INFLUENCE OF SUBMERSION OF THE ROOTS ON TRANSPIRA- TION, APPARENT PHOTOSYNTHESIS, AND RESPIRATION OF YOUNG APPLE TREES N. F. CHILDERS AND DAVID G. WHITE (WITH NINE FIGURES) Introduction In spring there are often places in the orchard where water stands be- neath the trees for a week or more. Within a short time the water recedes and the soil appears to be properly drained for the remainder of the season. The question arises as to the importance to the tree of these short periods of excess-soil-moisture conditions, especially when the tree is in leaf. Ex- periments are described in this paper in which transpiration, apparent photosynthesis and, in some cases, respiration of young apple trees were determined before and after the roots were submerged. In several experi- ments the determinations were continued after the excess water had been drained from the soil in order to ascertain how soon, if ever, the leaves recovered in activity. The literature pertaining to root submersion necessarily includes manv studies in soil aeration. The well-known monographs by CLEMIENTS (6) in 1922, and CANNON (3) in 1925, summarize the work to that period. Certain symptoms which accompany poor root aeration of mesophytes are common knowledge. It is known that poor aeration will cause the foliag'e to wilt, turn yellow, and die; theroots to develop slowly, become darker iu color, and finally decompose; and the soil complex becomes depleted in oxygen and higher in carbon dioxide. A proper aeration of the medium tends to correct these faults (1, 5, 6, 7, 11). Materials and methods The Stayman Winesap variety was selected for these experiments be- cause of its commercial importance and because it seems to be relatively susceptible to the effects of soil water-logrging. The shoots used wvere grown from two- and three-year stocks grafted on French Crab roots. Terminal buds had set on all trees by the time tests were made, with the exception of those shoots used in experiment VIII. The trees were potted in five-gallon crocks orslightly larger wooden tubs and were grown in the greenhouse until placed under test. A loam topsoil taken from an orchard was used for potting. No attempt was made, however, to correlate the soil type with the effects of root submersion. The term excess water, as used in this paper, infers that water constantly stood above the soil surface. Check trees were watered daily, or once every two days, in order to maintain the soil niear 603 Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. 604 PLANT PHYSIOLOGY field capacity. The HEINICKE-HOFFMAN (10) apparatus was employed for measuring therates of transpiration and apparent photosynthesis or respira- tion. Each determination lasted for a period of two and one-half hours. Four series of experiments were performed in the environment-control chamber (4) on a total of ten trees, and two series were performed outside the greenhouse on a total of five trees. The temperature in the chamber was nearly constant at levels of 800 or 850 F. The vapor pressure was maintained near 16 mm. of Hg. Light averaged from 2,000 to 5,000 foot candles at the surface of the leaves, depending on their distance from the source. The temperature and relative humidity outdoors were averaged TABLE I INFLUENCE OF ROOT SUB-MERSION ON APPARENT PHOTOSYNTHESIS AND TRANSPIRATION\ OF STAYMAANT WINESAP APPLE LEAVES. EXPERIMENT 8 APPARENTPHOTOSYNTHESIS TRANSPIRATION PERCENT- PERCENT- CO2/100 EXPECTED AGEOF H2O/100 EXPECTED AGEOF DDAA.TSTEE,, C%.2/HOUR RATE EXPREACTTEED CM.2/HOUR RATE EXPRAETCETED TEST TROL B X100 7788.5* 00 TEST TTRROOLL F X100 895tXlo0 A B C D E F G H March 20 5.76 7.62 76 97 0.85 0.99 86 101 21 11.36 13.78 82 104 1.05 1.23 85 100 22 10.94 13.60 80 102 0.84 0.97 87 102 23 11.08 14.63 76 97 0.82 0.99 83 98 ROOTS SUBMERGED 26 9.94 13.90 72 92 0.91 0.91 100 118 28 9.79 12.19 80 102 0.76 0.88 116 136 30 11.42 13.78 77 98 0.99 1.04 95 112 April 1 13.43 16.05 84 107 1.11 1.29 86 101 3 13.75 17.79 77 98 1.08 1.28 84 99 4 12.82 15.82 81 103 1.01 1.09 93 109 6 11.43 13.78 83 106 0.94 1.32 71 84 8 14.67 14.67 100 127 0.84 0.87 97 114 10 12.28 13.94 88 112 0.87 0.84 104 122 14 11.09 14.78 75 96 0.89 0.87 102 120 16 8.33 13.20 63 80 0.69 0.70 99 116 18 8.19 12.07 68 87 0.58 0.71 82 96 20 5.92 11.72 51 65 0.59 0.69 86 101 22 4.80 13.78 35 45 0.41 0.80 51 60 24 3.08 14.31 22 28 0.33 0.73 45 53 26 2.47 13.42 18 23 0.25 0.75 33 39 28 0.35 11.42 3 4 0.13 0.75 17 20 30 1.92 12.09 16 20 0.12 0.70 17 20 May 2 0.00 11.38 0 0 __ .. * Average (78.5) of expected rate. f Average 85.0 of expected rate. Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. CHILDERS AND WHITE: S1JBMERSION 605 from three measurements at the beginning, middle, and end of each de- termination. A sling psychrometer was used to determine the dew point which was then converted to vapor pressure by use of psychrometric tables (13). The average foot candles of light outside was calculated from the records of a Micromax continuous recorder connected with a photoelectric cell in the inmmediate vicinity of the trees. Supplementary experiments, described later, were arranged in the greenhouse to make measurements of leaf petiole angrles and to afford observation of root growth. METHOD OF CALCULATION The percenitage of the expected rate of apparent photosynthesis was cal- culated as followvs: The average milligrams of carbon dioxide absorbed by the proposed test leaves was divided by the average milligrams absorbed by the check leaves. The quotients multiplied by 100 express the percentage relationship between test and check leaves. The average of these per- centages found before treatment began was then considered as 100 per cent., or that rate which the proposed test leaves would be expected to maintain if they were not affected by the treatment. Thereafter, the percentage re- lationships between test and check leaves were divided by the average per- centage relationship of the pre-treatment period and multiplied by 100. These products are plotted as percentages of expected rates for each experi- ment. A typical set of data is presented in table I. Respiration and transpiration were calculated in a similar manner. Discussion of results DESCRIPTIONS OF TREES USED IN CHAMBER Symptoms of leaf injury which accompanied submersion of the roots appeared on the lower leaves first and progressed acropetally. Abscission of two or more lower test leaves often occurred before termination of an experiment. In experiment I the leaves on the test tree developed light green areas between the veins. The foliage wilted and drooped mostly from the distal ends of the petioles. At the end of experiment IV the leaves on test trees showed only a greater devlopment of anthocyanin pigments as compared with the check leaves. No apparent differences in the foliage occurred betwveen the test trees and controls in experiment V. The leaves on the test trees in experiment VIII developed light green areas between the veins. The foliage wilted and drooped (fig. 1) and finally appeared similar to the treated tree in experiment I. DESCRIPTIONS OF TREES USED OUTDOORS Considerable tip and marginal burning had occurred within eight days after flooding the roots of one tree outside in July (experiment II). The Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. 606 PLANT PHYSIOLOGY leaves on a second tree of the same experiment only wilted and drooped, similar to the foliage of the test tree in experiment I in the control chamber. The leaves on trees having roots submerged from late September to late October, experiment III, were slower in developing injury, probably because of the cooler autumn temperatures. The lower leaves showed yellowish-red FIG. 1. Roots of the tree on the left were submerged in water for 45 days in the enivironiment-control chamber. Tree on the right was watered every second day. Both trees were of equal vigor at the outset. See figure 8 for comparison of transpiration and apparent photosynthesis. Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. CHILDERS AND WHITE: SUBMERSION 607 splotches which finally became necrotic. The blades curled upward at the margins but did not droop. At the end of the experiment the upper leaves appeared similarto theupper leaves ofthe check tree except for the presence of considerable anthocyanin pigments. The symptoms of leaf injury which appeared in these experiments were similar to descriptions given by HEINICKE, et al. (9) for orchard trees purposely flooded. EXPERIMENT I. PHOTOSYNTHESIS AND TRANSPIRATION Experiment I was conducted in the chamber at a temperature of 85° F. Six comparable leaves on each of two trees were selected for study. The roots of one tree were constantly submerged beginning June 22, 1940. The percentages of the expected rates