Báo cáo khoa học: " Photosynthesis and shoot water status of seedlings from different oak species submitted to waterlogging"

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Original article Photosynthesis and shoot water status of seedlings from different oak species submitted to waterlogging E P Biron M Colin-Belgrand Dreyer 1Laboratoire de Bioclimatologie et d’Ecophysiologie Forestière, INRA Nancy, Champenoux, 54280 Seichamps; 2 Laboratoire d’Étude des Sols et de la Nutrition, INRA Nancy, Champenoux, 54280 Seichamps, France (Received 16 August 1990; accepted 8 January 1991) Summary — Stress effects induced on shoot photosynthesis and leaf water status by root hypoxia due to waterlogging have been assessed on saplings of Quercus robur, Q petraea, Q rubra and Q palustris in 2 successive experiments. Daily (first experiment) and weekly (second experiment) measurements of leaf gas exchange were made during 2 and 7 wk of waterlogging with a water ta- ble at 3 (1 st) and 6 cm below the soil surface (2nd experiment). Net CO assimilation rate (A), and 2 leaf conductance to CO were rapidly and strongly affected by waterlogging in almost every 2 (g) case. CO diffusion analysis of gas exchange data revealed that both stomatal and non stomatal lim- 2 itations apparently induced this decline. Predawn leaf water potential remained high in all cases, in- dicating that reductions in photosynthesis were not due to altered leaf water status. Possible mecha- nisms relating root hypoxia and leaf physiology are discussed. Within this general framework, some species-related differences could be detected: reactions of Q roburwere in general much more limit- ed than those of Q rubra and Q palustris, being virtually absent when the water table remained at 6 cm below soil surface. This observation could be connected with the ability of Q robur to produce more adventitious roots when waterlogged. No significant long term trend parallelling phases of root decay and subsequent root regeneration could be observed in photosynthesis for this species. stomatal conductance / water / Quercus robur / Quercus petraea / Ouercus palus- potential trls / Quercus rubra Résumé — Photosynthèse et état hydrique de jeunes semis de chênes soumis à un en- noyage. Nous avons analysé les effets d’une hypoxie racinaire due à un ennoyage sur la photosyn- thèse foliaire et l’état hydrique de jeunes plants de Quercus robur, Q petraea, Q rubra et Q palustris au cours de 2 expériences successives. Des mesures quotidiennes (1 expérience) et hebdoma- re daires (2 expérience) d’échanges gazeux ont été réalisées pendant 2 et 7 semaines d’ennoyage e contrôlé, avec une nappe d’eau à 3 (1 expérience) et à 6 cm (2 expérience) de la surface du sol. re e L’assimilation nette de CO (A) et la conductance foliaire pour le CO (g) ont été très fortement et ra- 2 2 pidement réduites par la contrainte au cours des 2 expériences dans presque tous les cas. L’utilisa- tion d’un modèle de diffusion du CO vers les tissus mésophylliens indique que les limitations obser- 2 vées seraient dues à des facteurs stomatiques et non stomatiques. Le potentiel hydrique de base est resté élevé pendant toute la phase d’ennoyage. De ce fait, les perturbations foliaires observées ne peuvent pas être expliquées par une dégradation de l’état d’hydratation des tissus foliaires. La possibilité d’une intervention de métabolites racinaires est discutée. Un certain nombre de diffé- * Correspondence and reprints
rences entre espèces ont pu être détectées à l’intérieur de ce cadre général. Q robur s’est révélé beaucoup moins sensible que Q rubra et Q palustris dans nos conditions. En particulier, les réduc- tions de photosynthèse ont été pratiquement absentes au cours de la seconde expérience, avec une nappe à 6 cm de la surface. Ces différences peuvent être mises en parallèle avec les capacités de production de racines adventives de cette espèce en conditions d’hypoxie. Cependant, l’alternance d’une phase de dégradation de racines et d’une phase de régénération racinaire intense ne s’est pas traduite par des fluctuations de la photosynthèse foliaire. hypoxie / ennoyage / assimilation nette / stomate / potentiel hydrique / Quercus robur / Quer- petraea /Quercus palustris /Quercus rubra cus lowski, 1982; Pezeshki and Chambers, INTRODUCTION 1985, 1986; Savé and Serrano, 1986; Da- vies and Flore, 1986a, b; Harrington, 1987; Osonubi and Osundina, 1987; Smit and of different oak Seedlings