Soil moisture is frequently manipulated by wetland managers to achieve a desired composition and production of plant species. Pink smartweed (Polygonum pensylvanicum) is a species valued by wetland managers because of its potential seed production and food base for migrating and wintering waterbirds. To improve ability to manage pink smartweed, we measured the influence of four growing-season soil moisture regimes (flooded, field capacity, prescribed moist-soil management, and continuously dry) in playa wetlands of the Southern High Plains of Texas. We used xylem water potential as an index of soil moisture available to the plants and compared vegetation and seed production among the four moisture treatments. Daily net photosynthesis was measured in each playa at 0900, 1200, and 1700 hours. The continuously-flooded wetland had the lowest absolute xylem water potential value (−0.294 MPa), followed by the playa at field capacity (−0.446 MPa), moist-soil managed playa (−0.758 MPa), and dry playa (−1.039 MPa). Vegetation biomass (F3,40 = 97.7, P < 0.001) and seed production (F3,40 = 54.3, P < 0.001) of pink smartweed differed among soil moisture treatments. Conducting moist-soil management (x̄ = 6816 kg/ha) increased vegetation biomass by 44% over the dry treatment (x̄ = 4706 kg/ha). As soil moisture increased to field capacity (x̄ = 9010 kg/ha) vegetation increased by 32% above the moist-soil treatment. Maintaining standing water in a playa maximized vegetation production (x̄ = 12497 kg/ha) of pink smartweed. Seed production was greatest when soil moisture was maintained at field capacity (x̄ = 695 kg/ha). There was no difference in seed production between the moist-soil managed (x̄ = 492 kg/ha) and flooded playas (x̄ = 514 kg/ha), which was 28% lower than the field capacity treatment. Seed production in the dry treatment (x̄ = 377 kg/ha) was 46% lower than the field capacity treatment and 25% below the flooded and moist-soil managed treatments. Net photosynthesis and xylem water potential decreased throughout the day in all treatments except continuously flooded, which corresponded to the increased vegetation production in this treatment. Slight increases in water stress relative to the continuously flooded treatment resulted in a redistribution of resources from vegetation to seed production. Managers should consider maintaining wetland soils at field capacity to increase seed production of pink smartweed.
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Vol. 26 • No. 1