Effects of Substrate Volumetric Water Content on English Lavender Morphology and Photosynthesis

There is currently little information regarding the impact of soil moisture on morphology and physiology of English lavender ( Lavandula angustifolia ). Therefore, our goal was to determine the impact of substrate volumetric water content ( θ = volume of water ÷ volume of substrate) on this plant. We grew ‘Munstead’ and ‘Hidcote’ lavender at one of four θ: 0.1, 0.2, 0.3, or 0.4 L·L −1 for 54 days using a capacitance sensor-automated irrigation system. Plant height, greatest width, inflorescence number, and total leaf number and area of both cultivars increased with increasing θ. Shoot fresh and dry weight of lavender irrigated at θ ≥ 0.3 L·L −1 was generally twice that of those grown at the lowest θ (0.1 L·L −1 ). Leaf-level instantaneous net photosynthetic rate (A N ) and transpiration (E) of ‘Munstead’ decreased with decreasing θ. This reduction in A N was likely due to the concurrent reduction in stomatal conductance ( g S ) at lower θ. Similar reductions in A N , E, and g S of ‘Hidcote’ were observed at lower θ (0.2 and 0.3 L·L −1 ) 5 weeks after the initiation of the study, but not at the end of the study probably due to acclimation of ‘Hidcote’ to mild drought.