gen and chlorine becomes evident from the intensification of blue color of starch solution in the titration vessel (left-ward swing of galvanometer needle of the titrator from its initial setting), before the normal fading due to sulfur dioxide begins. The tolerance to chlorine is much greater than to nitrogen because at low concentration chlorine is liberated as hydrochloric acid under the conditions of combustion used. No interference due to chlorine and nitrogen was encountered in this work. The combustion method measures total sulfur in the candle irrespective of its source. The depositing of the zinc oxide layer on the stripped candle material slows down the vigorous reaction and prevents the formation of fine beads of metallic lead. The attractive feature of the method is dry ashing, which destroys the active ingredient, lead dioxide, and eliminates any possibility of sulfur contamination from the laboratory atmosphere. It also eliminates the time consuming procedures like extractions, filtrations, ion exchange, evaporations, and pH adjustments. Burning the sample in a high frequency induction furnace offers the obvious advantage of speed. One candle requires 30 minutes to analyze. The average yield of ash per candle is about 7.5 grams. One gram is normally used for analysis, leaving behind enough for storage and rechecking. If desired, the exposure period of the candles can be considerably shortened because the method is particularly
suitable for the determination of low sulfur values. The method has been in satisfactory use for more than a year. Acknowledgment
The author thanks D. A. Moddle and W. 0. Taylor for their valuable suggestions and comments, and B. R. Dreisinger and A. C. Rayner for providing the material for this work and permission to publish the results. Literature Cited Am. SOC. Testing Materials; ASTM Standards Industrial Water; Atmospheric Analysis, 813, 1966. Am. SOC.Testing Materials; ASTM Standards on Petroleum Products and Lubricants, 949,1956. Bowdon, S. R., Znt. J . Air Water Poll., 8, 101 (1964). Conrad, A. L., Evans, J. K., Gaylor, U. F., Anal. Chem. 31, 422 (1959).
Gerhardt, P. B., Dyroff, G. V., Anal. Chem. 28,1725 (1956). Gt. Brit. Dep. Sci. Ind. Research, Fuel Research, 10, 22 (1952).
Holler, A. C., Klinkenberg, R., Anal. Chem. 23, 1696 (1951). Kanno, S., Znt. J . Air Poll., 1, 231 (1959). Laboratory Equipment Corp., St. Joseph, Mich., “Leco Method for Sulfur Determination,” (1956). Nagel, B. E., General Motors Corp., Detroit, Mich., private communication, 1960. J 16,418 (1966). Rayner, A. C., Air Pollution Control ASSOC., Received for review September 20, 1968. Accepted April 24, 1969.
Effects of Air Pollutants on Growth, Leaf Drop, Fruit Drop, and Yield of Citrus Trees C. Ray Thompson and 0. C. Taylor Statewide Air Pollution Research Center, University of California, Riverside, Calif. 92502
Commercially producing lemon and navel orange trees were studied to determine the effects of the air pollutant complex, especially photochemical oxidants and fluorides, in the Los Angeles Basin on the following responses: growth; weight of prunings; leaf drop; fruit drop; and yield of mature fruit. The results showed that overall growth was not affected significantly. Leaf drop was significantly less in lemons where carbon filtered air was supplied to the trees. A similar trend was present in oranges but was not significant statistically. Fruit drop in navel oranges was significantly less in carbon filtered air than in ambient. Yield of fruit is also reduced significantly by photochemical oxidants, sometimes by as much as 50%.
T
he deleterious effects of photochemical smog on economic plants are becoming well recognized wherever the emissions from automobiles and other fossil fueled combustions are high and weather patterns are stable (Middleton, 1961; Middleton, Emik, et al., 1965). Fluorides emitted from phosphate fertilizer manufacture, aluminum reduction, steelmaking, ceramic firing, and some chemical processing can cause plant damage if levels are not controlled (Thomas, 1961). Air pollutants were suspected as the cause of reduced productivity of citrus in the Los Angeles Basin in the early 934 Environmental Science & Technology
1950’s but because these trees fail to show outward, easilyrecognized pathological symptoms from either photochemical smog or fluoride except under severe conditions of exposure, proof of actual injury was unavailable. Also, if damage occurred, an accurate determination of the actual economic losses being suffered by agriculture forced the devising of a field scale study under a unique cooperative venture (Richards and Taylor, 1960) which was supported by agriculture, industry, local and national governments, various private organizations, and the University of California. The details on greenhouse design (Thompson and Taylor, 1966) and the systems for air treatment with NO and H F have been published elsewhere (Thompson and Ivie, 1965). The effects of the treatments on apparent photosynthesis and water use of citrus trees were published previously (Thompson, Taylor, et a[., 1967) and showed that both responses were significantly reduced by the photochemical smog complex. Ambient fluoride levels had no demonstrable effect. The present manuscript gives final data on the growth, leaf drop, fruit drop, and yield of two species of citrus as they were affected by the air pollutant complex in the Los Angeles Basin.
Methods The experimental arrangement of the three citrus groves, two lemon and one orange, used in this study is detailed in a previous report (Thompson, Taylor, et al., 1967). The studies were begun on lemons in June 1961 and February
1963. These studies were run for five consecutive seasons. The orange study, begun in May 1964, was run for four seasons, terminating in February 1968. The experiments were as follows: 28 trees in three different locations in the Los Angeles Basin were selected for study. The atmosphere at these three locations was known to contain varying levels of both photochemical smog and fluoride. The 28 trees were divided according to a randomized block design into seven treatments of four replications each (Table I). Trees in six of the treatments were enclosed in plastic-covered greenhouses (Thompson and Taylor, 1966). The houses were ventilated with blowers which supplied an airstream equivalent to twice the volume of the greenhouses each minute. The treatment of the air for the various atmospheres was described in detail previously (Thompson, Taylor, et al., 1967). The “filtered air” treatment (Table I) consisted of activated carbon and limestone filtration; “filtered air plus fluoride” consisted of air drawn in through activated carbon and limestone filters to which hydrogen fluoride was added back to the level at which fluoride occurred in the outside air (Thompson and Ivie, 1965). “Low ozone air” consisted of ambient air to which nitric oxide was added to react with the ozone (Thomas, MacLeod, et al., 1956). “Low fluoride air” consisted of ambient air which was passed through dust and limestone filters. “Low ozone, low fluoride air” combined the use of nitric oxide addition and limestone filtration as described previously. “Ambient air” was whatever atmosphere O C C U K ~ in ~ the Upland-Cucamonga, Calif., area. “Check” was unenclosed check trees. The relative performance of the various treatments was detailed previously (Thompson, Taylor, et al., 1967). Gaseous fluoride was monitored continuously in ambient air by an SRI fluorometric analyzer (Ivie, Zielenski, et ul., 1965). Impinger samples for total fluoride were taken as a check on the SRI analyzer. Total oxidant was measured with a Mast ozone analyzer (Mast Development Co., Davenport, Iowa). Periodic determinations of oxides of nitrogen, both inside and outside of the various greenhouses, were made by hand sampling with Saltzman’s reagent (Saltzman, 1960) in midget impingers. Peroxyacetyl nitrate (PAN) was measured from hand samples taken in similar locations. The PAN was determined by a Panalyzer (Darley, Kettner, et al., 1963).
Table I. Experimental Field Installations on Citrus, Upland and Cucamonga, Calif. Tree Treatment of Toxicant Atmosphere Atmospheres P-emaining Filtered air Filtered air fluoride
+
Low ozone air Low fluoride air Low ozone, low F- air Ambient air Check 4
Peroxyacyl nitrates.
Activated carbon, ... limestone Limestone, activated Fluoride carbon, hydrogen fluoride Nitric oxide Fluoride, NO, NOz, PAN“ Limestone Ozone, PAN Limestone, nitric PAN, NO, NO2 oxide ... Fluoride, ozone, PAN Unenclosed trees Fluoride, ozone, PAN
The ratio of total fluoride to gaseous fluoride in ambient air was measured by drawing air through two warmed vertical glass tubes (Pack, HiU, et al., 1959). One tube had an inner coating of NaHCOa to absorb gaseous F- while the other allowed all fluoride to pass into the impingers. The per cent of gaseous fluoride was obtained by subtracting the values obtained colorimetrically (Bellack and Schouboe, 1958) on the impinger solutions. The fluoride content of leaves was determined from 20 leaves picked at random from each tree. Surface contamination was removed in 0.5x Alconox (Alconox, Inc., New York). The leaves were ground, frozen, and stored until subsampling. Five grams was transferred to a nickel crucible, 25 ml. of 8 calcium formate was added, and the sample was dried. The dry weight of tissue was determined and the tissue was ashed to 600OC. The ash was fused with 4.0 grams of NaOH, cooled, and dissolved in 15 ml. of distilled water. The solution was transferred to either a Willard-Winter distilling apparatus (Willard and Winter, 1933) or Technicon AutoAnalyzer (Weinstein, Mandl, et al., 1963) for distillation and measurement of fluoride. Leaf