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Chapter 8 Plant Nutrient Use

Chapter 8 Plant Nutrient Use. Part II Mechanisms Chapin, Matson, Mooney Principles of Terrestrial Ecosystem Ecology. Belowground resources control GPP, NPP and decomposition What controls acquisition of belowground resources?. Nutrient supply is a critical control over NPP.

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Chapter 8 Plant Nutrient Use

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  1. Chapter 8Plant Nutrient Use Part II Mechanisms Chapin, Matson, Mooney Principles of Terrestrial Ecosystem Ecology Chap.8

  2. Belowground resources control GPP, NPP and decompositionWhat controls acquisition of belowground resources? Chap.8

  3. Nutrient supply is a critical control over NPP Chap.8

  4. Most nutrients absorbed by plants are recycled from detritus Chap.8

  5. How do nutrients get to roots? • 1. Diffusion (most important) • 2. Mass flow (sometimes important) • 3. Root interception (unimportant) Chap.8

  6. How do nutrients get to roots? 1. Diffusion • Driving forces • Nutrient uptake • Mineralization • Consequence • Diffusion shell • Zone of nutrient depletion around each root • Large for mobile ions Chap.8

  7. How do nutrients get to roots? 2. Mass flow • Nutrient movement in flowing water • Transpirational water • Gravitational water after rain • Insufficient for growth-limiting nutrients • Replenishes diffusion shells Chap.8

  8. Chap.8

  9. How do nutrients get to roots?3. Root interception • Concentration in root higher than soil it displaces • No-win situation • Unimportant Chap.8

  10. What controls nutrient absorption by roots? Chap.8

  11. Nutrient supply is THE major control over nutrient uptake Chap.8

  12. Root elongation is main way plants can increase nutrient uptake • Increased root:shoot ratio • Increased investment in roots • Root proliferation in nutrient hot spots • Root growth occurs where it does the most good • Longer root hairs Chap.8

  13. Mycorrhizae increase soil volume used by plants • Trade carbohydrates for nutrients • Balanced parasitism • Most advantageous for immobile nutrients • e.g., phosphate Chap.8

  14. Types of mycorrhizae • Ectomycorrhizae • Form sheath around root • Common in woody plants • Arbuscular mycorrhizae • Proliferate around root • Common in grasses, herbs, and tropical trees Chap.8

  15. Mechanisms of nutrient uptake • Active transport most important • Requires energy • Moves against concentration gradient • Abundant nutrients may enter by diffusion or mass flow Chap.8

  16. Chap.8

  17. Some plants tap nutrients unavailable to other plants High-latitude plants absorb amino acids Prefer ammonium over nitrate Take whatever they can get Chap.8

  18. Chap.8

  19. N availability in Alaskan boreal forests Chap.8

  20. Nitrogen uptake and use • Nitrate must be reduced to ammonium • Nitrate reduction often expensive • Ammonium must be assimilated • Attached to a carbon skeleton • Amino acids must be transported through plant • Used for protein synthesis Chap.8

  21. Tapping Phosphorus • Phosphatase enzymes • Cleaves P from SOM • Siderophores • Solubilize mineral P • Chelate-P complex diffuses to root Chap.8

  22. Plants compensate for specific nutrient stresses Chap.8

  23. Strong correlation between nutrient uptake and production Chap.8

  24. Chap.8

  25. Nutrient uptake correlates with growth • Sometimes nutrient uptake drives growth • Sometimes growth drives nutrient uptake Chap.8

  26. Nutrient uptake influences rhizosphere • Reduces nutrient concentrations • Enhances decomposition • Changes pH • Excretes H+ when absorb cations Chap.8

  27. Summary • Nutrient supply constrains uptake • Diffusion is main mechanism of supply • Plants adjust uptake rate to meet demands • Root growth • Uptake capacity • Mycorrhizae • Enhance supply Chap.8

  28. Nutrient ratios don’t vary too much • Means availability of growth-limiting nutrient governs uptake of all nutrients, BUT • Ratios are somewhat variable • Similarity of ratios reflects regulation of uptake • Differences among ratios reflects storage Chap.8

  29. Chap.8

  30. Nutrient use efficiency Chap.8

  31. Nutrient use efficiency (NUE)(two definitions) • Physiological approach (plant level) • NUE = a t • a = nutrient productivity (photosynthesis/g N) • t = residence time of nutrient in plant • Ecosystem approach (stand-level) • NUE = g biomass/g nutrient in litter Chap.8

  32. A long residence time is the major adaptation to low-nutrient Habitats Plants don’t increase their carbon gain per unit nutrient Chap.8

  33. All species are similar in resorption efficiency No major difference in proportion of nutrients lost Chap.8

  34. All species are similar in the proportion of nutrients leached Chap.8

  35. Chap.8

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