Nearly 100 determinations of the absorption of oxygen and water were made

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1 RELATON BETWEEN ROOT RESPRATON AND ABSORPTON C. C. WL S ON AN D P. J. KRAM E R (WTH TWO FGURES) Received March 18, 1948 The rate of absorption of water by roots of transpiring plants is in general closely dependent upon the rate of transpiration, and a change in the rate of transpiration is soon followed by a corresponding change in the rate of absorption (3). Since the rate of absorption lags behind and apparently is dependent on the rate of transpiration it is usually considered that under conditions such that transpiration exceeds absorption the roots play a passive role in the absorption of water. t has been reported by certain workers, however, that a close relation exists between root respiration and water absorption. NEWTON (6) observed that the rate of root respiration was increased when the concentration of the culture solution in which the roots were iersed was increased. He suggested that this was caused by the greater expenditure of energy required to absorb a given volue of water fro a ore concentrated solution. HENDERSON (1) reported that there was a direct relation between respiration and water absorption in the roots of transpiring corn seedlings and concluded that the absorption of water was brought about by the expenditure of energy released in respiration. LOWENECK (5), on the other hand, found no relation between root respiration and rate of transpiration of Zea aize or Sonchus oleraceus. n view of these differences in opinion it seeed desirable to ake a further study of the proble, using large plants. Toato seeds of the Marglobe variety were gerinated in oistened quartz sand and the seedlings were transferred to solution cultures. The plants were grown in an unshaded greenhouse until approxiately two onths old. The ost vigorous plants were then selected and sealed at the level of the crown into 5 l. potoeters. Four potoeters were placed in a constant-teperature water bath and were connected to a coon source of aerated tap water. The oxygen content of the water in the potoeters was deterined by the Winkler ethod, deterinations being ade before and after each hour exposure of the plants to differing environental conditions. Since all four potoeters were connected to the sae source of aerated water, the four root systes were under siilar conditions, as indicated by the fact that the deterinations of oxygen content at the beginning of each experiental period were always in close agreeent. Nearly 1 deterinations of the absorption of oxygen and water were ade under conditions producing widely differing rates of transpiration and hence of water absorption. The results are presented in table. 55

2 56 PLANT PHYSOLOGY The relation between rate of respiration as easured by the absorption of oxygen, and rate of absorption of water is shown graphically in figure 1, where data fro four plants are presented separately. n no graph is there any obvious relation between rate -of respiration and rate of water absorption. A regression equation was calculated fro the data for TABLE RATES OF ABSORPTON OF WATER AND OXYGEN BY TOMATO ROOTS N.C 'S./HR. PLANT PLANT PLANT PLANT V C.C. H C.C. C.C. H C.C. c.. HO C.C. C.C. H C.C. AB- AB- AB- AB- AB- AB- AB- AB- SORBED SORBED SORBED SORBED SORbED SORBED SORBED SORBED each plant, and the regression coefficients were tested by an analysis of variance and found not to be significant. This statistical analysis of the data failed to establish any definite relation between rate of respiration and rate of water absorption. Regression equations were also calculated for the data obtained by Henderson fro her plants, nubers 8, 9, 1, and 11, for which the rate of root respiration, as easured by absorption of oxygen, was related to the absorption of water. These regression coefficients were also found not to be significant, indicating that no definite relation existed between the rate of respiration of the corn roots studied by Henderson and their absorption of water. Although this conclusion sees to be at variance with the graphs in Henderson's paper illustrating the parallelis between respiration and

3 WLSON AND KRAMER: ROOT RESPRATON AND ABSORPTON 57 absorption, a careful study of her data indicates that for any given rate of respiration alost any absorption rate can be found (fig. ). Apparently Henderson's conclusion that water intake and root respiration of corn seedlings were correlated was not actually supported by her.'5 cr PLANT 5 4 PLANT, 3 D cr fin a,.. 5 U4 U v w 3 En o -r.. S * * PLANT ob ' * * * PLANT 4 _, ABSORBED C.C./HR. ABSORBED C.C./HR. Fig. 1. Relation between rate of respiration as easured by absorption of and rate of absorption of water. own experiental data. Neither did such a correlation exist in the large toato plants studied by the writers. t sees quite unlikely that any such correlation could exist in freely transpiring plants, because in such plants absorption is deterined by the rate of water loss rather than bv the expenditure of energy by the root cells (4). This conclusion does not apply, of course, to the intake of water by isolated pieces of plant tissue or by root systes of plants with very low transpiration rates. Much evidence has been accuulated indicating that in such aterial water intake

4 58 PLANT PHYSOLOGY.1 O (.1 ~ ~~+a. + o w + o + 'O.6 * 3 is at least partly related to the release of energy in respiration (7). For instance, intake of water by root systes and pieces of plant tissue is re- < o.4 ro-. X X. ox Fig ABSORBED C.C./ HR. Relation between rate of respiration as easured by absorption of. and rate of absorption of water. Data of HENDERSON (1). duced by substances such as cyanide which inhibit respiration, and it is increased by indoleacetic acid, possibly because of increased respiration () (8). Suary Respiration, in ters of oxygen absorption, and water intake of toato roots were easured concurrently while the shoots were exposed to varied atospheric conditions which resulted in a wide range of rates of water intake. No definite relation could be established between rate of root respiration and rate of water absorption. A statistical analysis of data published by Henderson showed no significant correlation between water absorption and root respiration. t sees probable that the energy released by respiration plays no significant role in the intake of water through the roots of freely transpiring plants. UNVERSTY OF GEORGA ATHENS, GEORGA AND DUKE UNVERSTY DURHAM, NORTH CAROLNA

5 WLSON AND KRAMER: ROOT RESPRATON AND ABSORPTON 59 LTERATURE CTED 1. HENDERSON, L. Relation between root respiration and absorption. Plant Physiol. 9: KELLY, S. The relationship between respiration and water uptake in the oat coleoptile. Aer. Jour. Bot. 34: KRAMER, P. J. The relation between rate of transpiration and rate of absorption of water in plants. Aer. Jour. Bot. 4: LEVTT, J. The therodynaics of active (non-osotic) water absorption. Plant Physiol. : LOWENECK, N. Untersuchungen fuber Wurzelatung. Planta 1: NEWTON, J. R. The relation of the salt concentrations of the culture solution to transpiration and root respiration. Sci. Agr. 5: VAN OVERBEEK, J. Water uptake by excised root systes of the toato due to non-osotic forces. Aer. Jour. Bot. 9: VAN OVERBEEK, J. Auxin, water uptake and osotic pressure in potato tissue. Aer. Jour. Bot. 31: