Application of Photoacoustic Spectroscopy in Studies of Environment Contamination Effect on Needles of Scots Pine ( L.)

Dieback of forests has become a severe problem in Central Europe (Zielski 1997). Different species of trees exhibit a variable sensitivity to contamination. Generally, leafed trees are less sensitive than the conifers, partially since the whole surface exposed to contamination is smaller than that of needles. In addition, leaves, falling off every year, are shorter exposed to pollution than the needles. Scots pine (Pinus silvestris L.) belongs to a class of trees which experienced the greatest damages (Huttunen 1978; Palomaeki et al. 1996; Hoque and Remus 1999). In the studies of contamination effect on conifers several methods of damage classes are adopted. They are specified by forest research scientists according to the average needle loss of the whole tree, fluorescence spectroscopy, UV, IR, NMR, mass and reflection spectroscopy, microscopy and microscopic image analysis, and histochemical analysis (Hoque and Remus 1999). In the present paper we describe the application of photoacoustic spectroscopy (one of photothermal spectroscopy versions where a quantity of energy deactivated into heat is evaluated) to quantify the air pollution effect on Scots pine (Pinus silvestris L.) needles. The technique of photoacoustics (PA) has been successfully employed to study photosynthetic systems including the direct measurements of the photosynthetic energy storage (ES) (Bultts et al. 1982; Veeranjaneyulu et al. 1991; Tukaj and Szurkowski 1993; Szurkowski and Tukaj 1994; Szurkowski and Tukaj 1995; Szurkowski 1996) and oxygen evolution in intact leaves (Poulet et al. 1983; Kanstad et al. 1983; Malkin and Canaani 1994; Ageev et al. 1998; Malkin 1998; Szurkowski and Kwidzynska 1999). When a sample is exposed to modulated light, a part of the absorbed light energy is emitted in the form of modulated heat (photothermal signal), resulting from the thermal deactivation of pigments. The rest of the energy is dissipated in photochemical processes leading to modulated O sub(2) emission, and appears as a photobaric signal. Both contributions originate in chloroplasts, from where heat and oxygen diffuse to the cell envelope, and generate acoustic waves in the air phase near the boundary of the cell. The photothermal part of the photoacoustic signal is reduced by a fraction equal to that part of the absorbed energy which is stored by the photosynthetic process as chemical energy. By measuring heat emission in the presence or absence of a nonmodulated saturating light background,