Báo cáo khoa học: "Changes in dry weight and nitrogen partitioning induced by elevated CO depend on soil nutrient 2 availability in sweet chestnut (Castanea sativa Mill)"

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Nội dung Text: Báo cáo khoa học: "Changes in dry weight and nitrogen partitioning induced by elevated CO depend on soil nutrient 2 availability in sweet chestnut (Castanea sativa Mill)"

Original article Changes in dry weight and nitrogen partitioning induced by elevated CO depend on soil nutrient 2 availability in sweet chestnut (Castanea sativa Mill) A EI Kohen H Rouhier M Mousseau 1 CNRS, URA 121, Laboratoire d’Écologie Végétale, Bâtiment 362, Université Paris-Sud, 91405 Orsay Cedex; 2 CEFE-CNRS, route de Mende, BP 5051, 34033 Montpellier Cedex, France (Received 28 August 1991; accepted 4 November 1991) Summary — The effect of 2 levels of atmospheric carbon dioxide (ambient, ie 350 ppm, and double, ie 700 ppm) and 2 contrasting levels of mineral nutrition on dry weight, nitrogen accumulation and partitioning were examined in 2-year-old chesnut seedlings (Castanea sativa Mill), grown in pots out- doors throughout the vegetative season. Fertilization had a pronounced effet on dry weight accumu- lation, tree height, leaf area, and plant nitrogen content. Carbon dioxide enrichment significantly in- creased total biomass by about 20%, both on fertilized and on unfertilized forest soil. However, the partitioning of biomass was very different: on the unfertilized soil, only the root biomass was in- creased, leading to an increase in the root: shoot ratio. Contrastingly, on fertilized soil only stem bio- mass and diameter but not height were increased. Carbon dioxide enrichment significantly reduced the nitrogen concentration in all organs, irrespective of the nutrient availability. However, the bio- mass increase made up for this reduction in such a way that the total nitrogen pool per tree re- mained unchanged. elevated Castanea sativa Mill CO / dry weight partitioning / nitrogen partitioning / 2 Résumé — Les effets d’un enrichissement en CO sur la répartition de la matière sèche et de 2 l’azote chez le châtaignier (Castanea sativa Mill) dépendent de la fertilité du sol. On a étudié l’effet d’un doublement de la concentration en CO de l’atmosphère (soit 350 vpm, teneur actuelle et 2 700 vpm) sur la répartition de la biomasse et du contenu en azote chez de jeunes plants de châtai- gniers (Castanea sativa Mill). Les arbres, âgés de 2 ans, sont cultivés en pots à l’extérieur pendant toute une saison de végétation sous des tunnels ou miniserres recouvertes de propafilm et ventilées en permanence. Le doublement du CO ambiant est obtenu par addition constante de CO pur d’ori- 2 2 gine industrielle. Ces jeunes châtaigniers sont cultivés sous nutrition minérale contrastée (sol fores- tier auquel est ajouté ou non de l’engrais NPK en granulés). Une fertilisation du sol forestier d’origine augmente nettement la biomasse, la hauteur et la surface foliaire totale des arbres, ainsi que leur contenu en azote. L’augmentation de la biomasse due au doublement du CO (de l’ordre de 20%) est la même quelle que soit la fertilité du sol. Par contre, la 2 répartition de la matière sèche est très différente sur sol fertilisé ou non fertilisé. Sur sol pauvre, l’augmentation de biomasse est uniquement localisée dans les racines, d’où une augmentation du rapport parties souterraines/parties aériennes. Au contraire, sur sol fertilisé, l’augmentation de bio- * Correspondence and reprints
