but rhizome mass ratio increased from 2.7% in 0 cm to 7.2% in 9 cm sedimentation treatments, suggesting that production of long rhizomes changes biomass allocation pattern. The results show that plasticity of clonal growth forms, by which more spreading ramets are produced, is an effective strategy to avoid sedimentation stress under our experimental conditions.     

Morphological responses to different flooding regimes in Carex brevicuspis

Water regime can be described by the depth, duration, frequency, and timing and predictability of flooded and dry phases. Despite growing recognition of the importance of water regimes in the regulation of plant growth and distribution, which components of water regimes that determine plant growth are not well known. To identify the causative components, 72 ramets of Carex brevicuspis were grown under six different water regime treatments (treatment A: constant 0 cm water level; treatment B: constant 30 cm water level; treatment C: 0 cm water level to 30 cm water level for 30 days, repeated 2 times; treatment D: 30 cm water level to 0 cm water level for 30 days, repeated 2 times; treatment E: 0 cm water level to 30 cm water level for 5 days, repeated 12 times; and treatment F: 30 cm water level to 0 cm water level for 5 days, repeated 12 times). Biomass accumulation, below:above ground biomass ratio, number of ramets, and proportions of spreading and clumping ramet were assessed. Biomass accumulation decreased only in relation to length of flooding. The highest biomass accumulation occurred in the 120‐day + 0 cm water level treatment, it was intermediate in the four 60 day + 30 cm water level treatments, and lowest in the 120 day + 30 cm water level treatment. Likewise, the below:above ground ratio decreased only with increasing length of flooding. Ramet number was highest in the 120 day + 0 cm water level treatment, intermediate in the four 60 day + 30 cm water level treatments, and lowest in the 120 day + 30 cm water level treatment. The proportion of spreading ramets increased from 28.0% in the 120 day + 0 cm water level treatment to 76.4% in the 120 day + 30 cm water level treatment. These data suggest that the growth of C. brevicuspis was only limited by the duration of flooding. Reduction of the below:above ground ratio and change from phalanx to guerrilla growth form are effective strategies for C. brevicuspis to acclimate to flooding stress, because they allow the plant to grow above the water surface and escape from anoxic conditions. Our study provides experimental information on the role of different components of water regimes in regulating plant growth, and may assist in protection and restoration of the C. brevicuspis community.     

不同高程短尖苔草对水位变化的生长及繁殖响应

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

Physiological mechanisms for plant distribution pattern: responses to flooding and drought in three wetland plants from Dongting Lake, China

Both flooding and drought are important in determining plant distribution in wetlands. However, the roles of plant’s physiological response to flooding and drought in accounting for plant distribution are far from clear. To this end, three typical wetland plants with different distribution patterns (high-elevation species Miscanthus sacchariflorus, low-elevation species Carex brevicuspis and Polygonum hydropiper) in Dongting Lake were treated with three water levels (flooding 25 cm, control 0 cm, drought ?25 cm), and relative growth rate (RGR), malondialdehyde (MDA) content, electrolyte leakage and proline content were investigated. The RGR of the three species decreased significantly in both flooding and drought treatments. Compared to the control, the RGR of M. sacchariflorus decreased more in the flooding treatment but less in the drought treatment compared to the other two species. The contents of MDA in the three species increased in both flooding and drought treatments, except for P. hydropiper in the flooding treatment. MDA contents increased more in M. sacchariflorus in the flooding treatment but less in the drought treatment compared to the other two species. Only M. sacchariflorus had a higher electrolyte leakage in the flooding treatment, and drought led to a higher electrolyte leakage in P. hydropiper and C. brevicuspis. Proline content increased 69.2, 66.7 and 39.6 % in P. hydropiper, C. brevicuspis and M. sacchariflorus in the flooding treatment, and increased 44.2, 13.0 and 45.3 % in the drought treatment, respectively. These results suggest that M. sacchariflorus has a higher tolerance to drought but a lower tolerance to flooding than do the other two species, which might be the intrinsic mechanisms accounting for their different distribution patterns.     

