Arizona-Nevada Academy of Science

The Effect of Relative Humidity on Growth, Water Consumption, and Calcium Uptake inTomato PlantsAuthor(s): A. A. Swalls and J. W. O'LearySource: Journal of the Arizona Academy of Science, Vol. 10, No. 2 (Jun., 1975), pp. 87-89Published by: Arizona-Nevada Academy of ScienceStable URL: http://www.jstor.org/stable/40021784 .

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THE EFFECT OF RELATIVE HUMIDITY ON GROWTH, WATER CONSUMPTION, AND CALCIUM UPTAKE IN TOMATO PLANTS1

A. A. SWALLS2 and J. W. O'LEARY

University of Arizona, Tucson

[142]

INTRODUCTION. - The highest average annual insolation in the United States is found in an area comprised of most of the states of Arizona and New Mexico and small parts of southern Nevada and California (Calvin, 1974). In contrast to the high availability of sunlight, however, this area has an extremely low annual rainfall. Nevertheless, since water can be moved but sunlight can not, this area will become even more important as a crop growing center as food and energy needs continue to escalate. It will be imperative, though, to use the water in this area in the most efficient manner possible. In view of the high evaporative demand of the air in this region, this suggests increased use of greenhouses or other con- trolled environment enclosures (O'Leary, 1965b). Fur- thermore, for many reasons, mostly economic, tomatoes probably will be the food crop most often grown in southwestern greenhouses (Dalrymple, 1973).

Ironically, the use of greenhouses in arid areas to reduce water consumption by plants often results in a situation where the plants are growing in an atmosphere with an extremely high relative humidity. This is because high relative humidity inevitably develops in a relatively tightly closed greenhouse (Cotter and Walker, 1967; Walker and Cotter, 1968a, b; Wolfe, 1970). While the high relative humidity does reduce crop water consumption remarkably (O'Leary, 1975a), it also introduces certain physiological problems for the plant (O'Leary, 1975b). One of these problems is the poten- tial reduction in mineral uptake and delivery to leaves as a result of the greatly reduced transpiration rate (Gale and Hagan, 1966; O'Leary and Knecht, 1972).

This problem of potential reduced mineral uptake as a result of high humidity has been studied in red kidney bean plants (O'Leary and Knecht, 1972), as well as the effect of the high humidity on overall growth and water consumption (O'Leary and Knecht, 1971). However, as pointed out in that earlier work, similar studies are needed with other species of plants before any general conclusions can be made. In view of the commercial importance of tomatoes as a greenhouse crop, this seemed like a logical plant to use in further studies of the high humidity effects.

MATERIALS AND METHODS. - Seeds of tomato (Lycopersicon esculentum Mill. cv. 'Manapal') were germinated in rolled Kimtowel Disposable Shoptowels (Prisco and O'Leary, 1970) wet with a modified Hoagland solution (O'Leary and Prisco, 1970). This solution was used as the growth solution in all experi- ments described herein. Uniform seedlings were selected

1This research was supported by funds from the Rockefeller Foundation and is part of the research submitted by the senior author to the University of Arizona for the Ph.D. degree.

2 Deceased.

after seven days and transferred to one liter glass containers of aerated nutrient solution in three ISCO Model E-3 plant growth chambers. Each chamber contained 10 plants plus two containers with no plants used to correct for evaporative water losses from the containers. The volume of solution in each container was maintained at one liter by quantitative addition of fresh nutrient solution every day. All chambers were programmed for a 14 hour photoperiod with a day/ night temperature of 21/1 8C. Light was supplied by 3200 watts of Sylvania Metalarc lamps and 800 watts of incandescent light in each chamber. The plant tray level was adjusted every day to maintain an average of 5800 ft-candles at the tops of the plants throughout the experiment. The electronic control system simultane- ously controlled temperature and humidity using a wet and dry bulb thermistor bridge as the control and recording sensors and provided for close humidity control. The humidity levels were 35-40% (low), 80-85% (medium), and 95-100% (high). Relative humidity was measured in the bulk air which moved upward through the plant growing zone at 25 to 50 cm sec"1. On the 21st day, a 45Ca uptake experiment was conducted. One half of the plants in each chamber were left in the chamber in which they had been growing. The remaining half of the plants were transferred as follows: (1) from high to medium humidity, (2) from medium to low humidity, (3) from low to medium humidity. The plants were allowed to equilibrate in the new humidity conditions for three hours to eliminate uptake patterns resulting from short term water adjustments. Four hundred ml of half-strength nutrient solution with one-tenth strength Ca(NO'3)2 and 0.05 jlic of 45Ca were supplied to each plant. After a three-hr uptake period, plants were harvested and divided into roots, leaf blades, and stems plus petioles. Fresh and dry weights were determined, the tissue was wet digested, and 45Ca activity was measured. The 45Ca activity was determined with a Packard Tri-Carb Model 3320 liquid scintillation spectrometer.

