AMMONIA UPTAKE BY PLANTS V.M. ARTYOMOV, E.M. ARTYOMOV and SH.D. FRIDMAN Institute of Global Climate and Ecology, Glebovskaya 20b, Moscow107258, Russia.
(Received: September 1991; revised: July 1993)
Abstract. The paper considers the methodology and results of experimental determination of dry deposition and ammonia uptake by isolated plant leaves. Analytical expressions are proposed which allow a transition from rates obtained in an isolated chamber to dry ammonia deposition by standing crops leaves.
1. Introduction Dry ammonia deposition is one of the major components of nitrogen loadings on vegetation ecosystems. Its contribution to nitrogen load is found to be significant. The nitrogen balance over the former USSR territory is given in ref. [1], where it is stated that 60% of nitrogen is removed from the atmosphere in the form of NHx, more than 30% of which (or around 20% of the total atmospheric nitrate and ammonium nitrogen removed) is dry ammonia deposition. Similar results on the ratio of dry and wet NHx depositions are given in ref. [2]. Dry ammonia deposition is mainly related to its uptake by plants. The uptake of ammonia by plants under artificial and natural conditions has been confirmed in refs. [3-5]. Measurements of vertical ammonia concentration profiles inside the plant canopy demonstrated that it is taken up in the zone of plant habitat [6,7]. References [8,9] directly revealed the uptake of ammonia by plants. A field growing plant covered by a chamber was fumigated with (15NH3) ammonia which was comlpetely taken up by the plant. In the process of isotopic analysis the heavy isotope was detected in all plant organs, including roots. Reference [9] shows that the assimilated heavy nitrogen isotope was retained after fumigation of winter wheat plants before the yield was formed, and was then detected in the grain. In order to calculate the magnitude of ammonia dry deposition one uses the velocity of its dry deposition over the vegetation ecosystems, Vd which, according to refs. [3-5], varies between 0.3 and 5.5 cm/s in laboratory experiments under different conditions. The above spread in values of dry deposition velocity, obtained in specific experiments, does not allow us to estimate with any great confidence the contribution of ammonia to nitrogen loads on vegetation ecosystems, since it does not provide a notion about a real rate of dry depositions in the open atmosphere. The work reviewed above suggests an approach for obtaining a real rate of ammonia dry deposition velocity in the open atmosphere, and of giving its analytical expression. Environmental Monitoring and Assessment 29: 221-228, 1994. (~) 1994 Kluwer Academic Publishers. Printed in the Netherlands.
222
V.M. ARTYOMOV ET AL.
If one is to develop an approach for obtaining a real rate of dry ammonia deposition velocity over the plants one should consider the mechanism of its supply to a plant's assimilative organs. A model for a plant canopy with turbulent mixing was adopted for modelling gas supply to assimilative organs of the plant [10-11]. The model selected made it possible to obtain quite precise results when calculating the agrobiocenosis productivity.
2. Theory The velocity with which d r y ammonia deposits over plants under any weather conditions can be found by analysing ammonia fluxes to plants. The ammonia fluxes to plants can be found from the relation
F = kz d C / d z or F
= Vd C ,
(1)
where: F = the ammonia flux; kz = the turbulent diffusion coefficient at height z; d C / d z = the ammonia concentration gradient; C = the ammonia concentration; Vd = the velocity of the dry ammonia deposition over plants. The vertical change in the ammonia concentration inside the vegetation ecosystem is determined by two processes; the process by which the ammonia is delivered to vegetative organs of the plant and its ability to uptake ammonia. Under real conditions there are two fluxes of ammonia over plants: from the soil and from the atmosphere. Both fluxes can be found from the ammonia distribution inside the vegetation ecosystem, which is described by a diffusion equation. In accordance with the model [11], supposing that the assimilative organs of the plant evenly fill the volume above the soil of area S and height H, then density s is determined as a result of dividing the area of assimilative organs by the filled volume. The turbulent diffusion inside crops in the quasistationary regime, when the ammonia flux from air onto plants is constant, is described by the equation
d
kz
-sVuC=O
(2)
where: C = the ammonia concentration in the air layer at height z; Vu = the uptake velocity of the ammonia assimilative organs through diffusive mixing with a diffusion coefficient kz, which is approximated by the expression [10,11]