drop was recorded by two methods. All leaves that fell from each tree during a monthly period were raked, separated from small stones and soil, air dried, and weighed, Outside check trees had EO-cm. high poultry wire enclosures installed around the base of the tree which served to retain fallen leaves. A second procedure consisted of randomly selecting 10 individual branches on each tree just after the spring flush of leaves was set. These branches were tagged and the number of individual leaves on each branch was recorded. The leaves remaining were then counted monthly. Also, as new flushes of leaves appeared they were tagged and the duration of their life on the branch was recorded. If no new leaves appeared another branch was selected and tagged and the counting continued. Tree growth was determined by measurement of trunk girth and as prunings were removed they were air dried and weighed. Later in the experiment they were weighed green. Fruit drop was measured by periodic retrieval of fallen fruit and counting. Only fruits having a diameter greater than 1.5 cm. were considered. Fruit yield was measured in lemons by making three to five successive picks per year as is done commercially. As a portion of the fruit reached a small diameter of 5.24 cm. (picking ring No. 5 ) or attained a mature yellow color, it was picked, weighed, and counted. These picks usually occurred in September, November, January, and April. The total yield per year was lumped for statistical evaluation. Navel oranges were all picked at one time, usually in late January. Analysis of variance with treatment comparisons were calculated for each grove for each of the several types of data collected. Roportions (or per cents) were transformed to the arcsine of the square root of the proportion to obtain homogeneity of variance (Snedecor, 1956). The treatment comparison of filtered us. unfiltered consists essentially of :he trees having carbon filtered air us. those not having these filters, i.e., “filtered air” and “filtered air HF” us. “ambient air,” “low ozone air,” “low ozone, low fluoride air,” and “low fluoride air.” If the unfiltered treatments were different among themselves, they were compared with a multiple range HF” test. “Fiitered air” was compared with “filtered air and check was compared with the unfiltered treatments.
+
+
Results The iiir system in the greenhouses filtered through activated charcoal reduced the total oxidant content of the incoming air Yolume 3, Number 20, October 1969 535
to one-fourth or less of the outside levels (Thompson, Taylor, et QI., 1967). The addition of nitric oxide to react with ozone also reduced total oxidant levels to about one-fourth as measured by the Mast analyzer but increased the NO, level by an equimolar amount. Thus the reduction in ozone level may be slightly greater than the amount indicated on the Mast because the NO, formed in the reaction oxidizes KI about onetenth as rapidly as ozone. A limited number of measurements showed that PAN was removed by carbon filtration from the airstream completely. Total fluoride levels, particulate plus gaseous, varied from zero in wet weather to 1.2 micrograms per cu. meter (y per cu. meter). Sampling of the atmosphere by the heated glass tubes showed that during 1962 an average of 60x of the fluoride occurred as gas and that these levels measured by the SRI analyzer were 0.1 to 0.4y per cu. meter. In 1965, with total fluoride levels of 0.20 to 0.56 y per cu. meter at Lemon Division 2, 40x of the total fluoride was gaseous. At Orange Division 1 at the same time total fluoride levels were 0.15 to 0.41 y per cu. meter and 30x was gaseous. Of more importance was the accumulation of fluoride in the citrus leaves. Periodic samplings (Table 11) showed that the limestone filters in “filtered air,” “low fluoride air,” and “low ozone, low fluoride” treatments removed more than one-half of the gaseous fluoride which caused the accumulations in the leaves. Leaves inside the greenhouses retained more fluoride than those on check trees exposed to leaching by dew and rain. HF” treatment The addition of H F in the “filtered air averaged close to the “ambient air.” The results were not analyzed statistically because of the analytical errors in measurements at these low levels of accumulation. However, the amounts in all cas= were below 50 p.p.m. which from other studies (Brewer, Garber, et a/., 1967) would be expected to have little or no gross effect. Photochemical oxidant levels in all three locations were similar (Thompson, Taylor, et a/., 1967). During November,