of apparent photosynthesis and transpira- tion are plotted in the upper graph of figure 2. The points oni the chart EXPERIMENT I 110 -1-..0.... A 75 05 WAETXECRESSADDED U H25POTOSYNTHESIS --TRANSPIRATION U0 22 24JUNE26 28 30 12940 4 6 8 K e JU4LY 16 e8 2 22 llI 11, ',~*~~~~~N~-1 75 75 1 . N. :~ ~ LIC r 5 WArERADDED\ a 50 WAETXECRESASDDED WAETXECRESSREW40VFD - \ X; PHOTOSYNTHESIS X25-PHOTOSYNTHESIS --TRANSPIRATION --TRANSPIRATION TREE-A- TREE -B- 9n ,, 1J3ULY ,-5 17 19 9 , 13 15 JU17LY 19 21 23 25 EXPERIMENT 1 FIG. 2. Ilnfluence of submersion of roots on apparenit photosylnthesis anid transpira- tionl of apple leaves. Expressed as percentage of expected rate. Horizontal line at 100 represents photosyntliesis anid transpiration of check leaves. Experiment I was performed in environment-control chamber; experiment II was out-of-doors. during the pre-treatment period exemplify the usual variation in activity of the test leaves as compared with the check leaves. Both apparent photo- Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. 608 PLANT PHYSIOLOGY synthesis and transpiration gradually decreased to between 80 and 70 per cent. within the 30-day period of submersion. EXPERIMENT IL PHOTOSYNTHESIS AND TRANSPIRATION Experiment II was performed on two test trees and a check tree placed outside of the greenhouse in July, 1940. Four comparable leaves were used on each tree. The results are shown as percentages in the lower two graphs offigure 2. Therates ofphotosynthesis andtranspiration of test tree A had decreased to 25 per cent. seven days after the flooding period started on July 13. Extreme foliage injury occurred and prevented further measurements EXPERIMENT m 130 ¢> < ~~~~~~~~~PHOTOSYNTHESIS z= ~ ~~~~q~~~-~TR~AN~SP~IR~ATION SE OCT w ?~~~~I iQfi020'P*A HOTIOSYN0THESIS z TREE--A w -~~~~~~~~~~~PHOTOSYNTHESIS 8T0R-EBEx-m ~ ~ ~ ~ --TRANSPIRATION C~~~2~3~~2~5~ 27 9 1 34 7 9 19 21 23 SePT OCT W40 20 I23 25 27 29 1 3 5 7 9 II 13 15 I7 19 21 2 SPT 190OCT FIG. 3. Apparent photosynthesis and transpiration of trees A, B, and a in experi- ment III. Note differences in individual tolerance of trees to root submersion. Experi- ment performed out-of-doors. Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. CHILDERS AND WHITE: SUBMERSION 609 on this tree. The apparent rates of photosynthesis of test tree B decreased to 67 per cent. during the sameseven days of submersion, while transpiration decreased to 69 per cent. The soil of tree B was drained of free water after nine days of submersion; six days later the rates of leaf activity of the test tree were equivalent to its pre-treatment period. EXPERIMENT III. PHOTOSYNTHESIS AND TRANSPIRATION Experiment III was conducted outside the greenhouse dcuring late September and through most of October, 1940. The roots of three trees were submerged on September 29 and a fourth tree was used as a check. Three comparable leaves were used on each tree. The percentages of ex- pected rates of apparent photosynthesis and transpiration are given in figure 3. Both processes ultimately were severely reduced, with photo- synthesis less than 10 per cent. of its expected rate. The time of lowest leaf activity varied with individual trees. The roots of the trees were washed free ofsoil atthe end ofthe experiment. Several short, rather stubby, white roots had developed on or near the graft union of the flooded trees. EXPERIMENT IV. PHOTOSYNTHESIS, TRANSPIRATION, ANDSTOMATAL ACTIVITY Experiment IV consisted of two test trees and a check placed in the chamber at 800 F. Four leaves on each tree were used; the results are plotted in figure 4. As much as a 96 per cent. reduction in apparent photo- synthesis of test tree A and a 79 per cent. reduction in test tree B were associated with submersion of the roots. Transpiration rates were reduced also but not so severely. The free water was drained after 18 days of flooding, and within 4 to 6 days there was a trend toward recovery in leaf activity. The leaf activity of tree A did not completely recover by the end of the experiment. Transpiration of treeB evidently recovered while photo- synthesis continued between 85 and 100 per cent. of its expected rate. The roots were washed free of soil at the end of the experiment, 14 days after the excess water had been drained. Roots of the test trees were scanty as com- pared with those of the check tree. The test roots were