uniquement la partie aérienne, dont la tige grossit en diamètre hau- et masse concerne non en pas teur. L’enrichissement CO réduit de manière significative la concentration en azote de tous les or- 2 en ganes, quel que soit le degré de disponibilité en azote du sol. Cependant, l’augmentation de biomasse des organes compense cette réduction de telle manière que le pool d’azote par arbre reste constant. enrichissement en CO répartition de la matière sèche / distribution de l’azote/ / 2 Castanea sati- va Mill INTRODUCTION Sweet chestnut, Castanea sativa Mill, is relatively fast growing species, bearing a large leaves with a relatively high photo- Among the effects of the increase in atmos- synthetic capacity (Ceulemans and Saugi- pheric CO those concerning trees are par- , 2 er, 1991). Sweet chestnut is common in ticularly important because forest ecosys- the French deciduous forest, being the tems are the major carbon store of the major genus following Quercus and third biosphere. Earlier work on the effect of ele- Fagus in terms of area (one million hec- vated CO on young trees (Eamus and Jar- 2 tares) and productivity. These specific fea- vis, 1989) has shown a general increase in tures make Castanea a good model to in- total dry weight. Tree ring measurements vestigate the effects of elevated CO on2 over the past 100 years (Kienast and Lux- temperate tree species. moore, 1988) have provided direct evi- The experiment reported here was de- dence of increase in tree growth, although signed to investigate the effect of elevated this has not been directly related to elevat- CO in well-watered trees under full sun- 2 ed CO alone. One may thus assume that 2 light in 2 contrasting nutrient situations. an elevated CO will induce an increase in 2 the trees’ carbon storage despite wide- spread tropical deforestation that is counter- MATERIALS AND METHODS acting this effect (Houghton et al, 1991). Generally, tree responses to CO en- 2 richment include an increase in net photo- Two-year-old bare-root chestnut seedlings were obtained from a forestry nursery (Bauchery et synthesis and thereby in growth and dry Fils, Crouy sur Cosson, La Ferté-St-Cyr, weight production (Jarvis, 1989). In most France). The seedlings were planted in cylindri- of the experiments reported in the litera- cal pots (25 cm diameter, 50 cm height) filled ture, nutrients have been supplied in suffi- with 24 I of soil. The soil was taken from a near- cient amounts. However, forests frequently by chestnut stand; it consisted of the upper 15 grow on nutrient-poor soils and their pro- cm organic layer of forest soil sifted and homo- genized after litter removal. ductivity is strongly related to soil fertility. It has been demonstrated that a limitation in follows: The main soil characteristics were as resources does not preclude plant growth apparent density: 1.5 g.cm ; 3 response to CO enrichment (Norby et al, 2 field capacity: 15% (weight fraction); 1986b). However, the limit in the CO re- 2 available water: 10% (weight fraction); sponse may be connected with the total cation exchange capacity: 26 meq/1 000 g dry amount of nitrogen that could be obtained weight; from a poor environment: growth stimula- total nitrogen content: 0.37 g/1 000 g dry weight; tion will depend on the sink activity, which total organic matter: 10.6 g/1 000 g dry weight; is itself stimulated by nutrient availability (Cromer and Jarvis, 1990). C/N. 16.5.