Effects of sediment burial disturbance on the vegetative propagation of Phalaris arundinacea with different shoot statuses

Shoot status, such as orientation and connection to the root system, and sediment burial depth after flooding disturbances have important ecological consequences on the post-flooding growth and vegetative reproduction of emergent macrophytes in wetlands. In the present study, we investigated the effect of shoot status (vertical, prostrate, or detached) and sediment burial depth (0.5 or 10 cm) on biomass accumulation and propagule production in Phalaris arundinacea (Poaceae) using an outdoor mesocosm system. In contrast to our prediction that shallow sediment burial would activate the axillary buds on prostrate shoots and regenerate more ramets, significantly fewer new ramets, rhizomes, buds, and biomass accumulation formed in P. arundinacea as the shoots changed from vertical to prostrate. Deeper sediment burial resulted in lower biomass and propagule production in plants with prostrate shoots, whereas vertical shoots increased the number of ramets. P arundinacea with detached shoots also produced a number of propagules after shallow or deep sediment burial, which might be important for the long-distance dispersal of P. arundinacea. These results suggest that P. arundinacea is a potentially invasive species in many lacustrine wetlands, particularly those with a high sedimentation rate, due to its high capacity for vegetative propagation.     

Morphological responses of two plant species from different elevations in the Dongting Lake wetlands,China, to variation in water levels

The vegetation of wetlands show strong zonation patterns, but the mechanisms determining these patterns are not fully understood. In the present study, growth and morphological responses to a water level gradient (–20 cm (i.e. water level 20 cm below soil surface), –10 cm, 0 cm, 10 cm, 20 cm) were compared between a higher elevation plant (Imperata cylindrica) and a lower elevation plant (Carex brevicuspis) in the Dongting Lake wetlands of China. For both species, the aboveground, belowground, and total biomass were greater at –10 cm than at any other water level.. However, when the water level increased from –10 cm to 0 cm, there was a greater decrease in the biomass of I. cylindrica than in that of C. brevicuspis. Plant height, tiller number, leaf length, leaf width and leaf area showed greater variation along the water level gradient in I. cylindrica than in C. brevicuspis. Generally, with increasing water level, root length, rhizome number, and adventitious root biomass and number all decreased in I. cylindrica. However, in C. brevicuspis, neither the rhizome number nor the primary adventitious root biomass differed significantly among the five water levels. These results indicate that I. cylindrica have a lower tolerance for flooding and higher water sensitivity than C. brevicuspis and these differences may explain why I. cylindrica is found at relatively higher elevations that are not prone to flooding, while C. brevicuspis is found at comparatively lower elevations in the Dongting Lake wetlands.     

Responses of rhizomatous grass Phragmites communis to wind erosion: effects on biomass allocation

Background and aims

The ability of modifying biomass allocation to deal with different environmental stress is an important mechanism for plant population expansion and maintenance in the unstable dune environment where wind erosion persists. However, how biomass is partitioned between horizontal rhizome extension and vertical ramet growth in response to wind erosion has not been fully understood. The objective of this study was to explore how wind erosion affected the relationship between horizontal rhizome extension and vertical ramet growth using a common rhizomatous perennial grass, Phragmites communis.

Methods

We dug 300 cm?×?200 cm, 80 cm deep pits in a garden experiment plot. Clonal fragments of P. communis were planted individually at a depth of 40 cm in these pits for 4 weeks before treatments. Surface sand was gradually removed to the final depth of 0 (control), 10, 20, 30 and 40 cm (maximum sand removal). Ramet emergence time, rhizome-based and tiller-based ramet number, rhizome number and length, biomass of vertically and horizontally oriented structures were monitored at the end of the experiment.

Results

With increasing erosion depth, the proportion of tiller-based ramets (in total number of ramets) increased, whereas that of rhizome-based ramets decreased. With increasing erosion depth, the percentage of vertically oriented structures biomass in total biomass increased significantly, whereas that of horizontally oriented structures biomass decreased.

Conclusions

The changes in biomass allocation (i.e., more allocation in vertical than horizontal biomass) together with a trade-off in tiller-based and rhizome-based ramets may enable P. communis to make better use of the resources in erosion conditions and maximize plant population expansion and maintenance.     

Growth and Physiological Responses to Water Depths in Carex schmidtii Meinsh

A greenhouse experiment was performed to investigate growth and physiological responses to water depth in completely submerged condition of a wetland plant Carex schmidtii Meinsh., one of the dominant species in the Longwan Crater Lake wetlands (China). Growth and physiological responses of C. schmidtii were investigated by growing under control (non-submerged) and three submerged conditions (5 cm, 15 cm and 25 cm water level). Total biomass was highest in control, intermediate in 5 cm treatment and lowest in the other two submerged treatments. Water depth prominently affected the first-order lateral root to main root mass ratio. Alcohol dehydrogenase (ADH) activity decreased but malondialdehyde (MDA) content increased as water depth increased. The starch contents showed no differences among the various treatments at the end of the experiment. However, soluble sugar contents were highest in control, intermediate in 5 cm and 15 cm treatments and lowest in 25 cm treatment. Our data suggest that submergence depth affected some aspects of growth and physiology of C. schmidtii, which can reduce anoxia damage not only through maintaining the non-elongation strategy in shoot part but also by adjusting biomass allocation to different root orders rather than adjusting root-shoot biomass allocation.     

