Báo cáo khoa học: "The study of tree fine root distribution and dynamics using a combined trench and observation window method"

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Original article The study of tree fine root distribution and dynamics using a combined trench and observation window method M. Bédéneau D. Auclair INRA, Station de Sylviculture, Centre de Recherches d’Orl6ans, Ardon, F 45160 Olivet, France (received 5 février 1988, accepted 6 d6cembre 1988) Summary — Root distribution and growth were studied in a natural oak-birch coppice, by combining the trench and observation window methods. Root weight was estimated while digging the trench, showing that 90 percent of dry weight is situated in the upper 50 centimetres of soil. Root position was analyzed, using variograms : a cluster effect was observed, around 50 cm for old roots and 20 cm for new roots. Oak and birch appeared to have different seasonal root elongation patterns. The results discussed in relation to the methods employed. are Tree - root - distribution - profile - spatial distribution - coppice - birch - oak Résumé — Etude de la distribution et de la dynamique des fines racines combinant les tech- niques de tranchée et de fenêtre d’observation en forêt. Différentes méthodes ont été utilisées pour observer in situ et caractériser le système racinaire d’arbres forestiers dans un taillis mélangé de chênes et de bouleaux. La biomasse racinaire, estimée au moment du creusement de la tran- chée, se trouve localisée en grande partie (90%) dans 50 centimètres supérieurs. La position es / racines, des étudiée à l’aide de variogrammes, montre des phénomènes d’agrégation de l’ordre de 50 cm pour les vieilles racines et de 20 cm pour les racines jeunes. Chêne et bouleau présentent des vagues de croissance racinaire différentes. Ces résultats sont discutés en fonction des tech- niques utilisées. Arbre - racine - distribution - profil - distribution spatiale - taillis - Betula - Quercus Introduction However, young seedlings and plantlets have different growth patterns from adult trees. Isolated plants in pots, or in artificial observation chambers, also differ from The great majority of studies concerning those growing in natural conditions, due to forest tree root systems has been carried differences in biological (competition) and out on artificially cultivated young plants. physical (light, water, soil) environment. It Only a few studies have dealt with adult is therefore hazardous to make any gene- forest trees, mainly due to the conside- ral conclusion from results obtained in rable technical problems involved (B6hm, each laboratory experiment. 1979).
This may also explain why the amount Each (1 x 1 ) m square was covered with gation. 8-cm thick polystyrene sheet and a black an of experimental data concerning root plastic foil. The entire trench was then covered development of larger trees is rather scar- with polystyrene. This assembly maintained an ce (Persson, 1983; Santantonio and Her- adequate temperature regulation. mann, 1985; Ries, 1988). In the present study, various observation methods and Measurements techniques are discussed. Several types of data were collected : A trench and an observation window 1. Root weight was measured while digging tested in order to estimate root distri- were the trench. Dead and live roots were carefully bution and growth in a natural oak-birch and separately sampled in each 25 cm soil hori- stand in central France, with a view to zon. They were then sorted into diameter classes (< 1 mm. 1 -2 mm, > 2 mm), and oven- applying this method to a coppicing expe- dried at 105°C. riment (Bedeneau and Auclair, in prepara- 2. Root position on each side of the trench : tion). in each elementary (5 x 5) cm square, the roots cut during the excavation were counted and sorted according to : age : new/old (difference appreciated by the - Materials and Methods colour); oak/birch (difference assessed on species : - the basis of general appearance, form, colour). Site For each (x,y) coordinate the number and The experimental site was located at the INRA quality of roots was thus obtained. This presen- experimental station 20 km south of Orléans, tation allowed mathematical calculations to be France (1.54° E, 47.52° N). The natural forest is 1 11 1 an ancient coppice containing mostly Betula pendula Roth., Quercus robur L. with a few scattered Castanea sativa Mill. and Robinia pseudoacacia L. The root systems are of un- known age; the stems are 25 yrs old. The soil is acid, of the brown crytopodzolic type with a moderate humus. It has developed in a terrace material consisting of homometric sand, essentially quartzic, unstructured in the upper 40 cm and rapidly becoming gravelly and heterometric. It can be characterized as filtering well, with a very low mineral reserve. The study plot was situated between Quer- and Betula stools, at least 1 m away from cus each stump in order to minimize disturbance of the underground system. A trench 4 m long, 1 m wide and 1 m deep was dug by hand (Fig. 1 ). Installation On each side of the trench 4 (1 x 1 ) m squares were bordered with a wooden frame. Each of these large squares contained 400 (5 x 5) cm elementary squares which were numbered according to their horizontal and vertical posi- tion. Coordinates were marked on the separa- tion boards. Transparent plastic plates were then fixed on the boards, to observe root elon-
