干旱区生态环境知识资源中心

Hydrothermal time models are often used to predict seed germination rates. In this study, soil water potential data from three resistance-type sensors (Colman cells, Watermark brand sensors, and Delmhorst gypsum blocks) and from a time-domain reflectometry (TDR) probe (Campbell Scientific 615) were input into a hydrothermal time model to predict seedling emergence in a growth chamber experiment for six desert grass species, including Brachypodium distachyon, Bromus fasciculatus, Crithopsis delilianus, and Stipa capensis from the Negev Desert, and naturalized downy brome (Bromus tectorum) and bottlebrush squirreltail (Elymus elymoides) from the Great Basin Desert. Seeds were sown in a structureless sandy loam soil that was irrigated approximating 0.58, 1.25, 1.50, and 2.00 times field capacity volumetric water content and allowed to dry in a growth chamber programmed to simulate spring temperatures in Provo, UT. Colman cells and Delmhorst gypsum blocks indicated more rapid soil surface drying than did Watermark sensors and TDR probes. Inputs provided by the sensors correctly predicted seedling emergence of these rapidly germinating grasses when water potential was high, but incorrectly predicted emergence when rapidly decreasing water potentials inhibited emergence. These results suggest that more accurate measurement or prediction of seed zone water potentials may be necessary before hydrothermal time models can effectively predict seedling emergence in the field.