Báo cáo lâm nghiệp: "partitioning and production of 15 N-labelled litter in beech trees"

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Original article N 15 partitioning and production of 15 N-labelled following [ spray N]urea 15 litter in beech trees Bernd Zeller Micheline Colin-Belgrand a Étienne Dambrine Francis Martin Écosystèmes forestiers, Centre Inra Nancy, 54280 Champenoux, France (Received16 June 1997; accepted12 November 1997) Abstract - The leaves of 10-year-old beech trees grown in a plantation were sprayed once in late summer in 1993, 1994 and 1995 with [ to determine the 15 utilization by beech (Fagus N N]urea, 15 sylvatica L.) and to obtain homogeneous15 litter. One day after spraying, leaves had N-labelled incorporated 42 % (1993) to 55 % (1995) of the applied [ The leaf amino acid content N]urea. 15 and N concentration increased shortly after application. During leaf senescence, approximately 88 % of the incorporated 15 was translocated and mainly stored in the above-ground biomass. N After spraying, N concentration and 15 enrichment of leaves were measured until abscission. In N spring, trees were sampled and15 allocation in above- and below-ground organs were determined N to assess 15 partitioning. Buds and bark showed the highest 15 enrichment, but the largest N N amounts of foliarly applied 15 were stored in bark and wood. 15 enrichment of fallen leaves (i.e. N N litter) increased after each 15 urea spray, from 2.11% 15 atom excess in 1993, to 2.97 % 15 N N N in 1994 and 3.14 % 1in 1995. Annual litter contained 4.7%, 7.3 % and 7.8 % of the sprayed N5 15 Soluble and insoluble N fractions showed an identical 15 atom excess indicating a homo- N N. geneous distribution of 15 in the labelled leaves as well as litter. (© Inra/Elsevier, Paris.) N N 15 / urea / beech litter / forest / nitrogen Résumé - Répartition de 15 dans le hêtre et production d’une litière marquée après pul- N vérisation de [ Afin de déterminer l’utilisation de l’azote par le hêtre (Fagus sylvatica N]urée. 15 L.) et pour obtenir une litière homogène marquée au15 de l’urée enrichie en 15 a été pulvé- N N, risée en fin d’été 1993, 1994 et 1995 sur le feuillage de jeunes hêtres. Après la pulvérisation, les concentrations en N et 15 dans les feuilles et la litière ont été mesurées jusqu’à l’abscission. Un N jour après la pulvérisation, les feuilles ont incorporé entre 42 % (1993) et 55 % (1995) de N]urée. 15 l’[ Une brève augmentation de la teneur en acides aminés et de la concentration en N 1994, un prélèvement sur cinq arbres a été foliaire a eu lieu peu après l’application. Au printemps effectué, pour déterminer la répartition de 15 dans les organes aériens et souterrains des arbres. N Pendant la sénescence des feuilles, 88 % de l’azote incorporé est transféré dont la plus grande part * Correspondence and reprints E-mail: mcolin@nancy.inra.fr
stockée dans les organes aériens des arbres. Les bourgeons et l’écorce sont les tissus les plus est enrichis en 15 mais l’écorce et le bois accumulent l’essentiel de l’azote 15 L’enrichissement N, N. en 15 des feuilles sénescentes (litière) augmente après chaque pulvérisation d’[ l’excès N N]urée ; 15 isotopique15 mesuré en 1993 est de 2,11% et il atteint 3,14 % en 1995. La chute annuelle de N litière représente 4,7, 7,3 et 7,8 % de 15 pulvérisé. Les composés azotées solubles et insolubles N présentent des enrichissements identiques en 15 indiquant une distribution homogène de 15 dans N N, les feuilles et également dans la litière. (© Inra/Elsevier, Paris.) N 15 / urée / litière / hêtre / forêt / azote 1. INTRODUCTION lization by beech (Fagus sylvatica L.) of N 15 sprayed on leaves and to obtain urea homogeneous 15 beech litter. N-labelled Little is known on the dynamics of The major aims of this study were to ascer- leaching, accumulation and release of N tain i) that N originating from 15 leaf N in decomposing forest litter in beech labelling was properly distributed into ecosystems. A major aim of the current beech organs, andii) that fallen leaves (i.e. investigations was to study the mecha- litter) exhibited homogeneous 15 N nisms involved in the uptake and release of labelling. N from litter. The determination of the sizes of the N pools involved and esti- mates of their turnover in litter and soil had been efficiently obtained by 15 tracer N 2. MATERIALS AND METHODS experiments [1, 2]. Plant residues enriched in 15 have been widely used as tracers N 2.1. 