松嫩平原野古草种群构件结构动态

野古草是根茎型无性系禾草,在松嫩平原草甸经常形成单优种群落。采用单位面积挖掘取样、分株按营养繁殖世代划分龄级、根茎按实际生活年限划分龄级的方法,对松嫩平原单优群落和混生群落的野古草种群构件结构进行了调查与分析。结果表明,在生长季初期两群落野古草种群均以春性分株和根茎芽占优势,且分株及芽构件结构相对稳定,芽库的输出率单优群落为80.4%,混生群落为62.5%;整个生长季分株由2—3个龄级组成,1a分株数量是2a的2.9—10.2倍,其生物量各月份所占比例平均为93%,随着龄级的增加依次明显减少,呈增长型年龄结构;根茎由3—4个龄级组成,根茎累积长度及生物量均以2a占绝对优势,为稳定型年龄结构;分株生产力1a明显高于2a,对种群贡献最大;根茎贮藏力除个别月份以3a、4a最高外,两群落大部分以2a最高,在生长季后期,1a根茎物质积累的速率最快。     

Negative Plant–Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community

Increasing evidence shows that facilitative interaction and negative plant–soil feedback are driving factors of plant population dynamics and community processes. We studied the intensity and the relative impact of negative feedback on clonal growth and seed germination of Scirpus holoschoenus, a ‘ring’ forming sedge dominant in grazed grassland, and the consequences for species coexistence. The structure of aboveground tussocks was described. A Lithium tracer assessed belowground distribution of functional roots. Seed rain and seedling emergence were compared for different positions in relation to Scirpus tussocks. Soil bioassays were used to compare growth on soil taken from inside and outside Scirpus tussocks of four coexisting species (Mentha acquatica, Pulicaria dysenterica, Scirpus holoschoenus and Dittrichia viscosa). We also compared plant performance of dominant plant species inside and outside Scirpus tussocks in the field. The ‘ring’ shaped tussocks of S. holoschoenus were generated by centrifugal rhizome development. Roots were functional and abundant under the tillers and extending outside the tussocks. The large roots mats that were present in the inner tussock zone were almost all dead. Seedling emergence and growth both showed a strong negative feedback of Scirpus in the inner tussock zone. Scirpus clonal development strongly reduced grass biomass. In the degenerated tussock zone, Pulicaria and Mentha mortality was lower, and biomass of individual plants and seed production were higher. This positive indirect interaction could be related to species-specific affinity to soil conditions generated by Scirpus, and interspecific competitive release in the degenerated tussock zone. We conclude that Scirpus negative feedback affects its seedling emergence and growth contributing to the development of the degenerated inner tussock zone. Moreover, this enhances species coexistence through facilitative interaction because the colonization of the inner tussock zone is highly species-specific.     

扎龙湿地不同生境芦苇种群根茎数量特征及动态

采用单位土体取样,计测长度和生物量的调查与统计方法,对扎龙湿地保护区4个生境芦苇种群根茎数量特征进行比较分析。结果表明,芦苇5月10日左右返青后进入营养生长期,根茎长度6—8月份缓慢增加,8—10月份显著增加,后期是前期的3.5—10.3倍,生长季中后期是种群新根茎补充和生长的主要时期,不仅实现了种群空间扩展,并为营养繁殖储备更多繁殖芽;根茎生物量和干物质贮量6—8月份逐渐减少,8—10月份又逐渐增加,均以生长季末期的10月份最大,并均显著地(P0.05)高于其他月份,种群根茎养分的消耗主要供给根茎芽的萌发和幼株生长,根茎养分的储藏又为翌年种群的更新及扩展提供物质保障,种群对地下根茎存在明显的养分"超补偿性"贮藏现象。种群根茎长度和生物量均以湿生生境最大,依次为旱生生境、水生生境,盐碱生境最小,根茎干物质贮量以旱生生境最大,依次为湿生生境、水生生境,盐碱生境最小。种群根茎长度与返青后实际生长时间之间均较好地符合直线函数关系,种群根茎生物量和干物质贮量与生长时间之间较好地符合二次曲线函数关系,R2在0.804—0.997之间,拟合方程均达到了显著或极显著(P0.01)水平。4个生境芦苇种群在根茎长度、生物量、干物质贮量等数量特征均表现出由遗传因素控制的比较稳定的季节动态规律,在生境间的差异及其差异序位又均基本稳定,均表现出明显的土壤因子环境效应,其中土壤含水量、有机质、速效氮为正向驱动,p H、速效磷为负向驱动,土壤含水量、p H对根茎数量特征的驱动作用更突出。     

