adaptation strategies in wetland plants: links between ecology and physiology. proceedings of a...

Rhizome Architecture in Phragmites Australis in Relation to Water Depth: Implications forWithin-Plant Oxygen Transport DistancesAuthor(s): Stefan E. B. Weisner and John A. StrandSource: Folia Geobotanica & Phytotaxonomica, Vol. 31, No. 1, Adaptation Strategies in WetlandPlants: Links between Ecology and Physiology. Proceedings of a Workshop (1996), pp. 91-97Published by: SpringerStable URL: http://www.jstor.org/stable/4181420 .

Accessed: 15/06/2014 21:35

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Springer is collaborating with JSTOR to digitize, preserve and extend access to Folia Geobotanica&Phytotaxonomica.

http://www.jstor.org

This content downloaded from 185.44.78.129 on Sun, 15 Jun 2014 21:35:18 PMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=springer

http://www.jstor.org/stable/4181420?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


Folia Geobot. Phytotax. 31: 91-97, 1996

RHIZOME ARCHITECTURE IN PHRAGMITES AUSTRALIS IN RELATION TO WATER DEPTH: IMPLICATIONS FOR WITHIN-PLANT OXYGEN TRANSPORT DISTANCES

Stefan E.B. Weisner') & John A. Strand

Limnology, Department of Ecology, Lund University, Ecology Building, S-223 62 Lund, Sweden; fax +46 462224003, 1) tel. +46 462228435, E-mail: [email protected]

Keywords: Clonal plants, Growth strategy, Littoral zone, Vegetative spreading, Wetland vegetation

Abstract: Phragmites australis (CAV.) TRIN. ex STEUD. is a perennial plant, largely relying on its rhizomes for resource storage, spreading and anchorage in the substrate. Vertical distribution and length of horizontal rhizomes of Phragmites australis were investigated at the reed bed edge in a lake in southern Sweden. In deep water, horizontal rhizomes were relatively short and superficially situated in the substrate. It is hypothesised that this is an adaptation to water depth by keeping 02-transport distances through shoots and rhizomes as short as possible. In shallow water, P australis rhizomes generally penetrated deeply into the substrate, probably improving anchorage and nutrient uptake possibilities. Further, horizontal rhizomes were longer in shallow water, which may increase the rate of vegetative spread. Because of these changes in rhizome architecture, "critical within-plant oxygen transport distances" did not change with water depth. This indicates that P australis maximises the extension of its rhizomes in relation to spatial differences in water depth. This may limit the ability of P. australis to tolerate sudden temporal increases in water depth or eutrophication.

INTRODUCTION

The important role of the rhizomes for the survival and spreading of reed stands dominated by the perennial plant Phragmites australis (CAV.) TRIN. ex STEUD. has been acknowledged for many years (HURLIMANN 1951, BJORK 1967, HASLAM 1969, RODEWALD-RUDESCO 1974). Rhizome resources are utilised to support spring shoot growth and rhizomes are "reloaded" during summer and autumn through a basipetal transport of resources (e.g. DYKYJOVA & HRADECKA 1976, FIALA 1976,1978, SCHIERUP 1978, GRANEIi et al. 1992). However, rhizome standing stocks of biomass and nonstructural carbohydrates are only affected to a minor degree, elucidating that the rhizomes have other important functions than resource storage, e.g. rhizomes are the primary means of clone enlargement, provide structural support for the roots, supply oxygen to the roots, and contribute to anchoring the plant in the substrate (GRANELI et al. 1992).

The pattern of biomass allocation in plants is related to the acquisition of limiting resources. Root growth is generally promoted, at the expense of shoot growth, by low mineral nutrient or water availability (CHAPIN 1980, IWASA & ROUGHGARDEN 1984). A decreased relative allocation of biomass to below-ground parts in response to an increased nutrient supply has been reported for P. australis (BOAR & CROOK 1985, ULRICH & BURTON 1985). It has also been shown that wetland plants have the capacity of morphological responses to flooding and various water depths (e.g. GRACE 1989, COOPS & SMIT 1991, WATERS & SHAY 1992,



92 S.E.B. Weisner & J.A. Strand

4 DIRECTION OF GROWTH

Fig. 1 . A generalised growth pattern of Phragmites australis. Grey - long, mainly horizontal rhizomes, black - shoots and short, mainly vertical rhizomes. Older shoots and rhizomes have been drawn thicker than younger ones. Based on data from HASLAM (1969) and FIALA (1976), and own observations in lakes in southern Sweden.

w~~~~~

D|

Fig. 2. Illustration of the oxygen transport pathway (dotted line) from an emergent shoot of P australis to the apical shoot tip of a horizontal rhizome. D - rhizome depth as measured in the field study, L - rhizome length as measured in the field study, W - water depth.

