MILENA RYCHNOVSK/~ Botanical Institute of the Czechoslovak Academy of Sciences, Brno, Star~ 18

A Contribution to the Autecology of Phragmites communis TRIN. i. Physiological Heterogeneity of Leaves

Abstract

The plant Phragmitescommuniswas subject to an analysis ofphysiological gradients along the leaf blade and level of insertion of separate leaves. The gradients were established in the following aspects: fresh weight, dry matter, specific leaf area, water content, water saturation deficit and its resaturation, rate of desiccation and photosynthetic capacity. Indistinct gradients under normal conditions become more marked in extreme circumstances. The significance of leaf heterogeneity for all sorts of eco-physiological analysis of the plant under study was discussed. INTRODUCTION

I n recent years m u c h attention has been devoted to the study of the productivity o f natural plant communities. O n e of the main items of the International Biological P r o g r a m m e is to investigate, analyze and explain the productivity o f vegetational covers a n d to a p p r e h e n d the processes t h r o u g h which solar energy (as the p r i m a r y source of energy for living organisms) is fixed in them. It is obvious that such a complicated problem should be investigated in simple, model ecosystems in which most of the interferring environmental factors can be eliminated. O n e of those ecosystems under study in various areas of Europe are the Phragmites-communities. The successful solution of the problem depends first of all on our knowledge of the test material, its variability and heterogeneity. The variability of Phragmites-stands and separate reed plants has been studied by other authors ( D v K y j o v k 1966, KvP:r 1966--personal communications, etc.); this paper aims at an analysis of some physiological

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g r a d i e n t s o f o n e p l a n t i n d i v i d u a l . T h i s is a n i m p o r t a n t m e t h o d o l o g i c a l step w h i c h l e a d s to f u r t h e r e c o p h y s i o l o g i c a l a n a l y s e s , e s p e c i a l l y for f u r t h e r s t u d i e s o n w a t e r r e l a t i o n s a n d p h o t o s y n t h e s i s i n t h e n a t u r a l covers o f r e e d . MATERIAL AND METHODS The test plants were collected from homogeneous covers in the litoral zone of H2~skovsk]7 rybnik (Lake H~rskovsk~) near the village of Deht~i[e in southern Bohemia in July, 1965. The plants have developed about 7 to 12 consecutive leaves on the culm, and some of them already showed signs of inflorescence. In the course of study the following factors were ascertained: A. Heterogeneity of leaves according to the level of insertion in the following aspects: a) fresh weight and dry matter of whole leaves b) specific leaf area expressed by the ratio of leaf area in sq. mm. and the corresponding dry matter in rag. (As) c) water content in % of dry matter under varying water balance d) appearance of the water saturation deficit (WSD) and its restauration e) water retention capacity estimated from the rate of desiccation f) photosynthetic capacity B. Axial gradients of leaf blades in the following aspects: a) specific leaf area water content in % of dry matter under varying water balance bl appearance of the water saturation deficit and its resaturation I n addition to these physiological gradients, the plotting of the water resaturation curve after exposing the leaf discs for several hours had to be performed in order to detect the error due to the infiltration of water into the mesophyll or to the growth of discs (as noted by CATs~q 1960). The analysis of the above-mentioned properties was performed as follows: the test plants were cut off in early morning hours and quickly transported to the laboratory in polyethylene bags. No measurable water saturation deficit emerged during the transport. A. In order to establish fresh weight and dry matter of whole leaves, the leaves were cut off the culm and weighed, their dry matter being established after desiccation at 105 ~ For the establishment of the specific leaf area and the water content 10 discs (with a diameter of 8 ram.) were cut out of each leaf blade; a special knife described by BARTO~, ~ETLiK and KUBIN (1960) was used. The physiological gradients caused by wilting of the plant were studied during the desiccation of both the whole intact overground part of the plant and the separated leaves, according to the level of insertion, as stated under the respective graph. The desiccation of leaves and their water retention capacity were studied gravimetrically on whole leaves cut off from the culm. The photosynthetic capacity was established in leaf discs cut off from one plant individual after preliminary experiments showing the optimal method of the selection of parallel samples (BARTOS,KUBiN and SETLtK1960; gETLIK,BARTOS and KUBiN 1960). 20 discs were cut off from every leaf blade (alternately from the right and left halves zigzag); 10 of them were used as a control group and 10 were exposed for a period of 4 hours in an open field under a cloudy sky at an air temperature of 20 to 22 ~ To enable water saturation, the discs were placed in polyurethane foam soaked with distilled water. All questions concerning the water balance in plants, the water saturation deficit and its resaturation were studied in a similar way. Water saturation deficit was expressed in % of fully turgescent water content in the discs after a 2-hour period of water saturation. B. Heterogeneity of the leaf blade was always studied only on the 5 central leaves of the plant, so that the gradients obtained by measurement correspond to an average of 5 successive leaves of the same plant.