kz = kH[--a(1 - z/H)]
(3)
where: kH = the turbulent diffusion coefficient at a height H; a = the dimensionless coefficient which assumes the value 2 over a wide range of variations. The solution of Equation (2) has the form
C(z) = v~[BII1 (d vf-x) + B2K1 (d v~)]
(4)
AMMONIA UPTAKE BY PLANTS
223
d = (2H/a)
(4a)
where x = exp a(1 - z/H);
Sv/'~u/kH,
/31 and B2 are integration constants, and K1 and [1 are the first-degree modified Bessel functions. From Equation (4) it follows that
dC/dz =
sv/~u/kH * x * [B2Ko(d vZx) - BlIo(d v/x)]
(5)
I0 and K0 are zero modified Bessel functions. The approximation of vertical profiles of ammonia inside the vegetation ecosystem obtained by measurements through expression (4) allows us to find integration constants B1 and/32. By substituting/31 and/32 in formula (5) and then into one of relations (1), real ammonia fluxes on plants from soil and atmosphere may be calculated, and consequently the ammonia taken up by plants. In the case of a well developed vegetative system the intereffect of the ammonia fluxes is insignificant, i.e. the ammonia flux from soil does not affect the process of formation of the ammonia concentration above the plant and the ammonia flux from the atmosphere does not affect its formation near the soil. This circumstance allows us to calculate ammonia fluxes from the soil and the atmosphere individually. Supposing the ammonia flux from the atmosphere onto the plant is equal to the value of the ammonia uptaken by the plant, we proceed to find the relationship between Vd and Vu. The ammonia flux from the atmosphere onto the plant is calculated from relations (4) and (5) at/31 = 0 and relation (1), when x = 1
kH dC/dz = B2Ko(d) ~
= VdC = VdBzKI(d)
(6)
from (6) Vd :
[Ko(d)/Ka(d)] ~
.
(7)
For most cases of practical importance the relation Ko(d)/K1 (d) is close to unity i.e. Vd =
(8)
While there is a sufficient number of techniques for measuring k n in (8), and the value s is the result of measuring leaf area and soil area, as well as plant height, there is no universal technique for calculating the ammonia uptake rate V,. The value of Vu can be obtained experimentally when the mixing coefficient is known, when the ammonia delivery velocity is constant and does not depend on experimental conditions. Such conditions can be realized in an isolated chamber where mixing is provoked exclusively by molecular diffusion with a factor D = 0.196 cmZ/s. The process of change in the ammonia concentration in the sealed chamber with a plant density sc and initial concentration Co is described by equation
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V.M. ARTYOMOV ET AL.
D d2C/dr 2 - scVuC = dC/dt
(9)
where dC/dt is the rate of change of ammonia concentration in the chamber with time. The ammonia concentration change in time can be expressed through the dry ammonia deposition velocity (Vdc) on plants in the chamber. It is described by the equation
V dC/dt = SVdeC
(10)
V = the chamber volume, S = the leaf area of the plant in the chamber, sc in (9) is equal to S/V, and consequently
dC/dz = scVdcC
(11)
It follows from (9) and (11) that Vdc = ~
(12)
when Vu > Vdc, or Vu > soD. Excluding the unknown value Vu from (8) and (12) we obtain the analytical relation between Vd and Vdc Vd = Vdc" x/kH s/Ds~
(13)
Having determined experimentally the ammonia dry deposition velocity on the plant in the chamber (Vdc) with diffusive mixing of ammonia, and measuring kH in natural conditions, one can calculate the ammonia dry deposition velocity, and consequently its flux over vegetation ecosystems under various meteorological conditions.
3. Experimental Theoretically it has been demonstrated that the dry ammonia deposition velocity on vegetation ecosystems in the open atmosphere can be obtained through the velocity of the ammonia dry deposition in the chamber with diffusive mixing and freshly cut plant leaves evenly distributed in volume. We have conducted an experiment to determine the velocity of dry ammonia deposition in the chamber with diffusive mixing. The chamber is a glass cylinder with a diameter of 25 cm and a height of 40 cm. With the help of a specially made stop valve the ammonia is fed into the chamber and an air sample is taken. The whole inside surface of the chamber is parraffin coated, excluding the leaf surfaces, of course. The ammonia was fed into the lower part of the chamber. The sample was taken in the middle of the volume. The sample volume did not exceed 50 cm 3, and amounted to 0.25% of the total volume of the chamber.
225
AMMONIA UPTAKEBY PLANTS
c/c o
e c/% a
I,O
a
~
~
~'
a
+
0,5
o i
20
I
I
40
I
I
Jc m g n
60
Fig. 1. Temporal ammonia concentration variations in the chamber.