SOUKUPOVA 1994). P australis has been shown to respond to deep water with a decreased below-ground biomass, as well as rhizome biomass, in relation to shoot biomass (SQUIRES & VAN DER VALK 1992, STRAND 1992).

Further understanding of the functioning of P. australis rhizomes requires more detailed studies on the growth dynamics and architecture of the rhizome systems. HAsLAM(1969) presented some studies on the growth habit and maturation sequence of horizontal and vertical rhizomes. FIALA (1976) investigated the growth periodicity of rhizomes and the role of rhizome age on the carbohydrate balance of reed stands. P. australis tends to produce two distinct types of rhizomes: long, mainly horizontal rhizomes (hereafter called "horizontal rhizomes") and short, mainly vertical rhizomes (HASLAM 1969, FIALA 1976, and our observations in southern Sweden). Fig. 1 illustrates schematically the growth habit of the rhizomes of P. australis, based on the studies mentioned above.

Since oxygen is usually absent in the substrate, emergent macrophytes are largely dependent on 02 transported from the shoots to support aerobic metabolism in below-ground parts (ARMSTRONG 1978). An efficient 02-supply to the roots may also protect the plant from harmful substances produced in inundated sediments or soils (CRAWFORD 1992). A pressurised mass flow of gases, driven by solar energy and/or wind, occurs between emergent shoots of P australis, via the rhizomes, considerably improving 02-transport to below-ground parts as compared to if 02-transport was mediated only by diffusion (ARMSTRONG & ARMSTRONG 1991, ARMSTRONG et al. 1992). However, before the apical shoot of a horizontal rhizome emerges above the water surface, 02 can only be transported through this rhizome by diffusion along concentration gradients. This suggests that 02-transport, through new

horizontal rhizomes to the actively growing apical tip, may be a bottle-neck putting an upper limit to the length and substrate depth penetration of horizontal rhizomes. Oxygen has to be transported through the water column, within an emergent shoot, in addition to through the rhizome before reaching the growing apical tip (Fig. 2). A negative influence of water depth



Rhizome architecture in Phragmites 93

120 -

A y =75 - 0.227x r2= 0.093 100*

E

C

100 0--g

S 60 * *0

!i 40

20 . e. g

0 100

BC y = 65 - 0.365x r2 =0.376

80

E

o. 60

o 40 .

_ C

20 ., : 0

300

C ~~~~y=206-O0.955x r2=0.361 UE 250.

C 200

150. 0

o so 0

01 0 50 100 150 200

Water depth (cm)

Fig. 3. Relationship between water depth and (A) length of horizontal rhizomes of P. australis, (B) substrate depth penetration of horizontal rhizomes, and (C) below-ground 02-transport distance through the rhizome estimated as L + 2D where L = rhizome length and D = rhizome depth. Measurements were made along the reed edge towards open water in the shallow, eutrophic Lake Krankesjbn in southern Sweden.

on 02-transport through the emergent shoots to below-ground parts has been shown in a field study on internal 02-concentrations in shoot bases (WEISNER 1988). Therefore, we hypothesise that P. australis may adapt to deep water by producing shorter horizontal rhizomes, more superficially located in the substrate, whilst in shallow water, long horizontal rhizomes, penetrating deeply into the substrate, are produced to benefit e.g. vegetative expansion and anchorage.

To understand mechanisms regulating the horizontal distribution of reed stands, it is more important to understand the rhizome dynamics at the reed edges than within the stands. HASLAM (1973) pointed out that the rhizome dynamics may differ substantially between the reed edge and within a stand. The aim of this paper is to increase the understanding of reed edge dynamics by investigating the architecture of horizontal rhizomes in relation to water depth, at the open water edge of a Phragmites reed bed.