Comparison of Belowground Biomass in C3- and C4-Dominated Mixed Communities in a Chesapeake Bay Brackish Marsh

Belowground biomass is a critical factor regulating ecosystem functions of coastal marshes, including soil organic matter (SOM) accumulation and the ability of these systems to keep pace with sea-level rise. Nevertheless, belowground biomass responses to environmental and vegetation changes have been given little emphasis marsh studies. Here we present a method using stable carbon isotopes and color to identify root and rhizomes of Schoenoplectus americanus (Pers.) Volk. ex Schinz and R. Keller (C₃) and Spartina patens (Ait.) Muhl. (C₄) occurring in C₃− and C₄-dominated communities in a Chesapeake Bay brackish marsh. The functional significance of the biomass classes we identified is underscored by differences in their chemistry, depth profiles, and variation in biomass and profiles relative to abiotic and biotic factors. C₃ rhizomes had the lowest concentrations of cellulose (29.19%) and lignin (14.43%) and the lowest C:N (46.97) and lignin:N (0.16) ratios. We distinguished two types of C₃ roots, and of these, the dark red C₃ roots had anomalously high C:N (195.35) and lignin:N (1.14) ratios, compared with other root and rhizome classes examined here and with previously published values. The C₄-dominated community had significantly greater belowground biomass (4119.1 g m⁻²) than the C₃-dominated community (3256.9 g m⁻²), due to greater total root biomass and a 3.6-fold higher C₃-root:rhizome ratio in the C₄-dominated community. C₃ rhizomes were distributed significantly shallower in the C₄-dominated community, while C₃ roots were significantly deeper. Variability in C₃ rhizome depth distributions was explained primarily by C₄ biomass, and C₃ roots were explained primarily by water table height. Our results suggest that belowground biomass in this system is sensitive to slight variations in water table height (across an 8 cm range), and that the reduced overlap between C₃ and C₄ root profiles in the C₄-dominated community may account for the greater total root biomass observed in that community. Given that future elevated atmospheric CO₂ and accelerated sea-level rise are likely to increase C₃ abundance in Atlantic and Gulf coast marshes, investigations that quantify how patterns of C₃ and C₄ belowground biomass respond to environmental and biological factors stand to improve our understanding of ecosystem-wide impacts of global changes on coastal wetlands.     

扎龙湿地芦苇种群不同龄级根茎构件的季节动态

克隆植物根茎具有营养繁殖和扩展种群的功能,也是芽和分株生理整合的通道。根茎构件具有出生、死亡及年龄等种群统计特征,不同龄级根茎的季节动态可以反映根茎的存活和衰老过程。采用单位土体挖掘取样,对扎龙湿地4个生境芦苇种群根茎构件进行野外调查,比较不同龄级根茎长度、生物量和干物质贮量的季节动态。结果表明:7—10月份,1a根茎长度、生物量和干物质贮量均呈指数函数增加,在生长季中后期有一个持续时间较长的生长和物质积累时期。6—10月份,2a、3a根茎长度呈线性函数增加,4—6a根茎长度呈线性函数减少;2—4a根茎生物量和2—5a根茎干物质贮量呈二次函数先减少后增加,5a、6a根茎生物量和6a根茎干物质贮量呈幂函数减少。整个生长期内,根茎长度和根茎生物量均以3a最大,根茎长度以最高的6a最小,根茎生物量以最低的1a最小;根茎干物质储量以5a最大,以最低的1a最小。4个生境芦苇种群根茎长度、生物量和干物质贮量在龄级间的差异及差异序位稳定,在新根茎的产生、老根茎的存活以及根茎寿命与养分消耗和储藏上均具有稳定的生物学特性,不同龄级根茎在种群中的地位和作用以及对种群的贡献不同。     

Relationship between morphological and physiological responses to waterlogging and salinity in Sporobolus virginicus (L.) Kunth