made on the variable &dquo;root density per square did not develop below 50 cm, whereas a centimetre&dquo;. few coarse roots were observed at a 3. Elongation : the path followed by the roots depth of 75 cm. during growth was drawn on the transparent plastic plates, using a different colour for each observation date. Total elongation between 2 Root distribution observations was obtained by following each coloured line with an opisometer. This type of The root position data collected on each data was recorded at irregular intervals, depen- side of the trench was grouped to form ding on growth, between March and December two (4 x 1 ) m grids. Variograms were then on each (1 x 1 ) m square (4 on the &dquo;right&dquo; side, computed for each grid in order to analyze numbered 1 4, and 4 on &dquo;left&dquo; side, numbered - 5-8). the spatial distribution of the roots. 4. Additional data : to simplify tedious elonga- The method used here is that of regio- tion measurements, an attempt was made to nalized variables developed by Matheron use infrared photography and video recording. These techniques did not prove satisfactory, (1965) for prospecting and evaluating geo- mostly due to the outdoor environmental condi- logical deposits. It consists of the study of tions. variables F(X) whose values depend only on the supporting coordinates X : it has been used for studying competition in forest plantations (Bachacou and Decourt, Results 1976), animal population distribution (Pont, 1987) or soil physical variables Root dry weight t (Goulard et al., 1987). The mean root dry weight excavated per random intrinsic F(X) is considered as a cubic metre was distributed by diameter function, thus, for any vector h, the mathe- classes as follows : matical expectancy and variance of the increment F(X + h) - F(X) are independant diameter 90 percent of the dry weight was function of h, in particular at its origin, pro- found in the upper 50 cm. This result vides a basis for describing the random agrees with the soil description : fine roots structure of the variable F :
if g(h) is parabolic, it shows To have a clearer view of this phenome- great a - non, we computed a moving average of spatial regularity; each square with the 8 surrounding if g(h) is linear the regularity is poorer; - squares. The smoothed curves obtained (Fig. 3) outline the cluster points. This can if g(h) shows a discontinuity at the ori- - be clearly observed at approximately gin there is a great irregularity. 50-cm intervals, in particular for old oak roots on the left side and at a lesser In the present study the variable is the degree for new roots. number of roots occurring at coordinates (x,y). A variogram can be obtained for each root parameter : old, new, birch, oak, Elongation on each side of the trench (left, right). The step of the variogram (h) is 5 cm. each (1 x 1 ) m square, we Returning to measured the length of all new roots All variograms (Fig. 2) show that the appearing at each observation. During starts at approximately half the line curve one growing season we thus obtained determined by the &dquo;a priori variance&dquo;. This total root elongation per square, on each indicates a cluster effect, varying with root side of the trench (Fig. 4). type and side of the trench = 50 cm for old On the right side, root growth began in roots and 20 cm for new roots (value read at the starting point of the variogram). March and reached a peak in early July.
Growth ceased in August and a second squares 5 and 6 showed a pattern - growth flush appeared from September to similar to that observed on the right side; December. square 8 was intermediate. - Square 7 was mostly occupied by birch On the left side, several elongation roots and square 8 by a mixture of birch flushes were observed : and oak, whereas the other squares square 7 showed intensive contained only oak roots : this suggests growth - until June, followed by a gradual that birch has a different growth pattern growth inhibition until November; from that of oak.
