14- Plant Nutrition III and Ecosystem Nutrient Cycling(2)

Page 1: Introduction to Plant Nutrition and Ecosystem Nutrient Cycling

• Overview of essential concepts related to plant nutrition and nutrient cycling in ecosystems.

Page 2: Class Announcements

• Important updates for students:

  • Practice exam is now available.

  • Office hours scheduled for tomorrow from 4:45-5:45 PM via Zoom.

  • Reminder: One week to report any grading mistakes.

  • Review session on Sunday at 5 PM with Dr. Chapman and Dr. Wieder (Zoom link provided).

  • Upcoming exam next Monday covering material until Friday's lecture. Students should bring computers.

  • Wednesday lecture will be in person; next Friday designated for project catch-up.

• Topics to be covered in class include:

  • Plant nutrient limitations and the role of fertilizers.

  • Eutrophication and its effects.

  • Overview of nutrient cycling with a Hawaiian case study.

Page 3: Science News

• Importance of salmon:

  • Key fishery for Native American tribes; integral to their lifestyles.

  • Salmon contribute to fertilizing soils and forests.

• Historical challenges:

  • Logging, dams, water extraction, and pollution have severely reduced wild salmon populations since the 1950s.

• Restoration efforts:

  • Fifty years of research leading towards successful projects aimed at salmon restoration.

  • Restoration often involves improving water flow to facilitate salmon migration up to 850 miles.

Page 4: Encouraging Beneficial Soil Organisms

• Mechanisms attracting beneficial soil organisms include:

  • Nitrogen-fixing bacteria and mycorrhizae associations.

• Nitrogen fixation requires a conducive environment that is typically provided within rhizobium nodules in legumes.

Page 5: Nitrogen Fixation in Wild Plants

• Energy costs of nitrogen fixation:

  • Lab conditions illustrate that nitrogen fixation consumes 25% of growth in carbohydrates given to bacteria.

  • Nitrogen uptake from soil is less costly.

• Fertilizer effects:

  • When inorganic nitrogen is supplied through fertilizers, plants often reduce nitrogen fixation.

• Crop rotation practices:

  • Farmers utilize nitrogen-fixing plants in crop rotations (e.g., corn followed by legumes) to replenish soil nitrogen.

Page 6: Soil Nutrient Depletion in Agriculture

• Comparison of agriculture vs. natural ecosystems:

  • Agriculture depletes soil mineral content, strains water reserves, and encourages erosion.

  • Natural ecosystems cycle nutrients effectively and restore their own reserves.

• Soil conservation strategies aim to reduce agricultural damage:

  • Implementing no-till agriculture and utilizing cover crops.

Page 7: Fertilizer Use in Agriculture

• Purpose and composition of fertilizers:

  • Fertilizers are used to supplement nutrient removal in agriculture.

  • Commercial fertilizers: minerals either mined or synthetically produced (e.g., Haber-Bosch process for nitrogen).

  • "Organic" fertilizers are made from manure, fishmeal, or compost.

• Environmental impacts:

  • Energy-intensive fertilizer production contributes significantly to greenhouse gas emissions.

  • Excess fertilizer leads to nutrient runoff, algal blooms, and eutrophication.

Page 8: Human Impact on Nutrient Cycling

• Focus on nitrogen deposition:

  • Human activities contribute to both wet and dry nitrogen deposition.

  • Organic nitrogen deposition accounts for approximately one-third of total deposition.

Page 9: Effects of Eutrophication

• Eutrophication process leads to:

  • Harmful algal blooms.

  • Fish kills due to dead zones characterized by:

    • Increased nutrients.

    • Rapid algal or bacterial growth.

    • Decreased oxygen levels.

    • Death of aquatic organisms affected by toxic algal blooms.

Page 10: Practice Exam Question Overview

• Understanding of the eutrophication cascade:

  • Key steps include increased nutrients, algal growth, oxygen depletion, and subsequent algal decline.

Page 11: Nutrient Recycling in Ecosystems

• Nutrient inputs and recycling mechanisms:

  • Chemical weathering of rocks increases available nutrients (P, K, Mg, Ca).

  • Biological processes contribute to fixed nitrogen in ecosystems.

  • Atmospheric deposition introduces nutrients via rain, airborne particles, or gases.

• Importance of recycling:

  • Most "active" nutrients in ecosystems are recycled; nutrient resorption is crucial.

  • Human activities tend to disrupt natural nutrient cycles, increasing both inputs and outputs.

Page 12: Soil Bacteria and Nitrogen Dynamics

• Analysis of nitrogen inputs and outputs:

  • Inputs include nitrogen fixation facilitated by specific bacteria.

  • Outputs account for denitrification processes and non-bacteria mediated nitrate leaching.

Page 13: State Factors in Soil Formation

• Key factors influencing soil characteristics:

  • Climate: affects weathering processes.

  • Organisms: contribute to soil through biological activity.

  • Relief: topography influences soil movement and weathering.

  • Parent material: original composition of the soil.

  • Time: duration of weathering and plant nutrient utilization plays a significant role.

• Influential figure in this context: Hans Jenny (1899-1992).

Page 14: Nutrient Inputs Case Study in Hawaii

• Research conducted on Hawaiian islands (volcanic origins) aims to evaluate the impact of time on nutrient availability:

  • Controlled conditions for plant type, slope, and rainfall to study nutrient changes.

  • Findings indicate an increase in nitrogen over time due to fixation and recycling, while phosphorus initially rises after volcanic eruption but declines due to weathering.

Page 15: Nutrient Changes Over Time in Hawaiian Chronosequence

• Overview of changes in nutrient types and concentrations:

  • Dramatic shifts in extractable nutrients, cations, and foliar N & P concentrations.

• Figure summaries illustrate variations in plant-available nutrients across different substrate ages.