Sediment Burial Intolerance of Marine Macroinvertebrates

The marine environment contains suspended particulate matter which originates from natural and anthropogenic sources. Settlement of this material can leave benthic organisms susceptible to smothering, especially if burial is sudden i.e. following storms or activities such as dredging. Their survival will depend on their tolerance to, and their ability to escape from burial. Here we present data from a multi-factorial experiment measuring burial responses incorporating duration, sediment fraction and depth. Six macroinvertebrates commonly found in sediment rich environments were selected for their commercial and/or conservation importance. Assessments revealed that the brittle star (Ophiura ophiura), the queen scallop (Aequipecten opercularis) and the sea squirt (Ciona intestinalis) were all highly intolerant to burial whilst the green urchin (Psammichinus miliaris) and the anemone (Sagartiogeton laceratus), showed intermediate and low intolerance respectively, to burial. The least intolerant, with very high survival was the Ross worm (Sabellaria spinulosa). With the exception of C. intestinalis, increasing duration and depth of burial with finer sediment fractions resulted in increased mortality for all species assessed. For C. intestinalis depth of burial and sediment fraction were found to be inconsequential since there was complete mortality of all specimens buried for more than one day. When burial emergence was assessed O. ophiura emerged most frequently, followed by P. miliaris. The former emerged most frequently from the medium and fine sediments whereas P. miliaris emerged more frequently from coarse sediment. Both A. opercularis and S. laceratus showed similar emergence responses over time, with A. opercularis emerging more frequently under coarse sediments. The frequency of emergence of S. laceratus increased with progressively finer sediment and C. intestinalis did not emerge from burial irrespective of sediment fraction or depth. Finally, and perhaps unsurprisingly, the greatest ability to emerge from burial in all other species was from shallow (2 cm) burial. Although survival was consistently highly dependent on duration and depth of burial as expected, emergence behaviour was not as easily predictable thereby confounding predictions. We conclude that responses to burial are highly species specific and therefore tolerance generalisations are likely to be oversimplifications. These data may be used to inform environmental impact models that allow forecasting of the cumulative impacts of seabed disturbance and may provide mitigation measures for the sustainable use of the seabed.     

The sediment burial depth and salinity control the early developments of Suaeda salsa in the Yellow River Delta

Sediment deposition is a common phenomenon in the estuary area. Pot control experiments were conducted to evaluate the interaction effects of sediment burial depth and salt stress on the seed germination and early seedling growth of Suaeda salsa (L.) Pall., an pioneer species of tidal wetland near the Yellow River Delta. The results showed that the percentage of seedling emergence, seedling emergence rate, seedling height, branch number, shoot biomass and root biomass were all significantly affected by salt stress and sediment burial depth. While the interaction of salt and burial depth significantly influenced the branch number, leaf biomass, shoot biomass and total plant biomass. Only 5 cm burial depth without salt stress should 6.25 ± 3.61% seedlings emergence. With the increasing of sediment burial depth and salt stress, percentage of seedling emergence, seedling emergence rate and plant height decreased significantly. However, under the salt treatment of 0 and 1%, the branch number increased dramatically with the increasing of sediment burial depth from 0 to 3 cm. The ratio of leaf to total biomass increased with increasing of burial depth, on the contrary, the ratio of root to total biomass decreased. 0–1 cm sediment burial depth was proved the suitable depths for seed germination of S. salsa in the coastal wetland of the Yellow River Delta. Our findings contribute to a better understanding of how to improve the seedling establishment of S. salsa under the dynamic changes of sediment deposition and salinity in the coastal wetland of the Yellow River Delta.     

