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CHAPTER 37
PLANT NUTRITION
OUTLINE
I. NUTRITIONAL REQUIREMENTS OF PLANTS
A. THE CHEMICAL COMPOSITION OF PLANTS PROVIDES CLUES TO NUTRITIONAL REQUIREMENTS
 PLANTS DERIVE MOST OF ORGANIC MASS FROM THE C02 OF AIR, BUT THEY ALSO DEPEND ON
SOIL NUTRIENTS IN THE FORM OF WATER AND MINERALS.
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B. PLANTS REQUIRE NINE MACRONUTRIENTS AND AT LEAST EIGHT MICRONUTRIENTS
 MACRONUTRIENTS INCLUDE C, H, 0, N, AND OTHER MAJOR INGREDIENTS OF ORGANIC
COMPOUNDS.
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MANY MICRONUTRIENTS HAVE CATALYTIC FUNCTIONS AS COFACTORS OF ENZVMES.
C. THE SYMPTOMS OF MINERAL DEFICIENCY DEPEND ON THE FUNCTION AND MOBILITY OF THE
ELEMENT
 DEFICIENCY OF A MOBILE NUTRIENT USUALLY AFFECTS OLDER ORGANS MORE THAN
YOUNGER ONES.
 THE REVERSE IS TRUE FOR NUTRIENTS THAT ARE LESS MOBILE WITHIN A PLANT.
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II. SOIL
A. SOIL CHARACTERISTICS ARE KEY ENVIRONMENTAL FACTORS OF TERRESTRIAL ECOSYSTEMS
 VARIOUS SIZES OF PARTICLES DERIVED FROM THE BREAKDOWN OF ROCK ARE FOUND IN SOIL,
ALONG ORGANIC MATERIAL (HUMUS) IN VARIOUS STAGES OF DECOMPOSITION.
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ACIDS DERIVED FROM ROOTS CONTRIBUTE TO PLANTS' UPTAKE OF MINERALS WHEN H+ DISPLACES MINERAL
CATIONS FROM CLAY PARTICLES.
B. SOIL CONSERVATION IS ONE STEP TOWARD SUSTAINABLE AGRICULTURE
 IN CONTRAST TO NATURAL ECOSYSTEMS, AGRICULTURE DEPLETES THE MINERAL CONTENT OF
SOIL, TAXES WATER RESERVES, AND ENCOURAGES EROSION.
 THE GOAL OF SOIL CONSERVATION STRATEGIES IS TO MINIMIZE THIS DAMAGE.
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III. THE SPECIAL CASE OF NITROGEN AS A PLANT NUTRIENT
A. THE METABOLISM OF SOIL BACTERIA MAKES NITROGEN AVAILABLE TO PLANTS
 NITROGEN-FIXING BACTERIA CONVERT ATMOSPHERIC N2 TO NITROGENOUS MINERALS THAT
PLANTS CAN ABSORB AS A NITROGEN SOURCE FOR ORGANIC SYNTHESIS.
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B. IMPROVING THE PROTEIN YIELD OF CROPS IS A MAJOR GOAL OF AGRICULTURAL RESEARCH
 SUCH RESEARCH ADDRESSES THE MOST WIDESPREAD FORM OF HUMAN MALNUTRITION:
PROTEIN DEFICIENCY.
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IV. NUTRITIONAL ADAPTATIONS: SYMBIOSIS OF PLANTS AND SOIL MICROBES
A. SYMBIOTIC NITROGEN FIXATION RESULTS FROM INTRICATE INTERACTIONS BETWEEN ROOTS
AND BACTERIA
 THE DEVELOPMENT OF NITROGEN-FIXING ROOT NODULES DEPENDS ON CHEMICAL CROSSTALK BETWEEN RHIZOBIUM BACTERIA AND ROOT CELLS OF THEIR SPECIFIC PLANT HOSTS.
 THE BACTERIA OF A NODULE OBTAIN SUGAR FROM THE PLANT AND SUPPLY THE PLANT WITH
FIXED NITROGEN.
B. MYCORRHIZAE ARE SYMBIOTIC ASSOCIATIONS OF ROOTS AND FUNGI THAT ENHANCE PLANT
NUTRITION
 THE FUNGAL HYPHAE OF BOTH ECTOMYCORRHIZAE AND ENDONRYCORRHIZAE ABSORB
WATER AND MINERALS, WHICH THEY SUPPLY TO THEIR PLANT HOSTS.
C. MYCORRHIZAE AND ROOT NODULES MAY HAVE AN EVOLUTIONARY RELATIONSHIP
 THERE IS EVIDENCE THAT ROOT NODULE DEVELOPMENT DEPENDS ON MOLECULAR
MECHANISMS OF SIGNALING AND ROOT-CELL RESPONSES THAT EVOLVED FIRST IN
MYCORRHIZAE.
V. NUTRITIONAL ADAPTATIONS: PARASITISM AND PREDATION BY PLANTS
A. PARASITIC PLANTS EXTRACT NUTRIENTS FROM OTHER PLANTS
 THEY DO SO EITHER DIRECTLY BY TAPPING INTO THE HOST'S VASCULAR TISSUE OR INDIRECTLY
VIA MYCORRHIZAE.
B. CARNIVOROUS PLANTS SUPPLEMENT THEIR MINERAL NUTRITION BY PREYING ON ANIMALS
 THIS PREDATION IS MOST COMMON IN ECOSYSTEMS WITH NUTRIENT-POOR SOIL.