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THE RESULTS OF EXPERIMENTS AND DISCUSSION The gradients found in our experiments are expressed graphically in appended Figs. I--9. A. H e t e r o g e n e i t y o f t h e c o n s e c u t i v e l e a v e s a c c o r d i n g to t h e l e v e l of insertion The simplest example of a basic anatomic-physiological gradient from the basis to the apex of a plant is depicted in Figs. 1 and 2. It shows that not only the absolute weight of leaves--whether the fresh weight in fully turgescent state (FW) or the dry weight ( D W ) - - h a s its characteristic gradient from the base to the apex, but also the relative amount of dry weight, expressed in sq.mm./mg, as specific leaf area (As), varies from the basis to the apex.The water content expressed in % of dry weight in fully turgescent state shows the same characteristic gradient. When the water saturation deficit develops a similar variation can again be observed: WSD appears first in central leaves, while the younger apical leaves (except the topmost, highly sensitive l e a f ) r e m a i n fully turgid. This is probably an autoregulative phenomenon, as shown by another experiment with the desiccation of leaves which are separated from the plant and cannot compensate their water loss from the culm internodes (Fig. 3). In these conditions, each leaf reacts independently of the other parts and the water loss, expressed in % of fresh weight, proceeds most rapidly in the young apex leaves, while in the central and fully mature leaves the water output is slower and their drought resistance greater. / A similar relationship is de] monstrated by a series of k / k measurements revealing a gradual development of the ,o J water saturation deficit in \ ;\ i leaves of the intact plant as compared with leaves separated from the culm (Figs. 4 and 5). The water _\ g 9~ balance is again expressed as water content In % of dry matter. The metho\ dical difficulty of this exe\ periment is due to the heterogeneity of individual plants, although considerc~ i C

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Fig~ 1. Variations of dry matter (DW) and fresh weight (FW) of the leaves of Phragmites communis according to the level of insertion on the plant (in mg.).

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I-W 500

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FOLIA GEOBOTANICA ET PHYTOTAXONOMICA, 2, 1967

able effort has been m a d e to eliminate this error a n d m u c h care has b e e n d e v o t e d to the selection o f the test plants in the same p h e n o p h a s e a n d - - m o s t p r o b a b l y - - f r o m one p o p u l a t i o n . T h e results show that the characteristic g r a d i e n t in the w a t e r c o n t e n t f r o m the base to the apex can again be observed here as in the p r e c e d i n g plants. T h e central m a t u r e leaves have the lowest g

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Fig, 2. Variations of the specific leaf area in sq. mm.]mg. (As), water content in % of dry matter (W) and water saturation deficit in % of full saturation (WSD) of the leaves of Phragmites communis according to the level of insertion on the plant.

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Fig. 3. Water loss due to desiccation of separated leaves of Phragmites communis according to the level of insertion on the plant. The water content at the beginnlng in fully turgescent state = 100; the other data are related to that. The curves correspond to the length of leaf desiccation in the laboratory at a tempera ture of 20 ~ and 70 % of relative air humidity expressed in minutes.

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Fig. 4. The development of water saturation deficit (the lower curve) and its resaturation (the upper curve) in the leaves during desiccation of the whole plant Phragmites communis. X -- axis -- leaves according to the level of insertion Y -- axis -- water content in % of dry matter. T h e histograms correspond to the state of the plant after 0, 2, 4, 7 a n d 10 hours of desiccatiort in the laboratory at 20 ~ and at 70 % of relative air humidity.

