LU5-LU8 PP PDF

LU5.1 1. Transpiration: Loss of water from plants in the form of vapor. 2. Phases of Transpiration: - Evaporation of water in mesophyll...

LU5.1 1. Transpiration: Loss of water from plants in the form of vapor. 2. Phases of Transpiration: - Evaporation of water in mesophyll cells bordering intercellular spaces. - Diffusion of water vapor into the atmosphere, influenced by temperature. 1.DEFINITON & 2. IMPORTANCE 5. FACTORS INFLUENCING TRANSPIRATION PROCESS 1. Temperature: Higher temperatures increase transpiration; 1. Controls water movement in plants, affecting water uptake. extreme heat may cause stomatal closure. 2. Supplies water for photosynthesis. 2. Relative Humidity: High humidity reduces transpiration rates. 3. Transports minerals from roots to leaves for biosynthesis. LU5 3. Wind and Air Movement: Increases transpiration by replacing 4. Cools the plant via evaporation. humid air around leaves with drier air. 4. Soil Moisture: Limited water availability decreases transpiration by inducing stomatal closure. 5. Plant Type: Arid-adapted plants, such as cacti, transpire less. 3. MECHANISM & PATHWAYS 4. STOMATAL FUNCTIONS 1. Water movement is facilitated by a vascular system linking roots and shoots. 2. Water loss occurs through stomata, cuticle, and lenticels. - Stomatal Transpiration: Major pathway (80–90% water loss). 1. Stomata, controlled by guard cells, regulate - Cuticular Transpiration: Occurs through the cuticle (~20% water loss). water loss and gas exchange. - Lenticular Transpiration: Through lenticels in woody stems and fruits (1–5% water loss). 2. Guard cells swell and open stomata when turgid; they close stomata when flaccid. LU5.2 6. QUANTITATIVE INSIGHTS LU5 ROOT ABSORPTION 1. A leaf can transpire many times its weight in water - Cold roots or poor aeration reduce water during a growing season. uptake, leading to reduced transpiration. 2. An acre of corn may transpire 3,000–4,000 gallons of water daily, while a large oak tree may transpire 40,000 gallons annually. 7. CONTROL MECHANISMS STOMATAL REGULATION - Feedback mechanisms balance water absorption and loss.  LU6.1 - Definition: Conversion of light energy into chemical energy to produce carbohydrates (C6H12O6) from CO2 and H2O. - Equation: 6 CO2 + 6 H2O C6H12O6 + 6 O2. - Phases: - Light Reaction: - Occurs in thylakoid membranes. - Splits water into O2 and H+, producing ATP and NADPH. - Dark Reaction (Calvin Cycle): - Takes place in the stroma. - Fixes CO2 into carbohydrates using ATP and NADPH. - Produces Glyceraldehyde-3-Phosphate (G3P), which forms glucose and sucrose. 2. C3 AND C4 PHOTOSYNTHESIS 1.MECHANISM OF 4. RADIATION USE EFFICIENCY (RUE) PHOTOSYNTHESIS - Definition: Efficiency of converting photosynthetically active radiation (PAR) into biomass. - C3 Photosynthesis: - PAR: Radiation between 400–700 nm wavelength, - CO2 fixation occurs via the Calvin Cycle in mesophyll cells. accounting for 50% of solar radiation. - Enzyme: Ribulose-1,5-bisphosphate (RuBP) reacts with CO2 to - Under agricultural conditions, only 0.1–3% of radiant energy is converted into organic matter, depending on LU6 form 3-phosphoglycerate. - Example plants: Rice, soybean, sunflower. resources and practices. - Adapted to cooler, shaded environments. - Susceptible to photorespiration, which consumes O2 and releases CO2. 3. FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS - C4 Photosynthesis: - Nitrogen: - Two pathways: Hatch-Slack in mesophyll cells and Calvin Cycle in - Essential for chlorophyll production. bundle sheath cells. - Nitrogen deficiency leads to chlorosis, stunted growth, and reduced CO2 fixation. - Enzyme: Phosphoenol Pyruvate (PEP) binds CO2 to form oxaloacetate. - Moisture: - Example plants: Maize, sugarcane. - Affects leaf expansion and canopy size. - Adapted to warm, dry climates with higher water-use efficiency. - Drought reduces photosynthesis due to decreased leaf area. - Minimizes photorespiration due to high CO2 concentration at the Calvin - Temperature: Cycle site. - Photosynthesis rates increase with temperature up to an optimum. - High temperatures destabilize electron transport, reducing photosynthetic efficiency. - Plants adapt to their environments (e.g., alpine plants photosynthesize near 0°C, desert plants near 50°C). LU6.2 6. DIFFERENCES BETWEEN C3 AND C4 PHOTOSYNTHESIS LU6 - C3 plants rely solely on the Calvin Cycle, while C4 plants utilize an additional carbon fixation pathway. - C4 plants perform better in warm climates with limited CO2 due to PEP's higher affinity for CO2. - C3 plants are more efficient in cooler, CO2-rich environments but suffer from photorespiration. EXTRA LU7.1 - The maximum yield of a crop depends on the availability of photosynthetically active radiation (PAR) intercepted by the leaf canopy. - Incoming PAR is either absorbed or reflected by the first surface it contacts. If not intercepted by actively growing leaves, it is unavailable for growth. - The size of the leaf area in a canopy directly influences how much PAR is captured, affecting canopy photosynthesis and crop yield. - There is a linear relationship between light interception and crop dry matter production. 