MATERIAL AND METHODS

Horizontal rhizomes of P. australis were sampled along the reed edge towards open water in Lake Krankesjon (55042' N, 13028' E) in southern Sweden. This is a shallow eutrophic low-land lake with extensive reed belts (WEISNER 1987). Sampling was performed mainly in September and October 1991 by pulling up emerging

shoots with attached rhizomes, by hand (STRAND 1992). The length ("rhizome length") and substrate depth penetration ("rhizome depth") of horizontal rhizomes, as shown in Fig. 2, were measured on the rhizomes after sampling. Water depth at the reed edge was measured at each location. It is reported in relation to the water level in early September 1991, and ranged from 0.3 to 1.4 m. The lowest and highest water level during 20 years prior to sampling was 0.2 m lower and 0.9 m higher, respectively, according to weekly measurements. The




"below-ground 02-transport distance" was calculated as L + 2D, where L is rhizome length and D is substrate depth penetration of the rhizomes (Fig. 2).

RESULTS

Rhizome length was weakly negatively related to water depth (Fig. 3A; r 2= 0.093, F = 4.109, n = 41, P < 0.05). Substrate depth penetration of rhizomes was more strongly negatively related to water depth (Fig. 3B; r2 = 0.376, F = 25.857, n = 41, P < 0.001). The 02-transport distance through the below-ground rhizomes was also negatively related to water depth (Fig. 3C; r2 = 0.361, F = 22.638, n = 41, P < 0.001), though these tests are not independent.

DISCUSSION

The results suggest that P. australis adapts to deep water by making horizontal rhizomes shorter and by decreasing their vertical penetration into the substrate. It seems that this adaptation to deep water is important largely to keep 02-transport distances through shoots and rhizomes short enough to allow a sufficient 02-supply to growing shoot tips at the ends of horizontal rhizomes. As mentioned above, 02-transport through horizontal rhizomes to the growing shoot tip may be a limiting mechanism because it can only occur by diffusion. The decrease in 02-transport distance through the below-ground rhizomes with increased water depth was similar in size to the increase in water depth, i.e. the slope of the regression line was approximately -1 if water depth and below-ground 02-transport

A 02

B C 0 2 02

Fig. 4. A schematic illustration of the influence of different water depths on rhizome architecture and 02-transport distances in P. australis. A - permanently shallow water, B - permanently deep water (i.e. plants given time to adapt their rhizome architecture to deep water), C - after an increase in water depth, from shallow to deep water, occurring on a temporal scale not allowing changes in rhizome architecture (i.e. if plants are not given time to adapt their rhizome architecture to deep water). White sections of shoots and rhizomes illustrate the 02-transport distances from the aerial parts of the nearest emergent shoot, through the submerged portion of that shoot and through the rhizome to the rhizome tip before it penetrates the sediment surface.

distance were expressed in the same unit (Fig. 3C). The "critical whole-plant 02-transport distance" may be from the aerial parts of the nearest emergent shoot, through the submerged portion of that shoot and through the rhizome to the rhizome tip before it penetrates the sediment surface. It is likely that 02-supply to the rhizome/shoot tip is less critical once it emerges into the water column because oxygen availability in the surrounding water increases and some photosynthesis may even occur in the rhizome/shoot tip. The "critical whole-plant 02-transport distance" is thus the sum of the "below-ground 02-transport distance" and water




depth (i.e. 2D + L + W), which did not change with water depth because the decrease in below-ground 02-transport distance with increased water depth was similar to the increase in water depth. Mean critical whole-plant 02-transport distance over all water depths ? standard error was 2.09 ? 0.07 m (n = 41). We suggest that this relationship mirrors the capacity of P australis to maximise rhizome extension and 02-transport distances through submerged portions over different water depths (Fig. 4A and B).

Thus, in shallow water P. australis rhizomes are able to penetrate deeply into the substrate, thereby improving anchorage and nutrient uptake possibilities. The rate of vegetative spreading is presumably also increased in shallow water because horizontal rhizomes are longer. The plasticity in rhizome architecture for P australis that has been illustrated in this study probably contributes to the ability of the species to grow and to be competitive at very different water depths (e.g. FIALA & KVET 1971, ROMAN et al. 1985, SHAY & SHAY 1986, WEISNER 1991), i.e. to adapt to spatial differences in water depth. However, the tendency to maximise the extension of rhizomes at different water depths may limit the ability to tolerate sudden dramatic chianges in water level. This can be illustrated by the influence of a sudden dramatic increase in water level, occurring on a temporal scale not allowing changes in rhizome architecture, on 02-transport distances through shoots and rhizomes (Fig. 4).