The ammonia concentrations were measured in the nonresonance optical acoustic cell (OAC) using CO2 laser radiation in generation lines with a high ammonia uptake coefficient (10P32) and a small one (10P28). The generation power equality in both wavelengths was stabilized with an accuracy not worse than 1% and together with a fast radiation switching (38 Hz) from one wavelength to another it was possible to suppress the signal from OAC windows and obtain an ammonia sensitivity of around 2 ppb. Maize plants were used in the experiment. The field laboratory was in the immediate vicinity of the maize plants under study, growing under natural conditions. This allowed us to reduce the time between the cutting of maize leaves and the beginning of the fumigation in the chamber to 5 minutes. Freshly cut maize leaves with paraffin sections were put into the chamber, then the chamber was sealed with paraffin. Ammonia was fed through a stop valve into the chamber with leaves for a short time. The ammonia concentration change was observed by air sampling. The change in the ammonia concentration is shown in Figure lb. Figure lc shows the change in the ammonia concentration with time on a logarithmic scale. Figure 1a shows the same chamber without leaves. The ammonia concentration in this chamber is constant, being mixed in the initial period. Vac was determined from the change of the ammonia concentration in the chamber in the initial period (after mixing period) (Figure lc) with the help of Equation (10). The experiment also
226
V.M. ARTYOMOVET AL.
Vd¢
+
IO
++
8
'7
2
Vdcol
4d
6o
Q, j. cm-a. h r
Fig. 2. The relationship between the rate of the ammonia uptake by the maize leafs and PAR value.
included continuous measurement of the atmospheric meteorological parameters, including the magnitude of the physiological activity of the solar radiation (PAR). This was conducted during the field season, and it allowed observation of the plants under various meteorological conditions over a wide range of variations in the PAR value. The most suitable conditions for finding the dependence of Vdc on the PAR value (P) were measurements of Vdc during one light day, since the PAR value changes over a wide range during a light day, while other meteorological parameters (air and soil moisture etc.) change rather insignificantly. In total around 100 distributions were obtained at various values; initial ammonia concentration in the chamber (from 0.8 to 650 mg/m 3) and PAR value (from 7 to 80 J/cm2h). It is worth noting that, when the ammonia concentration in the chamber is close to 650 mg/m 3, necrosis spots appear on leaves, and one cannot make any statement about the ammonia uptake by plants. In general the dry ammonia deposition velocity on plants does not practically depend on its initial concentration, when changing from 0.8 to 200 mg/m 3. The analysis of Vdc and PAR values (calculated from Equation (10)), at the moment the leaves are cut down, just before they are put into the chamber, reveals their linear relationship (Figure 2) Vdc = OZl - I - / 3 t P
(14)
AMMONIA UPTAKE BY PLANTS
227
Values oq and/31 in Equation (14) for maize leaves are correspondingly equal to 1.4 x 10 -2 and 1.2 x 10 -3. However, under conditions of excessive moisture in soil and air, the value of/31 is 1.5 - 2 times smaller than that given above, and under conditions of extreme deficit of moisture in soil the/31 value is close to zero and toxic ammonia effects on plants are observed. From Equations (14) and (13) and the known values of diffusive mixing coefficient D, maize leaf area S, chamber volume 12 the velocity of the atmospheric ammonia dry deposition onto plants under field conditions can be presented as
vd =
(15)
+/3P)
where oLand/3 constant values for maize leaves are respectively equal to O.15 and 0.013, and s is the assimilative plant organ density in the field. 4. Discussion The analysis of the formula for dry ammonia deposition velocity Vd (15) indicates that when kB changes from 50 to 500 cm2/s and P changes from 0 to 80 J/cm2h and s has a typical value closed to 0.1 c m - 1 for most meadows, the velocity of the dry ammonia deposition, under field conditions of middle latitudes when o~ = 0.15 and fl = 0.013, changes from 0.2 to 8.4 cm/s, which is in good agreement with results obtained in ref. [4]. The relationship between Vd and ( ~ ) is the result of the ammonia supply to assimilative organs of the plant through turbulent mixing, and for general reasons, it should be a universal, regardless of the model selected for the vegetation canopy, plant species composition, absorbed gas, etc.; though in this work the velocity dependence is demonstrated for a specific model. At the same time the linear relationship of the PAR is apparently specific for the ammonia uptake by plants. Just for comparison, the relation between carbon dioxide absorption and the PAR value is known to be linear up to a specific value of PAR, then saturation takes place. This must be related to competition processes of CO2 incoming via stomata and releasing in the process of the cellular respiration (in the Krebs cycle). The competition is not observed when the ammonia is taken up. Amino acids, formed while aminating ketoacids of the Krebs cycle, are stable compounds, and that provides a continuous ammonia sink, related only to the extent that the plant stomata are open. The aminating process is universal for all plants, therefore the value of s ought to assume the stomata density value. The value of the stomata density of assimilative organs probably explains the relationship between Vd and the species composition of the plant. Studies into ammonia uptake by plants make it possible to calculate ammonia loads over vegetation ecosystems. To estimate ammonia loads one can use the obtained values of coefficients o~ and 3 for maize, since the change in species composition results in a change of coefficients c~ and fl by not more than 1.5-2.0
228
V.M.ARTYOMOVET AL.
