Growth response of loblolly pine (Pinus taeda L.) seedlings to ozone fumigation

Twenty-two week-old Pinus taeda L. (loblolly pine) seedlings of 30 open-pollinated and five full-sib families, representing a wide range in geographic origin, were grown in charcoal-filtered (CF) air or CF-air supplemented with 160 or 320 nl liter(-1) ozone for 8 h day(-1), 4 days week(-1), for 9 weeks. Visible foliar injury (banded chlorosis, tip burn and premature senescence) was apparent in many families after 3 weeks in 320 nl liter(-1) and 6 weeks in 160 nl liter(-1) ozone. Decreases in relative height and root collar diameter growth rates, total dry weight, root dry weight, shoot dry weight, and root/shoot ratios were evident after 9 weeks of treatment with both 160 and 320 nl liter(-1) ozone. For relative height growth rates, family differences in response to ozone were observed. By the study's end, net photosynthesis rates were 15% less for the 320 nl liter(-1) ozone treatment as compared to the CF-air treatment. Total soluble sugar and total starch content of roots were not changed after 9 weeks of ozone exposure.     

Effects of ozone on grain quality of wheat grown in open-top chambers: three years of experimentation

Field trials with winter wheat (Triticum aestivum L.) grown in open-top chambers and exposed to either ambient filtered (F) or unfiltered (NF) air were carried out for 3 years in northern Italy. The experiments were performed at two places, a rural and an urban site in the Po Plain. The data obtained show no significant difference in protein, starch and glucose contents between the treatments; nevertheless, a tendency towards an increase in glucose and a decrease in starch contents was observed in the F chambers compared with NF. In addition, potassium levels were lower in F than in NF treatment, while calcium were higher. Ozone levels observed in the Po Valley are not sufficiently high to cause significant differences in quality parameters of winter wheat.     

Effects of ozone on the yield of spring wheat (Triticum aestivum L., cv. Albis) grown in open-top field chambers

Spring wheat (Triticum aestivum L., cv. Albis) was grown in the field at a site located in central Switzerland, and exposed to chronic doses of ozone (O(3)) in open-top chambers to study impacts on yield. The experiment was carried out in 1986, 1987 and 1988. The treatments used included charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air to which constant amounts of O(3) (two levels, O(3)-1 and O(3)-2) were added daily from 09.00 until 17.00 local time. Mean solar radiation-weighted O(3) concentrations during the fumigation period were in the range 0.016-0.022 microl litre(-1) (CF), 0.036-0.039 microl litre(-1) (NF), 0.057-0.058 microl litre(-1) (O(3)-1, used in 1987 and 1988 only) and 0.078-0.090 microl litre(-1) (O(3)-2). Fumigation was maintained from the three-leaf stage until harvest. Ambient plots were used as a reference. Plant characteristics examined included straw yield, grain yield, number of grains per head, number of heads per surface area, weight of individual grains and harvest index (ratio of grain weight to total dry weight). Pollutant concentrations and other environmental parameters were monitored continuously inside and outside the chambers. In 1986 and 1987, enclosure mostly increased the values of different parameters, while in 1988, they were decreased. The negative enclosure effect was due to extremely turbulent winds, which caused lodging inside the chambers. In all 3 years, increasing O(3) concentrations negatively affected the parameters studied, except for the number of heads per surface area, which showed no treatment response. Grain yield showed a very sensitive response to O(3). The effect of O(3) on grain yield was due to an effect primarily on grain size and secondarily on grain number. The relative response of grain yield to O(3) was similar in all 3 years, despite year-to-year differences in climatic conditions and enclosure effects. The analysis of the data for combined years revealed an increase of about 10% in grain yield due to air filtration. The corresponding increase in straw yield was only about 3.5%. Exposure-response models were developed for individual years and combined years. It is concluded that, in the study area, ambient O(3) may affect grain yield in spring wheat.     

