Effects of Dissolved Oxygen Concentrations in Aero-hydroponics on ...


Effects of Dissolved Oxygen Concentrations in Aero-hydroponics on ...

Reprong>inong>ted from Vol. 113(2), Match 1988

Journal ong>ofong> the American Society for Horticultural Science

Alexandria, VA 22314

J. AMER. Soc. HORT. SCI. 113(2):218-221. 1988

ong>Effectsong> ong>ofong> ong>Dissolvedong> ong>Oxygenong> ong>Concentrationsong> ong>inong>

ong>Aeroong>-ong>hydroponicsong> on the Formation and Growth

ong>ofong> Adventitious Roots

Hillel Song>ofong>fer' and David W. Burger

Department ong>ofong> Environmental Horticulture, University ong>ofong> California, Davis, CA 95616

Additional ong>inong>dex words. vegetative propagation, aeroponics, ong>hydroponicsong>, rootong>inong>g, boundary layer, Chrysanthemum x

morifolium, (Dendranthema grandiflora tzvelv.) Ficus benjamong>inong>s, weepong>inong>g fig

Abstract. Cuttong>inong>gs ong>ofong> Fictis benjamong>inong>s L. and Chrvsanthemum x morifolium(Dendranthema grandiflora tzyelev.) were

rooted ong>inong> aero-ong>hydroponicsong> to study the effect ong>ofong> dissolved oxygen concentrations ong>inong> the range ong>ofong> 8 mg-liter. (ambient

saturation) to 0 mg-liter-'. The results ong>ofong> this study ong>inong>dicate that dissolved oxygen is essential to root formation and

root growth. Woody (Ficus) and herbaceous (Chrysanthemum) cuttong>inong>gs responded similarly. Lowerong>inong>g the dissolved

oxygen concentration ong>inong>creased the time required to form adventitious roots, reduced rootong>inong>g percentages, reduced

numbers ong>ofong> roots formed per cuttong>inong>g, and reduced average root lengths. Comparisons between stirred and unstirred

water suggested the development ong>ofong> an area ong>ofong> depleted oxygen concentration (boundary layer) at the stem-water

ong>inong>terface on cuttong>inong>gs immersed ong>inong> unstirred water. Cuttong>inong>gs ong>inong> water stirred constantly rooted sooner and formed more

roots than did those ong>inong> unstirred water. Maximum rootong>inong>g occurred ong>inong> misted (high dissolved oxygen concentrations)

sections ong>ofong> cuttong>inong>gs suspended ong>inong> the aero-ong>hydroponicsong> chambers. Chemical name used: potassium salt ong>ofong> 1H-ong>inong>dole-3but-vric

acid (K-IBA).

Any medium used for rootong>inong>g must provide mechanical support, water, and oxygen.

Whereas a great deal ong>ofong> ong>inong>formation is available regardong>inong>g the importance ong>ofong> water ong>inong> the

rootong>inong>g process, ong>inong>formation on the effects ong>ofong> oxygen is relatively scarce. The actual

requirement for 02, and its availability ong>inong> the rootong>inong>g medium durong>inong>g adventitious root

formation have seldom been studied, although the importance ong>ofong> 02, ong>inong> supportong>inong>g the

ong>inong>tensive metabolic processes associated with root formation and subsequent growth is


Zimmerman (14) has shown that cuttong>inong>gs from various plant species required different

levels ong>ofong> 02, for rootong>inong>g ong>inong> water. Willow (Salix pendula) and English ivv (Hedera helix) ong>inong>

tap water required 02, concentrations ong>ofong> 1 and 10 mg-liter 02, respectively. Zimmerman

achieved dissoived 02, concentrations greater than ambient saturation levels by bubblong>inong>g

pure 02 ong>inong>to water (14). Measurements ong>ofong> 02 concentrations were ong>inong>termittent and, ong>inong>

some ong>inong>stances, after roots emerged, thus affectong>inong>g dissolved 02, concentrations. Tong>inong>ga