15 N labelling in N-cycling experiments in agricultural systems [7,11].In forest ecosystems, 15 N- A field experiment was conducted on a labelled corn straw was used as a source of calcareous brown earth soil (Calcisol) in a N and C in studies on N mineralization large natural regeneration area at Puvenelle [2]. However, replacing of straw from near Pont-à-Mousson (France). The 10- herbaceous species by labelled litter from year-old beech trees selected for the 15N- the species under investigation (e.g. beech) labelling experiment, had a mean height of would make it possible to quantify the 1.25 m. A 25-m plot containing 350 trees 2 decomposition and mineralization of litter was carefully cleaned of understorey veg- with few modifications to the litter layer. etation and litter from previous years. Dur- N-labelled 15 needle litter has been used ing late summer, tree shoots were sprayed in several studies on N decomposition and in the evening with a 50-mM aqueous mineralization in conifer ecosystems [1, solution of [ (99.5 % 15 (pH N]urea 15 N) 13]. This approach is, however, limited 6.2) using a hand-sprayer. The urea solu- by the production of large amounts of 15N- tion (3.0 g urea L was sprayed as a fine ) -1 labelled litter for the species under inves- mist, which limited the formation of drops tigation. In horticulture, massive labelling and consequently the contamination of the of trees has successfully been achieved by soil surface. Nevertheless, the uptake of urea spraying [12, 14, 15]. Uptake of urea N 15 by the could not be excluded. roots N by leaves is much faster than for NH- + 4 following amounts of 15 were N The N and NO [3], and this compound is -N - 3 tree: 56.6 mg 15 on I N applied per rapidly converted into amino acids [10] September 1993, 26.9 mg 15 on 22 N and later to proteins. August 1994 and 58.2 mg 15 on 30 N In the present study, a field experiment August 1995. In 1994 and 1995, plots conducted to determine the 15 uti- N were covered with a plastic sheet during was
and for the following 36 h to All tree and soil samples were weighed spraying avoid volatilization of 15 whereas in N, and dried at 65 °C. After dry-weight deter- 1993 they were not covered. The highest mination, all samples (tree organs, litter, application dose on 1 ha corresponded to leaf, soil) were milled using a ball mill 8.0 kg N. (Fritsch Pulverisette 6) to pass a 100-μm mesh. For N concentration and 15 anal- N yses of litter, tree and soil samples, about 6-10 mg of each sample were weighed in 2.2. Sampling silver cups and carefully closed. Samples were then combusted, N reduced to N 2 and the 14 ratio measured on a N 15 N/ Fifteen leaves from the upper, inner Finnegan MAT Delta S mass spectrome- and lower crowns were randomly taken ter at the Service Central d’Analyse from different trees at regular intervals (CNRS, Vernaison, France). (weekly and fortnightly in 1993; monthly in spring 1994 and 1995) and before and The incorporation of [ into N]urea 15 after the application of [ From N]urea. 15 beech leaves was calculated on a tree basis mid September until November, senes- as the difference between sprayed 15 and N cent brown leaves (hereafter referred to the total amount of new 15 in all leaves N as litter) were collected weekly just before 1 day after spraying. 