Effects of drought and root injury on plant-generated CS₂ emissions in soil

Abstract

Conditions under which some plants emit carbon disulfide (CS₂) in the soil are unknown. A pot assembly was constructed to measure soil CS₂ emissions by Mimosa pudica under conditions of undisturbed growth, root injury, and drought stress. When M. pudica was grown without disturbance, soil CS₂ emissions were below the limit of detection (≤0.1 ng CS₂ mL⁻¹) for the entire 8-wk sampling period. However, when the roots of 6-wk-old M. pudica plants were cut to a depth of 10 cm, a maximum of 0.5 and 0.4 ng CS₂ mL⁻¹ was emitted within minutes at the 5- and 10-cm depths, respectively. These emissions declined slowly to undetectable levels after 50 min. No detectable CS₂ emissions were observed at the 0- and 15-cm depths. No CS₂ was emitted when 6-wk-old M. pudica plants were subjected to drought stress, however, when the same plants were watered, a maximum of 0.3, 0.4, and 0.5 ng CS₂ mL⁻¹ was emitted within minutes at the 5-, 10- and 15-cm depths, respectively. These emissions were detectable for at least 2 hr at the 10- and 15-cm depths. No detectable CS₂ emissions were observed at the 0-cm depth after watering. No detectable CS₂ emissions were observed at any depth under any conditions of undisturbed growth, root injury, or drought stress followed by watering for assemblies containing either no plants or Albizia julibrissin, a plant that is closely related to M. pudica but does not emit CS₂. Mimosa pudica emitted detectable CS₂ under conditions of root injury and rewetting of dry soil but not under conditions of undisturbed growth. Release of such a biocidal sulfide only during conditions of root injury or rewetting of dry soil would be advantageous to M. pudica.