All data were analyzed with the LSD test. Any differences described as significant in the following dis- cussion were found to be different at the 95% confidence level.

RESULTS AND DISCUSSION. - As can be seen from Table 1, there was a direct effect of the relative humidity of the atmosphere on plant growth. The fresh weight of all parts of the plant increased with increasing humidity. Most of the increase in total fresh weight was due to increase in shoot growth as reflected by the increased shoot/root ratio at the high humidity. Similar trends are found in dry weight (Table 2), although all parts of the plant increase in weight with increasing humidity to the same degree. This is shown by the lack

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88 JOURNAL OF THE ARIZONA ACADEMY OF SCIENCE Vol. 10

Table 1. Fresh weight (g/plant) of plants grown under three humidity levels.

Relative Leaf Stems & Total Shoot/root humidity blades Petioles Shoots Roots plant ratio

35-40% 52.6 61.8 114.3 34.6 148.9 3.3

80-85% 71.2 81.1 152.3 42.6 195.9 3.6

95-100% 92.2 158.8 251.0 60.1 310.8 4.2

Table 2. Dry weight (g/plant) of plants grown under three humidity levels.

Relative Leaf Stems & Total Shoot/root humidity blades Petioles Shoots Roots plant ratio

35-40% 8.00 4.79 12.79 2.04 14.82 6.3

80-85% 9.25 5.56 14.81 2.31 17.12 6.4

95-100%) 10.20 8.63 18.83 2.86 21.70 6.6

of significant difference in shoot/root ratio at all humidities. Thus, the increased shoot/root ratio on a fresh weight basis simply illustrates the increased hydration of the tissue at the higher humidity. The important point is that the dry weight of the plants was significantly increased with increasing humidity.

The total water consumed by each plant did not vary significantly among treatments (Table 3). However, due to the increase in dry weight production with increasing humidity, the transpiration ratio varied significantly among treatments. The amount of water consumed per gram of dry weight produced in the high humidity was only 60% and 70% as much as it was in the low and medium humidities, respectively.

Table 3. Water consumption by plants grown under three humidity levels.

Transpiration ratio Total water use (ml H20/g DW

Relative humidity (ml/plant) of plant)

35-40% 4,194 283

80-85% 3,931 230

95-100% 3,529 163

To see if this reduced water consumption in the high humidity could lead to reduced mineral transport to leaves, we measured water and 45Ca uptake during a 3-hour period. Calcium was used because its transport to leaves has been found to be correlated with rate of water transport to leaves (O'Leary, 1965). This relationship was tested by transferring plants from the environment in which they were growing to either higher or lower humidity, which resulted in significantly increasing or decreasing the rate of water uptake. In two out of the three cases (B, C, E), This resulted in significantly altering the 45Ca content of the leaves in the same direction (Table 4). Thus, we are confident that our assumption regarding correlation between calcium transport and water movement up the stem was valid.

As expected on the basis of the total water consumption data from Table 3, there were no significant differences in water uptake by the plants remaining in each of the three humidities in which they had grown (A, D, F). This indicates that the increase in evaporating surface with increasing humidity apparently is counterbalanced sufficiently by the decreased vapor pressure gradient for water to result in similar rates of water consumption per plant in all three humidities. However, the 45Ca contents of roots and stems plus

Table 4. Uptake of 45Ca and water under different humidity levels.

