Plant Water Use and Environmental Stress on Two Opposite Slopes: from Water and Carbon Stable Isotopic Perspective

Climate-soil-vegetation dynamics are among key research focuses in the emerging ecohydrology discipline. Topographic relieves on landscapes provide various hydroclimatic conditions to examine vegetation functions and its responses to climate variation and changes in a short distance. In this study, we investigate ecohydrologic processes on two slopes of contrasting orientation and soil conditions in a native vegetation catchment with mean annual precipitation of 716 mm in South Australia, using water and carbon stable isotopes.

Throughfall, soil water, twig water, and groundwater stable isotopes were measured and integrated into an isotope incorporated soil-plant-atmosphere model to examine different plant water use patterns on two slopes with different environmental conditions. The focuses are on how ecosystems on the two slopes receive, store, and use soil moisture in different manners.

On these two slopes, trees are under different water stresses. Both leaf and soil ¹³C/¹²C ratio were measured for the two slopes to examine if δ¹³C can be used as an water stress indicator in this small catchment, and if the potential difference in δ¹³C can be observed in the soil organic matter. We monitored one-year leaf δ¹³C of two tree species, Eucalyptus leucoxylon and Acacia pycnantha. Our results indicate that leaf δ¹³C reflects different water stress conditions between slopes, seasons, and different locations on the slopes.