Plant Nutrition and Soils Soil o Highly weathered outer layer of earth s crust Soil sand rocks clay silt humus mineral and organic matter o 92 natural elements most in minerals microorganisms o most roots in topsoil mineral particles of varying sizes relative amounts of sand silt clay soil decomposition determines degree of water and nutrient binding to soil particles o only minerals dissolved in water spaces are available for uptake o membrane potential maintained by root and water potential difference inside and outside root o negative ions outside the root pull positive ions outside of the root cells active transport required to acquire and maintain positive ions in root o soil volume is pores some water is unavailable because it drains because of gravity Soil Loss o If topsoil is lost soil can t hold as much water o Drought and poor farming led to wind erosion in 1930s and great plains became dust bowl o Preventing erosion Intercropping mixing crops in fields Conservation tillage minimal or no till approaches o Measures to prevent fertilizer runoff Site specific farming Integrated nutrient management Acidic and Saline Soils o Acidic soils release minerals that are toxic o Saline soils alter water potential leading to loss Plant Nutrients o Photosynthesis is a major source of nutrition fixation o Macronutrients C O H N K Ca Mg P S o Micronutrients Cl Fe Mn Zn B Cu Mo o Deficiency of any can have severe effects on growth o Growing in hydroponic culture to assess nutritional requirement Seedling grown in complete nutrient Seedling transplanted to lacking one essential ingredient Growth is monitored for abnormal symptoms Hydroponic cultures plant roots are suspended in aerated water containing nutrients o Food security and avoiding starvation Food fortification Increasing mineral uptake and storage GMs Special Nutrient Strategies o Plants need ammonia or nitrate to build proteins but lack chemical pathways for N2 and NH3 o Symbiotic relationships have evolved between plants and nitrogen fixing bacteria Legumes form nodules that house Rhizobium Require oxygen and carbs to support nitrogen fixer life o Symbiotic associations with mycorrhizal fungi found in 90 vascular plants Expand surface area and enhance uptake of phosphorus and micronutrients Carnivorous Plants o Acidic soils that lack nitrogen o Trap and digest small animals o Modified leaves for trapping prey Digestion with enzymes secreted from specialized glands Pitcher plants pitcher shaped leaves with digestive juices Venus flytrap hairs sense and leaves snap together Sundews glands secrete mucilage and digestive enzymes Waterwheel trigger hairs and snaps to capture small aquatic animals Snap trap mechanism was acquired by common ancestor of venus flytrap and water wheel pitcher plants aren t related to clade Parasitic Plants o 3 000 types o wrapping around host hooking onto host trees through mycorrhizae Carbon Nitrogen Balance o IPCC concluded that CO2 is at highest in 20 million years o CO2 levels can alter C N ratio in plants o Calvin cycle fixes CO2 into sugar o C2 photosynthesis in mesophyll o C4 photosynthesis shuttles carbon into leaf reducing photorespiration limiting calvin cycle o CO2 increases calvin cycle becomes more efficient Lead to increased growth Plants with less nitrogen and minerals increases C N ration Lower nutritional value for herbivores o Free Air CO2 Enrichment studies Rings of tower release CO2 towards center so studies can be conduced at ecosystem level CO2 increases slightly less N and macronutrients found in leaves Herbivores eat more biomass Phytoremediation o Plants to concentrate or breakdown pollutants o Phytodegredation contaminant broken down o Phytovolitization contaminant take up and released through stomata o Phytoaccumulation contaminant take up and concentrated in shoots and harvested o TCE removed from soil by poplar trees degraded into CO2 and chlorine Some moves through xylem and released through stomata o TNT removed from soil and degraded by poplar and bean plants Toxic at high concentration o Heavy metals are toxic to animals in small quantities 400 plant species can accumulate toxic metals from soil animals eating these plants could expose them to toxic compounds in high concentrations o costs are 50 80 cheaper than cleanup methods o 1998 Aznalcollar mine in Spain removed mechanically at first plants species accumulated metals later