The effects of waterlogging and salinity on morphological and physiological responses in the marsh grass Sporobolus virginicus (L.) Kunth were investigated in a 4×2 factorial experiment. Plants were subjected to four salinity levels (0, 100, 200 and 400 mol m^–3 NaCl) and two soil inundation conditions (drained and flooded) for 42 days. Flooding at 0 mol m^–3 NaCl caused initiation of adventitious surface roots, increased internal acration and plant height, induced alcohol dehydrogenase activity (ADH), and decreased belowground biomass and the number of culms per plant. Salinity increase from 0 to 400 mol m^–3 NaCl under drained conditions increased leaf and root proline concentrations and decreased photosynthesis, aboveground biomass, number of culms per plant and number of internodes per culm. Concurrent waterlogging and salinity induced ADH activity and adventitious surface roots but decreased plant height and aboveground biomass. Internal air space increased with waterlogging from 0 to 100 mol m^–3 NaCl but further increases in salinity to 400 mol m^–3 reduced air space. Combined waterlogging and salinity stresses, however, had no effect on photosynthesis or on the concentrations of proline in leaves or roots. These results are discussed in relation to the widespread colonization by S. virginicus of a wide range of coastal environments varying in soil salinity and in the frequency and intensity of waterlogging.     

Resprouting after disturbance in the short-lived herb Rorippa palustris (Brassicaceae): an experiment with juveniles

The impact of plant age, severity of injury and nutrient levels on the ability to resprout from roots was experimentally assessed in juveniles of the short-lived herb Rorippa palustris (L.) Besser. In a chamber experiment, six cohorts of young plants (1–6 week old) were injured to obtain data on the threshold age for the ability to resprout from roots. We found that plant age was an important factor influencing resprouting ability: injured individuals older than 5 weeks were able to resprout, but not plants younger than 3 weeks. The impact of injury severity (defoliation and removal of axillary buds) and nutrient levels on resprouting ability was assessed on juveniles in a greenhouse experiment. Injury induced growth of new shoots from root buds, while the number of adventitious buds on roots was not influenced by injury. Both injury treatments had a similar effect in this respect, and the amount of regenerated biomass and the extent of regeneration were not different among injury treatments. The number of new shoots produced after injury was higher at the high nutrient level, but the number of formed adventitious buds on roots was not influenced by nutrient level. Nutrient level also influenced the amount of regenerated biomass, but the extent of regeneration (regenerated/removed biomass) was not influenced. The short-lived monocarpic species R. palustris is able to resprout from roots relatively easily. This ability seems to be advantageous in disturbed habitats and this idea is discussed throughout the paper.     

Predicting the Effectiveness of <Emphasis Type="Italic">Phragmites</Emphasis> Control Measures using a Rhizome Growth Potential Bioassay

In the last century, Phragmites australis (common reed) has expanded from a minor component of the mid-Atlantic tidal wetlands to a dominant species in many locations. Expansion of Phragmites results in decreased plant diversity and alterations to the tidal characteristics of the marsh, resulting in decreased wetland value. Management efforts have used a variety of strategies in an attempt to control its expansion. We tested a greenhouse bioassay that provided insight into the rhizome vitality of six herbicide-treated sites in the Alloway Creek Watershed, NJ well in advance of the growing season. At three sites, rhizomes were exhumed and classified by depth (0–25 cm and 25–75 cm) and appearance (color and firmness). Concurrently, the same protocol was followed, but conducted on an areal basis at three additional sites. Material was grown in sand under greenhouse conditions void of nutrient supplements for 70 days, after which shoots were removed and the rhizomes replanted for 30 days. Effectiveness of control strategies was quantified by examining rhizome color, vitality, and shoot densities in the field. Color was indicative of quality of rhizome reserves. Less than 0.2% of the firm, brown rhizomes produced shoots upon initial planting and none produced shoots upon replanting, whereas 50.9% of white rhizomes produced shoots on initial planting. Rhizome vitality was quantified by examining shoot emergence and the morphology of the shoots. Coupling rhizome vitality with observed field densities resulted in a predictive capability, and shoot density and biomass predictions were compared to field measurements in July 2001. We tested and accurately predicted the relative shoot densities and shoot biomass of the three sites for which we collected rhizome material on an areal basis. The result is a rapid, valuable, and cost-effective monitoring tool that can quickly quantify the effects of past control methods and predict future growth potential.     

Nitrogen sequestration capacity of two salt marshes from the Tagus estuary

The role of salt marshes as nitrogen sink is examined taking into consideration the seasonal variation of above and belowground biomass of Spartina martima and Halimione portulacoides in two marshes from Tagus estuary, Pancas and Corroios, and the degradation rates of belowground litter. Total nitrogen was determined in plant components, decomposing litter and sediment. Biomass was higher in Corroios, the saltier marsh, with 7190 g m⁻² y⁻¹ dw of S. maritima and 6593 g m⁻² y⁻¹ dw of H. portulacoides and the belowground component contributed to 96% and 90% of total biomass, respectively. In the other marsh, Pancas, belowground biomass contributed to 56% and 76% of total biomass for S. maritima and H. portulacoides, respectively. Litterbag experiment showed that between 25% and 50% of nitrogen is lost within the first month and remained relatively constant in the next four months. Slower decomposition is observed in sediments with higher nitrogen concentration (max. 0.7% N in the saltier marsh). Higher concentrations of N were found in the sediment upper layers. Considering the sediment-root system, most of the nitrogen is stored in the sediment compartment and only about 1–4% of the total N was found in the roots. Considering these results, Tagus salt marshes act as a sink for nitrogen.     

