CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) Biogeochemical Cycles (Cycles of Matter): A biogeochemical cycle is defined as the movement of elements, like those mentioned just a moment ago, through organisms and the environment. A way to remember this is to break apart the word 'biogeochemical' into pieces. The first part of the word, bio, involves biological organisms, like bacteria, plants, and animals. The next part of the word, geo, involves geological processes, like weathering of rocks. The last part of the word indicates chemical processes, such as the formation of molecules. Unlike the one-way flow of energy, matter is recycled within and between ecosystems. Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through cycles that connect living things to the earth. Biogeochemical cycles connect living things to the earth. The four chemicals that make up 95% of living things are: carbon, hydrogen, oxygen and nitrogen. These elements are constantly being cycled through living and non-living organic matter. Nutrient cycles within ecosystems 1. Energy flows through an ecosystem and nutrients cycle within an ecosystem. Nutrients are substances such as water, carbon and nitrogen which are necessary for the survival of living things. Scientists create models to represent natural interactions in the environment which make it easier to study and understand the 'big picture' without having to physically measure an entire ecosystem. Diagrams of the nutrient cycles could be considered models of the actual cycles as they occur in nature. The use of models also allows scientists to make predictionsabout how a particular event might effect an ecosystem without having to expose the real ecosystem to that event. For example, how might the loss of trees, and therefore transpiration, affect rainfall in a particular ecosystem? 2. In an Ecosystem the Three Primary Nutrient Cycles: A. The Water Cycle B. The Carbon Cycle C. The Nitrogen Cycle 77 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) The Carbon Cycle: 1. Together, photosynthesis and cellular respiration form the basis of the carbon cycle. Carbon is found in all of the major macromolecules (carbohydrates, nucleic acids, proteins and lipids) which are necessary for all living systems. 2. The Earth's atmosphere contains carbon in the form of carbon dioxide (CO2). There are five major reservoirs of carbon: the atmosphere the terrestrial biosphere oceans ocean sediments and the earth's interior. 3. Processes of the Carbon Cycle: Photosynthesis: During photosynthesis, plants and other autotrophs use CO2 along with water and solar energy, to build organic molecules (carbohydrates), thus storing the carbon for themselves and other organisms. Cellular Respiration: Both autotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration. Consumers obtain energy-rich molecules that contain carbon by eating plants and animals. Volcanic Eruptions and geothermal vents: carbon from deep within the earth's interior is brought back to the surface during eruptions of steam, gasses and lava Decomposition: Carbon is returned to the environment through decomposers and cellular respiration (breathing releases CO2 back to the atmosphere). Combustion: When wood or fossil fuels are burned, the chemical reaction releases carbon dioxide back into the atmosphere Deposition: Coal, petroleum, and calcium carbonate rock are deposited in sediment and underground. Calcium carbonate deposits are eroded by water to form carbon dioxide. Large amounts of carbon are tied up in wood, only returning to the atmosphere when wood is burned. 78 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) The black numbers in the image above indicate how much carbon is stored in various reservoirs, in billions of tons ("GtC" stands for GigaTons of Carbon. The figures are circa 2004. The dark blue numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen. 79 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) The Nitrogen Cycle: 1. All organisms need nitrogen, an important nutrient, to make proteins and nucleic acids. 2. Most nitrogen is found in the atmosphere (80%) as N2, and most living things cannot use it. All organisms rely on the actions of bacteria that are able to transform nitrogen gas into a usable form. 3. Nitrogen-fixing bacteria (Cyanobacteria and Rhizobium) play a key role in the nitrogen cycle. They live in the soil and in the roots of some kinds of plants, such as beans, peas, clover, and alfalfa. These bacteria have enzymes that can break the atmospheric N2 bonds. Nitrogen atoms are then free to bond with hydrogen atoms to form Ammonia (NH3). Processes of the Nitrogen Cycle: Nitrogen fixation is the conversion of nitrogen gas to ammonia; Ammonia can be absorbed by plants from the soil, and used to make proteins, and enter the food web for consumers. 