Evidence for potential impacts of ozone on Pinus cembra L. at mountain sites in Europe: an overview

We summarize what is known about the impact of ozone (O(3)) on Pinus cembra in the timberline ecotone of the central European Alps and the Carpathian Mountains. In the central European Alps exposure to ambient and two-fold ambient O(3) throughout one growing season did neither cause any visible injury nor affect the photosynthetic machinery and biochemical parameters in current to 1-year-old needles. By contrast, in the southern French Alps and in the Carpathians 1-year-old needles of Pinus cembra trees showed visual symptoms similar to those observed in O(3) stressed pine stands in southern California. For the southern French Alps the observed symptoms could clearly be attributed O(3) and differences in O(3) uptake seems to be the likely key factor for explaining the observed decline. For the Carpathians however, other reasons such as drought may not be excluded in eliciting the observed symptoms. Thus, the action of O(3) has always to be evaluated in concert with other environmental impacts, determining the tree's sensitivity to stress.     

Response to ambient ozone of two white clover (Trifolium repens L.cv. "Regal") clones, one resistant and one sensitive, grown in a Mediterranean environment

Two clones of white clover (Trifolium repens L.) differing in ozone tolerance were grown in southern Italy during 1997 and 1998 to study the effects of ambient ozone exposure on yield, leaf morphology and water use. Ambient ozone levels were high in both years with values exceeding the threshold for leaf injury reported in the literature. In both years ozone injury was observed on the sensitive clone (NC-S) but not on the resistant one (NC-R), and leaf and stolon dry matter production was significantly lower in NC-S than in NC-R. However, it cannot be excluded that other factors, such as high temperature, interacted with the effect of ozone on biomass production. The clones differed in morphological characteristics. Lower total leaf area in NC-S plants was due to a smaller number of leaves per plant, but the average area per leaf was higher in NC-S. Specific leaf weight and net assimilation rate were higher in the more productive clone (NC-R). Cumulative plant water use was higher in NC-R in each growth period because of the larger leaf area; by contrast, water use per unit leaf area was higher in NC-S, indicating higher leaf conductance to water vapour. The results suggest that ozone significantly reduces the yield of sensitive white clover plants under well-watered conditions, and that the difference in ozone tolerance between clover clones is related to differences in leaf morphology and water use.     

Day-of-Week behavior of atmospheric ozone in three U.S. cities

The weekly cycles of atmospheric ozone (O3) are of interest because they provide information about the response of O3 to changes in anthropogenic emissions from weekdays to weekends. The weekly behavior of O3 in Chicago, IL; Philadelphia, PA; and Atlanta, GA, is contrasted. In Chicago and Philadelphia, maximum 1-hr average O3 increases on weekends. In Atlanta, O3 builds up from Mondays to Fridays and declines during weekends. In all three areas, volatile organic compound (VOC)/nitrogen oxides (NOx) ratios are higher during weekends, resulting from greater than proportionate decreases in NOx relative to VOC emissions. The VOC/NOx ratios correlate with maximum 1-hr O3 concentrations in Chicago, a response consistent with a VOC-sensitive airshed. A weak correlation between O3 concentrations and VOC/NOx ratios in Philadelphia suggests the impact of transported O3, which is formed in upwind VOC-sensitive locations that may be hundreds of kilometers away. Ozone concentrations in Atlanta do not correlate with VOC/NOx ratios but with concentrations of NOx and total reactive nitrogen (NOy) carried over from the previous day. When data from 1986-1990 and 1995-1999 are compared, only small differences in the weekly behavior of O3 are observed in Chicago and Philadelphia. The day-of-week differences in O3 are amplified in the more recent period in Atlanta, a possible result of urban growth.     

Effects of ozone on yield, growth, and root starch concentrations of two alfalfa (Medicago sativ A L.) cultivars