(13) ong>inong>jected gas mixtures ong>ofong> N2 contaong>inong>ong>inong>g 0%, 5%, 10%, and 15% 02 ong>inong>to water

culture and showed ong>inong>creased rootong>inong>g ong>ofong> carnation with assumed dissolved 02

concentrations (no direct dissolved 02 measurements were made). Usong>inong>g

Chrysanthemum, he compared rootong>inong>g ong>inong> water bubbled with air (21% 02 ) and rootong>inong>g ong>inong>

water contaong>inong>ong>inong>g no 02 (bubbled N2 ong>inong> water) and found that rootong>inong>g occurred only ong>inong> the

presence ong>ofong> 02 (13). In none ong>ofong> these studies was the water surroundong>inong>g the cuttong>inong>gs

agitated. If cuttong>inong>gs use dissolved 02 from the water durong>inong>g the rootong>inong>g process as do

roots, the lack ong>ofong> agitation might lead to an area ong>ofong> depleted 02 concentrations at the

stem-water ong>inong>terface.

Regardless ong>ofong> the absence ong>ofong> substantial data on the specific requirements for dissolved

02 ong>inong> the rootong>inong>g process, it has been shown that periodic aeration with 02 ong>ofong> the

propagation medium improved survival and rootong>inong>g ong>ofong> rootstock cuttong>inong>gs (2). Komissarov

(4) reported on gravel culture as a successful method ong>ofong> rootong>inong>g woody cuttong>inong>gs and

suggested water culture as a simple and efficient rootong>inong>g method worthy ong>ofong> practical

application. Experiments with water culture, ong>inong> which the water was changed every 2

days, showed that out ong>ofong> 30 species tested, 20 gave almost equal percentages ong>ofong> rootong>inong>g

ong>inong> water and ong>inong> sand. Some species rooted more rapidly ong>inong> water and developed more

vigorous roots than ong>inong> sand. No reference was made to dissolved oxygen concentrations

ong>inong> the rootong>inong>g medium.

These fong>inong>dong>inong>gs imply an important role for 02 ong>inong> the formation ong>ofong> adventitious roots and

ong>inong>dicate the need for further study ong>ofong> the effects ong>ofong> 02 on rootong>inong>g. The objectives ong>ofong> the

present study were three-fold: 1) to determong>inong>e the effects ong>ofong> dissolved 02 concentrations

(from air) withong>inong> the range ong>ofong> its solubility ong>inong> water on rootong>inong>g ong>ofong> woody (Ficus) and

herbaceous (Chrysanthemum) cuttong>inong>gs; 2) to assess the importance ong>ofong> a boundary layer

that may surround cuttong>inong>gs rootong>inong>g ong>inong> water; and 3) to assess the feasibility ong>ofong> water

servong>inong>g as the sole rootong>inong>g medium.

Materials and Methods

Propagation unit. All rootong>inong>g experiments were performed usong>inong>g the Eong>inong> Gedi System

(E.G.S.) mong>inong>i unit (11) an aero-ong>hydroponicsong> device consistong>inong>g ong>ofong> an 18-liter reservoir

contaong>inong>ong>inong>g 10 liters ong>ofong> recirculatong>inong>g, deionized water (Fig. 1).

Water is drawn from the bottom center ong>ofong> the reservoir via a hollow, rotatong>inong>g impeller

and, by centrifugal force, thrown horizontally ong>inong> to the air space, which creates a mist.

The mist descends gently back to the agitated water, facilitatong>inong>g gas exchange. Changong>inong>g

the impeller's rotatong>inong>g speed (maximum ong>ofong> 3000 rpm) changes the flow ong>ofong> water

(maximum ong>ofong> 2 liters-mong>inong>- 1) through the impeller. The contong>inong>uous flow ong>ofong> water and

creation ong>ofong> mist results ong>inong> water saturated with dissolved 02 (accordong>inong>g to temperature

and barometric pressure) throughout the contaong>inong>er.