Floral induction and development in Phalaenopsis in vitro

Adventitious shoots formed from nodal sections of floral-stalks of Phalaenopsis Pink Leopard Petra that had been propagated on Hyponex medium with 6-benzyladenine (BA). After subculturing adventitious shoots on Vacin-Went medium with BA, more than 70% of the shoots formed floral buds, and 10% of the floral buds flowered in 9-month-old shoots. Floral buds were not formed on the adventitious shoots cultured on Vacin-Went medium lacking BA. A high concentration of total nitrogen inhibited the development of floral buds, and low-temperature treatments failed to induce the formation of floral buds in vitro.     

Rapid in vitro adventitious shoot propagation of <Emphasis Type="Italic">Scopolia parviflora</Emphasis> through rhizome cultures for enhanced production of tropane alkaloids

A rapid micropropagation system for Scopolia parviflora Nakai (Solanaceae), a rare medicinal plant native to Korea, was established using rhizome cultures. Shoots that originated from adventitious shoots of the rhizome were multiplied when the rhizomes were cultured on half-strength B5 liquid medium supplemented with various growth regulators. Optimum shoot multiplication was observed in half-strength B5 medium containing 3% (w/v) sucrose and 5.77 M gibberellic acid (GA₃). Each rhizome gave rise to an average of 12 shoots. Shoot elongation and root induction from multiple shoots occurred on growth regulator-free half-strength B5 solid medium. Healthy plantlets were transferred to a peat moss:vermiculite mixture for acclimatization, which was successful. The concentrations of tropane alkaloids, hyoscyamine and scopolamine were determined in different tissues of native growing plants, in vitro-propagated plants and acclimatized plants by high-performance liquid chromatography. The analysis revealed that the levels of hyoscyamine and scopolamine were higher in in vitro-propagated plants than in the native growing plants. When the rhizome was cut into segments and transferred to optimal culture conditions for multiple shoot propagation, only 12 weeks were required to produce a mature plant. We conclude that in vitro propagation techniques through rhizome cultures provide an efficient and rapid method for shoot propagation of S. parviflora.Abbreviations BA Benzyladenine - 2,4-D 2,4-Dichlorophenoxyacetic acid - GA₃ Gibberellic acid - HPLC High-performance liquid chromatography - IBA Indole-3-butyric acid - NAA -Naphthaleneacetic acid     

Root and rhizome distribution as an indicator of upper salt marsh wetland limits

Four wetland plant species, Deschampsia cespitosa, Distichlis spicata, Grindelia integrifolia, and Salicornia virginica, were tested to determine the effect of soil moisture on the vertical distribution of roots and rhizomes. In an 8-month greenhouse experiment involving plants grown from seeds and rhizomes the occurrence of more than 65% of the root and rhizome mass in the upper 10 cm of soil was indicative of saturated conditions. Roots and rhizomes were more evenly distributed under field capacity and low moisture conditions. The percent of total root and rhizome biomass in the upper 10 cm of a 35 cm core may be useful in determining whether or not a plant is experiencing saturated soil conditions, a criterion often used for defining wetlands. Limited field studies support the conclusion of the greenhouse study.     