times. For grasslands and agricultural plants coefficients o~ and/3 do not practically differ from those for the maize. The ammonia sink value, due to its uptake by meadow grass and agricultural crops over the former USSR territory, is estimated (in the given suppositions) as 1.6 million t/y.
5. Conclusion An analytical relation has been suggested for calculating the velocity of dry ammonia deposition over plants. It has been found experimentally that the dry deposition velocity is linearly related to the value of the physiologically active radiation and in dark times of the day it differs from zero. In relation to the turbulent diffusion coefficient value in the open atmosphere and the PAR value the dry deposition value is 0.2-8.4 cm/s. The dry deposition velocity under excessive soil and air moisture decreases 1.5-2 times, and under extreme deficit of soil moisture it practically does not differ from that of the dark time of the day (0.14 cm/s).
References 1. Artjomov,E., Vasilenko,V., Nasarov,I., and Fridman, Sh.: 1990, 'AtmosphericBalance of Nitric Compounds in the Territory of the USSR', in 'Problemy Fonovogo Monitoringa Sostoyania Prirodnoi Sredy', Leningrad, Gidrometisdat,vyp. 8, pp. 30-38 (in Russian). 2. Moiler,D., and Schieferdeker, H.: 1989, 'Ammonia Emission and Deposition of NH~ in the G.D.R.',Atm. Env. 2, 1187-1193. 3. Aneja,V.P.,Rodgers, H.H., and Stahel,E.P.: 1986, 'Dry Depositionof Ammonia at Environment Concentrations on Selected Plant Species', JAPCA 36, 1338-1341. 4. Duyzer,J.H., Bouman, A.M.H., Diederen, H.S.M.A., and Van Aalst, R.M.: 1987, 'Measurement of Dry Deposition Velocities of NH3 and NH4 over Natural Terrains', TNO-Report: R87/273, Netherlands Organisation for Applied ScientificResearch, MT-TNO, Delft, the Netherlands. 5. Sutton,M.A., Fowler, D., and Moucrieff, J.B.: 1989, 'Measurement of Atmospheric Ammonia and the Assessment of its Exchange with Vegetated Surfaces', Species Environmental Report No. 17, WMO--No. 27, Extended abstracts of papers presented at the WMO Technical conference on the Monitoring and Assessment of Changing Composition of the Troposphere, pp. 154-157, Sofia, 23-27 October. 6. Denmead,O.T., Freney, J.R., and Simpson, J.R.: 1976, 'A Closed Ammonia Cycle within a Plant Canopy', Soil Sci., Biochem. 8, 161-164. 7. Shatilov, I.S., Artyomov, V.M., Artyomov, E.M., Fridman, Sh.D., Zamorajev, A.G., and Chapovskaya, G.V.: 1988, 'The Use of the Ammonium Nitrogen by the Plants from Air', Vestn. S.-H. Nauki, Moskva 7, 65-71 (in Russian). 8. Hutchinson, G.L., Millington, R.J., Peters, D.B.: 1972, 'Atmospheric Ammonia: Absorption by Plant Leaves', Science 175, 771. 9. Shatilov,I.S., Zamorajev, A.G., Artyomov,V.M., Artyomov, E.M., and Fridman, Sh.D.: 1988, 'Ammonia Absorption by Field Plants', Vestn. S.-H. Nauki, Moskva 1, 43-49 (in Russian). 10. Bojko, A.P.: 1976, 'Calculated Turbulent Regim in Agricultural Crops', Trudy IEM 8 (67), 37-48 (in Russian). 11. Sirotenko,O.D., Bojko, A.P.: 1976, 'A Dynamik Model of Agrocenosis', Trudy IEM 8 (67), 13-35 (in Russian).