Ozone (O3) is considered to be a major air pollutant that affects the yield of several sensitive crop species. Its concentration may reach phytotoxic levels several times during the growing season in Eastern Canada. This study was initiated to evaluate the O3 effects on alfalfa, a major crop species. The objective was to compare the yield and growth parameters of the main alfalfa cultivar used in Québec, Apica, to a cultivar more tolerant to O3, Team. Effects on root starch concentrations were also examined as this parameter is an important indicator of alfalfa perennity. The results obtained have shown that the forage yield of Apica was more reduced by O3 during two growing seasons than the yield of Team. For O3 concentrations of 20 to 40 nl liter(-1), yield reductions were 14-26% for Apica and 0-20% for Team. Whereas Apica could be considered more susceptible to O3 than Team, the latter has shown contrasting responses from year to year. This fact suggests that the mechanisms involved in O3-tolerance could be modulated by environmental conditions. At low O3 levels, Apica has shown reduced root growth in terms of dry matter and length. However, contrary to the current hypothesis that O3 would affect more root than shoot growth, we were unable to show a consistent alteration of the biomass allocation between the two. Ozone seems to reduce globally the growth of the whole plants. The greater O3-tolerance of Team could partly be associated to its capacity to maintain more leaves, to delay their senescence, or to keep a larger leaf:stem ratio under increasing levels of O3. At the end of the two growing seasons, the amount of starch reserves stored below ground was shown to be reduced by the current O3 levels. This reduction was mainly associated with a decrease in root biomass under O3 stress. This result support the hypothesis that O3 may accelerate alfalfa decline under field conditions.     

Growth and nutrition of Quercus rubra L. seedlings and mature trees after three seasons of ozone exposure

Seedling growth and nutritional status have been shown to be sensitive to ozone, but the influence of multi-season ozone exposure on mature tree growth and nutrition has not been examined. To determine if seedlings and mature trees were similarly affected by ozone exposure, growth and nutrient concentrations in northern red oak (Quercus rubra L.) 4-year-old seedlings and 32-year-old mature trees were examined after treatment with subambient, ambient and twice ambient concentrations of ozone for three growing seasons. SUM00 values summed over the three growing seasons were 147, 255 and 507 ppm-h, respectively, for the subambient, ambient and twice ambient exposures. For mature trees, no influence of ozone treatment on lower stem diameter growth, stem growth within the mid-canopy and foliar biomass was observed. Seedling height was increased by ozone, but biomass and diameter were unaffected. A reduction in the specific leaf weight of leaves in response to ozone coincident with the loss of recurrent flushing was observed in seedlings. Ozone exposure reduced foliar nitrogen concentrations and increased woody tissue nutrient concentrations in seedlings and mature trees at the end of the third growing season. These results suggest an influence of ozone on retranslocation processes in seedlings and mature trees.     

Cadmium concentration and distribution in corn (Zea mays L.) grown on a calcareous soil for three years after three annual sludge applications.

The disposal of digested sewage sludge on crop-producing land appeals to municipalities as an option but may pose a hazard to human and animal health if the plant material contains elevated levels of some heavy metals. This paper reports the levels of cadmium in corn grain and stover for six years -- three years with sludge applied annually and for three years after sludge applications were terminated. The cadmium concentration in corn grain from the sixth year was similar to values found in corn grown on non-sludged plots. In corn stover from treated plots the cadmium concentration was greater than from untreated plots. Our study indicated that phytotoxic levels of cadmium did not exist even though elevated levels occurred in the corn stover.     

Effects of simulated acid rain and ozone on foliar chemistry of field-grown Pinus ponderosa seedlings and mature trees

We investigated the additive and interactive effects of simulated acid rain and elevated ozone on C and N contents, and the C:N ratio of one-year-old and current-year foliage of field-grown mature trees and their half-sib seedlings of a stress tolerant genotype of ponderosa pine. Acid rain levels (pH 5.1 and 3.0) were applied weekly to foliage only (no soil acidification or N addition), from January to April, 1992. Plants were exposed to two ozone levels (ambient and twice-ambient) during the day from September 1991 to November 1992. The sequential application of acid rain and elevated ozone mimicked the natural conditions. Twice-ambient ozone significantly decreased foliar N content (by 12-14%) and increased the C:N ratio of both one-year-old and current-year foliage of seedlings. Although similar ozone effects were also observed on one-year-old foliage of mature trees, the only statistically significant effect was an increased C:N ratio when twice-ambient ozone combined with pH 3.0 rain (acid rain by ozone interaction). Enhancing the effect of twice-ambient ozone in increasing the C:N ratio of one-year-old foliage of mature trees in June was the only significant effect of acid rain.     

