Effects of plant morphology on root–soil hydraulic interactions of Schefflera heptaphylla

Abstract

Root water uptake induces additional soil suction by soil water extraction. However, induced soil suction restricts root water uptake when beyond a threshold (st) and tends to stop water uptake at a limiting suction (sl). This process is called root–soil hydraulic interactions, whose relationship with plant morphology (e.g., plant height, leaf area, and root length) is unclear. This study aims to investigate the effects of plant morphology on response of the sink term (water uptake intensity; WUI) to soil suction for Schefflera heptaphylla. Laboratory tests were conducted on 26 individuals in five different height groups. A new empirical model was derived to consider effects of plant morphology on root water uptake distribution in the full soil suction range. The locations of maximum root length density (RLD) and WUI for taller individuals were relatively deeper and farther from centreline. Before soil suction reached st, water uptake length ability (WULA) remained at a maximum level, positively related to LR ratio (ratio between leaf area, LA, and root length, RL), but less affected by plant height. For taller plants, the decreasing rate of st with LR ratio was larger, while the decreasing rate of WULA with soil suction beyond st appeared smaller. sl appeared independent of height, LA, and RL.