In the rootong>inong>g experiments described here, four dissolved-02 concentrations were

established, each ong>inong> two propagation units: 0, 2.5, 5.0, and =8.0 mg-liter-1 (actual

saturation values were between 7.8 and 8.7, dependong>inong>g on prevailong>inong>g temperatures).

fig. 1. The Eong>inong> Gedi System propagation unit and the three designated segments ong>ofong> a cuttong>inong>g ong>inong> relation to water and mist.

The subsaturation concentrations were established by a barostatically controlled flow ong>ofong>

N2 gas bubbled ong>inong>to the contaong>inong>ers. In two additional units the impeller motor was turned

ong>ofong>f, thus creatong>inong>g no mist and leavong>inong>g the water ong>inong>side unstirred to determong>inong>e the effects

ong>ofong> stirrong>inong>g on root ong>inong>itiation (02 concentrations ranged between 8.0 and 7.5 mg-liter-1).

ong>Dissolvedong> 02 concentrations were measured contong>inong>uously with an 8500 ong>Dissolvedong> ong>Oxygenong>

monitor (Nester Instruments), the probe ong>ofong> which consumes no 02, durong>inong>g 02,

measurements and is unaffected by water turbulents.

The cuttong>inong>gs were placed ong>inong> the units so as to create three distong>inong>ct segments ong>ofong> each

stem. The lower 5 cm ong>ofong> the stem (segment 1) was immersed ong>inong> water. The center 5 cm

(segment 2) was exposed to mist, and the upper 5 cm (segment 3) was above the mist

(Fig. 1). The remaong>inong>der ong>ofong> the cuttong>inong>g (leaves and termong>inong>al apex) was outside the

propagation unit.

Plant material. Hardwood cuttong>inong>gs (25 cm long) ong>ofong> weepong>inong>g fig were collected ong>inong> Sept.

1986 from greenhouse-crown (Oki Nurserv, Sacramento, Calif.) stock plants. All but the

upper three to four leaves were removed from the cuttong>inong>gs. The bottom 2 cm ong>ofong> the

cuttong>inong>gs was dipped ong>inong> 5000 mg-liter K-IBA for 15 sec and immediately placed ong>inong> the

aero-hydroponic propagation units ong>inong> groups ong>ofong> 10. There were three groups ong>ofong> 10

cuttong>inong>gs ong>inong> each ong>ofong> the two propagation units at each dissolved oxygen concentration (60

cuttong>inong>gs per treatment). The experiment was located ong>inong> a greenhouse (20° to 25°C and

60% to 100% RH). The water temperature ong>ofong> the aero-ong>hydroponicsong> units was 24° +/- 1°

durong>inong>g the experiment. The experiment with weepong>inong>g fig was unrepeated.

Herbaceous cuttong>inong>gs ong>ofong> 'Bright Golden Anne', 'Intrepid White', and 'Intrepid Gold'

chrysanthemum were collected from plants (obtaong>inong>ed from Yoder Bros. Nursery, Salong>inong>as,

Calif.) grown ong>inong> the greenhouse under long days. Cuttong>inong>gs (25 cm long) with three to four

leaves were dipped (bottom 2 cm submerged) for 5 sec ong>inong> 3000 mg-liter-1 K-IBA and

then placed ong>inong> groups ong>ofong> 10 ong>inong> each ong>ofong> the 10 propagation units (20 cuttong>inong>gs per

treatment). The rootong>inong>g experiment with the chrysanthemum cultivars was repeated six

times, three times with 'Bright Golden Anne', twice with 'Intrepid White', and once with

'Intrepid Gold'. The propagation units were placed ong>inong> a growth chamber at a controlled

temperature ong>ofong> 24°C, 60% to 70% RH, and 14- hr photoperiod with photosynthetic

photon flux (PPF) ong>ofong> 400 µmol.s-¹.-m-² from metal halide lamps.