species (Q ro- Stachowiak, 1990; Lewty, 1990), although bur, Q rubra and Q palustris) display large Wample and Thornton (1984) reported de- differences in root reactions to waterlog- creasing A without noticeable stomatal clo- ging (Colin-Belgrand et al, 1991).In partic- sure (Lycopersicon esculentum). These ular, waterlogged Q robur seedlings exhib- stress effects generally appear very rapid- ited important adaptive reactions, ly, after a few d (even a few h in some producing a large number of adventitious cases) of exposure to a degassed water roots from the 4th week of treatment on, table (Pezeshki and Chambers, 1985; Pe- while those of Q palustris and Q rubra pre- Sundström, 1988; Smit and zeshki and sented only limited root adaptations (Colin- Stachowiak, 1990). Belgrand et al, 1991).What are the conse- quences of these differences in root reac- With respect to the important effects of tions on seedling physiology ? Are they ac- on root functions evidenced earli- flooding companied by differences in patterns of er, it was of primary importance to test possible correlations between root and shoot gas exchange? shoot behaviour. Early effects of waterlog- Reactions of tree shoots to waterlog- ging may be mediated by root signals of ging and associated root hypoxia include different nature (Bradford, 1983). The sub- strong decreases in CO assimilation rates 2 sequent strong decay of submerged roots (A) in almost every species studied (Child- and possible formation of adventitious ers and White, 1942; Regehr et al, 1975; transformed roots could have strong ef- Peterson and Bazzaz, 1984; Pezeshki and fects on photosynthesis and leaf water Chambers, 1985; Davies and Flore, status. The contrasting behaviour of Q ro- 1986a, b). These reductions even affect bur and Q rubra in this respect (Colin- species with the highest degrees of toler- Belgrand et al, 1991) is an interesting ba- ance such as Taxodium distichum (Pe- sis, for experimental investigation. zeshki et al, 1986). Only very few reports of an absence of reaction have been pub- tolerance to waterlogging Contrasting lished (Zaerr, 1983; with Pinus silvestris). only seldom been related to differ- has These reductions in A are generally ac- ences in the intensity of stress reactions at companied by marked decreases in stom- shoot level. Do all species suffer from the same magnitude of A and g impairment, as atal conductance (g) (Childers and White, observations with fairly tolerant trees like 1942; Regehr et al, 1975; Tang and Koz-
were equipped with external transpar- The pots Taxodium distichum (Pezeshki al, 1986) et tubing allowing a precise control of water ta- ent there some differ- indicate, to seem or are tall when the ble level. ≈ 50 Seedlings were cm related to the degree of tolerance? ences measurements were begun (July 1986). The aims of this study were: 1), to es- The pots were flooded with tap water on July tablish the nature and intensity of the reac- 18th. The upper water table level was main- tions of A and g of oak seedlings to root tained at 3 cm from soil surface by daily rewater- ing. The oxygen content of the water table, as hypoxia; 2), to test the possible correla- measured with an oxygen electrode (Orbisphère tions between root adaptations appearing 27141),reduced to≈ 0.20 ppm. The pots were during long term flooding, and shoot photo- drained after 15 d. The seedlings were kept in synthesis, leaf conductance to CO and 2 the greenhouse and gas exchange measure- water status; 3), to analyze the differences ments were performed daily under controlled in the behavior of oak species with con- conditions. Three trees were used for each spe- trasting waterlogging tolerance (Q robur, Q cies. petraea, Q rubra and Q palustris). A (net CO assimilation rate, μmol.m ) -1 .s -2 2 and g (equivalent leaf conductance to CO , 2 mmol.m were measured daily on the ) -1 .s -2 same leafy shoot of 3 seedlings per species. MATERIALS AND METHODS Plants were removed from the greenhouse just prior to the measurements. Three series of measurements were made daily from the day Photosynthetic functions have been analyzed in preceding waterlogging onwards. Each series 2 successive experiments. The first experiment aimed at assessing the effects of severe water- consisted of 3 plants of a given species meas- logging conditions (water table at 3 cm below ured in parallel. The ranking of species was the soil surface). In this experiment special