Technique for ecological studies of seed germination in relation to soil water potential

Summary Seeds were germinated in soils of known matric potential (ψ_m) achieved by adding the requisite amount of water to air-dry soil and mixing for several days. The quantity of water was derived from calibration curves of water content against ψ_m by use of pressureplate extraction equipment. Soils were transferred to plastic Petri dishes in which seeds were sown. Variations of the technique permitted germination counting through the transparent dish lid, or by opening the dish and either resealing or discarding the replicate dish. Measurements of ethylene and carbon dioxide in the soil atmosphere suggest that neither gas accumulated to a level which could interfere with interpretation of results. Some species showed sensitivity of germination to water potential which was correlated with the relative wetness of their habitats.