Seasonal changes of pigments concentration in the leaves of "Vaccinium myrtillus" and "Vaccinium vitis-idaea" and the influence of industrial emissions

The current-year leaves of both Vaccinium species show a similar chloro­ phyll a level in summer, ca. 3.0 mg/g d.w., however, they differ in the earliest period of possible analysis. The Vaccinium myrtillus leaves showed at that time a level of ca. 6 mg/g d.w., decreasing by one half in mid June, i.e. in the period in which the fastest increase in leaf dry matter was noted. Autumn depression reaches about 20°/o. The pigment level in biennial leaves of Vaccinium vitis-idaea is rather constant and typical of the current year ones, in the triennial leaves it is lower by ca. 20%. Zinc--plant emissions influence differently the two species, both showing some defence reaction. Chlorophyll b level, in summer in the range of 1.6--1.9 mg/g d.w., shows seasonal changes rather similar to those of chloro ­ phyll


INTRODUCTION
The investigations of the buffer capacity of aqueous homogenates of leaves of Vaccinium myrtillus and Vaccinium vitis-idaea collected from areas influenced by industrial emission show considerable differences between the two species (Czuchajowska, 1979). Studies on heavy metal content in Vaccinium species (H u 11 u n e n, 1975; C zucha j owska et al., 1980) also led to the conclusion that they accumulate metals to a different degree. It seemed, therefore, interesting to check the seasonal changes of the content of chlorophylls and carotenoids in the leaves of the two species and investigate the influence of pollution originating from a zinc-plant. This could help, in the future, to answer the question, whether the accumulation of metals in leaves of different 552 Z. Czuchajowska, T. Strączek Vaccinium species is connected with the content and state of pigments in them. Substantial differences in the anatomy of the leaf of Vaccinium myrtillus and Vaccinium vitis-idaea and the different behaviour of these dwarf shrubs in the highly industrialised region (Buszman, Lorek. 1979) made the present authors' approach even more justified.
It is worth mentioning that seasonal changes of the pigment level and the influence of the emissions on them is so far not known for the Vaccinium species. Gorishina and Zabotina (1977) and Schultz (1972) investigated only the effect of shadowing on the concentration of chlorophylls and carotenoids in Vaccinium myrtillus leaves.

MATERIAL AND METHODS
The leaves of both Vaccinium species were collected from an area relatively free from industrial pollution near Kokotek, Forest District Lubliniec, and from three stands influenced by a zinc-plant at Miastecz ko Śląskie. They were: the Zyglinek stand at a distance of 0.9 km north--east of the zinc-plant, Brynica I and Brynica II -2.5 km and 5 km, respectively, to the east. They represent stands with different levels of pollution, which are always high: 2150 mg Zn/kg dry soil in the 0-5 cm layer, 2800 mg Pb/kg d.s. and 33 mg Cd/kg d.s. at Zyglinek, and re spectively, 920, 1100, 16 mg/kg d.s. at Brynica I, and 130, 133 and 5 mg/kg d.s-at Brynica II. The character of the stands is typical for moist coniferous forest. The control area at Kokotek, located 24 km apart from the other stands in north-east direction, represents a stand with a much lower degree of pollution, the content of Zn, Pb and Cd being 22, 38 and 0.6 mg/kg d.s., respectively.
The year-round cycle of research started in the beginning of November 1976 and ended in November 1977. From every dwarf shrub, taken from hundred specimens randomly chosen, one shoot was collect ed. In the case of Vaccinium vitis-idaea it contained current-year, biennial and triennial leaves, in that of Vaccinium myrtillusthere existed only current-year leaves. After transportation to the laboratory, the leaves were torn off under dimmed light. All dead and necrotic parts were removed and the remaining material was carefully mixed; every leaf was washed with cool water in order to remove surface impurities, the same was done with the control leaves from Kokotek. The content of chlorophyll a, b and total carotenoids was determined, in 8 replications, in the leaves cut into small, ca. 1-mm pieces, according the Linder (1974) method. Faster formation of Vaccinium myrtillus leaves made it possible to measure their pigment content as early as the third decade of May, whereas for Vaccinium vitis-idaea it was possible only a month later.
The substantial changes in water content in the leaves, particularly in the current-year ones, during the study period (the greatest change of dry matter equalled 34 and 29% of the highest value for Vaccinium myrtillus and Vaccinium vitis-idaea, respectively) made it necessary to express the content of the pigments in milligrams per 1 gram of dry weight, i.e. in relation to the dry matter of leaves, this way of presenta tion being most frequently used. The authors tried to avoid the error connected with expressing the pigment level in relation to the leaf area unit. In the latter case, instead of taking into consideration the material characteristic for a large area, a typical feature of every ecophysiological approach, one would have to rely on a few leaves only; also cutting the discs out of very small, young leaves would not be possible.