+
uecember, January, and February total oxidant levels exceeded 0.10 p.p.m. for only 5 to 30 hours per month but for March through October they averaged 40, 65, 90, 130, 280, 275, 207, and 100 hours, respectively. The maximum levels on many days rose to 0.30 p.p.m. and reached peaks of 0.50 p.p.m. at times indicating that the trees were subjected to heavy photochemical oxidants for extended periods. Rate of tree growth was measured by determining the annual rate of increase in tree girth (Table 111). Comparisons were made between the filtered and unfiltered treatments, the enclosed trees us. the outside checks, and the “filtered air” us. the “filtered air plus HF,” but all were the same statistically. The weight of prunings removed annually was determined during the seasons from 1962 to 1964 by air drying to constant weight, but beginning in 1965 the fresh weight only was determined and a correction factor of 40x dry weight was applied to all green weights to obtain comparable data for evaluation. The results (Table 111) showed that in Lemon 1, the amount of prunings removed from the enclosed but unfiltered trees was greater statistically than that from the outside check trees, 12.3 us. 5.5 kg., and in Lemon 2 trees receiving filtered air the amount was less than unfiltered air, 10.0us. 11.7 kg. No statistical differences were shown in the orange grove. These data represent the variation encountered when individual workers attempt to prune trees in the same way. The extra bearing foliage which was left on the “check” trees in Lemon 1 could have influenced the yield and leaf drop data. The average differences between those cited in Lemon 2, while statistically valid, are of such little magnitude that they are probably without effect. Leaf drop, another index of health in trees, was measured in two ways as indicated previously. Leaves which fell were collected monthly during the course of the study from 1962 to 1967. Some loss of leaves occurred during two violent windstorms which tore plastic from the greenhouses and blew leaves away. The results (Table IV) showed that leaf drop in
Table 11. Citrus Leaf Accumulations of Atmospheric Fluoridea
Grove Lemon 1
Lemon 2
Orange 1
(1
Year Set
1962 1963 1964 1965 1966 Average 1963 1964 1965 1966 1967 Average 1964 1965 1966 1967 Average
Mo./Yr. Sampled
Filtered Air
Filtered Air HF
Low Ozone Air
Low Fluoride
12/62 5/64 1/65 2/66 4/67
12 27 7 4 13 13 6 12 13 25 17 15 7 1 8 5 5
31 48 53 16 30 36 17 48 23 36 26 30 40 11 25 16 23
23 35 32 23 35 30 27 37 27 38
14 17 14 7 18 14 15 13 12 24 26 18 7 2 17 5 8
5/64 1/65 2/66 4/67 1/68 1/65 2/66 4/67 1/68
Parts per million of fluoride on a dry weigh basis.
936 Environmental Science & Technology
+
40
34 18
10 31 13 18
Air
Low Ozone, Low Fluoride Air
11 10 16 4 13 11 14 13 9 28 17 16 6 0 17 7 8
Ambient Air
Check
27 47 33 24 43 35 21 30 32 47 34 33 15 14 31 12 18
28 35 23 12 24 24 34 33 25 30 23 29 13 6 24 10 13
Table In. Effect of Air Pollutants on Annual Increase in Tree Circumference and Weight of Prunings Removed Tree Circumferenceo Pruning9 Lemon Lemon Orange Lemon Lemon Orange 1 2 1 1 2 1 2 . 7 4 1 . 3 2 1 . 8 0 11.6 10.1 3 .7 Filtered air 2.44 1.65 1.47 10.4 9.8 3.3 Filtered air HF Low ozone air 2.31 1.29 1.78 12.6 12.0 3.9 Low fluoride air 2.08 1.17 1.73 13.6 12.7 5.2 Low ozone, low 2.18 1.57 1.60 11.9 11.9 3.8 fluoride air 2.11 1.57 1.70 11.2 10.1 5.0 Ambient air 1.93 1.37 1.95 5.5 9.9 3.5 Check
+
a
Av. cm. per tree.
* Kg. prunings per tree.
Filtered air Filtered air HF Low ozone air Low fluoride air Low ozone, low fluoride air Ambient air Check
+
a
Table IV. Effect of Air Pollutants on Leaf and Fruit Drop Per Cent Leaves Dropped, Lemon 1 Kg. Leaves Dropped an nu ally^ Lemon Lemon Orange 12 18 1 2 1 Mo. Mo. 3.45 4.27 5.11 8.4 32.0 3.50 4.20 4.93 6.9 23.1 3.94 4.37 5.59 12.3 40.2 4.23 4.62 5.65 37.3 93.7 3.99 4.59 5.36 14.8 58.5 3.86 4.31
4.68 5.97
5.66 5.81
19.2 12.8
70.1 56.9
Per Cent Fruit Drop Lemon Lemon 1 2 2.3 6.0 2.7 6.6 3.2 8.4 3.3 11 .o 2.6 8.8 3.4 6.2
9.8 7.9
Lemon 1, 1962-1967; Lemon 2 and Orange 1, 1963-1968.