Discussion fact thatwe observed no major change in above-ground parts of the trees. Results relative to root weight are simi- Root systems of mature trees can be stu- lar to those reported by others (Duvi- died in different ways, but all methods are gneaud et al., 1977; Gholz et aL, 1986). complex and time-consuming. The study However, our results are somewhat bia- of underground system architecture, by sed, for we collected the roots more than 1 excavation, which has some disadvan- metre away from any stem. Thus we tages (necessarily destructive, time- and excluded from our estimations the main power-consuming; Pages, 1982) can. pro- structural roots accounting for the major vide some interesting information on grow- part of the underground biomass. th in different situations (Bedeneau and Above-ground biomass amounts here to Pages, 1984). However, the study of coar- = 80-100 t.ha-! (Auclair and Metayer, se roots gives insufficient information 1980). The underground parts we have about dynamics. measured represent 6 percent of this bio- Fine root dynamics may be studied with mass. This figure is, however, an underes- various techniques, involving core sam- timation of total underground biomass as it pling or more costly methods, such as does not account for the coarse roots endoscopy (Maertens and Clauzel, 1982) close to the stems and the stumps. We or video recording (Upchurch and Ritchie, must also be cautious in generalizing on 1984). The environmental conditions in the sampling technique basis, an area as our forest would, however, entail additional intended for that (small sampling was not equipment at an excessive cost. not random, no replicates, etc.). area, The trench method used here has its The statistical data showed that the drawbacks (B6hm, 1979) : it causes dis- roots were not randomly distributed in the turbances in both the soil dynamics (late- soil : in particular, birch roots were inter- ral water movements) and the root dyna- mingled with oak roots. This might be due mics (cutting of roots during the digging of to different growth behaviour and phenolo- the trench). In this study we therefore gy of the 2 species : combined the static description of root dis- root elongation in birch began earlier tribution with a root observation window - and decreased when oak root elongation technique in order to follow the growth of initiated; fine roots in situ. was the horizons occupied were different : In the dynamic experiment with observa- - the soil surface for birch, deeper in tion windows, we assumed that: near the soil for oak.. damage to soil remains slight because - The position of the new roots suggested of the carefuldigging by hand; that root growth was derived from older root growth capacity, as described by - ramifications. The distance between new Sutton (1980) remains unchanged; roots and old roots always remained short. the edaphic factors subject to change - The section of each side of the trench dis- are the following : lateral water runoff, and played &dquo;channels&dquo; left by dead roots, and hence mineral runoff (Callot et al., 1982), occupied by growing roots, a phenomenon as well as gas exchange (0 )- 2 previously described by others (B6hm, 1979). New roots were also found to deve- Our assumption that we observed nor- lop from the sectioned area of cut roots : mal growth rather than tree or root system to form ramifications has been response to the trench is supported by the this ability
heterogeneities would again require referred to &dquo;root growth capacity&dquo; by a as great number of replications. Sutton (1980). The limitations underlined here join the This suggests that elongation of the pri- views (B6hm, 1979; Santantonio general mary axes was followed by ramification and Hermann, 1985), stating how time- and elongation of several secondary axes, consuming precise root studies can be. An and that the disturbance induced by the improvement of the methods described trench did not inhibit root growth. here might be to provide for the possibility A growth activity during root strong of taking samples at various precise deve- Spring and Summer was demonstrated lopmental stages, giving access to studies (Fig. 4). This agrees with other investiga- on root turnover and productivity, and to tions suggesting a relationship between the study of nutrient cycles. root growth and accumulation of the pre- The present data only concerns one vious year’s photosynthates (Bonicel and growing season, and to have a reliable Gagnaire-Michard, 1983). This suggests interpretation of the difference between that cutting during the vegetation period oak and birch growth