Effects of ozone on foliar leaching in Norway spruce (Picea abies L. Karst): confounding factors due to NOx production during ozone generation

Previous experiments with conifers fumigated with O(3), produced by air-operated electric discharge ozonators, have provided evidence that O(3) increases the leaching of NO(3)(-), NH(4)(+), K(+), Ca(2+), Mg(2+) and some other cations from needles, when the trees are treated with acid mist. This evidence has provided the foundation of the ozone-acid mist hypothesis of spruce decline. We report experiments with Norway spruce saplings fumigated with purified and unpurified O(3). The results show that the accumulation of NO(3)(-) in the needles arises from the rapid deposition of N(2)O(5) and HNO(3) formed from N(2) in the ozonator. An increase in removal of NH(4)(+), Na(+), Ca(2+), Mg(2+), Zn(2+) and Mn(2+) from the needles during soaking in H(2)SO(4), pH3, was also observed, which was related to the increase in NO(3)(-) but was independent of O(3) concentration. It is concluded that results of previous experiments cited in support of the ozone-acid mist hypothesis arose from effects which were at least partly caused by N(2)O(5) produced as a contaminant, and were incorrectly attributed to ozone. Other effects, such as growth stimulations, visible symptons, enhanced frost sensitivity, and infestation by pests or pathogens, which have been attributed to O(3) generated by electric discharge in air, should be interpreted with caution. Future experiments with ozone must eliminate this problem by either using O(2)-driven ozonators, or by purifying the output from air-driven ozonators using cold and/or water traps.     

Effects of copper deficiency and copper toxicity on organogenesis and some physiological and biochemical responses of Scots pine (Pinus sylvestris L.) seedlings grown in hydroculture

The morphological, physiological, and biochemical parameters of 6-week-old seedlings of Scots pine (Pinus sylvestris L.) were studied under deficiency (1.2 nM) and chronic exposure to copper (0.32, 1, 2.5, 5, and 10 μM CuSO₄) in hydroculture. The deposit of copper in the seed allowed the seedlings to develop under copper deficiency without visible disruption of growth. The high sensitivity of Scots pine to the toxic effects of copper was shown, which manifested as a significant inhibition of growth and development. The loss of dominance of the main root and a strong inhibition of lateral root development pointed to a lack of adaptive reorganization of the root system architecture under copper excess. A preferential accumulation of copper in the root and a minor translocation in aerial organs confirmed that Scots pine belongs to a group of plants that exclude copper. Selective impairment in the absorption of manganese was discovered, under both deficiency and excess of copper in the nutrient solution, which was independent of the degree of development of the root system. Following 10 μM CuSO₄ exposure, the absorption of manganese and iron from the nutrient solution was completely suppressed, and the development of seedlings was secured by the stock of these micronutrients in the seed. The absence of signs of oxidative stress in the seedling organs was shown under deficiency and excess of copper, as evidenced by the steady content of malondialdehyde and 4-hydroxyalkenals. Against this background, no changes in total superoxide dismutase activity in the organs of seedlings were revealed, and the increased content of low-molecular-weight antioxidants was observed in the roots under 1 μM and in the needles under 5 μM CuSO₄ exposures.

     

Effects of environmental biomass-producing factors on Cd uptake in two Swedish ecotypes of Pinus sylvestris

A factorial design was used to study direct effects of external biomass-producing factors such as light, temperature and photoperiod on cadmium (Cd) uptake and indirect effects, via change in biomass production in two ecotypes of Scots pine (Pinus silvestris). The aim was to find out if the external factors affect the Cd uptake directly or via change in biomass production, and if the effect differs between ecotypes. Seedlings were grown under 10 combinations of external factors, i.e. temperature (15 and 20 degrees C), light intensity (50 and 200 micromol photons m(-2) S(-1)), photoperiod (18 h light/8 h darkness and continuous light) and external Cd concentration (totally 1.88 and 7.50 micromol). The treatment lasted for 18 days and Cd concentrations in roots and shoots were determined by AAS. The results showed that an increased biomass production increased the total Cd uptake but had a dilution effect on the Cd concentration, especially in the root tissues. The external factors tested did not have any direct effects on the Cd untake, only in the case of Cd translocation to the shoot did the higher temperature show a direct increase, but only in the southern ecotype. The two ecotypes reacted differently in Cd uptake and translocation to the external factors studied. The relative Cd uptake creased with increasing photoperiod in the northern but not in the southern ecotype. The southern ecotype decreased the Cd concentration in the shoot with increased light intensity caused by a dilution effect due to extensive shoot growth of this ecotype. The conclusion is that the uptake in pine seedlings is mainly regulated via biomass production, and not directly by light and temperature and that resulting plant Cd contents to a certain extent depend on plant origin.     