Fertilization of the soil was provided monthly with fertilizer granules spread over the pots’ sur- face. These mineral granules (Engrais SECO, Ribécourt, France) contained 17% nitrogen (6.2 NO and 10.8 NH 17% P (16% water- - 3 ), + 4 , -- 5 O 2 soluble) and 17% K soluble in water. Forty O 2 granules were distributed monthly in each pot, providing 0.82 g N, 0.78 g P and 0.4 g K. These quantities were 3 times as high as the final min- eral content of a tree at the end of 1 year’s growth. These nutrients were progressively dis- solved into the soil via an automatic drip system. Twenty-four trees were planted in each mini- greenhouse. For various reasons (pests, breaks, etc), the number of trees analysed in each experimental situation varied between 16 and 20. This number is given in each specific table. t-Test was used for comparison of means and ANOVA to assess the interaction between CO and fertilization treatments. 2 The pots were placed in trenches 2 m long and 1 m wide, covered with ventilated mini- greenhouses made of polypropylene films glued onto aluminium frames (1 m high). Air was blown continuously over the plants at a rate of 150 l.s which was sufficient to maintain the air -1 temperature close to that of the outside air (+ 2 °C max). In half of these mini-greenhouses, a double CO concentration (ie, 700 ppm) was 2 maintained with pure industrial CO introduced at 2 a constant rate (120 l.h into the main air flow. ) -1 The other half was ventilated with normal air. The trees were watered daily with tap water in order to compensate for daily evapotranspira- tion (ie about 200 g water per pot). Total leaf per tree was computed by area length (L) and width (W) of all measurements of shoots and roots in the fertilized and unfer- leaves (S L x W x 0.65). After leaf fall, all dead = tilized situation. In normal air, there was leaves were collected and weighed. Later, in more than a doubling in dry biomass pro- January, the plants were dug up, roots were duction of the seedling with the increase in washed under water, and shoot and root dry weight were evaluated. nutrient availability. This confirms that trees’ mineral nutrition was a strong growth limiting factor. It can also be noticed that RESULTS fertilization enhanced the shoot (x 3) pro- duction more than the root (x 2) produc- tion. It followed that the root/shoot ratio Dry weight partitioning decreased significantly, as previously de- scribed (Agren and Ingestad, 1987). 1 shows the effect of double CO 2 Figure The percentage of total dry weight in- a partitioning between the dry weight due to CO enrichment was equiva- 2 on crease
lent in the unfertilized fertilized situation: cies (Sionit et al, 1985). Therefore, when or the doubling of atmospheric CO was re- stem dry weight was increased (ie in the 2 sponsible for an increase of about 20% in fertilized situation), this was mainly due to total dry weight. However, CO enrichment stem diameter increase (table I). 2 had a specific effect on dry weight parti- No effect of elevated CO could be not- 2 tioning to roots and shoots: on poor forest ed on leaf area development in unfertilized soil, the whole dry weight increase due to trees (table I) as reported earlier (Mous- elevated CO was allocated to the roots. 2 seau and Enoch, 1989). This was not the The stem dry weight had been reported to case with fertilized trees, for which leaf be negatively affected by elevated CO in 2 area per plant was significantly increased this species (Mousseau and Enoch, 1989) by the CO treatment (table I). 2 which was not significant in the present ex- periment. Contrastingly, on the fertilized soil, ele- Nitrogen distribution within the trees vated CO affected mostly stem + branch- 2 es (+ 33%) and litter (+ 35%) dry weight Under both fertilization treatments, elevated accumulation (fig 1).A significant interac- CO decreased nitrogen concentration in all 2 tion between fertilization and CO treat- 2 organs. This decrease was especially signif- ment was observed for these parameters icant in roots (table II). Litter (and not leaf) (F 5.06 and 5.39 respectively; df 1.67). = = nitrogen content is mentioned in table II be- The corresponding increase in root dry cause the analyses were performed in win- weight, although noticeable in figure 1, ter, after leaf fall and nitrogen redistribution was not significant at P < 5% and no inter- to other plant parts. The analysis made on a action was noted. few green leaves at the end of the growing season (before yellowing: 1st September) In both fertilized and unfertilized situa- showed a decrease in leaf nitrogen concen- tion, neither an increase in stem length nor tration in response to CO enrichment simi- any effect on branching due to the CO 2 2 lar to that found in other organs, irrespective treatment was noted (results not shown) of the fertilization treatment (table III). although it has been reported in other spe-
