Effects of Water Deficit Stress on Competitive Interaction of Peanut and Sicklepod

Abstract

AbstractOne of the potentially deleterious effects of weeds on crop production is competition for water. In this study, competitive interactions between peanut (Arachis hypogaea L.) and sicklepod (Senna obtusifolia L.) were investigated. The two species were grown alone and mixed in a glasshouse in 118‐L barrels (0.65 deep and 0.48 m wide) filled with a Molena sandy soil (sandy, mixed, thermic Psammentic Hapludults). Treatments were either continuously irrigated (WET) or periodically dried (DRY). Measurements included daily soil water content (τ), continuous water uptake, stomatal conductance (g), leaf xylem water potential (Ψ1) and leaf osmotic potential. Water uptake and g were well correlated to τ. With both species, water uptake, g, and Ψ1 all declined when τ in the top half of the barrel was approximately one‐third of the available water (5.8 to 7.4% v/v; equivalent soil water potential, Ψs, −0.20 and −0.08 MPa). The τ‐values at which water uptake and g began to decline (here called inflection points) were always lower for peanut (5.9 to 6.1%; Ψs = The τ‐values at) than for sicklepod (7.4 to 7.5%; Ψs = − 0.08 to − 0.07 MPa). Ψ1 was similar for the two species. The inflection points of water uptake, g, and Ψ1 for both species were always higher when related to τ‐values in the bottom half of the barrel (8.6% to 13.1%, Ψs = − 0.04 and − 0.005 MPa) than when related to τ in the top half of the barrel. This response occurred even though the fraction of fine root length density in the bottom half was more than 45% of the total fine root length density in the DRY treatment of sicklepod and both species mixed. Significant osmotic adjustment was detected in both species following water deficit stress. At full turgor, leaf osmotic potential of all WET treatments reached − 0.99 MPa; at zero turgor, it reached −1.12 MPa. For the DRY treatments, leaf osmotic potential at full turgor dropped to −1.22 and −1.24 MPa in sicklepod and peanut, respectively; at zero turgor, it dropped to − 1.31 and − 1.34 MPa in sicklepod and peanut, respectively, but the difference between species was not significant. As the soil dried, water use by peanut mixed was significantly higher than sicklepod mixed. It appears that peanut can use more water under water deficit stress and can recover faster than sicklepod in a mixed community of the two species.