埋深和播种密度对豚草种子出苗及幼苗生长的影响

豚草是一种全球性的恶性入侵杂草,给我国生物多样性及经济发展造成了巨大威胁。为研究豚草种子出苗和幼苗生长的影响因素,采用盆栽实验分析了种子大小（L、M、S）与埋深（2、4 cm和6 cm）或播种密度（2、4粒/盆和8粒/盆）对豚草（Ambrosia artemisiifolia）种子的出苗和幼苗生长的影响。研究结果表明,埋深对豚草种子出苗的影响高于播种密度及种子大小的影响,较浅的埋深有利于豚草种子出苗;出苗率在不同播种密度下均具有较高水平,达到67.9%-100%,这种高出苗率是豚草在不同生境成功定植的原因之一。豚草的幼苗生长受埋深或播种密度的影响大于种子大小的影响,且小种子更易受埋深或播种密度的影响。种子大小显著影响豚草幼苗的株高和基径（P<0.05）,总体上较大种子的株高和基径高于小种子,此外更小的种子会将生物量更多的分配给根以促进幼苗的生长。幼苗的株高和基径在较浅的埋深下更高,而豚草幼苗的单株生物量、单株地上和地下生物量随埋深的增加而增加。播种密度的增加会加剧豚草幼苗之间对水分、营养、光照等资源的竞争,导致其单株地上、地下及总生物量显著降低（P<0.05）。研究发现豚草在浅埋深、低密度生境中更容易入侵成功,因此可以通过对土壤进行深翻,采取替代控制,种植竞争能力强的本地植物等手段有效管理和防治豚草。     

Assessment of Regeneration Potential in the Clonal Macrophyte Miscanthus sacchariflorus (Poaceae) after Burial Disturbance Based on Bud Bank Size and Sprouting Capacity

The demography of the bud bank and its sprouting capacity are important for understanding the population dynamics of clonal plants and their potential responses to disturbances. To this end, we investigated the size and composition of the bud bank of Miscanthus sacchariflorus (Maxim.) Hack. immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the wetlands of Dongting Lake. We then examined the sprouting capacity of axillary buds after sediment burial at 0, 5, 10, 15, and 20 cm. Total bud density of M. sacchariflorus ranged from 2524 buds m^-2 in November to 4293 buds m^-2 in March. Rhizome segments with inactive axillary buds, which represented the majority of the bud population (88.7% in November, 93.3% in May), did not sprout during the 140 days of the experiment (n = 250). The sprouting ratio was the highest for active axillary buds buried at 0 cm (64%) and decreased when buried at 10–20 cm (34%–40%). Due to the large number of active axillary buds in the bud bank (211–277 buds m^-2 from November to the following March), M. sacchariflorus could completely replace its aboveground shoot population, except in May (142 buds m^-2). Increasing burial depth delayed bud emergence and reduced the growth period of shoots; however, burial depth did not affect the resulting plant height and only reduced the accumulated biomass at 20 cm. Therefore, the belowground bud bank and its strong sprouting capacity are important factors in the maintenance of local populations and colonization of new habitats for M. sacchariflorus after burial disturbances. The present methodology, which combined measurements of bud bank demography and sprouting capacity, may reflect the regeneration potential of clonal plants after burial disturbances.     

Clonal integration enhances survival and performance of Potentilla anserina, suffering from partial sand burial on Ordos plateau, China

On Ordos plateau, a semi-arid, desertified area in China, sand burial is a common stress factor for plants. The extent to which sand burial occurs is heterogeneous and unpredictable in space and in time. Therefore, clonal fragments (i.e., interconnected ramets of a clonal plant) often experience partial sand burial, with some ramets buried in sand while the rest may remain unburied. It was hypothesized that clonal fragments are able to benefit from clonal integration, in case they experience partial sand burial. A pot experiment was conducted with Potentilla anserina, a stoloniferous herb often found on Ordos plateau. We used clonal fragments consisting of four interconnected ramets. In the experiment, the two proximal (older) ramets were unburied while the two distal (younger) ramets were either unburied (control) or buried with a 2, 4 or 6 cm deep layer of sand (burial treatments). The stolon connection between the proximal and the distal ramets was either severed or left intact. Stolon severing dramatically decreased the survival of buried ramets. Stolon severing and sand burial had significant effects on plant performance in terms of biomass production, number of leaves and leaf area. A cost–benefit analysis based on performance measures shows that the proximal ramets supported their connected distal ramets and did not incur any cost from this resource export. These results suggest that clonal integration, which is one of the functionally most important consequences of clonal growth, contributes significantly to our test species' capacity to withstand partial sand burial on Ordos plateau, a semi-arid and desertified area of China.     

