DIURNAL MEASUREMENTS OF HONEY MESQUITE TRANSPIRATION USING STEM-FLOW GAUGES

Honey mesquite (Prosopis glandulosa Torr. var. glandulosa) stem flow was measured on days with contrasting environmental conditions during the 1989 growing season in Texas. Midday stem flow varied from near 10 to about 300 g hour-1 and daily totals varied from about 1,000 to 2,000 g day-1. On days with low potential evaporation, regardless of precipitation totals for the previous 20 days, stem flow mirrored potential evaporation. On a day with high potential evaporation and high precipitation totals for the previous 20 days, stem flow was greatest and the diurnal pattern was similar to that of potential evaporation. On a day with high potential evaporation and little precipitation for the previous 20 days, stem now mirrored potential evaporation until about 1030 and decreased throughout the day, while potential evaporation remained high. Variability of stem flow between stems was large, with a C.V. of about 30% for midday rates and a seasonal average C.V. of 37% for daily rates. Stem flow gauges provide continuous and accurate measurements of honey mesquite transpiration. They respond to changing environmental conditions and are useful for evaluating short-term responses of stem flow to physiological and environmental factors in the field and glasshouse.