RESULTS
Seasonal changes of chlorophyll a concentration in leaves of Vaccinium myrtillus and Vaccinium vitis-idaea, together with the changes in dry matter, as dependence of air pollution, are shown in Figs. 1 and 2.
When considering the changes of chlorophyll a level in the leaves from the unpolluted area, one sees that in the period from July to the end of September, the current-year leaves of both Vaccinium species show a similar level of chlorophyll a concentration, about 3.0 mg/g d.w.with ca. 10% more for Vaccinium myrtillus than for Vaccinium vitis-idaeathey differ, however, greatly in the earlier period, i.e. in May and June, in favour of Vaccinium myrtillus.
The newly formed leaves of the latter species show a chlorophyll o level of ca. 6 mg/g d.w., almost two-times higher than the mean content during the greater part of the vegetation period; an intense decrease in the extremely high starting level occurs from the third decade of May, or perhaps even earlier, till the half of June. The last possible measurements of chlorophyll a level before the Vaccinium myrtillus leaves fall prove that the pigment concentration is only by 20% lower than the mean summer value. The decrease corresponds to the period of stabilisation of the leaf dry matter, it seems therefore to be of a different character than concentration decrease observed in the earlier period.
The Vaccinium vitis-idaea leaves, after a temporary decrease in December, preserve the chlorophyll a concentration during the winter period strictly equal to the mean summer value and keep it constant Z. Czuchajowska, T. Strączek during the whole second year of the leaf life with the exception of the spring period (May) when a temporary decrease, by ca. 30%, occurs. It is compensated, to some extent, by the increase in dry matter. During the third year, in general, the leaves contain by 10% less of the pigment than the biennial ones and the spring depression, although it does not become deeper, lasts almost three months. The influence of pollution on the chlorophyll a level also was different in the not injured leaves of Vaccinium myrtillus and Vaccinium vitis-idaea. The intensification of pollution increases its mean concentra tion in Vaccinium myrtillus during early summer, by ca. 20%, but results also in its distinct decrease in late autumn, which does not take place in the current-year Vaccinium vitis-idaea leaves. In general, the curves showing changes of chlorophyll b content are similar to those for chlorophyll a, however, there appear differences in the absolute values because chlorophyll b concentration corresponds to the range of 1.5-2.0 mg/g d.w. It is characteristic that the mean summer level of chlorophyll b is higher for the current-year leaves of Vaccinium vitis-idaea than of Vaccinium myrtillus, 1.8 vs. 1.5 mg/g d.w., and that the early spring depression lasts longer: from Aprill till mid June for the biennial leaves, and as long as four months, starting from mid March, for the triennial ones.
The Vaccinium vitis-idaea leaves also show a little higher level of total carotenoids than those of Vaccinium myrtillus, ca. 0.8 as compared to ca. 0.65 mg/g d.w. This level reaches its highest values of ca. 1.0 mg/g d.w. for the biand triennial leaves of Vaccinium vitis-idaea in the period of January and February.
The difference between the location of all investigated stands and the content of chlorophyll a and b was found significant for the leaves of Vaccinium myrtillus, but not for the current-year leaves of Vaccinium vitis-idaea. The calculations were performed according to Snedecor (1956).

DISCUSSION
Vaccinium myrtillus possesses only current-year leaves while Vacci nium vitis-idaea also has biennial and triennial ones. Therefore only the current-year leaves of both species were comparable from the point of view of seasonal changes of pigment content. The real difference, in favour of the newly formed Vaccinium myrtillus leaves (in the first month of their life) proves that the seasonal shedding of Vaccinium myrtillus leaves requires, from the very beginning, a higher concentra tion of chlorophyll a. This resembles the behaviour of the Larix species leaves, also with a one-year life period, growing in the same ecosystem, and contrasts with the multi-seasonal leaves of Pinus Silvestris (C z uchajowska, Niemtur, 1978).
The influence of industrial emissions on the pigments level in current-year leaves of Vaccinium myrtillus and Vaccinium vitis-idaea is not very pronounced, however, it shows some differences between the species during summer, particularly in July, what is not at all surprising if we consider the marked differences in the morphology and anatomy of both species. In view of this fact, together with the previously noticed differences in the seasonal changes of the buffer capacity of the leaves of the two Vaccinium species (Czuchajowska, 1979) it is reasonable to expect their different reaction towards factors disturbing their life processes.