Lemon Division 1 was greatest in outside check trees followed by the unfiltered treatments. Statistical comparisons on an overall basis showed that both “filtered air” (3.45 kg.) and HF” (3.50 kg.) were less than the unfiltered “filtered air treatments at the 1 % level. Comparison of the “check” (4.31 kg.) us. the unfiltered treatments, and “filtered air” us. “filtered air HF” showed them to be nonsignificant. A comparison of the “check” us. the unfiltered treatments by year showed the check to be greater at the 1 % level. Similar results were obtained from 1963 to 1967 at Lemon Division 2 (Table IV). Statistical comparisons showed that leaf drop in the filtered treatments was less than in the unfiltered treatments with significance at the 1 level. Leaf drop in the check plots was also greater than the unfiltered treatments at the 1 % level. “Filtered air” and “filtered air HF” were not statistically different. However, when the data from 1967 to 1968 were added, the variability was so great that the filtered treatments were no longer statistically less than the unfiltered treatments but the average kilograms of leaf drop tended to be less. With navel oranges (Table IV) the average kilograms of leaf drop of the filtered treatments was less than the unfiltered but was not statistically different. Likewise, the average drop of the unfiltered treatments was less than the “check” but these two were the same statistically. Thus the same trend in navel oranges is seen as with lemons, but the variation is greater. Generally, supplying the citrus trees with carbon filtered air resulted in less leaf drop than the other treatments. Lemons seemed to be more sensitive than navel oranges to the photochemical air pollutants. The more precise measure of leaf drop made by making periodic leaf counts on 10 randomly selected branches on each tree was carried out at Lemon 1. The per cent of leaves
+ +
+
dropped during 12 and 18 month periods in each treatment is shown in Table IV. The computations of the per cent, following cohort life table procedure, allowed flushes observed for only a few months to be included as well as those observed for the complete twelve or eighteen months. These results showed that trees receiving carbon filtered air retained their leaves much longer, 1 % level, than the enclosed, unfiltered trees after 12 or 18 months. The data are particularly striking for 18 months when the filtered trees had dropped only 27.6% of the leaves but the unfiltered trees had dropped 65.6%. Evaluation of the “filtered air” us. the “filtered air plus fluoride” showed the addition of H F to have no measurable effect. Likewise, a comparison of outside check trees us. the unfiltered treatments for the two periods was not significant. Statistical analysis was done on the arcsine of the square root of the proportion. Since the unfiltered treatments are different from each other, they were compared with a multiple range test and showed that the “low fluoride” treatment lost more leaves than all other treatments (1 % level). “Ambient air” was next in degree of leaf drop. These results suggest that the removal of ozone from the air by nitric oxide could be having a limited effect in preventing leaf drop. To further evaluate the results on leaf drop the data from monthly flush counts were broken down into spring (March to May), summer (June to September), and winter (October to February) flushes. Since there were very few winter flushes, the analysis of the proportion of leaves remaining on the trees for 15 months was made for spring and summer. The 18-month proportion, which was examined previously, was not used because the number of leaves in each season subdivision was quite small for some trees by 18 months. The results showed that summer flushes stayed on the trees Volume 3, Number 10, October 1969 937
significantly longer (1 level) than spring flushes. There was no interaction between treatments and season; summer flushes remained longer in all treatments. Figure 1 shows the improvement for summer flushes and the greater retention of leaves by the filtered trees os. the unfiltered treatments. When leaves were picked up, fallen fruit was retrieved and counted as a measure of the total yield which aborted before reaching mature size. In lemons, these amounts represented a small percentage, averaging less than one-tenth of the total which was the sum of the number dropped plus those harvested. Data were accumulated for five seasons beginning in 1963-64 (Table IV). Statistical comparisons in Lemon 1 showed that the outside checks lost more fruit than the unfiltered trees, 6.2 us. 3.1 but the amounts are not different statistically. Also, the filtered trees lost 2.5 us. 3.1 for the unfiltered trees but the differences are not different statistically, In Lemon 2, fruit drop in all treatments was statistically the same, averaging less than one-tenth of the total yield. With navel oranges, fruit drop is a much more serious problem. A continuous record was made of the number of fruit dropped plus those harvested for three seasons beginning in June 1965. The number dropped was recorded and evaluated for both summer and fall plus winter to find out when the greater loss occurred. The results (Table V) showed that checks lost significantly more fruit than the enclosed unfiltered trees, 82.5 us. 5 9 . 7 z . In addition, the two filtered treatments lost significantly less fruit than the unfiltered trees, 39.6 us. 59.7 %. The greatest losses occurred during summer, and because they are often associated with high temperatures in June, this effect is referred to as “June Drop.” The total number of fruit set is of interest. These were
z,
z
3 O J I 1 0 1. 2
,
3
,
4
,
,
5
6
,
7
,
8
,
,
,
,
,
,
+
91011121314lb
Age of leaves in month Figure 1. Comparison of the rates of leaf drop from lemon trees exposed to carbon filtered and ambient air
analyzed statistically and although the absolute average values for the filtered treatments were greater than the others, the differences were not statistically significant. Of greatest economic and practical importance is the yield of marketable citrus fruit. When the experimental treatments were begun in early 1962 at Lemon 1 their effect on apparent photosynthesis of the trees during the morning hours was recorded. This necessitated a reduction in airflow from 80 cubic meters to 20 cubic meters per minute and caused a temperatures rise to 2 to 6OC. until 10 to 11:OO A.M. each day. After several weeks of higher teniperatures, it was
Table V. Fruit Drop of Navel Oranges.