Effects of ethylenediurea and ozone on the antioxidative systems in beans (Phaseolus vulgaris L.)

To study the biochemical mechanism of EDU protection against ozone injury, peroxidase, ascorbate-dependent peroxidase, and catalase activities, and the contents of ascorbic acid, dehydroascorbic acid, malondialdehyde and soluble protein were measured in Phaseolus vulgaris L. cv. Lit exposed to ozone and ethylenediurea (EDU) in open-top chambers. Plants not treated with EDU showed foliar bronzing due to ozone, while EDU-treated plants were not affected. EDU application modified the reaction of biochemical parameters to ozone. Soluble protein content was elevated by EDU. Peroxidase activity increased with ozone exposure in untreated plants only, while ascorbate-dependent peroxidase activity was lower in EDU treated plants. Catalase activity decreased in EDU-untreated plants. The ratio of ascorbic acid to dehydroascorbic acid was significantly increased in EDU treated plants. These results suggest that EDU might induce ascorbic acid synthesis and therefore provide the plant with a very potent antioxidant. Or the content of hydrogen peroxide was reduced due to other unknown processes and caused a delay in foliar senescence, regardless of whether these processes were ozone-induced or due to natural aging processes.     

Growth and yield responses of spring wheat (Triticum aestivum L. CV. Turbo) grown in open-top chambers to ozone and water stress

Spring wheat (Triticum aestivum L.) cv. Turbo was exposed to different levels of ozone and water supply in open-top chambers in 1991. The plants were grown either in charcoal filtered air (CF), not filtered air (NF), in charcoal filtered air with proportional addition of ambient ozone (CF1), or in charcoal filtered air with twice proportional addition of ambient ozone (CF2). The mean seasonal ozone concentrations (24 h mean) were 2.3, 20.6, 17.3, and 24.5 nl litre(-1) for CF, NF, CF1, and CF2 treatments, respectively. Ozone enhanced senescence and reduced growth and yield of the wheat plants. At final harvest, dry weight reductions were mainly due to reductions in ear weight. Grain yield loss by ozone mainly resulted from depressions of 1000 grain weight, whereas numbers of ears per plant and of grains per ear remained unchanged. Pollutants other than ozone did not alter the response to ozone, as was obvious from comparisons between CF1 and NF responses. Water stress alone did not enhance senescence, but also reduced growth and yield. However, yield loss mainly resulted from reductions in the number of ears per plant; 1000 grain weight was not influenced by water stress. No water supply by ozone treatment interactions were detected for any of the estimated parameters.     

Effects of ozone on managed pasture: I. Effects of open-top chambers on microclimate, ozone flux, and plant growth

Open-top chambers (OTC) were established in a field of managed pasture, and environmental parameters were recorded inside and outside to study the influence of OTCs on radiation, air temperature (T(air)), saturation vapour pressure deficit (svpd), and soil water content in relationship to plant growth and yield. Canopy development in OTCs supplied with non-filtered air (NF) and in ambient (AA) plots was followed by measuring leaf area index (LAI). The dry matter yield was determined after three growth periods in each of two consecutive seasons. Boundary layer conductance (g(bw)) and wind speed (u) were measured along a vertical profile, and day-time flux were measured along a vertical profile, and day-time flux of O(3) was estimated throughout the experiment on the basis of a mass balance. The vertical profile of u showed values in the range 1-1.2 m s(-1) at the top of the canopy, and maximum g(bw) was 20-25 mm s(-1). Average reduction in global radiation in OTCs was 25%, and volumetric soil water content was reduced by about 5%. Daily mean T(air) was increased by 1.3 degrees C, mean daily maximum svpd by 0.08 kPa, and the temperature sum (degree days with base temperature of +5 degrees C) by 12%. Fluctuations in the difference in daily mean T(air) and svpd during the daytime between OTCs and ambient air were related to canopy structure. Differences were largest after each cut and declined with increasing LAI. A small effect of changes in LAI on T(air) and svpd occurred during periods with low soil water content. The flux of O(3) in OTCs was largest (>100 microg m(-2) min(-1)) before and smallest (<20 microg m(-2) min(-1)) after each cut. Calculated deposition velocities for O(3) (nu(d)) in the range 0-3 cm s(-1) were generally higher than those measured under most field conditions. Overall, in OTCs the deficit in soil and atmospheric moisture was larger than in the open field, and the increase in daily mean T(air) was strongly influenced by the stage of canopy development. Changes in microclimate and incoming radiation affected pasture development. LAI was slightly reduced in OTCs as compared to AA plots. The total accumulated dry matter yield for all six growth periods was only about 7% lower in OTCs, but the contribution of clover to total forage mass declined during the experiment. OTCs had no significant effect on weeds. The results indicate that OTCs reduced the competitiveness of clover, and that the increase in growth of grasses compensates for the loss in clover yield. The shift in species composition caused by OTCs must be considered when studying the effect of pollutants on pasture.     