Results and Discussion

Root ong>inong>itiation ong>ofong> weepong>inong>g fig occurred on the 13th day ong>inong> air-saturated water (8 mg-liter-

¹ 02). Roots appeared on the 15th day ong>inong> 5.0 mg-liter-1 ong>ofong> 02 and on the 18th day ong>inong> 2.5

mg-fiter-¹, a delay ong>ofong> 2 and 5 days after the cuttong>inong>gs ong>inong> 8 mg-liter-¹ 02 rooted. Roots

ong>inong>itiated from the base ong>ofong> the cuttong>inong>gs.

On day 21, there was a relationship between 02 concentration and rootong>inong>g expressed ong>inong>

percent rootong>inong>g, number ong>ofong> roots, and length ong>ofong> the longest root (Table 1). Between days

21 and 38, rootong>inong>g ong>inong> 5.0 and 2.5 mg-liter-¹ 02 improved considerably compared with the

cuttong>inong>gs rootong>inong>g ong>inong> 8 mg-liter-¹ 02. All cuttong>inong>gs were ong>inong> deionized water for the entire

period. No changes occurred ong>inong> pH or EC ong>ofong> the deionized water. The cuttong>inong>gs ong>inong> 0 Mgliter-¹

02 remaong>inong>ed essentially unchanged throughout the 38-day period. No callus or root

development was observed.

Table 1. Effect ong>ofong> the dissolved 02, concentration on rootong>inong>g ong>ofong> Ficus benjamong>inong>a cuttong>inong>gs at 15, 21, and 38 days. Means +/- SD ong>ofong> two replications,

20 to 30 cuttong>inong>gs each.

ong>Oxygenong> concn




























DAY 15

DAY 21

DAY 38




1.5 +/- 0.7

2.5 +/- 1.8

4.8 +/- 3.3


7.6 +/- 2.3

12.3 +/- 3.2

8.0 +/- 2.7

Avg. length ong>ofong>

longest root



055 +/- 0.25

1.88 +/- 1.46

5.06 +/- 3.25


7.6 +/- 2.6

19.4 +/- 3.9

23.4 +/- 3.9

Exposong>inong>g cuttong>inong>gs ong>inong> one ong>ofong> the two 0 mg-liter-¹ dissolved 02 propagation units to 8 mgliter-¹

02 at day 21 by elimong>inong>atong>inong>g N2 gas flow for the followong>inong>g 17 days resulted ong>inong> root

formation (percent rootong>inong>g = 32.0, number ong>ofong> roots/cuttong>inong>g = 4.5, and average length ong>ofong>

the longest root = 0.82 cm). This response ong>inong>dicates that the potential for rootong>inong>g ong>inong>

weepong>inong>g fig can be restored after long periods ong>ofong> complete 02 absence from the rootong>inong>g

medium, as long as cuttong>inong>gs remaong>inong> ong>inong>tact. Chrysanthemum cuttong>inong>gs responded similar to

weepong>inong>g fig cuttong>inong>gs to dissolved 02 concentrations; number ong>ofong> roots (Figs. 2 and 3) and

total root length (Fig. 3) ong>inong>creased as dissolved 02 concentrations ong>inong>creased. The three

chrysanthemum cultivars differed little ong>inong> their response to concentrations ong>ofong> dissolved

O2. Chrysanthemum cuttong>inong>gs rooted along the entire stem, although there were some

differences ong>inong> the rootong>inong>g response among the three segments. There was no rootong>inong>g ong>inong>

any ong>ofong> the segments ong>inong> the complete absence ong>ofong> 02; however, roots formed ong>inong> the misted,

center section ong>ofong> the stem and a few formed above the mist long>inong>e ong>inong> the 2.5 mg-liter-' 02

treatment (Fig. 3).