(Received: September 1991; revised: July 1993)
Abstract. The paper considers the methodology and results of experimental determination of dry deposition and ammonia uptake by isolated plant leaves. Analytical expressions are proposed which allow a transition from rates obtained in an isolated chamber to dry ammonia deposition by standing crops leaves.
1. Introduction Dry ammonia deposition is one of the major components of nitrogen loadings on vegetation ecosystems. Its contribution to nitrogen load is found to be significant. The nitrogen balance over the former USSR territory is given in ref. [1], where it is stated that 60% of nitrogen is removed from the atmosphere in the form of NHx, more than 30% of which (or around 20% of the total atmospheric nitrate and ammonium nitrogen removed) is dry ammonia deposition. Similar results on the ratio of dry and wet NHx depositions are given in ref. [2]. Dry ammonia deposition is mainly related to its uptake by plants. The uptake of ammonia by plants under artificial and natural conditions has been confirmed in refs. [3-5]. Measurements of vertical ammonia concentration profiles inside the plant canopy demonstrated that it is taken up in the zone of plant habitat [6,7]. References [8,9] directly revealed the uptake of ammonia by plants. A field growing plant covered by a chamber was fumigated with (15NH3) ammonia which was comlpetely taken up by the plant. In the process of isotopic analysis the heavy isotope was detected in all plant organs, including roots. Reference [9] shows that the assimilated heavy nitrogen isotope was retained after fumigation of winter wheat plants before the yield was formed, and was then detected in the grain. In order to calculate the magnitude of ammonia dry deposition one uses the velocity of its dry deposition over the vegetation ecosystems, Vd which, according to refs. [3-5], varies between 0.3 and 5.5 cm/s in laboratory experiments under different conditions. The above spread in values of dry deposition velocity, obtained in specific experiments, does not allow us to estimate with any great confidence the contribution of ammonia to nitrogen loads on vegetation ecosystems, since it does not provide a notion about a real rate of dry depositions in the open atmosphere. The work reviewed above suggests an approach for obtaining a real rate of ammonia dry deposition velocity in the open atmosphere, and of giving its analytical expression. Environmental Monitoring and Assessment 29: 221-228, 1994. (~) 1994 Kluwer Academic Publishers. Printed in the Netherlands.
222
V.M. ARTYOMOV ET AL.
If one is to develop an approach for obtaining a real rate of dry ammonia deposition velocity over the plants one should consider the mechanism of its supply to a plant's assimilative organs. A model for a plant canopy with turbulent mixing was adopted for modelling gas supply to assimilative organs of the plant [10-11]. The model selected made it possible to obtain quite precise results when calculating the agrobiocenosis productivity.
2. Theory The velocity with which d r y ammonia deposits over plants under any weather conditions can be found by analysing ammonia fluxes to plants. The ammonia fluxes to plants can be found from the relation
F = kz d C / d z or F
= Vd C ,
(1)
where: F = the ammonia flux; kz = the turbulent diffusion coefficient at height z; d C / d z = the ammonia concentration gradient; C = the ammonia concentration; Vd = the velocity of the dry ammonia deposition over plants. The vertical change in the ammonia concentration inside the vegetation ecosystem is determined by two processes; the process by which the ammonia is delivered to vegetative organs of the plant and its ability to uptake ammonia. Under real conditions there are two fluxes of ammonia over plants: from the soil and from the atmosphere. Both fluxes can be found from the ammonia distribution inside the vegetation ecosystem, which is described by a diffusion equation. In accordance with the model [11], supposing that the assimilative organs of the plant evenly fill the volume above the soil of area S and height H, then density s is determined as a result of dividing the area of assimilative organs by the filled volume. The turbulent diffusion inside crops in the quasistationary regime, when the ammonia flux from air onto plants is constant, is described by the equation
d
kz
-sVuC=O
(2)
where: C = the ammonia concentration in the air layer at height z; Vu = the uptake velocity of the ammonia assimilative organs through diffusive mixing with a diffusion coefficient kz, which is approximated by the expression [10,11]
kz = kH[--a(1 - z/H)]
