Download the nitrogen cycle

NUTRITIONAL REQUIREMENTS
• PLANTS REQUIRE 9 MACRONUTRIENTS
AND AT LEAST 8 MICRONUTRIENTS
• AN ESSENTIAL NUTRIENT IS ONE THAT IS
REQUIRED FOR A PLANT TO GROW FROM
A SEED AND COMPLETE ITS LIFE CYCLE
• MACRONUTRIENTS-REQUIRED BY
PLANTS IN LARGE AMOUNTS
• MICRONUTRIENTS-REQUIRED IN SMALL
AMOUNTS
THE UPTAKE OF NUTREINTS BY A PLANT
VIDEO: MINERALS IN PLANTS
QuickTime™ and a Cinepak decompressor are needed to see this picture.
MINERAL DEFICIENCIES
• SYMPTOMS OF MINERAL DEFICIENCIES
DEPEND ON:
– 1) THE ROLE OF THE NUTREINT IN THE PLANT
– 2) ITS MOBILITY WITHIN THE PLANT
• DEFICIENCIES OF NUTREINTS MOBILIE IN THE
PLANT APPEAR IN OLDER ORGANS FIRST SINCE
SOME ARE PREFERENTIALLY SHUNTED TO
GROWING PARTS
• DEFICIENCIES OF N, K. AND P ARE THE MOST
COMMON
SOIL
• SOIL CHARACTERISTICS ARE KEY
ENVIRONMENTAL FACTORS IN
TERRESTRIAL ECOSYSTEMS
• PLANTS GROWING IN AN AREA ARE
ADAPTED TO THE TEXTURE AND
CHEMICAL COMPOSITION OF THE SOIL
SOIL TEXTURE AND
COMPOSITION
• SOIL IS PRODUCED BY THE WEATHERING OF
SOLID ROCK.
• HORIZONS = DISTINCT SOIL LAYERS
• TOPSOIL = MIXTURE OF DECOMPOSED ROCK
OF VARYING TEXTURE, LIVING ORGANISMS,
AND HUMUS (DECOMPOSING ORGANIC
MATERIAL)
• THE TEXTURE OF A TOPSOIL DEPENDS ON
PARTICLE SIZE
• THE MOST FERTILE SOILS ARE LOAMS, A
MIXTURE OF SAND, SILT, AND CLAY
HUMUS
• HUMUS
– PREVENTS CLAY FROM PACKING
TOGETHER
– BUILDS A CRUMBLY SOIL THAT RETAINS
WATER BUT IS STILL POROUS FOR GOOD
ROOT AERATION
– ACTS AS A RESERVOIR OF MINERAL
NUTRIENTS
SOIL WATER AVAILABILITY
• SOME WATER IS BOUND SO TIGHTLY TO
HYDROPHILIC SOIL THAT IT CANNOT BE
EXTRACTED BY PLANTS
• WAER BOUND LESS TIGHTLY IS GENERALLY
AVAILABLE TO THE PLANT AS A SOIL
SOLUTION CONTAINING MINERALS. THIS
SOLUTION IS ABSORBED INTO THE ROOT
HAIRS AND PASSES VIA THE APOPLAST TO THE
ENDODERMIS
• POSITIVELY CHARGED MINERALS (K+, Ca+,
Mg+) ADHERE BY ELECTRICAL ATTRACTION TO
NEGATIVELY CHARGED CLAY PARTICLES
– CLAY PROVIDES MUCH S.A. FOR BINDING
– PREVENTS LEACHING OF MINERAL NUTRIENTS
CATION EXCHANGE
• CATION EXCHANGE = H IONS IN SOIL
DISPLACE POSITIVELY CHARGE MINERAL
IONS FROM CLAY, MAKING THEM
AVAILABLE TO PLANTS
– STIMULATED BY ROOTS WHICH RELEASE
ACIDS TO ADD H+ TO THE SOIL SOLUTION
• NEGATIVELY CHARGED MINERALS (NO3-,
H2PO4-, SO4-) ARE NOT TIGHTLY BOUND TO
SOIL PARTICLES
– TEND TO LEACH AWAY MORE QUICKLY
SOIL NUTRIENTS
SOIL CONSERVATION
• 3 IMPORTANT ASPECTS OF SOIL
MANAGEMENT:
– FERTILIZERS
– IRRIGATION
– EROSION PREVENTION
NITROGEN
• THE METABOLISM OF SOIL BACTERIA
MAKES NITROGEN AVAILABLE TO
PLANTS
– PLANTS CAN NOT USE NITROGEN IN
GASEOUS FORM (N2)
– TO BE USED BY PLANTS, NITROGEN MUST
BE IN THE FORM OF AMMONIUM (NH4+) OR
NITRATE (NO3-)
THE NITROGEN CYCLE
• OVER THE SHORT TERM, THE MAIN SOURCE OF
NITROGENOUS MINERALS IS THE
DECOMPOSITION OF HUMUS BY
MICROBES(AMMONIFYING BACTERIA)
– NITROGEN IN ORGANIC COMPOUNDS IS
REPACKAGED INTO INORGANIC COMPOUNDS THAT
CAN BE ABSORBED AS MINERALS BY ROOTS
– NITROGEN IS LOST FROM THIS CYCLE WHEN SOIL
DENITRIFYING BACTERIA CONVERT NO3- TO N2,
WHICH DIFFUSES FROM THE SOIL TO THE
ATMOSPHERE
– NITROGEN-FIXING BACTERIA RESTOCK
NITROGENOUS MINERALS IN THE SOIL BY
CONVERTING N2 TO NH3 (AMMONIA)
BACTERIA IN THE NITROGEN CYCLE
NITROGEN FIXATION
• NITROGEN FIXATION IS THE PROCESS OF