Water solution Relative humidity uptake Calcium content after 3 hr uptake

During During (cpm x lQ-Vg DW) '

growth uptake (ml/plant/3 hr) Leaf blades Stems & petioles Roots

A) Low Low 155 22.3 514 12,745 B) Low Med 106 5.2 158 10,343 C) Med Low 170 16.4 1112 11,482 D) Med Med 133 5.9 409 11,766

E) High Med 232 7.4 244 8,902 F) High High 143 7.1 147 8,270

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June 1975 THE EFFECT OF RELATIVE HUMIDITY ON TOMATO PLANTS 89

petioles were significantly reduced by increasing humidity. The 45Ca content of leaves was significantly less in medium and high humidity than in low humidity, but the difference between the medium and high humidities was not significant.

The results agree reasonably well with those of O'Leary and Knecht (1972) concerning calcium delivery to the leaves. There was no significant reduction in calcium delivery to leaves by the high humidity when compared to the medium humidity in both cases. As discussed by O'Leary and Knecht (1972), this can be explained by differences in the concentration of calcium in the transpiration stream reaching the leaves. There were, however, significant differences in the amount of 45Ca retained in stems and petioles and roots of the tomato plants while the same was not true for bean plants. This, however, may simply be due to the differences in dry weight of these parts among

treatments and be a consequence of expressing the results on a dry weight basis. The results of this study do, however, support the conclusion of O'Leary and Knecht (1972) that the low transpiration rates of plants grown at high relative humidities do not significantly reduce the amount of calcium delivered to leaves.

SUMMARY. - Lycopersicon esculentum Mill. cv. 'Manapal' plants were grown at 35-40%, 80-85%, and 95-100% relative humidities in controlled environment chambers. The fresh and dry weights of the plants were significantly increased by higher humidity, and the transpiration ratio was significantly decreased. The total amount of 45Ca uptake and delivery to leaves was not significantly affected by the high humidity, however. The results support the conclusion that plants appar- ently can tolerate extremely low transpiration rates without reducing salt delivery to leaves.

LITERATURE CITED

CALVIN, M., 1974. Solar energy by photosynthesis. Science 184:375-381.

COTTER, D. J., and J. N. WALKER, 1967. Occurrence and biological effect of humidity in greenhouses. Proc. 17 Int. Hort. Congress. 3:353-368.

DALRYMPLE, D. G., 1973. Controlled Environment Agricul- ture: A Global Review of Greenhouse Food Production. USDA, Washington, D.C. 150 pp.

GALE, J., and R. M. HAGAN, 1966. Plant antitranspirants. Ann. Rev. Plant Physiol. 17:269-282.

O'LEARY, J. W., 1965. The transpiration stream and upward translocation of mineral ions. Ohio J. Sci. 65:357-362.

, 1975a. Environmental influence on total water consumption by whole plants. In Perspectives of Biophysi- cal Ecology. Ed. by D. M. Gates and R. Schmerl. Springer Verlag, N.Y. (in press).

, 1975b. The effect of humidity on crop production. In Physiological Aspects of Dryland Farming, Vol. II. Ed. by U. S. Gupta. IBH Publishing Co., Oxford (in press).

, and G. N. KNECHT, 1971. The effect of relative humidity on growth, yield and water consumption of bean plants. J. Amer. Soc. Hort. Sci. 96:263-265.

, and , 1972. Salt uptake in plants grown at constant high relative humidity. J. Ariz. Acad. Sci. 7:125-128.

, and J. T. PRISCO, 1970. Response of osmotically stressed plants to growth regulators. Adv. Front. Plant Sci. 25:129-139.

PRISCO, J. T., and J. W. O'LEARY, 1970. Osmotic and toxic effects of salinity on germination of Phaseolus vulgaris L. seeds. Turrialba 20:177-184.

WALKER, J. N., and D. J. COTTER, 1968a. Condensation and resultant humidity in greenhouses during cold weather. Trans. ASAE 11:263-266.

, and , 1968b. Control of high humidity in greenhouses during warm weather. Trans. ASAE 11:267-269.

WOLFE, J. S., 1970. Feasibility and economics of conditioning recirculated greenhouse air by means of evaporative cool- ing. J. Agric. Eng. Res. 15:265-273.

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