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Fig. 5. The development of the water saturation deficit (the lower curve) and its resaturatiort (the upper curve) in the leaves separated from the plant and desiccated in the laboratory at the temperature of 20 ~ and at 70 % of relative air humidity. X-axis -- leaves according to the level of insertion. Y-axis -- water content in % of dry matter. The histograms correspond to the state of the plant after 0, 1, 2 and 5 hours of desiccation in the laboratory.

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ET PHYTOTAXONOMICA,

2, 1967

water content, while the youngest apical leaves as well as the oldest bottom leaf are richer in water. During gradual desiccation the water saturation deficit develops and its rate corresponds to the area between the lower WSD curve and the upper fully turgid curve in Figs. 4 an 5. It is shown that during gradual wilting the highest WSD develops in the lowest leaves while towards the young apical leaves it decreases (similarly to Fig. 2). If, however, separated leaves are subject to desiccation the gradient in the water content remains similar, but the gradient in WSD of leaves along the culm becomes less pronounced. As far as the rate of water loss and water , J retention capacity are concerned Zaleni\ j ski's Law is apparently valid for intact i plants only, not for separated leaves. The photosynthetic capacity of separate leaves h was tested at full water saturation, when g all the discs from all the consecutive leaves were exposed to equal illumination. Differ rences in the potential photosynthetic capacity of separate leaves could thus be e specified (Fig. 6). Central leaves can be d considered as mature from the photosynthetic point of view, while the youngest, c apical leaves show lower capacity. The photosynthetic capacity also rapidly de/ creases toward the base so that the otdest a\ leaf, apparently fresh and deep green, a showed passive dry matter production under t h e above-mentioned experimental 0 2 0 6 mg/dm~lh conditions. Fig. 6. Variations of the photosynthetic capacity of the leaves of Phragmites communis according to the level of insertion B. H e t e r o g e n e i t y o f t h e l e a f b l a d e on the plant. The photosynthetic capaIn addition to physiological differencity is expressed as the increase (or decrease) of dry matter in mg. /sq. dm. ces along the culm, conspicuous graafter 1 hour. dients can be traced even within one leaf blade (Fig. 7) ; a similar phenomenon as minutely described by SLAViK (1959, 1963). The relative increase of dry matter on the leaves of Phragmites is basipetal, which leads to a decrease in the specific leaf area (As). The water content (W) in fully turgescent state (a) reveals the same tendency; during the development of water saturation deficit it becomes more pronounced (b) and further wilting makes it still more conspicuous (c). The curve of the developing WSD corresponds to these facts: the loss of water in the leaf blade proceeds from the apex to the base and the WSD develops similarly as it markedly increases towards the apex. The basal parts of leaves are richer in water and desiccate most slowly of all, even if the leaves are separated from the culm. The development of WSD and its resaturation can be similarly followed in series of histograms in Fig. 8. T h e y give

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R Y C H N O V S K , ~ : A U T E C O L O G Y OF P H R A G M I T E S C O M M U N I S

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Fig. 7. The gradient of specific leaf area in sq. mm./mg. (As), water content in % of dry matter (W), and water saturation deficit in % of full saturation (WSD) along the blade of the central leaves of Phragmites communis. The a curve corresponds to the fully turgescent state, b to the passive water balance state, and c to considerable water stress. The diagram of the leaf shows the position of the test discs.

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Fig. 8. The development of water saturation deficit (the lower curve) and its saturation (the upper curve) along the blade of the central leaves of Phragmites communis. x - a x i s - the discs along the blade (according to the diagram). y-axis -- water content in % of dry matter. The histograms correspond to the state of the plant after 0, 1, 2 and 6 hours of desiccation m the laboratory at 20 ~ and at 70 % of relative air humidity.

