Water Competition Among Mixed Species In The Northeast US.

Competition for water and nutrients by plants plays a major role in controlling multispecies pastures growth, resource use, and soil availability of reactive forms of nutrients. However, to describe and model competition with process based models many questions remain unanswered. The goal of this investigation is to unravel the mechanisms controlling competition for water among roots of different plants. We report results for an experiment with the model annual plants maize (Zea mays L.) and sunflower (Helianthus annuus L.). Plants were grown in rhizotrons in five treatments. Treatments consisted pure and mixed plants. To introduce water competition, plants were allowed to progressively advance towards water deficit stress, with competition for light and nutrient suppressed through plant spacing and high soil fertility. Daily transpiration and leaf area were measured during the stress period. Measurements of soil, xylem and leaf water potential were obtained in the end the stress period. Plants were sampled at three different times. Sunflower had a higher daily and cumulative transpiration rate than maize. Sunflower maintained a gradient of -200 to 1,100 J/kg between the soil and transpiring leaves, and maize a gradient of -115 to 930 J/kg. Since transpiration was higher in sunflower, resistance to water flow in this species was approximately a half of maize. Rhizotrons with sunflower and maize loss water at a rate in-between that of rhizotrons with pure stands. Results indicate that sunflower will outcompete maize if sharing the same soil because of its profligate use of water, a proposition that will be tested with an algorithm that simulates competition. Complementary research is currently being conducted with mixed pastures, where understanding competition is critical to predict the productivity and water use of multispecies stands.