15 excess N abscission. In February 1994, five trees = atom % 15 sample-0.3663 atom % 15 N N were harvested and separated into the fol- lowing compartments: buds, bark (1993 year of growth), wood (1993), bark = (1991-1992), wood (1991-1992), bark 3. RESULTS and wood (branches), bark (1991 and ear- lier), wood (1991 and earlier), roots (< 1 mm), roots (> 1 mm), roots (> 3 mm). Soil 3.1. Amino acid composition samples (n = 5) were taken at a depth of of beech leaves 0-5 cm and 5-20 cm within the plot. During late summer, the most abun- dant free amino acids in leaves (lower 2.3. Analyses crown) of 10-year-old beech trees was asparagine (about 400 nmol g fwt) fol- -1 lowed by glutamate and glutamine (fig- Sampled leaves were rinsed twice with ure 1). After application of [ N]urea, 15 distilled water and weighed. One sub- asparagine concentration in leaves dra- sample was dried at 65 °C until constant matically decreased, whereas glutamine mass. In 1993, the fresh leaves from the and glutamate concentrations drastically other subsample were stored at -20 °C increased (figure 1). Glutamate concen- and used later to determine the free amino tration reached a peak (600 nmol g fwt) -1 acid composition after extraction in I day after spraying and then rapidly methanol/water (70/30, v/v) as described decreased to its initial concentration. Glu- by Genetet et al. [4]. Fallen leaves (i.e. tamine concentration increased until day 3 leaf litter) collected weekly in autumn after spraying to reach 400 nmol g fwt -1 were air-dried and stored for further use and then levelled off. Increased glutamate as substrate for N decomposition studies and glutamine concentrations after urea (Zeller et al., unpublished results). A com- application indicate a rapid assimilation posite litter sample from each harvest was of NH produced by urea catabolism. + 4 dried at 65 °C.
N 15 incorporation in leaves 6.12 excess % 15 Foliar uptake N). 3.2. versus N]urea 15 [ increased with leaf biomass of suggested by the increased urea incor- as N 15 concentration in leaves sharply poration from 1993 to 1995 (table 1). increased after [ application and N]urea 15 then rapidly decreased during the follow- ing weeks (figure 2A) suggesting that a 3.3. 15 N partitioning significant part of the applied 15 was N translocated to other tree parts rapidly Leaf senescence began in mid Septem- and/or lost by leaching. One day after ber at the upper crown and had spread to spraying, leaves had incorporated 42 % the whole tree crown approximately (1993) to 55 % (1995) of the applied N]urea, 15 [ whereas 32.1 % of the applied 3 weeks later. During leaf senescence, 88 % of the 15 incorporated in leaves N N 15 reached the soil (1993). The differ- was allocated to perennial tissues of beech ence (27.4 %) was most probably due to trees, whereas the remaining part was volatilization of NH (table I). After the 3 found in fallen leaves. 15 distribution in N first [ application in 1993, leaf N]urea 15 N 15 concentration showed a high differ- the different perennial parts of trees har- vested in February 1994 is presented in ence (figure 2A) resulting from a large variability in 15 incorporation between N figure 3.15 from urea incorporated by N leaves was allocated to the various organs and lower-crown leaves (0.37 and upper- 1.01 mg 15 g dwt, respectively). 15 N N -1 of beech. The buds formed in 1993 showed the highest 15 concentration of N enrichment of leaves from the upper crown all plant parts (approximately 700 μg 15 N was approximately two times lower than in -1 g dwt). Bark and wood tissues of various leaves of the inner and lower crowns (2.21
where the the growing leaves, ported to ages showed similar 15 concentrations, N N 15 concentration reached the values whereas roots presented slightly lower 15 N observed after urea application (figure 2A). concentrations. The highest amount of 15 N In August, the 15 content of leaves dras- N %) was accumulated in wood (25.2 decreased indicating an active inter- tically (< 1991), the largest compartment of nal N cycling within the tree. The decrease beech, followed by wood + bark of in 15 was stronger (-65 %) than the N branches (16.6 %), bark (< 1991) (14.0 decrease in total leaf N (-40 %) suggesting %) and coarse roots (16.3 %). that a large part of 15 com- N-labelled In May 1994, the 15 stored in peren- N pounds corresponded to easily catabolized nial tissues was remobilized and trans- metabolites, such as amino acids.