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FOLIA GEOBOTANICAET PHYTOTAXONOMICA, 2, 1967

a dynamic picture of the water balance of the leaves along their blades; differences not only in actual WSD but also in the capacity of its full resaturation from the base of the blade to the apex apparently become more pronounced as their turgor decreases. The error caused by the growing of discs (CATsK'2 1960) during exposition in the polyurethane foam is negligible for eco-physiological purwses , as shown by Fig. 9. Saturation for two hours was found to be sufficient for introducing the dynamic equilibrium between the disc and surrounding water. Data shown in this study again testify to the importance of preliminary analysis of the natural gradients in % the plant species under study; especially when the research is dealing with comparison of physiological manifestations of plant J organs. As shown by FELFbLDI i i z ! (1955), eco-physiological measu5 0 84 rements of some plant functions, especially those which provide data for comparison of plants i, in situ, often bring no results if the natural gradients are ne/o' 15' 3O' ~J' 7Y IJS" Z75'J~' glected: e.g. leaves of the same 9. W a t e r s a t u r a t i o n c u r v e o f l e a f discs o f plant (even though they seem Fig. Phragmites communis in t h e c o u r s e o f t i m e . morphologically identical at first x-axis - - t i m e in m i n u t e s . glance) produce great differeny-axis - - w a t e r c o n t e n t in % o f fully s a t u r a ted weight at the end of the experiment. ces in the desiccation rate according to their insertion. These differences, greater than those between species, have already been noted by m a n y authors, chiefly concerning water relations in plants (MAxlMOV 1952, STALFELT 1956, etc.) A detailed study of the origin and the causes of these gradients was made by PRAT (1948, 1951). Nevertheless, it is necessary to verify these gradients (though generally known) for every plant species and to ascertain their extent. It is also possible to find considerable differences within the area of one leaf blade. This must be borne in mind, especially when using methods based on analysis of discs excised from the leaf blade. Convincing facts about this were published by SLAViK (1959, 1963); they fully coincide with the gradients described in the present paper. Finally, another aspect should be stressed here. All the gradients (either according to the insertion or in the area of one leaf blade), which are not too distinct under normal conditions become clearly marked in extreme circumstances. They may constitute a source of errors and of unexplainable variability of analytical results if they are neglected. An autecological study of a certain plant species should always be preceded by a study of the physiological properties of the plants under investigation. This should b~ as common as the comprehensive taxonomical verification of the species under study. :

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Acknowledgement The author is indebted to Miss Z. Pueellkov~. and Miss M. gindelM'ov~.,students of Charles University in Prague, and to Miss M. Gilbert, student of the Universitv of Greifswald, for their assistance in carrying out laboratory tests. SUMMARY 1. The fully turgescent plant Phragmites communis T R I N . shows gradients from the base to the apex in the following aspects: fresh weight and dry matter of leaves, specific leaf area, water content in % of dry matter. 2. Water saturation deficit of the whole plant develops first in the lower leaves, while turgescenee of the upper leaves is preserved for a larger period. 3. Desiccation of leaves separated ti'om the plant varies according to the level of insertion; the upper young leaves lose water first, while towards the base the desiccation of leaves is slower. 4. The development of WSD in the whole plant also varies. The lower leaves develop a higher deficit than the upper ones. Separated leaves reveal less pronounced differences between W S D of the lower and the higher leaves. 5. The photosynthetic capacity of leaves also varies according to the level of insertion. Central leaves are definitely most productive of all. The photosynthetic capacity decreases towards both the apex and the base; the oldest leaf has a passive metabolism, even though it is deep green and fresh. 6. Along the leaf blade gradients can be found in specific leaf area, water content and water saturation deficit. The specific leaf area decreases basipetally and the water content increases. 7. The water saturation deficit develops from the apex of the leaf to its base. The gradient of WSD becomes more characteristic along the blade at increasing water stress. ZUSAMMENFASSUNG 1. In einer voll turgeszenten Pflanze Phragmites communis Tmn. wurden die physiologischen Gradiente yon der Basis zum Apex in tblgenden Ph~inomenen einer Analyse unterworfen: Frisch- und Trockengewicht der Bl~itter, spezifische Blattflache, Wassergehalt in % des Trockengewichts. 2. Bei der intakten Pflanze entwickelt sich das Wassersattigungsdefizit eher in den unteren Etagen, wogegen die oberen Bl~itter l~inger turgeszent bleiben. 3. Der Wasserverlust der yon der Pflanze abgetrennten Bl~itter schwankt nach der Insertionsh~he, u. zw. so, dass diejtingsten oberen Blatter am schnellsten austrocknen; je wt'iter basipetal desto langsamer verl~iuft der Wasserverlust. 4. Das S~ittigungsdefizit entwickeh sich bei der intakten Pflanze ebenso basipetal: die unteren Bl~itter weisen tin gr/isseres Wasserdefizit als die oberen auf. Bei den yon der Pflanze abgetrennten Bltittern sind die Unterschiede weniger deutlich. 5. Die photosynthetische Kapazit~it der Bl~itter schwankt angemessen der Insertionshbhe. Als leistungsfahigst kann man die mittleren Bliitter bczeichnen.