More nitrogen in the soil increased the IIA) into their fine roots. This was not true in the fertilized situation as shown by the overall nitrogen concentration and content of the seedlings. The nutrient pool sizes results from ANOVA analysis on fine roots. were calculated by multiplying the mean The same conclusion may be drawn nutrient concentration by the mean dry from table II for all organs and this resulted weight. In all cases, the increase in dry in a similar overall nitrogen content of the weight due to elevated CO seemed to 2 tree in normal and enriched CO. 2 make up for the decrease in nitrogen con- centration so that the total leaf nitrogen pool size remained similar. However, as DISCUSSION more fine roots were produced in the un- fertilized situation (results not shown) their The effect of elevated CO on dry weight 2 N pool size was higher (table IIB). So, accumulation did not differ in the fertilized plants seem to invest a larger amount of and unfertilized situation. This result is very their lower nitrogen concentration (table
similar to the study on yellow poplar (Lirio- total nitrogen uptake by the size of the dendron tulipifera) described by Norby and This could suggest that even in the pots. O’Neill (1991).However, these authors did fertilized situation, the dry weight produc- not find any differences in dry weight parti- tion could have been nutrient limited. This tioning of their trees. We may conclude, as was not probable because the total nitro- did Idso et al (1991),that if there is no nutri- gen amount that was added to the pots ment limitation, an increase in CO will be was 3 times greater than the total plant ni- 2 of great benefit to tree growth. trogen content at the end of the season. However, we cannot eliminate the hypo- Our results agree with the predicted thesis because a leaching of nitrogen with general dependence of root/shoot ratios watering is always possible. on internal nitrogen concentration (Thorn- ley, 1972; Ågren and Ingestad, 1987). In forest ecosystems, these lower nitro- gen concentrations could lead to nutrient In general, higher CO concentrations 2 deficiencies which would probably be com- produce tissues with lower nitrogen con- pensated by an increase in the amount of centration(Williams et al, 1986; Brown, fine roots and mycorrhiza (O’Neill et al, 1991).The comparison of chestnut behavi- 1987) which would extract nutrients from a in different nutritional conditions dem- our wider surrounding area. onstrates that internal nitrogen concentra- tion decreased both on fertile and unfertile In after 1 year of 2 CO experiment, our enrichment, the leaves that abscised from soil under elevated CO We may assume . 2 either: 1),a slower increase in nutrient up- the enriched seelings contained a higher nitrogen level (table II) than the control take than in carbon assimilation; or 2), no leaves, although the reverse situation was increase in nitrogen uptake and a progres- found in green leaves (table III). It may be sive dilution of this nitrogen into the plant: assumed that the amount of nitrogen com- the second hypothesis is more probable in pounds sent to the reserve organs in the our case because the roots were limited in