Year 1965-66
Season Summer Fall Winter Total Total No. of Fruit
+
1966-67
Summer Fall Winter Total Total No. of Fruit 1967-68 Summer Fall Winter Total Total No. of Fruit Av. Summer Av. Fall Winter Yearly Av. Av. Total No. of Fruit
+ +
+
Filtered Air 35.5 11.2 46.7 802 30.2 10.1 40.3 636 23.5 4.2 27.7 516 29.7 8.5 38.2 651
Filtered Air+HF 38.5 17.5 56.0 909
Low Ozone Air 54.2 13.9 68.1 762
29.1
49.8 10.3 __ 60.1 571
11.6 40.7 756 22.5 3.9 26.4 454
54.1 5.2 59.3 274
30.0 11.0 41 .O 706
52.7 9.8 62.5 536
Treatment Comparisons* Filtered us. unfiltered air “Check” us. unfiltered air “Filtered air” us. “Filtered air -O1-F us. other unfiltered air
+ HF”
**
Significa,ntly different at 1 %. NS-Not stgnificant. Av. per cent of total fruit set per tree. b Analysis based on arcsine of sq. root of proportion.
938 Environmental Science & Technology
Low Low Ozone Fluoride Low Fluoride Ambient Air Air Air 51.9 42.9 52.7 15.3 16.7 12.0 67.2 59.6 64.7 81 1 877 726 36.2 31.2 56.9 14.0 13.3 7.1 50.2 44.5 64.0 487 621 421 54.7 38.9 75.7 3 . 3 3 . 1 3.2 58.0 42.0 78.9 355 442 374 47.6 37.7 61.8 10.9 11 .o 7.4 58.5 48.7 69.2 551 647 507 Kilograms 3 9 . 6 us. 59.7** 8 2 . 5 us. 59.7** 38.2 us. 4 1 . 0 NS 4 8 . 7 us. 6 3 . 4 NS
Check 75.2 10.8 86.0 663 84.1 5.5 89.6 403 68.8 3.3 72.1 459 76.0 6.5 82.5 508
obvious that the enclosed trees had failed to set a normal number of blossoms. Because of this adverse effect on the trees the measurement of apparent photosynthesis was discontinued except before mid-morning but the yield was reduced in all treatments. The yield in the filtered treatments was 4 to 6 fold the amounts in the unfiltered, enclosed trees, but because the experimental conditions were so abnormal the yield data of 1962-63 were excluded from the statistical evaluations of the results from the ensuing four seasons, all of which are recorded in Table VI. The evaluation of fruit size data required that the figures be adjusted for number of fruit per tree because, as is well known, trees with larger numbers have smaller sized fruit. This was observed in the test of covariance and the values shown represent the adjusted fruit weights. Statistical evaluation of results showed that the trees receiving filtered air had significantly larger fruit than those receiving unfiltered air, but all other comparisons were not significant. These studies (Table VI) showed that the kilograms of fruit on the “check” trees and the unfiltered trees were not different statistically, 78.6 US. 60.4,but there was a greater number of lemons on the outside trees, and they were significantly smaller. The trees receiving filtered air had more fruit than the unfiltered treatments and both the number and size were statistichlly greater. HF” showed Comparison of the “filtered” and “filtered them to be equal in total kilograms, number and size of individual lemons. The kilograms of fruit on the “low ozone, low fluoride air” trees was not statistically greater than the other unfiltered treatments, i.e. “ambient air,” “low ozone air,” or “low fluoride air” but numerically it was greater. The duplicate study of lemons in the other location, Lemon
+
Division 2, was begun in 1963 and continued for five seasons. The results (Table VII) are somewhat similar to Lemon I . The checks had more kilograms of fruit, greater numbers and smaller fruit, statistically. Filtered trees had more kilograms of fruit and greater numbers than unfiltered trees, but the size was the same. “Filtered air” and “filtered air HF” were the same with regard to kilograms, number and size. All trees which were enclosed but which were without carbon filters were statistically the same, but as in Lemon 1, the “low ozone, low fluoride air” treatment was numerically greater than the unfiltered trees. The study of navel oranges was started in May 1964 and continued for four seasons (Table VIII). The dates given are the years during which the fruit was set and grew to near maturity. Statistical evaluation of the yields in kilograms and number of fruit showed that activated carbon filtration of the incoming air gave highly significant increases which amounted to more than twofold. The “filtered air HF” was statistically and numerically similar to “filtered air.” “Low ozone, low fluoride air” yielded more than the remaining unfiltered treatments statistically with the oranges. This trend was apparent with the lemons but was not significant. The data for the “check” trees were omitted in this calculation because of the very small number of fruit especially during the first three years of the study. This group of four trees must have been atypical for the grove because a comparison of their average yield of 11.7 kg. per tree for the four years is less than one-half of the average grove yield (600 trees) which was 24.1 kg. per tree. This latter figure compares better with the yields of the unfiltered trees (29.8 kg.) and the ambient figure of 23.9 kg.
