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Phosphorus : High demand – because … Supply relatively low … Available forms derived 1° from apatite

Phosphorus : High demand – because … Supply relatively low … Available forms derived 1° from apatite Ca 5 (PO 4 ) 3 (F,Cl,OH) = Calcium (Fluoro,Chloro,Hydroxyl) Phosphate Availability pH dependent – highest at pH range of 6-7 (per text). See also Brady&Weil: Fig 14.16).

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Phosphorus : High demand – because … Supply relatively low … Available forms derived 1° from apatite

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  1. Phosphorus: • High demand – because … • Supply relatively low … • Available forms derived 1° from apatite • Ca5(PO4)3(F,Cl,OH) = Calcium (Fluoro,Chloro,Hydroxyl) Phosphate • Availability pH dependent – highest at pH range of 6-7(per text) See also Brady&Weil: Fig 14.16)

  2. “Old”, wet systems – tropics • Also some aquatic systems Phosphorus: • Limits primary (plant) production – where less limiting? … why there? … • High P content geology • Arid systems • What kind of ecosystems expect P limitation? …

  3. weathered mineral P (total potentially available P) Soil P [concentration] Development of P limitation occluded P soluble P organic P Time (”geologic” scale) (after Walker and Syers 1976) • P: • Changes in soil P availability with time: …

  4. Plant Adaptations to low nutrient supply Roots of alpine plants - exposed by erosion • A. Biomass allocation • Greater allocation to roots over shoots …

  5. zone of high soil resource availability } • “Proteoid” or Cluster Roots •  P capture • Rootlets produce organic acids, chelating agents • Proteaceae, … • B. Root proliferation • High number of fine roots in fertile soil patches – Especially for less mobile resources

  6. C. Root uptake kinetics – Biochemical capacity to take up nutrients • Greater production of nutrient carriers on surface of roots (cost?) • Benefit varies depending on the mobility of the nutrient … •  best for highly mobile elements (e.g. NO3– ) more readily diffuse in soil water •  On other hand, increased root allocation[last slide] better for less mobile (e.g. P) • D. Low growth rates, small size • Reduce nutrient demand by growing at a slow rate • Potential tradeoffs?… • lower competitive ability

  7. Nutrient addition experiments +P +N control + N & P Nutrient Limitation • Plants require same elements in roughly same proportions • – Some variation by plant type & environment • How determine what’s limiting? • Liebig’s Law of the Minimum Niwot Ridge LTER – alpine tundra

  8. Forb (dicot herbs) Graminoid (grasses and sedges) (dominant sedge) Kobresia 400 ) -2 300 Aboveground 200 Biomass (g m 100 0 Control P N N+P Example of results: • What is your interpretation of the results?? • Physiological compensation • Differing species response • Competitive exclusion

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