of incorporation (60-80 %) have rates 5-8 % of the applied 15 N In this study, reported for apple trees [5, 6]. Several been was found in fallen leaves, i.e. litterfall reasons can be suggested to explain the (table I). In these leaves, the 15 enrich- N lower urea incorporation in sun (upper)- ment of total N and insoluble N (i.e. pro- crown leaves after the first spraying in tein and lignin N) was identical (2.06 and 1993. Enhanced urea volatilization from 2.11 excess % 15 Unlike the high vari- N). upper leaves can be ruled out for the fol- ability of 15 enrichment in the leaves, N lowing years because the plot was cov- the 15 enrichment of litterfall remained N ered with a plastic sheet. Higher applica- nearly constant in autumn (1993). In 1993, tion of urea on the lower crown leaves, leaf litter showed a mean enrichment of was observed due to the fall of urea 2.11% excess15 In autumn 1994 and N. droplets from the upper crown to the lower 1995, a higher enrichment (2.97 and crown. This is suggested by the soil con- 3.14% excess 15 respectively) was mea- N, tamination as measured in 1993. Lower sured in this litter as a result of successive urea incorporation in the upper crown was N]urea 15 [ applications. During the course presumably due to a lower metabolic of this labelling experiment, 4.9, 7.3 and activity of these leaves senescing earlier 8.5 kg of 15 beech litter were N-labelled than the leaves of lower crowns. The dra- produced in 1993, 1994 and 1995, respec- matic increase of free glutamate and glu- tively. tamine in sprayed leaves (figure 1) sug- gests that the catabolism of incorporated urea is rapid and the released ammonium 4. DISCUSSION N is assimilated into glutamate and glu- tamine. The efficiency of the foliar uptake of sprayed [ by beech trees grown N]urea 15 Under field conditions, urea uptake by in forest plantations depends on leaf den- leaves of 10-year-old beech trees was effi- sity. cient and a large and increasing propor- tion (42-55 %) of the applied [ N]urea 15 Remobilization of leaf N in senescent was incorporated into plant tissues. This increasing incorporation probably resulted leaves allowed an efficient translocation of incorporated 15 to perennial tissues of N from the increase in leaf biomass, as indi- cated by the amount of litter. Even higher beech trees. About 88 % of incorporated
work in the forest of Puvenelle. We would like N 15 found in buds, bark, wood and was to thank all colleagues of the ’Équipe Cycles buds of branches exhibited the roots. The Biogéochimiques’ for help in the field or in N 15 excess, but most (>80 %) of highest the laboratory. the 15 was found in bark and wood tis- N sues. This partitioning is in agreement with that found in other deciduous trees [17]. In REFERENCES other tree species, retranslocated N is stored mostly in a specific family of gly- Berg B., Dynamics of nitrogen ( in N) 15 [1] coproteins, called vegetative storage pro- decomposing Scots pine (Pinus sylvestris) needle litter. Long-term decomposition in a teins, in buds, bark, wood and roots [8, 9, Scots pine forest, VI, Can. J. Bot. 66 (1988) 17]. Despite an efficient translocation of 1539-1546. applied 15 to perennial tissues, a signif- N Bottner P., Austrui F., Cortez J., Billes G.. [2] icant proportion of 15 was measured in N Couteaux M.M., Decomposition of 14 and C fallen leaves and litter. As a result of [ N] 15 N 15 labelled plant material, under controlled conditions, in coniferous forest soils from urea application during late summer, N a North-South climatic sequence in Western translocation to other plant parts was