+
+
Table VI. Average Annual Yield of Lemons,Division 1 Low Low Ozone Filtered Filtered Low Ozone Fluoride Low Fluoride Ambient Air Year Air Air+HF Air Air Air Kg. of Fruit No. of Fruit Grams per Fruit“
1963-67 1963-67 1963-67 Treatment Comparisons Filtered us. unfiltered “Check” us. unfiltered “Filtered air” us. “Filtered air F-” Not filtered ** Significant at 1 %.
84.2 841 104
+
93.0 56.1 940 597 103 97 Kilograms 88.5 us. 60.4** 78.6us. 60.4NS 84.3us. 93.1 NS NS
57.1 65.1 600 679 98 101 Number 890 us. 641 ** 970 us. 641 ** 841 us. 940 NS NS
Check
63.4 78.6 688 970 97 91 Grams/Fruit 103 us. 98 ** 91 us. 98 ** 104 us. 103 NS NS
NS-Not significant. 4 Adjusted for number of fruit.
~~
Table VII. Average Annual Yield of Lemons, Division 2 Low Low Ozone Filtered Filtered Low Ozone Fluoride Low Fluoride Ambient Air Year Air Air HF Air Air Air
+
1963-68 Kg. of Fruit No. of Fruit 1963-68 Grams per Fruita 1963-68 Treatment Comparisons Filtered us. unfiltered “Check” US. unfiltered “Filtered air” us. “Filtered air F-” Not filtered
+
69.0 641 111
62.5 30.2 583 292 110 106 Kilograms 65.5us. 31.5 ** 70.8 us. 31.5 ** 68.7us. 62.3 NS NS
26.7 34.2 279 316 110 108 Number 612 us. 294 ** 747 us. 294 ** 641 us. 583 NS NS
Check 30.6 71.1 289 747 109 103 Grams/Fruit 110 us. 108 NS 103 us. 108 ** 111 us. 110 NS NS
** Significant at 1 %.
NS-Not significant. Z . Adjusted for number of fruit. Volume 3, Number 10, October 1969 939
Table VIII. Average Annual Yield of Navel Oranges, Division 1 Low Low Ozone Low Ozone Fluoride Low Fluoride Ambient Filtered Filtered Air Air Air Air Year Air Air+HF
Kg.of Fruit No.of Fruit Oranis per Fruit‘
1964-67 1 W 7 1964-67
Treatment Comparisons Filtered us. unfiltered “Check” us. unfiltered “Filtered air” os. “Filtered air HF” “Low ozone, low fluoride air” us. other not filtered Other not filtered
+
66.7 286 264
21.6 96 223
62.0 287 248
41.8 190 233
32.4 132 237
Kilogram
Number
64.4us. 29.9** 11.7 us. 29.9** 66.7us. 62.0NS 41.8 us. 26.0**
286 us. 132 ** 57 us. 132 ** 286 us. 287 NS 190 us. 112 **
NS
NS
Check
23.9 109 219
11.7 57
-
Grams/Fruit
256 us. 228 **
...
267 us. 248 NS 233 us. 226 NS NS
** Significant at 1 %.
NS-Not significant. Adjusted for number of fruit.