Rhizome dynamics and resource storage in Phragmites australis

Seasonal changes in rhizome concentrations of total nonstructural carbohydrates (TNC), water soluble carbohydrates (WSC), and mineral nutrients (N, P and K) were monitored in two Phragmites australis stands in southern Sweden. Rhizome biomass, rhizome length per unit ground area, and specific weight (weight/ length ratio) of the rhizomes were monitored in one of the stands.Rhizome biomass decreased during spring, increased during summer and decreased during winter. However, changes in spring and summer were small (< 500 g DW m-2) compared to the mean rhizome biomass (approximately 3000 g DW m^–2). Winter losses were larger, approximately 1000 g DW m-2, and to a substantial extent involved structural biomass, indicating rhizome mortality. Seasonal changes in rhizome length per unit ground area revealed a rhizome mortality of about 30% during the winter period, and also indicated that an intensive period of formation of new rhizomes occurred in June.Rhizome concentrations of TNC and WSC decreased during the spring, when carbohydrates were translocated to support shoot growth. However, rhizome standing stock of TNC remained large (> 1000 g m^–2). Concentrations and standing stocks of mineral nutrients decreased during spring/ early summer and increased during summer/ fall. Only N, however, showed a pattern consistent with a spring depletion caused by translocation to shoots. This pattern indicates sufficient root uptake of P and K to support spring growth, and supports other evidence that N is generally the limiting mineral nutrient for Phragmites.The biomass data, as well as increased rhizome specific weight and TNC concentrations, clearly suggests that reloading of rhizomes with energy reserves starts in June, not towards the end of the growing season as has been suggested previously. This resource allocation strategy of Phragmites has consequences for vegetation management.Our data indicate that carbohydrate reserves are much larger than needed to support spring growth. We propose that large stores are needed to ensure establishment of spring shoots when deep water or stochastic environmental events, such as high rhizome mortality in winter or loss of spring shoots due to late season frost, increase the demand for reserves.     

Micropropagation of seed-derived plants ofCynara scolymus L., cv. ‘Green Globe’

Growth of Cymbidium kanran rhizome was enhanced by higher NAA:BAP ratios in modified Murashige & Skoog (MS) media. Only vegetative shoots resulted from rhizomes cultured in vitro when lower NAA:BAP ratios were used. The rhizomes were induced from the axils of leaves when shoots were explanted to medium containing higher concentrations of NAA. Root formation of C. kanran was inhibited by the addition of either auxin or cytokinin to the culture media. Differentiation of the rhizomes into plantlets occurred when the concentrations of ammonium nitrate and potassium nitrate in MS medium wewe reduced. The modified MS medium containing lesser amounts of potassium nitrate and ammonium nitrate than those of the original MS media, and was optimal for the production of plantlets from rhizomes of C. kanran without addition of auxin and cytokinin.Abbreviations NAA -naphthaleneacetic acid - BAP N⁶-benzylaminopurine - MS medium Murashige & S Skoog medium     

Habitat modification by the stream macrophyte Justicia americana and its effects on biota

We conducted an in-stream experiment to determine if and by what mechanisms the emergent macrophyte, Justicia americiana, enhances streambed stability and influences associated benthic organisms. Treatments included removal of aboveground stems, removal of stems and rhizomes, and a control. Stone stability and embeddedness were higher within intact patches of Justicia compared with areas where stems and rhizomes were removed. Presence of belowground structures binding stones and higher embeddedness were responsible for differences in stone stability among treatments. Sediment deposition was highly variable among treatments; however, silt and clay deposition was highest in the control when Justicia stems reached maximum biomass. Response of neighboring benthic organisms to Justicia treatments varied with organism mobility and trophic level. Sedentary unionid mussels were more abundant in the control than in the stem and rhizome-removal treatment, whereas abundance of mobile snails (Elimia ucheensis) and sessile plants (Podostemon ceratophyllum and mosses) did not differ among treatments. Justicia appears to modify the stream environment by: (1) increasing stability of streambed sediments, and (2) reducing current velocity, thereby enhancing deposition of fine sediments and organic matter.     

Effects of rhizome age on the decomposition rate of Phragmites australis rhizomes

The change in dried rhizome samples that were left to decompose was investigated to elucidate the effects of rhizome age on the decomposition rate of Phragmites australis. Rhizomes were classified into five age categories and placed 30 cm below the soil surface of a reed stand. After 369 days of decay, new (i.e., aged less than one year) rhizomes had lost 84% of their original dry mass, compared with a loss of 41–62% for that of older rhizomes. The exponential decay rates of older rhizomes were nearly identical to that of aboveground biomass. The nitrogen (N) concentration increased to two times its original values, but the phosphorus (P) concentration remained constant after an initial loss by leaching. The carbon to nitrogen (C:N) and carbon to phosphorus ratios (C:P) leveled out at 22:1 to 38:1 and 828:1 to 1431:1, respectively, regardless of rhizome age. The results are important to understand the nutrient cycles of reed-dominant marsh ecosystems.     