It is also possible that the tendency of P. australis to optimise the extension of rhizomes may have a negative impact on the species ability to tolerate eutrophication. When 02-supply from the shoots is restricted, oxygen concentrations in rhizomes have been shown to be lower in low compared to high-redox substrates, probably because of increased 02 leakage from roots in low-redox sediments (WEISNER & GRANELI 1989). An increased 02 leakage from roots due to 02 consumption in eutrophicated sediments will result in an insufficient 02-supply to the growing rhizome tip if P. australis, even under eutrophicated conditions, produces rhizomes that have an extension that would have been optimal under less eutrophicated conditions.

In conclusion, we propose that the rhizome growth strategy of P australis may make it a species well adapted to spatial differences in water depth, but not as well adapted to sudden temporal increases in water depth and to low-redox sediments. The causes behind reed decline (BOAR et al. 1989, BOORMAN & FULLER 1981, CIZKOVA-KONCALOVA et al. 1992, KLOTZLI 1971, KRUMSCHEID et al. 1989, OSTENDORP 1989, SCHRODER 1987, SUKOPP & MARKSTEIN 1989) might involve the influences of changes in water depth, or redox conditions in sediments, on oxygen supply to horizontal rhizomes of P. australis.

REFERENCES

ARMSTRONG W. (1978): Root aeration in the wetland condition. In: HOOK D.D. & CRAWFORD R.M.M. (eds.), Plant life in anaerobic environments, Ann Arbor Science, Ann Arbor, pp. 269-298.

ARMSTRONG J. & ARMSTRONG W. (1991): A convective through-flow of gases in Phragmites australis (CAV.) TRIN. ex STEUD. Aquatic Bot. 39: 75-88.

ARMSTRONG J., ARMSTRONG W. & BECKETr P.M. (1 992): Phragmites australis: venturi- and humidity-induced convections enhance rhizome aeration and rhizosphere oxygenation. New Phytol. 120: 197-207.

BJORK S. (1967): Ecological investigations of Phragmites communis. Folia Limnol. Scand. 14: 1-248. BOAR R.R. & CROOK C.E. (1985): Investigations into the causes of reedswamp regression in the Norfolk

Broads. Verh. Int. Verein Limnol. 22: 2916-2919. BOAR R.R., CROOK C.E. & MOSS B. (1989): Regression of Phragmites australis reedswamps and recent

changes of water chemistry in the Norfolk Broadland, England. Aquatic Bot. 35: 41-55.




BOORMAN L.A. & FULLER R.M. (1981): The changing status of reedswamp in the Norfolk Broads. J. Appl. Ecol. 18: 241-269.

fiiZKOVA-KON4ALOVA H., KVET J. & THOMPSON K. (1992): Carbon starvation: a key to reed decline in eutrophic lakes. Aquatic Bot. 43: 105-113.

CHAPIN F.S. (1980): The mineral nutrition of wild plants. Annual Rev. Ecol. Syst. 11: 233-260. COOPS H. & SMIT H. (1991): Effects of various water depths on Scirpus maritimus L.: Field and experimental

observations. Verh. Int. Verein Limnol. 24: 2706-2710. CRAWFORD R.M.M. (1992): Oxygen availability as an ecological limit to plant distribution. Advances Ecol.

Res. 23: 93-185. DYKYJovA D. & HRADECKA D. (1976): Production ecology of Phragmites communis. 1. Relations of two

ecotypes to the microclimate and nutrient conditions of habitat. Folia Geobot. Phytotax. 11: 23-61. FIALA K. (1976): Underground organs of Phragmites communis, their growth, biomass and net production.

Folia Geobot. Phytotax. 11: 225-259. FIALA K. (1978): Seasonal development of helophyte polycormones and relationship between underground

and aboveground organs. In: DYKYJOVA D. & KvET J. (eds.), Pond littoral ecosystems, Springer-Verlag, Berlin, pp. 174-181.

FIALA K. & KvET J. (1971): Dynamic balance between plant species in South Moravian reedswamps. In: DUFFEY E. & WArr A.S. (eds.), The scientific management of animal and plant communitiesfor conservation, Blackwell Scientific Publications, Oxford, pp. 241-269.

