DETERMINATION OF THE QUANTITY OF CARBON AND NITROGEN IN THE RHIZOSPHERE OF YOUNG PLANTS

Transcription

1 I -r~ SEP DETERMINATION OF THE QUANTITY OF CARBON AND NITROGEN IN THE RHIZOSPHERE OF YOUNG PLANTS By Dr. G. W. HARMSEN and Dis.G. JAGER INSTITUUT VOOR iodemvruchtbaarheit GRONINGEN ƒ (Reprinted frnlwature, Vl. 195, N. 4846, pp , Sentemhtr September 15, 1V1QSO\ 1962)

2 (Reprinted frm Nature, Vl. 195, N. 4846, pp , September 15, 1962) Determinatin f the Quantity f Carbn and Nitrgen in the Rhizsphere f Yung Plants HILTNEB 1 intrduced the cncept f the rhizsphere t express the zne in which the living rt exerts an influence n micrbes in the sil. Much infrmatin has been gleaned since then n the micrflra f the rhizsphere and n the substances given ff by the rts ; but there is much less infrmatin n the ttal quantities f rganic substances which the rts lse. The facts s far knwn are in relatin t plants grwn in sterile nutrient slutins r in sterile quartz sand withut any adsrptin capacity 2- *. The quantities f nitrgen given ff by leguminus plants can be estimated frm the ttal nitrgen present in nnleguminus plants cultivated tgether with the frmer in a nitrgen-free sil 6 ' 6. Scarcely anything is knwn abut the ttal quantity f the substances given ff by the rts, especially cncerning their carbn and nitrgen amunt and their C/N rati in a sil with a natural absrptin capacity in which the rhizsphere is smewhat limited in space. In general, the extent f the rhizsphere is insufficiently knwn. In a recent publicatin Papavizas and Davey 7 discussed this subject, and made estimatins frm a set f micr-brings in the rhizsphere f yung lupins. In these small sil samples they estimated the ttal amunts f bctaeria, fungi and actinmycetes using the dilutin plate technique. The B/S values (ttal numbers f micrrganisms in the rhizsphere/ttal numbers f micrrganisms in nn-rhizsphere sil) were thus btained, and indicated that the rhizsphere is rather extensive and can have a radius up t 18 mm in unamended sils. In amended sils the rhizsphere may be negligible. We have attempted t btain exact infrmatin cncerning the quantities f rganic matter (that is, carbn and nitrgen) given ff by the rts and the distance which these substances spread frm the rt surface. The rts are frced t grw in a small chamber made frm a thin nickel plate (<V1 mm thick) densely perfrated with punctures 60fx in diameter. This chamber is placed in a big cntainer, and bth are filled with the same substrate. The space within the perfrated chamber becmes filled with a mat f rts, and cnsequently may be cnsidered t belng entirely t the rhizsphere, while the space utside the chamber is still in cnnexin with the rts and serves as a stck f misture and nutrients. The substrate used cnsisted f a mixture f 70 per cent pure sand, 25 per cent finely grund ptassiumfeldspar and 5 per cent kalinite with sme finely

3 Fig.l. Diagrammaticschemef the apparatus..4, Bt chamber; B, black plastic sheet t prevent grwth f algse ; 0, glass pt with sil granulated pumice stne t imprve the structure and aeratin f this artificial sil. In sme experiments the amunt f feldspar and kalinite was higher. This substrate is very pr in rganic substances, cntaining nly per cent carbn n dry-weight basis. 200 ml. f a slutin f Crne's mixture, cntaining 1-5 g/1., is added t the cntent f every cntainer hlding abut 600 g f dry sil. During the experiment water is added if necessary. The nickel plate prved nt t be harmful t the rts and had scarcely any ligdynamic effect n the micr-rganisms in the sil. It is als inert against the substances prduced by the rts and is impervius t the rts. In the upper part f the rt chamber germinated sterilized seeds are planted and allwed t grw fr a required perid. A diagram f the apparatus is shwn in Fig. 1. A B Fig. 2. A, rt chamber pened ; the rtsgrwn in itare visible ; B, thesame rts, washedfree frm sil

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5 T determine the amunts f carbn and nitrgen in the rhizsphere the cntent f the pened rt chamber (Fig. 2) is washed free frm sil. The washing is dried at 105 C and analysed (Table 1, a). Further analyses are perfrmed n the 1-cm thick layer f sil surrunding the rt chamber (&) and n the rest f the sil in the cntainer (c). The nitrgen is determined by the micr-kjeldahl methd; the carbn by the dry-cmbustin methd. The preliminary results s far btained are given in Table 1. The carbn figures are crrected fr the blank (0-022 per cent carbn); the nitrgen figures culd nt be crrected in this experiment since ammnium nitrate was added in the Crne mixture; they are therefre less reliable. A distinct cncentratin gradient frm the rt chamber utward is apparent in these experiments. The technique cnsequently prved wrkable; but the distance f diffusin f the substances given ff is smaller than was expected. This may be brught abut by the cnstant flw f water and slutes twards the rts as a result f the transpiratin f the plants. Enhancement f the srptin cmplex f the sil seems t lead t larger amunts f carbn preserved in the rhizsphere. When cnsidering the figures in Table 1 it must be realized that these experiments were nt perfrmed under aseptic cnditins. Part f the rganic substances given ff by the rts certainly had already been decmpsed by micr-rganisms. The results therefre represent the minimum f excretin, crrect figures presumably being higher. Fllwing and imprving this technique further, experiments are being started t btain mre infrmatin abut the ttal quantities f carbn and nitrgen prduced in the rhizsphere f different plants f varius ages, grwn under sterile, as well as nn-sterile circumstances, in sils f different cmpsitin. It might be expected that thereby a better insight will be gained in the part played by the rhizsphere in the cycle f carbn and nitrgen in the sil, prviding us als with new infrmatin abut frmatin and disintegratin f humus. G. W. HAEMSBN G. JAGER Institute fr Sil Fertility, Grningen, The Netherlands. 1 Hiltner, R., Arb. Deutsch, landw. Ges., 98, 59 (1904).! Lyn, T. L., and Wilsn, J. K., N.T. (Crnell) Agric. Exp. Sta. Mem., 40, 1 (1921). 8 Demidenk (1928), after Krasifnikv, W. A., Sil Micr-Organisms and Higher Plants, 1958 (Israel Prgramme fr Scientific Translatins, 1961). 4 Rvira, A. D., Plant and Sil, 7, 178 (1956). «Lipman, J., N.T. Agric. Exp. Sta. Bull.,253, 3 (1912). 8 Virtanen, A. I., Hausen, S. v., and Karström, H., Bichem. Z., 258, 106 (1933). Virtanen, A. I., Lantbr. Eögsle. Ann., 5, 429 (1938). ' Papavizas, G. C, and Davey, C. B., Plant and Sil, 14, 215 (1961). Printed in Great Britain by Fisher, Knight & C., Ltd., St. Albans.