Volatile losses of sulfur by intact alfalfa plants

An apparatus was developed for the quantitative collection of volatile sulfur compounds released by intact plants and was used to study the effects of leaf temperature and stomatal aperture on the amount and pattern of release. An air stream sweeps volatiles released by the plants through a water‐cooled condenser system in which the air is dried prior to trapping the volatile sulfur compounds on activated carbon. Tests with 35S‐labelled 1‐butanethiol gave a mean recovery of 95.8 ± 4.3%. The yield of volatile sulfur compounds increased greatly when air flow rate increased from 1 to 2 1 min‐1 , but was independent of flow rate over the range 2 to 6 1 min‐1. About 93% of the trapped activity originated from plant shoots, about 1% from stem bases and roots and about 4% from culture solutions. Release of volatile sulfur compounds from intact plants followed a diurnal pattern, maximum rates occurring around midday and minimum rates overnight. Maximum rates of release ranged from 30 to 41 ng S g dry weight of shoots‐1 2 hr ‐1, while minimum rates ranged from 1.5 to 2.1 ng S g dry weight of shoots‐1 2hr‐1. Leaf temperature rather than stomatal aperture seemed to be the major factor controlling rate of release of volatile sulfur compounds. The rate of release was almost doubled by an increase of 7–9°C in leaf temperature.