behaviour, more prevents the root system from expanding frequent observations should be underta- and new roots from growing, thus hinde- ken at several important dates in relation ring the growth of the following coppice phenology (budbreak, budset, fall). to cycle. Acknowledgments Conclusions We wish to thank A. Riedacker, J. Gagnaire- Michard and L. Pages for their advice concer- The present study was aimed at perfecting ning root observation and biometrics, J. Roque methods for root observation in natural (INRA - SESCPF) for the soil description, M. Bariteau, L. Bouvarel and the technical staff forest stands, and interpretation tech- of the Orl!ans INRA Sylviculture and Biomass niques. laboratories for their hard work. This study was The excavation method gives static partly supported by the French Energy Manage- ment Agency (AFME). results on root biomass, and its distribu- tion in different diameter classes. It is, however, insufficient for total underground production studies which entail a greater References number of observations. The root observation window gives a Auclair D. & Metayer S. (1980) Méthodologie de dynamic view of root distribution, but its 1’6valuabon de la biomasse aérienne sur pied et interpretation is most delicate. Root grow- de la production en biomasse des taillis. Acta th has been described by mathematical OecoL Oecol. Appl. 1, 357-377 models (Rose, 1983; Belgrand et al., Bachacou J. & Decourt N. (1976) Etude de la à competition dans les plantations régulières 1987). The geostatistical approach used t’aide de variogrammes. Ann. Sci. For. 33 (4), here should be considered as an attempt 177-198 to describe the spatial distribution of root Bedeneau M. & Pages L. (1984) Etude des systems. A cluster effect has been shown, cernes d’accroissement ligneux du système but its interpretation in relation to the racinaire d’arbres trait6s en taillis. Ann. Sci. structure and growth of roots, and to soil For. 41 (1), 59-68
Belgrand M., Dreyer E., Joannes H., Velter C. & plantes cultivee(Sorghum vulgare et Lolium (1987) A semi-automated data pro- Scuiller 1. multiflorum). Agronomie2 (7), 677-680 cessing system for root growth analysis : appli- Matheron G. (1965) Les Variables R6gionali- cation to a growing oak seedling. Tree Physiol. sées et Leur Estimation. Masson, Paris, pp. 306 3, 393-404 Pages L. (1982) Etude méthodologique de 1’ef - B6hm W. (1979) Methods of Studying Root fet du recepage sur le syst6me racinaire de Systems. Ecological Studies 33, Springer Ver- bouleau (Betula verrucosa et Betula pubes- lag, Berlin, pp. 188 cens). Mémoire ENITEF, Doc. INRA, Station de sylviculture d’0r!eans, 82/39, pp. 105 Bonicel A. & Gagnaire-Michard J. (1983) Varia- tions de la croissance du rejet en fonction de la Persson H. (1983) The distribution of fine roots date de recespage dans les taillis de peupliers in boreal forests. Plant Soil71, 87-101 (P. trichocarpa x P. delto clone Raspalge). des, y Pont D. (1986) Structure spatiale d’une popula- In : Mesures des Biomasses et des Accroisse- tion du cyclopide Acanthocyclops robustus ments Forestiers D. Auclair, (Ed.), Colloq. dans une rizibre de Camargue (France). Acta INRA, 19, INRA, Versailles, 277 Oecol. Oecoi Gen. 7 (3), 289-302 Callot G., Chamayou H., Maertens C. & Salsac Ries S. (1988) Fonctionnement d’un 6cosyst6- L. (1982) Mieux Comprendre les Interactions me forestier. Le compartiment racines d’un Sol-Racines. INRA, Paris, pp. 323 taillis de Châtaigniers du Sud-Est de la France : biomasse, structure et evolution. These 3e Duvigneaud P. & Kestemont P. (1977) Produc- cycle USTM, Gre!noble, pp. 186 tivit! Biologique en Belgique. Duculot, Paris- Gembloux, 707-731 Rose D. (1983) The distribution of the growth of root systems. Plant Soil 75, 405-415 5 W.P. Jr. Gholz H.L., Hendry L.C. & Cropper (1986) Organic matter dynamics of fine roots in Santantonio D. & Hermann R.K. (1985) Stan- plantation of slash pine (Pinus elliottii) in North ding crop, production, and turnover of fine roots Florida. Can. J. For. Res. i 6, 529-538 on dry, moderate, and wet sites of mature Dou- glas fir in western Oregon. Ann. Sci. For. 42 (2), Goulard M., Voltz M. & Monestiez P. (1987) 113-142 Comparaison d’approches multivariables pour 1’6tude de la variabiiite spatiale des sols. Agro- Sutton R.F. (1980) Root system morphogene- nomie(9), 657-665 sis. N. Z J. For. ,Sci. 10 (1), 264-292 Maertens C. & Clauzel Y. (1982) Premi6res Upchurch D.R. & Ritchie J.T. (1984) Battery- operated color video camera for root observa- observations sur l’utilisation de fendoscopie dans l’étude de 1’enracinement in situ des 7 tion in mini-rhizol:rons. Agron. J. 76, 1015-1017