2. LEAF AREA EXPANSION The canopy size and ability to intercept light are determined by: 5. EXTINCTION COEFFICIENT (K) 1. LIGHT INTERCEPTION 1. Time of Crop Emergence: - Influenced by photoperiod (length of day). - Definition: Quantifies the effectiveness of a leaf area in - Long-day plants in decreasing photoperiod extend vegetative growth, capturing light. producing larger canopies. - Determines how light is distributed among leaves at different canopy heights. LU7 * - Spring-emerging crops (in increasing photoperiod) flower earlier, limiting canopy growth. 2. Phyllochron: (ONLY APPLIED ON GRASS FAMILY- corn,rice,paddy) - Rate of leaf appearance, influenced by photoperiod, temperature, and crop type. - Long-day crops in decreasing photoperiod grow leaves more slowly but 4. CANOPY ARCHITECTURE sustain growth longer. - Differences in leaf orientation (erect vs. horizontal) and - Day-neutral crops are unaffected by photoperiod and rely solely on arrangement affect light penetration and interception. temperature. - Erect leaves allow more penetration, enabling light 3. Leaf Expansion Rate: interception at deeper canopy levels. - Water stress and poor nitrogen nutrition reduce leaf size and expansion. - Horizontal leaves intercept more light at the canopy 4. Axillary Leaf Production: surface but reduce penetration to lower layers. - Early production of axillary leaves increases leaf area exponentially, enhancing light capture. - Annual species produce axillary leaves faster than perennials. 5. Leaf Senescence: - Senescence reduces photosynthetic potential as nutrients (e.g., nitrogen) are mobilized to younger leaves or storage organs.  LU7.2 3.2 LIMITATIONS 3. LEAF AREA INDEX (LAI) - Even at high LAI, some light is lost due to canopy gaps or Definition: - The Leaf Area Index (LAI) quantifies the total LU7 reflection. 100% light interception is unattainable. - High LAI values may lead to higher energy costs in green leaf area per unit ground area (e.g., m² of maintaining excess biomass without significant yield leaf area per m² of ground). benefits. - Example: If a 1 m² ground area has 1 m² of green 3.3 FACTORS INFLUENCING LAI leaf area, the LAI is 1.0. 3.4 IMPORTANCE 1. Temperature: - Crop productivity depends on maintaining an - Affects crop emergence, leaf and branch production, leaf expansion, and Key Concepts: senescence. optimal LAI: 1. Light Interception Efficiency: - Higher temperatures promote faster canopy growth but may accelerate - Too low LAI: Insufficient light interception - A canopy with LAI = 1.0 intercepts less than 50% senescence if stress levels increase. and reduced photosynthesis. of photosynthetically active radiation (PAR) due to - Too high LAI: Increased self-shading, large gaps. 2. Nitrogen Status: senescence, and inefficient resource use. - Higher LAI values capture more PAR, which - Nitrogen is critical for chlorophyll synthesis and leaf expansion. - Agricultural practices, such as nitrogen enhances photosynthesis and crop yield. - Higher nitrogen levels support larger and longer-lasting leaves, increasing LAI. fertilization, irrigation, and planting density adjustments, can optimize LAI for maximum 3.1 CRITICAL LEAF AREA INDEX (LAICRIT) yield. 3. Plant Population Density: - High density increases competition for resources but enhances light interception - LAIcrit is the threshold where 95% of incoming PAR is 3.5PRACTICAL APPLICATION intercepted by the canopy. by reducing gaps in the canopy. - Beyond LAIcrit, additional leaf growth has diminishing returns - Monitoring LAI helps farmers manage because: crops efficiently by: 4. Water Availability: - Excessive overlapping of leaves increases self-shading. - Identifying nutrient or water deficiencies. - Drought stress limits leaf expansion and longevity, reducing LAI. - Older leaves at the base experience higher rates of - Determining planting density. - Adequate water supports sustained growth, maximizing the interception of PAR. senescence. - Timing harvest or interventions to - Increased leaf biomass does not translate to proportional maintain optimal photosynthetic efficiency. 5. Environmental Stresses: photosynthesis or yield gains. - Frost, high temperature, herbivory, diseases, and other hazards reduce LAI by causing leaf damage or early senescence. LU8.1 Photosynthesis and the movement of photosynthetic products occur simultaneously. Early in growth, products are used for vegetative organ formation; later, they form storage organs like grains, fruits, and tubers. 