at- changed every day to limit artifacts related to tention was paid to the short term (d) effects of diurnal variations in photosynthetic capacity. Each series of measurements lasted≈ 2.5 h (1 h In the second experiment, the ef- waterlogging. fects of moderate waterlogging (water table at 6 for the installation and removal of the plants and cm below the soil surface) were tested. The du- 1.5 h of equilibration to the chamber climate). ration of this experiment was long enough (7 wk) to allow seedlings to present potentially Experiment 2 adventitious rooting and possible consequences on shoot gas exchange. Acorns were collected during the autumn of 1987, under individuals of Q robur L (Amance Forest), Q rubra L (Fénétrange Forest, Moselle, Plant material and experimental set-up France) and Q palustris Muenchh (Pujo Forest, Hautes Pyrénées, France). Seedling preparation Experiment 1 was carried out in February as indicated above, and measurements were made in July 1988. Acorns were collected in the autumn of 1984 un- Height growth was monitored weekly. The der adult trees of the following species: Quercus growth conditions and soil characteristics have robur L (Amance Forest), Q petraea (Matt) Lieb ] been described by Colin-Belgrand et al (1991). (Villey St Etienne Forest) and Q rubra L (Brin The plants were waterlogged with tap water sur Seille) all located near Nancy, north-easten June 15th. The upper level of the water table on France. was adjusted daily to 6 cm from the soil surface, The stored at -1 °C and and was maintained during 7 wk. Sixty plants acorns were sown during the following August in individual pots were used for each species, 30 randomly select- containing a 50/50 v/v mixture of peat/sandy ed ones as controls and 30 as treated samples. loam. They were transplanted int 5-I, 25-cm Gas exchange was monitored weekly on 4 seed- deep pots with the same substrate in March, lings (3 treated and one control) which had been and were grown in a glasshouse near Nancy. randomly selected at the beginning of the exper-
iment. The remaining seedlings were used for The climate regulated as follows: air was weekly measurements of shoot and root growth, 24 ± 0.2 °C; CO molar temperature (ta): 2 fraction at the inlet: 350 μmol.mol and in water potential, and mineral status in xylem sap -1 the chamber )c 310 ± 20 μmol.mol depend- -1 and stems (see Colin-Belgrand et al, 1991). a (: ing on the rate of A; leaf to air difference in mo- A and g were measured weekly in the same lar fraction of water vapor (Δw): 12.0 ± 1.5 Pa shoot bearing 3-4 leaves of 4 seedlings per ; -1 kPa PPFD: 600 ± 20 μmol.m Total leaf . -1 .s -2 species (3 waterlogged and 1 control). Meas- area was measured with a planimeter. Each sin- urements were made in 4 series (waterlogged gle measurement was preceded by a period of plants of each species plus 3 controls) on 1 d acclimation to the chamber atmosphere of 90 each week. The same design as in experiment min. Calculations of total leaf conductance (g) 1 was used. The plants were measured once and of intercellular CO molar fraction (c were 2 ) i before, and 7 times during waterlogging. Prob- made according to Ball (1988). lems in the measurement of transpiration affect- Results were represented as time courses of ed our results during the first few weeks; these A and g, or as A vs c diagrams displaying pho- i data were removed from the data set. tosynthetic demand and supply functions (Jones, 1985; Guehl and Aussenac, 1987). De- mand functions are defined as the A/c relation- i Gas exchange measurements ship, and supply functions are straight lines join- ing the points (0, C and (A, cthe slope of ); i ) a these lines is nearly equal to -g. On these dia- Measuring device grams we drew demand functions on the hy- pothesized basis of a linear relationship betwen Net CO assimilation rates (A) and total leaf 2 A and c until c 250 μmol.mol . -1 i i = conductance to Cg) were measured in an 2 (O open flow gas exchange system. The measur- ing device consisted of 3-altuglass assimilation Measurements of water status chambers which were connected in parallel to the same main gas flow (180 l.h The CO ). -1 2 molar fraction of the incoming air was measured Shoots of randomly selected plants (2 control with an ADC Mk II infrared gas analyzer, and and 2 treated per species) were cut off once maintained at 350 μmol.mol by injection of a -1 weekly after being submitted to at least 12 h