| A | B |
|---|
| bacteroids | form of Rhizobium contained within the vesicles formed by the root cells of a root nodule |
| cation exchange | positively charged minerals enter a plant when hydrogen ions in the soil the mineral ions from clay particles |
| crop rotation | planting a nonlegume one year and a legume the next year to restore concentration of fixed nitrogen |
| ectomycorrhizae | mycelium forms a dense sheath |
| endomycorrhizae | microscopic fungal hyphae extend from the root into the soil |
| epiphyte | nourishes itself but grows on the surface of another plant for support |
| essential element | required for the plant to grow from a seed and complete the life cycle |
| haustorium | specialized hyphae that can penetrate the tissues of host organisms |
| horizon | distinct layer of soil |
| humus | decomposing organic material found in topsoil |
| inflorescence | group of flower tightly clustered together |
| loam | most fertile of all soils made up of roughly equal amounts of sand silt and clay |
| macronutrient | chemical substance that an organism must obtain in relatively large amounts |
| micronutrient | element that an organism needs in very small amounts |
| mineral nutrient | chemical element absorbed from the soil in the form of inorganic ions |
| mycorrhizae | mutualistic associations of plant roots and fungi |
| nitrogen fixation | assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous compounds usable by plants |
| nitrogenase | enzyme complex unique to certain prokaryotes that reduces N2 to NH3 |
| nitrogen-fixing bacteria | microorganisms that restock nitrogenous minerals in the soil by converting nitrogen to ammonia |
| nodule | swelling on the root of a legume |
| phytoremediation | use of some plant species to extract heavy metals and other pollutants from the soil |
| sustainable agriculture | long-term productive farming methods that are environmentally safe |
| topsoil | mixture of particles derived from rock |