Effects of salinity and ozone,individually and in combination,on the growth and ion contents of two chickpea (Cicer arietinum L.) varieties

The aim of this study was to determine the effects of ozone and salinity, singly and in combination, on the growth and ion contents of two chickpea (Cicer arietinum L.) varieties. Chickpea plants were grown in non-saline and saline conditions, with and without a repeated exposure to ozone. Salinity at a concentration of 30 mM NaCl caused a substantial reduction in plant height, number of leaves and the dry weights of the leaves, stems and roots. Biomass allocation to the leaves increased, predominantly at the expense of the roots. Ozone at a concentration of 85 nmol mol(-1) for 6 h per day for 25 days reduced plant height and dry weights but had no effect on leaf number. The results show substantial effects of salinity and ozone on chickpea growth and ion concentrations. When ozonated plants are grown in the presence of salinity, further reductions in growth occur.     

Effects of ozone on growth, yield and leaf gas exchange rates of two Bangladeshi cultivars of wheat (Triticum aestivum L.)

To clarify the effects of O₃ on crop plants cultivated in Bangladesh, two Bangladeshi wheat cultivars (Sufi and Bijoy) were grown in plastic boxes filled with Andisol and exposed daily to charcoal-filtered air or O₃ at 60 and 100 nl l⁻¹ (10:00-17:00) from 13 March to 4 June 2008. The whole-plant dry mass and grain yield per plant of the two cultivars at the final harvest were significantly reduced by the exposure to O₃. Although there was no significant effect of O₃ on stomatal diffusive conductance to H₂O of flag leaf, net photosynthetic rate of the leaf was significantly reduced by the exposure to O_3. The sensitivity of growth, yield, yield components and leaf gas exchange rates to O₃ was not significantly different between the two cultivars. The results obtained in the present study suggest that ambient levels of O₃ may detrimentally affect wheat production in Bangladesh.     

Effects of elevated ozone concentration on the degradation of dichlorprop in soil.

An aerobic degradation study was conducted to estimate possible effects of elevated ozone concentration in air on the behaviour of dichlorprop. An average ozone concentration of 80 nL L-1 was chosen, which often occurs close to congested areas during late spring and summer. A control soil and an ozone exposed soil were kept under same conditions such as temperature, air flow and soil humidity. The use of 14C-labelled dichlorprop allowed to examine the fate of dichlorprop and follow the degradation products in soil. Exhaustive extraction of both soils yielded several fractions containing dichlorprop residues. Half lives of dichlorprop of both treatments were 5 days. After 32 days most of the residues in soil remained in the non extractable fraction. The elevated ozone concentration showed no significant effects on the degradation behaviour of dichlorprop and its metabolites but significant differences were found for the behaviour of the nonextractable residues and of the release of carbon dioxide, which were higher for control soil in comparison to the ozone variant. These findings suggest that even moderately elevated ozone concentration in air can effect mineralisation and fixation processes of dichlorprop.     

Effects of ozone on chlorophyll and quantum yield of tobacco (Nicotiana tabacum L.) varieties

Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.