0
Discussion The experimehtal methods in this study in which an attempt was made to approximate field growing conditions must of necessity involve some compromises. The enclosures were glazed with Tedlar (E. I. du Pont de Nemours & Co., Wilmington, Del.) plastic that admitted a good part of the total solar Spectrum and also allowed most of the longer wavelen&ths to escape but did allow an increase in both temperature and humidity. This would be expected to produce more vegetative growth and less fruit. The vegetative growth was evident by the larger leaf size inside the enclosures. The & c t on yield of fruit in lemons is definite showing a statistical validity of 1 % in Lemon 2 and a similar trend in Lemon 1 where the “check” and the unfiltered treatments were compared, In navel oranges the trend is in the opposite direction but this variatibn only stresses the difficulties inherent in comparing results from two sets of trees, one enclosed, the other outside, which require annual pruning. In a previous report of other phases of this work (Thompson, Taylor, et al., 1967) the photochemical smog complex present in the Los Angeles Basin reduced water use and the apparent photosynthesis of citrus trees. Ambient levels of fluoride had no measurable effect. The present studies show that other tree responses are severely affected by the photochemical smog. The smaller total leaf drop in trees which received filtered air as compared to the unfiltered treatments is somewhat significant but when measured for long periods tends to become equal in all trees because all leaves become senescent and fall eventually. The much more revealing work was the study in which the separate lemon branches with tagged, dated leaf flushes were counted periodically. These showed, after 18 months, that the trees receiving filtered air had lost 28 of their leaves while the unfiltered treatments had lost 66%. Fruit drop in lemons seems to be of little consequence but in navel oratlges represents a serious problem that occurs in areas of low air pollution but is accentuated by heavy photochemical smog. Fluoride levels in the experimental areas had little effect on the responSes measured. Navel oranges accumulated only one-half as much fluoride as lemons although the ambient air levels in Lemon Division 1 and Orange Division 1 were very similar. All levels remained below 50 p.p.m. and at the close of the experimental period were less than 30 p.p.m. in the outside tfees which benefit from leaching by dew and rain. The economic importance of the field data is self-evident. 940 Ehvironhentel Science & Technology
Apparently when the trees are impoverished by reduced C 0 2 absorption and water use plus increased leaf and fruit drop, yields are reduced in some cases to one half. Acknowledgment The authors wish to acknowledge the technical advice and aid of E. A. Cardiff, W. M. Dugger, Jr., M. D. Thomas, J. 0. Ivie, Carol J. Adams and Earl Hensel. Literature Cited Bellack, Ervin, Schouboe, P. J., Anal. Chem. 30, 2032-4
(1 958). Brewer, R. F., Garber, M. J., Guillemet, F. B., Sutherland, F.H.,Proc. Am. SOC.Hort. Sci. 91, 150-6 (1967). Darley, E. F., Kettner, K. A., Stephens, E. R., Anal. Chem. 35, 589-91 (1963).
Ivie, J. O., Zielenski, L. F., Thomas, M. D., Thompson, C. R., J. Air Pollution Control Assoc. 15, 195-7 (1965). Middleton, J. T., Ann. Rev. Plant Physiol. 12, 431-48 (1961). Middleton, J. T., Emik, L. O., Taylor, 0. C., J. Air PoUution Control Assoc. 15, 476-80 (1965). Pack, M. R., Hill, A. C., Thomas, M. D., Transtrum, L. G., Am. SOC.Testing Materials Symposium on Air Pollution Control Spec. Tech. Pub. 281, 27-44 (1959). Richards, B. L., Taylor, 0. C., J. Air Pollution Control Assoc. 11 (3), 125-8 (1960). Saltzman, B. E., Anal. Chem. 32, 135 (1960). Snedecor, George W., “Statistical Methods,” 5th ed., The Iowa State Univ. Press, Ames, Iowa, 1956. Thomas, M. D., World Health Organ. Monograph Ser. MD 46,
233-78 (1961). Thomas, M. D., MacLeod, J. A., Robbins, R. C., Goettleman, R. C., Eldridge, R. W., Rogers, L. H., Anal. Chem. 28, 1810-16 (1956).
Thomoson. C. R.. Ivie. J. 0..Intern. J . Air Water Pollution ~~
9, 799-805 (1965).
’
Thompson, C. R., Taylor, 0. C., Trans. Am. SOC.Agr. Eng. 9 (3), 338, 339, 342 (1966). Thompson, C. R., Taylor, 0. C.,Thomas, M. D., Ivie, J. O., ENVIRON. Scr. TECHNOL. 1, 644-50 (1967). Weinstein, L. H.,Mandl, R. H., McCune, D. C., Jacobson, J. S., Hitchcock, A. E., Contrib. Boyce Thompson Insr. 22, _207-20 _ _ _ (1963). \--
- - I .
Willard, H. H., Winter, 0. B., Ind. Eng. Chem., Anal. Ed. 5 ,
7-10 (1933).
Received for review November 27, 1968. Accepted April 15, 1969. This investigation was supported in part by Grant AP 00270 from the National Air Pollution Control Administration and by Kaiser Steel Corp., Sunkist, Inc., San Bernardino County Air Pollution Control District, Southern California Edison Co., and other members of the various donors to the Agricultural Air Research Program.
