scope:

Introduction

Due to their anatomical and physiological properties, epiphytic bryophytes and lichens are particularly sensitive to air pollutants, and have been used for decades as bioindicators of air quality (see e.g. [2; 7; 11]). Whereas concentrations of individual immission components are determined using technical methods, the use of bryophytes and lichens allows an understanding of the integral overall effect of biologically relevant environmental factors. In addition, they offer the advantage of a species-specific graduated sensitivity, by which, if particular species occur, conclusions on the respective air quality can be drawn.

Compared to other groups of plants, bryophytes exhibit the following important properties making them particularly suited for the bioindication of air pollutants:

• Bryophytes take up water containing dissolved nutrients (and pollutants) over their entire unprotected surface from rain, dew or fog. Thus, they are directly exposed to all environmental impacts such as acid rain, nitrogen oxides, etc., and react by either disappearing or dispersing.
• Bryophytes have no physiological adaptation mechanisms enabling them to remove or neutralize harmful substances.
• Since their temperature optimum is rather low, their metabolic activity reaches its maximum in late autumn and winter - when pollutant loads are increased by domestic heating and atmospheric inversion.
• Distribution areas of bryophytes are far greater than those of flowering plants. Thus, the same bry ophyte species can be used Europe-wide for heavymetal monitoring from Scandinavia to Italy.
• Due to their lightweight diaspores bryophytes are efficiently disseminated. It can be assumed that most bryophyte species are potentially omnipresent, i.e. spores are spread over large areas at any time and disperse into all potential growing areas. If environmental conditions change, bryophyte vegetation will change too.
• Bryophytes have short reproductive cycles. A developmental cycle can be completed within a minimum of four weeks, and within a period of six months for many species. Hence, fast response to environmental impacts is ensured.
• Studies on bryophytes can be carried out throughout the year.

Many mappings (see e.g. [3; 5; 6; 17]) and transplantation or fumigation experiments (see e.g. [10; 12; 13; 14; 18]) give evidence for the suitability of bryophyte species as bioindicators of air quality.