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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