of N 90/10 v/v mixture into the main flow. /CO 2 darkness, and water potential (Ψ for the ) wb The molar fraction of water vapour in the inject- whole shoot was measured with a pressure ed air was controlled by means of a dew point chamber. water trap. The temperature inside the cham- bers was controlled via Peltier cooled thermo- elements. A multichannel valve allowed sequen- RESULTS tial analysis of the gas mixtures at the outlet of each chamber at 5-min intervals. A was comput- ed from the difference measured in the CO mo- 2 Waterlogging had a marked short term ef- lar fraction between incoming and outcoming air fect on net CO assimilation rate (A), and 2 as monitored by an ADC Mk III infrared gas an- leaf conductance to Cg) in all species 2 (O alyzer and from the molar air flow at the cham- (fig 1, Exp 1); both A and g decreased rap- ber inlet as derived from a volumetric flow me- idly in Q robur, and after very few days in ter. The transpiration rate (E) was estimated from the difference in the molar fraction of water Q petraea and Q rubra. Some species- vapor between incoming and outcoming air, as related differences appeared: Q robur had displayed by a dew-point hygrometer Elcowa highest values of A and g before waterlog- western Electric (± 0.1 °C). Illumination was pro- ging but also showed the steepest de- vided by 3 (1 for each chamber) sodium lamps in both parameters between d 0 creases (SONT Philips, 400 W), and incident photosyn- and 1, while Q petraea maintained higher thetic photon flux density (PPFD) was meas- values during waterlogging. Q rubra ured with a Li-Cor quantum sensor.
showed both low initial values and a strong reduction. Calculated values of c in-i creased regularly, reaching levels of 250 = -1 μmol.mol at the end of the waterlogging period. After 12 d of drainage, recovery was very poor; only Q robur showed signif- icant but uncomplete recovery of g. tion joining c 330 μmol.mol and maxi- -1 a = mal A (slope -g) both describing the situ- Representing the same set of data as A = ation before waterlogging have been vs c diagrams yielded the graphs in figure i 2. A demand function and a supply func- drawn. The observed decreases in A fol-
be due to lowing waterlogging appeared to control and treated seedlings evolved in both decrease in leaf conductance (g, parallel, and no difference could be detect- a decrease of supply function slope), and an ed at any stage. For Q rubra, we observed a strong decrease in both A and g (less vis- even stronger decrease in demand. After ible in g due to lack of sufficient data). Q 12 d of drainage, demand functions did not palustris displayed an intermediate trend: recover in any species (dark points in fig 2). we did not observe a strong decrease in A or g, but the increase observed in the con- During exp 2, the evolution of net as- trol seedling was completely suppressed. similation rate (A) and leaf conductance to Drainage following the 7 wk of waterlog- CO as illustrated in figure 3 displayed 2 (g) ging was not followed by recovery of A or g some marked differences. For 2 species in Q rubra and Q palustris; only a slight in- (Q rubra and Q palustris), A of control crease in g was observed. plants increased, while it decreased slight- ly in Q robur. The same patterns appeared Predawn leaf water potential (Ψ of ) wb for g. Important differences among species waterlogged and control plants, measured appeared with regard to the waterlogging during exp 2, did not differ markedly during the entire waterlogging period (fig 4). A di- treatment. Q robur showed almost no re- action to waterlogging: A and g for both rect comparison of the mean values for
DISCUSSION Many of the oak seedlings tested during these experiments presented significant re- ductions in net CO assimilation rates (A) 2 and leaf conductance to CO in reac- 2 (g) tion to root hypoxia induced by waterlog- ging. Short term reactions generally ap- peared after very few days of waterlogging with tap water. Analog reductions of A and g with the same precocity have been ob- served in a wide range of tree species in- cluding Ulmus americana (Newsome et al, 1982), Fraxinus pennsylvanica (Sena Gomes and Kozlowski, 1980), Actinidia chinensis (Savé and Serrano, 1986), Taxo- dium distichum (Pezeshki et al, 1986), some of them having the reputation of be- ing fairly tolerant to flooding. A few tested oak species like Quercus macrocarpa (Tang and Kozlowski, 1982), Q falcata (Pe- zeshki