Brown KR (1991) Carbon dioxide enrichment ac- fall affected by the CO 2 treatment. was celerates the decline in nutrient status and et al (1986a) also found that Norby there relative growth rate of Populus tremuloides was less nitrogen to translocate in elevat- Michx seedlings. Tree Physiol 8, 161-173 ed CO However, Couteaux et al (1991) . 2 Brown K, Higginbotham KO (1986) Effects of showed that, after a 2-year CO enrich- 2 carbon dioxide enrichment and nitrogen sup- ment, the results were different: the chest- ply on growth of boreal tree seedlings. Tree nut litter nitrogen content was significantly Physiol 2, 223-231 decreased by a double CO concentration 2 Ceulemans R, Saugier B (1991) Photosynthe- and the total amount of nitrogen which re- sis. In: Physiology of Tree (Raghavendra AS, turned to the soil from litter decomposition ed) J Wiley (in press) was lowered, contributing to increase the Conroy JP, Milham PJ, Mazur M, Barlow EWR deficit in soil nutriment. Overall, the fact that (1960) Growth dry weight partitionning and the totality of additional dry weight in seed- wood properties of Pinus radiata D Don after 2 years of CO enrichment. Plant Cell Envi- 2 lings grown in high CO was allocated to 2 ron 13, 329-337 the roots in low nutritional conditions might Couteaux MM, Mousseau M, Celerier ML, Bott- confer an advantage to tree survival capaci- ner P (1991) Atmospheric CO increase and 2 ty in a double-CO world, particularly if the 2 litter quality: decomposition of sweet chestnut water stresses were expected to increase. leaf litter with animal food webs of different It is of interest to foresters that a tree is complexities. Oikos 61, 54-64 able to partition larger amounts of dry Cromer RN, Jarvis PG (1990) Growth and bio- weight to the trunk. This was the case of partitioning in Eucalyptus grandis seed- mass lings in response to nitrogen supply. Aust J the CO enriched chestnut in a well ferti- 2 Plant Physiol 17, 503-515 lized soil: although trunk height was not Eamus D, Jarvis PG (1989) The direct effects of changed, an increase in diameter led to a increase in the global atmospheric CO con- 2 greater wood volume. Such an increase centration on natural and commercial temper- depends on cell division in the cambium ate trees and forests. Adv Ecol Res 19, 1-55 which we may assume to be stimulated by Houghton RA, Skole DL, Lefkowitz DS (1991) high CO levels. Moreover, in the case of 2 Changes in the landscape of Latin America Pinus radiata, an elevated CO has been 2 between 1850 and 1985: net release of CO 2 shown to also increase wood density (Con- to the atmosphere. For Ecol Manage 38, roy et al, 1990). 173-199 ldso SB, Kimball BA, Allen SG (1991) CO en- Lastly, our results emphasize the need 2 richment of sour orange trees: 2.5 years into for controlling, or at least measuring, the a long-term experiment. Plant Cell Environ nutrient conditions of the experimental tree 14, 351-353 seedlings submitted to an increase in CO2 Jarvis PG (1989) Atmospheric carbon dioxide before any conclusions about the latter ef- and forests. Phil Trans R Soc Lond B 324, fect can be made and extrapolated to for- 369-392 est ecosystems. Kienast F, Luxmoore RL (1988) Tree ring analysis and conifer growth responses to increased at- mospheric CO levels. Oecologia 76, 487-495 2 REFERENCES Kramer PJ, Kozlowski TT (1979) Physiology of Woody Plants. Academic Press, NY Ågren GI, Ingestad T (1987) Root: shoot ratio as Mousseau M, Enoch ZH (1989) Carbon dioxide enrichment reduces shoot growth in sweet balance between nitrogen productivity and a chestnut seedlings (Castanea sativa Mill). photosynthesis. Plant Cell Environ 10, 579- Plant Cell Environ 12, 927-934 586
Norby RJ, Pastor J, Melillo JM (1986a) Carbon- in Pinus echinata and Quer- seedling growth nitrogen interactions in CO white alba in an enriched CO atmosphere. -enriched 2 2 cus oak: physiological and long-term perspec- Can J For Res 17, 878-883 tives. Tree Physiol 2, 233-241 Sionit N, Strain BR, Riechers GH, Jaeger CH Norby RJ, O’Neill EG, Luxmoore RJ (1986b) Ef- (1985) Long-term atmospheric CO enrich- 2 fects of atmospheric CO enrichment on the ment affects the growth and development of 2 growth and mineral nutrition of Quercus alba Liquidambar styraciflua and Pinus taeda seedlings in nutrient poor soil. Plant Physiol seedlings. Can J For Res 15, 468-471 82, 83-89 Thornley JHM (1972) A balanced quantitative Norby RJ, O’Neill EG (1991) Leaf area compen- model for root: shoot ratios in vegetative sation and nutrient interactions in CO en- Ann Bot 36, 431-441 plants. 2 riched seedlings of yellow poplar (Lirioden- Williams WE, Garbutt K, Bazzaz FA, Vitousek dron tulipifera L). New Phytol 117, 515-528 PM (1986) The response of plants to elevat- ed CO IV. Two deciduous tree communi- O’Neill EG, Luxmoore RJ, Norby RJ (1987) In- . 2 creases in mycorrhizal colonisation and ties. Oecologia 69, 454-459