GRACE J. (1989): Effects of water depth on Typha latifolia and Typha domingensis. Amer: J. Bot. 76: 762-768. GRANELI W., WEISNER S.E.B. & SYTSMA M.D. (1992): Rhizome dynamics and resource storage in Phragmites

australis. Wetlands Ecol. Managem. 1: 239-247. HASLAM S.M. (1969): Stem types of Phragmites communis TRIN. Ann. Bot. 33: 127-131. HASLAM S.M. (1973): Some aspects of the life history and autecology of Phragmites communis TRIN. A

review. Polish Arch. Hydrobiol. 20: 79-100. HURLIMANN H. (1951): Zur Lebensgeschichte des Schilfs an den Ufern der Schweizer Seen. Beitr. Geobot.

Landesaufn. Schweiz. 30: 1-232. IWASA Y. & ROUGHGARDEN J. (1984): Shoot/root balance of plants: optimal growth of a system with many

vegetative organs. Theor. Populat. Biol. 25: 78-104. KLOTZLI F. (1971): Biogenous influence on aquatic macrophytes, especially Phragmites communis.

Hidrobiologia 12: 107-111. KRUMSCHEID P., STARK H. & PEINTINGER M. (1 989): Decline of reed at Lake Constance (Obersee) since 1967

based on interpretations of aerial photographs. Aquatic Bot. 35: 57-62. OSTENDORP W. (1989): "Die-back" of reeds in Europe - a critical review of literature. Aquatic Bot. 35: 5-26. RODEWALD-RUDESCO L. (1974): Das Schilfrohr Phragmites communis TRINIUS. Binnengewasser 27: 1-302. ROMAN T., ROMAN L., RADUCA C. & MOLNAR A. (1985): Die Einwirkung einiger Umweltfaktoren des

Donaudeltas auf die Abgrenzung des Lebensraumes von Schilf-, Rohrkolben- und Seggengesellschaften. Arch. Hydrobiol. Suppl. 68: 149-162.

SCHRODER R. (1987): Das Schilfsterben am Bodensee - Untersee. Beobachtungen, Untersuchungen und Gegenmassnahmen. Arch. Hydrobiol. Suppl. 76: 53-99.

SCHIERUP H.-H. (1978): Biomass and primary production in a Phragmites communis TRIN. swamp in North Jutland, Denmark. Verh. Int. Verein Limnol. 20: 94-99.

SHAY J.M. & SHAY C.T. (1986): Prairie marshes in western Canada, with specific reference to the ecology of five emergent macrophytes. Canad. J. Bot. 64: 443-454.

SOUKUPOVA L. (1994): Allocation plasticity and modular structure in clonal graminoids in response to waterlogging. Folia Geobot. Phytotax. 29: 227-236.

SQUIRES L. & VAN DER VALK A.G. (1992): Waiter-depth tolerances of the dominant emergent macrophytes of the Delta Marsh, Manitoba. Canad. J. Bot. 70: 1860-1867.

STRAND J. (1992): Effects of water depth on the biomass allocation of Phragmites australis. A possible explanation for the distribution patterns of reed vegetation in lakes. M. Sc. thesis, Lund University.

SUKOPP H. & MARKSTEIN B. (1989): Changes of the reed beds along the Berlin Havel, 1962-1987. Aquatic Bot. 35: 27-39.




ULRICH K.E. & BURTON T.M. (1985): The effects of nitrate, phosphate and potassium fertilization on growth and nutrient uptake patterns of Phragmites australis (CAV.) TRIN. ex STEUDEL. Aquatic Bot. 21: 53-62.

WATERS I. & SHAY J.M. (1992): Effect of water depth on population parameters of a Typha glauca stand. Canad. J. Bot. 70: 349-351.

WEISNER S.E.B. (1987): The relation between wave exposure and distribution of emergent vegetation in a eutrophic lake. Freshwater Biol. 18: 537-544.

WEISNER S.E.B. (1988): Factors affecting the internal oxygen supply of Phragmites australis (CAV.) TRIN. ex STEUDEL in situ. Aquatic Bot. 31: 329-335.

WEISNER S.E.B. (1991): Within-lake patterns in depth penetration of emergent vegetation. Freshwater Biol. 26: 133-142.

WEISNER S.E.B. & GRANILI W. (1989): Influence of substrate conditions on the growth of Phragmites australis after a reduction in oxygen transport to below-ground parts. Aquatic Bot. 35: 71-80.



adaptation strategies in wetland plants: links between ecology and physiology. proceedings of a...

Documents