and Chambers, 1985), and Q mi- chauxii (Pezeshki and Chambers, 1986) behaved similarly. Most experiments were conducted with potted seedlings; however, Black (1984) showed that mature Quercus palustris in the stand showed the same stomatal reactions. Only a few reports of lack of stomatal closure with flooding are available (Alnus rubra and Populus tricho- carpa; Harrington, 1987). Was the limitation of A due to stomatal closure? In most cases decreases in A and in g presented a striking parallelism; but an control and waterlogged plants during the analysis of the A/c relationships led to the i waterlogging period (Fisher PLSD, n 14) = hypothesis that the observed limitations yielded the mean values indicated on the could only partly be attributed to stomatal graphs: for none of the tested species closure. A non stomatal inhibition of photo- were these differences statistically signifi- synthesis probably occurred. Bradford cant. Ψ was even slightly higher in flood- wb (1983, Lycopersicon esculentum) and Pe- ed plants than in controls. Therefore, high zeshki and Sundstrom (1988, Capsicum levels of roots senescence observed in re- annuum) made the same assumption while sponse to waterlogging on the same seed- observing that hypoxia promoted a reduc- lings and described in Colin-Belgrand et al tion in A at quasi-saturating c However, . i (1991) did not significantly alter leaf water of calculated values of c in reveal- the use i status in any tested plant or species. stomatal limitations of photosyn- ing non
thesis has been questioned (Downton et limited consequences on shoot water only al, 1988; Terashima et al, 1988; Epron and status because of reduced transpiration due to stomatal closure. Dreyer, 1990): artifacts due to patchy stomatal closure may appear. Heterogene- The trigger mechanism for stomatal clo- ity of stomatal closure in response to wa- and for hypothetical effects on meso- sure terlogging has not yet been tested. It may phyll photosynthesis must therefore be in- also be argued in favor of non-stomatal dependent of leaf water status. In the case limitations that other workers have arrived of short term reactions to flooding, abscisic at similar conclusions for waterlogging ef- acid (ABA) which accumulates in leaf tis- fects using different arguments. The fact sues may induce stomatal closure in the that A sometimes decreased without stom- absence of a water deficit (Jackson and atal closure (Guy and Wample, 1984; with Hall, 1987). This ABA could be synthe- Helianthus annuus), and a study of 13 C sized in root tips submitted to anoxia and isotopic discrimination (Guy and Wample, transported to leaves via the transpiration 1984) support the existence of a non stom- flux (Zhang and Davies, 1987), but the atal limitation of A in flooded plants. In any time lags observed between stomatal clo- case, a firm conclusion may only be ob- sure and ABA accumulation in leaves tained after careful analysis of leaf photo- (Jackson et al, 1988) do not allow firm con- synthetic properties, for example by chlo- clusion to be reached. Moreover, Smit and rophyll fluorescence techniques. Stachowiak (1990) confirmed the exis- tence of a factor promoting stomatal con- Stomatal closure in waterlogged plants ductance in xylem sap, but did not observe has sometimes been attributed to reduced increased ABA concentration in flooded water potential, but predawn leaf water po- Populus. There is still need for further re- tential (Ψ was not reduced by our treat- ) wb search to identify the signal involved. ments, even in the case of Q rubra which Q robur showed very different res- showed severe damage to roots as de- scribed in Colin-Belgrand et al (1991). ponses to waterlogging in both experi- Leaf water potential has sometimes been ments: strong decreases in A and g in the first, and almost no reaction in the second. reported to increase both in annuals (Brad- This discrepancy was probably related to ford, 1983; Jackson and Hall, 1987) and in the depth of the unsaturated upper soil trees (Pezeshki and Chambers, 1985, layer (3 cm in the first experiment vs 6 cm 1986) due to reduced transpiratory losses in the second one). Lévy et al (1986) following stomatal closure. Only a few re- showed that sensitivity of Q robur seed- ports have shown marked decreases in lings decreased markedly with a lowering water potential (Zaerr, 1983; Osonubi and of the water table, and disappeared below Osundina, 1987); such