lim- Europe, Soil. Biol. Biochem. (1997) (in ited to the remobilization processes tak- press). ing place during leaf senescence with Coker A., Court D., Sylvester W.B., Evalua- [3] little dilution and transfer of 15 by N tion of foliar urea applications in the pres- ence and absence of surfactant on the nitrogen import/export mechanisms characterizing requirements of conditioned Pinus radiata the developing leaves. After the first year seedlings, New Zealand J. For. Sci. 17 (1987) of[ application, 4.7 % of the 15 N N]urea 15 51-66. sprayed was found in litter (table I), and Genctet I., Martin F., Stewart G., Nitrogen [4] this proportion increased to 7.3 % in 1994 assimilation in mycorrhizas. Ammonium assimilation in the N-starved ectomycorrhizal and to 7.8 % in the last year (1995) of urea fungus Cenococcum graniforme. Plant. Phys- application. In 1995, the excess % 15 ofN iol. 76 (1984) 395-399. the harvested litter reached 3.14 and the Han Z., Zeng X., Wang F., Effects of autumn [5] incorporated 15 was homogeneously dis- N foliar application of 15 on nitrogen N-urea tributed in the soluble and insoluble N storage and reuse in apple, J. Plant. Nutr. 12 (1989) 675-685. fractions. Hill-Cottingham D.G., Lloyd-Jones C.P., [6] In summary, spraying [ on N]urea 15 Nitrogen-15in apple nutrition investigations, leaves of beech trees grown in the forest J. Sci. Food Agric. 26 (1974) 165-173. during late summer readily generates large Jordan D., Rice C.W., Ticdje J.M., The effect [7] amounts of 15 litter. Since incor- N-labelled of suppression treatments on the uptake of N 15 by intercropped com from labelled alfalfa porated 15 is homogeneously distributed N (Medicago sativa), Biol. Fert. Soils 66 (1993) between the different leaf N fractions, the 221-226. harvested litter produced could potentially Kang S.M., Titus J.S., Qualitative and quan- [8] be used to investigate uptake, leaching titative changes in nitrogenous compounds and mineralisation of beech litter in for- in senescing leaf and bark tissues of the apple, Physiol. Plant. 50 (1980) 285-290. est ecosystems. Kato T., Nitrogen metabolism and utilisation [9] in Citrus, Hortic. Rev. 8 (1986) 181-216. Karasuyama M., Yeneyama T., Kobayashi [10] ACKNOWLEDGEMENTS H., 15 study on the fate of foliarly applied N urea nitrogen in tea plant, Soil Sci. Plant Nutr. 31 (1985) 123-131. This study received financial support from the EC through the project NiPhys Norman R.J., Gilmour J.T., Wells B.R., Min- [11] (ENV4.CT.950053). The ONF (Office National eralization of nitrogen from nitrogen-15 de la Forêt, France) and Mr Claude Robert are labeled crop residues and utilization by rice, gratefully acknowledged for the possibility to Soil Sci. Soc. Am. J. 54 (1990) 1351-1356.
Oland K., Nitrogen feeding of apple trees by Shim K.K., Titus J.S., Splittstoesser W.E., [12] [15] The fate of carbon and nitrogen from urea post harvest urea sprays, Nature 185 (1960) 857. applied to foliage of senescing apple trees, J. Am. Soc. Hortic. Sci. 98 (1973) 360-366. Preston C.M., Mead D.J., Long-term recovery [13] in the soil profile of 15 from Douglas-fir N Stepien V., Contributionà l’étude des pro- [16] needles decomposing in the forest floor, Can. téines de reserve végétatives du Peuplier J. For. Res. 25 (1995) 833-837. (Populus x euramericana), Université de Nancy I, France. Shim K.K., Titus J.S., Splittstoesser W.E. [14] The utilization of post-harvest urea sprays by Stepien V., Sauter J.J., Martin F., Vegetative [17] senescing apple leaves, J. Am. Soc. Hortic. storage proteins in woody plants, Plant Phys- Sci. 97 (1972) 592-596. iol. Bioch. 32 (1994) 185-192.