7. ASSIMILATE PARTITIONING OVER TIME Early stages focus on vegetative organs. 1.PHOTOSYNTHESIS & 2. STORAGE & TRANSLOCATION During reproductive phases, assimilates shift to ASSIMILATE storage organs like grains and seeds. TRANSLOCATION For example, in soybeans, dry matter shifts from Excess photosynthates are stored in stalks and leaves leaves to grains as the plant matures. before being transported to growing parts. The transport of photosynthates to various plant parts is facilitated by phloem and plasmodesmata. 6. FEEDBACK REGULATION Accumulation of sugars or starch in leaves can LU8 suppress photosynthesis if sink demand is low. Increased sink demand can enhance photosynthesis. 3. EXPORT RATE OF PHOTOSYNTHATE 5. SOURCE AND SINK DYNAMICS 4. C4 VS. C3 PLANT Leaves may export 70-80% of photosynthates within 6 hours of photosynthesis. Source organs (e.g., mature leaves) produce SPECIES carbohydrates. Sink organs (e.g., fruits, seeds, tubers) store C4 plants exhibit a faster translocation and use assimilates. Young leaves are rate, potentially due to their kranz considered sinks until they mature. anatomy and increased phloem.  1.WATER SUPPLY LU8.2 2.NITROGEN NUTRITION Impact on Grain Yield: Nitrogen affects the size - Role of Water: Water influences leaf size, longevity, carbohydrate and duration of canopy expansion, enabling assimilation rate, and grain filling efficient solar radiation capture. Critical Periods: duration. Reduced water can shorten Chlorophyll Formation: Adequate nitrogen Leafy Vegetables: Sensitive during grain filling due to premature ensures sufficient chlorophyll, essential for active vegetative growth. senescence. photosynthesis and organic compound formation. Root Crops: Sensitive during storage 3.TEMPERATURE E.g: In cereal crops, water deficit organ or tuber development. Physiological Processes: Temperature regulates during canopy establishment reduces Fruit and Seed Crops: Sensitive during photosynthesis, respiration, flowering, assimilate leaf size, impacting overall yield. the reproductive stage. partitioning, leaf production, and crop maturity. Optimal Growth Range: Plants grow faster within 8. FACTORS Water Use Efficiency: Crops with favorable temperature ranges, provided other INFLUENCING YIELD higher water use efficiency (e.g., factors like nutrients, water, and light are not transpiring less and absorbing more LU8 limiting. 5.PLANT POPULATION water) can better handle water Specific Needs: Different crops and varieties have Optimal Population: A balanced density stress. specific optimal temperature ranges for growth and maximizes resource use efficiency and productivity. yield. Germination: Temperature impacts enzymatic 4.SOLAR RADIATION Overpopulation Effects: High densities lead to competition, reactions during water absorption by seeds, affecting Biomass Yield: Yield depends on the amount of light reducing weight per plant and economic germination rates. intercepted by the crop canopy under optimal yield. Partitioning Effect agronomic conditions. Assimilates are primarily partitioned Critical Stages: Reproductive and ripening stages into above-ground parts to ensure plant Cold Seasons (Autumn-Winter): More dry require active photosynthesis for assimilate survival, leaving less for roots and matter is allocated to roots. transport to sinks. seeds. Warm Seasons (Spring-Summer): More Interaction with Nitrogen: Enhanced chlorophyll dry matter is allocated to above- formation and increased leaf area due to nitrogen ground parts like shoots. improve responsiveness to solar radiation. 6.DISEASE, PESTS & WEEDS Yield Reduction: They reduce water and nutrient Light Intensity: Photosynthesis rate Critical Aspects use efficiency and increase production costs. increases with light intensity up to a Quality Impact: Lower crop quality results in saturation point. reduced market value for growers. Light Duration: Determines the duration of active photosynthesis. LU8.3 A measure of economic yield versus total biomass. High harvest index crops partition more assimilates into economically important parts, like grains or tubers. 12. STRATEGIES FOR 9.HARVEST INDEX 10. CROP YIELD DETERMINANTS MAXIMIZING YIELD Vary by crop type (e.g., cereals: panicles, grains, and weight; LU8 Enhance radiation interception. Opt for drought-tolerant or short- legumes: pods, seeds, weight; tubers: stems, tubers, weight). lifespan crops in arid regions. Success in increasing yield includes practices like selecting Apply fertilizers during critical short-stature cereal cultivars to reduce dry matter developmental stages. competition between stems and grains. 11. IMPACT OF SENESCENCE Photosynthesis declines with canopy aging. Assimilates from storage organs like stems and mature leaves are redirected to sinks.