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Stomatal conductance (SC) and chlorophyll concentration (CC) are sensitive to soil matric suction (ψ). The relationship between these two plant parameters and ψ in the root zone can help understand the water uptake efficiency and photosynthetic capacity of a plant. This paper aims to quantify the relationships between SC and CC with ψ, for Schefflera arboricola grown in compacted bare silty sand and biochar amended soil (BAS). Plant parameters (SC, CC, leaf area (LA), root length (RL)) and ψ were regularly monitored in an atmospheric controlled room. The maximum recorded SC was greater in BAS than that in bare soil due to the higher water demand of LA. Based on measured data upon evapotranspiration, two equations are proposed to interpret the effects of ψ on plant water uptake and photosynthesis. A fitting equation is established to relate normalized SC with ψ to identify a threshold suction ([Formula: see text]; indicator of drought stress resistance). The magnitude of [Formula: see text] is found to be mainly dependent on LA/RL ratio and root ends. Furthermore, a new relationship between CC and ψ is observed and developed. A decrease in CC at higher ψ is attributed to leaf senescence and stomatal closure, restricting plant to produce more chlorophyll.