There were no roots ong>inong> the basal segment immersed ong>inong> water. Roots developed ong>inong> all

three segments ong>inong> the 5.0 mg-liter-¹ 0², treatment; however, the number ong>ofong> roots and

the root length was only slightly greater than those ong>inong> 2.5 mg-liter-¹ 02- In 8.0 mg-liter-

¹, the number and length ong>ofong> roots ong>inong>creased ong>inong> each ong>ofong> the three segments, and the

majority developed ong>inong> the center, misted segment. When root ong>inong>itiation occurred, roots

always appeared first on the lowest segments, even if more subsequently developed

above (data not shown).

One more treatment was tested ong>inong> two other propagation units ong>inong> which no mist was

present and the water remaong>inong>ed unstirred durong>inong>g the entire rootong>inong>g period. The ong>inong>itial 02

concentration was 8.0 mg-liter-¹ (ambient saturation) and had dropped slightly to 7.5

mg-liter-¹ by the end ong>ofong> the experiment 38 days later. Weepong>inong>g fig roots ong>inong>itiated after

32 days ong>inong> the unstirred propagation units, compared to 13 days ong>inong> the stirred units. Only

50% ong>ofong> the weepong>inong>g fig cuttong>inong>gs rooted ong>inong> unstirred water; all rooted ong>inong> the units with

stirred water. Rootong>inong>g ong>ofong> chrysanthemum cuttong>inong>gs was delayed 2 days ong>inong> the unstirred

propagation units (Table 2). Root number and root length ong>inong> immersed sections ong>ofong>

weepong>inong>g fig and chrysanthemum were greater ong>inong> stirred water than ong>inong> unstirred water

(Table 2). Section 2 ong>ofong> cuttong>inong>gs ong>inong> stirred units was misted, whereas those sections ong>inong>

unstirred units were not. More roots formed and the root length ong>inong>creased ong>inong> misted

sections ong>ofong> 'Bright Golden Anne' cuttong>inong>gs (Table 2) compared to non-misted. Further

study is needed to understand fully this apparent beneficial effect ong>ofong> mistong>inong>g on the

cuttong>inong>g stem.

The results ong>ofong> this study ong>inong>dicate that dissolved 02 is essential to root formation. Both

woody (weepong>inong>g fig) and herbaceous (chrysanthemum) cuttong>inong>gs responded favorably, but

somewhat differently, to ong>inong>creased 02 concentrations ong>inong> the water. ong>Oxygenong> affected the

timong>inong>g ong>ofong> rootong>inong>g, rootong>inong>g percentage, number ong>ofong> roots, and root length.

It seems apparent, based on the rootong>inong>g ong>ofong> the immersed segment ong>ofong> cuttong>inong>gs ong>inong> stirred

and unstirred units, that the dissolved 02 concentration ong>ofong> greatest physiological ong>inong>terest

is at the ong>inong>terface between the cuttong>inong>g's stem surface and the water. Therefore,

measurements ong>ofong> air volume ong>inong> a given rootong>inong>g substrate or O2, concentrations ong>inong> a liquid

medium are ong>ofong> mong>inong>or importance to the rootong>inong>g process unless the 02 measurements are

representative ong>ofong> the stem-water ong>inong>terface surroundong>inong>g the stem. This measurement is

best done ong>inong> water that is agitated vigorously. Failure to do so may explaong>inong> the poor

correlation between adventitious root formation and volumetric air content ong>ofong> rootong>inong>g

media (1, 5-7, 9, 12). Volumetric air content may make little difference ong>inong> terms ong>ofong> root

formation if the cuttong>inong>g has an aqueous layer surroundong>inong>g it that ong>inong>hibits the diffusion ong>ofong>

02 from the air to the ong>inong>terior ong>ofong> the cuttong>inong>g. In liquid culture, the ong>inong>terface between the

stem and unstirred water may consist ong>ofong> a depletion gradient ong>ofong> dissolved 02

concentration, similar to that described and associated with mong>inong>eral uptake by roots (3,

8). An additional explanation may be that substances exuded from the cuttong>inong>g stem may

accumulate around the stem when placed ong>inong> unstirred water. The ong>inong>terface becomes

thong>inong>ner as the turbulence ong>ofong> the surroundong>inong>g liquid ong>inong>creases, hence the stirrong>inong>g effect

(10). A propagation device ong>inong> which water is the sole medium might serve efficiently,

provided the water is saturated with dissolved 02 and agitated sufficiently to mong>inong>imize or

elimong>inong>ate the boundary layer. ong>Aeroong>-ong>hydroponicsong> has the advantage ong>ofong> ong>inong>itiatong>inong>g roots

either ong>inong> mist or ong>inong> 02-saturated water and subsequent root growth and development ong>inong>

well-aerated nutrient solution.

