CHAPTER 37 PLANT NUTRITION

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

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 NITROGEN-FIXING 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