CHAPTER ONE

INTRODUCTION

1.1   Background of study

Macrophytes are the conspicuous plants that dominate wetlands, shallow lakes, and streams. Macroscopic flora includes the aquatic angiosperms (flowering plants), pteridophytes (ferns), and bryophytes (mosses, hornworts, and liverworts). Macrophytes may be floating, floating-leaved, submerged, or emergent (Sculthorpe, 1967), and may complete their life cycle in water (still and flowing) or on hydric soils (inundated and non-inundated).

          Aquatic macrophytes are considered photosynthetic organisms of freshwater habitats, comprising vascular plants, aquatic bryophytes and macro algae, easily seen with the naked eye and are normally found growing in or on the surface of water, or where soils are flooded or saturated long enough. Aquatic macrophytes as primary producers and habitat providers are important component of river ecosystems.

They play an important role in the structure and functioning of freshwater ecosystems (Wetzel, 2001; Hrivnaket al., 2009; Tamire and Mengistou, 2012). The macrophytes serve as a base of aquatic food-chains, besides they also actively contribute to the promotion and maintenance of food webs and services in freshwater ecosystems (Scheffer and Jeppesen, 2007; Smith, 2011).

Aquatic macrophytes also act as important bioindicators of environmental conditions and long term ecological changes in water quality (Lacoul and Freedman, 2006; Soliminiet al. 2006). The function of macrophytes in these ecosystems is related to their structural attributes like species composition, distribution, abundance and diversity which in turn relies on various environmental factors such as light, water, temperature, substrate composition, disturbance, competitive interactions, herbivory, epiphyte loading, water levels, quality of the lake water and sediment nutrients (Kaulet al., 1978; Pandit, 1984, 1992; Barko and Smart, 1986; Duarte et al., 1986; Lodge, 1991; Cronk and Fennessey, 2001; Wetzel, 2001; Capers, 2003; Pankhurst, 2005; Jaikumaret al., 2011; Sirajet al., 2011; Feldmann, 2012; Tamire and Mengistou, 2012). Apart from these, factors such as composition and properties of sediments also seem to have significant effect on the distribution of certain Macrophyticspecies (Dawson and Szoszkiewicz, 1999; Heegaardet al., 2001). Vegetative and clonal reproduction is considered to be the major mechanism for population growth and dispersal of macrophytes because sexual reproduction and genetic recombination are often subordinate strategies (Wetzel, 2001). The efficient reproduction strategies and good dispersal capabilities are the two factors that help some aquatic macrophytes to become cosmopolitan in distribution and display high levels of polymorphism and phenotypic plasticity in response to variations of environmental factors. (Sculthorpe, 1967; Barratsegretain, 1996; Santamaria, 2002).

        1.2 AQUATIC MACROPHYTE

Aquatic macrophytes are aquatic photosynthetic organisms, large enough to be seen with the naked eye, that actively grow permanently or periodically submerged below, floating on, or growing up through the water surface. Aquatic macrophytes do not belong to one distinct taxonomic group but rather form a collection of many plant taxa. The term "aquatic macrophytes" is commonly used for all macroscopic forms of aquatic vegetation; it includes macroscopic algae (stoneworts and the alga, Cladophora), some ferns and mosses (pteridophytes) and many flowering plants (angiosperms).These plants require special adaptations for living in submerged water, or at the water surface. The most common adaptation is aerenchyma but floating leaves and finely dissected leaves are also common. Aquatic plants can only grow in water or in soil that is permanently saturated with water. They are therefore a common component of wetlands.

1.3 TYPES OF AQUATIC MACROPHYTES

        ON The basis of their emergence or submergence and the manner of attachment or rooting in the bottom sediment, two main groups, with 3 subdivisions are commonly distinguished (wetzel, 1975).