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W e d e r d i e a p i k a l e n n o c h d i e b a s a l e n B1/itter e r r e i c h e n d i e p h o t o s y n t h e t i s c h e K a p a z i t ~ t d e r m i t t l e r e n Bl~itter, j a s o g a r d a s M t e s t e B l a t t w e i s t e i n e p a s s i v e S t o f f b i l a n z auf, o b w o h l es n o c h frisch u n d d u n k e l g r f i n ist. 6. E n t l a n g d e r B l a t t s p r e i t e k a n n m a n e b e n s o G r a d i e n t e i n d e r s p e z i f i s c h e n Blattfl~iche, i m W a s s e r g e h a l t u n d i m S ~ i t t i g u n g s d e f i z i t e n t d e c k e n , u. zw. b a s i p e t a l v e r m i n d e r t s i c h d i e s p e z i f i s c h e B l a t t f l ~ c h e u n d w ~ c h s t d e r Wasserghalt. 7. D a s S ~ i t t i g u n g s d e f i z i t e n t w i c k e l t sich v o m A p e x z u r B l a t t b a s i s . D e r Gradient entlang der Blattspreite wird bei wachsendem ,,water stress" mehr ausgepr~igt. LITERATURE

CITED

BARTOg, J., KUBiN, S. and SETLfK, I. (1960): Dry weight increase of leaf disks as a measure of photosynthesis. -- Biol. Plant., 2 : 201--215. CATSK'), J. (1960): Determination of water deficit in disks cut out from leaf blades. -- Biol. Plant., 2 : 76-- 78. FELF6LDY, L. (1955) : A let6pett lomblev61 kisz~trad~tsmenet6nek 61ettani vizsg~ilata (Physiological experiments on the desiccation rate of detached leaves). Hung. with english summary. -- Annal. biol. Tihany, 23: 111--154. MAXlMOV, N. A. (1952): Izbrannye raboty po zasukhoustoychivosti i zimostoykosti rasteny. Tom. I. Vodny rezhim i zasukhoustoychivost rasteny. (Selected papers on drought and cold resistance of plants. Vol. I. Water relations and drought resistance). Russian. Moskva. PRAT, H. (1948) : I-Iisto-physiologicalgradients and plant organogenesis. Part I. -- Bot. Rev., 14: 603--643. PRAT, H. (1951): Histo-physiological gradients and plant organogenesis. Part II. -- Bot. Rev., 17: 693--746. SLAVfK, B. (1959): Gradients of osmotic pressure of cell sap in the area of one leaf blade. -Biol. Plant., 1: 39--47. SLAVIK, B. (1963): The distribution pattern of transpiration rate, water saturation deficit, stomata number and size, photosynthetic and respiration rate in the area of the tobacco leaf blade. -- Biol. Plant., 5: 143-- 153. ST~gLLFELT,M. G. (1956) : Morphologie und Anatomie des Blattes als Transpirationsorgan. -Hb. d. Pflanzenphysiol., Bd. I I I : 324--341. Berlin-- G6ttingen-- Heidelberg. SETLII~, I., BARTOg,J. and KUBIN S. (1960) : Photosynthesis of leaf disks as a measure of photosynthetic capacity in crop plants. -- Biol. Plant., 2: 292--307. Received 14 November 1966