Chapter 13: Assimilation of Inorganic Nutrients

The fundamental driving force behind this transport system is transpiration, which creates negative pressure gradients that pull water upward through interconnected xylem conduits. The cohesion-tension theory serves as the primary explanatory model, demonstrating how hydrogen bonds between water molecules and adhesive forces between water and xylem walls enable continuous water columns to withstand enormous tensional forces during ascent. The chapter examines the specialized anatomy of xylem tissue, including tracheids and vessel elements with their perforation plates and bordered pits, which facilitate efficient long-distance transport while maintaining structural integrity. Environmental factors such as humidity, temperature, and light intensity significantly influence transpiration rates, while stomatal regulation provides plants with mechanisms to control water loss and maintain optimal water balance. The discussion includes critical challenges to xylem function, particularly cavitation and embolism formation, where gas bubbles disrupt water continuity, and explores various repair mechanisms plants have evolved to restore hydraulic function. Root pressure contributes to water movement under specific conditions, particularly when transpiration rates are low, creating positive pressure that aids in water ascent. The integration of hydraulic conductivity and resistance patterns throughout the plant body reveals how developmental changes, species-specific adaptations, and environmental stresses influence overall transport efficiency and plant survival strategies.