(3)
where: kH = the turbulent diffusion coefficient at a height H; a = the dimensionless coefficient which assumes the value 2 over a wide range of variations. The solution of Equation (2) has the form
C(z) = v~[BII1 (d vf-x) + B2K1 (d v~)]
(4)
AMMONIA UPTAKE BY PLANTS
223
d = (2H/a)
(4a)
where x = exp a(1 - z/H);
Sv/'~u/kH,
/31 and B2 are integration constants, and K1 and [1 are the first-degree modified Bessel functions. From Equation (4) it follows that
dC/dz =
sv/~u/kH * x * [B2Ko(d vZx) - BlIo(d v/x)]
(5)
I0 and K0 are zero modified Bessel functions. The approximation of vertical profiles of ammonia inside the vegetation ecosystem obtained by measurements through expression (4) allows us to find integration constants B1 and/32. By substituting/31 and/32 in formula (5) and then into one of relations (1), real ammonia fluxes on plants from soil and atmosphere may be calculated, and consequently the ammonia taken up by plants. In the case of a well developed vegetative system the intereffect of the ammonia fluxes is insignificant, i.e. the ammonia flux from soil does not affect the process of formation of the ammonia concentration above the plant and the ammonia flux from the atmosphere does not affect its formation near the soil. This circumstance allows us to calculate ammonia fluxes from the soil and the atmosphere individually. Supposing the ammonia flux from the atmosphere onto the plant is equal to the value of the ammonia uptaken by the plant, we proceed to find the relationship between Vd and Vu. The ammonia flux from the atmosphere onto the plant is calculated from relations (4) and (5) at/31 = 0 and relation (1), when x = 1
kH dC/dz = B2Ko(d) ~
= VdC = VdBzKI(d)
(6)
from (6) Vd :
[Ko(d)/Ka(d)] ~
.
(7)
For most cases of practical importance the relation Ko(d)/K1 (d) is close to unity i.e. Vd =
(8)
While there is a sufficient number of techniques for measuring k n in (8), and the value s is the result of measuring leaf area and soil area, as well as plant height, there is no universal technique for calculating the ammonia uptake rate V,. The value of Vu can be obtained experimentally when the mixing coefficient is known, when the ammonia delivery velocity is constant and does not depend on experimental conditions. Such conditions can be realized in an isolated chamber where mixing is provoked exclusively by molecular diffusion with a factor D = 0.196 cmZ/s. The process of change in the ammonia concentration in the sealed chamber with a plant density sc and initial concentration Co is described by equation
224
V.M. ARTYOMOV ET AL.
D d2C/dr 2 - scVuC = dC/dt
(9)
where dC/dt is the rate of change of ammonia concentration in the chamber with time. The ammonia concentration change in time can be expressed through the dry ammonia deposition velocity (Vdc) on plants in the chamber. It is described by the equation
V dC/dt = SVdeC
(10)
V = the chamber volume, S = the leaf area of the plant in the chamber, sc in (9) is equal to S/V, and consequently
dC/dz = scVdcC
(11)
It follows from (9) and (11) that Vdc = ~
(12)
when Vu > Vdc, or Vu > soD. Excluding the unknown value Vu from (8) and (12) we obtain the analytical relation between Vd and Vdc Vd = Vdc" x/kH s/Ds~
(13)
Having determined experimentally the ammonia dry deposition velocity on the plant in the chamber (Vdc) with diffusive mixing of ammonia, and measuring kH in natural conditions, one can calculate the ammonia dry deposition velocity, and consequently its flux over vegetation ecosystems under various meteorological conditions.
3. Experimental Theoretically it has been demonstrated that the dry ammonia deposition velocity on vegetation ecosystems in the open atmosphere can be obtained through the velocity of the ammonia dry deposition in the chamber with diffusive mixing and freshly cut plant leaves evenly distributed in volume. We have conducted an experiment to determine the velocity of dry ammonia deposition in the chamber with diffusive mixing. The chamber is a glass cylinder with a diameter of 25 cm and a height of 40 cm. With the help of a specially made stop valve the ammonia is fed into the chamber and an air sample is taken. The whole inside surface of the chamber is parraffin coated, excluding the leaf surfaces, of course. The ammonia was fed into the lower part of the chamber. The sample was taken in the middle of the volume. The sample volume did not exceed 50 cm 3, and amounted to 0.25% of the total volume of the chamber.
225
AMMONIA UPTAKEBY PLANTS
c/c o
e c/% a
I,O
a
~
~
~'
a
+
0,5
o i
20
I
I
40
I
I
Jc m g n
60
Fig. 1. Temporal ammonia concentration variations in the chamber.