CONVERTING ATMOSPHERIC NITROGEN
(GASEOUS STATE) TO NITROGENOUS
COMPOUNDS THAT CAN BE DIRECTLY
USED BY PLANTS (NITRATE OR
AMMONIA)
• THE PROCESS IS CATALYZED BY THE
ENZYME NITROGENASE
• SOME SOIL BACTERIA POSSESS
NITROGENASE
NUTRITIONAL ADAPTATIONS
• SYMBIOTIC NITROGEN FIXATION RESULTS
FROM INTRICATE INTERACTIOINS BETWEEN
ROOTS AND BACTERIA
– LEGUMES HAVE A BUILT-IN SOURCE OF FIXED
NITROGEN BECAUSE THEY POSSESS ROOT
NODULES
• NODULES= ROOT SWELLINGS COMPOSED OF
PLANT CELLS THAT CONTAIN NITROGENFIXING BACTERIA
• AS NODULE GROW, THEY FORM A
CONNECTION WITH THE XYLEM AND PHLOEM
-THIS ASSOCIATION IS MUTUALISTIC; THE
BACTERIA SUPPLIES FIXED NITROGEN, AND
THE PLANT SUPPLIES CARBOHYDRATES AND
OTHER ORGANIC COMPOUNDS
DEVELOPMENT OF A SOYBEAN ROOT NODULE
CROP ROTATION
• THE BASIS FOR CROP ROTATION IS THAT,
UNDER FAVORABLE CONDITIONS, ROOT
NODULES FIX MORE NITROGEN THAN THE
LEGUME USES. THE EXCESS IS SECRETED AS
AMMONIUM INTO THE SOIL
– ONE YEAR A NONLEGUME CROP IS PLANTED, AND
THE NEXT YEAR A LEGUME IS PLANTED TO
RESTORE THE FIXED NITROGEN CONTENT OF THE
SOIL
– LEGUMES MAY BE PLOWED UNDER TO FURTHER
INCREASE THE FIXED NITROGEN CONTENT OF THE
SOIL
ROOT NODULE FORMATION
• CHEMICAL SIGNALS BETWEEN PLANT ROOTS
AND BACTERIA DIRECT THEIR ASSOCIATION
AND THE FORMATION OF NODULES
• THE SPECIFICITY OF THE INTERACTION
BETWEEN A PLANT AND A PARTICULAR
BACTERIAL SPECIES IN THE SOIL RESULTS
FROM THE UNIQUE CHEMICAL STRUCTURE OF
THE SIGNAL MOLECULES
– THE INITIAL SIGNAL MOLECULE IS PRODUCED BY
THE PLANT
– IN RESPONSE TO THE PLANT SIGNAL, BACTERIA
PRODUCE AN “ANSWERING” SIGNAL
– THE SIGNALS ALTER GENE EXPRESSION IN CELL OF
THE RECIPIENT THAT RESULTS IN THE PRODUCTION
OF ENZYMES AND OTHER SIGNAL MOLECULES
NODULE FORMATION
MYCORRHIZAE
• MYCORRHIZAE ARE SYMBIOTIC ASSOCIATIONS
(MUTUALISTIC) BETWEEN PLANT ROOTS AND
FUNGI; THE FUNGUS EITHER FORMS A SHEATH
AROUND THE ROOT OR PENETRATES ROOT
TISSUE
– HELP THE PLANT ABSORB WATER
– ABSORB MINERALS, AND MAY SECRETE ACID THAT
INCREASES MINERAL SOLUBILITY AND CONVERTS
MINERALS TO FORMS EASILY USED BY THE PLANT
– MAY HELP PROTECT THE PLANT AGAINST CERTAIN
SOIL PATHOGENS
– THE PLANT NOURISHES THE FUNGUS WITH
PHOTOSYNTHETIC PRODUCTS
2 MAIN TYPES OF
MYCORRHIZAE
• ECTOMYCORRHIZAE- the mycelium forms a sheath
over the root, but does not penetrate it
• ENDOMYCORHIZAE - do not form a sheath
surrounding the root and hyphae extend into root cell
walls (but do not penetrate plasma membrane)
– More common than ectomycorrhizae, found in over 90% of
plant species, including crop plants
**MYCORRIHIZAE AND ROOT NODULES MAY HAVE
AN EVOLUTIONARY RELATIONSHIP
-the same plant genes that are activated in the early stages of
nodule formation are the same genes activated during the
early development of endomycorrhizae
PARASITISM AND
PREDATION BY PLANTS
• PARASITIC PLANTS EXTRACT NUTRIENTS
FROM OTHER PLANTS
– Some obtain xylem sap from their host plant (mistletoe)
EPIPHYTES-GROW ON THE SURFACE OF OTHER PLANTS,
ANCHORED BY ROOTS, BUT ARE NOT PARASITIC
-NOURISH THEMSELVES FROM THE WATER AND
MINERALS ABSORBED FROM RAIN (EX: SPANISH
MOSS AND STAGHORN FERNS)
CARNIVOROUS PLANTS
-LIVE IN HABITATS WITH POOR SOIL
-ARE PHOTOSYNTHETIC, BUT OBTAIN SOME
NITROGEN AND MINERALS BY KILLING AND
DIGESTING INSECTS