80 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) Assimilation: Consumers obtain nitrogen from the plants and animals they eat by digesting the food's proteins and using it to make their own proteins Ammonification: Decomposers return the nitrogen from the remains of dead plants and animals back to the soil. Nitrogen is also returned from animal and plant waste by decomposers (dung, urine, leaves and bark). Through ammonification, nitrogen that would be lost, is recycled back into the ecosystem. Denitrification: Denitrification occurs when anaerobic bacteria (chemoautotrophs) break down nitrates and release nitrogen gas back into the atmosphere. Nitrification: Bacteria convert ammonia into nitrogen compounds that plants can utilize more easily. Autotrophs (plants) are therefore DEPENDENT on nitrogen-fixing bacteria, and all other organisms are DEPENDENT on autotrophs! The Phosphorus Cycle: The phosphorus cycle: – Involves the movement of phosphorus throughout the biosphere and lithosphere – Important because phosphorus is an essential element for life and often is a limiting nutrient for plant growth. – Phosphorus is the key to energy in living organisms, for it is phosphorus that moves energy from ATP to another molecule, driving an enzymatic reaction, or cellular transport. 81 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) – The keystone of getting phosphorus into trophic systems is plants. Plants absorb phosphorous from water and soil into their tissues, tying them to organic molecules. Once taken up by plants, phosphorus is available for animals when they consume the plants. – When plants and animals die, bacteria decompose their bodies, releasing some of the phosphorus back into the soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles from where they were released by riding through streams and rivers. – In some cases, phosphorous will travel to a lake, and settle on the bottom. There, it may turn into sedimentary rocks, limestone, to be released millions of years later. Phytogeography, Climate, Vegetation and Botanical Zones of India According to Campbell (1926), the main theme of plant geography is to discover the similarities and diversities in the plants and floras of the present and past found in widely separated parts of the earth. Wulff (1943) states that Phytogeography is the study of distribution of plant species in their habitats and elucidation of origin and history of development of floras. According to Croizat (1952), Phytogeography is the study of migration and evolution of plants in time and space. 82 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) Phytogeography: There are two major divisions of Phytogeography: (i) Descriptive or Static Phytogeography (ii) Interpretive or Dynamic Phytogeography Descriptive Phytogeography: This deals with the actual description of floristic or vegetational groups found in different parts of the world. Early plant geographers described floras and attempted to divide earth into floristic and botanical zones. Interpretive or Dynamic Phytogeography: This deals with the dynamics of migration and evolution of plants and floras. It explains the reasons for varied distribution of plant species in different parts of the world. It is a borderline science involving synthesis and integration of data and concepts from several specialized disciplines like ecology, physiology, genetics, taxonomy, evolution, palaeontology and geology. Good (1931), Mason (1936), Cain (1944) and some others have pointed out the factors involved in the distribution of plants. Vegetation of any place is modified by the environmental factors; climate, geology and biotic factors. The great area of Indian subcontinent has wide range of climate and corresponding diversity in the vegetation. 83 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) India has been divided into the following botanical zones by D. Chatterjee (1962) Fig. 11.4: (1) Western Himalayas, (2) Eastern Himalayas, (3) Indus plain, (4) Gangetic plain, (5) Central India, (6) Deccan, (7) Western coasts of Malabar, (8) Assam, and (9) Bay Islands of Andaman and Nicobar. 1. Western Himalayas: The northern part of our country is bounded by highest ranges of Himalayas and is one of the important botanical regions of the world with climate and vegetation ranging from truly tropical near the low altitudes to temperate arctic types at the high altitudes. The northern mountain division can phytogeographically be divided into western, central and eastern zones. 84 CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016) Western Himalayas consist of north Kashmir, south Kashmir, a part of Punjab, H.P., Garhwal and Kumaon. This zone is wet in outer southern ranges and slightly dry in inner northern zone. The average annual rainfall in this region is from 100 to 200 cm.