The ammonia concentrations were measured in the nonresonance optical acoustic cell (OAC) using CO2 laser radiation in generation lines with a high ammonia uptake coefficient (10P32) and a small one (10P28). The generation power equality in both wavelengths was stabilized with an accuracy not worse than 1% and together with a fast radiation switching (38 Hz) from one wavelength to another it was possible to suppress the signal from OAC windows and obtain an ammonia sensitivity of around 2 ppb. Maize plants were used in the experiment. The field laboratory was in the immediate vicinity of the maize plants under study, growing under natural conditions. This allowed us to reduce the time between the cutting of maize leaves and the beginning of the fumigation in the chamber to 5 minutes. Freshly cut maize leaves with paraffin sections were put into the chamber, then the chamber was sealed with paraffin. Ammonia was fed through a stop valve into the chamber with leaves for a short time. The ammonia concentration change was observed by air sampling. The change in the ammonia concentration is shown in Figure lb. Figure lc shows the change in the ammonia concentration with time on a logarithmic scale. Figure 1a shows the same chamber without leaves. The ammonia concentration in this chamber is constant, being mixed in the initial period. Vac was determined from the change of the ammonia concentration in the chamber in the initial period (after mixing period) (Figure lc) with the help of Equation (10). The experiment also
226
V.M. ARTYOMOVET AL.
Vd¢
+
IO
++
8
'7
2
Vdcol
4d
6o
Q, j. cm-a. h r
Fig. 2. The relationship between the rate of the ammonia uptake by the maize leafs and PAR value.
included continuous measurement of the atmospheric meteorological parameters, including the magnitude of the physiological activity of the solar radiation (PAR). This was conducted during the field season, and it allowed observation of the plants under various meteorological conditions over a wide range of variations in the PAR value. The most suitable conditions for finding the dependence of Vdc on the PAR value (P) were measurements of Vdc during one light day, since the PAR value changes over a wide range during a light day, while other meteorological parameters (air and soil moisture etc.) change rather insignificantly. In total around 100 distributions were obtained at various values; initial ammonia concentration in the chamber (from 0.8 to 650 mg/m 3) and PAR value (from 7 to 80 J/cm2h). It is worth noting that, when the ammonia concentration in the chamber is close to 650 mg/m 3, necrosis spots appear on leaves, and one cannot make any statement about the ammonia uptake by plants. In general the dry ammonia deposition velocity on plants does not practically depend on its initial concentration, when changing from 0.8 to 200 mg/m 3. The analysis of Vdc and PAR values (calculated from Equation (10)), at the moment the leaves are cut down, just before they are put into the chamber, reveals their linear relationship (Figure 2) Vdc = OZl - I - / 3 t P
(14)
AMMONIA UPTAKE BY PLANTS
227
Values oq and/31 in Equation (14) for maize leaves are correspondingly equal to 1.4 x 10 -2 and 1.2 x 10 -3. However, under conditions of excessive moisture in soil and air, the value of/31 is 1.5 - 2 times smaller than that given above, and under conditions of extreme deficit of moisture in soil the/31 value is close to zero and toxic ammonia effects on plants are observed. From Equations (14) and (13) and the known values of diffusive mixing coefficient D, maize leaf area S, chamber volume 12 the velocity of the atmospheric ammonia dry deposition onto plants under field conditions can be presented as
vd =
(15)
+/3P)
where oLand/3 constant values for maize leaves are respectively equal to O.15 and 0.013, and s is the assimilative plant organ density in the field. 4. Discussion The analysis of the formula for dry ammonia deposition velocity Vd (15) indicates that when kB changes from 50 to 500 cm2/s and P changes from 0 to 80 J/cm2h and s has a typical value closed to 0.1 c m - 1 for most meadows, the velocity of the dry ammonia deposition, under field conditions of middle latitudes when o~ = 0.15 and fl = 0.013, changes from 0.2 to 8.4 cm/s, which is in good agreement with results obtained in ref. [4]. The relationship between Vd and ( ~ ) is the result of the ammonia supply to assimilative organs of the plant through turbulent mixing, and for general reasons, it should be a universal, regardless of the model selected for the vegetation canopy, plant species composition, absorbed gas, etc.; though in this work the velocity dependence is demonstrated for a specific model. At the same time the linear relationship of the PAR is apparently specific for the ammonia uptake by plants. Just for comparison, the relation between carbon dioxide absorption and the PAR value is known to be linear up to a specific value of PAR, then saturation takes place. This must be related to competition processes of CO2 incoming via stomata and releasing in the process of the cellular respiration (in the Krebs cycle). The competition is not observed when the ammonia is taken up. Amino acids, formed while aminating ketoacids of the Krebs cycle, are stable compounds, and that provides a continuous ammonia sink, related only to the extent that the plant stomata are open. The aminating process is universal for all plants, therefore the value of s ought to assume the stomata density value. The value of the stomata density of assimilative organs probably explains the relationship between Vd and the species composition of the plant. Studies into ammonia uptake by plants make it possible to calculate ammonia loads over vegetation ecosystems. To estimate ammonia loads one can use the obtained values of coefficients o~ and 3 for maize, since the change in species composition results in a change of coefficients c~ and fl by not more than 1.5-2.0
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times. For grasslands and agricultural plants coefficients o~ and/3 do not practically differ from those for the maize. The ammonia sink value, due to its uptake by meadow grass and agricultural crops over the former USSR territory, is estimated (in the given suppositions) as 1.6 million t/y.