also darker in color than the checkroots; no other differences were visible. In experiment IV stomatal activity of the leaves under study was ob- served through a Leitz "Ultrapak" microscope. The study was made on November 22, 23, and 24, when leaf activity had become low ow-inog to ex- tended root submersion. The counts recorded in each observation were an average from a part of three fields near the apex of a leaf. Each count included an observation of 25 to 40 stomata. Any stoma which did not appearto be completely closed was recorded as open. No attempt was made to note differences in degree of opening since there appears to be no positive method of knowing when a stoma is partly open or closed. The data are Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. 610 PLANT PHYSIOLOGY plotted in figure 5 as percentage of stomata open. There were no consistent differences between the activity of stomata of treated and check trees. Hence, the marked reductions in photosynthesis and transpiration (fig. 4) could not be correlated with stomatal activity during this 3-day period. EXPERIMENT IZ TREE-A- 128. ON FOUR LEAF ONFCURLEAF BASIS ON TFREE LEAF BASIS TREE-B- NOV 1940 DEC FIG. 4. Transpiration and apparent photosynthesis of test trees A and B in experi- ment IV. Soil was flooded on November 9 and drained 17 days later. EXPERIAIENT V. PHOTOSYNTHESIS, TRANSPIRATION, RESPIRATION, AND LEAP TEMPERATURE Experiment V was conducted with two trees in the chamber at a tem- perature of 850 F. This experiment was designed to measure any differ- ences in the activity of upper leaves as compared with middle leaves on a shoot with submerged roots. The experimental leaves were large and ma- ture. Afewofthebasalleaves of each treeyellowed and abscised soon after being placed in the chamber. Three of the top-most leaves which would fit the leaf-cups were used to compare with three leaves located approximately at the middle of the shoots. The shoots were about five feet in height. Ap- Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. CHILDERS AND WHITE: SUBMERSION 611 z 0 !- 2 0 U) hJ B. z I~- z aU: L; FIG. 5. Stomatal behavior of test and control leaves from November 22 to 24, inclu- sive, experiment IV. During this period apparent photosynthesis and transpiration were showing reductions of 20 to 95 per cent., 13 days after beginning submersion. Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved. 612 PLANT PHYSIOLOGY parent photosynthesis and respiration were measured on alternate days. The respiration determinations began about 6:00 P.M., when the chamber was darkened. Transpiration was measured in all determinations. The apparent photosynthesis and transpiration of the test tree in ex- periment V are shown in figure 6. In the upper leaves the trends of both EXPERIMENT v UPPER LEAVES oW . *. PHOOSYNTHESIS -: TRANSPIRATION--: us MIDDLE LEAVES A91FB a1.0~0 JAN i 0 12 12b2 8^2 24 28v28 0 9 ii 5' 17 19 2 FIG. 6. Transpiration and apparent photosynthesis of upper and middle set of leaves on one-year tree in experiment V. Roots were submerged on January 16; water was drained on February 9. processes were similar, showing 30 to 50 per cent. reductions throughout the 25-day period of submersion. Removal of the excess water was followed by apparent recovery in leaf activity. The photosynthesis of middle leaves was not consistently less than the expected rate after submersion, although an average of the twelve determinations for the period would fall well below the 100 per cent. line. Nevertheless, it appears that photosynthesis of the middle set of leaves was not affected as much as that of the upper set. Transpiration of middle leaves showed a reduction similar to that which occurred in the upper leaves. Respiration and transpiration, as determined at night, are plotted in figure 7. It should be emphasized that the amount of carbon dioxide re- leased by the leaves was relatively small, and the possibility of error in procedure could be somewhat greater. As shown in the graph, however, the trends were reasonably consistent from day to day. Apparent respira- tion after submersion was definitely increased in both upper and middle leaves. Indeed, on some days respiration of test leaves was almost double Downloaded from on April 11, 2019 - Published by www.plantphysiol.org Copyright © 1942 American Society of Plant Biologists. All rights reserved.