decreases have of- 8 cm. Q rubra, on the other hand, dis- ten been associated with anticipated shoot played very similar and strong reactions in senescence and appeared long time after both cases. stomatal closure (Lewty, 1990). The water relations of flooded trees are nevertheless Were the observed decreases of A and strongly affected by flooding; reductions in g in Q rubra and Q palustris related to the root hydraulic conductivity were observed observed root decay in these seedlings by Harrington (1987, Alnus rubra) and ap- (Colin-Belgrand et al, 1991)? Correlations between root growth rate and net assimila- peared after a few hours in Populus tricho- tion rates have been reported in transplant- carpa x deltoides (Smit and Stachowiak, ed seedlings (Guehl et al, 1989), even if 1988). These reductions probably have
growing the seedlings and for preparing the ex- the physiological link between both still has periments, and JM Guehl and 2 anonymous re- to be discovered. In Q robur we observed viewers for helpful criticism on a first draft of the a strong initial decay and subsequent new manuscript. root growth; these 2 phases were not ac- companied by any significant modification in A or g. REFERENCES An overall comparison of waterlogging tolerance between all tested species yield- Ball JT (1987) Calculations related to gas ex- ed the following results. In the first experi- change. In: Stomatal Function (Zeiger, Fraq- ment, Q petraea and Q robur displayed ap- uhar, Cowan, eds) Stanford University Press, proximately the same sensitivity, and Q 445-477 rubra was affected slightly more than the Black RA (1984) Water relations of Quercus pa- other species. In the second experiment, Q lustris: field measurements of an experimen- robur was the least affected, while Q rubra tally flooded stand. Oecologia 64, 14-20 displayed the strongest reaction and Q pa- Bradford KJ (1983) Involvement of plant growth lustris had a somewhat intermediate beha- substances in the alteration of leaf gas ex- viour (no decline, but a low initial A and a change of flooded tomato plants. Plant Phys- iol 73, 480-483 divergence from the control sapling). The same ranking (Q robur / Q palustris / Q ru- Childers NF, White DG (1942) Influence of sub- mersion of the roots on transpiration, appar- bra) was obtained when considering the in- photosynthesis, and respiration of young ent tensity of root reactions (Colin-Belgrand et apple trees. Plant Physiol 17, 603-618 al, 1991).This agrees well with observa- Colin-Belgrand M, Dreyer E, Biron P (1991) tions made under natural conditions, Sensitivity of seedlings from different oak where Q petraea and Q robur are known to species to waterlogging: effects on root be fairly tolerant, and Q rubra very intoler- growth and mineral nutrition. Ann Sci For 48 (Lévy et al, 1986). ant 193-204 The physiological basis of these differ- Davies FS, Flore JA (1986a) Short term flooding ences has yet to be elucidated. The ability effects on gas exchange and quantum yield to form adventitious roots in the unsaturat- of rabbiteye blueberry (Vaccinium ashei Reade). Plant Physiol 81, 289-292 ed soil layer is probably the major expres- sion of these differences. This ability does Davies FS, Flore JA (1986b) Flooding, gas ex- change and hydraulic root conductivity of not express a real tolerance to soil hypox- highbush blueberry. Physiol Plant 67, 545- ia; this is illustrated by the stronger reac- 551 tions of Q robur with higher water tables (3 Downton WJS, Loveys BR, Grant WJR (1988) vs 6 cm from the soil surface); complete Non-uniform stomatal closure induced by wa- flooding would be expected to induce even ter stress causes putative non-stomatal inhi- stronger reactions. There is still need for bition of photosynthesis. New Phytol 110, further experiments to test the effects of 503-509 water tables at different depths in soils, Guehl JM, Aussenac G (1987) Photosynthesis and to compare the physiological reactions decrease and stomatal control of gas ex- of various species. change in Abies alba Mill in response to va- por pressure deficit. Plant Physiol 83, 316- 322 ACKNOWLEDGMENTS Guehl JM, Aussenac G, Kaushal P (1989) The effects of transplanting stress on photosyn- thesis, stomatal conductance and leaf water The authors wish to thank P Gross for construct- potential in Cedrus atlantica Manetti seed- ing the gas exchange device, JM Gioria for
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