Literature Cited

1. Gislerod, H.R. 1983. Physical condition on propagation media and their ong>inong>fluence on the rootong>inong>g ong>ofong> cuttong>inong>gs: III. The

effect ong>ofong> air content and temperature ong>inong> different propagation media on the rootong>inong>g ong>ofong> cuttong>inong>gs. Plant & Soil 75:1-14.

2. Howard, B.H. 1975. Improved rootong>inong>g ong>ofong> cuttong>inong>gs by diffusion ong>ofong> oxygen through the rootong>inong>g medium. J. Hort. Sci.

50:173- 174.

3. Jacobson, L., B.R. Copper, and M.G. Voiz. 1971. The ong>inong>teraction ong>ofong> pH and aeration ong>inong> CI uptake by barley roots.

Physiol. Plant. 25:423-435.

4. Komissarov, D.A. 1968. Biological basis for the propagation ong>ofong> woody plants by cuttong>inong>g. Israel Program for Scientific

Translations. Jerusalem. p. 34-38.

5. Loach, K. 1985. Rootong>inong>g ong>ofong> cuttong>inong>gs ong>inong> relation to the propagation medium. Proc. Inti. Plant Prop. Soc. 35:472-485.

6. Matkong>inong>, O.A. 1965. Physical properties ong>ofong> propagation media. The Plant Prop. 11:18.

7. O'Dell, G.A. and L.P. Stolz. 1978. Media particle-size effect on rootong>inong>g. The Plant Prop. 1.4:4-8.

8. Olsen, C. 1950. The significance ong>ofong> concentration for the rate ong>ofong> ion absorption by higher plants ong>inong> water culture.

Physiol. Plant. 3:152-164.

9. Paul, J.L. and C.1. Lee. 1976. Relation between growth ong>ofong> Chrysanthemum and aeration ong>ofong> various contaong>inong>er media.

J. Amer. Soc. Hort. Sci. 101:500-503.

10. Polle, E.O. and H. Jenny. 1971. Boundary layer effects ong>inong> ion absorption by roots and storage organ ong>ofong> plants.

Physiol. Plant. 25:219-224.

11. Song>ofong>fer, H. 1986. A device for growong>inong>g plants aero-hydroponi- cally: The E.G.S. (Eong>inong> Gedi System) mong>inong>i unit. Soilless

Cult. 2:45-52.

12. Tilt, K.M. and T.E. Bilderback. 1987. Physical properties ong>ofong> propagation media and their effects on rootong>inong>g ong>ofong> three

woody ornamentals. HortScience 22:245-247.

13. Tong>inong>ga, J.H. 1952. The effect ong>ofong> five levels ong>ofong> oxygen on the rootong>inong>g ong>ofong> carnation cuttong>inong>gs ong>inong> tap water culture.

Thesis, Comell Univ., Ithaca, N.Y.

14. Zimmerman, P.W. 1930. ong>Oxygenong> requirements for root growth ong>ofong> cuttong>inong>gs ong>inong> water. Amer. J. Bot. 17:842-861.

Received for publication 3 Apr. 1987. The cost ong>ofong> publishong>inong>g this paper was defrayed ong>inong> part by the payment ong>ofong> page

charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to ong>inong>dicate this


Visitong>inong>g Horticulturist. Permanent address: Institute ong>ofong> Field and Garden Crops, Agriculture Research Organization, The

Volcani Center, Bet Dagan 50250, Israel.

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