Lecture 20 - BIO220

2008 how does human growth compare against the

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Unformatted text preview: alive, it was not all positive: -It allowed for the creation of bombs and explosive - propagating war and terror 12 Figure 1, Erisman et al. 2008 -How does human growth compare against the ability to convert N2 -> NH3? -50% of the world popln is sur viving today based on the ability to m ake N fertilizer 3 3/25/2013 The “Green Revolution” Technology evading previous limitations • Industrial chemistry makes fertilizer cheaper • Use conventional plant breeding techniques (artificial selection and hybridization) to evolve high yielding dwarf crop varieties (HYV) • What about limitations of the crops themselves? • • Irrigation brings water to dry areas • Fertilizer brings nutrients to poor soils • Life history theory: Recall that plants allocate resources to growth, competition, defense, reproduction, dispersal 13 E.g., IR8 rice at least tripled seed yield/area Norman Borlaug (1914-2009), Nobel Peace Prize (1970) • Introduce high intensity cultivation techniques Working in Mexico in 1950s, brought to India in 1961 because famines were considered imminent 14 -Plants lost the ability to sense the closeness of their neighbours, therefore they stayed short -If they can sense their neighbours, they grow taller to compete f or light -You also cannot plant them close together if they retain this s ensing ability -Without this ability, you can plant MORE plants per square metre -Increases in seed yield per area ! Why Ehrlich’s predictions didn’t come true, and Borlaug got the Nobel Plant allocations favoured in nature Changes under modern agriculture Now, hope for further improvements lies mostly with “genetically modified organisms” (GMOs) 15 -Resource growth must continue to grow exponentially (just like the h uman population is), or else….. -Resources per capita will decrease (How are we going to feed all these p eople)? • Less needed, competition prevented by mechanized cultivation & herbicides; other selection reduced • Extensive roots to capture scarce water & nutrients • Less needed, supplied by irrigation & fertilizer • Make physical and chemical defenses against herbivores and fungi But note the leveling off since the mid-1990s • Grow tall to compete for light & enhance pollination & seed dispersal • Less needed, protection conferred by insecticides & fungicides All these resources can be reallocated to seed production 16 -There is just no need for a modern plant to allocate all of these...
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This document was uploaded on 01/27/2014.

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