WATER RELATIONS AND TRANSPIRATION OF HONEY MESQUITE ON 2 SITES IN WEST TEXAS

Transpiration rates and internal water relationships of honey mesquite (Prosopis glandulosa) were investigated weekly during May through September 1986 on sandy loam and clay loam, both upland sites in west Texas. Average transpiration rates peaked at approximately 7 mmol m-2 s-1 at 1100 hr during wet periods and reached a plateau between 4 and 5 mmol m-2 s-1 between 1200 and 1400 hr. During dry periods, the average transpiration rates reached their maximum plateau of 2 mmol m-2 s-1 at 1000 hr and declined between 1200 and 1600 hr. The transpiration rates ranged from an average of 3.28 +/- 2.05 mmol m-2 s-1 for trees on a sandy loam site to an average of 3.85 +/- 1.94 mmol m-2 s-1 for those on a clay loam site. Stomatal closure in midsummer caused a substantial increase in leaf temperature. Mesquite has developed other means, such as leaf orientation, wax accumulation, and reduction in canopy development, to avoid drought. Stomatal conductance of mesquite is very responsive to soil water availability and dryness of the air, and is less responsive to internal water status. This research further substantiates that mesquite behaves like a facultative phreatophyte in west Texas.