Báo cáo khoa học: "growth in a sweet chestnut (Castanea sativa Mill.) coppice"

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Nội dung Text: Báo cáo khoa học: "growth in a sweet chestnut (Castanea sativa Mill.) coppice"

growth in a sweet chestnut Fine root (Castanea sativa Mill.) coppice P. Montpied France d’Ecotogie V6g6tale, CNRS URAt2t,Universite Paris-Sud, Orsay, Laboratoire until early August and then every 2 wk Introduction weekly until November, by means of mapping all roots visible behind the glass on a transparent plastic sheet. A distinction was made between long The root growth and turnover of fine roots roots and laterals, the former being defined as are known to be a major carbon pathway the ones bearing the latter. in forest ecosystems (Fogel, 1985). Dubroca (1983) showed that the carbo- hydrate reserves play a major role in both above- and belowground growth of a Results sweet chestnut (Castanea sativa Mill.) coppice. The aim of this study was to examine fine root phenology of a chestnut The patterns of fine root growth in the coppice with an emphasis on the influence older coppices (5 and 16 yr coppices) can of coppicing. be divided into 4 overlapping phases. Phase I: initiation of long roots (June) Materials and Methods phase began when the first roots This appeared in early June, viz. 1.5 mo after This study took place in sweet chestnut cop- a bud burst, and was completed in late 30 km SW of illuvi- Paris, growing pice, on an June: the destruction of roots during that ated acid soil. period in rhizotrons 5’ and 16’, when a 5 vertical rhizotrons, 40 wide, 50 cm cm rodent dug a gallery behind the glass, pre- deep, were built in March 1985, each of them facing a stump of average size at a distance of vented the root system from fully de- 1 m. One of them faced a stump entering its 1 st veloping until the end of the growing sea- year after coppicing (no. 1 ), others faced 5 yr son (Fig. 1 Since the destroyed roots stumps (nos. 5 and 5’), and the last 2 faced 16 were not replaced after that period, it yr stumps (nos. 16 and 16’). As soon as the first appeared to be critical. roots appeared, root growth was recorded
The long root growth rate was high from The rate of appearance of laterals growing June to August with a peak in July. From acropetally along the unbranched parts of September to November, the long root the long roots followed a pattern similar to growth was residual (Fig. 2): the complete the one of the long root growth rate with a development of the long root network was delay of about 3 wk (Fig. 3). The setting finished in late August. up of the laterals, viz. the absorbing root
system, occurred therefore from July system developed and then decreased to when it was early September, until November (Fig. 4). It remained rela- completed. tively high in autumn in contrast to the laterals appearing on unbranched long Phase lV: maintenance of the This kind of lateral absorbing roots. to seems root system (July to September) respond positively to soil rehydration (arrows Fig. 4). Stabilization of total root The rate of appearance of laterals on length in autumn (Fig. 1) was the result of already branched parts of long roots the domination of phase IV which com- increased until late July as the long root pensated for mortality.
Root growth slows down in autumn The first year coppice did not follow this when the root reserves are replenished. pattern, since the development of long The replenishment of root reserves occurs roots and therefore of laterals was weak later in the first year coppice than in the throughout the growing season (Figs. 2 older ones (Dubroca, 1983). A small and 3). There is some evidence of a com- amount of photosynthates is then directed pensating development of long roots and to root growth in the former when shoot laterals in autumn. However, it was not growth has stopped in autumn and before enough to compensate for the delay in the replenishment of root reserves. A growth compared to the older coppices compensatory growth of roots may then (Fig.1).. ) occur in autumn in the first year coppice. Discussion and Conclusion References Dubroca E. (1983) Evolution saisonnibre des In the older coppices, carbohydrate root reserves dans un taillis de chataigniers, Casta- directed to root growth, and reserves are nea sativa Mill., avant et aprbs la coupe. These shoot reserves to shoot growth in the de 3e cycle. Universite Paris-Sud, Orsay spring (Dubroca, 1983): there seems to be Fogel R. (1985) Roots as primary producers in no competition for carbohydrates between below-ground ecosystems. Jn: Ecological Inter- shoots and roots. In the first year coppice, actions in Soil. (Fitter A.H. et al., eds.), Special publication no. 4. of the British Ecological Socie- the shoot reserves are removed and the ty, Blackwell Scientific Publications, Oxford, root reserves have already been depleted pp. 23-26 by shoot growth when root growth Pontailler J.Y., t_eroux M. & Saugier B. (1984) resumes (Pontailler et al., 1984): the lack Evolution d’un taillis de chataigniers apr6s of carbohydrates prevents root growth coupe: photosynthese et croissance des rejets. Acta OecoL Ser Oecol. Plant. 5, 89-92 from occurring at the normal level.