PARENT SESSION
Oral Session #19: Plant Competition. Presiding: N. Slade.
Monday, August 6, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.

Plant growth-form effects on the spatial and temporal heterogeneity of soil moisture.

McLaren, Jennie¹, Wilson, Scott¹, Peltzer, Duane¹, ¹

ABSTRACT- There is increasing evidence that plants differ in their responses to heterogeneity but little evidence that they differ in their ability to create soil heterogeneity. We examined the effects of two plant growth forms (five species replicates each of woody plants and grasses) on the spatial and temporal variability of soil moisture. The experiment was conducted in three-year-old monocultures in a common garden at the University of Regina. Non-destructive soil moisture measurements were taken daily at 10 and 30cm below the soil surface during a wet period (7 rainfall events, high soil moisture) and a dry period (no rainfall events, low soil moisture). There was significant depth partitioning of soil moisture between growth forms. Soil moisture was lower under woody species than under grasses at 30cm, whereas soil moisture was lower under grasses at 10cm. There were also significant differences between growth forms in temporal variability. During the wet period, soil moisture variability beneath woody plants was significantly higher than that under grasses. During the dry period, soil moisture variability under grasses was significantly higher than that under woody species. Possible mechanisms for differences in variability between growth forms, including throughfall and evapotranspiration, were also examined. Throughfall was higher for woody species during large rainfalls. Evapotranspiration was higher for woody species at 30cm. We attribute differences in soil moisture variability primarily to differences in water uptake between these growth forms.

KEY WORDS: heterogeneity, soil moisture, temporal, spatial