Density- and growth stage-dependent responses to defoliation in two rhizomatous grasses

Summary Responses to defoliation were studied in two tallgrass prairie perennials (Andropogon gerardii and Panicum virgatum) established from seed at three densities. P. virgatum was also grown from transplanted rhizomes of established clones. Plants of both species displayed a continuum of responses to defoliation, from large reductions in biomass, tillering and seed production to significant increases in one or more performance measures. In crowded populations, defoliation shifted plants into subordinate positions within the competitive hierarchy. Plants competing intraspecifically and those that were initially small suffered more from defoliation than either plants grown at low density or those that were larger than their neighbors. At the highest plant density, the effects of defoliation or initial plant size were overshadowed by the effects of crowding. When defoliated and grown at similar densities, P. virgatum and A. gerardii grown from seed showed large reductions in biomass, seed production, and new rhizome production, but established P. virgatum ramets grown from rhizomes showed increases in these performance measures. Thus, herbivory may be particularly detrimental to P. virgatum during juvenile stages before perennating organs have developed. Overcompensation of P. virgatum clones in response to defoliation only occurred if all ramets within the clone were defoliated. In clones containing both defoliated and undamaged ramets, there were no differences in their performance, suggesting that genets are capable of integrating the effects of differential defoliation among shoots. Defoliated P. virgatum clones allocated a smaller fraction of their total biomass to new rhizomes, indicating that the short-term regrowth response following defoliation may incur a longer-term cost associated with gradual reduction in biomass of the perennating organs and reduced genet success.     

How does spittlebug oviposition affect shoot growth and bud production in two willow species?

We measured the effects of oviposition by the spittlebug Aphrophora pectoralis on shoot growth and bud production in two willow species, Salix miyabeana and Salix sachalinensis. In autumn, adult females of A.pectoralis insert their ovipositor into the apical region of 1-year-old shoots, resulting in the death of most shoot tips within 1week. Consequently, an increase in the number of dead buds and a decrease in the number of vegetative buds on 1-year-old shoots was recorded. In the following spring, the growth of current-year shoots was greatly increased on 1-year-old shoots damaged by spittlebug oviposition. Furthermore, spittlebug oviposition increased the production rate of vegetative buds in both S.miyabeana and S.sachalinensis. However, no impact on the production rate of reproductive buds was detected in either willow. We conclude that the compensatory growth of current-year shoots and an increase in vegetative buds in the two willow species was caused by oviposition of A.pectoralis.     

Primary production and nutrient budgets of Sarcocornia perennis ssp. alpini (Lag.) Castroviejo in the salt marsh of the Palmones River estuary (Southern Spain)

Biomass, primary production and nutrient budgets associated to Sarcocornia perennis subspecies (ssp.) alpini were studied in the Palmones River estuary salt marsh (Southern Spain) to evaluate the nutrient sequestration capacity of the low marsh. Above- and belowground living and dead biomass, as well as carbon, nitrogen and phosphorus content were monitored during 1 year. Additionally, the fate of aboveground detritus was evaluated in an experiment on litter decomposition. The detritus production of S. perennis ssp. alpini was almost equivalent to its annual primary production indicating a rapid turnover of biomass. We calculated that only 12% of the aboveground detritus was exported out of the low marsh while the rest was decomposed in the sediment with a rate of 0.8 year⁻¹. Changes in concentrations of total carbon, nitrogen and phosphorus in the sediment showed patterns related to S. perennis ssp. alpini belowground biomass. Our results suggested that the sediment functions as a net sink for nutrients accumulating 550 g C m⁻² year⁻¹, 55 g N m⁻² year⁻¹, and 13 g P m⁻² year⁻¹.     

Influence of hydrological fluctuations on the growth and nutrient dynamics ofPhalaris arundinacea L. in a riparian environment

Seasonal changes in aboveground and belowground tissues ofPhalaris arundinacea L. were studied in a population colonizing an ancient meander of the Garonne river (France) submitted to important fluctuations of the permanent water table. Waterlogged conditions in spring stopped the growth of rhizomes and promoted the translocation of nutrient to the shoots. The early senescence of plants after flowering could be related to the withdrawal of the water table. It was characterized by a distribution of nutrients in belowground tissues and a release in litter and soil. Aerated conditions in late summer permitted the growth of belowground tissues. At this time a partition of resources between aboveground and belowground biomass of a new generation of plants was observed. Rising water and decreasing temperatures in winter induced the death of aboveground parts. Reconstitution of nutrient stocks in rhizomes and losses by leaching then occured. Beside a very high primary production this strategy confers toPhalaris arundinacea a great interest in different uses, especially in the removal of nutrients from water in riparian zones as in artificial sites.