Chapter 29: Resource Acquisition, Nutrition, & Transport in Vascular Plants

Plants simultaneously function in aerial and belowground domains, with shoots capturing light and carbon dioxide while roots absorb water and mineral nutrients from soil. Structural adaptations reflect these constraints: broad leaves optimize photosynthesis while branching patterns reduce self-shading, root systems extend selectively toward nutrient-rich zones, and mycorrhizal associations dramatically enhance mineral acquisition. At the cellular level, plants manipulate solute concentrations and membrane permeability to control water movement according to water potential gradients. The three transport pathways—apoplastic movement through cell walls, symplastic flow through plasmodesmata, and transmembrane crossing via aquaporins—work in concert to move substances throughout tissues. Long-distance transport relies on fundamentally different mechanisms: xylem sap rises through the cohesion-tension framework generated by transpirational water loss in leaves, while phloem distributes photosynthetic sugars via pressure flow established by active loading in companion cells. Plants require seventeen essential elements categorized as macronutrients and micronutrients, with deficiency symptoms indicating which tissues mobilize nutrients. Soil chemistry, microbial communities, and management practices critically influence nutrient availability and plant performance. Nitrogen acquisition frequently depends on symbiotic relationships: rhizobia bacteria fix atmospheric nitrogen within root nodules of legumes, while mycorrhizal fungi exchange absorbed minerals for plant-derived carbohydrates. Alternative nutritional strategies—including parasitism, carnivory, and epiphytism—emerge when conventional nutrient sources become limiting. Stomatal regulation coordinates water conservation with photosynthetic demand through guard cell responses to light, carbon dioxide concentration, circadian signals, and stress hormone abscisic acid. Xerophytes exemplify extreme adaptations to arid environments through mechanisms like CAM metabolism, reduced leaf surface areas, and enhanced cuticle thickness. Source-sink relationships dynamically shift throughout the growing season as organs transition between roles in sugar production and accumulation, demonstrating the remarkable flexibility underlying plant resource management across diverse ecological contexts.