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

In arid and semi-arid inland deserts, one of the environmental stresses for plants is recurrent sand burial, which can influence the physical and biotic microenvironments of the plants and soil. Previous studies have shown that different levels of sand burial have different effects on plants. Slight sand burial could increase the height increment, leaf biomass and the number of new ramets of the plants while heavy sand burial could impair the growth of the plants and even decrease their chances of survival. In other words, below a certain threshold level of burial, the growth of plants is stimulated probably because of multiple factors. However, as the level of burial increases, the positive response starts to decline until it becomes a negative value. Arid and semi-arid inland deserts are frequently colonized and stabilized by many rhizomatous clonal plants. Clonal physiological integration often helps clonal plants buffer local environmental stress encountered by ramets. A rhizomatous clonal semishrub, Hedysarum laeve (H. laeve), is the dominant plant species and important for vegetation restoration in the Mu Us sandland. To investigate whether clonal integration can increase the threshold of sand burial and help rhizomatous H. laeve tolerate heavy sand burial, we conducted a field experiment. The results showed that slight sand burial could accelerate ramet growth and enhance leaf biomass, stem biomass and shoot biomass, while heavy sand burial reducesed the biomass of the plant and impairs survival and growth of the ramets. Clonal integration increased the threshold of sand burial. Under heavy sand burial, ramets connected to other ramets not buried in sand were more in terms of height increment, stem biomass, leaf biomass and shoot biomass compared to the ramets encountering sand burial but disconnected from other ramets. It suggested that clonal physiological integration could help H. laeve ramets tolerate relatively heavy sand burial. We also discussed that clonal integration plays a role in H. laeve presence in the Mu Us sandland. __________ Translated from Journal of Plant Ecology (formerly Acta Phytoecologica Sinica), 2006, 30(2): 278–285 [译自: 植物生态学报]     

Manganese tolerance and accumulation in six Mn hyperaccumulators or accumulators

This study used hydroponics cultivation to investigate the manganese (Mn) accumulation and tolerance abilities of six species—Phytolacca americana L., Poa annua L., Comnyza canadensis L., Cynodon dactylon L., Polygonum hydropiper L., and Polygonum perfoliatum L. We found that P. perfoliatum, P. hydropiper, and P. americana were Mn-hyperaccumulators and that P. perforliatum have superior Mn accumulation and toleration abilities over the other five species. The Mn concentration within the shoots of P. perfoliatum reached as high as 18,342.3 mg kg^?1. The root growth of P. perfoliatum was promoted under low-Mn treatments, but the growths of the five other species were inhibited by the Mn treatments and the damage intensified as Mn concentration increased. The biomass of P. perfoliatum was minimally affected by the Mn treatments. The chlorophyll (CHL), soluble protein (SP), and malondialdehyde (MDA) contents of P. perfoliatum were not adversely affected, but these parameters of the other five species showed significant (P?<?0.05) deterioration from the control. By comparison among the six species, the hyperaccumulator P. perfoliatum was the most suitable species for bioremediation of Mn-polluted environments. However, the findings need further study in soil cultivation.     

Burial depth and diameter of the rhizome fragments affect the regenerative capacity of a clonal shrub

Clonal plants in highly disturbed habitats are often broken into small fragments of various sizes and buried at various soil depths. As a storage organ, rhizome fragments play an important role in enabling plants to survive in such habitats. But few studies have been concerned about the regenerative capacity of rhizome fragments of clonal shrubs of different rhizome diameter and at different burial depths. Here, we investigated whether deeper burial decreased, and diameter of the rhizome fragment increased, the regenerative capacity of a clonal shrub. Research samples of rhizome fragment (rhizome diameters of 2, 5, 10, 15, and 20 mm) of the clonal shrub Calligonum arborescens were buried at different depths (0, 1, 5, 10, and 20 cm). Increasing the diameter of the rhizome fragments significantly increased the survival rate of fragments, and increased the above-ground, below-ground and total biomass production of fragments. Vegetative reproduction ability also increased with an increase in diameter of the rhizome fragments. With an increase in sand burial depth, above-ground, below-ground, total biomass production and vegetative reproduction ability first decreased and then increased, and no fragments survived at the 0 cm burial depth. These results indicate that sand burial depth and diameter of the rhizome fragments significantly affected the regeneration capacity of C. arborescens. Sand burial is one of the essential prerequisites for C. arborescens rhizome fragments’ survival. Moderate burial depth (5 cm) and larger fragment diameter (20 mm diameter) were more suitable for biomass production and vegetative reproduction. These results indicate that reserves stored in rhizome fragments can contribute greatly to the regeneration capacity of the C. arborescens—responses that are very important for C. arborescens survival and establishment in frequently disturbed habitats.     