A.    Aquatic macrophytes rooting in sediment

• Emergent aquatic macrophytes. 
  Reed is often found in monospecific stands, but also mixed with Typha spp., Scirpuslacustris,    Acoruscalamus , Dseudacorus, Butomusum  bellatus and Sagittaria  sagittifolia. Emergent macrophytes are rooted in the sediment and may grow to a water depth of 1m. During the growing season all members of this group produce aerial leaves and flowers.
• Floating-leaved aquatic macrophytes. 
  The floating-leaved plant communities are often   predominated by Nymphaea spp., Nupharlutea and Nymphoidespeltata.      Potamogeton natans and Polygonum hydropiper also belong to this group. The floating-leaved plants may root in water depths up to 3m and have floating or aerial flowers (reproductive organs).
• Submersed macrophytes. 
  This group includes the stoneworts (charophytes) Chara and Nitella, a few moss species like Fontinalis antipyretica and many flowering plants e.g. Myriophyllum spicatum, Elodea nuttallii, Potamogeton pectinatus and E. perfoliatus. The submersed macrophytes complete their life cycle under the water surface.

B.    Freely floating macrophytes

These macrophytes are not rooted in the sediment, but live unattached in the water. The life forms within this group range from macrophytes with floating or aerial leaves and well developed submersed roots (Hydrocharismorsus-ranae) to very small surface floating or submersed plants with few or no roots (Lemnatrisulca and the water fern Azolla ). Some plants in this group have aerial flowers (Utricularia vulgaris) others complete their life cycle under the water surface (Ceratophyllum demersum.).

1.4 Essential Nutrients for Plant Growth:

Nutrient Functions and Deficiency Symptoms

Plants, like all other living things, need food for their growth and development.         Plants require 16 essential elements. Carbon, hydrogen, and oxygen are derived from the atmosphere and soil water. The remaining 13 essential elements (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, zinc, manganese, copper, boron, molybdenum, and chlorine) are supplied either from soil minerals and soil organic matter or by organic or inorganic fertilizers. For plants to utilize these nutrients efficiently, light, heat, and water must be adequately supplied. Cultural practices and control of diseases and insects also play important roles in crop production. Each type of plant is unique and has an optimum nutrient range as well as a minimum requirement level. Below this minimum level, plants start to show nutrient deficiency symptoms. Excessive nutrient uptake can also cause poor growth because of toxicity. Therefore, the proper amount of application and the placement of nutrients are important. Soil and plant tissue tests have been developed to assess the nutrient content of both the soil and plants. By analyzing this information, plant scientists can determine the nutrient need of a given plant in a given soil. In addition to the levels of plant-available nutrients in soils, the soil pH plays an important role in nutrient availability and elemental toxicity. J.A. and R. Uchida (2000).

This topic describes the essential nutrients, the chemical forms in which they are available to plants, their function in plants and symptoms of their deficiencies.

The primary nutrientsnitrogen (N), phosphorus (P), and potassium (K) are commonly found in blended fertilizers such as 10-10-10, or equivalent grades. Primary nutrients are utilized in the largest amounts by crops, and therefore, are applied at higher rates than secondary nutrients and micronutrients.

Nitrogen

Symbol: N; available to plants as nitrate (NO3–), and bolammonium (NH4+) ions.

Nutrient functions

• Nitrogen is biologically combined with C, H, O, and S to create amino acids, which are the building blocks of proteins. Amino acids are used in forming protoplasm, the site for cell division and thus for plant       growth and development.

• Since all plant enzymes are made of proteins, N is needed for all of the enzymatic reactions in a plant.

• Nitrogen is a major part of the chlorophyll molecule and is therefore necessary for photosynthesis.

• Nitrogen is a necessary component of several vitamins.

• Nitrogen improves the quality and quantity of dry matter in leafy vegetables and protein in grain crops.

Deficiency symptoms

• Stunted growth may occur because of reduction in cell division.

• Pale green to light yellow color (chlorosis) appearing first on older leaves, usually starting at the tips. Depending on the severity of deficiency, the chlorosis could result in the death and/or dropping of the older leaves. This is caused by the translocation of Nitrogen from the older to the younger tissues.