5. Conclusion An analytical relation has been suggested for calculating the velocity of dry ammonia deposition over plants. It has been found experimentally that the dry deposition velocity is linearly related to the value of the physiologically active radiation and in dark times of the day it differs from zero. In relation to the turbulent diffusion coefficient value in the open atmosphere and the PAR value the dry deposition value is 0.2-8.4 cm/s. The dry deposition velocity under excessive soil and air moisture decreases 1.5-2 times, and under extreme deficit of soil moisture it practically does not differ from that of the dark time of the day (0.14 cm/s).
References 1. Artjomov,E., Vasilenko,V., Nasarov,I., and Fridman, Sh.: 1990, 'AtmosphericBalance of Nitric Compounds in the Territory of the USSR', in 'Problemy Fonovogo Monitoringa Sostoyania Prirodnoi Sredy', Leningrad, Gidrometisdat,vyp. 8, pp. 30-38 (in Russian). 2. Moiler,D., and Schieferdeker, H.: 1989, 'Ammonia Emission and Deposition of NH~ in the G.D.R.',Atm. Env. 2, 1187-1193. 3. Aneja,V.P.,Rodgers, H.H., and Stahel,E.P.: 1986, 'Dry Depositionof Ammonia at Environment Concentrations on Selected Plant Species', JAPCA 36, 1338-1341. 4. Duyzer,J.H., Bouman, A.M.H., Diederen, H.S.M.A., and Van Aalst, R.M.: 1987, 'Measurement of Dry Deposition Velocities of NH3 and NH4 over Natural Terrains', TNO-Report: R87/273, Netherlands Organisation for Applied ScientificResearch, MT-TNO, Delft, the Netherlands. 5. Sutton,M.A., Fowler, D., and Moucrieff, J.B.: 1989, 'Measurement of Atmospheric Ammonia and the Assessment of its Exchange with Vegetated Surfaces', Species Environmental Report No. 17, WMO--No. 27, Extended abstracts of papers presented at the WMO Technical conference on the Monitoring and Assessment of Changing Composition of the Troposphere, pp. 154-157, Sofia, 23-27 October. 6. Denmead,O.T., Freney, J.R., and Simpson, J.R.: 1976, 'A Closed Ammonia Cycle within a Plant Canopy', Soil Sci., Biochem. 8, 161-164. 7. Shatilov, I.S., Artyomov, V.M., Artyomov, E.M., Fridman, Sh.D., Zamorajev, A.G., and Chapovskaya, G.V.: 1988, 'The Use of the Ammonium Nitrogen by the Plants from Air', Vestn. S.-H. Nauki, Moskva 7, 65-71 (in Russian). 8. Hutchinson, G.L., Millington, R.J., Peters, D.B.: 1972, 'Atmospheric Ammonia: Absorption by Plant Leaves', Science 175, 771. 9. Shatilov,I.S., Zamorajev, A.G., Artyomov,V.M., Artyomov, E.M., and Fridman, Sh.D.: 1988, 'Ammonia Absorption by Field Plants', Vestn. S.-H. Nauki, Moskva 1, 43-49 (in Russian). 10. Bojko, A.P.: 1976, 'Calculated Turbulent Regim in Agricultural Crops', Trudy IEM 8 (67), 37-48 (in Russian). 11. Sirotenko,O.D., Bojko, A.P.: 1976, 'A Dynamik Model of Agrocenosis', Trudy IEM 8 (67), 13-35 (in Russian).