Growth responses and non-structural carbohydrates in three wetland macrophyte species following submergence and de-submergence

We investigated the responses of growth and non-structural carbohydrates to submergence and de-submergence in three wetland macrophyte species. Survival rate, recovery ability, and soluble sugar and starch contents of flood-tolerant Polygonum hydropiper and of flood-sensitive Phalaris arundinacea and Carex argyi from Dongting Lake wetlands were investigated after 20, 40, and 60 days of complete submergence without light and 10 days after de-submergence. Plant dry weight and soluble sugar and starch contents decreased in all species during the submergence period. The decreases were slowest in P. hydropiper, intermediate in C. argyi, and most rapid in P. arundinacea. After 60 days of submergence, survival rates were 100, 50, and 0 % in P. hydropiper, C. argyi, and P. arundinacea, respectively. After recovery, plant dry weight increased in P. hydropiper and in C. argyi, but decreased in P. arundinacea. Compared to pre-submergence, soluble sugar contents generally increased and then remained relatively constant after recovery in all species, while starch content increased in P. hydropiper and decreased in P. arundinacea with increasing submergence time. For C. argyi, starch content decreased after recovery from the 20-day submergence, but increased after recovery from the 40- and 60-day submergences. These data illustrate mechanisms behind the flood tolerance of P. hydropiper and the sensitivity to flooding in P. arundinacea and C. argyi. These mechanisms include lower consumption and quicker accumulation of non-structural carbohydrates in flood-tolerant plants.     

Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.     

Differential effects of water depth and sediment type on clonal growth of the submersed macrophyte <Emphasis Type="Italic">Vallisneria natans</Emphasis>

The response of clonal growth and ramet morphology to water depth (from 60 to 260 cm) and sediment type (sand versus organic clay) was investigated for the stoloniferous submersed macrophyte Vallisneria natans in an outdoor pond experiment. Results showed that water depth significantly affected clonal growth of V. natans in terms of clone weight, number of ramets, number of generations, clonal radius and stolon length. V. natans showed an optimal clonal growth at water depths of 110–160 cm, but at greater depths clonal growth was severely retarded. A high allometric effect was exhibited in ramet morphology. Along the sequentially produced ramet generations, ramet weight and plant height decreased while stolon length and the root:leaf weight ratio increased. When using ramet generations as covariate, sediment type rather than water depth more strongly affected the ramet characteristics. For plants grown in clay, ramet weight, ramet height and stolon length were greater, and plants exhibited lower root:leaf weight ratio. These data suggest that water depth and sediment type have differential effects on clonal growth of V. natans: Water depth appears primarily to affect numerical increase in ramets and spatial spread, whereas sediment type mainly affects biomass accumulation and biomass allocation. Handling editor: S. M. Thomaz     

Spacer elongation and plagiotropic growth are the primary clonal strategies used by Vallisneria spiralis to acclimate to sedimentation

The aim of this study is to identify how submerged macrophyte Vallisneria spiralis acclimate to sedimentation by investigating the growth, biomass allocation and clonal characteristics in a greenhouse experiment of 30 days. Experimental treatments combined two sediment types (mud and sand) with four sedimentation depths (0, 2, 4 and 8 cm) in a factorial design. Biomass accumulation (0.98–1.33 versus 0.36 g per plant) and relative growth rate (RGR, 0.082–0.093 versus 0.046 g g⁻¹ day⁻¹) decreased only in the 8 cm sand treatment. Neither sedimentation depth nor sediment type influenced biomass allocation. The ratio of spacer length to biomass was significantly higher in the 8 cm sand (20.4 cm g⁻¹) than in other treatments (6.0–8.5 cm g⁻¹). Branching angles and the depths between ramet basal and sediment surface were only affected by sedimentation depth. Clonal ramets developed nearly vertical branching angles (ranged from 78° to 101°) in the 0 cm sedimentation treatment, but the angles of treated plants decreased at the initial 3–5 ramets (ranged from 68° to 78° at the first ramet level), then remained a relatively constant value (about 90°) in the following spacers. These data indicate that plagiotropic stolons were formed to project the ramets to sediment surface and to escape sedimentation stress primarily by elongating spacer length and decreasing branching angle, rather than by adjusting biomass allocation.