Bryophytes: Natural Biomonitors
ABSTRACT
Bryophytes are the most successful nonflowering thallus land plants. Bryophyte life structure is the simplest, having recurring arrangements of photosynthetic tissues, which provide maximum primary production and minimum water loss. Different life forms are found, which is a specialty of bryophytes. Bryophytes are mainly known as amphibians of plant kingdom, as they can successfully survive on both land and water. Bryophytes are very much economically important. Bryophyte are proved as potential bioindicators of air pollution as they shows a wide range of habitat diversity, structural simplicity, totipotency, and fast multiplication rate. One most important feature of bryophytes is that they show high metal accumulation capacity. Bryometers are used for the measurement of phytotoxic air pollution. Bryophyta alone or along with lichens gives valuable information about air pollutant by an index of atmospheric purity (LAP), which is based on the number, frequency-coverage, and resistance factor of species. In this chapter, we will discuss about the role of bryophytes as bioindicators and the methods by which we can measure pollutants in the thallus of bryophytes.
INTRODUCTION
Bryophyta is a division of kingdom Plantae and contains a small group of lower plants, placed between algae and vascular plants. The word Bryophyta is derived from Greek words, “Bryon” meaning mass and “phyton” meaning plant. This division comprises of mosses, hornworts, and liverworts. They are groups of green plants that occupy a position between thallophytes (algae) and vascular cryptogams (pteridophytes). Bryophyta lacks a proper vascular tissues system and are not able to form seeds after fertilization; that is why they are considered as the most primitive type of embryophyta. Regarding the origin of bryophyte, two important scientific communities are there: one group believes that they are originated from algae, while the other believes that they are originated from pteridophytes. Bryophyata has alteration of generations, i.e., their life cycle contains two phases: gametophytic and sporophytic. These two generations have unique structures. Gametophytic- phase nutrients are directly absorbed by diffusion through the cells. These plants are veiy peculiar and sensitive and act as potent bioindicators for a few pollutants, and nowadays bioindicators are a very important field of concern. Lichens and bryophytes are two important bioindicators.
Le Blanc and Rao (1975) exploited an instrument called bryometer for the measurement of phytotoxic air pollution. Bryophyta alone or along with lichens gives valuable information about air pollutant by an index of atmospheric purity (IAP), which is based on the number, frequency coverage, and resistance factor of species.
Bryophytes can be of two types on the basis of indicators of pollution:
- 1. Species that are very sensitive and show visible symptoms or injuries at veiy low concentration of pollutants. These are a veiy good indicator.
- 2. Species that are able to absorb and retain pollutants at a very high level as compared to other plants growing in the same habitat. These plants trap and prevent the recycling of such pollutants in the ecosystem for different periods of time. Analysis of such plants gives a fair idea about the degree of metal pollution.
GASEOUS POLLUTANTS AND BIOMONITORS
Air pollution is mainly due to gases like carbon monoxide (CO), hydrogen sulfide (H,S), fluorides, hydrocarbons (HCs), nitrogen oxides (NOx), ozone (03), sulfur dioxide (SO,), aldehydes, and lead. NOx and NH, are primary gaseous pollutants that are strongly phototoxic (Greven, 1992). SO, and NO, are converted to strong acids by oxidation and react with atmospheric water to form acid rain. Nitrogen oxides, SO,, and smoke are produced by the combustion of fuels in automobiles, which releases various metals into the atmosphere.
Dust, particles of metal oxides, coal, soot and fly ash, cement, liquid particles, heavy metals, and radioactive materials are particulate pollutants. Ozone (03) is a secondaiy pollutant formed by the action of sunlight on nitrogen dioxide and certain hydrocarbons and is more phytotoxic. Pesticides and fertilizers are also pollutants, adding various foims of aquatic pollution. These pollutants are very harmful for the flora and fauna of the earth, while there are some plants that acts as biomonitors or bioindicators of pollution. Biomonitors are actually biological indicators that can detect changes in the physical and chemical properties of the abiotic environment. They act as direct indicators of the physical and chemical properties of the environmental pollution. Biological indicator organisms or plant species shows differences in their occurrence, vitality, and responses under changed environmental conditions.
